Vesicular lung sound amplitude mapping by automated flow-gated phonopneumography DENNIS M. O’DONNELL AND STEVE S. KRAMAN Department of Medicine, Section of Pulmonary Medicine, Veterans Administration Medical Center, and Division of Pulmonary Medicine, University of Kentucky Medical Center, Lexington, Kentucky 40511 . O'DONNELL,DENNIS M., AND STEVE S.KRAMAN. Vesicular lung sound amplitude mapping by automated flow-gated phonopneumography. J. Appl. Physiol.: Respirat. Environ. Ex- ercise Physiol. 53(3): 603-609, 1982.-A recently developed automated apparatus capable of determining vesicular lung sound amplitude rapidly and accurately was used to construct detailed inspiratory vesicular sound amplitude maps in eight healthy male subjects to determine the normal amplitude pat- terns on the chest wall. The sounds were recorded in 2-cm steps along the following lines bilaterally: A, vertically, clavicle to abdomen, 6 cm from the sternal border; B, vertically, from the level of T1 to the lung bases, 6 cm from the spine; and C, horizontally, from the sternal border to the spine at the level of the nipple. Sound amplitude was measured at an airflow rate of 1.3 l/s. The resulting amplitude maps revealed considerable intra- and intersubject variation with frequent amplitude het- erophony. Th patterns for the subjects as a group were as follows: series A, amplitude decreasing with distance from the clavicle; series B, amplitude increasing with distance from Ti with a peak at the bases; and series C, approximately equal amplitude at all positions. The findings in series B and C are, in general, consistent with an explanation of ventilation follow- ing hydrostatic gradients. The series A pattern and the inter- subject variability in amplitude are inconsistent with this ex- planation and suggest that the inspiratory vesicular sound amplitude is not simply a result of ventilation distribution but involves other as yet undefined factors. breath sounds; ventilation; amplitude heterophony PHONOPNEUMOGRAPHY, a technique of visually display- ing the amplitude and/or frequency of lung sounds, has previously been used by investigators to study regional ventilation and to evaluate the amplitude and frequency characteristics of lung sounds (1, 3, 9, 11). One inade- quately studied characteristic of the vesicular lung sound is the relative amplitude of this sound at various locations on the chest wall. To our knowledge, the most detailed vesicular sound amplitude maps have been constructed by Ploy-Song-Sang et al. (9, 10) and involved only four sites on the right anterior chest wall. Other investigators (7, ll), when studying comparative lung sound ampli- tudes, have included even fewer sites. The major reason that vesicular sound amplitude patterns have been so little studied lies with the difficulty in comparing one breath with another when the peak flow rates are not identical, as is almost invariably the case; also, no auto- mated measurement apparatus has yet been developed, so that measurements must be done manually, thus limiting the number of breaths that may be conveniently measured. The simultaneous display of an airflow signal along with the lung sound signal allows measurement of the latter at comparable flow rates but is so time consum- ing that few breaths can be so evaluated. An attractive alternative technique, using a large array of microphones attached to many points on the chest wall and measuring each breath simultaneously, could be employed but be- comes more complex and expensive as more microphones and strip-chart recorder channels are added. Detailed knowledge of lung sound amplitude patterns is important if intelligent interpretation of amplitude differences within and between subjects is to be accom- plished. We have recently developed an automated tech- nique that permits rapid, accurate lung sound amplitude determinations. We describe herein its use in mapping the amplitude patterns of the vesicular breath sound in normal subjects. METHODS Eight healthy medical personnel between the ages of 24 and 36 yr volunteered to participate in this study after informed consent was obtained. All subjects were lifetime nonsmokers and had normal pulmonary function as de- termined by history, physical examination, and spirom- etry (8). The subjects received training in breathing only insofar as was necessary to allow them to achieve an even increase in the rate of flow on inspiration. The recordings were performed with the subjects standing while they breathed through a pneumotachograph and watched a graphic display of the airflow rate at the same instant on an oscilloscope screen. The subjects were instructed to inspire from resting lung volume and to attempt to reach a peak inspiratory flow of approximately 2 l/s. They then exhaled normally. The method of sound amplitude analysis has been previously reported (6); briefly, (Fig. 1) a condenser mi- crophone with chest piece of 15 mm diameter and 9 mm depth was placed on the chest at each point of interest. The signal was pass-band limited to a center frequency of 400 Hz (6-dB points, 150 and 700 Hz) to attenuate extraneous sounds, passed through an oscilloscope for visual monitoring, various stages of amplification, and was then sent to a multichannel analog-to-digital con- verter and computer. The output signal of a Fleisch 0161-7567/82/0000-0000$1.25 Copyright 0 1982 the American Physiological Society 603