Inspired gas relative humidity affects systemic to pulmonary bronchial blood flow in humans

To our knowledge, the effects of humidity of inspired air on bronchial blood flow in humans are unknown. During total cardiopulmonary bypass, we measured systemic to pulmonary bronchial blood flow (Q̇br[s-p]) which is the volume of blood accumulating into the left side of the heart in the absence of pulmonary and coronary flow. A cannula was introduced into the right upper pulmonary vein and advanced into the lowermost portion of the left side of the heart. From this cannula Q̇br(s-p) was vented by gravity and measured. Inspired gas (10 L/min, endotracheal tube, 50 percent O ₂ + 50 percent N ₂O) relative humidity was <20 percent and > 85 percent in group A (n = 25) and in group B (n = 25), respectively. Mean (± SE) Q̇br(s-p) was 40.7 ± 0.06 ml/min or 1.32 ± 0.12 ml/min (percent cardiac output) in group A and 21.7 ± 1.8 ml/min or 0.68 ± 0.06 ml/min in group B. These data indicate that under these conditions Q̇br(s-p) is increased by dry gas lung inflation in humans.