Morning preference in onset of symptomatic third-degree atrioventricular heart block

The aim of this study was to examine 24h patterning in the symptoms indicative of third-degree atrio-ventricular (AV) heart block. We found a total of 227 cases (126 men and 101 women) of third-degree AV block that had been diagnosed by the Emergency Medical Department of the St. Anna Hospital in Ferrara, Italy between 1990 and 2001. Determination of the hour of onset of symptomatic third-degree AV block, however, was possible and listed in the records of only 161 or 70.9% of the cases (92 men and 69 women). The onset time of every event was categorized into one of four 6h spans of the 24h: night (00:00-05:59h), morning (06:00-11:59h), afternoon (12:00-17:59h), and evening (18:00-23:59h). The onset of the symptoms of third-degree AV block in the sample of 161 cases was significantly greater in the morning between 06:00 and 11:59h than any other 6h span of the day and night (chi2-test; p < 0.001). The same phenomenon was substantiated in the subgroup of the 92 males (chi2; p < 0.0001), although it could not be detected for the smaller subgroup of 69 women. The 24h pattern, with morning preference, in the onset of symptomatic third-degree AV block is similar to the one in sudden cardiac death and cardiogenic cardiac arrest. The etiology of the 24h pattern in symptomatic AV block is unknown; it may be an expression of intrinsic biological rhythmicity within the heart tissue or its control system, and/or the timing of environmental triggers resulting in coronary ischemia.     

Circadian variation in clinical features and outcome of intracerebral hemorrhage: The INTERACT studies

Previous studies consistently reported a diurnal variation in the occurrence of intracerebral hemorrhage (ICH), with a morning peak. However, limited knowledge exists on the circadian pattern of ICH severity and outcome. This study aimed to determine possible associations between ICH onset time and admission severity and 90-day outcomes using the combined data set of the pilot and main-phase Intensive blood pressure (BP) reduction in an acute cerebral hemorrhage trial (INTERACT). The ICH onset time was categorized into three groups (1: 00:00–07:59; 2: 08:00–15:59; and 3: 16:00–23:59). We found an association between onset time and low Glasgow Coma Scale score: aOR (time 1: 1.72, 95% CI 1.12–2.66; time 3: 1.95, 95% CI 1.31–2.89, p = 0.003; in comparison to time 2). There was no association between onset time and volume of ICH (adjusted p = 0.354) or 90-day outcomes of death or major disability, and death and major disability separately (all adjusted p > 0.4). The results showed that more severe cases of ICH patients, defined by a reduced level of consciousness, had late afternoon to early morning stroke onset, but this was unrelated to baseline hematoma volume or location. There was no circadian influence on ICH clinical outcome.     

Timing Light Treatment for Eastward and Westward Travel Preparation

Jet lag degrades performance and operational readiness of recently deployed military personnel and other travelers. The objective of the studies reported here was to determine, using a narrow bandwidth light tower (500 nm), the optimum timing of light treatment to hasten adaptive circadian phase advance and delay. Three counterbalanced treatment order, repeated measures studies were conducted to compare melatonin suppression and phase shift across multiple light treatment timings. In Experiment 1, 14 normal healthy volunteers (8 men/6 women) aged 34.9±8.2 yrs (mean±SD) underwent light treatment at the following times: A) 06:00 to 07:00 h, B) 05:30 to 07:30 h, and C) 09:00 to 10:00 h (active control). In Experiment 2, 13 normal healthy subjects (7 men/6 women) aged 35.6±6.9 yrs, underwent light treatment at each of the following times: A) 06:00 to 07:00 h, B) 07:00 to 08:00 h, C) 08:00 to 09:00 h, and a no-light control session (D) from 07:00 to 08:00 h. In Experiment 3, 10 normal healthy subjects (6 men/4 women) aged 37.0±7.7 yrs underwent light treatment at the following times: A) 02:00 to 03:00 h, B) 02:30 to 03:30 h, and C) 03:00 to 04:00 h, with a no-light control (D) from 02:30 to 03:30 h. Dim light melatonin onset (DLMO) was established by two methods: when salivary melatonin levels exceeded a 1.0 pg/ml threshold, and when salivary melatonin levels exceeded three times the 0.9 pg/ml sensitivity of the radioimmunoasssy. Using the 1.0 pg/ml DLMO, significant phase advances were found in Experiment 1 for conditions A (p?<?.028) and B (p?<?0.004). Experiment 2 showed significant phase advances in conditions A (p?<?0.018) and B (p?<?0.003) but not C (p?<?0.23), relative to condition D. In Experiment 3, only condition B (p?<?0.035) provided a significant phase delay relative to condition D. Similar but generally smaller phase shifts were found with the 2.7 pg/ml DLMO method. This threshold was used to analyze phase shifts against circadian time of the start of light treatment for all three experiments. The best fit curve applied to these data (R²?=?0.94) provided a partial phase-response curve with maximum advance at approximately 9–11 h and maximum delay at approximately 5–6 h following DLMO. These data suggest largest phase advances will result when light treatment is started between 06:00 and 08:00 h, and greatest phase delays will result from light treatment started between 02:00 to 03:00 h in entrained subjects with a regular sleep wake cycle (23:00 to 07:00 h).     

Differences in Sleep,Light, and Circadian Phase in Offshore 18:00–06:00 h and 19:00–07:00 h Shift Workers

Complaints concerning sleep are high among those who work night shifts; this is in part due to the disturbed relationship between circadian phase and the timing of the sleep‐wake cycle. Shift schedule, light exposure, and age are all known to affect adaptation to the night shift. This study investigated circadian phase, sleep, and light exposure in subjects working 18:00–06:00 h and 19:00–07:00 h schedules during summer (May–August). Ten men, aged 46±10 yrs (mean±SD), worked the 19:00–07:00 h shift schedule for two or three weeks offshore (58°N). Seven men, mean age 41±12 yrs, worked the 18:00–06:00 h shift schedule for two weeks offshore (61°N). Circadian phase was assessed by calculating the peak (acrophase) of the 6‐sulphatoxymelatonin rhythm measured by radioimmunoassay of sequential urine samples collected for 72 h at the end of the night shift. Objective sleep and light exposure were assessed by actigraphy and subjective sleep diaries. Subjects working 18:00–06:00 h had a 6‐sulphatoxymelatonin acrophase of 11.7±0.77 h (mean±SEM, decimal hours), whereas it was significantly later, 14.6±0.55 h (p=0.01), for adapted subjects working 19:00–07:00 h. Two subjects did not adapt to the 19:00–07:00 h night shift (6‐sulphatoxymelatonin acrophases being 4.3±0.22 and 5.3±0.29 h). Actigraphy analysis of sleep duration showed significant differences (p=0.03), with a mean sleep duration for those working 19:00–07:00 h of 5.71±0.31 h compared to those working 18:00–06:00 h whose mean sleep duration was 6.64±0.33 h. There was a trend to higher morning light exposure (p=0.07) in the 19:00–07:00 h group. Circadian phase was later (delayed on average by 3 h) and objective sleep was shorter with the 19:00–07:00 h than the 18:00–06:00 h shift schedule. In these offshore conditions in summer, the earlier shift start and end time appears to favor daytime sleep.     

Circadian Variation in Patient Characteristics and Outcomes in ST-Segment Elevation Myocardial Infarction

A morning peak in ST-segment elevation myocardial infarction (STEMI) has been described. The authors explored the relationship between variation of symptom onset, patient characteristics, and outcomes in two worldwide fibrinolytic trials. A total of 35 492 patients with STEMI were grouped into 8-h intervals by time of symptom onset: early (06:00 to 13:59?h), late-day (14:00 to 21:59?h), overnight (22:00 to 05:59?h). The authors correlated timing with patient characteristics and outcomes (adjusted for thrombolysis in myocardial infarction [TIMI] risk score) first in InTIME II-TIMI 17 trial (N?=?15 031), and confirmed in the ExTRACT-TIMI 25 trial (N?=?20 461). Timing was similar in the derivation (early 49%, late-day 30%, and overnight 21%; p?<?.001) and validation set (48%, 31%, and 21%, respectively; p?<?.001). Some patient characteristics consistently varied with time of symptom onset. Patients in the early cohort were older with poorer renal function. The late-day group had more smokers with higher initial heart rate and systolic blood pressure. Those with overnight symptom onset had higher rates of obesity, prior myocardial infarction, and treatment delays. Prior use of aspirin and beta-blockers was also highest in the overnight group. Relative to the early cohort, adjusted mortality was higher with late-day onset (derivation odds ratio [OR]: 1.19, p?=?.04; validation OR: 1.18, p?=?.01), but there was no excess in mortality overnight compared with early (derivation OR: .97, p?=?.72; validation OR: 1.01, p?=?.90). Composite endpoints followed similar patterns. This study indicates that circadian patterns in onset of STEMI continue to exist with patient characteristics differing by time of day. Despite a potential physiologic resistance to morning thrombolysis, outcomes were best in the early cohort, intermediate overnight, and worst with late-day symptom onset. Efforts to reduce smoking and improve control of blood pressure could reduce the number of patients with late-day onset of STEMI who experience the worst outcomes. (Author correspondence: owen@mogabgab.com)     

Light Exposure Among Adolescents With Delayed Sleep Phase Disorder: A Prospective Cohort Study

The objective of this study was to compare light exposure and sleep parameters between adolescents with delayed sleep phase disorder (DSPD; n?=?16, 15.3?±?1.8 yrs) and unaffected controls (n?=?22, 13.7?±?2.4 yrs) using a prospective cohort design. Participants wore wrist actigraphs with photosensors for 14 days. Mean hourly lux levels from 20:00 to 05:00?h and 05:00 to 14:00?h were examined, in addition to the 9-h intervals prior to sleep onset and after sleep offset. Sleep parameters were compared separately, and were also included as covariates within models that analyzed associations with specified light intervals. Additional covariates included group and school night status. Adolescent delayed sleep phase subjects received more evening (p?<?.02, 22:00–02:00?h) and less morning (p?<?.05, 08:00–09:00?h and 10:00–12:00?h) light than controls, but had less pre-sleep exposure with adjustments for the time of sleep onset (p?<?.03, 5–7?h prior to onset hour). No differences were identified with respect to the sleep offset interval. Increased total sleep time and later sleep offset times were associated with decreased evening (p?<?.001 and p?=?.02, respectively) and morning (p?=?.01 and p?<?.001, respectively) light exposure, and later sleep onset times were associated with increased evening exposure (p?<?.001). Increased total sleep time also correlated with increased exposure during the 9?h before sleep onset (p?=?.01), and a later sleep onset time corresponded with decreased light exposure during the same interval (p?<?.001). Outcomes persisted regardless of school night status. In conclusion, light exposure interpretation requires adjustments for sleep timing among adolescents with DSPD. Pre- and post-sleep light exposures do not appear to contribute directly to phase delays. Sensitivity to morning light may be reduced among adolescents with DSPD. (Author correspondence: auger.raymond1@mayo.edu)     

Association of the melatonin circadian rhythms with clock 3111T/C gene polymorphism in Caucasian and Asian menopausal women with insomnia

A comparative analysis of melatonin circadian rhythms in Caucasian (incoming population) and Asian (indigenous population) menopausal women with/without sleep disorders depending on the genotype of Clock 3111T/C gene polymorphism was realized.The melatonin level in the saliva was determined four times a day (6:00–7:00, 12:00–13:00, 18:00–19:00, 23:00–00:00 h). The Caucasian women—carriers of the TT-genotype with insomnia as compared to control group—had a higher morning melatonin level and a lower night melatonin level. The Asian women with TT-genotype and insomnia had a lower levels of melatonin as compared to control at daytime, evening and night. A significantly higher melatonin level in the early morning hours was detected in the Caucasian women—carriers of the TT-genotype with insomnia as compared to group womencarriers of the minor 3111C-allele. There were no statistically significant differences in the circadian rhythms of melatonin in the Asian women depending on the genotype of the Clock 3111T/C polymorphism. An assumption with respect to the protective role of the minor allele 3111C in the development of insomnia associated with the displacement of melatonin circadian rhythms in the representatives of the incoming population was made.     

Older Poor-Sleeping Women Display a Smaller Evening Increase in Melatonin Secretion and Lower Values of Melatonin and Core Body Temperature Than Good Sleepers

Melatonin concentration and core body temperature (CBT) follow endogenous circadian biological rhythms. In the evening, melatonin level increases and CBT decreases. These changes are involved in the regulation of the sleep-wake cycle. Therefore, the authors hypothesized that age-related changes in these rhythms affect sleep quality in older people. In a cross-sectional study design, 11 older poor-sleeping women (aged 62–72 yrs) and 9 older good-sleeping women (60–82 yrs) were compared with 10 younger good-sleeping women (23–28 yrs). The older groups were matched by age and body mass index. Sleep quality was assessed by the Pittsburgh Sleep Quality Index questionnaire. As an indicator of CBT, oral temperature was measured at 1-h intervals from 17:00 to 24:00?h. At the same time points, saliva samples were collected for determining melatonin levels by enzyme-linked immunosorbent assay (ELISA). The dim light melatonin onset (DLMO), characterizing the onset of melatonin production, was calculated. Evening changes in melatonin and CBT levels were tested by the Friedman test. Group comparisons were performed with independent samples tests. Predictors of sleep-onset latency (SOL) were assessed by regression analysis. Results show that the mean CBT decreased in the evening from 17:00 to 24:00?h in both young women (from 36.57°C to 36.25°C, p < .001) and older women (from 36.58°C to 35.88°C, p < .001), being lowest in the older poor sleepers (p < .05). During the same time period, mean melatonin levels increased in young women (from 16.2 to 54.1 pg/mL, p < .001) and older women (from 10.0 to 23.5 pg/mL, p < .001), being lowest among the older poor sleepers (from 20:00 to 24:00?h, p < .05 vs. young women). Older poor sleepers also showed a smaller increase in melatonin level from 17:00 to 24:00?h than older good sleepers (mean?±?SD: 7.0?±?9.63 pg/mL vs. 15.6?±?24.1 pg/mL, p = .013). Accordingly, the DLMO occurred at similar times in young (20:10?h) and older (19:57?h) good-sleeping women, but was delayed ～50?min in older poor-sleeping women (20:47?h). Older poor sleepers showed a shorter phase angle between DLMO and sleep onset, but a longer phase angle between CBT peak and sleep onset than young good sleepers, whereas older good sleepers had intermediate phase angles (insignificant). Regression analysis showed that the DLMO was a significant predictor of SOL in the older women (R²?=?0.64, p < .001), but not in the younger women. This indicates that melatonin production started later in those older women who needed more time to fall asleep. In conclusion, changes in melatonin level and CBT were intact in older poor sleepers in that evening melatonin increased and CBT decreased. However, poor sleepers showed a weaker evening increase in melatonin level, and their DLMO was delayed compared with good sleepers, suggesting that it is not primarily the absolute level of endogenous melatonin, but rather the timing of the circadian rhythm in evening melatonin secretion that might be related to disturbances in the sleep-wake cycle in older people. (Author correspondence: mdittmar@zoologie.uni-kiel.de)     

Myocardial Infarction Occurs with a Similar 24 h Pattern in the 4G/5G Versions of Plasminogen Activator Inhibitor-1

PAI-1 expression is regulated by a 4G/5G promoter polymorphism. The 4G allele is associated with greater circadian variation of PAI-1 levels. We hypothesized that the 24 h variation of cardiac risk is more pronounced among persons with the 4G4G genotype than among ones with 4G5G and 5G5G genotypes. We assessed the time of onset of symptoms in 623 consecutive patients with acute myocardial infarction (AMI) enrolled in the MISSION! Study between February 1, 2004, and October 29, 2006. All of the patients were genotyped for the PAI-1 4G/5G polymorphism. We quantified the amplitude of the 24 h variation of AMI with a generalized linear model with Poisson distribution. A morning peak, between 06:00–11:59 h (n?=?197; 32% of all cases), in the onset of symptoms of AMI was observed. The group composed of patients with the 4G4G genotype did not have a more pronounced morning peak than the groups composed of other genotypes; the 24 h variation was 38% (95% confidence interval 12–70%) in the group of 4G4G patients and 34% (14–58%) and 56% (20–100%) in the 4G5G and 5G5G groups of patients, respectively. Our findings show that 24 h variation of cardiac risk is not more pronounced among the 4G4G genotype of PAI-1. (Author correspondence: j.g.vanderbom@lumc.nl)     

Adipokine Levels Are Altered by Shiftwork: A Preliminary Study

Shiftwork is often associated with metabolic diseases, and in the past few years, several cytokines have been postulated to contribute to various diseases, including insulin resistance. The aim of this study was to compare the concentrations of adiponectin, tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6) in samples of young adult men exposed to a fixed (i) night shift (n?=?9), working from 22:00 to 06:00?h; (ii) early morning shift (n?=?6), working from 06:00 to 14:00?h; and (iii) day shift (n?=?7), working from 08:00 to 17:00?h. The fixed night-shift and early-morning-shift samples were considered collectively as a shiftworker group given their work times. Blood samples were collected during the regular working day at 4-h intervals over the course of 24?h, thus totaling six samples. Morphological and physical activity parameters did not differ between the three groups. Total energy intake was lowest on the early morning shifts (p?<?.03). Both shiftworker groups ingested a significantly higher percentage of fat (p?<?.003) and a lower percentage of carbohydrate (p?<?.0005) than the day group. The early morning group had a lower mean 24-h level of adiponectin than the other two groups (p?=?.016), and both the early morning and night groups exhibited higher mean 24-h levels of TNF-α than the day group (p?=?.0001). The 24-h mean levels of IL-6 did not differ significantly between the groups (p?=?.147). None of the groups exhibited a significant circadian effect on adiponectin (p?=?.829), TNF-α (p?=?.779), or IL-6 (p?=?.979) levels. These results indicate that individuals who are enrolled in shiftwork are susceptible to alterations in the secretion of cytokines that are involved in insulin resistance and cardiovascular disease, both of which are known to affect this population. (Author correspondence: tmello@demello.net.br)     

Circadian rhythms may not influence the outcomes of thrombolysis in patients with ischemic stroke: A study from China

ABSTRACT

Circadian rhythms can affect physical or mental activities as well as the time of stroke onset. The impact of circadian rhythms on acute ischemic stroke (AIS) patients treated by recombinant alteplase (rt-PA) is still incongruent. This study aims to consider whether the outcomes of thrombolysis differ depending on stroke onset time and rt-PA infusion time in patients with AIS. A total of 447 AIS patients, who underwent rt-PA intravenous infusion within 4.5 hours after stroke onset, were enrolled in this study consecutively from June 2010 through December 2016. All of the patients were grouped based on the stroke onset time and rt-PA infusion time into two exact 12-hour intervals as daytime (06:01–18:00) and nighttime (18:01–06:00) and further divided into four subgroups at 6-hour time intervals (00:01–06:00, 06:01–12:00, 12:01–18:00 and 18:01–24:00). Major neurological improvement at 1 hour, 24 hours and 7 days, 7-day mortality rate and 24-hour hemorrhage transformation was recorded. The results showed that a total of 295 patients (66.4%) appeared with AIS and 252 (56.4%) were treated during daytime. Higher NIHSS at admission was observed when stroke occurred in nighttime, especially during 00:01–06:00. Patients with stroke onset in nighttime especially during 18:01–24:00 had a significant shorter onset-door time and onset-needle time. No differences of the major neurological improvement at 1 hour, 24 hours and 7 days, 24-hour hemorrhagic transformation and 7-day fatality rate were found among either 12-hour time frames or 6-hour time frames according to the time of stroke onset or rt-PA infusion. In conclusion, there was no evidence to predict that circadian rhythms could influence the outcomes of AIS patients treated with rt-PA in China, although stroke onset during nighttime might aggravate neurological impairment before treatment. Further, multicenter and prospective clinical trials with larger number of subjects are still needed to draw more reliable conclusions.     

Role of Patient Chronotype on Circadian Pattern of Myocardial Infarction: A Pilot Study

Population-based studies indicate the risk of acute myocardial infarction (AMI) is greatest in the morning, during the initial hours of diurnal activity. The aim of this pilot study was to determine whether chronotype, i.e., morningness and eveningness, impacts AMI onset time. The sample comprised 63 morning- and 40 evening-type patients who were classified by the Horne-Östberg Morningness-Eveningness Questionnaire (MEQ) in the hospital after experiencing the AMI. The average wake-up and bed times of morning types were ～2?h earlier than evening types. Although the lag in time between waking up from nighttime sleep and AMI onset during the day did not differ between the two chronotypes, the actual clock-hour time of the peak in the 24-h AMI pattern did. The peak in AMI of morning types occurred between 06:01 and 12:00?h and that of the evening types between 12:01 and 18:00?h. Although the results of this small sample pilot study suggest one's chronotype influences the clock time of AMI onset, larger scale studies, which also include assessment of 24-h patterning of events in neither types, must be conducted before concluding the potential influence of chronotype on the timing of AMI onset. (Author correspondence: dryavuzselvi@yahoo.com).     

Effect of Time of Day on Aerobic Contribution to the 30‐s Wingate Test Performance

The purpose of this study was to evaluate the effects of time of day on aerobic contribution during high‐intensity exercise. A group of 11 male physical education students performed a Wingate test against a resistance of 0.087 kg · kg^?1 body mass. Two different times of day were chosen, corresponding to the minimum (06:00 h) and the maximum (18:00 h) levels of power. Oxygen uptake (V˙O₂) was recorded breath by breath during the test (30 sec). Blood lactate concentrations were measured at rest, just after the Wingate test, and again 5 min later. Oral temperature was measured before each test and on six separate occasions at 02:00, 06:00, 10:00, 14:00, 18:00, and 22:00 h. A significant circadian rhythm was found in body temperature with a circadian acrophase at 18:16±00:25 h as determined by cosinor analysis. Peak power (P_peak), mean power (P_mean), total work done, and V˙O₂ increased significantly from morning to afternoon during the Wingate Test. As a consequence, aerobic contribution recorded during the test increased from morning to afternoon. However, no difference in blood lactate concentrations was observed from morning to afternoon. Furthermore, power decrease was greater in the morning than afternoon. Altogether, these results indicate that the time‐of‐day effect on performances during the Wingate test is mainly due to better aerobic participation in energy production during the test in the afternoon than in the morning.     

Chronotype,gender, and time for sex

The study aimed at testing chronotype and gender differences in the time of day when humans feel the greatest need for sex and the time of day they actually undertake sexual activity. A Polish sample of 565 participants aged between 18 and 57 was tested. In females, regardless of chronotype, the greatest need for sex occurred between 18:00 and 24:00, but a secondary peak appeared only in morning types at 6:00–9:00. In males, the greatest need for sex occurred either in the morning or evening hours: in evening types at 9:00–12:00 and 18:00–3:00; in neither types at 6:00–9:00 and 18:00–24:00; in morning types at 6:00–12:00 and 18:00–24:00. Considering time of day when subjects were undertaking sexual activity most frequently, this appeared between 18:00 and 24:00 for all the participants, and prolonged until 3:00 at night in evening type males. Morningness preference was more strongly related to the timing of need for sex than to the timing of actual sexual activity (r?=??0.275 vs. r?=??0.174), while the timing of desire and the timing of sexual activity were positively, but moderately related (r?=?0.320).     

Effects of Waking Time and Breakfast Intake Prior to Evaluation of Physical Performance in the Early Morning

Diurnal variation in both core body temperature and indicators of physical performance are usually observed when measures are taken at 06:00 and 18:00 h. However, differences have been reported between findings in the literature; this may be in some part due to methodological reasons, such as if the experimenter allowed subjects to eat breakfast before the morning 06:00 h session, or even the waking time of subjects. Eleven diurnally active male subjects participated in four test sessions to examine if the time of morning wakening (04:00 or 05:00 h) and eating or not eating breakfast influence body temperature, flexibility, force production, and aerobic performance at 06:00 h. All four sessions were separated by ≥36 h and were completed in a counterbalanced order. Each test session comprised a sit‐and‐reach test, an arm maximal voluntary torque evaluation (isometric, concentric at 1.05 rad·s^?1 and at 4.19 rad·s^?1), and a 10 min all‐out cycle ergometer test. Our results indicate the effects of waking time or food intake depend on the parameter tested. Consequently, we advise researchers to take care in experimental design and to at least standardize the time of awakening and consumption of breakfast.     

MAXIMAL POWER,BUT NOT FATIGABILITY,IS GREATER DURING REPEATED SPRINTS PERFORMED IN THE AFTERNOON

The present study was designed to investigate if the suggested greater fatigability during repeated exercise in the afternoon, compared to the morning, represents a true time-of-day effect on fatigability or a consequence of a higher initial power. In a counterbalanced order, eight subjects performed a repeated-sprint test [10?×?(6 s of maximal cycling sprint?+?30 s of rest)] on three different occasions between: 08:00–10:00, 17:00–19:00, and 17:00-19:00?h controlled (17:00–19:00?h_cont, i.e., initial power controlled to be the same as the two first sprints of the 08:00–10:00?h trial). Power output was significantly (p?<?0.05) higher for sprints 1, 2, and 3 in the afternoon than in the morning (e.g., sprint 1: 23.3 ±1 versus 21.2 ±1 W·kg^?1), but power decrement for the 10 sprints was also higher in the afternoon. Based on the following observations, we conclude that this higher power decrement is a consequence of the higher initial power output in the afternoon. First, there was no difference in power during the final five sprints (e.g., 20.4 ±1 versus 19.7 ±1 W·kg^?1 for sprint 10 in the afternoon and morning, respectively). Second, the greater decrement in the afternoon was no longer present when participants were producing the same initial power output in the afternoon as in the morning. Third, electromyographic activity of the vastus lateralis decreased during the exercise (p?<?0.05), but without a time-of-day effect. (Author correspondence: sebastien.racinais@aspetar.com)     

Night shift work and osteoporosis among female blue-collar workers in Poland - a pilot study

ABSTRACT

Osteoporosis is an important public health problem worldwide. Although a number of factors that affect bone structure have been described; thus far, the current knowledge of occupational factors that may have an influence on bone tissue metabolism is strongly limited. Published studies indicate night shift work and the related circadian rhythm disruption may be considered as plausible underlying factors. The aim of the present study was to assess the potential association between night shift work and bone mineral density (BMD) among female blue-collar workers in Poland. A cross-sectional study was carried out among 194 female blue-collar workers >40 years of age employed in industrial plants. The operating system of work consisted of three work shifts clockwise rotation: morning (06:00–14:00 h), afternoon (14:00–22:00 h), and night (22:00–06:00 h), with five consecutive shifts per week followed by a free weekend. A questionnaire survey, based on a Polish version of The European vertebral osteoporosis study (EVOS) questionnaire, a validated instrument, was administered. Data on current job characteristics, job seniority, and lifetime duration of night shift work were also collected. BMD of the lumbar spine and hip (both total femur and femoral neck) was measured using dual-energy X-ray absorptiometry. Multivariate linear regression models were run, with bone mineralization parameters as dependent variables, as well as night work characteristics and important confounders. Statistical analysis was performed separately for premenopausal and postmenopausal women. The analyses adjusted for confounders did not reveal any significant differences between current or lifetime experience of night shift work and BMD among both premenopausal and postmenopausal women. However, the outcomes supported the well-established correlation with factors, such as age, BMI, and menopausal status. BMD at the three sites measured was significantly associated with BMI (p < .001) and inversely associated with age (p < .001) in the total study population. Postmenopausal women had significantly lower BMD than did premenopausal women (p < .001). The study findings indicate that in the population of Polish female blue-collar workers, the system of work does not seem to be associated with the development of osteoporosis.     

Time‐of‐Day Effects on Myoelectric and Mechanical Properties of Muscle During Maximal and Prolonged Isokinetic Exercise

The aim of this study was to examine the time‐of‐day (TOD) effects in myoelectric and mechanical properties of muscle during a maximal and prolonged isokinetic exercise. Twelve male subjects were asked to perform 50 maximal voluntary contractions (MVC) of the knee extensor muscles at a constant angular velocity of 2.09 rad · sec^?1, at 06∶00 and 18∶00 h. Torque and electromyographic (EMG) parameters were recorded for each contraction, and the ratio between these values was calculated to evaluate variations of the neuromuscular efficiency (NME) with fatigue and with TOD. The results indicated that maximal torque values (T₄₅Max) was significantly higher (7.73%) in the evening than in the morning (p<0.003). The diurnal variation in torque decrease was used to define two phases. During the first phase (1st to the 26th repetition), torque values decreased fast and values were higher in the evening than in the morning, and during the second phase (27th to the 50th repetition), torque decreased slightly and reached a floor value that appeared constant with TOD. The EMG parameters (Root Mean Square; RMS) were modified with fatigue, but were not TOD dependent. The NME decrease–significantly with fatigue, showing that peripheral factors were mainly involved in the torque decrease. Furthermore, NME decrease was greater at 18∶00 than at 06∶00 h for the vastus medialis (p<0.05) and the vastus lateralis muscles (p<0.002), and this occurred during the first fatigue phase of the exercise. In conclusion, the diurnal variation of the muscle fatigue observed during a maximal and prolonged isokinetic exercise seems to reflect on the muscle, with a greater contractile capacity but a higher fatigability in the evening compared to the morning.     

Seasonal Rhythms of Body Temperature in the Free‐Ranging Raccoon Dog (Nyctereutes procyonoides) with Special Emphasis on Winter Sleep

The raccoon dog (Nyctereutes procyonoides) is the only canid with passive overwintering in areas with cold winters, but the depth and rhythmicity of wintertime hypothermia in the wild raccoon dog are unknown. To study the seasonal rhythms of body temperature (T_b), seven free‐ranging animals were captured and implanted with intra‐abdominal T_b loggers and radio‐tracked during years 2004–2006. The average size of the home ranges was 306±26 ha, and the average 24 h T_b was 38.0±<0.01°C during the snow‐free period (May–November). The highest and lowest T_b were usually recorded around midnight (21∶00–02∶00 h) and between 05∶00–11∶00 h, respectively, and the range of the 24 h oscillations was 1.2±0.01°C. The animals lost approximately 43±6% of body mass in winter (December–April), when the average size of the home ranges was 372±108 ha. During the 2–9‐wk periods of passivity in January–March, the average 24 h T_b decreased by 1.4–2.1°C compared to the snow‐free period. The raccoon dogs were hypothermic for 5 h in the morning (06∶00–11∶00 h), whereas the highest T_b values were recorded between 16∶00–23∶00 h. The range of the 24 h oscillations increased by approximately 0.6°C, and the rhythmicity was more pronounced than in the snow‐free period. The ambient temperature and depth of snow cover were important determinants of the seasonal T_b rhythms. The overwintering strategy of the raccoon dog resembled the patterns of winter sleep in bears and badgers, but the wintertime passivity of the species was more intermittent and the decrease in the T_b less pronounced.     

BIOLOGICAL RHYTHMS OF SPINAL-EPIDURAL LABOR ANALGESIA

Pain exhibits temporal variations in intensity due to multiple factors, including endogenous neuroendocrine and various external influences that vary over the 24?h. Also, medications can vary in potency and/or toxicity according to the time when they are administered. However, there is no consensus among studies regarding the 24-h pattern of analgesia during labor. Taking into account the time-of-day when labor analgesia is administered, this study aimed to answer two questions: (i) Is there diurnal variation in visual analogue scale (VAS)–rated pain relief and duration of intrathecal analgesia in patients undergoing labor analgesia? (ii) If there is, what is the influence of the duration of labor on the diurnal variation of the level of pain relief and duration of intrathecal analgesia? This prospective cohort included 41 healthy, nulliparous women in the first stage of labor undergoing spinal-epidural (CSE) analgesia using fentanyl combined with bupivacaine. Subjects had an epidural catheter fitted for additional, patient-controlled analgesia (PCA) if their pain relief was unsatisfactory. The number of VAS assessments (n?=?558) was divided into six time periods of the 24?h. The adjusted coefficient of determination (r²), the proportion of the variance explained by the association between the duration of labor and the temporal pattern of the outcomes variable, was 58% (r²?=?0.58) for pain relief and 44% (r²?=?0.44) for duration of intrathecal analgesia. The peak effect of labor analgesia occurred between 02:00 and 05:59?h. However, the duration of intrathecal analgesia showed two peaks, i.e., at ～00:00 and ～12:00?h. These results demonstrate that labor analgesia achieved by fentanyl combined with bupivacaine shows a diurnal pattern in pain relief and duration of spinal analgesia. However, part of these temporal patterns was explained by the association with duration of labor. (Author correspondence: caumo@cpovo.net)