Title: The compensatory mechanisms of loaded and unloaded breathing in exercising men
Abstract: To characterize the ventilatory responses to the resistive loading or unloading, we studied the effect of breathing 79% helium – 21% oxygen (He-O2), 79% argon – 21% oxygen (Ar-O2) and 79% SF6 – 21% oxygen (SF6-O2) on the volume-time parameters, PETCO2, mouth pressure (PmI), work of breathing (WI), central inspiratory activity (dP/dtI) and electromyographic activity of parasternal muscles in 10 normal subjects at rest and during 3 min steady-state exercise. There were no significant changes in tidal volume (VT), breathing frequency (f), inspiratory (TI) and expiratory (TE) durations, minute ventilation (VE) and PETCO2 when air was replaced by He-O2 or SF6-O2 at rest. VE and PETCO2 were not significantly different after replacement of air by He-O2 or SF6-O2 during exercise. However inhalation of He-O2 decreased in VT and increased in f, whereas inhalation of SF6-O2 led to opposite effects compared with air during exercise. Both at rest and exercise, PmI, WI, dP/dtI and EMGps were significantly less during He-O2 breathing and higher during SF6-O2 breathing from the first respiratory cycle after room air was replaced by He-O2 or SF6-O2. Ar-O2 breathing did not affect on time-volume parameters both at rest and during exercise compared with air. The increase in PmI, WI, dP/dtI was observed at Ar-O2 inhalation during exercise relatively to air. We conclude that internal resistive loading or unloading breathing changes the neuromuscular output required to maintain constant ventilation. The mechanisms of load or unload compensation seem to be mediated by afferent impulsation from lung and respiratory muscle receptors as well as due to segmentary level reflexes and properties of the muscle fiber itself.
Publication Year: 2011
Publication Date: 2011-09-01
Language: en
Type: article
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