PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Cardiovascular Deconditioning”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3Linked to original sources
PubMed2001

Deterioration of left ventricular chamber performance after bed rest : "cardiovascular deconditioning" or hypovolemia?

BACKGROUND: Orthostatic intolerance after bed rest is characterized by hypovolemia and an excessive reduction in stroke volume (SV) in the upright position. We studied whether the reduction in SV is due to a specific adaptation of the heart to head-down tilt bed rest (HDTBR) or acute hypovolemia alone. METHODS AND RESULTS: We constructed left ventricular (LV) pressure-volume curves from pulmonary capillary wedge pressure and LV end-diastolic volume and Starling curves from pulmonary capillary wedge pressure and SV during lower body negative pressure and saline loading in 7 men (25+/-2 years) before and after 2 weeks of -6 degrees HDTBR and after the acute administration of intravenous furosemide. Both HDTBR and hypovolemia led to a similar reduction in plasma volume. However, baseline LV end-diastolic volume decreased by 20+/-4% after HDTBR and by 7+/-2% after hypovolemia (interaction P<0.001). Moreover, SV was reduced more and the Starling curve was steeper during orthostatic stress after HDTBR than after hypovolemia. The pressure-volume curve showed a leftward shift and the equilibrium volume of the left ventricle was decreased after HDTBR; however, after hypovolemia alone, the curve was identical, with no change in equilibrium volume. Lower body negative pressure tolerance was reduced after both conditions; it decreased by 27+/-7% (P<0.05) after HDTBR and by 18+/-8% (P<0.05) after hypovolemia. CONCLUSIONS: Chronic HDTBR leads to ventricular remodeling, which is not seen with equivalent degrees of acute hypovolemia. This remodeling leads to a greater decrease in SV during orthostatic stress after bed rest than hypovolemia alone, potentially contributing to orthostatic intolerance.

Adult↗
PubMed2002

Head down tilt combined with breathing assistance by the "IRON LUNG." A new simulation model for cardiovascular deconditioning, skin, and kidney function in weightlessness?

In 1951 Gauer, Henry and Sieker proposed that "central hyper-volemia" might produce a diuresis that serves to reduce blood volume, a postulated negative-feedback system for the control of blood volume. Recent surprising results from human spaceflight indicate that although a central hyper-volemia takes place in weightlessness, an increase in salt and urine excretion cannot be observed. We hypothesised that on earth the mediastinum is shaped by gravity because of the gravity dependent hydrostatic gradient in the blood filled cavities and that its unloading by weightlessness reduces the wall stretch in the atria, thus resulting in reduced sodium and urine excretion. Therefore we have applied the principle of the "Iron Lung" (lung pressure manipulator LPM) in combination with a simulation method of weightlessness, head down tilt bed rest (HDT), to test this hypothesis. We found that similar to weightlessness, not only urinary excretion, but also evaporative water loss was reduced and that diastolic blood pressure increased.

Journal Article↗
PubMed2001

Regulation of muscle sympathetic nerve activity after bed rest deconditioning.

Cardiovascular deconditioning reduces orthostatic tolerance. To determine whether changes in autonomic function might produce this effect, we developed stimulus-response curves relating limb vascular resistance, muscle sympathetic nerve activity (MSNA), and pulmonary capillary wedge pressure (PCWP) with seven subjects before and after 18 days of -6 degrees head-down bed rest. Both lower body negative pressure (LBNP; -15 and -30 mmHg) and rapid saline infusion (15 and 30 ml/kg body wt) were used to produce a wide variation in PCWP. Orthostatic tolerance was assessed with graded LBNP to presyncope. Bed rest reduced LBNP tolerance from 23.9 +/- 2.1 to 21.2 +/- 1.5 min, respectively (means +/- SE, P = 0.02). The MSNA-PCWP relationship was unchanged after bed rest, though at any stage of the LBNP protocol PCWP was lower, and MSNA was greater. Thus bed rest deconditioning produced hypovolemia, causing a shift in operating point on the stimulus-response curve. The relationship between limb vascular resistance and MSNA was not significantly altered after bed rest. We conclude that bed rest deconditioning does not alter reflex control of MSNA, but may produce orthostatic intolerance through a combination of hypovolemia and cardiac atrophy.

Adolescent↗
PubMed2006

Increased nitric oxide synthase activity and expression in the hypothalamus of hindlimb unloaded rats.

Upon return from spaceflight or resumption of normal posture after bed rest, individuals often exhibit cardiovascular deconditioning. Although the mechanisms responsible for cardiovascular deconditioning have yet to be fully elucidated, alterations within the central nervous system have been postulated to be involved. The paraventricular nucleus (PVN) and supraoptic nucleus (SON) of the hypothalamus are important brain regions in control of sympathetic outflow and body fluid homeostasis. Nitric oxide (NO) modulates the activity of PVN and SON neurons, and alterations in NO transmission within these brain regions may contribute to symptoms of cardiovascular deconditioning. The purpose of the present study was to examine nitric oxide synthase (NOS) activity and expression in the PVN and SON of control and hindlimb unloaded (HU) rats, an animal model of cardiovascular deconditioning. The number of neurons exhibiting NOS activity as assessed by NADPH-diaphorase staining was significantly greater in the PVN but not SON of HU rats. Western blot analysis revealed that neuronal NOS (nNOS) but not endothelial NOS (eNOS) protein expression was higher in the PVN of HU rats. In the SON, there was a strong trend for an increase in nNOS (p=0.052) and a significant increase in eNOS expression in HU rats. Our results suggest that increased nNOS in the PVN contributes to autonomic and humoral alterations following cardiovascular deconditioning. In contrast, the functional significance of increases in nNOS and eNOS protein in the SON may be related to alterations in vasopressin release observed previously in HU rats.

Animals↗
PubMed1991

Effect of the prelaunch position on the cardiovascular response to standing.

Astronauts spend a minimum of 2 h in the reclined seated position (prelaunch position) prior to the launch of the Space Shuttle. This position favors a cephalad shift of blood volume and subsequent loss of body fluid volume, a physiologic situation associated with cardiovascular deconditioning and orthostatic intolerance following spaceflight. It is not known if the prelaunch position results in cardiovascular deconditioning and, therefore, impaired cardiovascular performance during standing. If so, this might hinder the ability of the crewmember to make an emergency egress from the shuttle during the launch. The purpose of this study was to evaluate the cardiovascular responses of men and women to the stand test before and after 2 h in the prelaunch position. Nine men and nine women performed the stand test before and after 2 h in the seated position (SIT), the prelaunch position (PL), or seated immersed to the neck in water (WI). Heart rate, blood pressure, and cardiac output were measured. Men had higher blood pressures than women and demonstrated increases in blood pressure with standing. There were no other gender differences. SIT did not alter the cardiovascular response to standing, while PL and WI resulted in greater increases in heart rate after 2 h in the position. This increase was only 4 to 7 beats/min greater than after SIT, and was the same for PL and WI. Thus, a small, but significant, degree of cardiovascular deconditioning occurred during the minimum time astronauts spend in the prelaunch position.

Adult↗
PubMed2003

Nitric oxide in microgravity-induced orthostatic intolerance: relevance to spinal cord injury.

Prolonged exposure to microgravity results in cardiovascular deconditioning which is marked by orthostatic intolerance in the returning astronauts and recovering bed-ridden patients. Recent studies conducted in our laboratories at University of California, Irvine have revealed marked elevation of nitric oxide (NO) production in the kidney, heart, brain, and systemic arteries coupled with significant reduction of NO production in the cerebral arteries of microgravity-adapted animals. We have further demonstrated that the observed alteration of NO metabolism is primarily responsible for the associated cardiovascular deconditioning. Recovery from acute spinal cord injury (SCI) is frequently complicated by orthostatic intolerance that is due to the combined effects of the disruption of efferent sympathetic pathway and cardiovascular deconditioning occasioned by prolonged confinement to bed. In this presentation, I will review the nature of altered NO metabolism and its role in the pathogenesis of microgravity-induced cardiovascular deconditioning. The possible relevance of the new findings to orthostatic intolerance in patients with acute SCI and its potential therapeutic implications will be discussed.

Animals↗
PubMed1995

Relationship between severity of gonarthrosis and cardiovascular fitness.

Cardiovascular fitness was assessed in 3 groups of patients having varying severity of gonarthrosis. Group I consisted of 16 patients with severe knee symptoms scheduled for total knee arthroplasty. Group II included 17 patients with medically treated osteoarthrosis who were not considered surgical candidates because knee symptoms were not severe. Group III consisted of 14 healthy control patients with no lower extremity arthritis. All patients were evaluated with Hospital for Special Surgery knee scores, Arthritis Impact Measurement Scale questionnaires, and a cardiopulmonary exercise test using semi-upright bicycle ergometry. All patients achieved anaerobic threshold during exercise. Mean (+/- standard deviation) maximum oxygen consumption (VO2) at peak exercise was 13.9 +/- 3.3 for Group I, 16.2 +/- 4.1 for Group II, and 21.5 +/- 3.9 for Group III. Mean (+/- standard deviation) Hospital for Special Surgery score was 55 +/- 7 for Group I, 70 +/- 14 for Group II, and 100 +/- 1 for Group III. Lower Hospital for Special Surgery score was associated with lower VO2 at peak exercise, suggesting that inactivity secondary to more severe arthritic symptoms can result in cardiovascular deconditioning. The association between severity of gonarthrosis and cardiovascular deconditioning supports the concept that a regular exercise program should be recommended for patients with arthritis. Also, for patients who are surgical candidates, the practice of delaying total knee arthroplasty may be associated with worsening cardiovascular fitness, particularly when physical activity becomes more limited. The expected longevity of implant function as well as the effect of continued arthritic symptoms on cardiovascular fitness should be considered when determining the optimal time for a patient to undergo total knee arthroplasty.

Activities of Daily Living↗
PubMed2000

Recording of blood pressure, heart rate and aortic nerve activity during parabolic flight in the rat via radio-telemetry.

Exposure to microgravity induces cardiovascular deconditioning characterized by orthostatic hypotension when astronauts return to the earth. In order to understand the mechanism of cardiovascular deconditioning, it is necessary to clarify the changes in hemodynamics and the cardiovascular regulation system over the period of space flight. The telemetry system applied to freely moving animals will be a useful and appropriate technique for this kind of long term study of the cardiovascular system in the conscious animal during space flight. The purpose of the present study is twofold: firstly, to observe the detailed changes of arterial pressure and heart rate (HR) during microgravity elicited by the parabolic flight in order to study the acute effect of microgravity exposure on the cardiovascular system; and secondly, to test the feasibility of the telemetry system for recording blood pressure, HR and autonomic nervous activities continuously during space flight.

Animals↗
PubMedDate not supplied

Psychological factors in postoperative fatigue.

OBJECTIVE: To assess whether the fatigue commonly reported by patients following surgery is partly a result of somatization and/or cognitive-behavioral factors. METHODS: One hundred eighty-three patients completed questionnaires before surgery and then 2 days, 3 weeks and 6 months afterward. Multiple regressions were used to assess which of the following factors were important in predicting self-reported postoperative fatigue, controlling for preoperative fatigue and for various demographic and surgical variables: negative mood, history of mood disorder, preoperative expectations of fatigue, preoperative worry or optimism about surgery, preoperative beliefs about the benefits of activity or rest, self-reported postoperative activity, self-reported cardiovascular deconditioning, and availability of social support. RESULTS: Controlling for demographic and surgical variables and preoperative fatigue, postoperative fatigue showed significant associations with negative mood at each stage of follow-up (p < .001) and was significantly predicted by history of mood disorder at 2 days postoperatively (p = .02). Higher fatigue expectations were self-fulfilling at 3 weeks after surgery (p = .02), whereas preoperative belief in physical activity as being beneficial to recovery predicted reduced fatigue at 6 months (p < .001). Finally, self-reported breathlessness after exercise, an indicator of cardiovascular deconditioning, was also significantly associated with greater fatigue at 6 months (p = .02). CONCLUSION: The results indicate that psychological processes may well be relevant in the etiology of postoperative fatigue. In particular, the results relating to mood and expectations suggest that somatization may be particularly important in the first few weeks following surgery, whereas cognitive-behavioral factors and cardiovascular deconditioning may be more important in determining later-stage recovery.

Adolescent↗
PubMed2000

Salt-loading and simulated microgravity on baroreflex responsiveness in rats.

Cardiovascular adaptations observed during exposure to microgravity results in impairment of baroreflex activity partially as a result of fluid and electrolyte shifts. The head-down tilt rat model mimics some of the physiological observations that have been made in astronauts. We examined the effects of salt-loading on baroreflex activity after 7 day simulated microgravity (30 degrees tail-suspension) and the subsequent 6 hr post-suspension in Sprague-Dawley (SD) rats, using low salt (0.3% NaCl) and high salt (8% NaCl) diets. In suspended animals on a low salt diet, the baroreflex response curve was shifted to the left, while the heart rate (HR) range and MAP50 values were reduced compared to their parallel tethered, non-suspended controls. For non-suspended animals, salt-loading shifted the curve to the right with a reduced HR range. In salt-loaded, suspended animals, the curve and its parameters resemble those of non-suspended animals on a low salt diet. In summary, these data have demonstrated that a short-term (seven days) simulated weightlessness may elicit cardiovascular deconditioning in rats after release from the simulation manifested as an altered responsiveness in baroreceptor-heart rate reflex and a lowered blood pressure while the rats are tethered and horizontal. Our results also suggest the counteracting effect of salt loading on cardiovascular deconditioning.

Animals↗
PubMed2003

Muscles in microgravity: from fibres to human motion.

In simulated or actual microgravity, human and animal postural muscles undergo substantial atrophy: after about 270 days, the muscle mass attains a constant value of about 70% of the initial one. Most animal studies reported preferential atrophy of slow twitch fibres whose mechanical properties change towards the fast type. However, in humans, at the end of a 42-days bed rest study, a similar atrophy of slow and fast fibres was observed. After microgravity, the maximal force of several muscle groups showed a substantial decrease (6-25% of pre-flight values). The maximal power during very short "explosive" efforts of 0.25-0.30s showed an even greater fall, being reduced to 65% after 1 month and to 45% (of pre-flight values) after 6 months. The maximal power developed during 6-7s "all-out" bouts on an isokinetic cycloergometer was reduced to a lesser extent, attaining about 75% of pre-flight values, regardless of the flight duration. In these same subjects, the muscle mass of the lower limbs declined by only 9-13%. Thus, a substantial fraction of the observed decreases of maximal power is probably due to a deterioration of the motor co-ordination brought about by the absence of gravity. To prevent this substantial decay of maximal absolute power, we propose that explosive exercise be added to the daily in-flight training schedule. We also describe a system aimed at reducing cardiovascular deconditioning wherein gravity is simulated by the centrifugal acceleration generated by the motion of two counter rotating bicycles ridden by the astronauts on the inner wall of a cylindrical space module. Finally, cycling on circular or elliptical tracks may be useful to reduce cardiovascular deconditioning in permanently manned lunar bases. Indeed, on the curved parts of the path, a cyclist generates an outward acceleration vector (ac). To counterbalance ac, the cyclist must lean inwards, so that the vectorial sum of ac plus the lunar gravity tends to the acceleration of gravity prevailing on Earth.

Animals↗