Work of breathing in eucapnic and hypercapnic sleep apnea syndrome.
BACKGROUND
Upper airways in patients with obstructive sleep apnea syndrome (OSAS) are more likely narrower than those of normal subjects, a factor in increasing the work of breathing (WOB) in these individuals.


OBJECTIVE
To evaluate WOB while sitting and while supine, both awake and during stage 2 sleep, in patients with hypercapnic or eucapnic OSAS.


METHODS
Twenty normal control subjects without OSAS, 20 patients with eucapnic moderate or severe OSAS and another 8 patients with hypercapnic severe OSAS were studied. WOB was measured by esophageal manometry with the subjects seated and then with the subjects supine, both while awake and during stage 2 sleep.


RESULTS
In both the control and the eucapnic group, WOB was normal in the sitting position. When the eucapnic subjects lay supine, their WOB increased, both while awake and asleep. In contrast, the hypercapnic subjects had an abnormally high WOB both sitting and supine, whether awake or asleep.


CONCLUSIONS
WOB was increased in subjects with hypercapnic OSAS in both the sitting and supine positions. While eucapnic individuals with OSAS have increased WOB when supine, it is normal when they are sitting upright.
Mackay Medicine, Nursing and Management College, Mackay Memorial Hospital, Taipei, Taiwan.
Mei-Yu
MY
Lee
Ching-Chi
CC
Lin
Sheng-Yeh
SY
Shen
Chung-Hsin
CH
Chiu
Shwu-Fang
SF
Liaw
D000328:Adult; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D006935:Hypercapnia / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D011187:Posture; D015656:Respiratory Mechanics; D012890:Sleep; D012891:Sleep Apnea Syndromes / Q000503:physiopathology*