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PubMed2000

Achieving haemodynamic baseline values with Finapres in elderly subjects during supine rest.

BACKGROUND: Clear guidelines for the resting time necessary to achieve stable blood pressure (BP) levels are scant in gerontology research. Therefore, we aimed to determine the minimum period required for obtaining haemodynamic baseline values in elderly subjects during supine rest. In addition, we evaluated the effect of cardiovascular morbidity, such as diastolic heart failure, and the effect of complex comorbidity of geriatric patients, on haemodynamic changes during supine rest. METHODS: A total of 17 healthy subjects, 18 heart failure patients with normal systolic function and 24 geriatric patients, aged 70 years and more, participated. After an overnight fast, changes in systolic BP (SBP), diastolic BP (DBP), heart rate (HR), and stroke volume (SV) were determined by Finapres beat-to-beat non-invasive BP monitoring during a 20-min supine rest. The procedure was repeated in the healthy subjects and geriatric patients on a second day. RESULTS: Complete BP stabilization was reached in each group within 5 min of supine rest, as SBP remained essentially unchanged and DBP did not change significantly anymore after the fourth minute. In the heart failure patients, HR decreased and SV increased until the twelfth minute of rest. The SBP, DBP, HR, and SV changes during supine rest showed good reproducibility. CONCLUSIONS: A span of 5 min of supine rest ensured achievement of reliable and reproducible baseline BP values by Finapres in elderly subjects. However, we recommend at least 12 min of rest to obtain full haemodynamic stability in elderly patients with diminished cardiac compliance and diastolic function.

Adaptation, Physiological↗
PubMed1985

Bed rest and increased diuretic treatment in chronic congestive heart failure.

To elucidate the effect of bed rest used as an adjunct to increased diuretic treatment, twelve patients with chronic congestive heart failure (CHF) had a 50% increase in loop diuretic dosage and were allocated to either continuous bed rest or bed rest during nights only. The 24-hour bed rest group reduced their weight significantly (mean +/- SEM: 2.00 +/- 0.79 kg, P less than 0.001), whereas the night bed rest group had no significant weight reduction (1.10 +/- 0.37 kg, 0.1 less than P less than 0.2) during three days of observation. Furthermore, the 24-hour bed rest group had a significantly increased diuresis (P less than 0.05) during the first day of the study and a tendency towards increased natriuresis. The cumulated diuresis for the two groups (24-hour bed rest versus night bed rest) during the three days of study were 7773 +/- 700 ml and 5861 +/- 909 ml (0.05 less than P less than 0.1), respectively. Plasma concentrations of adrenaline, noradrenaline, renin and aldosterone were increased, as measured in the supine position. No significant differences were found between the two groups. Plasma concentrations of antidiuretic hormone were within normal limits. In conclusion, continuous bed rest is a reasonable adjunct to diuretic treatment in patients with CHF.

Adult↗
PubMed2001

The volume effect of the stomach on intestinal activity on same-day exercise--rest Tc-99m tetrofosmin myocardial imaging.

PURPOSE: The aim of this study was to investigate quantitatively the volume effect of the stomach on the prevention of intestinal artifacts in the rest phase on same-day exercise--rest Tc-99m tetrofosmin myocardial perfusion scintigraphy. MATERIALS AND METHODS: The study was performed in 81 consecutive patients (43 men, 38 women; mean age, 57 +/- 9 years) who were referred for routine Tc-99m tetrofosmin exercise--rest SPECT myocardial perfusion imaging with normal scintigrams or completely normal inferior wall perfusion on visual assessment of SPECT images. Group A (control group, n = 41) and group B (n = 40) were given 200 ml milk to enhance the hepatobiliary clearance of tetrofosmin 30 minutes before the exercise SPECT acquisition study and just after the injection for the rest SPECT acquisition study. For the rest SPECT acquisition study, patients in group B were given, in addition to milk, a standard solid and fluid meal to enhance the volume of the stomach after the injection of Tc-99m tetrofosmin. In all patients, both exercise and rest SPECT acquisitions were started 45 minutes after the injection of Tc-99m tetrofosmin. Myocardial and abdominal activity were assessed on three separate views in the rest phase of the study, and the mean myocardium-to-abdomen count ratios were calculated. In addition, the presence of interfering intestinal activity was assessed visually on SPECT images. Infracardiac activity was described as absent when it was equal to lung background. RESULTS: The myocardial-to-abdominal ratios were 1.38 +/- 0.05 and 1.95 +/- 0.04 in groups A and B, respectively (P < 0.0001). Interfering intestinal activity with varying degrees of intensity was seen in 20 patients in group A (49%) and in 5 patients in group B (13%; P < 0.001). CONCLUSIONS: These results suggest that filling of the stomach with some fluid and solid food before rest acquisition on the same-day stress--rest protocol, because of its volume effect, may provide a high target-to-nontarget ratio for myocardial imaging and thus may reduce the frequency of intestinal artifacts.

Artifacts↗
PubMed2002

Effect of rest on physicians' performance in an emergency department, objectified by electroencephalographic analyses and psychometric tests.

OBJECTIVE: The aim of the field study was to objectify physicians' vigilance, well-being, and cognitive performance in the course of 24-hr shifts with and without afternoon rest. SUBJECTS, SETTING, AND DESIGN: Eleven residents (four women, seven men; age, 33.5 +/- 4.7 yrs) were observed when doing two regular 24-hr shifts at the emergency department (randomized crossover design): one without rest, the other with a period of rest in the early afternoon (duration, 2:31 +/- 1:04 hrs) and the opportunity of having a nap (duration, 1:07 +/- 0:26 hrs, n = 6). Electroencephalography and psychometric tests were carried out at 8 am and at midnight. MEASUREMENTS: Measurements included subjective perception of workload, stress, and sleeping behavior; computer-analyzed electroencephalography; adjective checklist (Eigenschaftswörterliste 60 S, a self-rating scale); complex reaction time test; Pauli test (number of calculations during 3 mins); and numerical memory test. RESULTS: Electroencephalographic analyses showed a significant decrease in alpha power and a significant increase in beta power in the evening as compared with the morning on both days. The nocturnal increase observed in delta activity was significantly less pronounced in duties with rest than in duties without rest. Physicians felt deactivated at night. The Eigenschaftswörterliste 60 S indicated deactivation at night and a rest-induced activation in the subgroup that had taken the opportunity to sleep in the afternoon. Psychometric tests did not show any significant differences, neither between performance in the morning and evening nor between results with and without rest. CONCLUSION: As expected, electroencephalographic recordings showed nocturnal deactivation and a vigilance-promoting effect of the afternoon rest. These objective findings were in accordance with the results derived from self-rating scales. On the other hand, in short-lasting psychometric tests, performance was found unchanged after 16 hrs of routine work. In further studies, a discrimination between resting periods with and without sleep will be important.

Adult↗
PubMed2002

Variability within alpha- and beta-adrenoreceptor genes as a predictor of cardiovascular function at rest and in response to mental challenge.

OBJECTIVES: To investigate the association between polymorphic variation in alpha- and beta-adrenoreceptor genes and cardiovascular activity at rest and in response to psychological challenge in a sample in which the heritability of these cardiovascular phenotypes may be established. METHODS: Several common polymorphisms were characterized within ADRA1B (alpha1B), ADRA2A (alpha2A), ADRB1 (beta1) and ADRB2 (beta2) and examined in relation to heart rate (HR) and systolic (SBP) and diastolic (DBP) blood pressure, both at rest and in response to stress. Participants were 309 European-American, young adult men and women (including 101 monozygotic and 44 dizygotic twin pairs). RESULTS: In the full sample, participants carrying any G allele at base pair (bp) 1165 in ADRB1 exhibited elevated resting SBP and DBP and a larger DBP response to mental challenge compared to homozygotes for the C allele (P < 0.04). An AA genotype at bp 145 in ADRB1 was also associated with higher resting SBP and DBP than AG or GG genotypes (P < 0.03). At bp 46 in ADRB2, GG homozygotes had higher resting DBP than subjects possessing any A allele (P < 0.05). For the same polymorphism, however, AG heterozygotes showed lower SBP than both AA and GG homozygotes (P < 0.05). In a subsample of genetically unrelated individuals, ADRB1 (1165) continued to predict resting SBP, DBP and DBP response to stress (P < 0.03), while ADRB2 (46) was associated with resting SBP (P < 0.04) but not DBP. Finally, the degree of allele sharing at ADRB1 (1165) also predicted variability in SBP and DBP at rest among dizygotic twin pairs (P < 0.04). CONCLUSIONS: These results indicate that some polymorphic variation within adrenoreceptor genes contributes to interindividual variability in resting SBP and DBP and in DBP response to mental challenge.

Adult↗
PubMed1997

Cardiovascular consequences of bed rest: effect on maximal oxygen uptake.

Maximal oxygen uptake (VO2max) is reduced in healthy individuals confined to bed rest, suggesting it is independent of any disease state. The magnitude of reduction in VO2max is dependent on duration of bed rest and the initial level of aerobic fitness (VO2max), but it appears to be independent of age or gender. Bed rest induces an elevated maximal heart rate which, in turn, is associated with decreased cardiac vagal tone, increased sympathetic catecholamine secretion, and greater cardiac beta-receptor sensitivity. Despite the elevation in heart rate, VO2max is reduced primarily from decreased maximal stroke volume and cardiac output. An elevated ejection fraction during exercise following bed rest suggests that the lower stroke volume is not caused by ventricular dysfunction but is primarily the result of decreased venous return associated with lower circulating blood volume, reduced central venous pressure, and higher venous compliance in the lower extremities. VO2max, stroke volume, and cardiac output are further compromised by exercise in the upright posture. The contribution of hypovolemia to reduced cardiac output during exercise following bed rest is supported by the close relationship between the relative magnitude (% delta) and time course of change in blood volume and VO2max during bed rest, and also by the fact that retention of plasma volume is associated with maintenance of VO2max after bed rest. Arteriovenous oxygen difference during maximal exercise is not altered by bed rest, suggesting that peripheral mechanisms may not contribute significantly to the decreased VO2max. However reduction in baseline and maximal muscle blood flow, red blood cell volume, and capillarization in working muscles represent peripheral mechanisms that may contribute to limited oxygen delivery and, subsequently, lowered VO2max. Thus, alterations in cardiac and vascular functions induced by prolonged confinement to bed rest contribute to diminution of maximal oxygen uptake and reserve capacity to perform physical work.

Bed Rest↗
PubMed2007

Superficial lumbopelvic muscle overactivity and decreased cocontraction after 8 weeks of bed rest.

STUDY DESIGN: Longitudinal study. OBJECTIVE: To gain insight into the effects of inactivity on lumbopelvic stabilization. SUMMARY OF BACKGROUND DATA: Some authors have suggested a link between inactivity and lumbopelvic (LP) pain. Studies examining the superficial musculature in LP pain have shown overactivity and increased cocontraction. Studies in inactivity (bed rest, microgravity) have shown similar effects on the musculature of the legs. Here we examine the effect of bed rest on superficial LP activity and cocontraction. METHODS: Ten male subjects participated in the "Berlin Bed Rest Study" and underwent 8 weeks of bed rest with a 1-year follow-up. A repetitive knee movement model at four movement speeds in non-weightbearing was used to assess, via electromyography, activity (amplitude-ratios) in five superficial LP muscles and abdominal flexor-lumbar extensor cocontraction for LP stabilization. Testing was conducted at regular intervals during and after bed rest. RESULTS: Analysis of the amplitude-ratio data showed a significant effect of testing date (F = 2.38, P = 0.005). This effect was generalized across all muscles, however (F = 0.59, P = 0.989). During bed rest, subjects exhibited higher levels of activity but lower levels of cocontraction (F = 8.84, P < 0.001), and the changes were still present up to 1 year after bed rest. CONCLUSIONS: The bed rest protocol resulted in the development of superficial muscle overactivity but decreased cocontraction. These changes could reflect dysfunction of central nervous system control of LP stabilization. These changes were still apparent 1 year after bed rest, suggesting a stable change in motor control.

Bed Rest↗
PubMed1997

The interplay of central and peripheral factors in limiting maximal O2 consumption in man after prolonged bed rest.

1. The effects of bed rest on the cardiovascular and muscular parameters which affect maximal O2 consumption (VO2,max) were studied. The fractional limitation of VO2,max imposed by these parameters after bed rest was analysed. 2. The VO2,max, by standard procedure, and the maximal cardiac output (Qmax), by the pulse contour method, were measured during graded cyclo-ergometric exercise on seven subjects before and after a 42-day head-down tilt bed rest. Blood haemoglobin concentration ([Hb]) and arterialized blood gas analysis were determined at the highest work load. 3. Muscle fibre types, oxidative enzyme activities, and capillary and mitochondrial densities were measured on biopsy samples from the vastus lateralis muscle before and at the end of bed rest. The measure of muscle cross-sectional area (CSA) by NMR imaging at the level of biopsy site allowed computation of muscle oxidative capacity and capillary length. 4. The VO2,max was reduced after bed rest (-16.6%). The concomitant decreases in Qmax (-30.8%), essentially due to a change in stroke volume, and in [Hb] led to a huge decrease in O2 delivery (-39.7%). 5. Fibre type distribution was unaffected by bed rest. The decrease in fibre area corresponded to the significant reduction in muscle CSA (-17%). The volume density of mitochondria was reduced after bed rest (-16.6%), as were the oxidative enzyme activities (-11%). The total mitochondrial volume was reduced by 28.5%. Capillary density was unchanged. Total capillary length was 22.2% lower after bed rest, due to muscle atrophy. 6. The interaction between these muscular and cardiovascular changes led to a smaller reduction in VO2,max than in cardiovascular O2 transport. Yet the latter appears to play the greatest role in limiting VO2,max after bed rest (> 70% of overall limitation), the remaining fraction being shared between peripheral O2 diffusion and utilization.

Adult↗
PubMed1999

Quiet resting is not necessary prior to routine antenatal blood pressure measurement.

A premeasurement period of 5 minutes quiet resting is recommended prior to measuring blood pressure. The aim of this study was to determine the effect of this period of rest on the level of blood pressure in pregnant women. One hundred pregnant women had their blood pressure measured on a single visit using a QuietTrak ambulatory blood pressure monitor, used to remove human observer bias. Group 1 (n = 50) had blood pressure measured as soon as possible on entering the clinic room and again after 5 minutes rest. Group 2 were rested for 5 minutes on entry to the clinic room prior to the first blood pressure measurement and had the second measurement taken after a further 5 minutes rest. Results were compared in the 2 groups using ANOVA. In Group 1, the initial, mean systolic blood pressure was 116.6 versus 115.5 mmHg taken after 5 minutes quiet rest (p = 0.66). The corresponding diastolic values were 66.2 versus 64.1 (p = 0.40). In Group 2, the initial mean systolic blood pressure was 116.2 versus 115.6 taken after 5 minutes quiet rest (p = 0.85). The corresponding diastolic values were 68.5 versus 65.6 (p = 0.34). Blood pressure was as likely to rise as to fall after a period of quiet rest. It is not necessary to have pregnant women quietly resting during routine visits before having blood pressure measured.

Adolescent↗
PubMedDate not supplied

Effect of ischemia-reperfusion on the post-rest inotropy of isolated perfused rat heart.

UNLABELLED: This paper aims to study the effect of ischemia-reperfusion on the post-rest inotropy and to characterize post-rest B1:B2 ratio as an index of intracellular Ca(2+) overload. When the rest interval between the cardiac beats is increased, the magnitude of the post-rest beats is increased. First beat (B1) is maximally potentiated with exponential decline of the second (B2) and subsequent beats, thereby establishing a normal B1:B2 ratio of post- rest inotropy of the cardiac muscle. The rest potentiation of B1 and subsequent decay in the magnitude B2 is thought to develop from the time-dependent changes in the Ca(2+)-uptake and release from the sarcoplasmic reticulum (SR). Ca(2+)-kinetics of SR can be modulated by a variety of interventions which produce Ca(2+) loading of the SR. METHODS: Isolated perfused (K-H buffer, 34 degrees C) rat hearts were paced at 1 Hz (steady state frequency). Interbeat intervals between 1s and 10s were introduced and the recovery in the left ventricular contractile force (Pmax) of post-rest B1 and B2 for each interval was recorded. Their relative relationship was computed and compared under control and experimental conditions. RESULTS: High extracellular Ca(2+) (2.50 to 7.0 mM) or low extracellular Na(+) (50% of control), and ischemia (60 min, 34 degrees C) - reperfusion (30 min, 34 degrees C) caused the reversal of the control relationship of the B1 to B2, with B2 being more potentiated than B1, accompanied by the appearance of after-contractions during the rest intervals of 4s or more. The mean (+/- SE) control B1:B2 ratio (at 4s interval) of 1.12 +/- 0.05 was significantly (P<0.001) reduced to 0.93 +/- 0.07; 0.89 +/- 0.01; and 0.96 +/- 0.02 after high Ca(2+) (6 mM) perfusion, low Na(+)(50%) perfusion and ischemia-reperfusion respectively. Simultaneous perfusion with ryanodine (1 microM) abolished the after-contractions and significantly increased the reduced ratios. The time course of changes in B1:B2 ratio after graded ischemia-reperfusion showed a significant fall in the ratio between 30 and 60 min of ischemia. A parallel change in Pmax and a significant rise in the left ventricular end-diastolic pressure, indicating an irreversible phase of the injury was recorded. No significant changes in B1:B2 ratio were detected during the reversible phase (<30 min) of the ischemia-reperfusion injury. CONCLUSIONS: Ischemia-reperfusion induces significant alterations in the relative ratio of the post-rest contractions of the left ventricle in isolated perfused rat heart. The altered ratios were characterized to predict the irreversibility of the reperfusion injury and to index the extent of Ca(2+)-loading of the sarcoplasmic reticulum.

Animals↗
PubMed1993

Regulation of gluconeogenesis during rest and exercise in the depancreatized dog.

To assess the mechanism of the accelerated gluconeogenesis in the insulin-deficient state, chronically catheterized (carotid artery, portal vein, hepatic vein, vena cava) normal (C; n = 9) and depancreatized (PX; n = 7) dogs were studied during rest (40 min) and moderate exercise (150 min). Tracers ([14C]alanine, [3H]glucose) and dye were infused to measure determinants of gluconeogenesis in the gut and liver. Arterial levels, net gut output, hepatic load, and net hepatic uptake of alanine were similar in C and PX at rest. During exercise, alanine levels fell in C but rose approximately 100% in PX. Exercise did not affect gut output or liver uptake of alanine in C but increased these variables by approximately 50 and 100% in PX due to an increase in hepatic alanine load. Arterial lactate was similar at rest in C and PX but rose fourfold more in PX with exercise. Net gut lactate output was fivefold greater in PX during rest and exercise. Net hepatic lactate uptake was present in PX at rest, whereas net output was evident in C. In response to exercise, hepatic lactate uptake was increased further in PX due to a rise in hepatic lactate load. Net hepatic lactate uptake was not evident until the end of exercise in C. Net hepatic glycerol uptake was elevated at rest in PX and during the initial 60 min of exercise due to an elevated hepatic load. In contrast to the high rates of gut lactate and alanine output in PX, gut glycerol output was not present. Gluconeogenesis from lactate and alanine was 5- to 10-fold higher in PX than C during rest and exercise. At rest, this resulted, in part, from a twofold greater intrahepatic gluconeogenic efficiency. During exercise, the greater conversion occurred even though efficiency was not consistently greater. In summary, gluconeogenesis from alanine, lactate, and glycerol in the insulin-deficient diabetic state 1) is exaggerated at rest, due to an increased capacity for hepatic lactate extraction, increased hepatic precursor loads, and a greater gluconeogenic efficiency; 2) is accelerated further by exercise due to added increments in hepatic precursor loads; and 3) is exaggerated partly because of a greater net gut alanine and lactate output.

Alanine↗
PubMed1976

Plasma vasopressin and renin activity in women exposed to bed rest and +Gz acceleration.

To study the effect of prolonged recumbency on plasma vasopressin and renin activity, eight women (23-34 yr) were subjected to 17 days of absolute bed rest. The +3 Gz tolerance of the subjects was tested before and after 14 days of bed rest. From day 2 and through day 17 of bed rest, plasma arginine vasopressin (AVP) levels were reduced 33%. Plasma renin activity (PRA) increased 91% (P less than 0.05) above ambulatory control values from days 10 through 15 of bed rest. When compared to precentrifuge values, exposure to +3 Gz prior to bed rest provoked a 20-fold rise (P less than 0.05) in mean plasma AVP but resulted in only a slight increase in PRA. After bed rest, acceleration increased plasma AVP 7-fold (P less than 0.02); however, the magnitude of this increase was less than the post +3Gz value obtained prior to bed rest. After bed rest, no significant rise was noted in PRA following +3 Gz. This study demonstrates that prolonged bed rest leads to a significant rise in the PRA of female subjects, while exposure to +Gz acceleration provokes a marked rise in plasma AVP.

Adult↗
PubMed1986

Atropine unmasks bed-rest effect: a spectral analysis of cardiac interbeat intervals.

Bed-rest deconditioning is suspected to reduce cardiac reserve, possibly by impairing autonomic function. Heart rate response in normal subjects reveals considerable variability, reflected by a relatively broadband interbeat interval power spectrum. A reduction in this autonomically modulated variability would be predicted to cause a narrowing of the spectrum. We retrospectively analyzed data from 10 aerobically conditioned men (age range 35-49 yr) who had undergone orthostatic tolerance testing with lower body negative pressure pre-bed rest and after 7-10 days of bed rest, while on placebo and after intravenous atropine. Spectra were derived by Fourier analysis of 128 interbeat interval data sets. Spectral power was estimated by computing the root-mean-square (rms) values (mean +/- SD) for the band encompassing the 2nd to 64th harmonics from subjects with a sufficient number of beats: placebo rms is 93 +/- 33 ms for pre-bed rest and 84 +/- 38 ms for bed rest (NS, n = 6); atropine rms is 63 +/- 24 ms for pre-bed rest and 40 +/- 23 ms for bed rest (P less than 0.01; n = 7). These data suggest that atropine "unmasks" a deconditioning effect of bed rest in athletic men, evidenced by a reduction in interbeat interval spectral power not apparent with placebo. Spectral analysis offers a useful means of quantitating the effects of bed-rest deconditioning and autonomic perturbations on cardiac dynamics.

Adult↗
PubMed1994

Effects of head-down bed rest on complex heart rate variability: response to LBNP testing.

Head-down bed rest is used to model physiological changes during spaceflight. We postulated that bed rest would decrease the degree of complex physiological heart rate variability. We analyzed continuous heart rate data from digitized Holter recordings in eight healthy female volunteers (age 28-34 yr) who underwent a 13-day 6 degree head-down bed rest study with serial lower body negative pressure (LBNP) trials. Heart rate variability was measured on 4-min data sets using conventional time and frequency domain measures as well as with a new measure of signal "complexity" (approximate entropy). Data were obtained pre-bed rest (control), during bed rest (day 4 and day 9 or 11), and 2 days post-bed rest (recovery). Tolerance to LBNP was significantly (P < 0.02) reduced on both bed rest days vs. pre-bed rest. Heart rate variability was assessed at peak LBNP. Heart rate approximate entropy was significantly (P < 0.05) decreased at day 4 and day 9 or 11, returning toward normal during recovery. Heart rate standard deviation and the ratio of high- to low-power frequency did not change significantly. We conclude that short-term bed rest is associated with a decrease in the complex variability of heart rate during LBNP testing in healthy young adult women. Measurement of heart rate complexity, using a method derived from nonlinear dynamics ("chaos theory"), may provide a sensitive marker of this loss of physiological variability, complementing conventional time and frequency domain statistical measures.

Adult↗
PubMed1997

Differences between estimates and measured PaCO2 during rest and exercise in older subjects.

Arterial PCO2 (PaCO2) has been estimated during exercise with good accuracy in younger individuals by using the Jones equation (PJCO2) (J. Appl. Physiol. 47: 954-960, 1979). The purpose of this project was to determine the utility of estimating PaCO2 from end-tidal PCO2 (PETCO2) or PJCO2 at rest, ventilatory threshold (VTh), and maximal exercise (Max) in older subjects. PETCO2 was determined from respired gases simultaneously (MGA 1100) with arterial blood gases (radial arterial catheter) in 12 older and 11 younger subjects at rest and during exercise. Mean differences were analyzed with paired t-tests, and relationships between the estimated PaCO2 values and the actual values of PaCO2 were determined with correlation coefficients. In the older subjects, PETCO2 was not significantly different from PaCO2 at rest (-1.2 +/- 4.3 Torr), VTh (0.4 +/- 2.5), or Max (-0.8 +/- 2.7), and the two were significantly (P < 0.05) correlated at Vth (r = 0.84) and Max (r = 0.87) but not at rest (r = 0.47). PJCO2 was similar to PaCO2 at rest (-1.0 +/- 3.9) and Vth (-1. 3 +/- 2.3) but significantly lower at Max (-3.0 +/- 2.6), and the two were significantly correlated at Vth (r = 0.86) and Max (r = 0. 80) but not at rest (r = 0.54). PETCO2 was significantly higher than PaCO2 during exercise in the younger subjects but similar to PaCO2 at rest. PJCO2 was similar to PaCO2 at rest and Vth but significantly lower at Max in younger subjects. In conclusion, our data demonstrate that PaCO2 during exercise is better estimated by PETCO2 than by PJCO2 in older subjects, contrary to what is observed in younger subjects. This appears to be related to the finding that PETCO2 does not exceed PaCO2 during exercise in older subjects, as occurs in the younger subjects. However, PaCO2 at rest is best estimated by PJCO2 in both younger and older subjects.

Adult↗
PubMed1997

Bed rest suppresses bioassayable growth hormone release in response to muscle activity.

Hormonal responses to muscle activity were studied in eight men before (-13 or -12 and -8 or -7 days), during (2 or 3, 8 or 9, and 13 or 14 days) and after (+2 or +3 and +10 or +11 days) 17 days of bed rest. Muscle activity consisted of a series of unilateral isometric plantar flexions, including 4 maximal voluntary contractions (MVCs), 48 contractions at 30% MVC, and 12 contractions at 80% MVC, all performed at a 4:1-s work-to-rest ratio. Blood was collected before and immediately after muscle activity to measure plasma growth hormone by radioimmunoassay (IGH) and by bioassay (BGH) of tibia epiphyseal cartilage growth in hypophysectomized rats. Plasma IGH was unchanged by muscle activity before, during, or after bed rest. Before bed rest, muscle activity increased (P < 0.05) BGH by 66% at -13 or -12 days (2,146 +/- 192 to 3,565 +/- 197 microg/l) and by 92% at -8 or -7 days (2,162 +/- 159 to 4,161 +/- 204 microg/l). After 2 or 3 days of bed rest, there was no response of BGH to the muscle activity, a pattern that persisted through 8 or 9 days of bed rest. However, after 13 or 14 days of bed rest, plasma concentration of BGH was significantly lower after than before muscle activity (2,594 +/- 211 to 2,085 +/- 109 microg/l). After completion of bed rest, muscle activity increased BGH by 31% at 2 or 3 days (1,807 +/- 117 to 2,379 +/- 473 microg/l; P < 0.05), and by 10 or 11 days the BGH response was similar to that before bed rest (1,881 +/- 75 to 4,160 +/- 315 microg/l; P < 0.05). These data demonstrate that the ambulatory state of an individual can have a major impact on the release of BGH, but not IGH, in response to a single bout of muscle activity.

Adult↗
PubMed2002

Role of skin blood flow and sweating rate in exercise thermoregulation after bed rest.

Two potential mechanisms, reduced skin blood flow (SBF) and sweating rate (SR), may be responsible for elevated intestinal temperature (T(in)) during exercise after bed rest and spaceflight. Seven men underwent 13 days of 6 degrees head-down bed rest. Pre- and post-bed rest, subjects completed supine submaximal cycle ergometry (20 min at 40% and 20 min at 65% of pre-bed rest supine peak exercise capacity) in a thermoneutral room. After bed rest, T(in) was elevated at rest (+0.31 +/- 0.12 degrees C) and at the end of exercise (+0.33 +/- 0.07 degrees C). Percent increase in SBF during exercise was less after bed rest (211 +/- 53 vs. 96 +/- 31%; P < or = 0.05), SBF/T(in) threshold was greater (37.09 +/- 0.16 vs. 37.33 +/- 0.13 degrees C; P < or = 0.05), and slope of SBF/T(in) tended to be reduced (536 +/- 184 vs. 201 +/- 46%/ degrees C; P = 0.08). SR/T(in) threshold was delayed (37.06 +/- 0.11 vs. 37.34 +/- 0.06 degrees C; P < or = 0.05), but the slope of SR/T(in) (3.45 +/- 1.22 vs. 2.58 +/- 0.71 mg x min-1 x cm-2 x degrees C-1) and total sweat loss (0.42 +/- 0.06 vs. 0.44 +/- 0.08 kg) were not changed. The higher resting and exercise T(in) and delayed onset of SBF and SR suggest a centrally mediated elevation in the thermoregulatory set point during bed rest exposure.

Adult↗
PubMed2002

Branched-chain amino acid supplementation during bed rest: effect on recovery.

Bed rest is associated with a loss of protein from the weight-bearing muscle. The objectives of this study are to determine whether increasing dietary branched-chain amino acids (BCAAs) during bed rest improves the anabolic response after bed rest. The study consisted of a 1-day ambulatory period, 14 days of bed rest, and a 4-day recovery period. During bed rest, dietary intake was supplemented with either 30 mmol/day each of glycine, serine, and alanine (group 1) or with 30 mmol/day each of the three BCAAs (group 2). Whole body protein synthesis was determined with U-(15)N-labeled amino acids, muscle, and selected plasma protein synthesis with l-[(2)H(5)]phenylalanine. Total glucose production and gluconeogenesis from alanine were determined with l-[U-(13)C(3)]alanine and [6,6-(2)H(2)]glucose. During bed rest, nitrogen (N) retention was greater with BCAA feeding (56 +/- 6 vs. 26 +/- 12 mg N. kg(-1). day(-1), P < 0.05). There was no effect of BCAA supplementation on either whole body, muscle, or plasma protein synthesis or the rate of 3-MeH excretion. Muscle tissue free amino acid concentrations were increased during bed rest with BCAA (0.214 +/- 0.066 vs. 0.088 +/- 0.12 nmol/mg protein, P < 0.05). Total glucose production and gluconeogenesis from alanine were unchanged with bed rest but were significantly reduced (P < 0.05) with the BCAA group in the recovery phase. In conclusion, the improved N retention during bed rest is due, at least in part, to accretion of amino acids in the tissue free amino acid pools. The amount accreted is not enough to impact protein kinetics in the recovery phase but does improve N retention by providing additional essential amino acids in the early recovery phase.

Adult↗