A bioacoustic method for timing of respiration at cardiac investigations.

At cardiac investigations Doppler echocardiography is an established technique for the recording of intracardial and intravascular flow velocities. Transvalvular and venous flows are, however, markedly influenced by respiration. Since the start of inspiration is the important time of reference, accurate recording of the respiratory phase is important when analysing these flow velocities. A bioacoustic technique was therefore adopted to meet this demand and was tested in 10 normal subjects. Oesophageal balloon technique was used as a reference, and the bioacoustic technique was compared with a respiratory inductive plethysmograph. The average delay for the acoustic sensor signal compared to the oesophageal pressure changes was 205 +/- 46 (SD) ms, ranging from 160 to 320 ms for normal breathing, and is comparable to that of the respiratory inductive plethysmograph (210 +/- 90 ms). The bioacoustic technique is easier to apply than the respiratory inductive plethysmograph. The sensitivity to disturbances can be further reduced by signal processing and the method has clinical potential for the future.