Neural drive to nasal dilator muscles: influence of exercise
intensity and oronasal flow partitioning.
Fregosi, Ralph F., and Robert W. Lansing.
Departments of Exercise & Sport Sciences, Physiology and
Psychology, The University of Arizona Health Sciences Center, Tucson,
AZ 85721
APStracts 2:0234A, 1995.
Our aim was to test the following hypotheses: 1) neural drive to the
muscles of the alae nasi (AN) is proportional to nasal airflow, and
independent of the overall level of central respiratory drive; 2) the
switch from nasal to oronasal breathing corresponds to the onset of
marked flow turbulence in the nasal airway. Total and nasal inspired
ventilation rates (VI) and the EMG of the AN muscles were measured in
7 subjects during progressive-intensity bicycling exercise. In
separate experiments in 6 subjects the nasal VI corresponding to the
transition from laminar to turbulent airflow was determined by
measuring the pressure:flow relationship of the nasal airway with
anterior rhinomanometry. Nasal V I accounted for 70 +/- 11 % of total
VI at rest, and 27 +/- 8 % (SEM) at 90 % of the maximal attainable
power (max). Nasal VI and integrated AN EMG activities increased
linearly with exercise intensity up to 60 % of the max power, but
both variables plateaued at this level even though total VI (and
central respiratory drive) began to increase exponentially as
exercise intensity increased to 90 % max. The onset of the
exponential rise in total VI was associated with a sharp increase in
oral VI, and the onset of marked flow turbulence in the nasal airway.
The results suggest that, during incremental exercise: 1) changes in
AN EMG activities are highly correlated with changes in nasal VI; 2)
turbulent flow in the nose may be the stimulus for the switch to
oronasal breathing, so that total pulmonary resistance is minimized;
3) the correlation between nasal airflow and neural drive to the AN
muscles is probably mediated by mechanisms that monitor airway
resistance. Although these mechanisms were not identified, the most
likely possibilities are receptors in the upper and/or lower airways
that are sensitive to negative transmural pressure, or effort
sensations leading to greater corollary motor discharge to nasal
dilator muscle motoneurons.
Received 10 January 1995; accepted in final form 18 May 1995.
APS Manuscript Number A32-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 8 June 1995.