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PubMed2003

Conduction velocity of nerve and muscle fiber action potentials after a space mission or a bed rest.

OBJECTIVE: The purpose of the present investigation was to study the readaptation of a human muscle after a prolonged stay in microgravity and after a bed rest of several months. METHODS: The surface electromyogram of the soleus muscle was recorded in 6 cosmonauts and 6 bed rest subjects at 5 different torque levels and, in addition, the direct muscle responses (M responses) to supramaximal stimulation of the posterior tibial nerve were also recorded in the bed rest subjects. In a supplementary experiment in normal subjects, M response was recorded with an array of electrodes. RESULTS: The median frequency (MF) of the power spectrum of the surface electromyogram was reduced, at all torque levels, immediately after the test period. In the bed rest subjects, the latency of the M response peaks and the inter-peak interval increased during the test period. Recovery to normal occurred within about 10 days. In the normal subjects, the peaks of the M response were conducted along the muscle with a velocity between 21 and 30 m/s. CONCLUSIONS: All these results point to a reduction of the conduction velocity in the branching axon terminals and in the muscle fibers during space missions and bed rest.

Action Potentials↗

PubMed2005

Comparison of segmental and global systemic ventricular function at rest and during dobutamine stress between patients with transposition and congenitally corrected transposition.

The aim of the study was to evaluate segmental and global right ventricular function at rest and during stress in patients having a systemic morphologically right ventricle. We studied 17 patients after atrial correction for transposition, 13 with congenitally corrected transposition, and 11 age-matched controls using cardiovascular magnetic resonance at rest and during stress with dobutamine given at 15 micrograms per kilogram per minute. Blood was drawn to obtain levels of brain natriuretic peptide. Right ventricular ejection fraction was calculated, and wall-motion and wall-thickening were assessed, in 4 segments of a midventricular slice. The findings for the systemic right ventricle were compared to the left ventricle in controls. Patients with transposition showed a decreased ejection fraction at rest (57 percent versus 69 percent, p equal to 0.005), decreased wall motion of the anterior, lateral and septal wall (p less than 0.01, p less than 0.01, and p less than 0.01) and decreased thickening of the lateral wall (p less than 0.01). Patients with congenitally corrected transposition showed normal ejection fraction, wall thickening, and wall motion at rest. During dobutamine stress, we found no significant differences in wall motion and thickening between the two groups. Ejection fraction, also increased to comparable values during stress, at 67 percent versus 66 percent, p not being significant. In both groups, we observed similarly increased levels of brain natriuretic peptide (p equal to 0.02 and 0.03, respectively). We conclude that only patients with transposition showed segmental wall motion and wall thickening abnormalities at rest. After dobutamine stress, however, segmental and global right ventricular dysfunction was similar in both groups.

Adolescent↗

PubMed1997

Implementation of technetium-99m MIBI SPECT imaging guidelines: optimizing the two day stress-rest protocol.

OBJECTIVES: In a previous study in 460 patients, we found that in patients with suspected or known coronary artery disease undergoing stress-rest technetium-99m sestamibi (MIBI) SPECT myocardial perfusion imaging, rest SPECT imaging could be withhold in approximately 20% of patients because of a completely normal stress study. The present study was set up to evaluate the consequences of the implementation of this finding in a subsequent population of patients, and to set standards for the variety of protocols now used for MIBI SPECT imaging. METHODS: Within a period of 4 months, 235 consecutive patients referred for MIBI SPECT scintigraphy were studied. All patients had stable cardiac chest pain and underwent symptom-limited exercise MIBI SPECT perfusion imaging. The stress SPECT images were reconstructed and evaluated immediately after acquisition of the images. In case of a clearly normal stress SPECT study, rest imaging was cancelled. RESULTS: Twenty-six of 235 patients (11%) had a completely normal stress MIBI SPECT study and the rest SPECT imaging procedure could be subsequently cancelled. In 20 patients (9%) the stress SPECT was inconclusive, and in 189 (80%) of patients stress imaging was clearly abnormal. In the first month of the study, the nuclear medicine physicians and cardiologists would interprete only 6% of the stress images as normal, while this number increased to 13% after 9 weeks, with a mean of 11% for the whole investigation period of 4 months. CONCLUSION: In patients undergoing stress MIBI SPECT imaging, it was found justified to cancel rest MIBI SPECT imaging in at least 11% of patients because of a completely normal stress SPECT. As 9% of the images were inconclusive, the number of normal stress images could theoretically increase to 20% if reliable measures are taken to improve reading accuracy. This number is in close agreement with the number of normal stress studies previously reported by our institution and would lead to a considerable reduction of radiation dose, costs, and increased convenience for an important subset of patients.

Adolescent↗

PubMed2000

The distribution of rest periods affects performance and adaptations of energy metabolism induced by high-intensity training in human muscle.

The effect of the distribution of rest periods on the efficacy of interval sprint training is analysed. Ten male subjects, divided at random into two groups, performed distinct incremental sprint training protocols, in which the muscle load was the same (14 sessions), but the distribution of rest periods was varied. The 'short programme' group (SP) trained every day for 2 weeks, while the 'long programme' group (LP) trained over a 6-week period with a 2-day rest period following each training session. The volunteers performed a 30-s supramaximal cycling test on a cycle ergometer before and after training. Muscle biopsies were obtained from the vastus lateralis before and after each test to examine metabolites and enzyme activities. Both training programmes led to a marked increase (all significant, P < 0.05) in enzymatic activities related to glycolysis (phosphofructokinase - SP 107%, LP 68% and aldolase - SP 46%, LP 28%) and aerobic metabolism (citrate synthase - SP 38%, LP 28.4% and 3-hydroxyacyl-CoA dehydrogenase - SP 60%, LP 38.7%). However, the activity of creatine kinase (44%), pyruvate kinase (35%) and lactate dehydrogenase (45%) rose significantly (P < 0.05) only in SP. At the end of the training programme, SP had suffered a significant decrease in anaerobic ATP consumption per gram muscle (P < 0.05) and glycogen degradation (P < 0.05) during the post-training test, and failed to improve performance. In contrast, LP showed a marked improvement in performance (P < 0.05) although without a significant increase in anaerobic ATP consumption, glycolysis or glycogenolysis rate. These results indicate that high-intensity cycling training in 14 sessions improves enzyme activities of anaerobic and aerobic metabolism. These changes are affected by the distribution of rest periods, hence shorter rest periods produce larger increase in pyruvate kinase, creatine kinase and lactate dehydrogenase. However, performance did not improve in a short training programme that did not include days for recovery, which suggests that muscle fibres suffer fatigue or injury.

Adaptation, Physiological↗

PubMed2000

No effect of venoconstrictive thigh cuffs on orthostatic hypotension induced by head-down bed rest.

Orthostatic intolerance (OI) is the most serious symptom of cardiovascular deconditioning induced by head-down bed rest or weightlessness. Wearing venoconstrictive thigh cuffs is an empirical countermeasure used by Russian cosmonauts to limit the shift of fluid from the lower part of the body to the cardio-cephalic region. Our aim was to determine whether or not thigh cuffs help to prevent orthostatic hypotension induced by head-down bed rest. We studied the effect of thigh cuffs on eight healthy men. The cuffs were worn during the day for 7 days of head-down bed rest. We measured: orthostatic tolerance (stand tests and lower body negative pressure tests), plasma volume (Evans blue dilution), autonomic influences (plasma noradrenaline) and baroreflex sensitivity (spontaneous baroreflex slope). Thigh cuffs limited the loss of plasma volume (thigh cuffs: -201 +/- 37 mL vs. control: -345 +/- 42 mL, P < 0.05), the degree of tachycardia and reduction in the spontaneous baroreflex sensitivity induced by head-down bed rest. However, the impact of thigh cuffs was not sufficient to prevent OI (thigh cuffs: 7.0 min of standing time vs. control: 7.1 min). Decrease in absolute plasma volume and in baroreflex sensitivity are known to be important factors in the aetiology of OI induced by head-down bed rest. However, dealing with these factors, using thigh cuffs for example, is not sufficient to prevent OI. Other factors such as venous compliance, microcirculatory changes, peripheral arterial vasoconstriction and vestibular afferents must also be considered.

Adult↗

PubMed2001

Inactivity and muscle: effect of resistance training during bed rest on muscle size in the lower limb.

The present study aimed to investigate the effect of dynamic leg press training on the physiological cross-sectional areas (PCSAs) of human lower limb muscles during 20 days of 6 degrees head-down tilt bed rest. Five healthy men comprised the resistance training group (BR-Tr) and data from two previous studies were used to derive a 10-man control group (BR-Cont). The BR-Tr performed two sessions (morning and afternoon session) of dynamic leg press action including knee extension and plantar flexion daily for the bed rest period: (1) three sets of 10 repetitions at 90% of maximum load and (2) 40% of maximum load to exhaustion. The PCSAs of the knee extensor (KE), knee flexor (KF), plantar flexor (PF), and dorsiflexor muscle groups were estimated using serial axial magnetic resonance (MR) images of the right-thigh and leg. After the bed rest period, the BR-Tr showed a significant increase in the PCSA of the KE. Although PCSA of the KF in two groups significantly decreased after bed rest, percentage of change in PCSA of the biceps femoris (long head) and semitendinosus muscles in the BR-Tr, which occupied approximately 70% of the KF, was significantly higher than those in the BR-Cont. Both the BR-Tr and BR-Cont groups showed significant decreases in the PCSA of PF with similar magnitude of 11.6% (P < 0.001) and 11.9% (P < 0.001), respectively. These results suggest that dynamic leg press training during bed rest can prevent deteriorating of the KE and a part of KF, but not the calf muscles.

Adult↗

PubMed2000

Rest and activity states in a gray whale.

The behaviour of a female gray whale (Eschrichtius robustus) that had been rescued 14 months previously was recorded continuously on a video-recorder for 9 days at 'Sea World' in San Diego. On average, during the first six recording days, active wakefulness accounted for 37.9 +/- 1.7% of each 24 h; transitional stage for 17.4 +/- 1.4% and rest for 41.2 +/- 1.7%. In the rest stage the whale was lying on the bottom of the pool (13.2 +/- 1.7%) or hanging on the surface (28. 0 +/- 1.7%). During the rest stage, it was immobile most of the time and moved only for respiration. In the rest stage both eyes could be open, one eye could be open while the other was closed or, more rarely, both eyes could be closed. Characteristic jerks of the head, neck and sometimes of the whole body were observed in the whale during the rest stage. Most jerks were single and only 10% of all jerks were serial (occurring within 10 s of a prior jerk). Eyelid movements accompanied 40% of jerks. In two episodes, intense jerks followed each other continuously for 3 and 4 s and were accompanied by eyelid movements. These jerks resembled the twitches characteristic of paradoxical sleep in terrestrial mammals. During these episodes the whale was falling slowly onto its side and subsequently started to swim in the pool.

Animals↗

PubMed2003

Effects of 3 days of "postoperative" low caloric feeding with or without bed rest on insulin sensitivity in healthy subjects.

BACKGROUND AND AIMS: Insulin resistance after surgery is caused by the surgical trauma and presumably also by other factors, such as starvation and immobilization. The purpose of this study was to evaluate the effect of traditional postsurgical low caloric feeding and bed rest on insulin sensitivity and substrate utilization, in younger and older healthy subjects. METHODS: Twelve healthy subjects underwent hyperinsulinaemic, normoglucaemic clamps and indirect calorimetry before and after 3 days of bed rest and low caloric feeding. Six of the subjects underwent a second study with 3 days of low caloric feeding without bed rest. RESULTS: Insulin sensitivity decreased by 57+/-16 % after low caloric feeding combined with bed rest, with no difference between age groups, and by 56+/-9% after low caloric feeding only. Glucose oxidation decreased, while fat oxidation increased. No significant differences were seen between age groups or between the protocols. CONCLUSIONS: Low caloric feeding, a commonly used nutritional routine in clinical practice, induce marked alterations in insulin sensitivity and substrate utilization. Increasing age or bed rest did not seem to influence this development. These findings suggest that the routine low caloric feeding is capable of contributing to postoperative insulin resistance.

Adult↗

PubMed1997

Exercise-induced increase in serum creatine kinase is modified by subsequent bed rest.

This study was designed to find out if bed rest, which is known to markedly reduce peripheral lymph flow, immediately after strenuous exercise could affect the behaviour of creatine kinase activity (CK) in serum. Eleven endurance athletes performed an 18 km cross-country run, after which six of the subjects were placed in bed rest group (BR) for 23 hours, while a group of five control subjects maintained their normal habitual activity (C). After the bed rest all subjects performed a light jogging bout for 45 min. Seven hours after the exercise serum CK was increased threefold (p < 0.05) in both groups. During the next 16 hours serum CK increased further 30% in C (p < 0.05) but decreased (p < 0.05) in a similar magnitude in BR. Light jogging elicited a transient CK increase of 16% (p < 0.05) in C, but there was no change in BR. The fact that serum CK increased similarly in both groups during the first hours after the exercise shows that the transport of CK from muscles into circulation can be maintained for some hours despite absence of muscular activity. However, the later post-exercise serum CK response may be diminished by bed rest (effect of posture and/or lack of muscle function). The reduced response is also seen in the CK response to a repeated exercise. These observations suggest that a short-term physical inactivity (bed rest) may reduce both the lymphatic transport of CK and the release of enzyme from muscle fibres.

Adult↗

PubMed1986

How many days of bed rest for acute low back pain? A randomized clinical trial.

Bed rest is usually recommended for acute low back pain. Although the optimal duration of bed rest is uncertain, a given prescription may directly affect the number of days lost from work or other activities. In a randomized trial, we compared the consequences of recommending two days of bed rest (Group I) with those of recommending seven days (Group II). The subjects were 203 walk-in patients with mechanical low back pain; 78 percent had acute pain (less than or equal to 30 days), and none had marked neurologic deficits. Follow-up data were obtained at three weeks (93 percent) and three months (88 percent). Although compliance with the recommendation of bed rest was variable, patients randomly assigned to Group I missed 45 percent fewer days of work than those assigned to Group II (3.1 vs. 5.6 days, P = 0.01), and no differences were observed in other functional, physiologic, or perceived outcomes. For many patients without neuromotor deficits, clinicians may be able to recommend two days of bed rest rather than longer periods, without any perceptible difference in clinical outcome. If widely applied, this policy might substantially reduce absenteeism from work and the resulting indirect costs of low back pain for both patients and employers.

Absenteeism↗

PubMed1995

The treatment of acute low back pain--bed rest, exercises, or ordinary activity?

BACKGROUND: Bed rest and back-extension exercises are often prescribed for patients with acute low back pain, but the effectiveness of these two competing treatments remains controversial. METHODS: We conducted a controlled trial among employees of the city of Helsinki, Finland, who presented to an occupational health care center with acute, nonspecific low back pain. The patients were randomly assigned to one of three treatments: bed rest for two days (67 patients), back-mobilizing exercises (52 patients), or the continuation of ordinary activities as tolerated (the control group; 67 patients). Outcomes and costs were assessed after 3 and 12 weeks. RESULTS: After 3 and 12 weeks, the patients in the control group had better recovery than those prescribed either bed rest or exercises. There were statistically significant differences favoring the control group in the duration of pain, pain intensity, lumbar flexion, ability to work as measured subjectively, the Oswestry back-disability index, and number of days absent from work. Recovery was slowest among the patients assigned to bed rest. The overall costs of care did not differ significantly among the three groups. CONCLUSIONS: Among patients with acute low back pain, continuing ordinary activities within the limits permitted by the pain leads to more rapid recovery than either bed rest or back-mobilizing exercises.

Activities of Daily Living↗

PubMed2003

Comparison of abdominal aortic hemodynamics between men and women at rest and during lower limb exercise.

INTRODUCTION: Biologic variations between men and women have been hypothesized to contribute to the differences in atherosclerosis epidemiology of the two genders. Hemodynamics are also hypothesized to play an important role in the localization of atherosclerosis in the abdominal aorta. However, the hemodynamics of men and women have not been compared at this location at rest or during lower limb exercise conditions. METHODS: A magnetic resonance-compatible exercise bicycle, magnetic resonance imaging techniques, and custom data processing software were used to quantify blood flow rate, wall shear stress, and oscillations in flow and wall shear stress at the supraceliac and infrarenal levels of the abdominal aorta of young healthy men and women at rest and during lower limb exercise. RESULTS: Heart rate increased from 73 +/- 6.2 bpm at rest to 110 +/- 8.8 bpm during exercise (P <.0001). No statistical differences were found at the infrarenal level for mean blood flow rate (men, 0.9 +/- 0.4 L/min; women, 0.8 +/- 0.4 L/min) or mean wall shear stress (men, 1.2 +/- 0.5 dynes/cm(2); women, 1.4 +/- 0.7 dynes/cm(2)) at rest or mean blood flow rate (men, 5.9 +/- 1.3 L/min; women, 5.2 +/- 0.8 L/min) or mean wall shear stress (men, 5.1 +/- 0.8 dynes/cm(2); women, 5.4 +/- 2.1 dynes/cm(2)) during exercise. Also, no differences were seen in temporal flow and wall shear stress oscillations between men and women at rest or during exercise. Similarly, no significant hemodynamic differences were found between the genders at the supraceliac level. CONCLUSION: These similarities suggest that hemodynamics may not play a significant role in abdominal aortic disease differentiation between the genders and that biologic factors may be more important.

Adult↗

PubMed2006

Consistent resting-state networks across healthy subjects.

Functional MRI (fMRI) can be applied to study the functional connectivity of the human brain. It has been suggested that fluctuations in the blood oxygenation level-dependent (BOLD) signal during rest reflect the neuronal baseline activity of the brain, representing the state of the human brain in the absence of goal-directed neuronal action and external input, and that these slow fluctuations correspond to functionally relevant resting-state networks. Several studies on resting fMRI have been conducted, reporting an apparent similarity between the identified patterns. The spatial consistency of these resting patterns, however, has not yet been evaluated and quantified. In this study, we apply a data analysis approach called tensor probabilistic independent component analysis to resting-state fMRI data to find coherencies that are consistent across subjects and sessions. We characterize and quantify the consistency of these effects by using a bootstrapping approach, and we estimate the BOLD amplitude modulation as well as the voxel-wise cross-subject variation. The analysis found 10 patterns with potential functional relevance, consisting of regions known to be involved in motor function, visual processing, executive functioning, auditory processing, memory, and the so-called default-mode network, each with BOLD signal changes up to 3%. In general, areas with a high mean percentage BOLD signal are consistent and show the least variation around the mean. These findings show that the baseline activity of the brain is consistent across subjects exhibiting significant temporal dynamics, with percentage BOLD signal change comparable with the signal changes found in task-related experiments.

Brain↗

PubMed2024

Neuronal differentiation requires BRAT1 complex to remove REST from chromatin.

Repressor element-1 silencing transcription factor (REST) is required for the formation of mature neurons. REST dysregulation underlies a key mechanism of neurodegeneration associated with neurological disorders. However, the mechanisms leading to alterations of REST-mediated silencing of key neurogenesis genes are not known. Here, we show that BRCA1 Associated ATM Activator 1 (BRAT1), a gene linked to neurodegenerative diseases, is required for the activation of REST-responsive genes during neuronal differentiation. We find that INTS11 and INTS9 subunits of Integrator complex interact with BRAT1 as a distinct trimeric complex to activate critical neuronal genes during differentiation. BRAT1 depletion results in persistence of REST residence on critical neuronal genes disrupting the differentiation of NT2 cells into astrocytes and neuronal cells. We identified BRAT1 and INTS11 co-occupying the promoter region of these genes and pinpoint a role for BRAT1 in recruiting INTS11 to their promoters. Disease-causing mutations in BRAT1 diminish its association with INTS11/INTS9, linking the manifestation of disease phenotypes with a defect in transcriptional activation of key neuronal genes by BRAT1/INTS11/INTS9 complex. Finally, loss of Brat1 in mouse embryonic stem cells leads to a defect in neuronal differentiation assay. Importantly, while reconstitution with wild-type BRAT1 restores neuronal differentiation, the addition of a BRAT1 mutant is unable to associate with INTS11/INTS9 and fails to rescue the neuronal phenotype. Taken together, our study highlights the importance of BRAT1 association with INTS11 and INTS9 in the development of the nervous system.

Humans↗

PubMed1985

Resting heat production in Bos indicus and their F1 crosses with exotic breeds at a thermoneutral environment.

Resting heat production, 18 h post-feeding, was studied in Hariana cattle (Bos indicus; Zebu) and in their F1 crosses with Jersey, Brown Swiss and Holstein Friesian, at 18.5 degrees ambient temperature in a psychometric chamber at different ages. There was no significant change in the resting heat production on a per kg body-weight (W) 0.75 per 24 h basis from 16-19 to 37-40 months of age in any of the genetic groups. The daily resting heat production, however, increased with increases in body-weight and age. The resting heat production in all three F1 crosses was higher than that in Hariana cattle. Among the crosses, the resting heat production was highest in the Holstein Friesian X Hariana and lowest in the Jersey X Hariana. Metabolizable energy (ME) intake per 24 h was significantly different between genetic groups and in different age groups. However, ME intake per kg W 0.75 was not significantly different between genetic groups.

Aging↗

PubMed2001

Impact of added rest breaks on the productivity and well being of workers.

The impact of frequent short rest breaks on the productivity and well being of a group of 30 workers in a meat-processing plant was studied. Two rest break schedules were tested, both of which provided 36 min of extra break time over the regular break schedule (30-min lunch and two 15-min breaks). In the first experimental rest break schedule, workers were given 12 3-min breaks evenly distributed over the workday (3-min break for every 27 min of work). In the second schedule, workers were given four 9-min breaks evenly distributed over the workday (9-min break every 51 min of work). Outcome measures included production rate and discomfort and stress ratings. Results showed that neither of the two experimental rest break schedules had a negative effect on production, and the 9-min break schedule improved discomfort ratings for the lower extremities. The workers in the study mostly preferred the 9-min rest break schedule, indicating that workers in general might not as readily accept fragmentation of break time into short, frequent breaks.

Adult↗

PubMed1993

A psychophysical approach to determine the frequency and duration of work-rest schedules for manual handling operations.

The primary objectives of this study were: (1) to test whether rest allowances could be ascertained using a psychophysical methodology; and (2) to examine the effects of gender and frequency of handling on work-rest schedules. Two experiments were conducted, each experimental session at 4h. A psychophysical methodology was used where the subject was given control of the working and resting durations. The results of the study indicated that: (1) the total working time decreased and the total resting time decreased with an increase in the frequency of handling; (2) high frequency tasks required more frequent rest allowances; (3) for the same manual handling tasks, women needed more frequent and longer allowances than men; (4) experience with the manual handling of material reduced the variability collected from the psychophysical methodology. The application of the psychophysical methodology in industry is discussed.

Adult↗

PubMed1995

Resting energy expenditure of patients with gynecologic malignancies.

OBJECTIVE: To evaluate resting energy expenditure compared to predicted energy expenditure in patients with cervical or ovarian carcinoma who require specialized nutritional support. DESIGN: Women with biopsy-proven cervical or ovarian carcinoma referred to the Nutrition Support Service were studied. Resting energy expenditure was measured by indirect calorimetry and compared to predicted energy expenditure (PEE) as determined by the Harris-Benedict equation for females. RESULTS: Sixty one patients were studied. Patients with ovarian cancer (n = 31) had a significantly higher measured resting energy expenditure (% PEE) than patients with cervical cancer (109 +/- 18% vs. 98 +/- 16%, p < 0.02, respectively). This difference in measured resting energy expenditure between groups could not be explained by differences in the extent of disease, nutritional status, body temperature, or nutrient intake between groups. A greater proportion of patients with ovarian cancer were hypermetabolic (> 110% of predicted) in comparison to patients with cervical cancer (55% vs. 13%, p < 0.01, respectively). Measured resting energy expenditure varied between 53% and 157% of predicted for the entire population. CONCLUSION: Ovarian cancer patients are more hypermetabolic than cervical cancer patients. The Harris-Benedict equation for females is a unreliable estimate of caloric expenditure in patients with cervical or ovarian cancer receiving specialized nutritional support.

Adult↗