PROLONGED PULMONARY VASCULAR HYPERREACTIVITY IN CONSCIOUS DOGS AFTER CARDIOPULMONARY BYPASS

Although cardiopulmonary bypass (CPB) is required in all surgical proc edures involving open-heart surgery, the extent to which CPB alters pu lmonary vascular regulation has not been systematically investigated. Our objectives were to investigate the acute, subacute, and chronic ef fects of CPB on the left pulmonary vascular pressure-flow (LP-Q) relat ionship in conscious dogs. Continuous LP-and plots were generated in c hronically instrumented conscious dogs 2-4 days pre-CPB and again 4 h and 1, 2, 7, and 14 days after 2.5 h of closed-chest hypothermic CPB. In addition, pulmonary vascular reactivity was assessed by examining t he dose-response relationship to the thromboxane analogue U-46619 pre- and post-CPB. CPB resulted in an acute (4 h post-CPB) shift in the ba seline LP-and relationship, indicating an increase in pulmonary vascul ar resis tance (P < 0.01). The baseline LP-and relationship returned t o pre-CPB values by 1 day post-CPB. Despite this return of the baselin e LP-Q relationship to pre-CPB values, the pulmonary vasoconstrictor r esponse to U-46619 was markedly potentiated 2 days post-CPB compared w ith the pre-CPB response (P < 0.01). This enhanced pulmonary vasoconst rictor response to U-46619 was still apparent 7 days post-CPB (P < 0.0 1) but was not evident 14 days post-CPB. These results indicate that C PB results in a pronounced, but transient, increase in pulmonary vascu lar resistance. Moreover, CPB causes a protracted increase in pulmonar y vascular reactivity even when the baseline LP-and relationship has r eturned to pre-CPB values. This experimental model can be used to asse ss the specific effects of CPB on acute and chronic mechanisms of pulm onary vascular regulation.