Inspiratory flow effects on mechanically ventilated patients: lung volume, inhomogeneity, and arterial oxygenation.

Changes in the inspiratory flow rate of mechanically ventilated patients can affect arterial oxygenation. Although the mechanism producing this alteration is not certain, one possible mechanism is a change in ventilation inhomogeneity. This study was performed to determine if the inspiratory flow setting would affect ventilation inhomogeneity in patients who have minimal or no lung disease, but who require mechanical ventilation after cardiopulmonary bypass surgery. When inspiratory flows were doubled, PaO2 increased and FRC fell. However, no associated change in ventilation inhomogeneity was detected. It is concluded that inspiratory flow rate can affect arterial oxygenation of subjects without severe obstructive pulmonary disease through mechanisms other than altering ventilation inhomogeneity, such as changes in cardiac output or in distribution of perfusion.

Lung tissue volume during development of edema in isolated canine lungs.

The technique of estimating pulmonary tissue volume (Vt) by rebreathing a tissue-soluble gas is rapid and noninvasive. We examined the sensitivity of this technique for the estimation of Vt in isolated, perfused canine lungs during the development of pulmonary edema. Vt was 84 +/- 15% (mean +/- SD) of the associated lung weight for lung weights of up to 240% of base line but decreased to 70 +/- 2% when lung weight exceeded 310% of base line. Small rebreathing tidal volumes resulted in significantly smaller values for Vt in edematous lungs. An abrupt increase in pulmonary venous pressure increased lung weight due to vascular distension; Vt measurements detected less than half of this increase, implying that certain portions of the intravascular blood volume are not measured by this technique.