HH Kim, C LeMerre, CM Demirozu, AD Chediak and A Wanner
Division of Pulmonary and Critical Care Medicine, Mount Sinai Medical Center, University of Miami School of Medicine, Florida, USA.

The purpose of this study was to determine the effect of hyperventilation (40 L/min) with room air (25 degrees C; 70% relative humidity) and frigid air (-10 degrees C; 0% relative humidity) on airway mucosal blood flow (Qaw) in normal subjects (n = 7; 26 to 54 yr of age). Qaw was measured with the dimethyl ether uptake technique, which reflects blood flow in the mucosa of large airways corresponding to a 50-ml anatomic dead space segment extending distally from the trachea. Mean (+/- SE) baseline Qaw during quiet (room air) breathing was 6.6 +/- 0.6 ml/min (range, 3.9 to 10.9). Qaw failed to change significantly during and after eucapnic hyperventilation with room air (thermal stress, 224 cal/min). In contrast, eucapnic hyperventilation with frigid air (thermal stress, 720 cal/min) increased Qaw in every subject, with the peak value occurring either during or over a 30-min period after hyperventilation; by 60 min, Qaw had returned toward baseline. The mean maximal Qaw was 310 +/- 49% of baseline (p < 0.05). Neither type of hyperventilation had an effect on airway resistance. We conclude that in normal subjects, Qaw increases during and/or after eucapnic hyperventilation with frigid air, and that this response is related to the magnitude of the thermal stress rather than to the level of ventilation.

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