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At least 1,603 records · Page 89Linked to original sources
PubMed2001

Nycthemeral variations in core temperature and heart rate: continuous cycling exercise versus continuous rest.

Circadian rhythms have formed the subject of many researches in man during bed rest or usual routine, but have been little studied during continuous and sustained physical exercise. This study deals with the influence of time of day on biological markers in competitive cyclists during continuous physical exercise versus continuous rest. Ultra-distance cyclists were studied over a 24 h period (13:00 to 13:00 h the next day) in the laboratory. The subjects were requested to maintain a constant speed (set at 65% - 70% of their maximal aerobic speed obtained during a preliminary test) on their own bicycles which were equipped with home trainers. Workload, core temperature and heart rate were monitored continuously. The same measures were also recorded while the athletes were resting awake until 13:00 h the next day. Results show that in both situations, core temperature and heart rate exhibited significant circadian variations (p < 0.001). Furthermore, during exercise, an accentuation of amplitude and mean of every rhythm (p < 0.05) with a phase lag (p < 0.05) were observed. Despite a strenuous and continuous physical exercise requiring special physiological adaptations, the rhythmic variations observed at rest persisted, which highlighted the influence of biological clocks.

Adult↗
PubMed2004

Effect of acute hypoxia on heart rate variability at rest and during exercise.

The purpose of this study was to investigate sympathovagal balance as inferred from heart rate variability (HRV) responses to acute hypoxia at rest and during exercise. HRV was evaluated in 12 healthy subjects during a standardized hypoxic tolerance test which consists of four periods alternating rest and moderate exercise (50 % V.O (2)max) in normoxic and hypoxic conditions. Ventilatory responses were determined and HRV indexes were calculated for the last 5 min of each period. In well-tolerant subjects, hypoxia at rest induced a decrease of root-mean-square of successive normal R-R interval differences (RMSSD) (p < 0.05) and of absolute high frequency (HF) power (p < 0.001). All absolute HRV indexes were strongly reduced during exercise (p < 0.001) with no further changes under the additional stimulus of hypoxia. A significant increase (p < 0.05) in the HF/(LF+HF) ratio (where LF is low frequency power) was found during exercise in hypoxia compared to exercise in normoxia, associated with similar mean changes in ventilation and tidal volume. These results indicate a vagal control withdrawal under hypoxia at rest. During exercise at 50 % V.O (2)max, HRV indexes cannot adequately represent cardiac autonomic adaptation to acute hypoxia, or possibly to other additional stimuli, due to the dominant effect of exercise and the eventual influence of confounding factors.

Adaptation, Physiological↗
PubMed1996

Effect of combined parasympathetic and sympathetic blockade on left ventricular relaxation at rest and during exercise in trained and untrained men.

We investigated the influence of autonomic blockade (AB) on the left ventricular (LV) diastolic function at rest (R) and during bicycle exercise (EX) in eight endurance-trained (TR) and ten untrained subjects (UT). Two-dimensional and M-mode echocardiography at the parasternal long axis were performed at rest and during an exercise protocol, which consisted of two stages of 50 and 100 W. Using the digitized data from the M-mode echocardiogram, the normalized maximal increase in LV dimension during the rapid filling phase (nmD) was calculated according to Hörtnagl. Additionally the ECG was recorded at R and during Ex 60 min after this first test. 0.02 mg.kg body mass-1 propanolol and 0.04 mg.kg body mass-1 atropine were injected intravenously over a 5-min period and the test procedure was repeated as described above. Before AB nmD increased significantly from resting values to 100 W in both groups, whereas nmD tended to be lower in UT compared to TR. During AB nmD of UT was rather unchanged at R and during EX compared to pre-blockade conditions. In contrast nmD of TR was slightly reduced and this difference was significant at 100 W. No major difference in nmD between the TR and UT group could be observed during AB. Before and during AB HR of TR were significantly lower at rest, 50 and 100 W compared to UT. We conclude that the enhanced diastolic relaxation observed in endurance athletes seems to be due to a training-induced adaptation of the autonomic nervous system.

Adaptation, Physiological↗
PubMed1987

Physiologic responses to heavy-resistance exercise with very short rest periods.

Heavy-resistance exercise utilizing very short rest periods is commonly used by body builders to prepare for competition. The purpose of this study was to compare the acute responses of this type of heavy-resistance exercise protocol in competitive body builders (BB) and power lifters (PL). Nine male BB and eight PL were matched for age, size and experience. A ten-station heavy-resistance exercise protocol was used. Each subject performed three sets of 10 repetition maximum (RM) with 10-s rest between sets and alternated 30-s and 60-s rest periods between exercises. No differences were observed in total work between the groups, but BB used a significantly (P less than 0.05) higher percentage of their 1 RM in the bench press and leg press exercises. Heart rate, ratings of perceived exertion (RPE), and lactate levels were obtained during the exercise protocol; significant (P less than 0.05) increases were observed above rest for these variables. RPE was significantly correlated with lactate levels (r = 0.84). Plasma epinephrine, norepinephrine, dopamine, cortisol, and lactate levels significantly increased from pre- to 5 min post-exercise. Mean plasma volumes were reduced -16.6 (+/- 3.64)% and -20.6 (+/- 8.32)% following the exercise protocol for BB and PL, respectively. Significant (P less than 0.05) decreases in eosinophil counts were observed following exercise. No significant differences were observed between BB and PL for any of the physiologic responses measured. PL exhibited a higher incidence (100%) of clinical symptoms of dizziness and nausea compared to BB (11.1%).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2000

Long-term central hemodynamic effects at rest and during exercise of losartan in essential hypertension.

BACKGROUND: Losartan reduces blood pressure in patients with essential hypertension, but the long-term central hemodynamic effects at rest and during exercise are not known. METHODS AND RESULTS: After 8 months of losartan treatment (50 to 100 mg daily, mean 82 mg), intra-arterial pressure was reduced from 165/102 mm Hg to 145/91 mm Hg at rest and from 193/104 mm Hg to 179/96 mm Hg during 100 W exercise in 28 patients with essential hypertension. Cardiac index and heart rate remained unchanged, but total peripheral resistance index was reduced 12% to 15%. Stroke index was unchanged at rest but increased 7% to 9% during exercise. Twenty-four-hour ambulatory blood pressure was reduced 10% to 13%. Left ventricular mass was reduced 27% in patients with left ventricular hypertrophy (n = 18). CONCLUSION: Losartan lowers blood pressure by reducing total peripheral resistance at rest and during exercise but cardiac pump function is unchanged or slightly improved. In patients with left ventricular hypertrophy, losartan induces a sizeable reduction in left ventricular mass.

Adult↗
PubMed1987

Non-esterified long-chain fatty acid metabolism in fed sheep at rest and during exercise.

The role of circulating, non-esterified, long-chain fatty acids (NEFA) as a source of energy for the whole animal and skeletal muscle was investigated in fed non-pregnant sheep at rest and during exercise. Infusion of tracer quantities of [1-14C]oleic or [1-14C]stearic acid was combined with the use of arteriovenous difference studies on fed sheep at rest or during a 2 h period of exercise on a belt treadmill moving at 4.5 km h-1. At rest all parameters of NEFA metabolism indicated a minimal role for oxidation. Thus the concentration in plasma (0.07 +/- 0.01 mmol l-1), entry rate (0.08 +/- 0.02 mmol h-1 kg-1 body wt), contribution to whole animal oxidation (1.2 +/- 0.3%) and utilization of NEFA by skeletal muscle (0.046 +/- 0.008 mmol h-1 kg-1 muscle) were all low. Exercise prompted a shift to lipolysis and accordingly the above parameters increased markedly some 13-24-fold. The circulating concentration of ketone bodies showed only a small increase during exercise and consequently the role of ketone bodies as an energy source during exercise was minimal. Glucose utilization by skeletal muscle was considerable in animals at rest and it represented the most significant potential fuel of skeletal muscle. Exercise resulted in a sustained increase of 3-4-fold in the utilization of glucose by skeletal muscle. Thus the traditional view that NEFA and not glucose is a predominant fuel of skeletal muscle of fed sheep should be appraised.

3-Hydroxybutyric Acid↗
PubMedDate not supplied

Effects of inhaled sulfur dioxide (SO2) on pulmonary function in healthy adolescents: exposure to SO2 alone or SO2 + sodium chloride droplet aerosol during rest and exercise.

Recently we reported statistically significant changes in pulmonary functional measurements in asthmatic adolescents exposed at rest or during exercise. To demonstrate whether those results were due to the subjects' adolescence, or more likely, to their diagnosis of asthma, we repeated identical exposures in healthy adolescents. The changes after exposure to sulfur dioxide (SO2); however the changes were only slightly greater than those seen after sham exposure. After exposure at rest to 1.0 ppm SO2 + 1 mg/m3 sodium chloride (NaCl) droplet aerosol, the healthy adolescents showed small (3%) but statistically significant reductions in forced expiratory volume in one second (FEV1.0). No significant changes were seen following exposure to NaCl of SO2 alone at rest. Exposure to the SO2 modes during moderate exercise produced greater changes. Following exposure to either the SO2 + NaCl mixture or 1.0 ppm of SO2 alone, the reductions in FEV1.0 were slightly greater (6%) and prolonged compared with those seen at rest. Significant decreases also were seen in Vmax50 and Vmax75. A small decrease (4%) in FEV1.0 was seen following exposure to NaCl alone during exercise, but the change was not statistically significant. The changes seen in the healthy adolescents were slight compared to those seen in the asthmatic adolescents previously exposed (changes of 23-67%). We conclude that asthmatic adolescents are much more sensitive to the effects of inhaled SO2 than are healthy adolescents.

Adolescent↗
PubMed2006

Human pulmonary responses with 30-minute time intervals of exercise and rest when exposed for 8 hours to 0.12 ppm ozone via square-wave and acute triangular profiles.

Hazucha et al. (1992) compared pulmonary function responses during 8-h square-wave exposures to FA and to 0.12 ppm O3, as well as to an acute triangular exposure to a mean O3 concentration of 0.12 ppm. With 30 min of moderate exercise each hour during 8 h of continuous exposure, significantly greater pulmonary function responses were observed between 5 h and 7 h when O3 was varied in an acute triangular configuration from 0.00 ppm to 0.24 ppm over the first 4 h and back to 0.00 ppm during the last 4 h than when O3 concentration was maintained constant at 0.12 ppm throughout. These investigators employed equal periods of 30 min of exercise, in which mean VE was approximately 40 L/min, and 30 min of rest, with pulmonary function measurements taken at the end of each hour. This procedure (i.e., taking measurements at the end of each hour) could attenuate the full effect that would be observed very soon after exercise cessation, and permit some recovery to occur. Accordingly, in the present study, the primary objective was to determine what effect observations of pulmonary responses assessed immediately following repeated 30 min exercise bouts, as well as those at the end of each hour (following approximately 30 min rest) during 8-h square-wave exposures to FA and to 0.12 ppm O3, as well as to an acute triangular exposure to a mean O3 concentration of 0.12 ppm. During the last 4 h of the 8-h, 0.12-ppm square-wave exposure, the 30-min mean increases in FEV1.0 responses were consistently greater at the end of the first half hour immediately following exercise (-1.22%) than at the end of the second half-hour following 30 min of rest (+0.01%). Further, even though O3 concentration was steadily decreasing from 0.24 ppm to 0 ppm during the last 4 h of the triangular exposure, similar increases in FEV1.0 decrement (-1.38%) immediately after each 30 min exercise bout, and small recovery at the end of each 30 min rest (+0.56%) were observed. Symptom scores in both exposures during the last 4 h also showed this effect.

Adolescent↗
PubMed2006

Analysis of the QT interval and its variability in healthy adults during rest and exercise.

The aim of the present study was to quantify the variability of electrocardiographic QT and RR intervals during rest and dynamic physical exercise, and to interpret these variabilities in terms of relative autonomic modulation of the atrial and ventricular myocardium. We also sought to characterize the relationships between QT, heart rate-corrected QT (QT(c)) and RR intervals, and to consider their associations with differential autonomic regulation. Nine males and eight females of similar age (22.8 +/- 4.7 years), mass (75.5 +/- 13.0 kg) and aerobic fitness (43.6 +/- 7.7 ml kg(-1) min(-1)) (mean +/- SD) undertook progressive bicycle exercise. A three-lead Holter ECG was recorded continuously during pre-exercise, exercise and recovery, and mean values of RR, QT, QT(c), QT variability index (QTVI) and mean-normalized QT variance (QTVN) were determined. At the onset of exercise QTVI increased rapidly compared with rest and remained significantly elevated throughout exercise and recovery. There were significant differences between QT(a)VI and QT(e)VI (QT measured from Q wave onset to T wave apex (QT(a)) and T wave end (QT(e)), respectively) throughout the experimental protocol. QTVI was significantly reduced in males compared with females prior to exercise but was similar thereafter. We suggest that physical exercise perturbs the resting QT-RR relationship owing to the onset of differential parasympathetic modulation of the atrial and ventricular myocardium. QTVI can be used to quantify the relative autonomic influence on the atrial and ventricular myocardium during rest and exercise, and might be related to HR-dependent and HR-independent influences on the QT interval.

Adult↗
PubMed1983

Energy expenditure of pregnant women at rest or walking self-paced.

Energy expenditure during rest and self-paced walking was determined from early to late pregnancy either longitudinally or in a cross-section of women. The cross-sectional study was done with 16 women confined to a metabolic unit: six nonpregnant (NP), six early pregnant (EP 10 to 20 wk gestation), and four late pregnant (LP 30 to 40 wk gestation). In the longitudinal study, five of the six EP subjects from the cross-sectional study were studied at 5-wk intervals until parturition. Basal metabolic rate, measured by open circuit, indirect calorimetry, and expressed as kcal/min, was 13% greater (p less than 0.05) in EP compared to NP and was 28% greater (p less than 0.05) in LP compared to EP. Resting metabolism increased during gestation in the EP group from a value of 1.01 kcal/min at 15 to 25 wk to 1.15 kcal/min at 35 to 40 wk. When energy expenditure during rest is expressed as kcal/kg body weight/h, there were no significant differences due to stage of pregnancy. The time required for the women to walk 400 m at their own pace was measured. The pace of the LP women was 20% slower (p less than 0.05) than the EP women. But when the EP women were studied at 35 and 40 wk gestation their pace was only 4.5% slower than that at 15 to 25 wk. These data suggest that individual behavioral differences have a greater effect on pace than stage of gestation. A decrease in pace reduced the rate of energy expenditure per kilogram body weight for walking 400 m. But, body weight, rather than pace, was the major determinant of total energy expenditure for the walk (p less than 0.05). It is apparent from these data that body weight is the major determinant of energy expenditure during rest and self-paced weight bearing activity in pregnancy.

Adult↗
PubMed1993

Zinc and copper balances in healthy adult males during and after 17 wk of bed rest.

The effects of long-term bed rest on zinc and copper balances were measured in seven healthy men. Volunteers aged 22-54 y (mean +/- SD, 34 +/- 12 y), 168-185 cm in height (173 +/- 5 cm), and 64-86 kg in weight (74 +/- 9 kg) remained on a metabolic ward for 29 wk. Subjects were ambulatory during weeks 1-5, remained in continuous bed rest for weeks 6-22, and were reambulated during weeks 23-29. Copper and zinc were measured in weekly urine and fecal composites. Dietary intakes provided (mean +/- SD) 19.2 +/- 1.2 mumol Cu (1.22 +/- 0.08 mg), 211 +/- 11 mumol Zn (13.81 +/- 0.72 mg), 25.2 +/- 1.2 mmol Ca (1011 +/- 46 mg), 1086 +/- 46 mmol N (15.21 +/- 0.65 g), and 48.1 +/- 1.4 mmol K (1489 +/- 44 mg)/d. Bed rest increased fecal zinc excretion and decreased zinc balance, whereas copper balance was unchanged. Reambulation decreased fecal zinc excretion and increased both zinc and copper balances. These results suggest that during long-term bed rest or space flight, individuals will lose total body zinc and will retain more zinc and copper when they reambulate.

Adult↗
PubMed1988

Determinants of short-term blood pressure variability. Effects of bed rest and sensory deprivation in essential hypertension.

In 38 hospitalized patients with uncomplicated essential hypertension intra-arterial pressure was recorded continuously for 24 hours with the Oxford technique. On the basis of beat by beat analysis, hourly and 24-hour means of mean arterial pressure (MAP) and heart rate (HR) were obtained. The standard deviations and variation coefficients of the hourly means were used as a measure of absolute and relative blood pressure variability respectively. By randomization patients were ambulant during the day (group A; n = 19) or they were restricted to bed (group B). The patients of group B were sensory deprived during the first 4 hours of the blood pressure recording. During the night MAP, HR, and their respective variabilities were similar for both groups. During bed rest MAP was reduced as compared to ambulant values (P less than 0.05), but bed rest had no effect on HR, or on the variability of HR and MAP. During concomitant sensory deprivation HR and the variability of MAP and HR all declined to nightly values, though MAP did not change. In group B, HR-variability (absolute and relative) was inversely correlated to age, but no relationship between these two parameters was observed in group A. During concomitant sensory deprivation, but not during bed rest alone or during night rest, relative MAP-variability was also inversely correlated to age. It is concluded that sensory stimuli have an important effect on HR and on the variability of MAP and HR, but not on MAP itself, indicating that to some extent blood pressure and its variability are regulated independently.

Adult↗
PubMed1988

Aerobic exercise training reduces resting and exertional blood pressure in cardiac patients.

We evaluated the effects of exercise training (ET) on resting and exertional blood pressure in patients with cardiac disease. ET consisted of 20 to 30 minutes of aerobic activity three times weekly for 12 months. The study group comprised 17 males and three females (mean age 58 years, range 40 to 71 years). Blood pressure was evaluated at rest and during exercise after 6 and 12 months ET. A training effect was documented by an increase in functional capacity from 7.5 METs (1 MET = 3.5 mL oxygen consumption/kg/min) pre-ET to 8.8 and 9.2 METs after 6 and 12 months, respectively. The following significant (P less than 0.05) effects occurred on blood pressure in association with ET: resting systolic pressure pre-ET decreased from 131 to 124 mm Hg at 12 months ET; submaximal (50% pre-ET maximum capacity) systolic and diastolic pressures decreased from 150/84 to 142/80 mm Hg (6 months ET) and 144/80 mm Hg (12 months ET); diastolic pressure at maximal exertion fell from 83 to 77 mm Hg (6 months ET) and 78 mm Hg (12 months ET). Systolic blood pressure at maximal exertion was not increased despite significant increases in peak workload achieved at 6 and 12 months ET. Therefore, ET not only enhances functional capacity in cardiac patients but may be associated with a beneficial cardiac effect through attenuation of both rest and exertional blood pressure.

Adult↗
PubMed1993

Hyperventilation-echocardiography test for the diagnosis of myocardial ischaemia at rest.

The purpose of this study was to assess the feasibility, safety, specificity and sensitivity of the hyperventilation test performed under echocardiographic monitoring for the provocation of vasospastic ischaemia. Hyperventilation (approximately 30 cycles.min-1 for 5 min) was performed in 104 hospitalized patients, referred for pain typical of angina at rest, under 2-D echocardiographic and 12-lead electrocardiographic monitoring. All the tests were completed and no significant side effect was observed. In-hospital documentation of spontaneous myocardial ischaemia and/or ergonovine-induced ischaemia was achieved in 38 patients (group I). A positive hyperventilation-echocardiography test (occurrence of new transient asynergies or worsening of basal ones) was obtained in 32/38 patients. Among the group I patients, only 23 had diagnostic ST-T changes and only 16 experienced chest pain during the hyperventilation-echo test. Of the 66 patients without evidence of myocardial ischaemia at rest (negative ECG monitoring during hospitalization and/or negative ergonovine maleate-echo test)--Group II, none showed echocardiographic changes, seven presented ST-T changes and six complained of typical chest pain during the test. Thus, in relation to in-hospital documentation of myocardial ischaemia at rest, both spontaneous and/or ergonovine-induced episodes, the hyperventilation-echo test showed a specificity of 100%, a sensitivity of 84%, a positive predictive value of 100% and a negative predictive value of 92%. In conclusion, hyperventilation performed under echocardiographic monitoring is feasible and safe; it can be proposed as a screening test to unmask vasospastic myocardial ischaemia in patients with angina at rest, in whom documentation of spontaneous episodes is not available.

Adult↗
PubMed1989

Acute and chronic effects of nicardipine on rest and exercise haemodynamics in post-myocardial infarction patients with latent cardiac failure.

The acute and chronic haemodynamic effects of nicardipine were studied, at rest and during exercise, in 10 post-myocardial infarction patients with latent cardiac failure and no signs of residual myocardial ischaemia. Intravenous administration of nicardipine (5 mg over 10 min) was associated with a significant increase in cardiac index and significant reductions in mean pulmonary artery pressure, mean pulmonary wedge pressure, total pulmonary resistance and systemic vascular resistance under conditions of rest and peak exercise. After 3 weeks of oral treatment (20 mg three times daily) cardiac index did not change, but the improvements in mean pulmonary artery pressure, mean pulmonary wedge pressure and total pulmonary resistance were sustained at rest and during exercise, at the same workload attained prior to medication. Chronic treatment with nicardipine significantly increased exercise tolerance, while mean pulmonary artery pressure, mean pulmonary wedge pressure and total pulmonary resistance were maintained below the control values. It is concluded that nicardipine improves both rest and exercise cardiac performance in post-myocardial infarction patients with latent cardiac failure, thus avoiding the risk of pulmonary congestion.

Clinical Trials as Topic↗
PubMed1983

Acute hemodynamic effects of nifedipine at rest and during stress in severe aortic incompetence.

To determine whether afterload reduction with nifedipine is effective both at rest and during stress tests (rapid atrial pacing and contrast material overload), 14 patients with chronic severe isolated aortic insufficiency (10 asymptomatic) underwent right and left cardiac catheterization. Forty-five minutes after 20 mg of nifedipine (sublingually), left ventricular end-diastolic pressure, peak aortic pressure, systemic vascular resistance and double product decreased significantly at rest, at peak paced rate, and after angiography (P values from less than 0.05 to less than 0.001). Cardiac index increased at resting heart rate (P less than 0.01) but was unchanged during pacing. The reduction of systemic vascular resistances was inversely correlated with its initial value (r = -0.69). After nifedipine, average regurgitant fraction did not change; however its variations were significantly correlated with those of systemic vascular resistance (r = 0.69). It is concluded that in severe aortic insufficiency, nifedipine induces an effective reduction of left ventricular pre- and afterload, accompanied by an enhanced mechanical efficiency (unchanged or increased cardiac index with lower double product), both at rest and during stress tests.

Adult↗
PubMed1983

Left ventricular relaxation at rest and during handgrip in aortic valve disease before and after valve replacement.

In 14 patients (pts) with aortic valve disease (AVD) left ventricular (LV) relaxation was assessed by the time constant (T) of LV pressure (tipmanometer) fall before and 19 months after successful aortic valve replacement (AVR). 12 control pts (CO) were studied by the same technique. Preoperative LV ejection fraction in AVD (64%) and in CO (69%) did not differ. In AVD T was increased (60 ms) as compared to the CO (38 ms, P less than 0.05). During handgrip (HG) there was a similar increase of LV peak systolic pressure (LVSP), heart rate and peak measured contractile element velocity of shortening in AVD and in the CO. LV end-diastolic pressure varied minimally in both groups. T decreased during handgrip in CO (38 to 33 ms, P less than 0.01) and remained unchanged in AVD. Following AVR T at rest decreased insignificantly to 52 ms, but remained increased (P less than 0.025) as compared with CO. During postoperative HG however, a decrease to 47 ms (P less than 0.05) was noted. Postoperative angiographic LV muscle mass (105 g/m2) and LVSP at rest (137 mmHg) remained elevated (P less than 0.02) as compared to CO (72 g/m2; 119 mmHg). It is concluded that (1) in AVD with normal ejection performance LV relaxation at rest is prolonged and the reaction of relaxation to HG is abnormal despite preserved contractile response, (2) following AVR the response of LV relaxation to HG becomes normal and (3) elevated postoperative T at rest appears to be related to residual hypertrophy and probably also to the still increased LVSP rather than to intrinsic disturbances of myocardial relaxation.

Adult↗
PubMed1983

Bed rest, activity and the inflammation of rheumatoid arthritis.

Seventy-five patients with rheumatoid arthritis have been studied in order to assess the relative contributions of bed rest and planned activity on the observed improvement in arthritis during hospitalization. The benefit of bed rest was less than expected; only a third of patients showed significant improvement. A similar number improved during planned activity and although bed rest was superior the advantages were small. The features of those patients who responded to bed rest or planned activity showed small but important differences indicating that more careful selection to one or other regimen may increase the number of patients benefiting from hospitalization.

Adult↗