The local component of the acute cardiovascular response to simulated apneas in brain-dead humans.

Abstract

STUDY OBJECTIVES: To investigate the local cardiovascular response to hypoxemia and hypercapnia in a simulated central apnea model in which the central autonomic regulation was absent. DESIGN: Experimental study. SETTING: A university hospital. INTERVENTIONS: A simulated central apnea model achieved by a particular setting of the mechanical ventilator in 10 brain-dead patients. MEASUREMENTS: Hemodynamic studies using right-heart catheterization and continuous monitoring of arterial blood gas levels. RESULTS: Hypercapnic hypoxic apneas were associated with no change in heart rate, fall in mean systemic arterial pressure and systemic vascular resistance (from 83 +/- 9 to 68 +/- 7 mm Hg and 1,115 +/- 82 to 768 +/- 58 dyne.s.cm(-5), respectively; each p < 0.05), and rise in mean pulmonary artery pressure, pulmonary vascular resistance, and pulmonary capillary wedge pressure (PCWP) [from 17 +/- 1.5 to 26 +/- 3 mm Hg, 102 +/- 27 to 166 +/- 43 dyne.s.cm(-5), and 10 +/- 1 to 14 +/- 2 mm Hg, respectively; each p < 0.05]. CONCLUSION: Our results suggest that in the absence of central autonomic regulation in humans, apnea-induced hypoxemia and/or hypercapnia are associated with peripheral vasodilatation and pulmonary vasoconstriction, which are probably local in origin, as well as a significant increase in PCWP indicating cardiac dysfunction.