Pulmonary shunt and cardiovascular responses to CPAP during nitroprusside-induced hypotension.
The effects of continuous positive airway pressure (CPAP) on cardiovascular dynamics and pulmonary shunt (QS/QT) were investigated in 12 dogs before and during sodium nitroprusside infusion that decreased mean arterial blood pressure 40-50 per cent. Before nitroprusside infusion, 5 cm H2O CPAP significantly, P less than .05, decreased arterial blood pressure, but did not significantly alter heart rate, cardiac output, systemic vascular resistance, or QS/QT. Ten cm H2O CPAP  before nitroprusside infusion produced a further decrease in arterial blood pressure and significantly increased heart rate and decreased cardiac output and QS/QT. Nitroprusside caused significant decreases in arterial blood pressure and systemic vascular resistance and increases in heart rate, but did not change cardiac output or QS/QT. Five cm H2O CPAP during nitroprusside did not further alter any of the above-mentioned variables. However, 10 cm H2O CPAP decreased arterial blood pressure, cardiac output, and QS/QT. These data indicate that nitroprusside infusion rates that decrease mean arterial blood pressure by 40-50 per cent do not change cardiac output or QS/QT. During nitroprusside infusion low levels of CPAP do not markedly alter cardiovascular dynamics, but high levels of CPAP (10 cm H2O), while decreasing QS/QT, produce marked decreases in arterial blood pressure and cardiac output.
D000818:Animals; D001794:Blood Pressure; D002302:Cardiac Output; D004285:Dogs; D005292:Ferricyanides; D006339:Heart Rate; D006439:Hemodynamics; D007023:Hypotension, Controlled; D009599:Nitroprusside; D010100:Oxygen / Q000097:blood; D011175:Positive-Pressure Respiration; D011652:Pulmonary Circulation; D014655:Vascular Resistance
D005292:Ferricyanides; D009599:Nitroprusside; D010100:Oxygen