Journal of Applied Physiology, Vol 67, Issue 4 1349-1353, Copyright © 1989 by American Physiological Society
Tracheal hysteresis in sleep apnea
I. Katz, N. Zamel, A. S. Slutsky, A. S. Rebuck and V. Hoffstein
Department of Medicine, St. Michael's Hospital, Toronto, Ontario, Canada.
The collapsibility of pharyngeal walls, characteristic of patients with
obstructive sleep apnea, likely results from reduced tone of the pharyngeal
muscles. This reduction in the upper airway muscle tone may not end at the
pharynx but may extend further distally, e.g., into the trachea. Because
tracheal tone cannot be measured directly in conscious humans, we inferred
the tone from the relative hysteresis of the tracheal area compared with
the lung. Relative hysteresis was measured by plotting the cross-sectional
area of a tracheal segment obtained by the acoustic reflection technique
vs. lung volume. All measurements were performed during wakefulness. We
found that in 42 patients with obstructive sleep apnea (apnea/hypopnea
index greater than 10), relative hysteresis of the proximal trachea was
predominantly clockwise, i.e., smaller than that of the lung parenchyma; in
the 33 nonapneic patients (apnea/hypopnea index less than or equal to 10),
it was predominantly counter-clockwise, i.e., larger than that of the lung
parenchyma. For the distal trachea all patients, apneic and nonapneic, had
similar, clockwise, relative hysteresis. We conclude that reduction in the
upper airway muscle tone in patients with obstructive sleep apnea extends
into the trachea.
