Spectrophotometers With Catheters for Measuring Internal Tissue

In one aspect, the present invention relates to wearable apparatus for noninvasive determinations of the concentration of oxygen in a specific target region of tissue. More specifically, the present invention discloses a user-wearable system for monitoring the oxygen concentration, or oxygenation trend, in the tissue of a subject undergoing aerobic stress, such as an exercising person.

The increasing popularity of all forms of exercise over the last several decades has also lead to an increased interest in the measurement of individual athletic performance. However, at the present time, athletes are limited to obtaining heartbeat and blood pressure data while they are exercising. Although of some use, these data do not reflect peripheral circulatory capacity or the oxygenation state of specific muscle tissue.

In order to measure oxygen delivery to the capillary bed of the muscles, an athlete must be tethered to electrocardiogram apparatus and have blood samples drawn while running on a treadmill. These are essentially operating room apparatus and procedures, which do no simulate the actual conditions of exercise. The measurement of aerobic efficiency by analyzing the oxygenation state of a particular muscle while exercising is important due to a variety of persons. For example, as a casual jogger strives to become a marathon runner, the efficiency at which they use oxygen can severely impact performance; data reflecting the utilization of oxygen can provide information which allows an athlete to change pacing strategies or otherwise adjust their activity to produce better results. Other athletes, such as swimmers, cyclists and rowers would also find this information useful for evaluating performance. However, the use of blood oxygenation data is not limited to competitive athletes; even geriatrics who undergo mild aerobic exercise to maintain and improve their health can benefit from data concerning the changes in blood oxygenation brought about by exercise or other activity. Other animals, such as racehorses, can also benefit from this type of performance data. By measuring the oxygen delivery to the muscles, both the quality of training and the natural ability to exercise may be evaluated.

In addition to monitoring and maximizing athletic performance, information pertaining to the delivery of oxygen to the limbs and the brain is important in military and space applications where changes in gravity and other stresses may result in fatigue, and ultimately, blackouts.

Although apparatus are available which measure the oxygenation content of blood using data collected from a fingertip or ear lobe, these devices do not actually measure the oxygenation state of nearby muscle groups or the brain. To monitor athletic performance, or the condition of exerted muscles, data collection must be performed at the site of interest. For example, runners will wish to be provided with this information during a race, not in a laboratory. Therefore, for an apparatus measuring the metabolic condition of an athlete to be truly useful, a rugged, lightweight, user-wearable system must be provided.

One method by which the oxygen level in a muscle may be measured by tissue spectrometry. For example, red and near-red light, having wavelengths between about 600-800 nanometers (nm), will harmlessly penetrate body tissues. As the light penetrates the tissue, it migrates and is absorbed by deoxygenated hemoglobin in small blood vessels. Normally, tissue receives oxygen from hemoglobin contained in red blood cells, which circulate in the major blood vessels and eventually into the capillary bed, supplying muscle tissue with oxygen. Aerobic activity can cause the level of oxygen use to rise, causing a commensurate rise in the level of deoxyhemoglobin which is compensated for by increased blood flow in trained individuals. Near-red light is absorbed by tissue that is not receiving as much oxygen as the surrounding tissue due to increased levels of deoxyhemoglobin in less trained individuals. Thus, by determining the amount of incident radiation absorbed, the oxygenation state of a specific area of tissue, and the training level of an individual, can be determined.

The present invention provides a novel, wearable system for determining the metabolic condition of an aerobically stressed portion of the muscle tissue of an exercising person. The system comprises a lightweight rugged detector, worn against the skin surface of the subject, adjacent the muscle being monitored. The system of the present invention thus minimizes any performance impairment. The preferred system further comprises a wearable power pack and a wearable display means for displaying information indicative of the aerobic metabolic condition of the region being monitored. In a preferred embodiment intended for use while running or engaged in similar athletic activities, the display is worn on the wrist and displays information from a leg-mounted detector. In another embodiment, intended to provide information to coaches, a telemetry system is employed to transmit a signal carrying the data from the detector to a remote location, for processing and display.

The detector of the present invention preferably employs a continuous wave spectrophotometer having one or more sources of electromagnetic radiation with wavelengths between about 760 nanometers and about 800 nanometers directed into the tissue of the subject. The detector is efficiently coupled to the body tissue and utilizes the principle of photon migration to detect the portion of the transmitted radiation arriving at an adjacent skin region.

The present invention also discloses methods for displaying the aerobic metabolic condition of a subject. The percentage of deoxyhemoglobin in the blood of the subject is determined, and a signal representative of this percentage is converted into a graphic representation. The display may preferably be a digital display, a bar graph or a series of deoxyhemoglobin levels, placed on a time scale.

It is an object of the present invention to provide methods and apparatus which allow a rapid determination of the oxygenation state of tissue, such as muscle tissue, located beneath the surface of the skin of a subject, such as an athlete, without requiring the subject to be tethered or physically connected to laboratory or operating room monitoring equipment.

It is also an object of the present invention to provide apparatus which may be attached to a user which would determine the oxygenation state of a portion of the user's body and provide that information in a readily understandable form.

It is a further object of certain embodiments of the present invention to provide information pertaining to the oxygenation state of tissue directly to a user wearing the apparatus of the present invention.

It is another object of certain embodiments of the present invention to transmit information pertaining to the oxygenation state of tissue to a remote observer.

According to one aspect of the invention, an oximeter is provided for determining the oxygenation state of localized body tissue per se, constructed to be worn over a period of activity by a user and comprising a flexible, body-conformable support member which supports, adjacent the skin of a user, over the localized tissue of interest, at least a pair of spaced apart light sources, and intermediate thereof, at least a pair of wavelength-specific photo detectors, each light source exposed to transmit wavelengths of both of the specific wavelengths toward the localized tissue of interest lying below the skin and below the associated subcutaneous fat layer of the user, and each detector exposed to receive photons of the respective specific wavelength that have originated from each light source, and scattered from the localized tissue and passed back to the detectors through the subcutaneous fat layer and skin of the user, the support member including conformable barrier means disposed between each light source and the detectors, the barrier means being of substance capable of conforming to the contour of the wearer and preventing light energy proceeding laterally in the region of the barrier means from reaching the detectors.

Somewhat more generally, according to another aspect of the invention, an oximeter is provided for determining the oxygenation state of localized body tissue per se, constructed to be worn over a period of activity by a user and comprising a flexible support member which supports, over the localized tissue of interest, at least a pair of spaced apart light sources, and intermediate thereof, at least a pair of wave length-specific light detectors (e.g., photo detectors), each light source exposed to transmit wavelengths of both of the specific wavelengths toward the localized tissue of interest, and each detector exposed to receive photons of the respective specific wavelength that have originated from each light source, and scattered from the localized tissue and passed back to the detectors.

Preferred embodiments of these aspects of the invention have one or more of the following features.

The light sources comprise broad spectrum CW light sources.

The light sources comprise tungsten filament lamps.

The oximeter includes control means for simultaneously flashing the light sources to enable each detector to pick up light energy at its specific wavelength simultaneously from each light source.

Means are provided to flash the light sources at selected intervals unrelated to the interval of heart beats of the user.

According to another aspect of the invention, an oximeter is provided comprising a flexible support member comprised of a molded-elastomeric backing member, the backing member mounting at least one light source means capable of producing one or more (e.g., two) selected wavelengths and oriented to direct the light to tissue of a user and the backing member also mounting detector means capable of separately detecting energy at each of the wavelengths scattered by tissue of the user, integral elastomeric portions of the backing member defining a barrier exposed for conformable contact with an exposed surface of the user, in position to prevent lateral movement of light in subcutaneous layers from the source means to the detector means.

According to another aspect of the invention, an oximeter is provided comprising a flexible support member, the support member mounting at least one light source means capable of producing two selected wavelengths and oriented to direct the light to tissue of a user and the support member mounting detector means capable of separately detecting energy at each of the wavelengths scattered by tissue of the user, the support member supporting a barrier member exposed for conformable contact with an exposed surface of the user in position to prevent lateral movement of light from the source means to the detector means, the barrier comprising a member having an edge sized and positioned to indent skin and the flesh of the user thereby to intercept light migrating laterally in the subcutaneous fat layer and prevent such light from reaching said detector means.

Preferred embodiments of these aspects of the invention have one or more of the following features.

The barrier member is elastomeric, adapted to conform to the contour of the skin of the wearer.

The flexible support member comprises a molded-elastomeric backing member and the barrier member is integral with the backing member.

The member defining the flesh-indenting edge is about 0.5 cm thick in the region that engages the skin.

The barrier member comprises a rib-form member.

There are in series at least one (e.g., two) barrier members, one closely adjacent to the light source means and one closely adjacent to the detector means.

The support member mounts at least one (e.g., two) spaced-apart light sources and at least one (e.g., a pair) of detectors are disposed parallel to each other, disposed laterally relative to the line between the light sources and equal distance from each of the light sources.

The light sources comprise broad spectrum CW light sources.

Electronic control circuitry for the light source and the detector means are provided in which the circuitry is disposed upon a miniature semiconductor chip carried by the support member.

Electronic control circuitry is provided comprised of entirely non-magnetic components enabling use of the device in conjunction with nuclear magnetic resonance imaging.

The oximeter is combined with a real-time readout device constructed to be worn by the user and having a display responsive to the oximeter disposed for viewing by the user.

The oximeter is associated with means securing it to an appendage of the user and the readout device is constructed to be worn by a user.

The oximeter is combined with radio frequency telemetry means for transmitting oximeter data on a real time basis to a station remote from the user or to a receiver in a readout device constructed to be worn by a user.

The oximeter includes electronic control circuitry for the light source and the detector means, the circuitry disposed upon a miniature semiconductor chip carried by the support member in combination with radio frequency telemetry means controlled by the circuitry for transmitting oximeter data on a real time basis to a station remote from the user.

Means are provided for battery-operation of the oximeter and to record oximetry data in internal digital memory for subsequent display or data analysis on a computer.

The oximeter includes electronic control circuitry for the light source and the detector means, the circuitry disposed upon a miniature semiconductor chip carried by the support member, and means for battery-operation of the oximeter and means to record oximetry data in internal digital memory for subsequent display or data analysis on a computer.

According to still another device aspect of the invention, an oximeter is provided comprising a support mounting a light source and detector means at fixed spacing, and electronic control circuitry for the light source and the detector means, the circuitry disposed upon a miniature semiconductor chip carried by the support member, the oximeter encapsulated in biocompatible, water impermeable material, the oximeter constructed and arranged for implantation under the skin of a user for monitoring internal tissue oxygen trends.

The invention also features a number of methods. The method is provided of monitoring the derivative or rate of change of the time based curve representing detected change of tissue oxygen levels and blood volume and employing these rates as a quantitative standard of measurement of tissue oximetry.

The method is provided of assisting an aviator or other person engaged in activity that can subject the person to high G-forces including providing to the person a comfortable oximeter sensor suitable to be worn about the head (e.g., either integrally in a helmet or helmet lining) and capable of responding to tissue oxygen level and blood volume of brain tissue on a real time basis, employing the oximeter sensor to monitor oxygen level of brain tissue of the wearer as the wearer engages in the activity, comparing the monitored value to a standard and generating a signal, such as a warning or control signal, in the event the monitored level(s) violate(s) a pre-established standard.

Preferably, the oximeter is constructed to monitor the trend of oxygen level in the brain, and means are provided to evaluate the rate of change being detected and using the rate of change as the control value and alarm reference.

The method is provided of monitoring a person suspect of sleep apnea or sudden infant death syndrome including providing to the person a comfortable oximeter sensor capable of automatically responding to oxygen level of the person while permitting the person to sleep, automatically monitoring the output of the oximeter by comparing it to a standard and generating a signal, such as a warning or control signal, in the event the monitored level violates a pre-established standard. Preferably the oximeter sensor is taped comfortably to the head for monitoring. Also, preferably the method is used in conjunction with impedance pneumography (breathing rate measurement using chest-wall impedance) and/or EKG to provide an effective in-home apnea monitor to alarm the patient or other individuals in the area so as to wake the patient and prevent hypoxic tissue damage during sleep.

The method is provided of monitoring the cerebral tissue oxygen rate of change as a means of triggering alarm to awaken a subject in danger of infarct due to hypoxia.

The method is provided of monitoring both tissue oxygen level and blood volume in skin flaps such as are produced either by wound or surgery, as the flaps heal, the separation between the source and the detector being established in relation to the thickness of the skin flap to ensure tissue of the flap per se is being monitored.

The method is provided of emergency monitoring of cerebral tissue oxygen level and blood volume in an emergency care situation with the implantable device, in this case, preferably a stand-alone oximeter carried on a backing member with micro-circuitry to monitor the brain or other tissues in peril of damage due to hypoxia.

The method is provided of employing the device of any of the configurations described above wherein the oxygen levels, blood volume and/or rate of charge are measured in cancerous tissue to indicate the activity and viability of the tissue. Also preferably the method includes monitoring of the viability of a tumor following treatment intended to wipe out the cancerous tissue.

Another aspect of the invention is a helmet into which is molded a tissue oximeter in position to engage the head of the wearer when the helmet is put on, the oximeter being of the NIR type, comprising light source means for transmitting near infrared light into the head, detector means held in spaced position relative to the light source means for receiving light scattered by brain tissue and a barrier disposed to engage the head between the light source means and the detector means to prevent light traveling laterally from the light source means from reaching the detector means. Preferably the oximeter has other features described above. In particular, preferably, the oximeter in the helmet includes control circuitry on a miniature chip and preferably means are provided for determining the rate of change of oximetry readings and for comparing the rate of change to a standard and, e.g. producing an appropriate alarm and/or control signal.

Another feature of the invention is a tissue oximeter comprising a support, a detector fixed to the support and a light source mounted in an adjustable manner to the support to enable selection of the spacing between light source and detector for adjusting the mean depth of tissue to which the oximeter responds.

Still another feature of the invention is a tissue oximeter in combination with means connected to receive tissue oxygen readings from the oximeter, and to determine the rate of change of the readings, the rate of change serving as a quantified indication of the state of the charging metabolic process of the tissue.

Another feature of the invention is an oximeter as described, disposed on an endoscope, catheter or guidewire or the like for insertion via a body passge to internal tissue, and including means such as an inflatable balloon to press the oximeter sensor against the localized tissue of interest. Another feature includes providing a water impermeable coating over the device for use in the presence of water.

FIG. 1 is a depiction of a preferred configuration of an embodiment of the present invention.

FIG. 2 is a partially diagrammatic, partially schematic representation of a preferred embodiment detector.

FIG. 3 illustrates another preferred configuration of an embodiment of the present invention.

FIG. 4 is a partially diagrammatic, partial schematic representation of an alternate preferred embodiment detector.

FIG. 5 is a plan view of another preferred embodiment.

FIG. 6a is a plan view of the oximeter sensor of FIG. 5.

FIG. 6b is a longitudinal sideview of the oximeter sensor of FIG. 6a.

FIG. 6c is a longitudinal cross-sectional view taken on lines 6c of FIG. 6a;

FIG. 7 is a transverse cross-sectional view of a oximeter sensor according to the invention in place upon the flesh of a wearer;

FIGS. 8a, 8b and 8c are plan views of other preferred embodiments of the oximeter sensor;

FIG. 9a is a plan view of an implantable oximeter sensor according to the invention,

FIG. 9b is a longitudinal sideview of the oximeter of FIG. 9a, while

FIG. 9c is a cross-sectional view taken on line 9c of FIG. 9a.

FIG. 10 is a block diagram of an analog version of the control system for the oximeter of the previous figures.

FIG. 11 is a block diagram of a digital version of the control circuit of the oximeter of the previous figures.

FIG. 12 is a software flow diagram of the software used with the circuitry of FIG. 11.

FIG. 13 is a front of a helmet according to the invention.

FIG. 14 shows an endoscopic oximeter according to the invention.

A preferred embodiment of the apparatus of the present invention is illustrated in FIG. 2. In this embodiment an electro-optical pickoff detector unit 10 is worn on the leg of the exercising subject 50. It is preferred that the weight of the detector be kept to a minimum so that hindrance to a competing athlete is negligible. In a preferred embodiment, the detector will be housed in a flexible array constructed from a suitable non-irritating, lightweight material.

Power is provided to the detector unit 10 from a replaceable battery pack 30. The replaceable power pack 30 is preferably designed to be of minimal dimensions and weight. Most preferably, the battery pack 30 would be designed to last only for the duration of the activity, e.g., several minutes of sprinting, several hours for a marathon runner, etc. In competitive sports applications, the life of the battery pack is preferably based upon the interval between substitutions or other interruptions between periods of competition.

The embodiment illustrated in FIG. 1 further comprises an arm indicator 40, which is preferably worn on the arm in the manner of a wristwatch. The arm indicator 40 displays the percentage of deoxyhemoglobin (% Hb) as a measure of the subject's metabolic state. As seen in FIG. 1A, such a display may comprise a simple readout of this information, such as a bar graph. Alternatively, the information displayed may be placed on a time scale, to graphically illustrate the change in % Hb concentration over the course of the activity, as illustrated by FIG. 1B. In a most preferred embodiment, the graphic displays illustrated by FIGS. 1A and 1B are comprised of liquid crystal displays (LCD's), although other electrical or electronic display means may also be used. The amplitude interval of this embodiment is preferably divided into 6-10 levels, each covering a portion of the designated % Hb scale.

It will be appreciated that the range of the % Hb scale may be adjusted depending upon the range expected to occur during the activity. Since the precision of the present invention is limited by that of the indicator, the range which is displayed is an important variable parameter. In the most accurate embodiment of the present invention, with the endpoints of the % Hb scale set at 20% and 40%, the apparatus would have an accuracy of about 6%, which is about the limit of precision which can be obtained from a moving limb. One of ordinary skill will realize that the gain of the apparatus is preset, depending upon the intensity of the activity expected. In a most preferred embodiment, a button placed on the arm indicator 40 allows the gain to be set.

Referring now to FIG. 2, there is illustrated a partially schematic, partially diagrammatic representation of a preferred embodiment of a circuit which comprises the optical pickoff component of a DC tissue spectrophotometer detector 10 contemplated for use in the system of the present invention. The detector 10 is shown for illustrative purposes mounted against a skin surface 25 of a subject. In a typical configuration, the detector is mounted against either large, homogeneous muscles, such as the gastrocnemius or the quadriceps or against the forehead of an adult. Two lamps 12,14 and two detectors 16,18 are contained in a flexible waterproof array. Also contained in the array is an opaque specular barrier, which is a concentric ring of material 11 between the lamps 12,14 and the detectors 16,18 which acts as a barrier zone to light of a specified wavelength. Most preferably, the material which comprises the barrier zone will not only be opaque to light within a specified region, but will further act as an absorber as well. The configuration of dual wavelength light sources combined with a barrier zone is disclosed in "Optical Coupling System for Use in Monitoring Oxygenation State Within Living Tissue," Application Ser. No. 266,116; filed Nov. 2, 1988, which is incorporated herein by reference, as noted above.

Thus, superficial light rays from the skin are, in effect, blocked by the opaque barrier 11 from entering the detectors 16,18. This blocking action by the barrier 11 of these superficial rays enables the system to determine the oxygenation state of hemoglobin within the muscle rather than at the skin surface. The rays that migrate deep within the tissue are received by the detectors 16,18. The light rays that migrate superficially "escape" through the skin surface and will be absorbed by the opaque barrier 11. When, for example, a 760 nm impulse is applied, the deoxygenated hemoglobin (Hb) within the muscle is detected and when an 800 nm signal is applied, the oxygenated and deoxygenated hemoglobin (HbO.sub.2 and Hb) within the tissue region are detected. The system is able to ignore the oxygenation state at the skin surface and determine that within the tissue.

The lamps 12,14 may be, for example, 1/2 W flashlight bulbs that are periodically illuminated in the NR region. The lamps are provided with cutoff filters 13,15 so that only energy of a specified wavelength illuminates the tissue. The silicon diode detectors 16,18 are sensitive to 760.+-.20 nm and 800.+-.20 nm wavelengths respectively.

In a preferred embodiment, the lamps 12,14 are light emitting diode (LED) sources, which emit light having a wavelength of about 760 nanometers and about 800 nanometers respectively. In either embodiment, the lamps are flashed or pulsed at a predetermined repetition rate. The repetition rate of sampling, i.e., the rate at which the lamps are flashed determines the rate at which data may be collected. Thus, for a long distance runner, the lamps are flashed slowly; the output is commensurately changed for a sprinter, the lamps flashed rapidly to produce sufficient data to evaluate an exercise having a duration on the order of seconds. The selection of LEDs as sources of electromagnetic radiation provides a further advantage, since these sources produce a signal-to-noise ratio (S/N) approximately one order of magnitude greater than previously disclosed optical coupling systems using optical light fiber sources.

Referring now to FIG. 4, an alternate embodiment of a circuit for use with the present invention is illustrated. In this case a single detector 17 responding to separate light flashes collects and transmits signals to an amplifier 24, which has bipolar outputs that are connected intermittently to an integrator 27 by a switch 25. Another switch 26 adjusts the relative duration of the two light pulses to equalize the two signals. One of ordinary skill will understand that those portions of FIG. 2 and FIG. 4 having the same reference numerals perform substantially similar functions. Many details of the particular circuits comprising the present invention need not be set forth with particularity as they are well known or will be obvious to those of ordinary skill.

Referring to FIG. 2, it can be seen that the detectors 16,18 are also protected by a transmitting filter 19 to minimize the effect of background light. The filter 19 may be comprised of a separate member, a coating or integrated into the housing of the circuit. The DC output of each of the detectors 16,18 is timeshared into its respective differential amplifier 20,22. The amplifiers are connected in opposite polarity, one non-inverting, the other inverting. The dwell time of the switch 23 connecting the amplifiers 20,22 is adjusted to equalize the response of the two signals by appropriate circuitry 28. The signal from the integrator is coupled to a recorder (not illustrated). As shown in FIG. 4, the signal from the 800 nm lamp 12 may be simultaneously employed to vary the gain of the amplifier 24 so as to correct the signals for changes of blood volume and to produce the ratio of the two signals, and thus maintaining constant sensitivity for difference detection. One of ordinary skill will appreciate that a similar gain compensation circuit can be incorporated into the circuitry of the 800 nm detector amplifier 22, shown in FIG. 2. Whether incorporated into the circuits of FIG. 2 or FIG. 4, the 800 nm signal is also coupled to a second recorder channel to collect data reflecting total absorption or blood volume.

Another configuration of the present invention is illustrated in FIG. 3. In this embodiment, a radio-linked telemetry system comprised of a transmitter 60 attached to the subject and a receiver 62, allows the remote monitoring of the subject. A supervisor, coach, or clinician is thereby enabled to monitor the performance of the subject. The data display is remote, one of ordinary skill will appreciate that the displays utilized may be similar to those illustrated in FIGS. 1A and 1B, or may be more complex, displaying data using various scales, time overlays, colors, etc. In a most preferred embodiment the telemetry signal would be carried on the 220-400 MHz band, using a transmitter in the 100 MW range.

The configuration illustrated by FIG. 3 allows the present invention to monitor athletes in competition or workers and military/space personnel located in remote locations. For example, the apparatus of the present invention may be used in training to determine the duration of peak performance and the appropriate times for the substitution of fresh players or other adjustments. This configuration would also be preferred for monitoring the metabolic condition of an animal such as a racehorse, racing dog, or any animal whose metabolic condition is being studied for clinical or other purposes. A "postage stamp" oximeter may be provided for, e.g., emergency use, where the oximeter is held to the subject by an adhesive pad positioned peripherally around the device.

In any of the embodiments of the present invention, it is preferred that the data be integrated over at least about ten seconds to smooth out irregularities which normally occur in the concentration of deoxyhemoglobin during exercise. However, it will be understood that the period integration can be varied, depending upon the duration of the activity being monitored.

Although manual balancing of the apparatus of the present invention is required, in a preferred embodiment, the balancing is accomplished by depressing a button, which will normalize the output of the two wavelengths.

Another preferred embodiment of the oximeter is shown in FIGS. 5 and 6a-6c. A rubber-backing member 101, provides support for two lamps 100 spaced equi-distant from two detectors 102 also mounted on backing member 106. The backing member is formed of an opaque, e.g., black, silicone rubber of suitable durometer to enable it to conform to the curvature of the subject part of the human body to which it is applied. For this embodiment, which may be as long (L.sub.1) as e.g., 12, especially 8 centimeters, flexure configurations 106 are provided. Light barrier members 103, 104 serve to depress the subcutaneous fat layer and thereby reduce light interference directly between the light sources 100 and the detectors 102, see description below regarding FIG. 7. Behind the detectors 102 of FIG. 6a, as shown in FIG. 6c, housing 107, defined by the rubber wall, contains the supporting circuitry for these lamps and detectors. As shown in FIG. 6c, narrow band optical filter 110 lies over photodetector 111, which lies over circuitry 108. Depth D is typically 2 cm. Wiring harness 115 carries power to the lamp.

On the rubber supporting member 101 there are a number of integral raised members 103, 104, 105 and 106. Raised rib 105, which extends about the perimeter, both prevents external light from interfering with the reading and serves to support comfortably the backing member 101 on the subject. Rib 104 extending laterally, adjacent the lamp, and disposed across the line projected between the lamp 100 and the detectors 102, serves as a second light barrier to prevent interfering light transmission between light source 101 and detectors 102. Rib 103 closely surrounds the detectors, and serves as a primary eliminator of environmental light interference, and also serves to absorb light migrating along subcutaneous fat and other subsurface interposed layers, etc. All of these ribs are on the order of 1/2 centimeter high and 1/2 centimeter thick. Their outside flesh-engaging edges are rounded for comfort to the wearer. The supporting member 101 and its associated ribs are manufactured in one piece of molded rubber. A suitable mold is provided and black silicone rubber is poured into the mold, cured and dried, leaving the subsequent rubber backing 101 with integral ribs and structures. Suitable mounting sites are provided in the backing into which the detectors 102 and the lamp 100 are mounted during final manufacturing. The backing member for the oximeter sensor of FIGS. 6a-6c has width, W, length, L1, and depth, D, which may be varied depending upon the application. L2 represents the spacing between light source 100 and the center of detectors 102. Sensors with dimension (L.sub.2) from one centimeter to four or five centimeters with corresponding changes in L1 and W are appropriate. One centimeter separation L2 is useful for muscles of very shallow depth while L2 of four or five centimeters is useful for deeper tissue penetration, for example for the brain or other organs.

Small L2 spacings of as low as one centimeter are also appropriate for monitoring tissue flaps, though the best configuration of the sensor for flaps is that shown in FIG. 8c, described below, because flaps are of varying thickness and the adjustability of the device of FIG. 8c enables L.sub.2 adjustment proportional to the thickness of the flap. It will also be realized that monitoring may be achieved through wound dressings, bandages, etc.

In the currently preferred embodiment, the light sources 100 are lamps having tungsten filaments, are broad band light sources which eliminating the problem of matching the light sources to the detector filters.

Each detector is comprised of interference filter 110 which blocks out all light except for that which is desired, each of two detectors having a separate wavelength of interest. At this time 760 nm and 850 nm are preferred, although one can envision that changing, depending upon the application. Beneath the filter is a photosensitive detector which picks up the light and transduces it to an electrical signal which is amplified in the circuit 108 and later transmitted to the control circuitry represented in either FIG. 10 or 11.

In the presently preferred embodiment, the interference filter is manufactured by Omega, Inc., and the photodiode beneath it is Part No. F1227-66BR, available from Hamamatsu, having a large sensitive area for favorable signal to noise ratio and an NIR wavelength sensitivity. The sensitive area is approximately 6 millimeters squared.

In the present embodiment the filter and detector are epoxied together around and an electronic shield 115 surrounds the diode/filter pair 110 and 111. This surrounding electronic shield eliminates or reduces extraneous electronic interference. It is presently preferred to form this shield of copper in the form of a windowed box which surrounds the detector filter pair.

Once the two separate filter diode pairs are constructed, they are soldered together and then mounted directly to the circuit board 108. Connected also to circuit board 108 is an ultra low noise operational amplifier with high gain, which converts the current signal from the diodes to a voltage applicable to the control circuitry of FIGS. 10 or 11. The circuit board 108 can be connected via either telemetry or cabling to the oximetry system 99 of FIG. 5, which contains the circuitry shown in FIGS. 10 or 11. Power supply for the amplifier of 108 is supplied by the oximetry system 99 where a cable connection is employed. In other embodiments, a battery is provided for operating the oximeter sensor along with the telemetry system, to be described below in connection with an implantable embodiment.

Referring now to FIG. 7, the preferred embodiment of FIGS. 6a-6c is shown diagrammatically as it is placed upon the skin of a subject. The edges of the upstanding rib-form barrier members serve to concentrate pressure upon the skin, depressing the skin layer and the underlying fat layer. The barriers 103 and 104 serve to prevent light from migrating directly between the source 100 and the detectors 102 and because the barriers are placed with pressure upon the surface of the skin, they serve to reduce the area of the fat through which light can pass directly. If one were to imagine the situation without a barrier, one would see light passing almost directly between the source and the photodiodes, the fat layer serving, effectively as a light guide. The absorbing ribs reduce this noise effect. Light which is emitted by the sources 100 enters the skin directly beneath the source, passes through the fat to the underlying tissue, migrates through the tissue, is absorbed, scattered. and eventually is received by the photodiode. The path has been described in prior art as a banana-shaped path which is due to the photon migration between the source and the detector. "Banana-shaped" is a mean representation of the photon path, whereas the actual path constitutes many scattering changes of direction of the photons as they course between the light source and the photodiode.

FIG. 8a-8c show alternate preferred embodiments of the oximetry sensor.

The embodiment of FIG. 8a is useful for muscle. It is shown here as a comparison to FIGS. 6a-6c, wherein the overall length L1 and the overall width W depends upon the application and L2 as in FIGS. 6a-6c can vary dependent upon the application from one centimeter or less to five centimeters or more.

The overall length L1 is determined chiefly as a result of the source 100 to detector 102 spacings L2. The spacing determines the depth of penetration of the light which is scattered and migrated through the tissue. The farther the source is from the detector, the deeper the mean penetration. So for shallow penetrations, one would envision a short L2 and thereby L1. The penetration desired depends upon the muscle of interest. For a large muscle, for example, in the thighs or the calf, which tend to be fairly large, one needs a substantial separation to both (a) penetrate the thicker fat layer and (b) to sense deeper into the larger muscle.

For such muscles, a common dimension for L2 would be 3 to 5 centimeters and L1 would thereby be 7 to 11 centimeters.

The width of the sensor is chiefly dependent upon the size of the detectors 102. In the configuration of the presently preferred embodiment wherein each detector has a photosensitive area of approximately 6 millimeters squared, the width is dependent almost entirely upon those two dimensions. As the photodetectors reduce in dimension width W decreases.

The larger photodetector units provide better signal to noise ratio and thereby enable more accurate representation of the oxygenation state of the tissue. As improvements in technology occur and better photodetectors and initial amplification circuitry are developed, the detector size will decrease, with consequent decrease in W.

As with FIG. 6a-6c, the supporting member 101 of FIG. 8acarries numerous rib-form barriers. In this case barriers 103, 104 and 105 serve both support and light reduction functions. Perimeter barrier 105 in this case completely surrounds the light source and detector grouping. Between the light source and barrier 103, is barrier 104 on opposite sides of the detectors. Barrier 104, as previously mentioned, serves to reduce light as it travels between source and detector in the subcutaneous layer.

The embodiment of FIG. 8b represents an alternate to that of FIG. 8a wherein the dimensions of FIG. 6a are significantly reduced to achieve a smaller probe. In addition to the backing member 101 being reduced in size, in FIG. 8b, barrier 104 has been eliminated and barrier 103 serves as the primary and only eliminator of both external light and interference between source 100 and detector 102.

The typical dimensions for L2 of FIG. 8b would be 3 centimeters or less, L1 being 6 centimeters maximum or less. In comparison, the minimum size for the embodiment of FIGS. 8aand 6a-6c of L2 would be 3 centimeters or greater.

The embodiment pictured in FIG. 8b is suitable to be used for example in neonate applications where the desired tissue volume is extremely small and one needs a small probe. It would also be used for very shallow depth muscle and for example, skin flap measurements where skin flaps are created either by surgery or by wound. The sensor is placed over the skin flap to determine the health of that flap as it heals.

The smaller sensor sizes improve the flexibility of the device to correspond to perhaps smaller target muscles and smaller regions of interest.

Referring to FIG. 8c, a similar embodiment to that of FIG. 6a-6c is shown, but having a light source track 109 to enable variable spacing between the light source 100 and detector. Barrier 103 has been omitted in favor of allowing for user settable variations of L2. L2 may be varied between for example 2 centimeters to say 5 centimeters depending upon the application. This may be used for skin flap work in determining the health of a skin flap as described above, with the distance L2 set in accordance with measurement of the thickness of the skin flap.

For this adjustability, a slide mechanism is employed in manner to keep L2 equal on both sides, in dependent motion such that as the spacing of one varies, the spacing of the other will also change.

The embodiments of FIGS. 5-8 share the desirable features of a parallel pair of detectors 102, side-by-side extending across the line between the light source. By simultaneous flashing of both lamps each detector receives photons at its wavelength from both lamps, simultaneously.

FIG. 9 shows another preferred embodiment of the tissue oximeter sensor, in the form of an implantable probe. To further reduce size, one of the light sources 100 is omitted. As in FIG. 8b, light barrier 104 is omitted. The lone barrier in this case 117 serves to reduce direct light interference.

As previously mentioned, backing member 101 holds in fixed relation the light source 100 and the detectors 102. The length L1 is solely dependent upon a single L2 between the single source and the dual detectors. The spacing depends chiefly upon the muscle location internally of the organ which is being studied. As previously mentioned, from 1/2 centimeter or 1 centimeter to 5 centimeters may be appropriate, depending upon the application. Applications envisioned are horse muscle studies.

For application, the physician makes an incision in the skin and slips the oximeter sensor underneath the skin and cutaneous fat layer. There are suture points 113, e.g., biocompatible webbing, surrounding the backing member 101. A coating over the entire sensor is comprised of a biocompatible base material 112, which protects the circuitry from the human system, and protects the human from the invasive nature of the circuitry.

The thickness of the device is of the order of 1 to 2 centimeters maximum. That depth dimension will, as technologically changes, diminish. In FIG. 9c the supporting circuitry is shown. As previously described, the filter/photodiode pair 110, 111 is disposed above the circuit 108. In addition to receiving and amplifying the signal, the circuit, shown here is responsible for telemetric communication of the signal to a receiver outside of the body. A battery 114 powers that circuitry.

By employing a radio signal to transmit the information from within the body to a receiver outside the body there is no need for wires and the like puncturing the skin.

Referring to FIG. 10, one embodiment of the circuitry for driving the device is shown. This is an analog circuit wherein the signal from photodetectors 118 and 119 is amplified by amplifiers 120 and sent to three manipulative circuits that take the difference, the sum and the derivative of the signal. The difference is simply as described in much earlier work, in which circuit 123 simply subtracts 760 nm minus 850 nm to obtain a signal representing deoxygenation.

The sum circuit 124 takes a weighted sum of the 760 nm and 850 nm signals, weighting being chosen appropriate to the fact that the signal variation due to oxygenation or deoxygenation is greater for 760 nm than it is for 850 nm. Because these contrabestic wavelengths tend to cancel the signal due to the difference in oxygenation, the sum shows independent of the difference and is taken as representative of the blood volume changes in the tissue.

The derivative circuit 125 takes the simple derivative to show the rate of change of both of the signals. This is useful as described above to trigger alarm circuitry based upon established standards, wherein the higher the rate of the change, and the more sustained that rate of change, the more potentially dangerous the rate of change. This is useful, as mentioned, for example in monitoring aviators for possible black-out conditions and for apnea, as discussed above.

The outputs of these units 123, 124 and 125 are applied to the control circuit which controls where the signals are directed and how they are displayed and/or sent to a computer. The control circuit may be simply embodied as a switch to switch the output to an LCD display, for example. The analog signal from control circuit can be digitized in the display unit 127 and displayed as a digital number. Additionally it can be digitized and sent to a computer or sent in analog form to a computer for digitization.

The oscillator 121 is an independent source for determining the frequency of lamp flashing. Lamps flash at frequency of 1/2 Hz or 2 flashes per second or greater. This frequency may be independent of heart rate or any other external factor and is set externally by the user, and may be dependent upon application as mentioned earlier. For example, during exercise, the frequency chosen for the lamp will depend upon the frequency of the exercise, such as the the revolutions per minute on a bicycle. If one is expected to encounter a slow change in oxygenation due to the nature of the exercise or the muscle of interest, one can employ a fairly low flashing rate. There is no need for high resolution measure of the rate of change as is required in pulse oximetry.

The lamp rate is tied to the control circuit. The oscillator establishes the timing for the sum and difference circuits because the sum, difference and derivative circuits need to be synchronous. In operation, the lamp flashes, the signal is picked up by the photodetectors and while the lamps are on, the difference, sum and derivative are calculated and are thereby stored in the appropriate memories, and via the control circuit can be directed to the display and to the computer.

The derivative system is the basis of the alarm system. Output from the derivative is compared to a standard within the alarm circuitry, which then determines if there is, for example, a normal rate of change, represented say by a green light, a cautionary rate of change, which may be represented by a yellow light, and a fairly rapid and/or sustained rate of change, which would be for example shown by a red light, an alarm or a buzzer or the like, which would alarm both the wearer or act remotely for example to warn the parents of a neonate in the case of SIDS (Sudden Infant Death Syndrome).

In the alternative, digital version of the circuity of FIG. 11, the same photodetectors 118 and 119 and similar amplifiers output signal to an analog to digital conversion system 128 and a derivative circuit 124. The derivative circuit outputs signal to the analog digital converter, in this case for evaluation by the central processing unit, CPU, or microprocessor 129. Software, shown in FIG. 12, controls the system of data collection and lamp frequency 122 as well as the storing of data, interfacing with external computers and displaying/telemetrically communicating this information. The heart of this circuit is the central processing unit driven by software which will collect data, store it, display it and sound alarm if necessary.

FIG. 12 shows the software. Initialization of the system 140 takes place whereby the analog and digital system is set up and configured properly. The digital memory, communication and telemetry are configured as in FIG. 11. Secondly the device calibration takes place such that the gain of the amplifiers is set electronically by software. The gain of the amplifiers is set to an acceptable range so that digitization can take place accurately, as well as other small internal routines to determine whether the derivative is working properly or not. In the case that the calibration cannot take place, the program will stop and alarm the user. The alarm 134 represents "not working properly, please reset" etc. After calibration is completed successfully, data collection is begun. Data collection is taken in a loop format starting with 142. It starts with turning the lamp on, and sampling the signal, 143. Approximately 500 points of data are taken in rapid succession over approximately 1/2 second sampling interval or less. That data is accumulated, then the lamp is turned off after a delay period, which is set by the user and by the software. The samples are collected and then averaged at 144. This average is then used at 145 to calculate the sum, difference and derivative. In this case the calculated derivative serves as a redundant comparison with the analog derivative calculated in 125 of FIG. 11. In addition to the averaging of 760 and 850 nm, the derivative signal is also averaged and sampled in the same way, for example with 500 points. By this means a calculated derivative as well as a sample derivative are obtained which are compared to provide a much more repeatable and reliable result for an alarm.

The data after it has been manipulated in 145 will be stored, appropriately transmitted and/or displayed. In addition the alarm is set off if necessary at this point. Then finally an independent timer or delay would be introduced. The processor is delayed for a set period to obtain desired lampflash/data collections frequency.

The sequence is thus: lamp on, collect sample, lamp off, average sample, calculate sum, difference and derivative, then transmit, display etc., wait if necessary, and then turn on the lamp again and repeat the whole procedure.

Referring now to FIG. 13, a helmet 170 is shown having a tissue oximeter 172 molded at a position to snugly engage the head of the wearer when the helmet is put on, typically at a position free of body hair, e.g., at the forehead above the eyebrow. The oximeter is of the type, e.g., as described in FIG. 8b, having a source for transmitting NIR light, a detector to receive the light scattered from tissue such as brain tissue and a barrier to engage the head between the light source and the detector to prevent light traveling laterally between source and detector through subcutaneous layers. Preferably, the oximeter in the helmet includes a control circuitry on a miniature chip and preferably circuitry and/or software are provided for determining the rate of change of oximetry readings and for comparing the rate of change to a standard.

Referring now to FIGS. 14a-14b, an oximeter 180 is disposed on a catheter 150 (e.g., an endoscopic catheter), having an inflatable balloon 160 and endoscope optics 190. The oximeter 180 is preferably of the design illustrated in FIG. 7, and is molded or otherwise attached to the outer surface of the balloon. Controlling and detected signals may be passed to and received from the oximeter by wires passing through the balloon and a lumen within the catheter or by transmission from the oximeter to a receiver outside the body by telemetry as discussed, e.g., with respect to FIG. 9. In operation, the catheter, with the balloon deflated, is passed through a body lumen to the position of interest, guided for example, by fluorimetry or by endoscopic viewing. The balloon is then inflated to press the oximeter against the tissue of interest and measurements taken as described above. The technique and apparatus may be applied, for example, to body lumens such as the GI tract (e.g., for measurements of GI track wall ischemia or hypoxia as determined to be a preliminary indicator of multiple organ failure) or to blood vessels, employing an angiographic catheter for analysis and treatment of occlusions, etc. Still other embodiments are possible. For example, a "postage stamp" oximeter may be provided, e.g., for emergency use (self-contained system with alarm as discussed), where the oximeter is held to the subject by an adhesive pad, positioned peripherally around the device. Another embodiment includes providing a water impermeable coating about the device for applications in the presence of water, e.g., for scuba divers, etc. In yet another embodiment a phase modulation spectrophotometer may be employed for calibration of the oximeters described above, especially for in-home or long-term portable monitoring applications, e.g., greater than 3 hours. Such calibration allows more quantitive measure of blood oxygen levels, etc. One example of such a spectrophotometer can be found in U.S. Pat. No. 4,972,331, the entire contents of which is hereby incorporated by reference. It will also be understood that implantable probes may be configured using direct wiring, with corresponding punctures in the skin as an alternative to telemetry.

One of ordinary skill in the art will appreciate that the present invention is not limited to the particular embodiments described in detail. Modifications to the circuitry disclosed, and other aspects of the spectrophotometer configurations disclosed, as well as other modifications to the physical arrangement of the present apparatus will be obvious to those of ordinary skill. Further, the present invention is not limited to any of the uses described herein. In order to fully appreciate the scope of the present invention, reference should be made to the following claims.