Abstract
Pulmonary vascular responses to histamine(H) and acetylcholine (A) were studied in 5 unsedated newborn lambs (3-5 wks, 5-9 kg). Flow probes were placed around the right and left pulmonary arteries (RPA,LPA); 5-7 days were allowed for full recovery (respirations<36, clear lungs on X-ray). Catheters were then placed in the aortic root(Ao) and either R or LPA. The maximum PA gradient across a probe was 3 mmHg. Bolus injections of H (2-10μg) and A (2-10μg) were made into R or LPA and, as a control, into Ao. RPA flow, LPA flow, Ao and PA pressures were measured continuously. The fraction of total cardiac output directed to the injected lung (Qinj/QT), systemic and pulmonary vascular resistances (SVR, PVR) were calculated before, and 10, 20, 30, and 60″ after injections.
A into Ao reduced SVR(44%)* and PVR (18%)*, but there was no change in Qinj/QT (51 vs 52%). Injection of A into RPA or LPA yielded the same results: SVR fell 49%*, PVR fell 17%*, but again, no change in Qinj/QT (49 vs 52%). H into Ao also decreased SVR (34%)* and PVR(22%)* without changing Qinj/QT. However, H into RPA or LPA decreased Qinj/QT in all 6 experiments (62 vs 47%).*
In this experimental model, each lung “sees” the same neural input, as well as left atrial, intrathoracic, and PA pressures. Thus, one lung serves as a control for the other, allowing study under more physiologic conditions. The results indicate that, in newborn lambs, A has minimal direct effects on the lungs, and causes pulmonary “vasodilation” via its effect on the systemic circuit. In contrast. H is a direct pulmonary constrictor *p<0.02
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Lock, J., Coceani, F., Olley, P. et al. 138 PULMONARY VASCULAR RESPONSES IN UNSEDATED NEWBORN LAMBS. Pediatr Res 12 (Suppl 4), 386 (1978). https://doi.org/10.1203/00006450-197804001-00143
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DOI: https://doi.org/10.1203/00006450-197804001-00143