AIRWAY BLOOD-FLOW RESPONSES TO TEMPERATURE AND HUMIDITY OF INHALED AIR

We determined the effect of breathing cold dry air (-39 degrees C, 0.1 % relative humidity, RH) and warm humid air (43 degrees C, 100% RH) on airway mucosal blood how (Q(aw)) in normal human subjects (n = 8, age 25-53 years) at rest. Q(aw) was measured with a dimethylether uptake technique which reflects blood flow in the mucosa of large airways cor responding to a 50 ml anatomical dead-space segment extending distally from the trachea. Mean Q(aw) was 10.1+/-1.9 ml min(-1) (mean +/- S.D. ) during room air breathing (25 degrees C, 70% RH) and decreased to 4. 7+/-2.1 ml min(-1) during cold dry air breathing (p < 0.05). Within 20 min of resuming room air breathing, mean Q(aw) had returned to baseli ne. Breathing warm humid air had no significant effect on mean Q(aw) ( 8.2+/-1.4 ml min(-1)). These results indicate that quiet breathing of frigid air causes vasoconstriction in central airways.