A Tarasiuk and SM Scharf
Division of Pulmonary and Critical Care Medicine, Long Island Jewish Medical Center, New Hyde Park, New York.

Patients with sleep apnea may experience two types of apnea, central and obstructive. We compared cardiovascular effects of these two types of apnea matched for changes in arterial blood gas tensions and periodicity. In 12 anesthetized, closed chest dogs, obstructive apneas were induced by completely occluding the endotracheal tube at end- expiration for 1 min and allowing 1 min of spontaneous ventilation. Central apneas were produced by paralyzing and mechanically ventilating the animals, then turning the ventilator off and on with the same periodicity as obstructive apneas. During both types of apnea, changes in arterial PO2 and PCO2 were approximately the same. During obstructive apneas, mean blood pressure (BP) and cardiac output (CO) did not change significantly, heart rate (HR) decreased by 27% (p < 0.001), and stroke volume increased by 7.8 ml (p < 0.005). During central apnea, BP did not change, but HR and CO decreased by far more than with obstructive apneas: 44% (p < 0.001) and 27% (p < 0.05) respectively, and stroke volume increased by 5.0 ml (p < 0.05). During obstructive apneas, right atrial pressure increased, as did right heart blood volume. During central apneas, both right atrial pressure and left atrial pressure increased, as did pulmonary blood volume. We conclude that: (1) HR decreases are more severe during central apnea, most likely due to lack of respiratory mechanoreceptor input; (2) CO decreases more with central compared with obstructive apnea due to the heart rate response; (3) HR-induced cardiac dysfunction with central apnea could lead to pulmonary vascular congestion.

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