Probing upper thermospheric neutral densities at Mars using electron reflectometry

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95666/1/grl20594.pd

Left ventricular morphology and function in adolescents: Relations to fitness and fatness.

BACKGROUND: Obesity in childhood predisposes individuals to cardiovascular disease and increased risk of premature all-cause mortality. The aim of this study was to determine differences in LV morphology and function in obese and normal-weight adolescents. Furthermore, relationships between LV outcomes, cardiorespiratory fitness (CRF) and adiposity were explored. METHODS: LV morphology was assessed using magnetic resonance imaging (MRI) in 20 adolescents (11 normal-weight [BMI equivalent to 18kg/m(2)-25kg/m(2)] and 9 obese [BMI equivalent to ≥30kg/m(2)]); 13.3±1.1years, 45% female, Tanner puberty stage 3 [2-4]) using magnetic resonance imaging (MRI). Global longitudinal strain (GLS), strain rate (SR) and traditional echocardiographic indices were used to assess LV function. CRF (peak oxygen consumption), percent body fat (dual-energy x-ray absorptiometry), abdominal adipose tissue (MRI), and blood biochemistry markers were also evaluated. RESULTS: Adolescents with obesity showed significantly poorer LV function compared to normal-weight adolescents (P0.05). Moderate to strong associations between myocardial contractility and relaxation, adiposity, arterial blood pressure and cardiorespiratory fitness were noted (r=0.49-0.71, P<0.05). CONCLUSION: Obesity in adolescence is associated with altered LV systolic and diastolic function. The notable relationship between LV function, CRF and adiposity highlights the potential utility of multidisciplinary lifestyle interventions to treat diminished LV function in this population. CLINICAL TRIAL REGISTRATION: NCT01991106

Light sensitivity as a physiological factor that promotes irregular sleep/wake patterns: a model-based investigation

Introduction: Irregular sleep is a health risk factor. However, we currently have a poor understanding of physiological factors that contribute to individuals having irregular sleep/wake patterns. We used a validated mathematical model of sleep-wake and circadian physiology to systematically examine the influence of circadian, sleep homeostatic, and light sensitivity parameters on sleep regularity. Materials and Methods: Sleep-wake patterns were generated by a computational model, assuming a 5-day work schedule with enforced wakefulness from 7:00 to 19:00. We introduced daily random variation σ in the model’s sleep-onset threshold to mimic observed intra-individual variability in sleep/wake patterns. The Sleep Regularity Index (SRI) was calculated, ranging from 0 (random pattern) to 100 (perfectly regular pattern). Eight model parameters were varied to determine their effects on SRI: circadian period (τ); circadian amplitude (νvc); sleep homeostatic time constant (χ); and five light sensitivity parameters: delay bias of the phase response curve (b), sensitivity of the dose response curve (p), retinal output strength (G), photoreceptor recovery rate (β), and photoreceptor activation rate (α0). Results: Sleep regularity was meaningfully affected by six of the eight parameters. Responses occurred in three clusters: (1) light sensitivity parameters G and β had no effect on SRI; (2) circadian amplitude νvc modulated the effect of σ, such that weaker amplitude resulted in lower SRI (less regular patterns) for the same σ; and (3) the remaining five parameters τ, χ, b, p, and α0 all generated maximal SRI scores (most regular patterns) for default parameter values, with lower SRI scores when parameters deviated from default values. Conclusions: This is the first study to systematically investigate potential mechanisms of irregular sleep using mathematical modeling. Our findings suggest that irregular sleep can result from individual differences in the sensitivity to the timing and intensity of light exposure, as well as differences in circadian and sleep homeostatic parameters

Constraint is associated with earlier circadian phase and morningness: Confirmation of relationships between personality and circadian phase using a constant routine protocol

Associations amongst personality, diurnal preference, and circadian phase were investigated using a constant routine laboratory protocol. One hundred and sixty-eight healthy participants aged 18�30 years (Women n = 68) completed either a 30- or 50-hour constant routine under dim-light conditions (< 3 lx), during which circadian phase was measured from core body temperature and melatonin. Prior to laboratory admission, self-report measures of personality and diurnal preference were also obtained. The personality trait of Constraint correlated positively with morning diurnal preference and earlier circadian phase, with circadian phase partially mediating the relationship between Constraint and diurnal preference. No other personality variables correlated with circadian phase. Sex was an important covariate in several of the relationships investigated due to lower levels of Constraint and later CBT phase amongst men and was thus controlled for in all relevant analyses. Findings from this highly controlled study are consistent with previous field research in suggesting that earlier circadian phase is associated with the personality trait of Constraint. © 201

High sensitivity and interindividual variability in the response of the human circadian system to evening light

Before the invention of electric lighting, humans were primarily exposed to intense (&gt;300 lux) or dim (&lt;30 lux) environmental light�stimuli at extreme ends of the circadian system�s dose�response curve to light. Today, humans spend hours per day exposed to intermediate light intensities (30�300 lux), particularly in the evening. Interindividual differences in sensitivity to evening light in this intensity range could therefore represent a source of vulnerability to circadian disruption by modern lighting. We characterized individual-level dose�response curves to light-induced melatonin suppression using a within-subjects protocol. Fifty-five participants (aged 18�30) were exposed to a dim control (&lt;1 lux) and a range of experimental light levels (10�2,000 lux for 5 h) in the evening. Melatonin suppression was determined for each light level, and the effective dose for 50% suppression (ED50) was computed at individual and group levels. The group-level fitted ED50 was 24.60 lux, indicating that the circadian system is highly sensitive to evening light at typical indoor levels. Light intensities of 10, 30, and 50 lux resulted in later apparent melatonin onsets by 22, 77, and 109 min, respectively. Individual-level ED50 values ranged by over an order of magnitude (6 lux in the most sensitive individual, 350 lux in the least sensitive individual), with a 26% coefficient of variation. These findings demonstrate that the same evening-light environment is registered by the circadian system very differently between individuals. This interindividual variability may be an important factor for determining the circadian clock�s role in human health and disease. © 2019 National Academy of Sciences. All rights reserved

Increased sensitivity of the circadian system to light in delayed sleep–wake phase disorder

Patients with delayed sleep�wake phase disorder (DSWPD) exhibit delayed sleep�wake behaviour relative to desired bedtime, often leading to chronic sleep restriction and daytime dysfunction. The majority of DSWPD patients also display delayed circadian timing in the melatonin rhythm. Hypersensitivity of the circadian system to phase-delaying light is a plausible physiological basis for DSWPD vulnerability. We compared the phase shifting response to a 6.5 h light exposure (~150 lux) between male patients with diagnosed DSWPD (n = 10; aged 20.8 ± 2.3 years) and male healthy controls (n = 11; aged 22.4 ± 3.3 years). Salivary dim light melatonin onset (DLMO) was measured under controlled conditions in dim light (<3 lux) before and after light exposure. Correcting for the circadian time of the light exposure, DSWPD patients exhibited 31.5% greater phase delay shifts than healthy controls. In both groups, a later initial melatonin phase was associated with a greater magnitude phase shift, indicating that increased circadian sensitivity to light may be a factor that contributes to delayed phase, even in non-clinical groups. DSWPD patients also had reduced pupil size following the light exposure, and showed a trend towards increased melatonin suppression during light exposure. These findings indicate that, for patients with DSWPD, assessment of light sensitivity may be an important factor that can inform behavioural therapy, including minimization of exposure to phase-delaying night-time light. © 2018 The Authors. The Journal of Physiology and 2018 The Physiological Society

Sleep disturbances may influence lifestyle behaviours in women with self-reported polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is associated with a higher prevalence of sleep disturbances and obesity. Treatment of PCOS includes modifying lifestyle behaviours associated with weight management. However, poor sleep in the non-PCOS population has been associated with poorer lifestyle behaviours. The aim was to investigate whether sleep disturbance confounds or modifies the association between lifestyle factors and PCOS. This was a cross-sectional analysis from the Australian Longitudinal Study on Women’s Health cohort aged 31–36 years in 2009 were analysed (n 6067, 464 PCOS, 5603 non-PCOS). Self-reported data were collected on PCOS, anthropometry, validated modified version of the Active Australia Physical Activity survey, validated FFQ and sleep disturbances through latent class analysis. Women with PCOS had greater adverse sleep symptoms including severe tiredness (P = 0·001), difficulty sleeping (P < 0·001) and restless sleep (P < 0·001), compared with women without PCOS. Women with PCOS also had higher energy consumption (6911 (SD 2453) v. 6654 (SD 2215) kJ, P = 0·017), fibre intake (19·8 (SD 7·8) v. 18·9 (SD 6·9) g, P = 0·012) and diet quality (dietary guidelines index (DGI)) (88·1 (SD 11·6) v. 86·7 (SD 11·1), P = 0·008), lower glycaemic index (50·2 (SD 4·0) v. 50·7 (SD 3·9), P = 0·021) and increased sedentary behaviour (6·3 (SD 2·8) v. 5·9 (SD 2·8) h, P = 0·009). There was a significant interaction between PCOS and sleep disturbances for DGI (P = 0·035), therefore only for women who had adequate sleep was PCOS associated with a higher DGI. For women with poorer sleep, there was no association between PCOS and DGI. The association between PCOS and improved diet quality may only be maintained if women can obtain enough good quality sleep.Christie J. Bennett, Darren R. Mansfield, Lin Mo, Anju E. Joham, Sean W. Cain, Michelle L. Blumfield, Allison M. Hodge, and Lisa J. Mora

Annual variation in attentional response after methylphenidate treatment

Circadian clocks in health and diseas