Ascending aortic blood flow velocity is increased in children with primary snoring/mild sleep-disordered breathing and associated with an increase in CD8 + T cells expressing TNFα and IFNγ.

Sleep-disordered breathing (SDB) is associated with cardiovascular disease and systemic inflammation in adults but this remains to be explored in children, especially in children with the most common form of SDB, i.e. primary snoring/mild SDB. This pilot study investigated the relationship between the cardiovascular function and inflammation in children with mild SDB. Nineteen participants aged 5-14 years underwent overnight polysomnography, cardiac magnetic resonance imaging (aortic blood flow velocity and left and right ventricular systolic function) and assessment for inflammatory markers (intracellular cytokine analysis of T cells by flow cytometry). Parents also completed the Sleep Disturbances Scale for Children (SDSC). Children with mild SDB exhibited increased ascending aortic peak systolic velocity compared to controls (SDB 119.95 m/s vs. control 101.49 m/s, p < 0.05). No significant group differences were observed for left and right ventricular ejection fraction or mean aortic blood flow velocity from either the ascending aorta or pulmonary artery. Children with mild SDB had increased inflammatory markers as demonstrated by elevated T cell interferon gamma (IFNγ) (SDB 52 ± 4% vs. control 25 ± 3% positive cells, p < 0.005) and tumour necrosis factor alpha (TNFα) (SDB 39 ± 4% vs. control 20 ± 2% positive cells, p < 0.005) expression from CD8+ cells. A strong positive correlation was observed between ascending aorta peak blood flow velocity and both TNFα and IFNγ (TNFα, r = 0.54, p < 0.03; IFNγ, r = 0.63, p < 0.005, respectively). Polysomnography revealed that oxygen saturation (SaO2) nadir was significantly lower in children with mild SDB compared to controls (SDB 92.3 ± 2.7% vs. control 94.4 ± 1.6%, p < 0.05). A lower SaO2 nadir was associated with an increased ascending aorta peak systolic velocity (r = - 0.48, p < 0.05). As well, both a lower SaO2 nadir and an increased ascending aorta peak systolic velocity were associated with higher SDSC Sleep-Disordered Breathing and Disorder of Initiating and Maintaining Sleep subscale scores but not the polysomnographic-derived Obstructive Apnea-Hypopnea Index. The finding of elevated ascending aortic peak systolic blood flow velocity and its association with increased inflammatory markers suggests that the profile of cardiovascular changes noted in adult SDB may also occur in children with mild SDB.

Delayed brachial artery dilation response and increased resting blood flow velocity in young children with mild sleep-disordered breathing.

AIM: This study aimed to evaluate whether the vascular dysfunction perceived in adults with sleep-disordered breathing (SDB) was also evident in children with snoring referred for evaluation of clinically suspected SDB. OBJECTIVES: This study compared flow-mediated dilatation (FMD), measured at the brachial artery, at rest and during hyperaemic stress between children who snore [n = 23; mean standard deviation (SD) age = 7.51 (1.3) years] and healthy, non-snoring children [n = 11; age = 8.0 (1.3) years]. METHODS: Children with suspected obstructive sleep apnoea (OSA) and healthy non-snoring controls underwent overnight polysomnography (PSG). Using standard techniques, non-invasive FMD and brachial arterial blood flow velocity during rest and hyperaemia were subsequently measured by ultrasound imaging MEASUREMENTS: Resting and hyperaemic velocity time integral (area under the curve of mean systolic velocity × ejection time), maximal dilation response (highest percentage difference from baseline diameter) and the time taken to reach maximal dilation were calculated. RESULTS: Children awaiting adenotonsillectomy compared to healthy non-snoring control children had higher velocity time integrals at rest (14 ± 3 m vs. 20 ± 8 m, p < 0.01) and during hyperaemic stress (56 ± 6m vs. 63 ± 13m, p < 0.01) despite having only mild SDB on polysomnographic assessment. Lower nadir oxygen saturation values during non-rapid eye movement sleep were negatively associated with higher resting (r = -0.58, p <0.001) and hyperaemic (r = -0.36, p < 0.05) velocity time integrals. Maximal FMD dilatation response was not significantly different between snoring and non-snoring groups, but the estimated time to reach maximal dilation was significantly delayed in children who snored (60.7 ± 28.4 vs. 39.2 ± 13.2 s, p < 0.05). CONCLUSIONS: Children with mild SDB showed increased blood flow velocity at rest and during hyperaemic stress suggesting altered cardiovascular and haemodynamic function. The delay in time to maximal vessel dilatation in children who snored also suggests possible reduced vascular compliance in response to hyperaemic sheer stress. Mild SDB appears to alter the peripheral vascular response in young children. The long-term vascular implications of these changes in the growing child are unknown and warrant further investigation.

Gender, socioeconomic, and ethnic differences in sleep patterns in school-aged children.

OBJECTIVES: Age-related changes in sleep behavior are well described in children, yet the effect of gender, socioeconomic status (SES), and ethnicity is less clear. These factors are important when developing culturally and socially appropriate guidelines for healthy sleep. The objective of our study was to examine the effects of age, gender, SES, and ethnicity on sleep patterns in school-aged children. METHODS: A cross-sectional survey was conducted through primary schools in Adelaide, South Australia. Parents reported demographic information and sleep patterns for school and non-school days for 1845 children aged 5 to 10years. RESULTS: 48% of the cohort were boys (mean age, 7.7±1.7y), 85% were Caucasian, and there was an equal distribution across defined SES bands. Sleep duration reduced with age and was shorter on non-school than school nights as a result of later bedtimes. Boys, children from low SES areas, and non-Caucasian children reported shorter sleep times than girls, children from high SES areas, and Caucasian children, respectively. Non-Caucasian children from low SES areas reported the shortest sleep opportunity. CONCLUSIONS: The results from our study suggest that in addition to biological mechanisms, sleep behaviors are culturally and socially driven and should be considered when developing recommendations for healthy sleep in children.

Auditory evoked potentials remain abnormal after CPAP treatment in patients with severe obstructive sleep apnoea.

OBJECTIVE: To assess the effects of 3 months of optimal CPAP treatment on auditory event related potentials (AERP) in patients with severe obstructive sleep apnoea (OSA) compared with healthy controls. METHODS: Auditory odd-ball related N1, P2, N2 and P3 AERP components were assessed in 9 severe OSA subjects and 9 healthy controls at baseline evaluation and at ∼3 months follow-up in both groups, with OSA subjects treated with continuous positive air-way pressure (CPAP) during this period. RESULTS: Severe OSA subjects showed significantly delayed, P2, N2 and P3 latencies, and significantly different P2 and P3 amplitudes compared to controls at baseline (group effect, all p<0.05). At follow-up evaluation P3 latency shortened in treated OSA patients but remained prolonged compared to controls (group by treatment interaction, p<0.05) despite high CPAP compliance (6h/night). The earlier AERP (P2 and N2) components did not change in either controls or OSA patients at follow-up and remained different in patients versus controls. CONCLUSIONS: This study demonstrates that in severe OSA patients AERP responses show minimal or no improvement and remain abnormal following 3 months of optimal CPAP treatment. SIGNIFICANCE: Persistent cortical sensory processing abnormalities despite treatment in severe OSA may have implications for daytime neurobehavioral performance and safety in OSA patients. AERP responses may help identify residual performance deficits and risks.

Inconsistent sleep schedules and daytime behavioral difficulties in school-aged children.

OBJECTIVES: Current recommendations for healthy sleep in school-aged children are predominantly focused on optimal sleep duration (9-11h). However, given the importance of routine for circadian health, the stability of sleep/wake schedules may also be important, especially for daytime behavioral functioning. We examined the relationship between short sleep duration, sleep schedule instability and behavioral difficulties in a community sample of Australian children. METHODS: Children, aged 5-10 years (N=1622), without chronic health or psychological conditions, were recruited from primary schools in Adelaide, South Australia. A parent-report questionnaire was used to assess sleep/wake behavior. Behavioral functioning was assessed using the Strengths and Difficulties Questionnaire. RESULTS: Most children met sleep duration recommendations with approximately 5% reporting <9h and 3% >12h. Weekly variability of bed and rise times >1h were reported in up to 50% of children. Multinomial regression analysis revealed sleep duration <10h, bedtime latency >60 min, and bed and rise time variability >60 min significantly increased the risk of scoring in the 95th percentile for behavioral sub-scales. CONCLUSIONS: Inconsistent sleep schedules were common and, similar to short sleep duration, were associated with behavioral difficulties. Considering the lack of study in this area, further research is needed for the development of new recommendations, education and sleep health messages.

The validity of temperature-sensitive ingestible capsules for measuring core body temperature in laboratory protocols.

The human core body temperature (CBT) rhythm is tightly coupled to an endogenous circadian pacemaker located in the suprachiasmatic nucleus of the anterior hypothalamus. The standard method for assessing the status of this pacemaker is by continuous sampling of CBT using rectal thermometry. This research sought to validate the use of ingestible, temperature-sensitive capsules to measure CBT as an alternative to rectal thermometry. Participants were 11 young adult males who had volunteered to complete a laboratory protocol that extended across 12 consecutive days. A total of 87 functional capsules were ingested and eliminated by participants during the laboratory internment. Core body temperature samples were collected in 1-min epochs and compared to paired samples collected concurrently via rectal thermistors. Agreement between samples that were collected using ingestible sensors and rectal thermistors was assessed using the gold-standard limits of agreement method. Across all valid paired samples collected during the study (n = 120,126), the mean difference was 0.06°C, whereas the 95% CI (confidence interval) for differences was less than ±0.35°C. Despite the overall acceptable limits of agreement, systematic measurement bias was noted across the initial 5 h of sensor-transit periods and attributed to temperature gradations across the alimentary canal.

Driving simulator performance remains impaired in patients with severe OSA after CPAP treatment.

STUDY OBJECTIVES: To assess the effectiveness of CPAP treatment in improving 90-minute driving simulator performance in severe OSA patients compared to age/gender matched controls. DESIGN: Driving simulator performance was assessed at baseline and 3 months later, with OSA patients treated with CPAP during the interval. SETTING: University Teaching Hospital. PARTICIPANTS: Patients with severe OSA (n = 11) and control subjects without OSA (n = 9). INTERVENTIONS: CPAP MEASUREMENTS AND RESULTS: Simulator driving parameters of steering deviation, braking reaction time and crashes were measured at baseline and ∼3 months follow-up. At baseline, OSA subjects demonstrated significantly greater steering deviation compared to controls (mean [95% CI], OSA group, 49.9 cm [43.7 to 56.0 cm] vs control group, 34.9 cm [28.1 to 41.7 cm], p = 0.003). Following ∼3 months of CPAP treatment (mean ± SD 6.0 ± 1.4 h/night), steering deviation in OSA subjects improved by an average of 3.1 cm (CI, 1.4 to 4.9), p < 0.001, while no significant steering changes were observed in the control group. Despite the improvement, steering deviation in the OSA group remained significantly higher than in controls (OSA group, 46.7 cm [CI, 40.6 to 52.8 cm] vs control group, 36.1 cm [CI, 29.3 to 42.9 cm], p = 0.025). CONCLUSIONS: While driving simulator performance improved after ∼3 months of CPAP treatment with high adherence in patients with severe OSA, performance remained impaired compared to control subjects. These results add to the growing body of evidence that some neurobehavioral deficits in patients with severe OSA are not fully reversed by treatment. Further studies are needed to assess causes of residual driving simulator impairment and to determine whether this is associated with persistent elevated real-life accident risk. TRIAL REGISTRATION: Data presented in this manuscript was collected as part of a clinical trial "Experimental Investigations of Driving Impairment in Obstructive Sleep Apnoea" ACTRN12610000009011, http://www.anzctr.org.au/trial_view.aspx?ID=334979

Differences in parental attitudes towards sleep and associations with sleep-wake patterns in Caucasian and Southeast Asian school-aged children in Australia.

Caucasian (N = 47) and Southeast (SE) Asian (N = 36) families completed a questionnaire on their attitudes toward sleep, as well as a 7-day sleep diary for their children aged 5 to 11 years. Cultural differences were found in the perceived importance of sleep, particularly compared to homework and belief of how much sleep a child needs. Differences were also found in sleep-wake behaviors and amount of time spent on homework, with SE Asian children reporting a shift in sleep timing and increased homework load compared to Caucasian counterparts. Parental attitudes toward sleep, perception of sleep need, and homework load were not associated with the regulation of actual sleep behaviors in children, regardless of cultural heritage.

Adenotonsillectomy and neurocognitive deficits in children with Sleep Disordered Breathing.

BACKGROUND: Sleep Disordered Breathing (SDB) is a common childhood disorder that encompasses a range of sleep-related upper airway obstruction. Children with SDB demonstrate significant neurocognitive deficits. Adenotonsillectomy is the first line of treatment for SDB and whilst this improves respiratory disturbance, it remains to be established whether neurocognitive gains also result. METHODS: A total of 44 healthy snoring children aged 3-12 years awaiting adenotonsillectomy (SDB group), and 48 age and gender matched non-snoring controls from the general community, completed the study. All children underwent polysomnography and neurocognitive assessment at baseline and after a 6-month follow-up (after surgery in the snoring group). Our primary aim was to determine whether neurocognitive deficits in snoring children were significantly improved following adenotonsillectomy. RESULTS: Wide ranging neurocognitive deficits were found at baseline in SDB children compared to controls, most notably a 10 point IQ difference (P<.001) and similar deficits in language and executive function. Whilst adenotonsillectomy improved respiratory parameters and snoring frequency at 6 months post surgery, neurocognitive performance did not improve relative to controls. CONCLUSION: Adenotonsillectomy successfully treated the respiratory effects of SDB in children. However, neurocognitive deficits did not improve 6-months post-operatively.

Effects of alcohol and sleep restriction on simulated driving performance in untreated patients with obstructive sleep apnea.

BACKGROUND: Because of previous sleep disturbance and sleep hypoxia, patients with obstructive sleep apnea (OSA) might be more vulnerable to the effects of alcohol and sleep restriction than healthy persons. OBJECTIVE: To compare the effects of sleep restriction and alcohol on driving simulator performance in patients with OSA and age-matched control participants. DESIGN: Driving simulator assessments in 2 groups under 3 different conditions presented in random order. SETTING: Adelaide Institute for Sleep Health, Sleep Laboratory, Adelaide, Australia. PARTICIPANTS: 38 untreated patients with OSA and 20 control participants. MEASUREMENTS: Steering deviation, crashes, and braking reaction time. INTERVENTION: Unrestricted sleep, sleep restricted to a maximum of 4 hours, and ingestion of an amount of 40% vodka calculated to achieve a blood alcohol level of 0.05 g/dL. RESULTS: Patients with OSA demonstrated increased steering deviation compared with control participants (mean, 50.5 cm [95% CI, 46.1 to 54.9 cm] in the OSA group and 38.4 cm [CI, 32.4 to 44.4 cm] in the control group; P < 0.01) and significantly greater steering deterioration over time (group by time interaction, P = 0.02). The increase in steering deviation after sleep restriction and alcohol was approximately 40% greater in patients with OSA than in control participants (group by condition interaction, P = 0.04). Patients with OSA crashed more frequently than control participants (1 vs. 24 participants; odds ratio [OR], 25.4; P = 0.03) and crashed more frequently after sleep restriction (OR, 4.0; P < 0.01) and alcohol consumption (OR, 2.3; P = 0.02) than after normal sleep. In patients with OSA, prolonged eye closure (>2 seconds) and microsleeps (> 2 seconds of theta activity on electroencephalography) were significant crash predictors (OR, 19.2 and 7.2, respectively; P < 0.01). Braking reaction time was slower after sleep restriction than after normal sleep (mean, 1.39 [SD, 0.06] seconds vs. 1.22 [SD, 0.04] seconds; P < 0.01) but not after alcohol consumption. No group differences were found. LIMITATION: Simulated driving was assessed rather than on-road driving. CONCLUSION: Patients with OSA are more vulnerable than healthy persons to the effects of alcohol consumption and sleep restriction on various driving performance variables. PRIMARY FUNDING SOURCE: Australian National Health and Medical Research Council.

Differences in the association between obesity and obstructive sleep apnea among children and adolescents.

STUDY OBJECTIVES: Overweight and obesity are thought to increase the risk of obstructive sleep apnea syndrome (OSAS) among children. However, previous results have been inconsistent and appear to be confounded by both ethnicity and the different ages of children studied. To determine whether the association between excess weight and OSAS varies with age across childhood, we assessed polysomnographic data from a series of Caucasian children and adolescents referred for clinical evaluation of snoring. METHODS: Sleep and OSAS severity were assessed using polysomnography in 234 children aged 2.0 to 18.0 years. All children were referred for overnight evaluation of suspected OSAS. Severity of OSAS as a function of body mass and age were then evaluated. RESULTS: Risk of OSAS among adolescents (age > or =12 years) was increased 3.5 fold with each standard-deviation increase in body mass index z-score. Risk of OSAS was not significantly increased with increasing body mass among younger children. CONCLUSIONS: Similar to adults, adolescent children show an increased risk for having OSAS in association with overweight and obesity. For Caucasian children, overweight and obesity should be considered a significant risk for OSAS among adolescents or from age 12 years, especially when in combination with other established risk factors, including snoring and adenotonsillar hypertrophy.

Is there a clear link between overweight/obesity and sleep disordered breathing in children?

The proportion of children who are overweight or obese has risen steadily in recent decades and approaches a quarter of all children in Western countries. This global epidemic of excess weight and adiposity in humans is associated with increased morbidity and mortality, especially related to diabetes and poor cardiovascular health. It would appear that obesity is also generally accepted to be an important risk factor in the development of sleep disordered breathing (SDB), in children as well as adults. The article, "The prevalence, anatomical correlates and treatment of sleep-disordered breathing in obese children and adolescents", by Verhulst et al., also in this issue, reviews evidence supporting the view that obese children are at higher risk of developing SDB. We believe, however, that the available studies do not support a straightforward association of overweight or obesity with increased prevalence of SDB. Rather, the available data is clearly equivocal mainly due to methodological differences between the previous studies. This review nonetheless examines the factors which may modulate the relationship between overweight or obesity and prevalence of SDB, particularly ethnicity and age.

Obesity and risk of sleep related upper airway obstruction in Caucasian children.

BACKGROUND: Obesity is thought to be a significant risk factor for upper airway obstruction during sleep in children. However, the moderating influences of age and ethnicity have not been well explored and the relative contribution of obesity per se to upper airway obstruction has yet to be quantified. Given the markedly increasing prevalence of childhood obesity, an objective understanding of the impact of obesity on upper airway obstruction is important. The purpose of the present study was to examine the interaction between obesity, age and upper airway obstruction in Australian Caucasian children referred for evaluation of snoring. METHODS: This was a retrospective case study involving 190 children (4-12 y) who were referred for evaluation of upper airway obstruction and underwent one night of polysomnography at the Adelaide Women's and Children's Hospital Sleep Disorders Unit. Children were classified as Infrequent Snorers (n = 80), Habitual Snorers (n = 68) or Obstructive Sleep Apnea Syndrome (OSAS) (n = 42) (i.e., obstructive apnea hypopnea index (OAHI) > or = 1). RESULTS: Thirty-five percent (66/190) of children were overweight or obese. Body mass index but not age was a significant but weak predictor of OAHI (< 5% of the variance). CONCLUSION: In Australian Caucasian children aged 4-12 years who snore, obesity but not age was a significant, albeit weak, predictor of upper airway obstruction during sleep.

Sleep and errors in a group of Australian hospital nurses at work and during the commute.

There is a paucity of information regarding Australian nurses' sleep and fatigue levels, and whether they result in impairment. Forty-one Australian hospital nurses completed daily logbooks for one month recording work hours, sleep, sleepiness, stress, errors, near errors and observed errors (made by others). Nurses reported exhaustion, stress and struggling to remain (STR) awake at work during one in three shifts. Sleep was significantly reduced on workdays in general, and workdays when an error was reported relative to days off. The primary predictor of error was STR, followed by stress. The primary predictor of extreme drowsiness during the commute was also STR awake, followed by exhaustion, and consecutive shifts. In turn, STR awake was predicted by exhaustion, prior sleep and shift length. Findings highlight the need for further attention to these issues to optimise the safety of nurses and patients in our hospitals, and the community at large on our roads.

Perception of simulated driving performance after sleep restriction and caffeine.

OBJECTIVE: As feelings of alertness are reported to be highly correlated with performance perception, the objective of this study was to determine whether caffeine, a common countermeasure to driver sleepiness, affected a sleepy driver's ability to monitor his or her simulated driving performance. METHODS: Twelve healthy young adults (six males, six females) participated in three counterbalanced, blinded, daytime conditions: control [9 h time in bed (TIB)], 100 mg caffeine (4 h TIB), and placebo (4 h TIB). Driving performance was measured through lane drift on a series of 30-min simulated driving sessions. Subjective sleepiness and perception of driving performance were measured at 5-min intervals during driving sessions via the Karolinska Sleepiness Scale and a corresponding perception scale. RESULTS: Sleep restriction had a significant detrimental effect on driving performance and subjective measures. Caffeine resulted in significant improvements across all measures. Subjective measures were found to be significantly correlated after sleep restriction and prior to caffeine. Correlations between actual and perceived performance were nonsignificant across all conditions. CONCLUSIONS: The strong correlation between subjective measures supports the postulation that sleepiness is used as a cue for performance prediction when sleep restricted. The relationship between perceived and actual performance after fatigue countermeasures remains inconclusive. Further research, addressing limitations, is needed.

A pilot study of the safety implications of Australian nurses' sleep and work hours.

The frequency and severity of adverse events in Australian healthcare is under increasing scrutiny. A recent state government report identified 31 events involving "death or serious [patient] harm" and 452 "very high risk" incidents. Australia-wide, a previous study identified 2,324 adverse medical events (AME) in a single year, with more than half considered preventable. Despite the recognized link between fatigue and error in other industries, to date, few studies of medical errors have assessed the fatigue of the healthcare professionals involved. Nurses work extended and unpredictable hours with a lack of regular breaks and are therefore likely to experience elevated fatigue. Currently, there is very little available information on Australian nurses' sleep or fatigue levels, nor is there any information about whether this affects their performance. This study therefore aims to examine work hours, sleep, fatigue and error occurrence in Australian nurses. Using logbooks, 23 full-time nurses in a metropolitan hospital completed daily recordings for one month (644 days, 377 shifts) of their scheduled and actual work hours, sleep length and quality, sleepiness, and fatigue levels. Frequency and type of nursing errors, near errors, and observed errors (made by others) were recorded. Nurses reported struggling to remain awake during 36% of shifts. Moderate to high levels of stress, physical exhaustion, and mental exhaustion were reported on 23%, 40%, and 36% of shifts, respectively. Extreme drowsiness while driving or cycling home was reported on 45 occasions (11.5%), with three reports of near accidents. Overall, 20 errors, 13 near errors, and 22 observed errors were reported. The perceived potential consequences for the majority of errors were minor; however, 11 errors were associated with moderate and four with potentially severe consequences. Nurses reported that they had trouble falling asleep on 26.8% of days, had frequent arousals on 34.0% of days, and that work-related concerns were either partially or fully responsible for their sleep disruption on 12.5% of occasions. Fourteen out of the 23 nurses reported using a sleep aid. The most commonly reported sleep aids were prescription medications (62.7%), followed by alcohol (26.9%). Total sleep duration was significantly shorter on workdays than days off (p < 0.01). In comparison to other workdays, sleep was significantly shorter on days when an error (p < 0.05) or a near error (p < 0.01) was recorded. In contrast, sleep was higher on workdays when someone else's error was recorded (p = 0.08). Logistic regression analysis indicated that sleep duration was a significant predictor of error occurrence (chi2 = 6.739, p = 0.009, e beta = 0.727). The findings of this pilot study suggest that Australian nurses experience sleepiness and related physical symptoms at work and during their trip home. Further, a measurable number of errors occur of various types and severity. Less sleep may lead to the increased likelihood of making an error, and importantly, the decreased likelihood of catching someone else's error. These pilot results suggest that further investigation into the effects of sleep loss in nursing may be necessary for patient safety from an individual nurse perspective and from a healthcare team perspective.

The effects of chewing versus caffeine on alertness, cognitive performance and cardiac autonomic activity during sleep deprivation.

Chewing has been shown to alleviate feelings of sleepiness and improve cognitive performance during the day. This study investigated the effect of chewing on alertness and cognitive performance across one night without sleep as well as the possible mediating role of cardiac autonomic activity. Fourteen adults participated in a randomized, counterbalanced protocol employing a chewing, placebo and caffeine condition. Participants completed tasks assessing psychomotor vigilance, tracking, grammatical reasoning, alertness and sleepiness each hour across the night. All participants received either placebo or caffeine (200 mg), while the chewing condition also chewed on a tasteless and odorless substance for 15 min each hour. Heart rate (HR), root mean square of the successive differences in R-R intervals on the ECG (RMSSD), and preejection period (PEP) were simultaneously recorded. Alertness and cognitive performance amongst the chewing condition did not differ or were in fact worse when compared with placebo. Similarly, measures of HR and RMSSD remained the same between these two conditions; however, PEP was reduced in the later part of the night in the chewing condition compared with a relative increase for placebo. Caffeine led to improved speed and accuracy on cognitive tasks and increased alertness when compared with chewing. Relative increases in RMSSD and reductions in HR were demonstrated following caffeine; however, no change in PEP was seen. Strong associations between cardiac parasympathetic activity and complex cognitive tasks, as well as between subjective alertness and simpler cognitive tasks, suggest a differential process mediating complex versus simple cognitive performance during sleep deprivation.

Attenuated thermoregulatory response to mild thermal challenge in subjects with sleep-onset insomnia.

STUDY OBJECTIVES: To determine if heat loss capacity of sleep onset insomniacs was different from that of healthy sleepers. DESIGN: Measure skin temperature responses following brief exposure to a warm peripheral thermal challenge (PTC). SETTING: Sleep research laboratory in South Australia. PARTICIPANTS: Eight primary insomniacs with sleep onset insomnia according to DSM-IV-TR criteria (SOI; 5 male, 3 female; mean age +/- SEM = 35.2 +/- 4.2 years) and ten healthy sleeping control subjects (HS; 7 male, 3 female; mean age = 28.2 +/- 2.8 years). INTERVENTIONS: Two PTC conditions in counterbalanced order on non-consecutive days. During each condition, the subject's non-dominant forearm and hand were immersed for 3 minutes in Warm (45 degrees C) or Control water (i.e. same as the subject's non-dominant index finger temperature just prior to immersion, range 30-35 degrees C). MEASUREMENTS AND RESULTS: HS had a significantly higher maximum finger temperature response after immersion than SOI (P < 0.05). Expressed relative to Control PTC temperatures, the Warm PTC caused a significant increase in mean finger temperature for HS of 4.1 +/- 0.8 degrees C, compared with SOI of 0.9 +/- 0.4 degrees C. A significant negative relationship was observed between maximum finger temperature response and self-reported sleep onset latencies (R = -0.57, P < 0.05). There were no main effects of sleep status (SOI vs. HS) or interactions by time, in skin temperatures measured at either the back of hands or feet. CONCLUSIONS: SOI were observed to have significantly attenuated thermoregulatory responses to a mild positive thermal challenge, providing evidence that impaired heat loss capacity from the periphery is associated with sleep onset insomnia.

Melatonin as a hypnotic: con.

The physiological roles of melatonin are still unclear despite almost 50 years of research. Elevated melatonin levels from either endogenous nocturnal production or exogenous daytime administration are associated in humans with effects including increased sleepiness, reduced core temperature, increased heat loss and other generally anabolic physiological changes. This supports the idea that endogenous melatonin increases nocturnal sleep propensity, either directly or indirectly via physiological processes associated with sleep. The article "Melatonin as a hypnotic--Pro", also in this issue, presents evidence to support this viewpoint. We do not entirely disagree, but nevertheless feel this is an overly simplistic interpretation of the available data. Our interpretation is that melatonin is primarily a neuroendocrine transducer promoting an increased propensity for 'dark appropriate' behavior. Thus, it is our view that exogenous melatonin is only hypnotic in those species or individuals for which endogenous melatonin increases sleep propensity and is consequently a dark appropriate outcome. Evidence supporting this position is drawn primarily from studies of exogenous administration of melatonin and its varied effects on sleep/wake behavior based on dose, time of administration, age and other factors. From this perspective, it will be shown that melatonin can exert hypnotic-like effects but only under limited circumstances.