Oronasal distribution of respiratory airflow

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The oronasal distribution of respiratory airflow was determined during incrementally graded submaximal exercise in 30 (14 M, 16 F) healthy adult volunteers. Nasal airflow was measured by a pneumotachograph attached to a nasal mask. Oral airflow was determined as the difference between nasal airflow and total pulmonary airflow, the latter being measured by a head-out exercise body plethysmograph. The two airflow signals were sampled every 20 msec by a microprocessor, which calculated the oral and nasal minute volumes (separating inspiration and expiration) and produced an on-line print-out of the results. Twenty subjects (‘normal augmenters’) switched from nasal to oronasal breathing at a V̇ e of 35.3±10.8 l·min −1, four subjects (‘mouth breathers’) habitually breathed oronasally, five subjects (‘hose breathers’) persistently breathed through the nose only, and one subject showed no consistent nose/mouth breathing pattern. After the switch to oronasal breathing, the nasal portion of V̇ e decreased suddenly to 57% of total V̇ e , oral minute volume increased rapidly, equalling nasal minute volume at a V̇ e 45 l·min −1, and accounting for 61% of the total ventilation at high respiratory minute volumes (90 l·min −1). During oronasal breathing, normal augmenters inspired some 2 l·min −1 more nasally than they expired. Similarly, the nasal inspiration of mouth breathers expiration by 2 l·min −1 at rest, but the difference increased to 13.5 l·min −1 at a V̇ e of 81.5·min −1.