UCSD. US: People with moderate to severe obstructive sleep apnea may have
an intrinsic inability to burn high amounts of oxygen during strenuous
aerobic exercise, according to a new study led by researchers at
University of California, San Diego School of Medicine.
The study, reported in the current issue of Journal of Clinical Sleep Medicine,
shows that people with sleep apnea, in which breathing repeatedly
starts and stops during slumber, have a lower peak oxygen uptake during
aerobic activity than those who do not suffer from the sleep disorder.
People who suffer from apnea are more likely to be obese and thus
would be expected to be less fit as well. The researchers, however,
found that apnea patients had a reduced aerobic fitness, even compared
with those of similar body mass indices.
“Encouraging patients to exercise more is part of the story, but that
is not the whole story,” said lead author Jeremy Beitler, MD, assistant
clinical professor in pulmonary and critical care medicine. “We believe
the sleep apnea itself causes structural changes in muscle that
contributes to their difficulty exercising.”
For the study, researchers performed sleep studies of men and women
with a range of apnea symptoms. The sleep studies were performed to
clinically evaluate the severity of the patients’ apnea and to screen
participants for sleep disorders besides apnea that could confound the
study results.
Fifteen men and women with moderate to severe apnea and nineteen with
mild or no apnea were then asked to pedal a stationary bike at
incrementally harder resistance levels – similar to what a person would
experience climbing up a progressively steeper hill. The participants
were directed to pedal to exhaustion.
From the exercise test results, and previous measurements of
participants’ resting metabolic rates, scientists calculated each
person’s VO2 max – a measure of the maximum amount of oxygen the person
can uptake during strenuous exercise – and its deviance from the
expected VO2 max for a person of the same age, gender and body mass
index.
After adjusting for baseline differences, scientists showed that
people with sleep apnea had on average a 14 percent lower VO2 max than
control subjects. Furthermore, the number of times a person stopped
breathing, for 10-seconds or more, per hour of sleep, could predict 16
percent of the variability observed in the group’s peak VO2.
“This is a big discrepancy,” Beitler said.
Researchers believe that VO2 max measurements may be an early marker
for those who are at higher risk of stroke and heart attack and that VO2
max measurements could motivate early interventions to treat apnea,
which is underdiagnosed and often untreated.
Co-authors study include Karim M. Awad, Beth Israel Deaconess Medical
Center; Jessie P. Bakker, Bradley A. Edwards, Ina Djonlagic and Daniel
E. Forman, Harvard; Pam DeYoung and Atul Malhotra, UC San Diego; Stuart
F. Quan, Harvard and University of Arizona.
Funding for the study was provided, in part, by the American Sleep
Medicine Foundation PSTA Program of Distinction and National Institutes
of Health (grants UL1 RR025758-01 and T32 HL007633).