Oronasal distribution of respiratory airflow.

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 VE of 35.3 +/- 10.8 1 . min-1, four subjects ("mouth breathers") habitually breathed oronasally, five subjects ("nose 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 VE decreased suddenly to 57% of total VE. With a further increase of VE, oral minute volume increased rapidly, equalling nasal minute volume at a VE of 45 1 . min-1, and accounting for 61% of the total ventilation at high respiratory minute volumes (90 1 . min-1). During oronasal breathing, normal augmenters inspired some 2 1 . min-1 more nasally than they expired. Similarly, the nasal inspiration of mouth breathers exceeded expiration by 2 1 . min-1 at rest, but the difference increased to 13.51 . min-1 at a VE of 81.51 . min-1.