Time Of Day Variations Research Articles

Time of day does not impact spinal serotonin levels in humans.

Spinal serotonin enables neuro-motor recovery (i.e., plasticity) in patients with debilitating paralysis. While there exists time of day fluctuations in serotonin-dependent spinal plasticity, it is unknown, in humans, whether this is due to dynamic changes in spinal serotonin levels or downstream signaling processes. The primary objective of this study was to determine if time of day variations in spinal serotonin levels exists in humans. To assess this, intrathecal drains were placed in seven adults with cerebrospinal fluid (CSF) collected at diurnal (05:00 to 07:00) and nocturnal (17:00 to 19:00) intervals. High performance liquid chromatography with mass spectrometry was used to quantify CSF serotonin levels with comparisons being made using univariate analysis. From the 7 adult patients, 21 distinct CSF samples were collected: 9 during the diurnal interval and 12 during nocturnal. Diurnal CSF samples demonstrated an average serotonin level of 216.6 67.7nM. Nocturnal CSF samples demonstrated an average serotonin level of 206.7 75.8nM. There was no significant difference between diurnal and nocturnal CSF serotonin levels (p =.762). Within this small cohort of spine healthy adults, there were no differences in diurnal versus nocturnal spinal serotonin levels. These observations exclude spinal serotonin levels as the etiology for time of day fluctuations in serotonin-dependent spinal plasticity expression.

Ambulance location under temporal variation in demand using a mixed coded memetic algorithm

Emergency medical services (EMS) are among the most important services in any society due to their role in saving people’s lives and reducing morbidities. The location of ambulance stations and the allocation of ambulances to the stations is an important planning problem for any EMS system to ensure adequate coverage while minimising the response time. This study considers a mixed-integer programming model that determines the ambulance locations by considering the time of day variations in demand. The presented model also considers heterogeneous performance measures based on survival function and coverage for different patient types with varying levels of urgency. A memetic algorithm based-approach that applies a mixed chromosome representation for solutions is proposed to solve the problem. Our computational results indicate that neglecting time-dependent variation of demand can underestimate the number of ambulances required by up to 15% during peak demand. We also demonstrate the effectiveness of the proposed solution approach in providing good quality solutions within a reasonable time.

Assessment of commercial truck driver injury severity based on truck configuration along a mountainous roadway using hierarchical Bayesian random intercept approach

For the last decade, disaggregate modeling approach has been frequently practiced to analyze truck-involved crash injury severity. This included truck-involved crashes based on single and multi-vehicles, rural and urban locations, time of day variations, roadway classification, lighting, and weather conditions. However, analyzing commercial truck driver injury severity based on truck configuration is still missing. This paper aims to fill this knowledge gap by undertaking an extensive assessment of truck driver injury severity in truck-involved crashes based on various truck configurations (i.e. single-unit truck with two or more axles, single-unit truck pulling a trailer, semi-trailer/tractor, and double trailer/tractor) using ten years (2007–2016) of Wyoming crash data through hierarchical Bayesian random intercept approach. The log-likelihood ratio tests were conducted to justify that separate models by various truck configurations are warranted. The results obtained from the individual models demonstrate considerable differences among the four truck configuration models. The age, gender, and residency of the truck driver, multi-vehicles involvement, license restriction, runoff road, work zones, presence of junctions, and median type were found to have significantly different impacts on the driver injury severity. These differences in both the combination and the magnitude of the impact of variables justified the importance of examining truck driver injury severity for different truck configuration types. With the incorporation of the random intercept in the modeling procedure, the analysis found a strong presence (24%–42%) of intra-crash correlation (effects of the common crash-specific unobserved factors) in driver injury severity within the same crash. Finally, based on the findings of this study, several potential countermeasures are suggested.

Investigating occupant injury severity of truck-involved crashes based on vehicle types on a mountainous freeway: A hierarchical Bayesian random intercept approach

Earlier research on injury severity of truck-involved crashes focused primarily on single-truck and multi-vehicle crashes with truck involvement, or investigated truck-involved injury severity based on rural and urban locations, time of day variations, lighting conditions, roadway classification, and weather conditions. However, the impact of different vehicle-truck collisions on corresponding occupant injury severity is lacking. Therefore, this paper advances the current research by undertaking an extensive assessment of the occupant injury severity in truck-involved crashes based on vehicle types (i.e., single-truck, truck-car, truck-SUV/pickup, and truck-truck), and identifies the major occupant-, crash-, and geometric-related contributing factors. A series of log-likelihood ratio tests were conducted to justify that separate model by vehicle and occupant types are warranted. Injury severity models were developed using 10 years of crash data (2007–2016) on I-80 in Wyoming through binary logistic modeling with a Bayesian inference approach. The modeling results indicated that there were significant differences between the influences of a variety of variables on the injury severities when the truck-involved crashes are broken down by vehicle types and separated by occupant types. The age and gender of occupants, truck driver occupation, driver residency, sideswipes, presence of junctions, downgrades, curves, and weather conditions were found to have significantly different impacts on the occupant injury severity in different vehicle-truck crashes. Finally, with the incorporation of the random intercept in the modeling procedure, the presence of intra-crash and intra-vehicle correlations (effects of the common crash- and vehicle-specific unobserved factors) in injury severities were identified among persons within the same crash and same vehicle.

Interstate Speed Profiles

This paper draws the first set of high-level, national speed profiles for the entire Dwight D. Eisenhower National System of Interstate and Defense Highways (Interstate system) in the United States based on the 2016 year-long National Performance Management Research Data Set (NPMRDS) and a conflated NPMRDS-HPMS (Highway Performance Monitoring System) geospatial network. This set of quantitative profiles include: ( a) national average speeds of 2016, ( b) national average speed time of day variations, ( c) national average speed day of week variations, ( d) national average speed seasonal variations, and ( e) state average speed and travel time distributions in peak hours. This work demonstrates that the integration of the private sector’s emerging big travel-time data and the public sector’s HPMS has provided a powerful resource to monitor travel-time-related performance of the nation’s highways. As the United States is transforming the Federal-aid Highway Program into a performance-based program with enhanced accountability and transparency, this integrated resource will help states and metropolitan planning organizations (MPOs) to monitor their performance and progress towards achieving targets, and enable the Federal Highway Administration (FHWA) not only to draw high-level national highway performance profiles but also to pinpoint the exact where, when, and how much the challenges are.

Different types of errors in saccadic task are sensitive to either time of day or chronic sleep restriction.

Circadian rhythms and restricted sleep length affect cognitive functions and, consequently, the performance of day to day activities. To date, no more than a few studies have explored the consequences of these factors on oculomotor behaviour. We have implemented a spatial cuing paradigm in an eye tracking experiment conducted four times of the day after one week of rested wakefulness and after one week of chronic partial sleep restriction. Our aim was to verify whether these conditions affect the number of a variety of saccadic task errors. Interestingly, we found that failures in response selection, i.e. premature responses and direction errors, were prone to time of day variations, whereas failures in response execution, i.e. omissions and commissions, were considerably affected by sleep deprivation. The former can be linked to the cue facilitation mechanism, while the latter to wake state instability and the diminished ability of top-down inhibition. Together, these results may be interpreted in terms of distinctive sensitivity of orienting and alerting systems to fatigue. Saccadic eye movements proved to be a novel and effective measure with which to study the susceptibility of attentional systems to time factors, thus, this approach is recommended for future research.

Time of day variations in door to balloon time for STEMI patients in Los Angeles County: does time of day make a difference?

Time of day variations in door to balloon time for STEMI patients in Los Angeles County: does time of day make a difference?

Warm-Up Affects Diurnal Variation in Power Output

The purpose of this study was to examine whether time of day variations in power output can be accounted for by the diurnal fluctuations existent in body temperature. 8 recreationally trained males (29.8±5.2 yrs; 178.3±5.2 cm; 80.3±6.5 kg) were assessed on 4 occasions following a: (a) control warm-up at 8.00 am; (b) control warm-up at 4.00 pm; (c) extended warm-up at 8.00 am; and, (d) extended warm-up at 4.00 pm. The control warm-up consisted of dynamic exercises and practice jumps. The extended warm-up incorporated a 20 min general warm-up on a stationary bike prior to completion of the control warm-up, resulting in a whole body temperature increase of 0.3±0.2°C. Kinetic and kinematic variables were measured using a linear optical encoder attached to a barbell during 6 loaded counter-movement jumps. Results were 2-6% higher in the afternoon control condition than morning control condition. No substantial performance differences were observed between the extended morning condition and afternoon control condition where body temperatures were similar. Results indicate that diurnal variation in whole body temperature may explain diurnal performance differences in explosive power output and associated variables. It is suggested that warm-up protocols designed to increase body temperature are beneficial in reducing diurnal differences in jump performance.

Worldwide assessments of laser radar tactical scenario performance variability for diverse low altitude atmospheric conditions at 1.0642 μm and 1.557 μm

Spatial, spectral and temporal variations in operating conditions are major contributors to the expected variability/uncertainty in system performance. The ratio of signal-to-noise ratio (SNR) based on climatological data to a standard atmosphere is the primary performance metric used, with results presented in the form of histograms and maps of worldwide LADAR performance variation. This metric is assessed at 2 wavelengths, 1.0642 µm and 1.557 µm, for a number of widely dispersed land and maritime locations worldwide over oblique and vertical air to surface paths in which anticipated clear air aerosols and location specific heavy rain and 150 m thick fog occur. Seasonal, boundary layer, and time of day variations for a range of relative humidity percentiles are also considered. In addition to realistic vertical profiles of molecular and aerosol extinction, air-to-ground cloud free line of sight (CFLOS) probabilities as a function of location for this geometry are computed. Observations from the current study strongly indicate that use of the standard atmosphere to predict performance will produce overly optimistic, in many cases extremely so, estimates of expected performance. Locally heavy rain, when present, severely limits LADAR system performance at these wavelengths. Some operational capability exists for vertical looks through fog.

Effect of aging on 24-hour pattern of stress hormones and leptin in rats

This work analyzes the 24-hour changes of hypothalamic–pituitary–adrenal (HPA) axis activity and leptin release in aged rats. Three- and 22-month-old male Wistar rats were killed at 6 time intervals during a 24-hour cycle ( n = 8–10 rats/group). Aging augmented plasma ACTH while it decreased plasma and adrenal gland corticosterone levels. Plasma and adrenal corticosterone levels attained high levels during all the scotophase, concomitantly with the maxima in ACTH levels, whereas in aged rats only a brief plasma corticosterone peak at the early scotophase and no time of day variations of adrenal corticosterone were observed. Aging augmented circulating leptin, with a significant interaction “age × time” in the factorial ANOVA, i.e. only in young rats time of day changes were significant, with the lowest values of leptin at the middle of the light period and higher values at night. When plasma leptin was expressed on body weight basis, the age-related differences became not significant but the daily pattern of plasma leptin found in young rats persisted. Plasma and adrenal corticosterone levels correlated significantly with plasma ACTH only in young rats. Likewise, plasma leptin correlated with plasma corticosterone only in young rats. These changes can be attributed to a disrupting effect of aging on the homeostatic mechanisms modulating HPA activity and leptin release.

Daily rhythm of cerebral blood flow velocity

BackgroundCBFV (cerebral blood flow velocity) is lower in the morning than in the afternoon and evening. Two hypotheses have been proposed to explain the time of day changes in CBFV: 1) CBFV changes are due to sleep-associated processes or 2) time of day changes in CBFV are due to an endogenous circadian rhythm independent of sleep. The aim of this study was to examine CBFV over 30 hours of sustained wakefulness to determine whether CBFV exhibits fluctuations associated with time of day.MethodsEleven subjects underwent a modified constant routine protocol. CBFV from the middle cerebral artery was monitored by chronic recording of Transcranial Doppler (TCD) ultrasonography. Other variables included core body temperature (CBT), end-tidal carbon dioxide (EtCO2), blood pressure, and heart rate. Salivary dim light melatonin onset (DLMO) served as a measure of endogenous circadian phase position.ResultsA non-linear multiple regression, cosine fit analysis revealed that both the CBT and CBFV rhythm fit a 24 hour rhythm (R2 = 0.62 and R2 = 0.68, respectively). Circadian phase position of CBT occurred at 6:05 am while CBFV occurred at 12:02 pm, revealing a six hour, or 90 degree difference between these two rhythms (t = 4.9, df = 10, p < 0.01). Once aligned, the rhythm of CBFV closely tracked the rhythm of CBT as demonstrated by the substantial correlation between these two measures (r = 0.77, p < 0.01).ConclusionIn conclusion, time of day variations in CBFV have an approximately 24 hour rhythm under constant conditions, suggesting regulation by a circadian oscillator. The 90 degree-phase angle difference between the CBT and CBFV rhythms may help explain previous findings of lower CBFV values in the morning. The phase difference occurs at a time period during which cognitive performance decrements have been observed and when both cardiovascular and cerebrovascular events occur more frequently. The mechanisms underlying this phase angle difference require further exploration.

Ingestive Pattern Changes in Blinded Rats

Eating and drinking patterns were examined in intact and blinded adult male Sprague-Dawley rats fed a choice among isocaloric casein, sucrose/dextrin, and vegetable shortening/soybean oil diets. Weekly mean intake of all nutrients was altered in blinded rats, with increased lipid intake and decreased water intake in rats blinded for 2 weeks, lower carbohydrate but higher protein and water intakes in rats blinded for 4 weeks, while 2 weeks later blinded rats maintained high intakes of protein and water. The amplitudes of the daily rhythms for each nutrient behaved similarly to the weekly intakes. Delayed daily time of peak intake for all nutrients over successive weeks after blindness were found, indicating that the timing of peak intake free-runs. 24 h profile indicated time of day variations of nutrient intake tending to be less marked over successive weeks of blindness. Free-running animals maintained the link between carbohydrate intake and hypothalamus serotonin.

Time-of-day effects in maximal anaerobic leg exercise.

Time of day variations in maximal anaerobic leg exercise were studied in 23 men mean age 23 (SD 3) years. All the subjects performed two anaerobic tests (force-velocity and multi-jump tests) and those familiar with sprinting ran an additional 50-m dash (n = 16). The maximal anaerobic powers for cycling and jumping (Pcycling and Pjump) and maximal anaerobic velocity (vpeak) were performed consecutively in the same order for all tests. The force-velocity and force-power relationships were established to determine Pcycling. The flight time (tf) and the ground contact time (tc) were recorded from five consecutive jumps on a jump-ergometer to calculate Pjump. The vpeak was measured between the 35th and the 45th m during the dash-run. The test schedules were at 0900, 1400 and 1800 hours on separate days in random order. Rectal temperatures (Tre) and body mass (mb) were measured before each test. The Tre increased significantly from 0900 to 1800 hours (P < 0.001) but mb did not vary during the day (P > 0.05). The Pcycling and Pjump were higher at 1400 and 1800 hours than at 0900 hours. The differences between the morning and the afternoon reached 3% (P < 0.05) for Pcycling and 5%-7% for Pjump (P < 0.01). The time-of-day effect was significant for tf (P < 0.05) but not for tc. During the dash-run tests, the differences almost reached significance for vpeak between 0900 and 1800 hours (P = 0.0544). No significant variations were observed between 1400 and 1800 hours for cycling, jumping and running tests. A time-of-day effect in the maximal anaerobic power of cycle and multi-jump tests existed. Such variations would have pronounced effects when expressed in competitions.

Time of day variations in driving performance

Numerous factors may contribute to the 24-hour pattern of automobile accidents. One factor may be a time of day variation in driving ability. In the present study, 11 male subjects operated a driving simulator for 30 minutes at six times of day. Subjects were instructed to maintain a stable position in the left-hand lane and to drive at a constant speed of 80 km/hour. In addition subjects performed a secondary reaction time task. Subjective mood was measured at the beginning and end of each session. Driving performance was measured in terms of the mean and standard deviation of lateral position and speed. The mean and standard deviation of speed varied significantly across the day for both curved and straight segments. Reaction time was also affected by time of day. Performance was more impaired at 0600 and 0200 hours, with improvements in driving performance between 1000 and 2200 hours and an early afternoon dip. These results suggest that driving performance is subject to diurnal variations. Of particular importance is the result that impairments in driving performance in the early afternoon are of a similar magnitude to those occurring in the late evening and early morning.

Diurnal responses of mammals to acute exposure to a hyperdynamic environment

Acute exposure to hyperdynamic environments elicits significant depressions in core temperature in both diurnal squirrel monkeys and nocturnal rats. This study describes time of day variations in core temperature responses in squirrel monkeys and rats exposed for 70 min to a hyperdynamic environment (2 g) produced via centrifugation. Experiments were performed during the middle of the light or dark phase. After a 70-min control period, squirrel monkey resting core temperature was 38.6 +/- 0.2 (SE) and 36.8 +/- 0.2 degrees C during the day and night, respectively. At the end of a 7-min exposure to 2 g, squirrel monkey core temperature decreased 1.3 +/- 0.2 degree C during the day but remained a constant 36.8 +/- 0.4 degrees C at night. Core temperature of rats exposed to an identical 70-min 2 g profile decreased 1.5 +/- 0.4 degree C from a resting 37.1 +/- 0.6 degrees C during the day and 2.3 +/- 0.2 degrees C from a resting 37.8 +/- 0.3 degrees C at night. Thus, in both species, there were clear day-night differences in response to hyperdynamic environments, with the greatest fall in core temperature occurring during the animal's active period.

Time of Day Variations in Steady-State Accommodation to Square-Wave Gratings

Time of day variations were studied both in the dark focus of accommodation and in steady-state accommodation. All subjects (n = 16) were measured in the morning and again 12 hr later. The mean nighttime dark focus was 0.5 diopters (D) greater than the morning value. Overaccommodation to far targets (0 D) and underaccommodation to near targets (3-20 D) occurred for both 4.2 and 8.4 cycle/deg square-wave gratings. A shift in steady-state accommodation was found with the nighttime values being somewhat greater (0.25 D) than the morning values.