Biomedical subjects

Wouter D van Marken Lichtenbelt

Publications and source records attributed to Wouter D van Marken Lichtenbelt.

8 recordsLinked to original sources

PubMed2006

Validation of an individualised model of human thermoregulation for predicting responses to cold air.

Most computer models of human thermoregulation are population based. Here, we individualised the Fiala model [Fiala et al. (2001) Int J Biometeorol 45:143-159] with respect to anthropometrics, body fat, and metabolic rate. The predictions of the adapted multisegmental thermoregulatory model were compared with measured skin temperatures of individuals. Data from two experiments, in which reclining subjects were suddenly exposed to mild to moderate cold environmental conditions, were used to study the effect on dynamic skin temperature responses. Body fat was measured by the three-compartment method combining underwater weighing and deuterium dilution. Metabolic rate was determined by indirect calorimetry. In experiment 1, the bias (mean difference) between predicted and measured mean skin temperature decreased from 1.8 degrees C to -0.15 degrees C during cold exposure. The standard deviation of the mean difference remained of the same magnitude (from 0.7 degrees C to 0.9 degrees C). In experiment 2 the bias of the skin temperature changed from 2.0+/-1.09 degrees C using the standard model to 1.3+/-0.93 degrees C using individual characteristics in the model. The inclusion of individual characteristics thus improved the predictions for an individual and led to a significantly smaller systematic error. However, a large part of the discrepancies in individual response to cold remained unexplained. Possible further improvements to the model accomplished by inclusion of more subject characteristics (i.e. body fat distribution, body shape) and model refinements on the level of (skin) blood perfusion, and control functions, are discussed.

Adult↗

PubMed2006

Evaluation of wireless determination of skin temperature using iButtons.

Measurements of skin temperatures are often complicated because of the use of wired sensors. This is so in field studies, but also holds for many laboratory conditions. This article describes a wireless temperature system for human skin temperature measurements, i.e. the Thermochron iButton DS1291H. The study deals with validation of the iButton and its application on the human skin, and describes clinical and field measurements. The validation study shows that iButtons have a mean accuracy of -0.09 degrees C (-0.4 degrees C at most) with a precision of 0.05 degrees C (0.09 degrees C at most). These properties can be improved by using calibration. Due to the size of the device the response time is longer than that of conventional sensors, with a tau in water of 19 s. On the human skin under transient conditions the response time is significantly longer, revealing momentary deviations with a magnitude of 1 degrees C. The use of iButtons has been described in studies on circadian rhythms, sleep and cardiac surgery. With respect to circadian rhythm and sleep research, skin temperature assessment by iButtons is of significant value in laboratory, clinical and home situations. We demonstrate that differences in laboratory and field measurements add to our understanding of thermophysiology under natural living conditions. The advantage of iButtons in surgery research is that they are easy to sterilize and wireless so that they do not hinder the surgical procedure. In conclusion, the application of iButtons is advantageous for measuring skin temperatures in those situations in which wired instruments are unpractical and fast responses are not required.

Adult↗

PubMed2006

Heat production and body temperature during cooling and rewarming in overweight and lean men.

OBJECTIVE: To compare overweight and lean subjects with respect to thermogenesis and physiological insulation in response to mild cold and rewarming. RESEARCH METHODS AND PROCEDURES: Ten overweight men (mean BMI, 29.2 +/- 2.8 kg/m(2)) and 10 lean men (mean BMI, 21.1 +/- 2.0 kg/m(2)) were exposed to cold air for 1 hour, followed by 1 hour of rewarming. Body composition was determined by hydrodensitometry and deuterium dilution. Heat production and body temperatures were measured continuously by indirect calorimetry and thermistors, respectively. Muscle activity was recorded using electromyography. RESULTS: In both groups, heat production increased significantly during cooling (lean, p = 0.004; overweight, p = 0.006). The increase was larger in the lean group compared with the overweight group (p = 0.04). During rewarming, heat production returned to baseline in the overweight group and stayed higher compared with baseline in the lean group (p = 0.003). The difference in heat production between rewarming and baseline was larger in the lean (p = 0.01) than in the overweight subjects. Weighted body temperature of both groups decreased during cold exposure (lean, p = 0.002; overweight, p < 0.001) and did not return to baseline during rewarming. DISCUSSION: Overweight subjects showed a blunted mild cold-induced thermogenesis. The insulative cold response was not different among the groups. The energy-efficient response of the overweight subjects can have consequences for energy balance in the long term. The results support the concept of a dynamic heat regulation model instead of temperature regulation around a fixed set point.

Adult↗

PubMed2005

Cold-induced heat production preceding shivering.

Individual changes in heat production and body temperature were studied in response to cold exposure, prior to shivering. The subjects ten women (seven men) were of normal weight, had a mean age of 23 (SD 3) years and average BMI 22.2 (SD 1.6) Kg/m2. They were lying supine under thermoneutral conditions for 30 min and were subsequently exposed to air of 15 degrees C until shivering occurred. Heat production was measured with a ventilated hood. Body composition was measured with underwater weighing and 2H dilution. Body temperatures were measured with thermistors. Heat production during cold exposure prior to shivering increased and reached a plateau. Skin temperature decreased and did not reach a plateau during the test period. The non-shivering interval (NSI) ranged from 20 to 148 min, was not related to body composition and was not significantly different between women (81 (sd 15) min) and men (84 (sd 34) min). NSI was negatively related to skin temperature (r2 0.44, P=0.004), and skin temperature was related to heat production (r2 0.39, P=0.007). In conclusion, subjects with a relatively large heat production during cold exposure maintained a relatively high skin temperature but showed a short NSI, independent of differences in body composition.

Adult↗

PubMed2004

Bodybuilders' body composition: effect of nandrolone decanoate.

INTRODUCTION: The use of androgenic-anabolic steroids (AAS) among bodybuilders to increase muscle mass is widespread. Nandrolone decanoate (ND) is one of the most popular misused AAS, although the effects on body composition are equivocal. Therefore, the purpose of this study was to determine the effect of ND on body composition in male bodybuilders, with special reference to muscle mass alterations. METHODS: Using a randomized "double-blind" "placebo-controlled" design, 16 experienced male bodybuilders (age: 19-44 yr) either received ND (200 mg.wk(-1), intramuscularly) or placebo for 8 wk. Body composition was assessed using the four-component model, combining results from underwater weighing, dual-energy x-ray absorptiometry (DXA), and deuterium dilution. Total bone mineral content and density were measured using DXA. Water compartments (extracellular water [ECW] and intracellular water [ICW]) were determined using deuterium dilution and bromide dilution. RESULTS: ND administration resulted in significant increments of body mass (+2.2 kg), fat-free mass (FFM: +2.6 kg), and total body water (+1.4 kg). No significant changes in fat mass, percentage fat, ECW, ICW, ECW/ICW ratio, hydration of the FFM, and on bone mineral measurements were observed. CONCLUSIONS: The results show that the administration of 200 mg.wk(-1) of ND (intramuscularly) for 8 wk significantly increased body mass and FFM, whereas fat mass, bone mineral content, bone mineral density, and the hydration of the FFM remained unaffected. These data indicate that the changes can be attributed to an increase of muscle mass.

Adult↗

PubMed2004

Body composition changes in bodybuilders: a method comparison.

INTRODUCTION: Few studies report on validation of body composition changes using the four-compartment model (4C), and no such studies are available in strength training. Here we present such a validation study for the determination of body fat and fat-free mass changes in bodybuilders, who used exercise and androgenic-anabolic steroids. METHODS: The study was carried out with 27 male bodybuilders in a cross-sectional study. Fifteen of these subjects also participated in an intervention program where body composition changes were measured. The 4C model served as the gold standard. The alternative mechanistic methods were underwater weighing (uww), deuterium dilution (dil), three-compartment model incorporating total body water (3Cw), three-compartment model incorporating bone mineral content (3Cb), and descriptive methods, namely dual-energy x-ray absorptiometry (DXA), prediction equations based on body mass index (BMI), skinfold measurement, and bioimpedance analyses. RESULTS: From the cross-sectional study, it appeared that biases and errors of most mechanistic methods were small (maximal 0.5% BF and 3.4%BF, respectively; exception 3Cb model). The 3Cw model had the lowest error (0.9%BF). The descriptive methods had small biases (exception BMI) but relatively large errors (range: 5.5-8%). Results on body composition changes (intervention study) were comparable with the results from the cross-sectional study. CONCLUSIONS: Using the 4C model as the standard for determination of body fat and fat-free mass, this study revealed that apart from the prediction equation based on BMI and the 3Cb model, all methods gave acceptable group mean values. When accurate measurements on body composition and/or body composition changes on an individual level are needed, only the 3Cw model could serve as an alternative for the 4C method.

Absorptiometry, Photon↗

PubMed2003

Cold-induced metabolism.

PURPOSE OF REVIEW: Cold response can be insulative (drop in peripheral temperature) or metabolic (increase in energy expenditure). Nonshivering thermogenesis by sympathetic, norepinephrine-induced mitochondrial heat production in brown adipose tissue is a well known component of this metabolic response in infants and several animal species. In adult humans, however, its role is less clear. Here we explore recent findings on the role and variability of nonshivering thermogenesis in adults. RECENT FINDINGS: Large individual differences exist in mild cold response with respect to the relative contribution of the insulative response and the metabolic (nonshivering) response. In search for the possible explanations of this variation, recent studies on potential mechanisms of nonshivering thermogenesis in humans are presented. Emphasis is given to the role of uncoupling proteins, mitochondrial ATP-synthase, and calcium cycling. The potential contribution of human skeletal muscle to nonshivering thermogenesis is discussed. The differences in nonshivering thermogenesis can partly be attributed to factors such as age, gender, physical fitness, adaptation, and diet. There are indications that genetic variation affect cold response. SUMMARY: The implications of the observed large individual variation in cold response is that a low metabolic response to cold can partly explain increased risk to develop obesity. Both the effect of environmental factors and genetic factors on nonshivering thermogenesis require more well controlled studies. With extended knowledge on these factors it can be ascertained if a pharmacological regimen is possible which would mimic the effects of chronic cold or elevated catecholamine levels, without attendant side effects.

Adipose Tissue, Brown↗

PubMed2002

Individual variation in body temperature and energy expenditure in response to mild cold.

We studied interindividual variation in body temperature and energy expenditure, the relation between these two, and the effect of mild decrease in environmental temperature (16 vs. 22 degrees C) on both body temperature and energy expenditure. Nine males stayed three times for 60 h (2000-0800) in a respiration chamber, once at 22 degrees C and twice at 16 degrees C, in random order. Twenty-four-hour energy expenditure, thermic effect of food, sleeping metabolic rate, activity-induced energy expenditure, and rectal and skin temperatures were measured. A rank correlation test with data of 6 test days showed significant interindividual variation in both rectal and skin temperatures and energy expenditures adjusted for body composition. Short-term exposure of the subjects to 16 degrees C caused a significant decrease in body temperature (both skin and core), an increase in temperature gradients, and an increase in energy expenditure. The change in body temperature gradients was negatively related to changes in energy expenditure. This shows that interindividual differences exist with respect to the relative contribution of metabolic and insulative adaptations to cold.

Adaptation, Physiological↗