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PubMed2000

Perception and practice of rest during pregnancy among mothers and family decision-makers.

The incidence of low birthweight (LBW) in Bangladesh is one of the highest in the world. Inadequate rest of the mothers during pregnancy is a contributing factor to LBW. To assess the perception and practice of rest during pregnancy, 136 mothers and family members who make important decisions on family matter (FDM) were studied in rural Bangladesh. Eighty per cent of mothers perceived the importance of rest during pregnancy, whereas only 29 per cent practised rest (p < 0.003). Of the mothers who lacked perception, none practised. Eighty-five per cent of FDM perceived rest as important, yet only 27 per cent practised rest. Mothers' education and socioeconomic status were significantly associated with perception (p < 0.028,p < 0.001) and practice (p < 0.008,p < 0.006) of rest. The mother's education was also significantly (p < 0.000) associated with the socioeconomic status of the family. Our study suggests that the inability to take rest was due to workload at home, illiteracy, low socioeconomic status and failure of family members to share the workload.

Adolescent↗
PubMed2002

Minimum rest period for strength recovery during a common isokinetic testing protocol.

PURPOSE: The intent of this investigation was to determine the minimal time for a between sets rest period during a common isokinetic knee extension strength-testing protocol. Based on a review of the literature, a set was considered a group of four maximal coupled contractions at a specific velocity. METHODS: Eleven normal, healthy college-age men underwent unilateral knee extension testing to determine their individual isokinetic peak torque at 60, 120, 180, 240, and 300 degrees.s-1. Velocities were administered in ascending order. Between sets, rest periods of 15, 60, 180, and 300 s were assigned to subjects in a counterbalanced fashion. RESULTS: There were no differences in peak torque at the beginning velocity of 60 degrees.s-1 among any of the rest periods. At 120 degrees.s-1, peak torque production during the 15-s rest period trial was similar to 60 s but lower than 180 and 300 s. Peak torques at 180, 240, and 300 degrees.s-1 produced during the 15-s rest period test were significantly lower than measured torques at the same velocities during the 60, 180, and 300-s rest period tests (P < 0.05). There were no differences in peak torque production between the 60, 180, and 300-s rest period tests. CONCLUSION: These data demonstrate that during a common isokinetic strength testing protocol a between set rest period of at least 60 s is sufficient for recovery before the next test set.

Adult↗
PubMed1995

Whole-body 201Tl scintigraphy during one-leg exercise and at rest in normal subjects: estimation of regional blood flow changes.

To determine the effect of exercise intensity on regional blood flow in exercising and resting leg muscles and organs, we assessed relative changes in the regional distribution of 201Tl during one-leg ergometer exercise and at rest by whole-body scintigraphy as an estimate of regional blood flow changes in 10 healthy males. The regional 201Tl activity was expressed as a percentage of the whole-body activity, and relative changes in each region were compared to those at the anaerobic threshold (AT) and at peak exercise. In the legs, the distribution of 201Tl in the exercising thigh and calf increased significantly at the AT to 390.7 and 219.2% respectively of resting levels (both P < 0.01), but remained unchanged the resting thigh from rest to peak exercise. Conversely its distribution in the resting calf decreased significantly at the AT to 60.0% of the resting level (P < 0.01). However, there were no significant differences between AT and peak exercise. In the organs, the distribution of 201Tl in the lung, liver, spleen and kidneys decreased significantly at the AT to 88.4 +/- 10.4%, 67.0 +/- 11.5%, 62.4 +/- 11.8% and 67.0 +/- 8.6% respectively of resting levels (all P < 0.01). Redistribution of blood flow to the exercising leg occurs predominantly during mild to moderate exercise. Therefore, blood flow in the leg during strenuous exercise depends primarily upon an increase in cardiac output. The splanchnic organs are the major sources of redistribution.

Adult↗
PubMedDate not supplied

Depression, mood state, and back pain during microgravity simulated by bed rest.

OBJECTIVE: The objective of this study was to develop a ground-based model for spinal adaptation to microgravity and to study the effects of spinal adaptation on depression, mood state, and pain intensity. METHODS: We investigated back pain, mood state, and depression in six subjects, all of whom were exposed to microgravity, simulated by two forms of bed rest, for 3 days. One form consisted of bed rest with 6 degrees of head-down tilt and balanced traction, and the other consisted of horizontal bed rest. Subjects had a 2-week period of recovery between the studies. The effects of bed rest on pain intensity in the lower back, depression, and mood state were investigated. RESULTS: Subjects experienced significantly more intense lower back pain, lower hemisphere abdominal pain, headache, and leg pain during head-down tilt bed rest. They had higher scores on the Beck Depression Inventory (ie, were more depressed) and significantly lower scores on the activity scale of the Bond-Lader questionnaire. CONCLUSIONS: Bed rest with 6 degrees of head-down tilt may be a better experimental model than horizontal bed rest for inducing the pain and psychosomatic reactions experienced in microgravity. Head-down tilt with balanced traction may be a useful method to induce low back pain, mood changes, and altered self-rated activity level in bed rest studies.

Adult↗
PubMed1999

Biomechanics of increased exposure to lumbar injury caused by cyclic loading. Part 2. Recovery of reflexive muscular stability with rest.

STUDY DESIGN: Electromyographic responses from the lumbar multifidus muscle of the cat were recorded in vivo during 50 minutes of cyclic loading followed by 2 hours of rest. OBJECTIVE: To determine the rate of recovery of reflexive muscular stabilizing activity resulting from rest after viscoelastic laxity induced by 50 minutes of cyclic loading. SUMMARY OF BACKGROUND DATA: Muscular forces from agonists and antagonists were repeatedly shown to be the most significant stabilizing structures of the lumbar spine. Reflexive muscular coactivation force from the multifidus muscle elicited by mechanoreceptors in the spinal viscoelastic structures were, however, shown to diminish drastically with the onset of laxity in the viscoelastic structures. Data describing the rate of recovery of reflexive muscular coactivation forces resulting from rest after cyclic loading were not found. METHODS: Cyclic loading of the lumbar spine at 0.25 Hz was applied to L4-L5 for 50 minutes while electromyograms from the multifidus muscles of L1-L2 to L6-L7 were recorded. A rest period of up to 2 hours was given, during which electromyographic responses and load were measured every 10 minutes to sample recovery of laxity and reflexive muscular activity. RESULTS: Load and electromyographic response demonstrated an exponential decrease during the 50 minutes of cyclic loading. The first 10 minutes of rest allowed a significant recovery in laxity and muscle activity, with additional slow recovery over the next 20 to 30 minutes. The electromyographic response and load were increasing at an extremely slow rate thereafter. Overall, 2 hours of rest yielded only a 20% to 30% recovery in electromyographic response. Full recovery was never observed. A biexponential model was developed to predict loss and recovery of reflexive muscular activity and viscoelastic tension with laxity. CONCLUSIONS: Laxity in the viscoelastic structures of the lumbar spine desensitizes the mechanoreceptors within and causes loss of reflexive stabilizing forces from the multifidus muscles. The first 10 minutes of rest after cyclic loading results in fast partial recovery of muscular activity. However, full recovery is not possible even with rest periods twice as long as the loading period, placing the spine at an increased risk of instability, injury, and pain.

Animals↗
PubMed2000

The Cochrane review of bed rest for acute low back pain and sciatica.

STUDY DESIGN: A systematic review within the Cochrane Collaboration Back Review Group. OBJECTIVES: To assess the effects of advice to rest in bed for patients with acute low back pain (LBP) or sciatica. SUMMARY OF BACKGROUND DATA: Low back pain is a common reason for consulting a health care provider, and advice on daily activities constitutes an important part in the primary care management of low back pain. METHODS: All randomized studies available in systematic searches (electronic databases, contact with authors, and reference lists) were included. Two reviewers independently selected trials for inclusion, assessed the validity of included trials, and extracted data. Investigators were contacted to obtain missing information. RESULTS: Nine trials with a total of 1435 patients were included. Four trials compared bed rest with advice to stay active, and the overall results were heterogeneous. Overall, results from two high-quality studies indicate no difference in pain intensity at the 3-week follow-up (standardized mean difference 0.0; 95% confidence interval [CI] -0.3, 0.2]), and a small difference in functional status in favor of staying active (weighted mean difference 3.2 [on a 0-100 scale] 95% CI 0.6, 5.8). In two high-quality trials no differences were reported in pain intensity between 2-3 days of bed rest and 7 days of bed rest. In another two high-quality trials, no differences were found between bed rest and exercises in pain intensity or functional status. CONCLUSION: Bed rest compared with advice to stay active at best has no effect, and at worst may have slightly harmful effects on LBP. There is not an important difference in the effects of bed rest compared with exercises in the treatment of acute low back pain, or 7 days compared with 2-3 days of bed rest in patients with low back pain of different durations with and without radiating pain.

Activities of Daily Living↗
PubMed2005

The updated cochrane review of bed rest for low back pain and sciatica.

STUDY DESIGN: A systematic review within the Cochrane Collaboration Back Review Group. OBJECTIVES: To report the main results from the updated version of the Cochrane Review on bed rest for low back pain. SUMMARY OF BACKGROUND DATA: There has been a growing amount of evidence showing that bed rest is not beneficial for people with low back pain. However, existing systematic reviews are unclear regarding the effects of bed rest for different types of low back pain. METHODS: All randomized studies available in systematic searches up to March 2003 were included. Two reviewers independently selected trials for inclusion assessed the validity of included trials and extracted data. Investigators were contacted to obtain missing information. RESULTS: Two new trials comparing advice to rest in bed with advice to stay active were included. There is high quality evidence that people with acute low back pain who are advised to rest in bed have a little more pain (standardized mean difference 0.22, 95% confidence interval: 0.02-0.41) and a little less functional recovery (standardized mean difference 0.29, 95% confidence interval: 0.05-0.45) than those advised to stay active. For patients with sciatica, there is moderate quality evidence of little or no difference in pain (standardized mean difference -0.03, 95% confidence interval: -0.24-0.18) or functional status (standardized mean difference 0.19, 95% confidence interval: -0.02-0.41) between bed rest and staying active. CONCLUSION: For people with acute low back pain, advice to rest in bed is less effective than advice to stay active. For patients with sciatica, there is little or no difference between advice to rest in bed and advice to stay active.

Adolescent↗
PubMed1984

Hemodynamic effects of verapamil in essential hypertension at rest and during exercise.

In recent years the calcium antagonist verapamil has been used in the treatment of essential hypertension. Relatively little work has been done to elucidate its long-term haemodynamic effects at rest and during exercise. Ten males with previously untreated essential hypertension in WHO stage I, aged 35-55 years, were studied on an outpatient basis. Oxygen consumption, heart rate, cardiac output ( Cardiogreen ) and intra-arterial brachial pressure were recorded at rest in the supine and sitting position and during steady state work at 50, 100 and 150 W. As expected, the hypertension was associated with an increase in total peripheral resistance. The subjects were treated with verapamil 120-240 mg daily as the sole drug for one year. The haemodynamic study was then repeated. One subject demonstrated a slight increase in blood pressure at rest and during exercise, while there was a blood pressure reduction in the other 9. The nonresponding patient was excluded from the statistical evaluation. The main results were as follows: There was a statistically significant reduction in systolic, diastolic and mean arterial pressure at rest as well as during exercise. The reductions reached about 10% at rest, slightly less during exercise. The blood pressure reduction was associated with a statistically significant reduction in total peripheral resistance at rest only. During exercise, the reduction in resistance was modest (about 5%). The heart rate was practically unchanged during supine rest, but decreased about 8% at rest sitting and during exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2006

Uterine blood flow during supine rest and exercise after 28 weeks of gestation.

OBJECTIVE: To test the null hypothesis that, after 28 weeks of gestation, uterine blood flow during supine rest and supine exercise is no different than uterine blood flow at left-lateral rest. DESIGN: In vivo experimental study in pregnant women. SETTING: Department of Obstetrics, MetroHealth Medical Center, Cleveland, OH, USA. POPULATION: Fourteen, physically active, late-pregnant women who continued supine exercise throughout gestation. METHODS: Studies were carried out between 29 and 38 weeks of gestation. Maternal blood pressure, maternal heart rate, and ultrasound estimates of volume blood flow in the right ascending branch of the uterine artery were obtained serially at rest in the left-lateral position, at rest in the supine position, during and immediately after 10 minutes of supine exercise, and again at rest in the left-lateral position. Exercise sessions included alternating 60- to 90-second periods of abdominal crunches and leg exercise at moderate/high intensity (Borg's rating of perceived exertion 14 +/- 1). MAIN OUTCOME MEASURES: Blood pressure, heart rate, and uterine artery volume flow. RESULTS: Data are presented as the mean +/- SD. Maternal heart rate and blood pressure were unchanged at supine rest but increased during supine exercise (heart rate increased from 76 +/- 9 to 98 +/- 12 beats per minute, mean arterial pressure increased from 81 +/- 6 to 102 +/- 12 mmHg). Volume flow fell from 410 +/- 93 to 267 +/- 73 cc/minute after 5 minutes of supine rest and then, during supine exercise, increased to 355 +/- 125 cc/minute. Uterine artery luminal diameter and blood flow correlated directly with tissue weights at birth (r(2) values between 0.32 and 0.59). CONCLUSIONS: In physically active women, uterine blood flow decreases during both supine rest and supine exercise but the decrease in the former is twice that seen in the latter.

Adult↗
PubMed1996

Women's experience of bed rest in high-risk pregnancy.

OBJECTIVE: To explore women's experience of bed rest in high risk pregnancy. DESIGN: Naturalistic, qualitative. SAMPLE, SETTING: Twelve adult, pregnant women on prescribed bed rest of a minimum of 20 hours per day and for at least 3-weeks duration were interviewed in one Western state of the U.S.A. regarding their experiences. FINDINGS: Three major themes were perceptions of high risk pregnancy, perceptions of bed rest, and the experience of time and restricted movement. The women described a high level of physical, emotional, familial, and economic hardship resulting from the bed-rest experience. Having adequate income, health insurance, and a supportive relative to take over household responsibilities were dimensions of successful maintenance of bed rest in the women. CONCLUSIONS: The routine obstetric procedure of bed-rest should be reevaluated in light of its lack of demonstrated effectiveness and potential to seriously harm women and their families. CLINICAL IMPLICATIONS: Women should be fully informed about controversies surrounding the efficacy of bed rest in pregnancy and encouraged to participate in decisions when complications occur regarding the prescription of prolonged bed rest.

Adult↗
PubMed1974

Blood flow in resting (contralateral) arm and leg during isometric contraction.

1. Blood flow in resting forearm and calf were measured plethysmographically in healthy young men during isometric contraction performed both as a handgrip and as a dorsiflexion of the foot. The isometric contraction was maintained for 2 min at one third maximal voluntary contraction for the handgrip and half maximal voluntary contraction for the dorsiflexion of the foot. In some experiments the possible influence on blood flow of inadvertent muscle activation in the resting limb was checked by recording the e.m.g.2. Both handgrip and dorsiflexion of the foot produced substantial increases in heart rate and mean arterial pressure, the pressure rise being almost linear with time throughout the contraction.3. Isometric contraction produced a rapid increase in forearm blood flow which reached a maximum on average two and a half times the resting value after 1 min and then declined slightly. Similar increases in forearm blood flow were produced by handgrip and dorsiflexion of the foot.4. Unlike in the resting forearm, the blood flow in the resting calf increased only slightly during the first minute of contraction and then decreased again to the resting level.5. The flow increase in the resting limbs could not be ascribed to inadvertent muscle activation as judged from the e.m.g. recordings.6. It is concluded that isometric muscle contraction produces a rapid increase in blood flow in the resting forearm, but only a very slight flow increase in the calf. Since the flow increased faster than the arterial pressure it must to a certain extent be induced by active neurogenic vasodilatation. Similarly, the relative flow decrease during the latter half of the contraction concomitantly with a progressively rising arterial pressure suggests that the neurogenic effect on the resistance vessels changes character, becoming more vasoconstrictive, and this might be related to increased effort in sustaining the contraction.

Adult↗
PubMed1994

Effect of raised potassium on ventilation in euoxia, hypoxia and hyperoxia at rest and during light exercise in man.

The purpose of this study was to determine whether changes in arterial plasma potassium concentration [K+]a affect expired ventilation (VE) in euoxia, hypoxia and hyperoxia during rest and light exercise in humans. Three periods of ventilatory measurements were undertaken in eight healthy subjects at rest and in seven other subjects during cycle ergometry (70 W). The first period of measurement was before the ingestion of 64 mmol of potassium chloride (KCl), the second 20 min after ingestion of KCl when [K+]a levels were elevated, and the third 3 h after the ingestion of KCl when [K+]a had returned substantially to normal. During each period, end-tidal PO2 was cycled between euoxia, hypoxia and hyperoxia, whilst the end-tidal PCO2 was maintained constant. The acute ventilatory response to hypoxia (AHVR) was calculated as the difference in VE during hypoxia and hyperoxia within each period of measurement. Oral KCl produced a 1.3 +/- 0.2 mM (mean +/- S.E.M.) increase in [K+]a at rest and a 0.8 +/- 0.2 mM increase during exercise. There was no significant difference in ventilation during euoxia between the three periods of measurement at rest or during exercise. There was a significant increase in AHVR with the rise in [K+]a of 21 min-1 mM-1 at rest (arterial PO2 during hypoxia ca 57 Torr) and 10 l min-1 mM-1 during exercise (arterial PO2 during hypoxia ca 52 Torr). There was a significant difference in the absolute increase in AHVR with [K+]a between rest and exercise, but this difference was not significant if the increase in AHVR with [K+]a was expressed as a percentage of the initial AHVR. We conclude that changes in [K+]a of the order of 1 mM have little effect on euoxic ventilation at rest or during light exercise in humans. We also conclude that [K+]a changes of this order increase AHVR at rest and during light exercise and that increases in [K+]a contribute to the increase in AHVR with exercise in humans.

Adult↗
PubMed2002

Whole body and leg acetate kinetics at rest, during exercise and recovery in humans.

We have used a constant [1,2-(13)C]acetate infusion (0.12 micromol x min(-1) x kg( 1)) for 2 h at rest, followed by 2 h of one-legged knee-extensor exercise at 65% of leg maximal workload, and 3 h of recovery in six post-absorptive volunteers to quantify whole-body and leg acetate kinetics and determine whether the whole-body acetate correction factor can be used to correct leg substrate oxidation. The acetate whole-body rate of appearance (R(a)) was not significantly different at rest, during exercise or during recovery (365-415 micromol x min(-1)). The leg net acetate uptake was similar at rest and during recovery (approximately 10 micromol x min(-1)), but increased approximately 5-fold with exercise. At rest the leg acetate uptake (approximately 15 micromol x min(-1)) and release (approximately 5 micromol x min(-1)) accounted for 4 and 1.5 % of whole-body acetate disposal (R(d)) and R(a), respectively. When the leg acetate kinetics were extrapolated to the total body skeletal muscle mass, then skeletal muscle accounted for approximately 16 and approximately 6% of acetate R(d) and R(a). With exercise, leg acetate uptake increased approximately 6-fold, whereas leg acetate release increased 9-fold compared with rest. Whole-body acetate carbon recovery increased with time of infusion at rest and during recovery from 21% after 1.5 h of infusion to 45% in recovery after 7 h of infusion. Leg and whole-body acetate carbon recovery were similar under resting conditions, both before and after exercise. During exercise whole-body acetate carbon recovery was approximately 75%, however, acetate carbon recovery of the active leg was substantially higher (approximately 100%). It is concluded that inactive skeletal muscle plays a minor role in acetate turnover. However, active skeletal muscle enhances several-fold acetate uptake and subsequent oxidation, as well as release and its contribution to whole-body acetate turnover. Furthermore, under resting conditions the whole-body acetate correction factor can be used to correct for leg, skeletal muscle, substrate oxidation, but not during exercise.

Acetates↗
PubMed1989

Effect of 7 days of bed rest on dose-response relation between plasma glucose and insulin secretion.

Physical training decreases glucose-stimulated insulin secretion. To further explore the influence of the level of daily physical activity on beta-cell secretion, the effect of 7 days of bed rest was studied in six young, healthy men by sequential hyperglycemic clamp technique (7, 11, and 20 mM glucose, each step lasting 90 min). At 11 and 20 mM glucose, insulin concentrations in plasma were higher after (87 +/- 11 and 303 +/- 63 microU/ml) than before (63 +/- 5 and 251 +/- 50 microU/ml, P less than 0.05) bed rest. Also C-peptide levels were higher after bed rest than before during glucose stimulation. The responses of other hormones, metabolites, or electrolytes influencing beta-cell secretion were not influenced by bed rest. In spite of increased insulin levels after bed rest, glucose disposal at 20 mM of glucose was significantly lower after bed rest than before. It is concluded that bed rest for 7 days increases the glucose-stimulated insulin response, at least partly due to a beta-cell adaptation increasing glucose-stimulated insulin secretion. However, the insulin secretion does not increase adequately compared with the peripheral insulin resistance induced by bed rest.

3-Hydroxybutyric Acid↗
PubMed1990

Rest decay of calcium transients and contractility in feline ventricular myocytes.

To define the respective contributions of sarcoplasmic reticulum Ca2+ release and action potential-dependent Ca2+ influx to the activator Ca2+, rest decay of the cytosolic free Ca2+ (Ca2+i) transient and contractility was measured in feline ventricular myocytes loaded with the Ca2(+)-sensitive fluorescent dye indo-1. Myocytes were stimulated to a steady state and then rested for periods ranging from 2 to 120 s. Rest decay was assayed with both resumption of stimulation and rapid extracellular applications of caffeine. The protocol was then repeated after exposure to ryanodine. Ryanodine changed the Ca2+i transients during steady-state stimulation from large, rapidly rising transients starting near the resting Ca2+i level to small, slowly rising Ca2+i transients superimposed on an elevated diastolic Ca2+i. Under control conditions the stimulation- and caffeine-induced Ca2+i transients exhibited slow monotonic rest decay with similar time constants of decay (180 and 202 s, respectively, from a representative cell). After ryanodine, the rest decay of stimulation-induced Ca2+i transients was seemingly no different. However, no Ca2+i transient could be elicited by caffeine after 15 s of rest. These results suggest that 1) under normal conditions the primary source of activator Ca2+ is the sarcoplasmic reticulum, and 2) the rest decay of contractility seen in feline ventricular myocytes results from time-dependent loss of Ca2+ from this organelle.

Animals↗
PubMed1982

Induced venous pooling and cardiorespiratory responses to exercise after bed rest.

The purpose of this study was to deliberately induce venous pooling the lower extremities of bed-rested subjects to determine whether such distention may reverse the reduction in maximal O2 uptake that has regularly been observed. Bed-rest deconditioning was assessed in eight healthy male subjects by measuring submaximal and maximal O2 uptake (VO2 max), ventilation, and heart rate (HRmax) before and after 15 days of bed rest. During bed rest four subjects in the experimental group received daily treatments of venous pooling for 210 min/day with a reverse gradient garment (RGG), whereas the four subjects in the control group received no treatment. Compared with prebed-rest values, VO2max was reduced by 14.0 (P less than 0.05), HRmax was increased by 4.2 (P less than 0.05), and endurance time for the exercise test was decreased by 9.2% (P less than 0.05) in the control group. In the RGG group, VO2max, HRmax, and endurance time were essentially unchanged after bed rest. The plasma volume (PV) of the control group decreased by 16.7 (P less than 0.05) after bed rest compared with a 10.3% (not significant) reduction in the RGG group. The percent delta PV was related to the percent delta VO2 max (r = 0.75, P less than 0.05) and percent delta HR max (r = 0.65, P less than 0.05). The data support the hypothesis that the lack of venous pooling and associated fluid shifts contribute the decrement in VO2 max associated with bed-rest deconditioning.

Adult↗
PubMed1990

Head-down bed rest impairs vagal baroreflex responses and provokes orthostatic hypotension.

We studied vagally mediated carotid baroreceptor-cardiac reflexes in 11 healthy men before, during, and after 30 days of 6 degrees head-down bed rest to test the hypothesis that baroreflex malfunction contributes to orthostatic hypotension in this model of simulated microgravity. Sigmoidal baroreflex response relationships were provoked with ramped neck pressure-suction sequences comprising pressure elevations to 40 mmHg followed by serial R-wave-triggered 15-mmHg reductions to -65 mmHg. Each R-R interval was plotted as a function of systolic pressure minus the neck chamber pressure applied during the interval. Compared with control measurements, base-line R-R intervals and the minimum, maximum, range, and maximum slope of the R-R interval-carotid pressure relationships were reduced (P less than 0.05) from bed rest day 12 through recovery day 5. Baroreflex slopes were reduced more in four subjects who fainted during standing after bed rest than in six subjects who did not faint (-1.8 +/- 0.7 vs. -0.3 +/- 0.3 ms/mmHg, P less than 0.05). There was a significant linear correlation (r = 0.70, P less than 0.05) between changes of baroreflex slopes from before bed rest to bed rest day 25 and changes of systolic blood pressure during standing after bed rest. Although plasma volume declined by approximately 15% (P less than 0.05), there was no significant correlation between reductions of plasma volume and changes of baroreflex responses. There were no significant changes of before and after plasma norepinephrine or epinephrine levels before and after bed rest during supine rest or sitting.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Reduced spontaneous baroreflex response slope during lower body negative pressure after 28 days of head-down bed rest.

Effects of 28 days of continuous 6 degrees head-down tilt bed rest on spontaneous vagally mediated baroreflex response slope were evaluated from beat-by-beat relationships between R-R interval and systolic arterial blood pressure. Twelve healthy men (age 27-42 yr) were assigned to either countermeasure (CM) or no-countermeasure (no-CM) groups. CM consisted of strenuous short-term exercise once per day 6 days/wk from days 7 to 28 and lower body negative pressure (LBNP) for 15 min on days 16, 18, 20, and 22-28. Spontaneous baroreflex slope was evaluated by application of linear regression to sequences of at least three beats in which systolic blood pressure and R-R interval changed in the same direction. Measurements were made pre-, mid- (day 15), and post-bed rest at rest and during progressive LBNP tests (3 min at each of -20, -30, -40, and -50 mmHg). R-R interval decreased progressively and significantly (P < 0.0001) over duration of bed rest. Spontaneous baroreflex slope at rest in pre-bed rest was 18.5 +/- 2.1 ms/mm Hg for CM and 14.9 +/- 1.6 ms/mmHg for no-CM. There was a significant reduction in baroreflex slope as a function of bed rest, and it was further reduced during LBNP (P < 0.0001). Between CM and no-CM groups differences existed, but these were present pre-bed rest and appeared unaffected by countermeasures.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗