Effect of Ramadan on the Diurnal Variation in Short‐Term High Power Output

This study examined the effects of Ramadan fasting on anaerobic performances and their diurnal fluctuations. In a balanced and randomized study design, 12 subjects were measured for maximal power (P_max; force‐velocity test), peak power (P_peak), and mean power (P_mean) with the Wingate test at 07:00, 17:00, and 21:00 h on four different occasions: one week before Ramadan (BR), the second week of Ramadan (SWR), the fourth week of Ramadan (ER), and two weeks after Ramadan (AR). There was an interval of 28 h between any two successive tests. Oral temperature was measured before each test. Under each condition, the results showed a time‐of‐day effect on oral temperature. Analysis of variance revealed a significant (Ramadan×time‐of‐day of test) interaction effect on P_max. This variable improved significantly from morning to evening before Ramadan (1.1±0.2 W · kg^?1), during the second week of Ramadan (0.6±0.2 W · kg^?1), and two weeks after the end of Ramadan (0.9±0.2 W · kg^?1). However, daily fluctuations disappeared during the fourth week of Ramadan. For P_peak and P_mean, there was no significant Ramadan×test‐time interaction. These variables improved significantly from morning to evening before Ramadan ([1±0.3 W · kg^?1] for P_peak and [1.7±1.6 W · kg^?1] for P_mean) and in the second week of Ramadan ([0.9±0.6 W · kg^?1] for P_peak and [1.7±1.5 W · kg^?1] for P_mean). However, they were not affected by time‐of‐day in the fourth week of Ramadan. Considering the effect of Ramadan on anaerobic performances, in comparison with before Ramadan, no significant difference was observed during Ramadan at 07:00 h. The variables were significantly lower in the second week of Ramadan and in the fourth week of Ramadan at 17:00 h and 21:00 h. P_mean was not affected during the second week of Ramadan. In conclusion, the time‐of‐day effect on anaerobic power variables tends to disappear during Ramadan. In comparison with the period before Ramadan, anaerobic performances were unaffected in the morning but impaired in the evening during Ramadan.     

The Effect of Pedal Rate and Time of Day on the Time to Exhaustion from High‐Intensity Exercise

The aim of this study was to examine the supposed influence of pedal rate on the diurnal fluctuation of the time to exhaustion from high‐intensity exercise. Eleven male cyclists performed three tests at 06:00 h and three at 18:00 h at a free pedal rate (FPR) and two imposed pedal rates (80% and 120% of the FPR). They performed the tests until exhaustion using a power output corresponding to 95% maximal power (P_max). Time to exhaustion, rectal temperature, oxygen consumption (V˙O₂), M. quadriceps, vastus medialis, M. biceps femoris electromyographic Root Mean Square activity rise (RMS slope), and blood lactate concentration were measured. The mean time to exhaustion recorded at 18:00 h (270.6±104.8 sec) was greater than at 06:00 h (233.9±84.9 sec). The time to exhaustion was significantly greater when the pedal rate was imposed at 80% versus 120% FPR. The blood lactate concentration and absolute core temperature at the point of exhaustion were significantly higher during tests done at 18:00 h. There was no diurnal variation in core temperature increase, V˙O₂, and RMS slope. The time‐of‐day effect for every variable did not depend on pedal rate. Diurnal variations in maximal aerobic endurance cannot be explained by a change in aerobic metabolism or in muscular fatigue. The origin of the diurnal variation in the time to exhaustion is likely to lie in greater participation in anaerobic metabolism. Also, the influence of temperature on neuromuscular functioning as an explanation for the diurnal variation in performance cannot be excluded in this study. The hypothesis on the basis of which pedal rate would influence diurnal variations in time to exhaustion in cycling was not validated by this research.     

Effects of Context on Sleepiness Self‐Ratings during Repeated Partial Sleep Deprivation

Ratings of subjective sleepiness are often used in laboratory and field studies of sleep loss and shifted sleep hours. Some studies suggest that such ratings might fail to reflect sleepiness as shown in physiology or performance. One reason for this may be the influence of the context of the rating. Social interaction or physical activity may mask latent sleepiness. The present study attempted to approach this question. Nine subjects participated in a partial sleep‐deprivation experiment (five days of 4 h of time in bed [TIB]), preceded by two baseline days (8 h TIB) and followed by three recovery days (8 h TIB). Sleepiness was self‐rated on the Karolinska Sleepiness Scale (KSS; scores of 1–9) after a period of relaxation, after a reaction‐time test, and after 30 min of free activities. The results showed a strong increase in subjective sleepiness during sleep restriction and a significant difference between conditions. Free activity reduced the self‐rated subjective sleepiness by 1.1 KSS units compared to the level of sleepiness self‐rated at the end of the reaction‐time test. Thus, the results of this study indicate that the context of a sleepiness rating affects the outcome of the rating.     

Effect of Time‐of‐Day‐Specific Strength Training on Serum Hormone Concentrations and Isometric Strength in Men

A time‐of‐day influence on the neuromuscular response to strength training has been previously reported. However, no scientific study has examined the influence of the time of day when strength training is performed on hormonal adaptations. Therefore, the primary purpose of this study was to examine the effects of time‐of‐day‐specific strength training on resting serum concentrations and diurnal patterns of testosterone (T) and cortisol (CORT) as well as maximum isometric strength of knee extensors. Thirty eight diurnally active healthy, previously untrained men (age 20–45 yrs) underwent a ten‐week preparatory strength training period when sessions were conducted between 17:00–19:00 h. Thereafter, these subjects were randomized into either a morning (n=20, training times 07:00–09:00 h) or afternoon (n=18, 7:00–19:00 h) training group for another ten‐week period of time‐of‐day‐specific training (TST). Isometric unilateral knee extension peak torque (MVC) was measured at 07:00, 12:00, 17:00, and 20:30 h over two consecutive days (Day 1 & Day 2) before and after TST. Blood samples were obtained before each clock‐time measurement to assess resting serum T and CORT concentrations. A matched control group (n=11) did not train but participated in the tests. Serum T and CORT concentrations significantly declined from 07:00 to 20:30 h on all test days (Time effect, p<.001). Serum CORT at 07:00 h was significantly higher on Day 1 than Day 2 in the control and afternoon group, both in Pre and Post conditions (Day×Time interaction, p<.01). In the morning group, a similar day‐to‐day difference was present in the Pre but not Post conditions (Time×Group interaction, p<.05). MVC significantly increased after TST in both the morning and afternoon groups (Pre to Post effect, p<.001). In both groups, a typical diurnal variation in MVC (Time effect, p<.001) was found, especially on Day 2 in the Pre condition, and this feature persisted from Pre to Post in the afternoon group. In the morning group, however, diurnal variation was reduced after TST on both Day 1 and Day 2 (Pre to Post×Day×Time×Group interaction, p<.05). In conclusion, 10 weeks of morning time‐of‐day‐specific strength training resulted in reduced morning resting CORT concentrations, presumably as a result of decreased masking effects of anticipatory psychological stress prior to the morning testing. The typical diurnal pattern of maximum isometric strength was blunted by the TST period in the morning but not the afternoon group. However, the TST period had no significant effect on the resting total T concentration and its diurnal pattern and on the absolute increase in maximum strength.     

Accounting for Partial Sleep Deprivation and Cumulative Sleepiness in the Three‐Process Model of Alertness Regulation

Mathematical models designed to predict alertness or performance have been developed primarily as tools for evaluating work and/or sleep‐wake schedules that deviate from the traditional daytime orientation. In general, these models cope well with the acute changes resulting from an abnormal sleep but have difficulties handling sleep restriction across longer periods. The reason is that the function representing recovery is too steep—usually exponentially so—and with increasing sleep loss, the steepness increases, resulting in too rapid recovery. The present study focused on refining the Three‐Process Model of alertness regulation. We used an experiment with 4 h of sleep/night (nine participants) that included subjective self‐ratings of sleepiness every hour. To evaluate the model at the individual subject level, a set of mixed‐effect regression analyses were performed using subjective sleepiness as the dependent variable. These mixed models estimate a fixed effect (group mean) and a random effect that accounts for heterogeneity between participants in the overall level of sleepiness (i.e., a random intercept). Using this technique, a point was sought on the exponential recovery function that would explain maximum variance in subjective sleepiness by switching to a linear function. The resulting point explaining the highest amount of variance was 12.2 on the 1–21 unit scale. It was concluded that the accumulation of sleep loss effects on subjective sleepiness may be accounted for by making the recovery function linear below a certain point on the otherwise exponential function.     

Morphofunctional Analysis of Effect of Short-Term Sleep Deprivation on the Wakefulness–Sleep Cycle in Young and Adult Rats

The work presents comparative data on changes of neurophysiological, time characteristics of the wakefulness–sleep cycle (WSC) and morphofunctional state of neurosecretory cells in supraoptic nucleus of the hypothalamus, which develop under influence of a 6-h long sleep deprivation in adult and one-month old rats. It is shown that the rebound of sleep develops in adult animals with a delay, after the 3rd hour and is characterized by a moderate increase of portions of slow-wave (SSP) and fast-wave (FSP) sleep phases in WSC and by a decrease of the wakefulness portion. Morphological analysis of the hypothalamus nonapeptidergic system has revealed a rise of content of neurosecretory material in fibers of supraoptic nucleus cells an in area of supraoptic-pituitary tract, as well as marked hyperemia that indicates activation of processes of secretion of neurohormones into the general blood flow; these reactions are similar to reactions of this system to stress. In rat pups the sleep rebound develops in 0.5 h after the end of the deprivation procedure and is characterized by more pronounced, statistically significant changes in WSC. Individual WSC become very short and almost all of them are completed with episodes of FSP. A statistically significant rise of power of the -wave band in electrogram spectra of hippocampus and somatosensory cortex in SSP, whereas peak of the activity in FSP is shifted to -waves. Ratios of SSP and FSP to wakefulness in individual WSC in mature animals increase after the deprivation 1.53 and 1.85 times, while they are elevated in one-month old animals 5.25 and 6.75 times, respectively. The obtained morphofunctional data allow believing that deprivation is the stress factor of low intensity for adult animals, whereas it may be considered as the stress action of intermediate and even high intensity for rat pups, which changes essentially the interrelations in WSC. Participation of central mechanisms of regulation of sleep and vigilance, which provide processes of compensation of damaging action of deprivation on WSC in the maturing animals, is discussed.     

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.     

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.     

Morning Versus Evening Power Output and Repeated‐Sprint Ability

We investigated the effect of time‐of‐day on both maximal sprint power and repeated‐sprint ability (RSA). Nine volunteers (22±4 yrs) performed a RSA test both in the morning (07:00 to 09:00 h) and evening (17:00 to 19:00 h) on different days in a random order. The RSA cycle test consisted of five, 6 sec maximal sprints interspersed by 24 sec of passive recovery. Both blood lactate concentration and heart rate were higher in the evening than morning RSA (lactate values post exercise: 13±3 versus 11±3 mmol/L^?1, p<0.05). The peak power developed during the first sprint was higher in the evening than morning (958±112 vs. 915±133 W, p<0.05), but this difference was not apparent in subsequent sprints, leading to a higher power decrement across the 5×6 sec test in the evening (11±2 vs. 7±3%, p<0.05). Both the total work during the RSA cycle test and the power developed during bouts 2 to 5 failed to be influenced by time‐of‐day. This suggests that the beneficial effect of time‐of‐day may be limited to a single expression of muscular power and fails to advantage performance during repeated sprints.     

Sex Difference in Sleep‐Time Preference and Sleep Need: A Cross‐Sectional Survey among Italian Pre‐Adolescents,Adolescents, and Adults

The aim of this study was to examine sex differences in sleep‐time preference by age among Italian pre‐adolescents, adolescents, and adults. The final sample consisted of 8,972 participants (5,367 females and 3,605 males) from 10 to 87 yrs of age. To assess preferred sleep habits, we considered the answers to the open‐ended questions of the Morningness‐Eveningness Questionnaire (MEQ). In agreement with previous studies, we found that sleep‐time preference started to shift toward eveningness from the age of 13 yrs. Females reached their peak in eveningness earlier (about 17 yrs of age) than males (about 21 yrs of age). Thereafter, the ideal sleep‐time preference advanced in men and women with increasing age. Females presented a more significant advanced sleep phase than males only during the years when sexual hormones are typically active. Moreover, females reported a longer ideal sleep duration than males across all age groups examined, except in over 55 yrs one. (Author correspondence: vincenzo.natale@unibo.it)     

Changes in the Power Characteristics of the α-Rhythm in Students with Different Levels of Anxiety in Normal Sleep and Partial Deprivation Solving the Go/NoGo Problem

Human Physiology - The effect of partial sleep deprivation on cognitive control was studied in 26 students with different levels of trait anxiety. The synchronization–desynchronization...     

Circadian Time‐Effect of Orally Administered Loratadine on Plasma Pharmacokinetics in Mice

Little is known about the chronopharmacokinetics of loratadine, a long‐acting tricyclic antihistamine H₁ widely used in the treatment of allergic diseases. Hence, the pharmacokinetics of loratadine and its major metabolite, desloratadine, were investigated after a 20 mg/kg dose of loratadine had been orally administered to comparable groups of mice (n=33), synchronized for three weeks to 12 h light (rest span)/12 h dark (activity span). The drug was administered at three different circadian times (1, 9, and 17 h after light onset [HALO]). Multiple blood samples were collected over 48 h, and plasma concentrations of loratadine and desloratadine were determined by high performance liquid chromatography. There were no significant differences in T_max of loratadine and desloratadine between treatment‐time different groups. However, the elimination half‐life (t1/2) of the parent compound and its metabolite was significantly longer (p<0.01) following administration at 9 HALO (t1/2 loratadine and desloratadine 5.62 and 4.08 h at 9 HALO vs. 4.29 and 2.6 h at 17 HALO vs. 3.26 and 3.27 at 1 HALO). There were relevant (p<0.05) differences in C_max between the three treated groups for loratadine and desloratadine; 133.05±3.55 and 258.07±14.45 ng/mL at 9 HALO vs. 104.5±2.61 and 188.62±7.20 ng/mL at 1 HALO vs. 94.33±20 and 187.75±10.79 ng/mL at 17 HALO. Drug dosing at 17 HALO resulted in highest loratadine and desloratadine total apparent clearance values: 61.46 and 15.97 L/h/kg, respectively, whereas loratadine and desloratadine clearances (CL) were significantly slower (p<0.05) at the other administration times (loratadine and desloratadine CL was 57.3 and 14.22 L/h/kg at 1 HALO vs. 43.79 and 12.89 L/h/kg at 9 HALO, respectively). The area under the concentration‐time curve (AUC) of loratadine and desloratadine was significantly (p<0.05) greater following drug administration at 9 HALO (456.75 and 1550.57 (ng/mL) · h, respectively); it was lowest following treatment at 17 HALO (325.39 and 1252.53 (ng/mL) · h, respectively). These pharmacokinetic data indicate that the administration time of loratadine significantly affected its pharmacokinetics: the elimination of loratadine and its major metabolite desloratadine.     

Sleep and Sleepiness among Working and Non‐Working High School Evening Students

The aim of this study was to evaluate patterns of sleepiness, comparing working and non‐working students. The study was conducted on high school students attending evening classes (19:00–22:30 h) at a public school in São Paulo, Brazil. The study group consisted of working (n=51) and non‐working (n=41) students, aged 14–21 yrs. The students answered a questionnaire about working and living conditions and reported health symptoms and diseases. For seven consecutive days, actigraphy measurements were recorded, and the students also filled in a sleep diary. Sleepiness ratings were given six times per day, including upon waking and at bedtime, using the Karolinska Sleepiness Scale. Statistical analyses included three‐way ANOVA and t‐test. The mean sleep duration during weekdays was shorter among workers (7.2 h) than non‐workers (8.8 h) (t=4.34; p<.01). The mean duration of night awakenings was longer among workers on Tuesdays and Wednesdays (28.2 min) and shorter on Mondays (24.2 min) (t=2.57; p=.03). Among workers, mean napping duration was longer on Mondays and Tuesdays (89.9 min) (t=2.27; p=.03) but shorter on Fridays and Sundays (31.4 min) (t=3.13; p=.03). Sleep efficiency was lower on Fridays among non‐workers. Working students were moderately sleepier than non‐workers during the week and also during class on specific days: Mondays (13:00–15:00 h), Wednesdays (19:00–22:00 h), and Fridays (22:00–00:59 h). The study found that daytime sleepiness of workers is moderately higher in the evening. This might be due to a work effect, reducing the available time for sleep and shortening the sleep duration. Sleepiness and shorter sleep duration can have a negative impact on the quality of life and school development of high school students.     

Dosing Time‐Dependent Effect of Raloxifene on Plasma Fibrinogen Concentration in Ovariectomized Rats

The chronopharmacological effect of raloxifene, a selective estrogen‐receptor modulator, was evaluated by repeated dosing of ovariectomized rats. Bilateral ovariectomy or sham operation was performed at age 12 wks, and animals were kept in rooms with a 12 h light‐12 h dark cycle. Raloxifene (3 mg/kg, once daily for 10 wks) or vehicle was given repeatedly at either 2 h after lights‐on (2 HALO) or 14 h after lights‐on (14 HALO). Plasma fibrinogen concentration at the end of the study was reduced by the drug, and the reduction was significantly prominent in rats in whom the drug was dosed at 2 HALO rather than 14 HALO. Femur bone density decreased, and urinary excretion of deoxypyridinoline, an index of bone resorption capacity of osteoclasts, increased in ovariectomized animals at the end of the study. Treatment with raloxifene ameliorated these changes in a dosing time‐independent manner. Serum calcium, ALT, and total protein concentrations at the end of the study also did not differ acccording to treatment regime, which indicates that protein synthesis and liver function may not contribute to the effects. This is the first study to determine dosing time‐dependent changes in the efficacy of raloxifene in an animal model of osteoporosis. Because fibrinogen concentration is reported to be a marker of cardiovascular events, consideration of dosing time of raloxifene may be important to obtain a better cardioprotective effect of this medication when it is prescribed to postmenopausal women with osteoporosis.     

Erratum to: Changes in the Power Characteristics of the α-Rhythm in Students with Different Levels of Anxiety in Normal Sleep and Partial Deprivation Solving the Go/NoGo Problem

Human Physiology - An Erratum to this paper has been published: https://doi.org/10.1134/S0362119722440013     

Protein Aggregation in E. coli?: Short Term and Long Term Effects of Nutrient Density

During exponential growth some cells of E. coli undergo senescence mediated by asymmetric segregation of damaged components, particularly protein aggregates. We showed previously that functional cell division asymmetry in E. coli was responsive to the nutritional environment. Short term exposure as well as long term selection in low calorie environments led to greater cell division symmetry and decreased frequency of senescent cells as compared to high calorie environments. We show here that long term selection in low nutrient environment decreased protein aggregation as revealed by fluorescence microscopy and proportion of insoluble proteins. Across selection lines protein aggregation was correlated significantly positively with the RNA content, presumably indicating metabolic rate. This suggests that the effects of caloric restriction on cell division symmetry and aging in E. coli may work via altered protein handling mechanisms. The demonstrable effects of long term selection on protein aggregation suggest that protein aggregation is an evolvable phenomenon rather than being a passive inevitable process. The aggregated proteins progressively disappeared on facing starvation indicating degradation and recycling demonstrating that protein aggregation is a reversible process in E. coli.     

Effect of metalaxyl,fosetyl‐al,dimethomorph, cymoxanil on development and control Phytophthora on peach tree in vitro

Four fungicides were evaluated for their effectiveness against Phytophthora diseases of peach trees and their ability to absorbed and translocated by roots of peach tree in laboratory. Meta‐laxyl suppressed the development of P. cactorum and P. citwphthora on segments. Fosetyl‐Al showed variable fungicidal activity against P. cactorum and P. citwphthora. Both dimetho‐morph and cyraoxanil were not effective to inhibit the growth of fungi on segments. Section of tree trunks in 2‐yr‐old GF 677 trees were painted with one of the test fungicides. Strips of bark were removed 10 and 20 days after painting within treated area and inoculated with P. cactorum and P. citwphthora. Generally, the results agree with them obtained with excised stem and excised twig methods. Exception is the dimethomorph that reduced the development of P. cartorum and P. citrophthora. This study indicated that application with metalaxyl to the peach tree appears to be an effective procedure to control Phytophthora diseases on peach trees.     

Short Term Effects of Tucuruí Dam (Amazonia, Brazil) on the Trophic Organization of Fish Communities

A dam on a river course induces numerous changes in the aquatic environment both in the newly formed reservoir and in the river downstream. These changes modify the food resources available to fishes. As a consequence, fish communities undergo rapid transformations particularly in terms of trophic organization. Tucuruí Dam, closed on the Tocantins River, Brazil, in September 1984, formed a large reservoir of approximately 2200km². Analyses of fish stomach contents were performed before and after the completion of the dam in the downstream section of the river as well as in the reservoir. Resource availability was seen through the relative contribution of food items in supporting the biomass. Main changes caused by the dam consisted of an increase in fishes as a food resource and of a parallel decrease of sediment both in the reservoir and in the downstream part of the river. In addition, in the downstream section, the relative contribution of plankton as a food resource diminished after dam closure. We identified 8 feeding regimes before dam closure. From them the trophic structure of fish communities were established and compared. Most of the community biomass was from specialist feeders. Contribution of piscivores increased after closure; planktivores became unimportant after closure downstream. Some species were shown to change their diet in the transformed environments either downstream or in the reservoir. However, these changes in individual species diet did not seem to play a major role in the transformation of trophic structure of the fish communities.     

Myocardial Infarct Size and Mortality Depend on the Time of Day—A Large Multicenter Study

Background

Different studies have shown circadian variation of ischemic burden among patients with ST-Elevation Myocardial Infarction (STEMI), but with controversial results. The aim of this study was to analyze circadian variation of myocardial infarction size and in-hospital mortality in a large multicenter registry.

Methods

This retrospective, registry-based study was based on data from AMIS Plus, a large multicenter Swiss registry of patients who suffered myocardial infarction between 1999 and 2013. Peak creatine kinase (CK) was used as a proxy measure for myocardial infarction size. Associations between peak CK, in-hospital mortality, and the time of day at symptom onset were modelled using polynomial-harmonic regression methods.

Results

6,223 STEMI patients were admitted to 82 acute-care hospitals in Switzerland and treated with primary angioplasty within six hours of symptom onset. Only the 24-hour harmonic was significantly associated with peak CK (p = 0.0001). The maximum average peak CK value (2,315 U/L) was for patients with symptom onset at 23:00, whereas the minimum average (2,017 U/L) was for onset at 11:00. The amplitude of variation was 298 U/L. In addition, no correlation was observed between ischemic time and circadian peak CK variation. Of the 6,223 patients, 223 (3.58%) died during index hospitalization. Remarkably, only the 24-hour harmonic was significantly associated with in-hospital mortality. The risk of death from STEMI was highest for patients with symptom onset at 00:00 and lowest for those with onset at 12:00.

Discussion

As a part of this first large study of STEMI patients treated with primary angioplasty in Swiss hospitals, investigations confirmed a circadian pattern to both peak CK and in-hospital mortality which were independent of total ischemic time. Accordingly, this study proposes that symptom onset time be incorporated as a prognosis factor in patients with myocardial infarction.