Demonstration of regional phase differences in ventilation by breath sounds

Publisher Website
Google Scholar
Abstract
Phase and amplitude of compensated breath sounds (Ib/Tn), which are indexes of regional ventilation were measured with 2 microphones placed near the apex and base 10 cm apart on the chest wall, lateral to the right anterior axillary line in 4 seated normal subjects. Phase and amplitude of Ib/Tn were compared with phase and amplitude of esophageal pressure changes (Pes) measured by 2 balloons positioned 10 cm apart and at approximately the same horizontal levels as the microphones. When breathing tidally below closing volume (CV), apical Ib/Tn was louder and earlier than basal Ib/Tn, whereas basal Pes was greater and earlier than apical Pes. Above CV basal Ib/Tn was louder than apical and the phase differences either disappeared or followed phase differences in PES. Below CV, ventilation of lower zones lags behind upper ones probably due to airway closure. Pes measurements indicate that this may lead to an amplification of pleural pressure swings at the base. Above CV, all airways are open, the ventilation of lower zones is greater than that of upper zones, and the sequence of ventilation follows the sequence of pleural pressure changes.