The effect of body position on maternal cardiovascular function during sleep and wakefulness in late pregnancy.

INTRODUCTION: An association between the increased risk of late stillbirth and the maternal supine sleeping position has been recently established. The risk of stillbirth following supine sleep has been suspected to occur as a result of aortocaval compression by the gravid uterus. A number of studies conducted during wakefulness have reported compromised cardiovascular function during supine rest, as demonstrated by reductions in cardiac output, blood pressure and utero-placental blood flow. It remains unclear whether similar effects are also present during sleep, due to the presence of key sleep-specific changes in cardiovascular function. OBJECTIVE: To investigate the changes in maternal cardiovascular function between the supine and left-lateral positions during wakefulness and non-rapid eye movement (NREM) sleep in late pregnancy. METHODS: Twenty-nine women with a singleton pregnancy between 24.7 and 36.7 weeks' gestation participated in a single overnight sleep study. Physiological measures (blood pressure, heart rate, heart rate variability - HRV, and pulse arrival time - PAT) were measured and recorded throughout the night using standard polysomnography equipment and the Portapres Model-2 device. As the present study evaluated cardiovascular changes during natural rest and sleep in pregnancy, participants were not given explicit instructions on which position to adopt. Body position was continuously recorded using a position monitor and verified with video recording. RESULTS: No changes in systolic, diastolic or mean arterial blood pressure were observed between the left-lateral and supine positions during wakefulness or sleep. However, heart rate was significantly higher in the supine position compared to the left during wakefulness (p= .03), with a similar trend present during sleep (p= .11). A significantly shorter PAT was measured in the supine position (compared to the left) during wakefulness (p= .01) and sleep (p= .01). No change in HRV measures was observed between the left and supine positions in either state. CONCLUSION: Blood pressure did not appear to differ significantly between the left-lateral and supine positions during wakefulness and sleep. The lack of blood pressure differences may reflect elevated sympathetic activity during rest and sleep in the supine position (compared to the left), suggesting that some degree of compensation for aortocaval compression may still be possible during sleep.

Does Nasal Obstruction Induce Obstructive Sleep Apnea in Healthy Women?

PURPOSE: Obstructive sleep apnea (OSA) is less prevalent among women and is associated with different symptoms and consequences to OSA in men. The reasons for these differences are unknown and difficult to tease apart in clinical populations. If OSA could be temporarily induced in healthy men and women, the causes of some of these differences could be investigated. Nasal blocking has been used to induce OSA in healthy men but its effect in women has not been reported. PATIENTS AND METHODS: A total of 14 healthy individuals (10 women) underwent in-laboratory diagnostic sleep studies on two occasions separated by a week. On one occasion, the nasal passages were blocked, whereas on the other occasion, participants slept naturally. In both conditions, a full-face mask was used to monitor respiratory events. Participants' self-reported sleepiness, mood and performance on a motor learning task were assessed in the evening and morning of both sleep studies. Furthermore, endothelial function and self-reported sleep quality were assessed in the morning following each study. RESULTS: Nasal blockage induced OSA in healthy young (age=22±3 years) and slim (BMI=22.2±3.2 kg/m2) women (control AHI=2.0±2.6, blocked AHI=33.1±36.7 events/hr, p=0.02). One night of OSA was associated with poorer self-reported sleep quality (p<0.001) and increased self-reported snoring (p<0.04), choking and gasping during sleep (p<0.001) but was not associated with alterations in mood, neurocognitive or endothelial function on the following morning. CONCLUSION: Nasal blockage induces OSA in healthy, young, and normal weight women. However, whether the induced OSA is representative of naturally occurring OSA and the technique useful for future studies is unclear.