Gr. Manecke et al., AUSCULTATION REVISITED - THE WAVE-FORM AND SPECTRAL CHARACTERISTICS OF BREATH SOUNDS DURING GENERAL-ANESTHESIA, International journal of clinical monitoring and computing, 14(4), 1997, pp. 231-240
Although auscultation is commonly used as a continuous monitoring tool
during anesthesia, the breath sounds of anesthetized patients have ne
ver been systematically studied. In this investigation we used digital
audio technology to record and analyze the breath sounds of 14 health
y adult patients receiving general anesthesia with positive pressure v
entilation. Sounds recorded from inside the esophagus were compared to
those recorded from the surface of the chest, and corresponding airfl
ow was measured with a pneumotachograph. The sound samples associated
with inspiratory and expiratory phases were analyzed in the time domai
n (RMS amplitude) and frequency domain (peak frequency, spectral edge,
and power ratios). There was a positive linear correlation (R-2 > 0.9
) between inspiratory flow and sound amplitude in the precordial and e
sophageal samples of all patients. The RMS amplitude of the inspirator
y and expiratory sounds was approximately 13 times greater when record
ed from inside the esophagus than from the surface of the chest in all
patients at all flows (p < 0.001). The peak frequency (Hz) was signif
icantly higher in the esophageal recordings than the precordial sample
s (298 +/- 9 vs 181 +/- 10, P < 0.0001), as was the 97% spectral edge
(Hz) (740 +/- 7 vs 348 +/- 16, P < 0.0001). In the adult population es
ophageal stethoscopes yield higher frequencies and greater amplitude t
han precordial stethoscopes. Quantification of lung sounds may provide
for improved monitoring and diagnostic capability during anesthesia a
nd surgery.