August 25, 1998
View Full PaperSympathetic Activity in Obese Subjects With and Without Obstructive Sleep Apnea
Structured PICO
Does obesity without obstructive sleep apnea increase muscle sympathetic nerve activity compared to normal weight?
P
Population
55 subjects including 25 healthy normal-weight subjects and 30 healthy sedentary obese subjects, screened to exclude hypertension.
I
Intervention
Obesity without obstructive sleep apnea
C
Comparator
Normal-weight without obstructive sleep apnea, and obesity with occult obstructive sleep apnea
O
Outcome
Muscle sympathetic nerve activity (MSNA) measured as bursts per 100 heartbeatssurrogate
Increased sympathetic activity in obese individuals appears to be driven by co-occurring obstructive sleep apnea rather than obesity itself.
Abstract
BACKGROUND: Obese humans are reported to have increased muscle sympathetic nerve activity (MSNA). Obstructive sleep apnea (OSA) may also be accompanied by increased MSNA. Because there is a high prevalence of OSA in obese humans, it is possible that high MSNA reported in obese subjects may in fact reflect the presence of OSA in these subjects. We tested the hypothesis that obesity, per se, in the absence of OSA, is not accompanied by increased MSNA. METHODS AND RESULTS: We measured MSNA in 25 healthy normal-weight subjects and 30 healthy sedentary obese subjects. All subjects were screened by history and examination to exclude subjects with OSA or hypertension. OSA was further excluded by overnight polysomnographic studies. Despite careful screening, polysomnography revealed that 1 of 25 normal-weight subjects and 9 of 30 obese subjects had occult OSA (P=0.015). MSNA was similar in normal-weight subjects (41+/-3 bursts per 100 heartbeats) and obese subjects without sleep apnea (42+/-3 bursts per 100 heartbeats, P=0.99). MSNA in the 9 obese subjects with occult OSA was 61+/-8 bursts per 100 heartbeats, which was higher than MSNA in normal-weight subjects without sleep apnea (P=0.02) and higher than MSNA in obese subjects without sleep apnea (P=0.02). CONCLUSIONS: Obesity alone, in the absence of OSA, is not accompanied by increased sympathetic activity to muscle blood vessels.