Tidal volume and respiratory frequency in infants with bronchopulmonary dysplasia (BPD).

To examine the respiratory pattern in infants with BPD, we compared measurements in 4 infants not retaining CO2 (PACO2 = 40) with those in 4 infants retaining CO2 (PACO2 = 52). We also studied 14 healthy preterm infants, 7 not retaining CO2 (PACO2 = 32) and 7 retaining CO2 (PACO2 = 45). In infants with BPD, minute ventilation (VE) was 0.996 (mean) and 1.0021 l/min with and without CO2 retention (P greater than 0.5). Tidal volume (VT) was 12.6 and 21.1 (P less than 0.001) and total duration of the respiratory cycle (Ttot) 0.77 and 1.33 (P less than 0.005) with and without CO2 retention. VT/Ti were 45.00 and 44.89, respectively (P greater than 0.5). In preterm infants, VE was 0.537 and 0.710 l/min with high and low CO2 (P greater than 0.1). VT was 15.4 and 11.00 (P greater than 0.2) and Ttot 1.63 and 0.99 (P less than 0.002) with high and low CO2. VT/Ti was 32.08 and 30.56 (P greater than 0.5). These findings suggest: (1) in infants with BPD, VT and frequency (f) change in much the same way as in adult subjects with chronic obstructive lung disease, i.e., VT decreases and Ttot shortens (f) in association with high PACO2; (2) mean inspiratory flow is essentially the same in infants with BPD who do and do not retain CO2; and (3) in infants with normal lungs, VT and Ttot increase (f) in association with high PACO2, breathing pattern being entirely controlled via changes in the timing mechanism, the inspiratory drive remaining unaltered.