Sensing Device for Cardio-Pulmonary Functions

The present invention encompasses sensing means for monitoring the cardio-pulmonary functions of a patient, especially new born babies in an intensive care unit. According to the present invention up to four functions or parameters; PO.sub.2, PCO.sub.2, the respiration rate and encardiography are measured in both a simultaneous and transcutaneous way. Among the above four functions the first two are relatively new while the latter items have been practiced for a long time.

As is generally known, the respiration rate and encardiography are measured such that two electrodes 2, 2' are applied to predetermined portions on the skin of the human subject 1 and fluctuations in the potential between the electrodes are taken as a measure of encardiography, while fluctuations in the impedance between these electrodes are used to measure the respiration rate. Referring to FIG. 1, signals related to the two mentioned functions are led to a resistor R, and signals related to the heartbeat (of low frequency) are taken out by means of a low-pass filter 3 connected across the resistor R, while an alternate source of 50 kHz supplied for measurement is taken out by means of a tuning circuit 4 and detected in order to measure the respiration rate. Accordingly, two electrodes must be applied to the surface of the human body.

In addition, the transcutaneous measurement of PO.sub.2 and PCO.sub.2 require the attachment of a PO.sub.2 sensitive polarographic sensor and a pH sensitive PCO.sub.2 sensor, respectively, on the surface of the body. FIG. 2 shows a sectional view of typical PO.sub.2 non-invasive sensor assembly.

A rod-shaped cathode 5 is disposed in the center, and an anode 7 is mounted about the cathode 5 with intervening glass insulation 6. The ends of the anode contact an electrolyte 9 which is covered by an electrode membrane 8. The peripheral portion of the electrode 7 is covered by a metal heating ring 10 and a skin-heating metal plate 11. An exposed portion of the skin-heating metal plate 11 is made to contact the skin surface when the sensor assembly is attached to the surface of the body. As described above, four sets of electrodes need be attached to the surface of the human body when the above four functions are to be measured simultaneously. When such a large number of electrodes and sensors are required to be attached to a limited surface area of the patient, it often happens that some of the functions must be measured later due to space limitations. In addition, as the number of electrodes or sensors to be attached increases, the number of electric lead wires will naturally increase and cause difficulties in the handling of the electrodes or sensors in an intensive care unit.

It is the object of the present invention to provide an improved sensor device for measurement of the four above mentioned cardiopulmonary functions which enables simultaneous and continuous measurement of the human body in a non-invasive manner. As previously mentioned, each of the PO.sub.2 and PCO.sub.2 sensors uses a skin-heating metal plate in order to obtain a sufficient and stable state of vasodilation of the tissues under the surface of the skin. Therefore, the present invention is characterized in that a skin-heating plate is utilized as an electrode for measuring the respiration rate and encardiography, so that the four functions can be determined by means of only two electrode sets or sensors.

FIG. 1 is a circuit diagram of a device for measuring heartbeat and respiration;

FIG. 2 is a sectional diagram of a preferred embodiment of the present invention.

FIG. 3 is a circuit diagram of a preferred embodiment of the present invention.

A preferred embodiment of the present invention will now be described with reference to FIG. 3. In FIG. 3, an AC power source 12 is connected to a primary coil 14 of a transformer 13. Three coils 15, 16 and 17 are wound on the secondary side of the transformer 13. The coil 15 is connected through a transformer 18 to a PO.sub.2 measuring circuit 19, the coil 16 is connected through a transformer 20 to a PCO.sub.2 measuring circuit 21, and the coil 17 is connected through a transformer 22 to a heartbeat and respiration measuring circuit 23. As the PO.sub.2 measuring circuit 19, the PCO.sub.2 measuring circuit 21 and the heartbeat and respiration measuring circuit 23, conventional circuits may be used, respectively. Reference numeral 24 designates the PO.sub.2 sensor shown in FIG. 2. Electrodes 24a, 24b are connected to the PO.sub.2 measuring circuit 19 through lead wires 25. Similarly, electrodes 26a, 26b of the PCO.sub.2 sensor 26, which has the same construction as the above mentioned PO.sub.2 sensor 24, are connected to the PCO.sub.2 measuring circuit 21 through lead wires 27. Rings 24c, 26c, illustrated by circles drawn about the electrodes of the PO.sub.2 sensor 24 and the PCO.sub.2 sensor 26 are similar to the skin-heating metal plates 11 shown in FIG. 2, and are connected to the heartbeat and respiration measuring circuit 23 through lead wires 28 and 29 respectively. In other words, the rings 24c, 26c serving as skin-heating metal plates also function as the electrodes 2, 2 shown in FIG. 1. There are no particular differences in electrical operation between the rings 24c, 26c and conventional ones.

In conducting measurement using the preferred embodiment, the PO.sub.2 sensor 24 and the PCO.sub.2 sensor 26 are attached at positions suitable for measuring heartbeat and respiration. PO.sub.2 is then measured through the electrodes 24a, 24b while PCO.sub.2 is measured through the electrodes 26a, 26b as usual. At the same time, heartbeat and respiration can be measured using the rings 24c, 26c as electrodes. In other words, it becomes possible to conduct the measurement of four parameters simultaneously by attaching only two sensors.

For the lead wires 25, 25 and 28, a three-wire cable can be used, and for the lead wires 27, 27 and 29 a second three-wire cable can be used likewise. The number of cords thus decreases, so that handling is facilitated.

As mentioned above, according to the present invention, it is possible to conduct the measurement of four functions simultaneously using only two sets of electrodes. In addition, the handling of the equipment is facilitated due to the decreased number of electrode or sensor lead wires.