Method and system for detecting apnea
Existing monitors for apnea miss many serious events because they do not adequately distinguish the heart signal in chest impedance from the respiratory signal. Described herein is a respiratory monitoring system and method for improved detection and response to apnea, particularly in a NICU setting but also useful in a home setting. This method filters from the chest impedance the part of the impedance that is caused by the beating of the heart in a human subject, and then identifies in real time significant silence in the filtered chest impedance signal, including determining the probability of apnea. If the probability of apnea exceeds a threshold value, the apneic subject can be stimulated using automated interactions such as a vibrating mattress or air blower.
1. A method for detecting and responding to apnea in a human subject comprising:
measuring in real time the chest impedance signal and heartbeat of a human subject;
converting said chest impedance signal per second to a re-sampled chest impedance signal per heartbeat;
filtering said re-sampled chest impedance signal to provide a filtered chest impedance signal per heartbeat;
renormalizing said filtered chest impedance signal;
calculating in real time the running variance of said filtered chest impedance signal; and
calculating a probability of apnea from a histogram compiled from the running variance of the filtered chest impedance signal for a set of apneic infants;
wherein said histogram is interpreted as a statistical mixture of a first distribution corresponding to apnea events and a second distribution corresponding to regular breathing, and said first distribution divided by the sum of said first distribution and second distribution produces a probability of apnea for each variance; and
wherein said filtered chest impedance signal attenuates the impedance caused by the heartbeat.
2. The method of claim 1 , wherein the method correctly identifies at least 90% of apnea occurrences compared with expert analysis.