SUMMARYThe e f f e c t s of fluorocarbon v e n t i l a t i o n on cardiopulmonary f u n c t i o n were s t u d i e d i n 8 preterm lambs, 132-136 days g e s t a t i o n . A f t e r mechanical v e n t i l at i o n with 100% oxygen ( c o n t r o l p e r i o d ) . t h e lambs were v e n t i l a t e d with f l u o r ocarbon (PIOX = 622 t o r r ) . The l i q u i d was t h e n removed from t h e i r lungs and gas v e n t i l a t i o n resumed (recovery p e r i o d ) . During nomothennic l i q u i d b r e a t h i n g t h e a l v e o l a r -a r t e r i a l 02 g r a d i e n t (A-a 002) decreased (P < 0.01) from c o n t r o l by 154 t o r r and remained decreased (P c 0.05) by 85 t o r r during recovery. Dynamic lung compliance (CL) i n c r e a s e d 50% (P < 0.05); Pa02 i n c r e a s e d 50% (P e 0.05); and PaC02 decreased 29% (P < 0.01) a s compared t o c o n t r o l v a l u e s , The change i n A-a DO2 and Pa02 b e f o r e and a f t e r l i q u i d v e n t i l a t i o n was c o r r e l a t e d ( r = 0.79 and P c 0.01) with c o n t r o l CL, There was a gradual decrease (P < 0.01) i n mean a r t e r i a l p r e s s u r e from 62 t 5 . 4 t o r r ( c o n t r o l ) t o 53.1 t 9.3 t o r r (recovery); however, t h e r e were no s i g n i f i c a n t a l t e r a t i o n s i n mean c e n t r a l venous p r e s s u r e , h e a r t r a t e , o r mean e l e c t r i c a l a x i s . SPECULATIONThese d a t a demonstrate an improvement i n gas exchange and dynamic lung compliance i n p r e t e m lambs a f t e r l i q u i d fluorocarbon v e n t i l a t i o n , Regression a n a l y s i s suggests t h a t t h e improvement i n Pa02 and A-a DO2 was b e s t i n those lambs with t h e lowest i n i t i a l lung compliance.Furthermore, t h e secondary e f f e c t s of improved v e n t i l a t i o n and pulmonary blood flow, i n t h e long run could f a c i l i t a t e s u r f a c t a n t s y n t h e s i s .

The relationship between pulmonary function and the migration of meconium to distal airways was determined in 10 rabbits (mean weight 2.6 kg) after insufflation of a meconium-saline mixture (1--2 ml/kg). Animals were anesthetized, cannulated, intubated, and mechanically ventilated with 100% oxygen. Lung mechanical dysfunction was most severe during the early phase of meconium migration, 15 min postinsufflation. Substantial increases in inspiratory lung resistance (RI) and expiratory lung resistance (RE) suggest that the site of obstruction at 15 min was the large airways. A decrease in dynamic lung compliance with unchanged static compliance characterizes the obstruction as partial. At 15 min and throughout the migration process, RE was greater than RI, demonstrating a check-valve effect. This phenomenon was substantiated by an increased functional residual capacity (FRC) in all rabbits, presumably due to gas trapping. Secondary to these changes, marked hypoxemia, hypercapnea, and acidosis developed in spite of assisted ventilation with 100% oxygen. At 60 and 120 min postinsufflation, both RI and RE decreased as compared to 15 min. This suggests that the predominant site of obstruction shifted to medium and small airways concomitant with the migration of meconium. Widespread and uneven distribution of meconium still produced significant frequency dependence of lung compliance. Static compliance remained unchanged, indicating that meconium does not affect surface-active or tissue properties of the lung within 120 min postinsufflation. These data suggest that effective respiratory management after meconium aspiration is dependent on the degree of meconium migration, as reflected by pulmonary mechanics.

Cardiovascular adjustments during liquid ventilation were investigated in seven cats. Cardiac output (CO) and regional blood flow were measured with radioactive microspheres during both spontaneous air breathing (control) and ventilation with fluorocarbon liquid, FC-80. CO was found to decrease 48% (P less than 0.05) during liquid breathing as compared to control. This decrease largely reflected a reduced stroke volume. Despite the decreased CO, mean arterial pressure remained unchanged, indicating a 48% increase (P less than 0.002) in total peripheral resistance (TPR). Secondary to the reduced CO and increased TPR, extensive redistribution of blood flow occurred during liquid ventilation. The arterial lactate concentration and lactate-to-pyruvate ratio (L/P) were significantly increased (P less than 0.02). Furthermore, the increase in L/P correlated with the decrease in CO (r = 0.70; P less than 0.01). In turn, the significant decrease in pH during liquid breathing was found to correlate with the increase in L/P (r = 0.85; P less than 0.001). These data clearly demonstrate signficant alterations in cardiovascular dynamics during liquid ventilation with secondary hyperlactatemia and acidosis.

W e t e s t e d t h e hypothesis t h a t n e t L+R d u c t shunt c o n t r i b u t e s t o PBF surge i n premature lambs during t h e f i r s t hour of l i f e (Pediat. Res., 8:433, 1974) and t o high PBF seen l a t e r i n lambs with severe HMD ( P e d i a t . Res., 5:393, 1975). T o t a l PBF, r i g h t v e n t r i c u l a r output (RVO) and d u c t shunt were measured d u r i n g f i r s t hours of l i f e i n 1 lamb with and 1 without HMD. At 129-130d g e s t a t i o n , a p r e -c a l i b r a t e d electromagnetic flow transducer with non-occlusive zero was implanted on t h e main pulmonary a r t e r y (PA) t o measure RVO; a s i m i l a r transducer was implanted on t h e p o s t d u c t a l p o r t i o n of t h e common PA t o measure PBF. Duct shunt was c a l c u l a t e d a s t h e d i f f e r e n c e between PBF and RVO.