The Difference Between Activity When in Bed and Out of Bed. II. Subjects on 27-Hour “Days”

Nine healthy subjects have been studied while exposed to the normal alternation of light and dark, but with their sleep and activity pattern adjusted to a 27-h “day” for 17 imposed “days.” Rectal temperature showed clearly the competing influences of 27-h and 24-h components, and these were separated by the method of “purification.” The method indicated that the endogenous component had a constant amplitude throughout the experiment and remained entrained to solar (24-h) time; by contrast, the exogenous component followed the imposed 27-h “day” and increased rectal temperature in proportion to the amount of subjects' activity. Wrist movement was used to assess activity while in bed (attempting sleep) and out of bed (when naps were forbidden). While these results confirmed adherence of the subjects to the imposed 27-h “days,” they also showed that the dichotomy between “out of bed” activity and “in bed” inactivity depended on the phase relationship between endogenous (24h) and exogenous (27h) components. Thus, the dichotomy was highest and was equal to that during control days (with a conventional 24-h life-style) when the two components were in phase and lowest when the solar and imposed day were in antiphase. This was due to changes in activity, both during time spent in bed and out of bed.

We confirm that this protocol can produce valuable information about the properties of the circadian system in humans and the value of the process of purification of temperature data. We have established also that the very simple and noninvasive measurement of wrist movement, coupled with its use to calculate dichotomy indices, provides valuable information that both confirms and extends the results obtained from the more conventional (butalso more invasive) measurement of rectal temperature.     

The Difference Between Activity When in Bed and out of Bed. III. Nurses on Night Work

Eight nurses have been studied during rest days and three successive night shifts. Measurements of wrist activity have been made and used to assess the extent to which the pattern of daily activity changes between control (rest) days and days involving night work. One analysis considered wrist activity during time spent in bed; this appears to decrease in parallel with the amount of time in bed that is lost during night work but, when this effect is corrected for, there is greater activity during time spent in bed in the daytime compared with control days (when time in bed is during the night). The dichotomy of activity (between lower values during time spent in bed and higher values when out of bed) also decreases if time in bed is during the daytime while on night shifts. These changes in the amount of wrist activity and the dichotomy between activity in and out of bed are related to the changed quality and quantity of sleep that has been measured by self-report questionnaires and the sleep EEG. It is concluded that results from wrist actimetry can provide valuable information regarding the process of adjustment to night work, and that its convenience (to subject and experimenter), coupled with the new analytical approaches described here, make it a viable method for field studies. (Chronobiology International, 13(4), 273-282, 1996)     

Metabolic Effects of 2 Days of Strict Bed Rest

ObjectiveTo examine the possibility of whether 2 days of strict hospitalized bed rest would alter the metabolic profile (including insulin resistance as calculated by the quantitative insulin sensitivity check index or QUIC- KI) in both normal subjects and patients with type 2 diabetes in comparison with 2 days of normal activity.MethodsThe design of this pilot study was a randomized, crossover protocol that evaluated the effects of strict bed rest versus normal activity in 5 healthy normal subjects and 5 healthy patients with type 2 diabetes. All study participants completed a screening visit for assessment of baseline health.ResultsAll 10 study subjects completed the protocol without adverse events. Fasting plasma glucose, insulin, and C-peptide levels as well as several known risk factors for atherosclerosis were unchanged in both the subjects without diabetes and the patients with type 2 diabetes after 2 days of hospitalized bed rest. Insulin resistance demonstrated no significant change during the 48 hours of bed rest when compared with the mean value at baseline.ConclusionThis study demonstrates that 48 hours of bed rest has no significant effect on insulin resistance or standard metabolic variables in normal subjects and patients with type 2 diabetes. Therefore, achieving good glucose control in patients hospitalized for a period of 2 days or less does not necessitate early ambulation to prevent an increase in insulin resistance. (Endocr Pract. 2008;14:564-569)     

The difference between in bed and out of bed activity as a behavioral marker of cancer patients: A comparative actigraphic study

The current study was conducted to provide normative data on actigraphic dichotomy index (I?<?O) (the percentage of in bed activity counts that are less than the median of out of bed counts) in healthy population and to assess whether the I?<?O could be an effective index in discriminating the circadian motor activity of cancer patients from healthy controls. In this retrospective study, we recovered 408 actigraphic records from two databases: healthy controls (n?=?182; 79 males; mean age 38.7?±?12.6) and patients with metastatic colorectal cancer (n?=?226; 149 males; mean age 58.4?±?11.4). Beside the usual actigraphic sleep parameters (time in bed, sleep onset latency, total sleep time, wake after sleep onset, sleep efficiency, number of awakenings, and mean motor activity), we also computed the dichotomy index and number of actigraphic wake parameters, namely, diurnal motor activity, diurnal total sleep time, number of sleep episodes, and the mean duration of the longest diurnal sleep episode. Using the Youden index, we calculated the cut off value that performed the best for I?<?O and actigraphic wake parameters. Finally, we created Receiver Operator Characteristic curves to test the efficacy of each actigraphic parameter to discriminate cancer patient from healthy controls. Mean I?<?O was 99.5% (SD, 0.48%) in the healthy group, as compared to 96.6% (SD, 3.6%) in the cancer group (p?<?0.0001). Important age-related effects appeared unlikely after performing both the main analysis with age as a covariate, and a subset analysis in 104 subjects matched for age and sex. In the main analysis, all actigraphic parameters, except total sleep time, significantly differentiated the two groups of participants. However, the I?<?O was the one that clearly performed best. Here, we provide the first large dataset on I?<?O in healthy subjects, we confirm the relevance of this circadian index for discriminating advanced stage colorectal cancer patients from healthy subjects, and we lay the grounds for further investigations of this circadian index in patients with other chronic diseases.     

Immobilization on the day 14th does not disrupts the basic diurnal rhythm of bone resorption

Weight bearing and physical activity are important mechanical stimuli to bone growth and metabolism, and microgravity, such a space flight and/or bed rest, induces bone resorption and bone loss. An increased excretion of urinary Ca, an increased bone resorption and a decreased bone mineral density (BMD) have been observed in bed rest experiment of healthy subjects. Bone resorption markers show the specific circadian rhythms in human. Cross-linked carboxyl-terminal telopeptide of type I collagen (ICTP) and the urinary excretion of deoxypyridinoline (Dpy) are the highest in the early morning and the lowest late at night. Bed rest immobilization might influence these rhythms, due to no mechanical loading with loss of daily life activity. Bone resorption markers in healthy subjects had been compared between before and during bed rest to determine disruption of diurnal rhythms of bone resorption.     

Bed rest reduces metabolic protein content and abolishes exercise-induced mRNA responses in human skeletal muscle

The aim was to test the hypothesis that 7 days of bed rest reduces mitochondrial number and expression and activity of oxidative proteins in human skeletal muscle but that exercise-induced intracellular signaling as well as mRNA and microRNA (miR) responses are maintained after bed rest. Twelve young, healthy male subjects completed 7 days of bed rest with vastus lateralis muscle biopsies taken before and after bed rest. In addition, muscle biopsies were obtained from six of the subjects prior to, immediately after, and 3 h after 45 min of one-legged knee extensor exercise performed before and after bed rest. Maximal oxygen uptake decreased by 4%, and exercise endurance decreased nonsignificantly, by 11%, by bed rest. Bed rest reduced skeletal muscle mitochondrial DNA/nuclear DNA content 15%, hexokinase II and sirtuin 1 protein content ～45%, 3-hydroxyacyl-CoA dehydrogenase and citrate synthase activity ～8%, and miR-1 and miR-133a content ～10%. However, cytochrome c and vascular endothelial growth factor (VEGF) protein content as well as capillarization did not change significantly with bed rest. Acute exercise increased AMP-activated protein kinase phosphorylation, peroxisome proliferator activated receptor-γ coactivator-1α, and VEGF mRNA content in skeletal muscle before bed rest, but the responses were abolished after bed rest. The present findings indicate that only 7 days of physical inactivity reduces skeletal muscle metabolic capacity as well as abolishes exercise-induced adaptive gene responses, likely reflecting an interference with the ability of skeletal muscle to adapt to exercise.     

Bed rest increases the amount of mismatched fibers in human skeletal muscle

The effects of a37-day period of bed rest on myosin heavy chain (MHC) expression onboth mRNA and protein level in human skeletal muscle fibers werestudied. Muscle biopsies from vastus lateralis muscle were obtainedfrom seven healthy young male subjects before and after the bed-restperiod. Combined in situ hybridization, immunocytochemistry, and ATPasehistochemistry analysis of serial sections of the muscle biopsiesdemonstrated that fibers showing a mismatch between MHC isoforms at themRNA and protein level increased significantly after the bed-restperiod, suggesting an increase in the amount of muscle fibers in atransitional state. Accordingly, fibers showing a match in expressionof MHC-1 and of MHC-2A at the mRNA and protein level decreased, whereasfibers showing a match between MHC-2X mRNA and protein increased after bed rest. Overall, there was an increase in fibers in a transitional state from phenotypic type 1  2A and 2A  2X.Furthermore, a number of fibers with unusual MHC mRNA and isoproteincombinations were observed after bed rest (e.g., type 1 fibers withonly mRNA for 2X and type 1 fibers negative for mRNA for MHC-/slow,2A, and 2X). In contrast, no changes were revealed after an examination at the protein level alone. These data suggest that the reduced load-bearing activity imposed on the skeletal muscles through bed restwill alter MHC gene expression, resulting in combinations of mRNA andMHC isoforms normally not (or only rarely) observed in musclessubjected to load-bearing activity. On the other hand, the present dataalso show that 37 days of bed rest are not a sufficient stimulus toinduce a similar change at the protein level, as was observed at thegene level.     

Effects of Head-Down Bed Rest on the Executive Functions and Emotional Response

Prolonged bed rest may cause changes in the autonomic nervous system that are related to cognition and emotion. This study adopted an emotional flanker task to evaluate the effect of 45 days -6° head-down bed rest (HDBR) on executive functioning in 16 healthy young men at each of six time points: the second-to-last day before the bed rest period, the eleventh, twentieth, thirty-second and fortieth day during the bed rest period, and the eighth day after the bed rest period. In addition, self-report inventories (Beck Anxiety Inventory, BAI; Beck Depression Inventory, BDI; Positive Affect and Negative Affect Scale, PANAS) were conducted to record emotional changes, and the participants’ galvanic skin response (GSR), heart rate (HR) and heart rate variability (HRV) were assessed as measures of physiological activity. The results showed that the participants’ reaction time on the flanker task increased significantly relative to their responses on the second-to-last day before the period of bed rest, their galvanic skin response weakened and their degrees of positive affect declined during the bed rest period. Our results provide some evidence for a detrimental effect of prolonged bed rest on executive functioning and positive affect. Whether this stems from a lack of aerobic physical activity and/or the effect of HDBR itself remains to be determined.     

Tonic-to-phasic shift of lumbo-pelvic muscle activity during 8 weeks of bed rest and 6-months follow up.

Prior motor control studies in unloading have shown a tonic-to-phasic shift in muscle activation, particularly in the short extensors. Tonic muscle activity is considered critical for normal musculoskeletal function. The shift from tonic-to-phasic muscle activity has not been systematically studied in humans in unloading nor at the lumbo-pelvic (LP) region. Ten healthy young male subjects underwent 8 wk of bed rest with 6-mo follow up as part of the "Berlin Bed-Rest Study." A repetitive knee movement model performed in the prone position is used to stimulate tonic holding LP muscle activity, as measured by superficial EMG. Tonic and phasic activation patterns were quantified by relative height of burst vs. baseline electromyographic linear-envelope signal components. Statistical analysis shows a shift toward greater phasic activity during bed rest and follow up (P < 0.001) with a significant interaction across muscles (P < 0.001) specifically affecting the short lumbar extensors. These changes appear unrelated to skill acquisition over time (P all > or = 0.196). This change of a shift from tonic LP muscle activation to phasic is in line with prior research on the effects of reduced weight bearing on motor control.     

Vascular adaptation to deconditioning and the effect of an exercise countermeasure: results of the Berlin Bed Rest study.

Deconditioning is a risk factor for cardiovascular disease. The physiology of vascular adaptation to deconditioning has not been elucidated. The purpose of the present study was to assess the effects of bed rest deconditioning on vascular dimension and function of leg conduit arteries. In addition, the effectiveness of resistive vibration exercise as a countermeasure for vascular deconditioning during bed rest was evaluated. Sixteen healthy men were randomly assigned to bed rest (BR-Ctrl) or to bed rest with resistive vibration exercise (BR-RVE). Before and after 25 and 52 days of strict horizontal bed rest, arterial diameter, blood flow, flow-mediated dilatation (FMD), and nitroglycerin-mediated dilatation were measured by echo Doppler ultrasound. In the BR-Ctrl group, the diameter of the common femoral artery decreased by 13 +/- 3% after 25 and 17 +/- 1% after 52 days of bed rest (P < 0.001). In the BR-RVE group this decrease in diameter was significantly attenuated (5 +/- 2% after 25 days and 6 +/- 2% after 52 days, P < 0.01 vs. BR-Ctrl). Baseline blood flow did not change after bed rest in either group. After 52 days of bed rest, FMD and nitroglycerin-mediated dilatation of the superficial femoral artery were increased in both groups, possibly by increased nitric oxide sensitivity. In conclusion, bed rest deconditioning is accompanied by a reduction in the diameter of the conduit arteries and by an increased reactivity to nitric oxide. Resistive vibration exercise effectively attenuates the diameter decrease of leg conduit arteries after bed rest.     

Impaired Orthostatic Response in Patients With Type 2 Diabetes Mellitus After 48 Hours of Bed Rest

ObjectiveTo compare the effect of bed rest on orthostatic responses of patients with type 2 diabetes mellitus and nondiabetic control subjects.MethodsSix patients with type 2 diabetes and 6 nondiabetic control subjects underwent 48 hours of bed rest and 48 hours of ambulatory activity in randomized order. A 10-minute tilt test was conducted before and after each period of hospitalization, and cardiovascular responses to 80° head-up tilt were analyzed with use of a 2-factorial (study group and bed rest condition) analysis of variance design. We hypothesized that patients with diabetes would experience more severe changes in orthostatic response after bed rest.ResultsNo significant differences in orthostatic responses were observed before bed rest between control subjects and patients with diabetes. After bed rest, control subjects had a greater (P = .01) increase in heart rate during tilt in comparison with before bed rest (before versus after bed rest, 9 ± 4 versus 24 ± 7 beats/min) and maintained their blood pressure during tilt. After bed rest, patients with diabetes did not have a compensatory increase in heart rate and had a greater (P = .02) decline in systolic blood pressure during tilt in comparison with before bed rest (before versus after bed rest, -7 ± 10 versus -21 ± 11 mm Hg). Their arm and leg skin vasomotor responses (laser Doppler flowmetry) during tilt were not altered after bed rest and were similar to those in control subjects before and after bed rest.ConclusionCardiac neuropathy in patients with type 2 diabetes may prevent a compensatory heart rate response after bed rest deconditioning and result in a more severe orthostatic response. A greater decrease in blood pressure with upright tilt is evident after a relatively short period of bed rest. (Endocr Pract. 2009;15:104-110)     

Accentuated and irregular post-maximal deflection in thromboelastographic tracings: occurrence in various pathologies

The increased and irregular post-maximal deflection of the two limbs of thromboelastographic traces has been variably interpreted by the Authors who utilize TEG as a global screening test for haemostasis evaluation. These thromboelastographic patterns have been attributed either to enhanced fibrinolytic activity or to raised clot's rectractility or even to incorrect technique. In our study, 1701 TEG's traces carried out in the last five years have been reviewed in order to evaluate the incidence of such patterns in both healthy subjects and in patients affected by different diseases. The data obtained show that such irregular post-maximal deflection's patterns are quite absence in healthy subjects while reaches a statistically significant incidence only in patients affected by diabetes mellitus, obesity or systemic hypertension. The results seem to suggest that the increased and irregular post-maximal TEG deflection is not a simply product of technique's mistake but may represent an useful index of some haemostatic alterations which need further studies.     

The Local Complement Activation on Vascular Bed of Patients with Systemic Sclerosis: A Hypothesis-Generating Study

ObjectiveThe role of complement system in the pathogenesis of systemic sclerosis (SSc) has been debated during the last decade but an evident implication in this disease has never been found. We carried out an explorative study on SSc patients to evaluate the expression of soluble and local C5b-9 complement complex and its relation with a complement regulator, the Membrane Cofactor Protein (MCP, CD46) on skin vascular bed as target distinctive of SSc disease. We also analyzed two polymorphic variants in the complement activation gene cluster involving the MCP region.MethodsC5b-9 plasma levels of SSc patients and healthy subjects were analyzed by ELISA assay. Archival skin biopsies of SSc patients and controls were subjected to immunofluorescence analysis to detect C5b-9 and MCP on vascular endothelial cells. The expression of MCP was validated by immunoblot analysis with specific antibody. Polymorphic variants in the MCP gene promoter were tested by a quantitative PCR technique-based allelic discrimination method.ResultsEven though circulating levels of C5b-9 did not differ between SSc and controls, C5b-9 deposition was detected in skin biopsies of SSc patients but not in healthy subjects. MCP was significantly lower in skin vessels of SSc patients than in healthy controls and was associated with the over-expression of two polymorphic variants in the MCP gene promoter, which has been related to more aggressive phenotypes in other immune-mediated diseases.ConclusionsOur results firsty document the local complement activation with an abnormal expression of MCP in skin vessels of SSc patients, suggesting that a subset of SSc patients might be exposed to more severe organ complications and clinical evolution due to abnormal local complement activation.     

Effects of three-day bed rest on metabolic, hormonal and circulatory responses to an oral glucose load in endurance or strength trained athletes and untrained subjects.

The study was designed to find out (1) whether the effect of 3-day bed rest on blood glucose (BG) and plasma insulin (IRI) responses to glucose ingestion depends on preceding physical activity and (2) whether plasma adrenaline (A), noradrenaline (NA) and cardiovascular changes following a glucose load are modified by bed rest. Eleven sedentary students (22.5+/-0.3 yrs), 8 long distance runners (18.6+/-0.3 yrs) and 10 strength trained athletes (21.2+/-2.1 yrs) were examined before and after bed rest. Plasma IRI, BG, NA, A, heart rate (HR), and blood pressure (BP) were measured during 2 hrs following glucose (75 g) ingestion. The responses of BG and IRI to glucose load were calculated as incremental areas under the curves (auc). Both in athletes and untrained subjects bed rest markedly increased IRIauc, while BGauc was elevated only in sedentary subjects (p<0.05). The greatest increases in IRIauc and IRI/BG ratios were found in the endurance athletes. The data from all subjects (n = 29) revealed that the initial plasma NA and glucose-induced increases in NA and A were lowered after bed rest (p < 0.01). These effects were most pronounced in the endurance athletes. Bed rest did not influence HR or BP in any group. It is concluded that (1) the athletes have more adequate compensation for the bed-rest-induced decrement in insulin sensitivity than sedentary men; (2) three-day bed rest diminishes basal sympathetic activity and attenuates sympathoadrenal response to oral glucose; (3) endurance athletes have greater sympathetic inhibition than strength athletes or sedentary men.     

Bugging Forecast: Unknown,Disliked, Occasionally Intimate. Bed Bugs in Germany Meet Unprepared People

Bed bugs appear to be feared more than vector insects and other household pests. The reasons for this exaggerated fear are not fully understood. One hypothesis is that the folk knowledge on recognising and controlling bed bugs decreased as bed bugs became rarer in the 1960s and led to irrational perceptions. Here, we examine people’s ability to recognise a bed bug and their response what to do in case of an infestation. We found that 13% of a sample of 391 people in four large German cities recognised a bed bug; 15% of all respondents would call a pest controller in case of bed bug infestation. This results in the pessimistic estimate that 97% of all early-stage infestations could go untreated. We discuss additional scenarios. The effectiveness of efforts to educate people about the presence of bed bugs has never been tested, but our sample is useful to guide future studies. We found three sources of information were associated with increased recognition rates of bed bugs: a) previous contacts with bed bugs (60% recognition), b) knowledge from friends or relatives (25%) and school or education courses (15%). By contrast, people who heard of bed bugs from television, print media or the Internet showed reduced recognition rates. We propose that the former factors be tested for educational interventions. In Germany, the bed bug is an estranged creature to many people, a fact that seems to hinder rational approaches to their control.     

Hemorheological Status of a Body with a Normal vs. Changed Vascular Bed

The results of a comprehensive study of blood rheology in subjects with a normal or changed vascular bed show that chronic venous and arterial insufficiency in the lower limbs, caused by morphological changes in vessels, is accompanied by a decrease in the blood fluidity. This impairs the efficiency of oxygen supply to tissues. The authors detected rheological shifts that facilitate increases in the blood viscosity.     

Alterations of the Characteristics of the Circadian Rest‐Activity Rhythm of Cancer In‐Patients

The aim of the present study was to evaluate the characteristics of the circadian rest‐activity rhythm of cancer patients. Thirty‐one in‐patients, consisting of 19 males and 12 females, were randomly selected from the Regional Cancer Center, Pandit Jawaharlal Nehru Medical College, Raipur, India. The rest‐activity rhythm was studied non‐invasively by wrist actigraphy, and compared with 35 age‐matched apparently healthy subjects (22 males and 13 females). All subjects wore an Actiwatch (AW64, Mini Mitter Co. Inc., USA) for at least 4–7 consecutive days. Fifteen‐second epoch length was selected for gathering actigraphy data. In addition, several sleep parameters, such as time in bed, assumed sleep, actual sleep time, actual wake time, sleep efficiency, sleep latency, sleep bouts, wake bouts, and fragmentation index, were also recorded. Data were analyzed using several statistical techniques, such as cosinor rhythmometry, spectral analysis, ANOVA, Duncan's multiple‐range test, and t‐test. Dichotomy index (I<O) and autocorrelation coefficient (r24) were also computed. The results validated a statistically significant circadian rhythm in rest‐activity with a prominent period of 24 h for most cancer patients and control subjects. Results of this study further revealed that cancer patients do experience a drastic alteration in the circadian rest‐activity rhythm parameters. Both the dichotomy index and r24 declined in the group of cancer patients. The occurrence of the peak (acrophase, Ø) of the rest‐activity rhythm was earlier (p<0.001) in cancer patients than age‐ and gender‐matched control subjects. Results of sleep parameters revealed that cancer patients spent longer time in bed, had longer assumed and actual sleep durations, and a greater number of sleep and wake bouts compared to control subjects. Further, nap frequency, total nap duration, average nap, and total nap duration per 1 h awake span were statistically significantly higher in cancer patients than control subjects. In conclusion, the results of the present study document the disruption of the circadian rhythm in rest‐activity of cancer in‐patients, with a dampening of amplitude, lowering of mean level of activity, and phase advancement. These alterations of the circadian rhythm characteristics could be attributed to disease, irrespective of variability due to gender, sites of cancer, and timings of therapies. These results might help in designing patient‐specific chronotherapeutic protocols.     

Alterations of the characteristics of the circadian rest-activity rhythm of cancer in-patients

The aim of the present study was to evaluate the characteristics of the circadian rest-activity rhythm of cancer patients. Thirty-one in-patients, consisting of 19 males and 12 females, were randomly selected from the Regional Cancer Center, Pandit Jawaharlal Nehru Medical College, Raipur, India. The rest-activity rhythm was studied non-invasively by wrist actigraphy, and compared with 35 age-matched apparently healthy subjects (22 males and 13 females). All subjects wore an Actiwatch (AW64, Mini Mitter Co. Inc., USA) for at least 4-7 consecutive days. Fifteen-second epoch length was selected for gathering actigraphy data. In addition, several sleep parameters, such as time in bed, assumed sleep, actual sleep time, actual wake time, sleep efficiency, sleep latency, sleep bouts, wake bouts, and fragmentation index, were also recorded. Data were analyzed using several statistical techniques, such as cosinor rhythmometry, spectral analysis, ANOVA, Duncan's multiple-range test, and t-test. Dichotomy index (I相似文献   

Bone resorption is induced on the second day of bed rest: results of a controlled crossover trial.

The aim of the study was to analyze the kinetics of short-term changes in bone turnover. We studied in a randomized crossover design the effects of 6 days of bed rest on eight healthy male subjects (mean body wt: 70.1 +/- 5.7 kg; mean age: 25.5 +/- 2.9 yr). The metabolic ward period was divided into three parts: 4 ambulatory days, 6 days of either bed rest or non-bed rest periods, and 1 recovery day. The diet was identical in both bed rest and non-bed rest phases. Continuous urine collection started on the first day in the metabolic ward to analyze excretion of bone resorption markers, namely C-telopeptide (CTX) and N-telopeptide (NTX), creatinine, urea, and 3-methylhistidine. On the second ambulatory day and on the fifth day of bed rest or during the non-bed rest phase, blood was drawn to analyze bone formation markers and amino acid concentrations. Urinary calcium excretion was increased as early as the first day of bed rest (P < 0.01). CTX and NTX excretion stayed unchanged during the first 24 h of bed rest compared with the non-bed rest period. However, already on the second day, both resorption markers had increased significantly. NTX excretion increased by 28.7 +/- 14.0% (P < 0.01), whereas CTX excretion rose by 17.8 +/- 8.3% (P < 0.001). Creatinine, urea, and 3-methylhistidine excretion did not change. We conclude that 24 h of bed rest are sufficient to induce a significant rise in osteoclast activity in healthy subjects.     

Diurnal variation of aldosterone and plasma renin activity: timing relation to melatonin and cortisol and consistency after prolonged bed rest.

Exposure to prolonged bed rest is known to induce changes in the renin-angiotensin-aldosterone system (RAAS) by way of posture, sodium and potassium balance, and stress, which may have serious consequences for patients. We focused on the diurnal variation of the RAAS by investigating changes in the levels of plasma renin activity (PRA) and aldosterone; for comparison to markers of the intrinsic pacemaker and to stress, we measured melatonin and cortisol. PRA, aldosterone, melatonin, and cortisol were measured hourly in 10 normal subjects with standardized sleep patterns, posture, and diet at baseline and after 11 days of prolonged bed rest conducted under a light-dark cycle. Circadian characteristics of hormone secretion patterns were estimated by multiple harmonic regression with excellent goodness-of-fit measures. Variability in the melatonin and cortisol patterns across subjects was minimal. Even for pulsatile hormones, this technique successfully estimated the acrophase, which was the salient feature. Baseline hormone peak times started with melatonin near the middle of the sleep period, followed by PRA, then aldosterone, and then cortisol around wake time. Prolonged bed rest did not induce significant changes in any timing characteristic of the secretion patterns. Baseline and prolonged bed rest peak times for melatonin and cortisol and amplitude characteristics for all hormones were highly correlated, indicating consistency within individuals. These data provide strong evidence that prolonged bed rest of 11 days' duration does not disrupt either the timing characteristics of the RAAS or the intrinsic pacemaker.