Influence of the respiratory route on the resting breathing pattern in humans

It has been shown that the pattern of breathing is modified when breathing through a mouthpiece (MP) with a noseclip (NC), although the reasons for this are not clear. We studied 14 healthy naïve subjects during unrestrained breathing, while connected to a spirometer without NC, and while connected to a spirometer with NC. Breathing pattern, studied with an inductive plethysmograph (Respitrace), was recorded during 4 min in each case, once a steady state was attained. During unrestrained breathing, all subjects breathed exclusively through the nose. During spirometric testing without NC, 9 of 14 subjects still breathed through the nose only (since the oropharynx is closed by the soft palate and the tongue, and flow proceeds through the nose). Tidal volume (VT), frequency (f), minute ventilation (VE), inspiratory time, mean inspiratory flow, and duty cycle (Tl/Ttot) were not different during the first 2 procedures (p greater than 0.1 by analysis of variance). By contrast, during spirometric testing with NC, mean VT increased from 530 (during unrestrained breathing) to 700 ml (p less than 0.02), whereas f decreased from 14.9 to 13.6 breaths X min-1 (p greater than 0.05), VE did not change, and Tl/Tot increased from 37 to 41% (p less than 0.05). These data suggest that the change in the pattern of breathing depends on the breathing route. To further confirm this, we asked 8 separate subjects to simply breathe through either the nose or the mouth (half of them starting with mouth breathing, half with nose breathing) while respiration was monitored with the Respitrace without any connection to the airways.(ABSTRACT TRUNCATED AT 250 WORDS)