fig1 a shows heart sound activity , picked up by an accelerometer and amplified . fig1 b shows a surface ecg . fig1 c shows the left ventricular pressure respectively , as functions of the same time line . the opening and closing of the aortic valve can be clearly observed in the accelerometer signal and are indicated in the corresponding curve . from fig1 a , 1b and 1c , it appears that the amplitude of the heart sounds varies with the respiration . this appears still more clearly from fig2 a and 2b . fig2 a shows the accelerometer signal after high - pass filtering ( the cut - off frequency being 100 hz ), rectifying and smoothing . fig2 b shows the signal out of a respirator for determining the respiration in this case . as appears from these diagrams , the respiration frequency is very well reproduced in the sensed heart sound signal . a very close correlation between the mechanical heart activity and the respiration and the respiration rate thus can be directly extracted from the heart sound curve . as mentioned above the invention can be used in a pacemaker to provide a rate responsive pacemaker , based on the respiration of the patient . fig3 shows such a pacemaker 2 with an accelerometer 4 mounted inside the pacemaker can . the accelerometer 4 , which is shown more in detail in fig4 is of a piezoelectric type . the accelerometer 4 has an l - shaped piezoelectric rod 6 having a weight 8 fixed at a free end of the rod 6 . the other end of the rod 6 is attached to a printed circuit board 10 having the associated electronics . the electronics include a non - inverting amplifier 12 with a lower cut - off frequency of about 20 hz and a gain of 2000 , a high - pass filter 14 , a rectifier stage 16 , a signal smoothing stage 18 and an analyzer 20 ( see fig5 ). thus the signal from the piezoelectric element 6 is first amplified and then high - pass filtered . the cut - off frequency of the high - pass filter 14 is selected to be to 100 hz . frequencies related to body movements of the patient are thus removed from the sensed signal which makes the device and the apparatus function reliably even when carried by a patient in motion . the analyzer 20 is a data processor , like a computer . if normal variation is detected in the amplitude of the sensed heart sound signal the apparatus gives an &# 34 ; ok &# 34 ; audio signal . if heart sounds with an amplitude variation which is too low are detected and last beyond a period of time of predetermined length of time , a first alarm 22 , preferably a high intensity audio buzzer , is triggered to indicate an apnea episode . if no heart sounds are sensed during a predetermined time , a second alarm 24 is triggered to indicate a failure , probably due to dislodgement of the sensor . these two alarms are preferably realized by a single alarm unit which delivers acoustic and / or visual signals and / or mechanical vibration signals of two different qualities . the necessary electric supply to the electronics is delivered by a battery 26 provided with a low battery guard circuit 28 . the device according to the invention can be mounted inside a 10 pacemaker can as described above . it can , however , also be mounted in a housing intend to be attached to the skin of the patient &# 39 ; s chest . the device is then disc - shaped with a diameter of 30 mm and a thickness of a few mm . to allow for change of battery the housing has a replaceable , preferably sticky surface layer for attachment to the skin . fig6 shows an embodiment with a recording and storage device 30 having a heart sound sensor in the form of a piezoelectric sensor 32 , and a memory 34 for storing sensed data . the device 30 is intended to be attached to the skin of the chest wall of the patient by a sticky pad , at the side 36 , with the piezoelectric sensor 32 adjacent to the chest wall . a second sensor in the form of a finger worn oxygen sensor ( oximeter ) 38 attachable to the finger of a patient to continuously measure the degree of blood oxygen saturation . this sensor 38 is suitably a light emitting oxygen measuring sensor and this sensor is connected to the memory 34 of the device 30 via a radio frequency telemetry link or an optical or wire communication link , indicated at 40 . in addition , data from a body movement sensor ( not shown in fig6 ), can also be supplied to the memory 34 . after the data collection or recording phase , which is suitably performed by the patient at home , the device 30 is sent , e . g . by mail , to a hospital , where an analyzer is available . the data stored in the memory means 34 is then transferred to the computer of the analyzer . for that purpose the device 30 can be designed for being directly plugged into an ordinary pcmcia adapter of the computer . the device 30 preferably has a data compression stage 42 for facilitating storage , transfer and even analysis of large volumes of data . by simultaneous recording of respiration information by heart sound sensing , degree of blood oxygen saturation and body movements for analysis , more accurate assessment and reliable diagnosis of respiration disorders are obtained . although modifications and changes may be suggested by those skilled in the art , it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art .
a device for determining the respiration rate and / or respiration depth of a patient includes a sensor for sensing heart sounds and an analyzer for analyzing the variation of the amplitude of the sensed heart sounds to determine the respiration rate and / or respiration depth from this amplitude variation . an apparatus for monitoring the respiration of a patient includes such a device and the analyzer is arranged to determine an anomaly in the amplitude variation of the sensed heart sounds as an indication of a respiration anomaly .