The American review of respiratory disease
-
Am. Rev. Respir. Dis. · Jan 1984
Redistribution of pulmonary blood flow induced by positive end-expiratory pressure and dopamine infusion in acute respiratory failure.
The mechanism by which mechanical ventilation (MV) with positive end-expiratory pressure (PEEP) improves hypoxemia in patients with acute respiratory failure (ARF) is unclear, and may be attributed in part to a decrease in cardiac output inducing by itself a reduction of the shunt. Using the multiple inert gas elimination technique we evaluated the effects of PEEP on ventilation-perfusion (VA/Q) distribution in 8 patients while cardiac output was maintained at control value by means of a dopamine infusion. In each patient, evaluation was performed during MV without PEEP (control) then with PEEP (17 +/- 2 cm H2O) and dopamine. ⋯ Dead space increased slightly with PEEP, from 44 to 49% (p less than 0.01) of total ventilation. The pattern of ventilation distribution was essentially unaltered; specifically, no additional high VA/Q mode was observed during PEEP. It is concluded that cardiac output maintenance with dopamine infusion during PEEP does not suppress the beneficial effects of PEEP on gas exchange, but induces a redistribution of pulmonary blood toward the main VA/Q ratio.
-
Am. Rev. Respir. Dis. · Jan 1984
Isoproterenol and aminophylline improve contractility of fatigued canine diaphragm.
We investigated the effects of aminophylline and isoproterenol on diaphragmatic fatigue produced by phrenic stimulation in dogs. With a cast around the abdomen, the diaphragm contracted quasi-isometrically while the thorax was open and the animal was ventilated. We assessed contractility by measuring transdiaphragmatic pressure during supramaximal stimulation of the phrenic nerves at different frequencies and also during spontaneous inspiratory efforts. ⋯ In addition, isoproterenol caused a marked decrease in the time course of relaxation. We conclude that aminophylline and isoproterenol improve contractility of the fatigued diaphragm by increasing the amplitude of the underlying small twitch. Furthermore, the smaller effect of isoproterenol may be the result of reduced relaxation time of the twitch.