LUNG SOUNDS IN NEONATES WITH AND WITHOUT AN ADDED DEAD SPACE

Previous studies have reported great difficulty in recording lung soun ds from neonates and have found conflicting results. We studied lung s ounds in neonates during the inspiratory phase of the respiratory cycl e as monitored by inductive plethysmography (A) and by a pneumotachogr aph and a face mask (B) which added a dead space of 12 mt. Sixteen ter m babies were tested 12 hr to 6 days (median 45 hours) after birth. Lu ng sounds were recorded and then analysed using overlapping and non-ov erlapping fast Fourier transforms. The two methods of analysis showed a difference in intensity but not in frequency. Fourteen babies provid ed enough breaths for comparison; a total of 596 inspirations were ana lysed. The intensity of lung sounds on occasion B was higher in all bu t two babies with a mean BIA ratio of 2.4. The mean (SD) power on occa sions A and B was 13.9 (8.5) mW and 26.9 (21.0) mW, P = 0.02, respecti vely. In all but 4 babies the B/A ratios of the median (f(50)) and 90t h centile (f(90)) frequencies were scattered randomly within 20% of un ity. The mean (SD) f(50) on occasions A and B was 205.5 (51.1) Hz and 225.8 (32.3) Hz, P = 0.10, respectively; the mean f(90) was 370.3 (91. 0) Hz and 396.1 (67.8) Hz, P = 0.25, respectively. Linear regression s howed that there is a third-order polynomial relationship between soun d intensity and air flow at the mouth. A weaker positive association e xists between frequency and air flow, showing that the median and 90th centile frequencies approach an asymptote as flow increases. We concl ude that adding a dead space increases the intensity of lung sounds in neonates due to increased flow, but has no consistent effect on frequ ency content. Pediatr Pulmonol, 1995; 19:348-354. (C) 1995 Wiley-Liss, Inc.