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Department of Medicine, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada T2N 4N1
Received 17 September 1996; accepted in final form 29 April 1997.
Isono, Shiroh, Thom R. Feroah, Eric A. Hajduk, Rollin Brant,
William A. Whitelaw, and John E. Remmers. Interaction of
cross-sectional area, driving pressure, and airflow of passive velopharynx. J. Appl. Physiol. 83(3):
851-859, 1997.
Previous studies have shown that, when the
pharyngeal muscles are relaxed, the velopharynx is a highly compliant
segment of the pharynx. Thus, under these circumstances,
cross-sectional area of the velopharynx (AVP), driving
pressure across the velopharynx (
P), and inspiratory airflow
(
I) will
be mutually interdependent variables. The purpose of the present
investigation was to describe the interrelation among these three
variables during inspiration. We studied 15 sleeping patients with
obstructive sleep apnea/hypopnea when the pharyngeal muscles were
rendered hypotonic by applying continuous positive airway pressure to
the nasal airway.
AVP, determined by endoscopic imaging, was significantly greater at onset of
I limitation
than at minimum oropharyngeal pressure
(P < 0.01). Snoring was never
observed during
I
limitation. In a subgroup of six patients, values for P,
I, and
AVP were obtained
at 0.1-s intervals at various levels of mask pressure. For these six
patients, the mathematical expression
I = 0.657(AVP/Amax) · P0.332,
where Amax is
maximal AVP,
described the relationship among the three variables
(R2 = 0.962) for
flow-limited and non-flow-limited inspirations. The impedance of the
passive velopharynx, defined as
P0.33/,
was inversely related to
AVP and increased
dramatically when AVP was <0.3
cm2. In summary, we observed a
progressive decrease in
AVP during flow-limited inspiration in patients with obstructive sleep apnea. This
constriction of the velopharynx contributes to an increase in
velopharyngeal impedance that, in turn, counterbalances the increase in
P during flow limitation.
obstructive sleep apnea; pharyngeal mechanics; fluid flow dynamics; flow limitation; dynamic collapse
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