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

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.