DISTRIBUTION OF REGIONAL VENTILATION MEASURED BY BREATH SOUNDS

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Abstract
An index of breath-sound intensity (Ib) and the transmission of white noise (Tn) over 4 lung regions between apex and base in 5 normal subjects in the upright and supine postures was recorded. Ib and Tn were recorded over the whole lung volume range from residual volume to total lung capacity, Ib and Tn were computed and expressed as a fraction of the value over the apical region with the help of an analog divider. The ratio of Ib to Tn was used to correct for differences in Ib due to differences in sound transmission, and Ib/Tn was also expressed as a fraction of the value over the apex. The ratio of basal to apical Ib/Tn, which is a measurement of the relative total ventilation to each region, increased from residual volume to total lung capacity, indicating that the ventilation to lower portions of the lung increases as lung volume increases. The differences between Ib/Tn in the upright and supine postures was due to the effect of gravity on total regional ventilation. If the change in lung volume under each microphone is similar for all regions in changing from the upright to the supine posture and if ventilation per unit of lung volume is regionally equal between apex and base in the supine posture, then the ratios between upright Ib/Tn and corresponding supine Ib/Tn are measurements of regional ventilation per unit of volume of different regions in the upright posture. These regional ventilations per unit of volume were similar to data in the literature obtained with radioactive gases.

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