Mechanisms underlying the prolonged activation of the genioglossus following arousal from sleep

STUDY OBJECTIVES

Transient arousal from sleep has been shown to elicit a prolonged increase in genioglossus muscle activity that persists following the return to sleep and which may protect against subsequent airway collapse. We hypothesized that this increased genioglossal activity following return to sleep after an arousal is due to persistent firing of inspiratory-modulated motor units (MUs) that are recruited during the arousal.

METHODS

Thirty-four healthy participants were studied overnight while wearing a nasal mask with pneumotachograph to measure ventilation and with 4 intramuscular genioglossus EMG electrodes. During stable N2 and N3 sleep, auditory tones were played to induce brief (3-15s) AASM arousals. Ventilation and genioglossus MUs were quantified before the tone, during the arousal and for 10 breaths after the return to sleep.

RESULTS

A total of 1089 auditory tones were played and gave rise to 239 MUs recorded across arousal and the return to sleep in 20 participants (aged 23 ± 4.2 years and BMI 22.5 ± 2.2 kg/m2). Ventilation was elevated above baseline during arousal and the first post-arousal breath (p < .001). Genioglossal activity was elevated for five breaths following the return to sleep, due to increased firing rate and recruitment of inspiratory modulated MUs, as well as a small increase in tonic MU firing frequency.

CONCLUSIONS

The sustained increase in genioglossal activity that occurs on return to sleep after arousal is primarily a result of persistent activity of inspiratory-modulated MUs, with a slight contribution from tonic units. Harnessing genioglossal activation following arousal may potentially be useful for preventing obstructive respiratory events.

Severe Obstructive Sleep Apnea Is Associated with Higher Brain Amyloid Burden: A Preliminary PET Imaging Study

Background: Obstructive sleep apnea (OSA) has been linked to an increase risk of dementia. Few studies have cross-sectionally examined whether clinically-confirmed OSA is associated with a higher brain amyloid burden. Objective: The aim of this study was to compare brain amyloid burden in individuals with untreated OSA and healthy controls, and explore associations between amyloid burden and polysomnographic and subjective measures of sleep, demographics, and mood. Methods: Thirty-four individuals with OSA (mean age 57.5±4.1 y; 19 males) and 12 controls (mean age 58.5±4.2 y; 6 males) underwent a clinical polysomnogram and a 11C-PiB positron emission tomography (PET) scan to quantify amyloid burden. Results: Amyloid burden was elevated in the OSA group relative to controls, and was significantly higher in those with severe OSA relative to mild/moderate OSA. Correlation analyses indicated that higher amyloid burden was associated with a higher Non-REM apnea hypopnea index, poorer sleep efficiency, and less time spent in stage N3 sleep, when controlling for age. Conclusion: Severe OSA is associated with a modest elevation of brain amyloid, the significance of which should be further investigated to explore the implications for dementia risk.

Sleep-disordered breathing does not impact maternal outcomes in women with hypertensive disorders of pregnancy

Objective

Sleep-disordered breathing (SDB) is characterised by intermittent hypoxemia, sympathetic activation and widespread endothelial dysfunction, sharing pathophysiologic features with the hypertensive disorders of pregnancy. We sought to determine whether coexisting SDB would adversely impact the outcomes of women with gestational hypertension (GH) and preeclampsia (PE), and healthy matched controls.

Study design

Women diagnosed with GH or PE along with BMI- and gestation-matched normotensive controls underwent polysomnography in late pregnancy to establish the presence or absence of SDB (RDI ≥ 5). Clinical outcomes of hypertensive disease severity were compared between groups, and venous blood samples were taken in the third trimester and at delivery to examine for any impact of SDB on the anti-angiogenic markers of PE.

Results

Data was available for 17 women with PE, 24 women with GH and 44 controls. SDB was diagnosed in 41% of the PE group, 63% of the GH group and 39% of the control group. Women with PE and co-existing SDB did not have worse outcomes in terms of gestation at diagnosis of PE (SDB = 29.1 (25.9, 32.1) weeks vs. no SDB = 32.0 (29.0, 33.9), p = n.s.) and days between diagnosis of PE and delivery (SDB = 20.0 (4.0, 35.0) days vs. no SDB = 10.5 (9.0, 14.0), p = n.s.). There were also no differences in severity of hypertension, antihypertensive treatment and biochemical, haematological and anti-angiogenic markers of PE between SDB and no SDB groups. Similar results were observed among women with GH. Healthy control women with SDB were no more likely to develop a hypertensive disorder of pregnancy in the later stages of pregnancy (SDB = 5.9% vs. no SDB = 7.4%, p = n.s.). Increasing the threshold for diagnosis of SDB to RDI ≥ 15 did not unmask a worse prognosis.

Conclusion

The presence of SDB during pregnancy did not worsen the disease course of GH or PE, and was not associated with high blood pressure or anti-angiogenic markers of hypertensive disease amongst healthy pregnant women. Given the numerous reports of the relationship between SDB and diagnosis of hypertensive disorders of pregnancy, it appears more work is required to distinguish causal, versus confounding, pathways.

The presence of coexisting sleep-disordered breathing among women with hypertensive disorders of pregnancy does not worsen perinatal outcome

Objective

To determine whether the presence of co-existing sleep-disordered breathing (SDB) is associated with worse perinatal outcomes among women diagnosed with a hypertensive disorder of pregnancy (HDP), compared with normotensive controls.

Study design

Women diagnosed with HDP (gestational hypertension or preeclampsia) and BMI- and gestation-matched controls underwent polysomnography in late pregnancy to determine if they had coexisting SDB. Fetal heart rate (FHR) monitoring accompanied the sleep study, and third trimester fetal growth velocity was assessed using ultrasound. Cord blood was taken at delivery to measure key regulators of fetal growth.

Results

SDB was diagnosed in 52.5% of the HDP group (n = 40) and 38.1% of the control group (n = 42); p = .19. FHR decelerations were commonly observed during sleep, but the presence of SDB did not increase this risk in either the HDP or control group (HDP group—SDB = 35.3% vs. No SDB = 40.0%, p = 1.0; control group—SDB = 41.7% vs. No SDB = 25.0%, p = .44), nor did SDB affect the total number of decelerations overnight (HDP group—SDB = 2.7 ± 1.0 vs. No SDB = 2.8 ± 2.1, p = .94; control group—SDB = 2.0 ± 0.8 vs. No SDB = 2.0 ± 0.7, p = 1.0). Fetal growth restriction was the strongest predictor of fetal heart rate events during sleep (aOR 5.31 (95% CI 1.26–22.26), p = .02). The presence of SDB also did not adversely affect fetal growth; in fact among women with HDP, SDB was associated with significantly larger customised birthweight centiles (43.2% ± 38.3 vs. 16.2% ± 27.0, p = .015) and fewer growth restricted babies at birth (30% vs. 68.4%, p = .026) compared to HDP women without SDB. There was no impact of SDB on measures of fetal growth for the control group. Cord blood measures of fetal growth did not show any adverse effect among women with SDB, either in the HDP or control group.

Conclusion

We did not find that the presence of mild SDB worsened fetal acute or longitudinal outcomes, either among women with HDP or BMI-matched normotensive controls. Unexpectedly, we found the presence of SDB conferred a better prognosis in HDP in terms of fetal growth. The fetus has considerable adaptive capacity to withstand in utero hypoxia, which may explain our mostly negative findings. In addition, SDB in this cohort was mostly mild. It may be that fetal sequelae will only be unmasked in the setting of more severe degrees of SDB and/or underlying placental disease.

Light sensors for objective light measurement in ambulatory polysomnography

Ambulatory polysomnography (PSG) does not commonly include an objective measure of light to determine the time of lights off (Loff), and thus cannot be used to calculate important indices such as sleep onset latency and sleep efficiency. This study examined the technical specifications and appropriateness of a prototype light sensor (LS) for use in ambulatory Compumedics Somte PSG.Two studies were conducted. The first examined the light measurement characteristics of the LS when used with a portable PSG device, specifically recording trace range, linearity, sensitivity, and stability. This involved the LS being exposed to varying incandescent and fluorescent light levels in a light controlled room. Secondly, the LS was trialled in 24 home and 12 hospital ambulatory PSGs to investigate whether light levels in home and hospital settings were within the recording range of the LS, and to quantify the typical light intensity reduction at the time of Loff. A preliminary exploration of clinical utility was also conducted. Linearity between LS voltage and lux was demonstrated, and the LS trace was stable over 14 hours of recording. The observed maximum voltage output of the LS/PSG device was 250 mV, corresponding to a maximum recording range of 350 lux and 523 lux for incandescent and fluorescent light respectively. At the time of Loff, light levels were within the recording range of the LS, and on average dropped by 72 lux (9–245) in the home and 76 lux (4–348) in the hospital setting. Results suggest that clinical utility was greatest in hospital settings where patients are less mobile. The LS was a simple and effective objective marker of light level in portable PSG, which can be used to identify Loff in ambulatory PSG. This allows measurement of additional sleep indices and support with clinical decisions.

The effect of body mass and sex on the accuracy of respiratory magnetometers for measurement of end-expiratory lung volumes

Respiratory magnetometers are increasingly being used in sleep studies to measure changes in end-expiratory lung volume (EELV), including in obese obstructive sleep apnea patients. Despite this, the accuracy of magnetometers has not been confirmed in obese patients nor compared between sexes. Thus we compared spirometer-measured and magnetometer-estimated lung volume and tidal volume changes during voluntary end-expiratory lung volume changes of 1.5, 1, and 0.5 l above and 0.5 l below functional respiratory capacity in supine normal-weight [body mass index (BMI) < 25 kg/m] and healthy obese (BMI > 30 kg/m) men and women. Two different magnetometer calibration techniques proposed by Banzett et al. [Banzett RB, Mahan ST, Garner DM, Brughera A, Loring SH. J Appl Physiol (1985) 79: 2169–2176, 1995] and Sackner et al. [Sackner MA, Watson H, Belsito AS, Feinerman D, Suarez M, Gonzalez G, Bizousky F, Krieger B. J Appl Physiol (1985) 66: 410–420, 1989] were assessed. Across all groups and target volumes, magnetometers overestimated spirometer-measured EELV by ~65 ml (<0.001) with no difference between techniques (0.07). The Banzett method overestimated the spirometer EELV change in normal-weight women for all target volumes except +0.5 l, whereas no differences between mass or sex groups were observed for the Sackner technique. The variability of breath-to-breath measures of EELV was significantly higher for obese compared with nonobese subjects and was higher for the Sackner than Banzett technique. On the other hand, for tidal volume, both calibration techniques underestimated spirometer measurements (<0.001), with the underestimation being more marked for the Banzett than Sackner technique (0.03), in obese than normal weight (<0.001) and in men than in women (0.003). These results indicate that both body mass and sex affect the accuracy of respiratory magnetometers in measuring EELV and tidal volume.