Impedance pneumography for long-term monitoring of respiration during sleep in adult males.

Impedance pneumography is based on the relationship between respired volume (delta V) and changes of transthoracic impedance (delta/Z/) during breathing. The impedance signal, the relationship between delta V and delta/Z/ and the success rate during long-term recording was studied in 11 healthy adult males, aged 21-46, by a portable tape recorder (Oxford Medilog 4-24). The signals from the tape recorder (delta/Z/), and from a spirometer (delta V) were recorded simultaneously on a mingograph during normal breathing, apnoea, deep sighs, and coughs. The relationship between delta V and delta/Z/ was also analysed on an X-Y recorder. Delta/Z/ was delayed in relation to delta V and during one respiratory cycle the relationship was not linear. The time constant of delta/Z/ was 6 s. A significant correlation was found between peak values of delta V and delta/Z/ for 0 less than delta V less than 2.5 litres. Long-term recording of delta/Z/ during one night's sleep resulted in a success rate of 63-100%, mean 90%. Invalidation of the impedance signal was caused by overloading (81%) and interference (19%). It is concluded that the Medilog respiratory recorder enables determination of respiratory frequency, periods of apnoea and a semiquantitative estimate of volume, but artifacts may invalidate the signal.