Why the study?
Why do impedance apnoea alarm systems fail to detect apnoea?
Why do impedance apnoea alarm systems fail to detect apnoea?
Impedance apnoea alarm systems must be paired with a heart rate (ECG) detector because bradycardia-associated apnoea can produce cardiac impulses that mimic respiration and falsely suppress the alarm.
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Identifies mechanism for missed apnoea alarms with bradycardia; leaves open whether ECG co-monitoring improves detection in practice.
24-hour recordings of the ECG and respiration, the latter from an impedance technique, have shown a phenomenon which could account for hitherto unexplained failures of impedance apnoea alarm systems. Whenever apnoea is accompanied by bradycardia there is a pronounced increase in the amplitude of the cardiac impulse on the respiration carrier. This imitates the respiration signal and prevents the alarm from sounding. Conversely, apnoea unaccompanied by bradycardia does not present this problem and is detected by the alarm. If impedance alarm systems are to be used to detect apnoea they must be accompanied by a heart rate (ECG) detector.
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Southall et al. (1980) studied this question.
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