DETERMINATION OF RESPIRATORY RATE ON THE BASIS OF RESPIRATORY SINUS ARRHYTHMIA

In the clinical setting, the observation of undisturbed spontaneous re spiration and direct measurement of an ''unbiased'' respiratory rate i s not a practical option. However, the respiratory modulation of the h eart rate (respiratory sinus arrhythmia, RSA) offers a possibility of recording the respiratory rate indirectly. The present work introduces a novel procedure for extracting the respiratory rate from the ECG, a nd compares the results thus obtained with those of a previously appli ed method. The latter is based on the determination of dominant peaks in the amplitude spectrum of a five-minute RR interval time series. Th e new method presented here is based on the band pass filtering of a o ne-minute RR interval time series with subsequent analysis of the maxi ma, minima and zero crossings of the resulting RSA curve. The methods were compared by determining the respiratory rates of 16 healthy male subjects measured in 15 different experimental situations, including s pontaneous and controlled breathing, The respiratory rate as determine d by thermistor recording of nasal breath temperature was used as cont rol. The mean deviation from directly measured respiratory rate was 2. 9 min(-1) for the new and 7.2 min(-1) for the previous method. The new method proved superior under all conditions except controlled breathi ng at low frequencies. The present study thus demonstrates the high pr ecision of respiratory rate determined indirectly by analysing the RSA curve. Since it requires no special instrumentation, this procedure i s ideally suited for clinical application, and permits the continuous recording of respiratory rate over long periods of time.