Abstract
Some newborns with pulmonary hypertension (PHN) have been noted to have increased SVR. To assess whether this is a reflex response to an increase in pulmonary artery pressure (PPA), we acutely produced balloon distension of the left PA. Fourteen lambs (1-3 days) were anesthetized with chloralose and instrumented to enable measurement of systemic blood flow (Qs), (PPA), aortic pressure (PAo), heart rate (HR), and right atrial pressure (PRA). PA distension was performed 47 times in 14 lambs (1-7/lamb). The mean PAo (±S.D.) increased from 55±13 mmHg to 58 ± 15 mmHg (p<0.05) and the SVR increased from 82 ± 20 mmHG/L/min to 84 ± 19 mmHg/L/min (p<0.05) while the mean Qs and PRA did not change. In two lambs, alpha-blockade eliminated any changes in SVR. In another lamb, neither beta-blockade nor right vagotomy obliterated the changes whereas a left vagotomy did, suggesting that the reflex is under autonomic control.
In conclusion, some reflex interdependence appears to exist between the systemic and pulmonary vascular beds. The magnitude of the systemic changes is small and probably of no clinical significance when triggered acutely postnatally in infants with normal vasculature. However, if there is long standing PA distension in utero, it may account for the increase in SVR observed in some newborns with PHN. We postulate that the reflex changes in the systemic vascular bed may be most important in fetal life when it may affect redistribution of cardiac output in the hypoxemic fetus.
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Milstein, J., Goetzman, B. & Bennett, S. 121 EFFECTS OF PULMONARY ARTERY DISTENSION ON SYSTEMIC VASCULAR RESISTANCE (SVR). Pediatr Res 19, 131 (1985). https://doi.org/10.1203/00006450-198504000-00151
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DOI: https://doi.org/10.1203/00006450-198504000-00151