BREATH SOUNDS AND REGIONAL VENTILATION

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Abstract
An index of breath sound pressure and the transmission index of white noise was recorded phonopneumographically from the mouth over 4 lung regions between apex and base in 15 normal subjects upright and supine. In 10 subjects, these measurements were correlated with the regional distribution of inhaled 133Xe. The ratio, breath sound index/sound transmissions, partially corrects for differences in breath sound index due to differences in sound transmission. The 133Xe and breath sound indices were expressed as a percentage of the value over the apex. In both postures, breath sound index/sound transmissions correlated best with raw counts after inhalation of a bolus of 133Xe. Raw counts are measures of total ventilation, i.e., the ventilation per alveolus .times. the number of alveoli seen by the scintillation counter. Breath sound index/sound transmissions correlated as well with raw counts after equilibrium with 133Xe, which is a measure of the number of alveoli. Breath sound index correlated less well than breath sound index/sound transmissions with 133Xe bolus raw counts in upright posture but did not correlate with 133Xe bolus raw counts in supine posture. The same was found when breath sound index was correlated with 133Xe equilibration raw counts. The uncompensated breath sounds (breath sound index) heard by clinicians cannot be used confidently in both upright and supine postures to assess regional ventilation. The compensated breath sounds (breath sound index/sound transmissions), which partially account for differences in breath sound index due to differences in sound transmissions, are much better indices of total regional ventilation than breath sound index in both upright and supine postures. They appear to reflect not only regional ventilation but also the number of sound generators under the microphone.

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