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PULMONARY BLOOD FLOW (PBF) IN LAMBS WITH HYALINE MEMBRANE DISEASE (HMD)

Effective PBF is low during the course of HMD (Chu et al, Pediatrics, 35:733, 1965). It is not known whether this change is central in the etiologic chain of events or simply a secondary phenomenon. Total PBF was measured during the first 4 hr of life in lambs with and without HMD. At 129-133 days' gestation a pre-calibrated electromagnetic flow transducer with non-occlusive zero was implanted on the postductal portion of the common pulmonary artery of 8 fetal lambs which were returned to the amniotic cavity for 7 days and then delivered by C-section at 136-140 days' gestation. After birth a Swan-Ganz catheter was floated into a branch pulmonary artery for pressure measurements. By clinical and blood gas criteria, 4 lambs had no distress or developed mild HMD; 4 developed moderate or severe HMD. PBF increased sharply from less than 50 ml/Kg/min just before delivery to 299-735 ml/Kg/min 21 to 33 min after the first gasp and stabilized at lower levels by 1 hr of age. No differences in the pattern of the PBF surge or in the PBF levels attained during and subsequent to the surge were observed between the two groups. Severely acidotic lambs with HMD had pulmonary vascular resistance (PVR) values similar to those of lambs with no distress or mild HMD. The data suggest that decreased PBF is not central in the pathogenesis of ovine HMD and that the prematurely born lamb with HMD lacks the ability to increase PVR when acidotic.