Chest
-
We have evaluated systemic oxygen consumption (VO2), systemic oxygen transport, and tissue perfusion variables in 30 patients with preexisting cardiac and underlying pulmonary disease during continuous positive-pressure ventilation and positive end-expiratory pressure [PEEP], during intermittent mandatory ventilation (IMV and PEEP), and during spontaneous ventilation (continuous positive airway pressure [CPAP]), with end-expiratory pressure held constant during all ventilatory modes. Using radionuclide angiography together with invasive determinations of pressure and flow, we also measured left and right ventricular ejection fractions and calculated the end-systolic (ESVI) and end-diastolic (EDVI) volume indices of both ventricles. We found that oxygen transport was significantly greater during CPAP (583 +/- 172 ml/min/M2)(mean +/- SD) than during either IMV and PEEP (543 +/- 151 ml/min/sq; p less than 0.01) or CPPV and PEEP (526 +/- 159 ml/min/M2; p less than 0.01); however, we found no significant change in systemic VO2 with conversion from CPPV and PEEP to CPAP. ⋯ Enhanced oxygen transport during CPAP was also associated with an increase in mixed venous oxygenation and a decrease in arterial lactate. Although neither the mean left ventricular EDVI nor ESVI changed from CPPV and PEEP to CPAP, the mean pulmonary capillary wedge pressure increased (CPPV and PEEP, 12 +/- 5 mm Hg; CPAP, 14 +/- 7 mm Hg) (p less than 0.01), suggesting the possibility of a decrease in left ventricular compliance with the spontaneous ventilatory mode. This study suggests that in the absence of ventilatory failure, spontaneous ventilation provides for better systemic oxygen transport and overall tissue perfusion than either controlled ventilation or IMV; however, this benefit of enhanced oxygen delivery with spontaneous ventilation may potentially be offset by a decrease in left ventricular compliance.
-
The use of systemic vasodilator drugs in reducing pulmonary artery pressures in patients with pulmonary hypertension is controversial. The effect of hydralazine in four patients with pulmonary hypertension resulting from interstitial lung disease (group 1) and nifedipine in four patients with pulmonary hypertension secondary to progressive systemic sclerosis (group 2) was investigated. Hydralazine blunted exercise induced elevations in pulmonary arterial pressures in individual group 1 patients; nifedipine failed to effect significant salutory hemodynamic changes in any group 2 patients.