Voluntary changes in breathing pattern and N₂ clearance from lungs

¹ Division of Aviation Medicine, Institute of Physiology, University of Lund, Lund, Sweden; and Laboratory of Clinical Physiology, University Hospital, Leiden, The Netherlands

Lung N₂ clearance curves were recorded in three normal and two symptom-free asthmatic subjects at breathing rates of 10–60/min and tidal volumes of 350–1,950 ml. A change toward more uniform gas distribution at larger tidal volumes was found in one subject. Changes in breathing rate did not affect gas distribution demonstrably. The washout ventilation per liter lung volume (lung clearance index) did not show significant changes with either breathing rate or tidal volume except for an increase at tidal volumes of less than 450 ml. These findings agree with the assumption of a constant dead space volume at tidal volumes within the range studied. The results are of practical importance for the use of the lung clearance index as a measure of the effect of broncho-active substances on the lung ventilation in man.

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