Effects of menopause and nasal occlusion on breathing during sleep.

Prevalence of sleep-disordered breathing (SDB) is reported to increase in menopausal women. We examined response to a nocturnal respiratory challenge (nasal occlusion) during overnight polysomnography in 31 women (45 to 55 yr). Thirteen were premenopausal, four perimenopausal, and 14 postmenopausal by history and hormonal assay. Nasal occlusion increased the apnea hypopnea index (AHI) (occlusion mean = 6.6 +/- 8.0 versus baseline mean = 1.6 +/- 2.6, p < 0.01) and arousal index (occlusion mean = 35.1 +/- 20.1 versus baseline mean = 20.7 +/- 11.6, p < 0.001), but did not change the oxygen saturation nadir in those with respiratory events (occlusion mean = 91.8 +/- 4.2 versus baseline mean = 92.0 +/- 11.6). Menopausal groups did not differ on AHI, arousal index, or oxygen saturation nadir in either condition. Key variables were compared between occlusion responders (n = 11) and nonresponders (n = 20). Responders and nonresponders were not distinguished by age, menopausal status, nor several cephalometric or anthropometric variables. Body mass index (31.1 +/- 8.5 versus 24.3 +/- 3.4, p < 0.003), neck circumference (34.0 +/- 2.5 versus 32.5 +/- 1.7 cm, p < 0.05), and mandibular-hyoid distance (18.5 +/- 3.8 versus 14.5 +/- 5.7 mm, p < 0.05) were greater in responders. These findings suggest hormonal factors may be less important than weight and facial morphology in midlife development of SDB in women.

The prevalence of obstructive sleep apnoea in an obese female population.

Obstructive sleep apnoea (OSA) has been estimated to affect between 1 and 4% of the total population. OSA may be more frequent among women than studies based on subjects presenting for treatment would indicate. The aim of this study was to determine the prevalence of OSA in an obese female population (BMI > 30 kg/m2, age > 18 years) who presented to a hospital-based obesity clinic. The women were screened by an overnight ambulatory sleep study (MESAM) to detect OSA. Subjective sleep quality and sleep disturbance were assessed by a 19-item questionnaire, the Pittsburg sleep quality index (PSQI). From a population of 108 women, 29 were screened by MESAM. OSA was determined on the basis of respiratory disturbance index (RDI). The prevalence of OSA, defined as five or more respiratory disturbances per hour, was 37.9%. The mean age of the women was 43.6 +/- 2.57 years (mean +/- s.e.m.) and they had a mean BMI of 40.7 +/- 1.40 kg/m2. There was a significant positive correlation for RDI and BMI (r = 0.71; P < 0.001). Our findings indicate that over one third of women had OSA, yet they did not complain of symptoms even though the PSQI questionnaire indicated that they were poor sleepers. Non-specific symptomatology of OSA may be important diagnostically, particularly in women, and obese women should be considered at risk of OSA.

The nature of selective attention effects on auditory event-related potentials.

The purpose of the research reported here was to examine a number of issues relating to the nature of selective attention effects on auditory event-related potentials (ERPs), namely, to determine the relative contribution of N1 and slow wave (SW) to the early and late components of Nd respectively, where Nd is defined as the negative shift of attended ERPs relative to unattended ERPs; to examine whether individual differences in Nd morphology are related to performance and the strategies that subjects use; and to determine the contribution of changes in the attended and unattended ERPs to Nd. Auditory ERPs were recorded from subjects as they carried out an auditory selective attention task and a visual target detection task. The auditory selective attention task was a multidimensional task in which stimuli varied on location, pitch and duration and in which the subject's task was to pay attention to a particular location/pitch combination and respond whenever they detected a long-duration target tone. In the visual target detection task, subjects were required to respond whenever they detected a colour change in a light-emitting diode which also acted as a fixation point. Auditory ERPs recorded during the visual task were used to provide a measure of exogenous components uncontaminated by differential effects of selective processing of auditory stimuli. The results suggested that early Nd and N1 are independently generated as Nd did not exhibit the contralateral scalp focus typical of N1, and that late Nd is independent of SW. While substantial differences in Nd morphology were observed over subjects, these differences showed no consistent relationships to performance or to task strategies. Comparison of auditory ERPs during active auditory attention with auditory ERPs recorded during the visual control task indicated that there was an early negative shift of the attended ERP, a later negative shift of the attended ERP which had a frontal focus and a later positive shift of the unattended ERP. These results suggest that there are active processes involved in the processing of stimuli from both the attended and unattended source.