Wrist Temperature Research Articles

Influence of shift-work schedule on circadian disruption in nursing staff

Many shift work schedules (SWS) have been proposed to promote performance and to reduce circadian impairment, however, few studies have been devoted to demonstrate the benefits of such shifts under real work conditions. The aim of this study was to characterize the impact of different SWS, on circadian disruption assessed by ambulatory circadian monitoring (ACM), in nursing staff. To this, wrist temperature (T), motor activity (A), body position (P), light exposure (L) and environmental temperature (ET) were recorded. Two hundred eighty-six healthy nursing staff (45 males and 241 females) enrolled in eight different SWS (Permanent 8 h-day, PD; Permanent night, PN; morning with nights, MN; evening with nights, EN; permanent 12 h-day, 12D; anti-stress, AS and rotating three-shifts, R3), from 22 to 62 years old, participated in this study. Volunteers were monitored by ACM during 7–10 days using a multichannel device (KronowiseTM, Chronolab, Univ. of Murcia). Circadian robustness was assessed by the circadian function index (CFI) of composite TAP variable. The regularity of life style was measured by calculating Interdaily stability (IS). Restfulness (RS), a measure of sleep quality, was calculated from L5 of TAP and expressed as a score from 0 to 10 (10 = very restfully sleep). As phase marker was selected the midpoint of TL5 from TAP (the midpoint of five consecutive hours of minimum values). The circadian status evaluation on nurses staff by ACM showed that those subject engaged in both PD and 12D shifts presents higher stability (IS) and RS scores than those subjects on PN, MN, EN and R3 schedules. However, the more disruptive shift seems to be PN, since nurses under this schedule show the lowest stability, CFI and RS values, besides presenting the most delayed TL5. The remaining shifts present an intermediate situation between PD and PN. As expected, the two permanent day shifts (PD and 12D) are the less chonodisruptive, since nurses under this schedule present more robust and regular rhythms with deeper sleep during the night. On the contrary a PN shift produces higher rhythm instability and more superficial sleep. So according to our results when working during the night is a must rotating shifts (AS, R3) seems to be more recommendable than MN or EN. To RETICEF (RD12/0043/0011), MINECO (BFU2010–21945-C02–01), and INNPACTO (IPT-2011–0833-900000) with FEDER cofounding to JAM.

Ambulatory circadian monitoring (ACM), a complementary tool in sleep medicine

In developed societies it is common to suffer from sleep disorders due to primary alterations in the circadian system (CS). Moreover, sleep disorders lead to CS disturbances, thus diagnosis and treatment of circadian and sleep disorders should not be addressed separately. The aim of this work is to present the ambulatory circadian monitoring (ACM) and its utility for sleep medicine. To this, wrist temperature (T), motor activity (A), body position (P), light exposure (L) and environmental temperature (ET) were monitored in subjects suffering from different sleep pathologies. Eight healty volunteers and eight patients, attending to two sleep clinics3,4, with different pathologies (SHAOS, ASP, DSP, free-running rhythm, short sleeper, aging and menopause), participated in this study. Volunteers were subjected to ACM during a week using a multichannel device (KronowiseTM, Chronolab, Univ. of Murcia) integrating five sensors: three built into a wristwatch (T, L, ET) and two on a bracelet (A and P). Sleep-wake states were inferred using the integrated variable TAP and Circadianware software (Chronolab, Univ. Murcia). Rhythmic and sleep analysis were performed by non- parametric, Fourier and periodogram analysis. Circadian robustness was assessed by the circadian function index (CFI) calculated from rhythm stability, fragmentation and amplitude of TAP variable. Polygraphic representation of variables recorded by ACM allowed the differentiation of sleep pathologies. Accurate circadian phase estimation, and thus, ASP and DSP detection, was determined using the L5 timing (the five consecutive hours of minimum TAP). SHAOS was associated with impaired T rhythm, together with increased A during the five consecutive hours of minimum activity (L5). Sleep pathologies can be discriminated by biphasic representation of CFI and one index of sleep depth, (L5 for A or TAP). Patient with SHAOS, DSP and free-running sleep, suffered from chronodisruption (dissociation between T and A, P and sleep rhythms). The ACM allows a reliable assessment of CS status and the detection of sleep pathologies, particularly abnormal sleep phase and non-deep and fragmented sleep, such occurs in SAHOS, insomnia, and hot flushes. The proposed procedure contributes to an integrated diagnosis and treatment for sleep and circadian disorders in sleep clinics. Study supported by RETICEF (RD12/0043/0011), MINECO (BFU2010-21945-C02-01), TIN2009-14372-C03–01 to MC and INNPACTO (IPT-2011-0833-900000) to JAM.

Assessing the delayed sleep phase disorder by ambulatory circadian monitoring

The circadian system is responsible for the generation of biological rhythms synchronized to environmental 24 h cycle. The delayed sleep phase disorder (DSPD) refers to a delay between the sleep-wake rhythm and the desired bed and rise times and patients suffer chronic difficulty to fall asleep, rising and impaired performance during day. The aim of this work is to test an innovative ambulatory circadian monitoring (ACM) system based on wrist temperature (T), motor activity (A), body position (P), light exposure (L) and environmental temperature (ET) rhythms, to evaluate patients affected by this syndrome. Fourteen patients between 10 and 86 yr old from the Sleep Unit of the Virgen de las Nieves Hospital and the Estivill Sleep Clinic, and 14 healthy volunteers (from 10 to 80 yr old) were included in the study. Their T, A, P, L and ET rhythms were registered by the ACM device Kronowise® (Cronolab, University of Murcia, Spain) during a week. Sleep-wake states were infered using the integrated variable TAP using Circadianware® software (Chronolab, Univ. Murcia). Reliable circadian phase markers can be calculated from all variables, being the timing of five consecutive hours of maximum values for T and sleep (TM5) and of five consecutive hours of minimum values for A, P, TAP and L (TL5), the most accurate ones. Most DSPD subjects showed a similar phase-delay with respect control subjects in the TM5 or TL5 in all ACM variables (02:30–04:30 h for control subjects vs. 06:00 to 09:40 h for DSPD). However, a 21% of DSPD patients exhibited internal desynchronization between T and A, P or sleep phases. DSPD subjects showed higher fragmentation, lower regularity in all variables, together with lower light exposures than the standard scores specially during the morning. Our results showed that ACM provides objective markers to detect DSPD and chronodisruption. Besides differences in circadian phase, DSPS subjects showed more irregular, fragmented and less robust rhythms, worse sleep quality and less diurnal activation than controls, probably caused to the duty of sleep within a social schedule that differs from their endogenous biological propensity. Insufficient light exposure during early morning contribute to maintain their circadian phase delay. Study supported by RETICEF (RD12/0043/0011), MINECO (BFU2010–21945-C02–01), TIN2009–14372-C03–01 to MC and INNPACTO (IPT-2011–0833-900000) to JAM.

The glycemic index of a mid morning snack modifies the body temperature rhythm

The structure of a circadian rhythm depends on the activity of the suprachiasmatic clock, on the presence of zeigebers, and on the presence of masking factors. Regarding body temperature, a clear circadian rhythm is well recognized, with maximal values approaching dusk and minimal in the small hours, near dawn. However, masking factors can enhance or reduce the amplitude of the circadian rhythms. Food eating is a masking factor on the body temperature rhythm, probably related to the Thermal Effect of Food (TEF), a measure of the energy spent for the digestion, absorption, and disposal of a given amount and type of food. Also, the Glycemic Index (GI) shows how quickly blood glucose rises after eating a given amount and type of food. As high GI foods require lower digestive processing, their TEF should be lower than that of lower GI. The present study aims at recording the consequences of modifying the GI of a mid morning snack on the whole 24 h body temperature cycle in young human subjects. The study was conducted on 15 university students (8 female, 7 male, 19–25 years old). Each subject was provided with an activity meter and a wrist temperature holder during two non consecutive periods of 5 days. During the experimental days, each subject ingested between 10.30–11.30 AM one of two snacks of precise composition with low and high GI. Each participant was blind to the GI of the snack ingested. Significant differences were found between the averaged peripheral temperature of the subjects during light and dark periods. Also, the 2nd harmonic component (12 h) was modified. From the well known phase opposition between central and peripheral temperature, the results point to changes in the central temperature cycle. Arguably, TEF dependent changes in the peripheral dissipation could occur without real changes in the core temperature. However, the TEF consequences does not extend beyond 6 h after ingestion, while the recorded changes in peripheral temperature showed long term effects, being extended up to the whole 24 h cycle. Therefore, the body temperature seems to have been modified as a consequence of the nutritional properties of a small mid morning snack. The body temperature cycle shows a high sensitivity to the GI of a minor meal.

Circadian rhythm of wrist temperature and night shift-work

Due to the increasing industrialization of society, the work in shifts is becoming increasingly common, as well as the development of night work, although with a pronounced negative effect on the workers sleep, performance and health. Objective: to investigate the patterns of sleep-wake cycle and the circadian rhythmicity of peripheral body temperature, through measures taken at the wrist of nursing students who study during the day and work on the night shift. longitudinal descriptive study, with a quantitative approach, involving 27 adult subjects, nursing assistants and technicians who worked on the night shift and were students of undergraduate nursing at a private college in São Paulo State, during the daytime. The following instruments were used: Identification Form, Morningness Eveningness Questionnaire of Horne and Östberg, Sleep Diary, for 32 days, divided into school term and school vacations, and a thermistor (Thermochron iButton) on the non-dominant hand wrist to check the temperature of the wrist every 30 min. The adjustment of the temperature data of the wrist to a cosine curve, within a 24-h period, a significant rhythmicity was verified in 35.3% of subjects in the school term and 93.7% of subjects in the vacation period, apart from the existence of different rhythms of the 24 h such as 12 h and 16 h. There was a statistically significant difference in the time that the acrophase occurred, when comparing the school term on the days-off and on working days ( p < 0.0001), school vacation on the days-off and working days ( p < 0.0001). The sleep time during the school vacation was higher when compared to the school term, as well as on the days off and on the days when the subjects did not sleep immediately after work. There was a significant difference when comparing the sleep time on the vacation period and days off (8:34) and school term and days off (7:24), p < 0.0001, and also on vacation on working days (5:11) and school term on working days (4:19), p = 0.0496. For the Middle Phase of Sleep (MPS) there was a statistically significant difference between the school and vacation periods on working days and days off. The presence of rhythms different than 24 h, was observed especially during the school term, and the phase transfer of the wrist temperature, according to the period of work/study, with phase opposition on working days when compared to days off. The greatest spectral power was observed in the 24-h rhythm, either during school term or vacation, confirming the hypothesis that the region of the wrist shows a well-defined and robust rhythmic expression. The findings reinforce the idea that the study favors the establishment of routine, but has little influence in displacing the body temperature, which proved to be strongly influenced by the night shift work. Similar to the acrophase, the MPS showed great diversity in times of occurrence, but with a phase relation maintained between the rhythms on the different times of study. CAPES.

Circadian rhythmicity as a predictor of weight-loss effectiveness

Some of the major challenges associated with successful dietary weight management include the identification of individuals not responsive to specific interventions. The aim was to investigate the potential relationship between weight loss and circadian rhythmicity, using wrist temperature and actimetry measurements, in women undergoing a weight-loss program, in order to assess whether circadian rhythmicity could be a marker of weight-loss effectiveness. Participants were 85 overweight and obese women (body mass index, BMI: 30.24±4.95 kg m(-2)) subjected to a weight-reduction program. Efficacy of the treatment was defined as total weight loss, percentage of initial weight and weekly weight loss rates. Circadian rhythmicity in wrist temperature motor activity and position were analyzed using different sensors. Lower weight loss was related with a more flattened pattern measured as amplitude from cosinor (r=0.235, P=0.032), a higher fragmentation of rhythms determined by higher intradaily variability (IV) (r=-0.339, P=0.002), and an impaired wrist temperature circadian rhythm determined by the means of Circadian Function Index (r=0.228, P=0.038). Further analyses showed that low responders displayed lower amplitude (0.71±0.36 versus 1.24±0.62, P=0.036) and higher fragmentation of the circadian rhythm (0.24±0.11 versus 0.15±0.07, P=0.043) than high responders. Whereas we did not find significant differences in total activity rates between high responders and low responders, we found significant differences for the mean values of body position for high responders (39.12±3.79°) as compared with low responder women (35.31±2.53°, P=0.01). Circadian rhythms at the beginning of the treatment are good predictors of future weight loss. Further treatment should consider chronobiological aspects to diagnose obesity and effectiveness of treatments.

Evening physical activity alters wrist temperature circadian rhythmicity

The adequate time to perform physical activity (PA) to maintain optimal circadian system health has not been defined. We studied the influence of morning and evening PA on circadian rhythmicity in 16 women with wrist temperature (WT). Participants performed controlled PA (45 min continuous-running) during 7 days in the morning (MPA) and evening (EPA) and results were compared with a no-exercise-week (C). EPA was characterized by a lower amplitude (evening: 0.028 ± 0.01 °C versus control: 0.038 ± 0.016 °C; p < 0.05) less pronounced second-harmonic (power) (evening: 0.41 ± 0.47 versus morning: 1.04 ± 0.59); and achrophase delay (evening: 06:35 ± 02:14 h versus morning: 04:51 ± 01:11 h; p < 0.05) as compared to MPA and C. Performing PA in the late evening might not be as beneficial as in the morning.

Circadian rhythm of wrist temperature and night shift-work

The stability of the circadian rhythms, especially regarding their amplitude and phase relationship, is a major factor for health. Shift-work and working night shifts are known to be associated with a variety of health problems caused, at least partially, by the disturbance of biological rhythms. Seventeen undergraduate nursing students attending the morning program at Nursing School, and working night shifts as Nursing Technicians, were submitted to the morningness–eveningness questionnaire, sleep logs, and wrist temperature assessment, during two periods of 2 weeks (school term and vacation). The observed prominent ultradian periods and reduced amplitude of the daily rhythm of wrist temperature, in addition to the reduced sleep duration during the school term, reinforce the idea that the mixed routine contributes to the disruption of the expression of the circadian rhythms and may have detrimental effects on safety and performance at work.

Sleepiness in Spanish nursing staff – influence of chronotype and care unit in circadian rhythm impairment: research protocol

To determine how prevalent circadian rhythm impairments are in nurses working in medical, surgical and intensive care units in five Spanish hospitals and how the quality of night-time sleeping and sleepiness affect the nurses' morning and evening chronotypes. Shift work is a recognized work pattern for nurses in all countries. Given the important role that nurses play in hospital care, it is vital to establish what repercussions this has on the nurses' working schedules and how any disturbance in circadian rhythm affects patient safety. A multicentre, observational, descriptive and cross-sectional study in seven hospitals in the Spanish National Health System. A stratified sample of 1,300 nurses is being collected in three types of units: medical, surgical and intensive care. The 3-year study started in January 2012 and will continue until December 2014, with no exclusion criteria. The Kronowise(®) will be used to monitor the nurses' circadian rhythms, by recording their activity, position and wrist temperature. We will also use three questionnaires to evaluate sleep quality, daytime drowsiness and chronotype: (a) Pittsburg Sleep Quality Index; (b) Epworth Daytime Sleepiness Scale; and (c) Morning and Evening Questionnaire. Data will be collected from each hospital and statistical analysis will be carried out using the SPSS 19.0. The study findings will show the current state of the nurses' circadian rhythms and how shift work can affect them and their job performance. Funding for this 3-year study was granted in December 2011 by the Spanish Health Research Fund (PI 11/00646, Health Ministry). This project is also funded by the Instituto de Salud Carlos III (RETICEF, RD12/0043/0011, RD12/0043/0006).

Novo instrumento de aferição do ritmo de temperatura periférica em humanos: um estudo de caso

Recent studies have considered wrist temperature as a possible phase indicator in human circadian system. The present study shows results of a new device – ACT10 – which provides longterm data and continuously measures wrist temperature and rest/activity rhythm. An adult man wore the ACT10 and other thermal sensors positioned in the wrist (dorsal and ventral superficies), axillar and rectal regions to monitor his temperature during 48 h. Differences in wrist and rectal temperature acrophases’ can be explained by the thermoregulation process. The results obtained confirm the use of ACT10 as a reliable and less invasive alternative to access the status of the human circadian system

Differences in circadian rhythmicity in CLOCK 3111T/C genetic variants in moderate obese women as assessed by thermometry, actimetry and body position

Genetics is behind our circadian machinery. CLOCK (Circadian Locomotor Output Cycles Kaput) 3111T/C single-nucleotide polymorphism (SNP) has been previously related to obesity and weight loss. However, phenotypic association and functionality of CLOCK 3111 locus is still unknown. The aim of this study was to determine, in free-living conditions, if the presence of CLOCK 3111C in overweight women could be related to (a) circadian disorders, and (b) changes in sleep quality, to improve understanding of the previously demonstrated associations with obesity and reduced weight loss of the C carriers. Wrist temperature, actimetry and position (TAP) and TAP variables were measured as markers of circadian functionality during 8 consecutive days. A rest-activity and food diary was also completed, whereas sleep quality was determined by domiciliary polysomnography. We recruited 85 women who were overweight with body mass index (BMI) of 28.59±4.30 kg m(-2) and age 43±12 years. From this sample, we found that 43 women were carrying the minor allele (C) for CLOCK 3111T/C SNP and 42 women were TT carriers (major allele carriers). Both groups of patients were matched for number, age, obesity parameters and energy intake. Compared with TT subjects, who showed more robust circadian rhythm profiles, patients with the C allele displayed significant circadian abnormalities: lower amplitude and greater fragmentation of the rhythm, a less stable circadian pattern and a significantly weakened circadian function, as assessed by the circadian function index (CFI). C subjects were also less active, started their activities later in the morning and were sleepier during the day, showing a delayed acrophase that characterizes 'evening-type' subjects. C genetic variants in CLOCK 3111T/C display a less robust circadian rhythm than TT and a delayed acrophase that characterizes 'evening-type' subjects. We support the notion that identifying CLOCK genotypes in patients may assist the therapist in characterization of the roots of the metabolic problem.

Wrist Skin Temperature, Motor Activity, and Body Position as Determinants of the Circadian Pattern of Blood Pressure

Although the circadian blood pressure (BP) pattern has been extensively studied, the determinants of this rhythm are not fully understood. Peripheral vasodilatation is a regulatory mechanism for BP maintenance. However, it remains to be established whether the increase of nocturnal distal skin temperature associated with heat loss could also reflect the dipping status. For the first time, this paper investigates the relationship between BP and skin wrist temperature (WT), to evaluate whether the WT circadian rhythm can serve as screening procedure to detect dipping/non-dipping BP patterns. In addition, the authors compare the relationship between WT and other variables previously described as determinants of the BP pattern, such as physical activity and body position. Measurements of WT, motor activity, and body position for 5 d, plus ambulatory BP for 24-h during that span, were obtained from 28 diurnally active normotensive volunteers. WT was negatively correlated, whereas activity and body position were positively correlated, with systolic and diastolic BPs. However, these relationships were stronger during the rest than activity phase. In addition, a 78.6% concordance was detected between the observed dips in BP and the predicted BP pattern calculated based on the WT rhythm. Thus, these results suggest that the increase in WT produced by heat loss during the rest phase through peripheral skin blood vessels is the result of blood vessel vasodilatation reflexes in response to a shift from a standing to a supine position, together with shift in the circadian sympathetic/parasympathetic balance (nocturnal parasympathetic activation). In conclusion, WT could be considered as a potential new screening procedure to implement the diagnosis of non-dipping BP pattern. (Author correspondence: angerol@um.es)

Daily rhythms of native Brazilians in summer and winter

Access to electricity, granting relative independence of human activity on the dark phase of the day, has been pointed out as an important cause for the absence of seasonal changes in the daily rhythms of humans living in urban areas. Featuring a population of adult Guarani natives living without access to electricity, the present naturalistic study was designed to explore possible effects of different natural photoperiods and temperature on human circadian rhythms. We compared time series of wrist temperature (WT) and motor activity in winter and summer, respectively, of 24 individuals aged 18 to 80. Twenty-four-hour rhythms of WT showed lower amplitudes and higher mean levels in summer, with no significant seasonal differences in acrophase. In contrast, rest-activity (RA) rhythms exhibited a significantly later rest on- and offset in summer, but no seasonal changes in duration, amplitude and mean level. We furthermore identified a phase advance of both the WT acrophase and rest onset with increasing age of the individuals. We concluded that in our study the effect of different seasons was reflected in the amplitude and mean level of the WT rhythm, as well the onset of nighttime rest, which was delayed in summer.

Crosstalk Between Environmental Light and Internal Time in Humans

Daily exposure to environmental light is the most important zeitgeber in humans, and all studied characteristics of light pattern (timing, intensity, rate of change, duration, and spectrum) influence the circadian system. However, and due to lack of current studies on environmental light exposure and its influence on the circadian system, the aim of this work is to determine the characteristics of a naturalistic regimen of light exposure and its relationship with the functioning of the human circadian system. Eighty-eight undergraduate students (18–23 yrs) were recruited in Murcia, Spain (latitude 38°01′N) to record wrist temperature (WT), light exposure, and sleep for 1 wk under free-living conditions. Light-exposure timing, rate of change, regularity, intensity, and contrast were calculated, and their effects on the sleep pattern and WT rhythm were then analyzed. In general, higher values for interdaily stability, relative amplitude, mean morning light, and light quality index (LQI) correlated with higher interdaily stability and relative amplitude, and phase advance in sleep plus greater stability in WT and phase advance of the WT circadian rhythm. On the other hand, a higher fragmentation of the light-exposure rhythm was associated with more fragmented sleep. Naturalistic studies using 24-h ambulatory light monitoring provide essential information about the main circadian system input, necessary for maintaining healthy circadian tuning. Correcting light-exposure patterns accordingly may help prevent or even reverse health problems associated with circadian disruption. (Author correspondence: angerol@um.es)

Differences in Daily Rhythms of Wrist Temperature Between Obese and Normal-Weight Women: Associations With Metabolic Syndrome Features

The circadian rhythm of core body temperature is associated with widespread physiological effects. However, studies with other more practical temperature measures, such as wrist (WT) and proximal temperatures, are still scarce. The aim of this study was to investigate whether obesity is associated with differences in mean WT values or in its daily rhythmicity patterns. Daily patterns of cortisol, melatonin, and different metabolic syndrome (MetS) features were also analyzed in an attempt to clarify the potential association between chronodisruption and MetS. The study was conducted on 20 normal-weight women (age: 38 ± 11 yrs and BMI: 22 ± 2.6 kg/m2) and 50 obese women (age: 42 ± 10 yrs and BMI: 33.5 ± 3.2 kg/m2) (mean ± SEM). Skin temperature was measured over a 3-day period every 10 min with the “Thermochron iButton.” Rhythmic parameters were obtained using an integrated package for time-series analysis, “Circadianware.” Obese women displayed significantly lower mean WT (34.1°C ± 0.3°C) with a more flattened 24-h pattern, a lower-quality rhythm, and a higher intraday variability (IV). Particularly interesting were the marked differences between obese and normal-weight women in the secondary WT peak in the postprandial period (second-harmonic power [P2]), considered as a marker of chronodisruption and of metabolic alterations. WT rhythmicity characteristics were related to MetS features, obesity-related proteins, and circadian markers, such as melatonin. In summary, obese women displayed a lower-quality WT daily rhythm with a more flattened pattern (particularly in the postprandial period) and increased IV, which suggests a greater fragmentation of the rest/activity rhythm compared to normal-weight women. These 24-h changes were associated with higher MetS risk. (Author correspondence: garaulet@um.es)

Joint posture, volumetric and temperature changes during repetitive hand movements

The study assessed finger and wrist joint motion, temperature and volumetric measurements and reports a qualitative assessment resulting from repetitive industrial hand movements. Participants mimicked a series of industrial repetitive tasks incorporating the following hand movements: wrist flexion/extension task, repetitive grasp/release task; and pinch task. Each task was performed for a period of 5 minutes. Hand temperature and volumetric measurements were reported. Descriptive statistics and ANOVA were performed. Power analysis was performed to determine sample size (0.8) and significance was set at p=0.05. The results indicate that an increase in hand volume is accompanied by an increase in final temperature of the hand. Of the three tasks mimicking an industrial repetitive activity, the repetitive grasp/release task produced the most range of motion (RoM), followed by the wrist flexion/extension task and then the pinch task. From the subjects' perception the wrist flexion/extension task was considered to be the most stressful task.

A New Integrated Variable Based on Thermometry, Actimetry and Body Position (TAP) to Evaluate Circadian System Status in Humans

The disruption of the circadian system in humans has been associated with the development of chronic illnesses and the worsening of pre-existing pathologies. Therefore, the assessment of human circadian system function under free living conditions using non-invasive techniques needs further research. Traditionally, overt rhythms such as activity and body temperature have been analyzed separately; however, a comprehensive index could reduce individual recording artifacts. Thus, a new variable (TAP), based on the integrated analysis of three simultaneous recordings: skin wrist temperature (T), motor activity (A) and body position (P) has been developed. Furthermore, we also tested the reliability of a single numerical index, the Circadian Function Index (CFI), to determine the circadian robustness. An actimeter and a temperature sensor were placed on the arm and wrist of the non-dominant hand, respectively, of 49 healthy young volunteers for a period of one week. T, A and P values were normalized for each subject. A non-parametric analysis was applied to both TAP and the separate variables to calculate their interdaily stability, intradaily variability and relative amplitude, and these values were then used for the CFI calculation. Modeling analyses were performed in order to determine TAP and CFI reliability. Each variable (T, A, P or TAP) was independently correlated with rest-activity logs kept by the volunteers. The highest correlation (r = −0.993, p<0.0001), along with highest specificity (0.870), sensitivity (0.740) and accuracy (0.904), were obtained when rest-activity records were compared to TAP. Furthermore, the CFI proved to be very sensitive to changes in circadian robustness. Our results demonstrate that the integrated TAP variable and the CFI calculation are powerful methods to assess circadian system status, improving sensitivity, specificity and accuracy in differentiating activity from rest over the analysis of wrist temperature, body position or activity alone.

Circadian rhythm of wrist temperature in normal-living subjects: A candidate of new index of the circadian system

Most circadian rhythms are under the control of a major pacemaker located in the hypothalamic suprachiasmatic nucleus. Some of these rhythms, called marker rhythms, serve to characterize the timing of the internal temporal order. A marker rhythm, (e.g., one used in chronotherapy) has to be periodic and easy to measure over long periods using non-invasive methods. The most frequent reference variables for human chronotherapy include salivary melatonin or cortisol, urinary 6-sulfatoximelatonin, actimetry and core body temperature (CBT). Recent evidence suggests that sleepiness may be more closely linked to increased peripheral skin temperature than to a core temperature drop, and that distal skin temperature seems to be correlated and phase-advanced with respect to CBT, suggesting that heat loss from the extremities may drive the circadian CBT rhythm. The aim of the present study was to evaluate whether the wrist skin temperature rhythm could be used as a possible index of the human circadian system. To this end, wrist skin temperature (WT1), as determined by a wireless data logger in healthy normal living subjects, was correlated with sleep-wake diaries and oral temperature (OT) recordings. WT and sleep habits were studied in 99 university students. Each subject wore a wireless iButton sensor attached to the inner side of a sport wristband. Our results show that the WT rhythm exhibits an inverse phase relationship with OT, and it is phase-advanced by 60 min with respect to OT. WT started to increase in association to bed time and dropped sharply after awakening. A secondary WT increase, independent of feeding, was observed in the early afternoon. In conclusion, WT wireless recording can be considered a reliable procedure to evaluate circadian rhythmicity, and an index to establish and follow the effects of chronotherapy in normal living subjects.

Comparative analysis of rhythmic parameters of the body temperature in humans measured with thermistors and digital thermometers

In this paper we compare rhythmic parameters of human body temperature simultaneously measured with digital thermometers and thermistors with memory (Thermochron iButtons®). Thirteen healthy male and female volunteers (mean age of 25) measured oral and axillary temperatures with digital thermometers every hour during wakefulness for two days and every three hours for three days, totalling five consecutive days. Concomitantly, they wore badges with thermistors in the thorax and the wrist. Temporal series circadian rhythmicity was evaluated with the Cosinor technique. Acrophases average were 17:32 h±2:02 h for axillary temperature, 10:12 h±7:26 h for thoracic temperature, 17:18 h±00:50 h for oral temperature and 4:15 h±1:55 h for wrist temperature. The rhythmic parameters of the wrist are more robust than those of the thorax. The collection of data in humans, generally performed with digital thermometers, is restricted to the waking phase and depends on the discipline of the volunteers. We suggest that the use of the thermistor with memory in the wrist can be adopted as alternative methodology to studies of human body temperature rhythmicity, especially recommended for long temporal series.