Sleep and breathing disorders

A major focus of this issue of JSR is devoted to the topic of respiratory sleep medicine—as many as seven papers stem from this discipline of clinical sleep medicine. Agha and Johal (2017), probably for the first time ever, present a systematic review and meta-analysis on facial phenotypes in obstructive sleep apnea–hypopnea syndrome (OSAS). Interestingly, and as expected, for neck circumference five studies with a total of 906 participants (included in the analysis) showed increased mean differences compared to control subjects. However, the authors noted extensive heterogeneity between the analysed studies. Only two studies, with a sum of 467 participants, looked at other parameters such as mandible length, mandible width, lower facial height and anterior mandible height parameters. The pooled results demonstrated that OSAS was coupled with larger parameters than controls. Summarizing, this systematic review and meta-analysis can be seen as a first step in the right direction—combining data from several studies and meta-analysing them is usually very useful to bring structure into a field and to evaluate which findings are stable or not. Concluding, it might be said that further research is necessary, especially according to well-devised guidelines on how to measure facial phenotype, in order to develop a more solid data base. Two papers in this issue (Chang et al., 2017; Kim et al., 2017) look at the relationship between snoring, sleep apnea and atherosclerosis. Kim et al. measured carotid intima-media thickness (IMT) in a sample of 180 non-apneic and non-snorers (snoring was recorded objectively by a microphone). The study showed that mean carotid IMT increased with the severity of snoring in females, but not in males. Thus, the authors conclude that ‘snoring during at least one-fourth of a night's sleep is associated independently with sub-clinical changes in carotid intima-media thickness in women but not in men’. Chang et al. measured, among other parameters, carotid IMT in 121 OSA patients (without metabolic syndrome) and 27 controls. It was shown that, in the patients with OSA, mean systolic blood pressure and other parameters correlated independently with carotid IMT. This is worth noting, because the investigated sample of patients with OSA was selected specifically for not having a metabolic syndrome. A second major focus of this issue of JSR originates from investigations into sleep–wake homeostasis, circadian rhythms and chronobiology. In a careful polysomnographic study in 11 healthy young adults, the Zurich group (Rusterholz et al., 2017) looked at interindividual differences in the dynamics of the homeostatic ‘Process S’. They found that the time constants of the build-up and dissipation of Process S varied independently among subjects, indicating two distinct traits. The authors concluded that the interindividual differences in the parameters of the dynamics of the sleep homeostatic Process S are trait-like. Another highlight comes from the same group (Borbély et al., 2017). Here, Alexander Borbély, one of the founding fathers of European sleep research, presents his own personal data of actigraphy collected over a period of more than 3 decades, starting in 1982. This is probably the largest single case data set ever published on actigraphic measurements. Interestingly, as the data set includes data during active work (before retirement) and after retirement, differences between these two periods of life became obvious. Before retirement there was a dominant 7-day rhythm of sleep duration as well as an annual periodicity (revealed by spectral analysis). These variations were attenuated or vanished during the years after retirement. Several papers looked at school-aged children, students or young adults. Gariepy et al. (2017) report data from Canada about school starting times and sleep in Canadian adolescents. Data were taken from 362 schools from almost 30 000 students aged 10–18 years. Mean school starting time was 08:43 hours and varied from 07:57 to 09:37 hours. Students slept an average of 8:36 hours on weeknights and 9:45 at weekends. As expected, bedtimes shifted to later times at the end of the week (for more than 3 h at weekends compared to weeknights). Interestingly, the data analysis showed that students with later school times slept more and were less likely to report feeling tired in the morning. This study adds weight to the mounting evidence that delaying school start time may benefit adolescent sleep and wake patterns.

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