The circadian rhythm of core temperature: Effects of physical activity and aging

Weinert, Dietmar; Waterhouse, Jim

doi:10.1016/j.physbeh.2006.09.003

Cited by 162 publications

(104 citation statements)

References 78 publications

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“…This change (ca 6 0.5 C) has an approximately sinusoidal shape with the plateau of highest rectal temperatures (ca 37 6 0.2 C) between 10 am and 8 PM (25,26). Although our volunteers were measured in this time period, individual deviations cannot be excluded.…”

Section: Resultsmentioning

confidence: 90%

Human brain MR spectroscopy thermometry using metabolite aqueous‐solution calibrations

Covaciu

Rubertsson

Ortiz-Nieto

et al. 2010

Magnetic Resonance Imaging

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Purpose: To estimate absolute brain temperature using proton MR spectroscopy ( 1 H-MRS) and mean brain-body temperature difference of healthy human volunteers. Materials and Methods:Chemical shift difference between temperature-dependent water spectral line position and temperature-stable metabolite spectral reference was used for the estimations of absolute brain temperature. Temperature calibrations constants were obtained from the spectra of the N-acetyl aspartate (NAA line at $2.0 ppm), glycero-phosphocholine (GPC line at $3.2 ppm), and creatine (Cr line at $3.0 ppm) aqueous solutions with pH values within physiologically pertinent ranges. Single-voxel PRESS sequence (TR/TE 2000/ 80 ms) was used for this purpose. Brain temperature was determined by averaging the temperatures computed from water-Cho, water-Cr, and water-NAA chemical shift differences. Results:The mean brain temperature of 18 healthy volunteers was 38.1 6 0.4 C and mean brain-body (rectal) temperature difference was 1.3 6 0.4 C.Conclusion: Improved accuracy of the temperature constants and averaging the temperatures computed from water-Cho, water-Cr, and water-NAA chemical shift differences increased the reliability of the brain temperature estimations. CURRENT KNOWLEDGE ABOUT brain temperature in healthy humans is limited because direct and accurate measurements cannot be made without the need for surgery. The importance of brain temperature and its fluctuations due to biochemical and physical processes is, in the meantime, well acknowledged (1).The factors thought responsible for brain temperature regulation are the temperature of incoming arterial blood, metabolic heat production, heat removal by blood flow, heat conductance of the tissues, and heat exchange with the environment. In mammals, the most important factors are the temperature of the incoming arterial blood, brain metabolism, and external temperature (2). It has been theoretically estimated that the normal human brain produces ca 0.66 J of heat every minute per gram of brain tissue (3). The internal heat is removed mainly by blood flow. The cooling effect of external temperature seems to be less important because it is limited to superficial brain regions of several millimeters of thickness and depends on brain size and ambient temperature (4,5). Theoretical simulations (3,6), animal studies (7), and measurements of venous (internal jugular vein) versus arterial (aortic artery) temperatures in healthy volunteers (8) suggest that there is a positive difference 0.3-0.5 C between brain and body. These observations are in the qualitative agreement with direct measurements of injured head or stroke patients that reveal the brain-body temperature difference in the range 1-2 C (9).Because invasive measurement of the brain temperature cannot be made in healthy volunteers, research has focused on noninvasive MR techniques. Proton MR spectroscopy ( 1 H-MRS) and MR spectroscopic imaging (MRSI) are now validated methods that are capable of estimating absolute brain temperatures (10-17). Thes...

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Section: Resultsmentioning

confidence: 90%

Human brain MR spectroscopy thermometry using metabolite aqueous‐solution calibrations

Covaciu

Rubertsson

Ortiz-Nieto

et al. 2010

Magnetic Resonance Imaging

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“…In its simplest portrayal, the function of thermoregulation is to hold the central body temperature to within a small tolerance of a set point value that for adults is taken to be 37 C. However, it is also well known that the target does not remain constant, resulting a circadian thermal cycle in which the core temperature varies by approximately 1 C over a 24-hr-period [22][23][24][25]. This cyclic core temperature variation is achieved by modulation in the magnitudes and balance between rates of internal energy generation and heat exchange with the environment.…”

Section: Introductionmentioning

confidence: 99%

Heat Transfer in Health and Healing1

Diller

2015

Journal of Heat Transfer

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1Our bodies depend on an exquisitely sensitive and refined temperature control system to maintain a state of health and homeostasis. The exceptionally broad range of physical activities that humans engage in and the diverse array of environmental conditions we face require remarkable strategies and mechanisms for regulating internal and external heat transfer processes. On the occasions for which the body suffers trauma, therapeutic temperature modulation is often the approach of choice for reversing injury and inflammation and launching a cascade of healing. The focus of human thermoregulation is maintenance of the body core temperature within a tight range of values, even as internal rates of energy generation may vary over an order of magnitude, environmental convection, and radiation heat loads may undergo large changes in the absence of any significant personal control, surface insulation may be added or removed, all occurring while the body's internal thermostat follows a diurnal circadian cycle that may be altered by illness and anesthetic agents. An advanced level of understanding of the complex physiological function and control of the human body may be combined with skill in heat transfer analysis and design to develop life-saving and injury-healing medical devices. This paper will describe some of the challenges and conquests the author has experienced related to the practice of heat transfer for maintenance of health and enhancement of healing processes.

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“…Also body temperature, oxygen consumption (Weinert & Waterhouse, 2007) and catecholamine levels (Ayako & Keiichi, 1995) are peaked in the afternoon. In addition, in the previous study we reported that energy expenditure and oxygen consumption during 30-min treadmill exercise at intensities of 65% of VO 2 max, were higher at 18:00 than 08:00 (Rahmani-Nia, Azizi, & Mohebbi, 2009).…”

Section: Introductionmentioning

confidence: 99%

Maximal fat oxidation at the different exercise intensity in obese and normal weight men in the morning and evening

Hamid

Azizi

2011

JHSE

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Mohebbi H, Azizi M. Maximal fat oxidation at the different exercise intensity in obese and normal weight men in the morning and evening. J. Hum. Sport Exerc. Vol. 6, No. 1, pp. 49-58, 2011. Introduction: Circadian rhythms regulate some metabolic and hormonal variables that affect fat oxidation rates. Thus, the purpose of this study was to investigate Maximal fat oxidation (MFO) at a different exercise intensity in obese and normal weight men in the morning and evening. Methods: MFO was measured in 12 normal weight (BMI 20-25 kg/m 2 ; VO 2 max 45.7±3.44 ml/min/kg) and 10 obese (BMI >30 kg/m 2 ; VO 2 max 37.2±3.6 ml/min/kg) men during incremental running exercise test with 3 min stages on the treadmill by indirect calorimetry method. Student's t-test and one-way ANOVA with repeated measures were used to analysis variables. Results: We found that fat oxidation rates and energy expenditure in both groups in the evening were higher than morning; there were no significant differences in MFO between obese and normal groups. Furthermore, the fat oxidation rate in low intensity exercise (<60% VO 2 max) was similar in obese and normal weight groups, but in high exercise intensities, in normal weight men were significantly higher than obese men. Conclusion: Our results suggest that independent of exercise intensity and body fat mass, exercising in the evening is more effective on fat oxidation and decrease body fat mass; therefore, it is better for weight loss purposes in obese and normal weight men.

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The circadian rhythm of core temperature: Effects of physical activity and aging

Cited by 162 publications

References 78 publications

Human brain MR spectroscopy thermometry using metabolite aqueous‐solution calibrations

Human brain MR spectroscopy thermometry using metabolite aqueous‐solution calibrations

Heat Transfer in Health and Healing1

Maximal fat oxidation at the different exercise intensity in obese and normal weight men in the morning and evening

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