FLOW-VOLUME RELATIONSHIPS IN INFANTS WITH HYALINE MEMBRANE DISEASE

Abstract

Flow-volume (V/V) loops and pressure-volume loops (P/V) were obtained during the performance of crying vital capacity (CVC) maneuvers in 31 infants ranging in birth weight from 960 to 2750 grams and in gestational age from 26 to 40 weeks. Eighteen of the 31 infants were diagnosed as having respiratory distress due to hyaline membrane disease (HMD) on clinical and radiological criteria. As reported in previous investigations, CVC was reduced in infants with HMD. Peak expiratory flow rate (PEFR) was not significantly related to CVC (r=.16). When CVC was standardized for body size a significant relationship (r=.25,p<.025) was found. Peak inspiratory flow rate (PIFR) demonstrated higher correlations with CVC (r=.70,p<.001) and CVC per cm of body length (r=.64,p<.001). Similar patterns of V/V loops were found in normal and HMD infants with HMD infants demonstrating smaller loops due to low flows and loss of lung volume due to disease. Their loops returned to normal with recovery. Expiratory flow was 25% of inspiratory flow in normal infants and 33% of inspiratory flow in HMD infants. During performance of CVC both HMD and non-distressed premature infants may generate pressures as high as 30 cm H₂O during expiration. Taken in conjunction with the significant reduction in PEFR/PIFR when compared with normal children and adults, this suggests that airway compliance in premature infants is high, and that airway closure during CVC may limit CVC and cause air-trapping during normal breathing.

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