Nocturnal transcutaneous carbon dioxide tension in postmenopausal estrogen users and non-users

Objective The effect of menopause on breathing is not fully understood. We have previously shown that postmenopausal women have a higher sleep-induced increase in transcutaneously measured carbon dioxide tension (TcCO2) than premenopausal women. Therefore, we hypothesized that estrogen therapy (ET) would normalize this sleep-induced TcCO2 increase. Methods Nine postmenopausal ET users and nine non-users went through an overnight polygraphic sleep study including continuous monitoring of TcCO2. Results TcCO2 levels were higher during sleep than evening wakefulness (awake median 6.55 kPa versus sleep median 6.90 kPa, P = 0.001). ET users had a greater sleep-induced increase in TcCO2 than non-users when comparing the difference between wakefulness and slow-wave sleep (0.85 kPa versus 0.28 kPa, P = 0.004). Lower sleep efficiency was associated with higher sleep-induced increase in TcCO2. Conclusions In contrast to our initial hypothesis, postmenopausal ET users have a higher sleep-induced increase in TcCO2 than women without ET. Thus, TcCO2 may be sensitive in measuring the peripheral estrogen effect. These findings warrant placebo-controlled intervention studies to confirm the effects of ET on TcCO2 measurements.