DECREASED PULMONARY VASCULAR-RESISTANCE DURING NASAL BREATHING - MODULATION BY ENDOGENOUS NITRIC-OXIDE FROM THE PARANASAL SINUSES

Nitric oxide is present in high concentration in the human nasal airwa ys. During inspiration through the nose a bolus is transported to the lungs. In a randomized cross-over study the effect of two different pa tterns of breathing, nasal breathing and mouth breathing, was evaluate d in 10 patients (mean age 65 years), breathing room air the morning o f the first post-operative day after open heart surgery. Nasal breathi ng is defined as inspiration through the nose and expiration through t he mouth. whilst mouth breathing is the converse of this: inspiration through the mouth and expiration through the nose. Pressure in the pul monary artery and left atrium or pulmonary artery wedge was measured t ogether with thermodilution cardiac output and arterial and mixed veno us oxygenation and acid-base parameters. Pulmonary vascular resistance index (PVRI), venous admixture and alveolar-arterial gradient were ca lculated. Nasal breathing resulted in a lower PVRI. 256 dyn s cm(-5) c m(-2) vs. 287 (P < 0.01). The oxygen and carbon dioxide tension and pH of arterial and mixed venous blood, venous admixture and the alveolar -arterial gradient remained unchanged. The decreased level of PVRI dur ing nasal breathing compared to that during mouth breathing supports t he notion, that endogenous nitric oxide acts as an airborne messenger to modulate the pulmonary vascular tone during normal breathing.