Journal of Applied Physiology, Vol 64, Issue 6 2659-2666, Copyright © 1988 by American Physiological Society
Respiratory load compensation in neuromuscular disorders
K. Axen, M. Bishop and F. Haas
Department of Rehabilitation Medicine, School of Medicine, New York University, New York 10016.
First-breath ventilatory responses to graded elastic (delta E) and
resistive (delta R) loads from 10 people with spinal muscular atrophy
(SMA), 15 people with Duchenne muscular dystrophy (DMD), and 80 able-bodied
people were compared. The SMA and DMD groups produced equal tidal volume,
respiratory frequency, inspiratory duration (TI), expiratory duration, mean
inspiratory airflow, and duty cycle responses to both delta E and delta R.
Thus SMA (primarily a motoneuron disorder) and DMD (primarily a muscle
disorder) have the same net effect on loaded breathing responses. The SMA
and DMD groups failed to duplicate the normal group's short expirations
during delta E, long inspirations during delta R, and thus, extended duty
cycles during both delta E and delta R. The deficit in load compensation
therefore was due to impaired regulation of respiratory timing (reflecting
neural mechanisms) but not airflow defense (reflecting mechanical and
neural mechanisms). One-fifth of the normal but none of the SMA or DMD
subjects actively generated an "optimal" TI response (defined theoretically
as TI greater than 160% control during large delta R and TI less than 75%
control during large delta E). This lack of optimal responses, which is the
same abnormality exhibited by quadriplegic people, suggests that SMA and
DMD also impair human ability to discriminate between large delta R and
delta E. These findings support the hypothesis that neuromuscular disorders
can lead to disturbances in respiratory perception.
