The physiological basis for the influence of weightlessness on heart and lungs.
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Animals↗
Biomedical subjects
F Bonde-Petersen
Publications and source records attributed to F Bonde-Petersen.
Effects of mild supine exercise during 20 days bed rest on maximal oxygen uptake rate in young humans.
Fourteen sedentary young volunteers performed a maximal exercise test on a bicycle ergometer before, after and eight or nine weeks after 20 days bed rest. They were divided into four groups. They all went through 20 days bed rest; 5 females and 6 males as controls while 3 males performed mild pedaling supine exercise for 30 minutes twice a day. Three other males from the control group started a retraining programme after bed rest performing mild pedaling exercise in the sitting position for an hour a day, 3-4 days a week for eight weeks. VO2max was reduced after bed rest in all groups. In the control group the 6 males decreased VO2max from 2.82 +/- 0.09 1.min-1 before bed rest to 2.42 +/- 0.14 1.min-1 after. The female controls decreased from 2.55 +/- 0.24 1.min-1 to 2.22 +/- 0.23 1.min-1. The exercise regime performed by the three males during bed rest did not prevent a fall in VO2max in that group from 2.76 +/- 0.06 to 2.57 +/- 0.09 1.min-1. The three males who performed bicycle exercise in the recovery period did not attain higher recovery values at 8-9 weeks than the other males. However the 5 female controls did not recover their > 13% loss in VO2max after 8-9 weeks of recovery. Calculation of peak oxygen pulse from VO2max divided by heart rate indicated that these changes in VO2max were caused exclusively by a reduction in stroke volume of the heart, a finding supported by resting echocardiography of left ventricular end-diastolic diameter and stroke volume.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Cardiovascular effects of 20 days bed rest in healthy young subjects.
To evaluate the effects of inactivity on the cardiovascular system in normal subjects, left ventricular echocardiography and vascular ultrasound of the common carotid artery, abdominal aorta and femoral artery, and lower body negative pressure tests were performed in 14 healthy volunteers (mean age: 22 years) before and after 20 days of strict bed rest. Cardiac output was calculated from echocardiographic measurements and peripheral arterial flows by multiplying cross-sectional area of an artery by heart rate and time-velocity integral measured by pulsed Doppler ultrasound with angle correction. Systemic vascular resistance, lower body vascular resistance, leg vascular resistance and head vascular resistance were also calculated. After bed rest, heart rate increased (69 +/- 2 to 79 +/- 3 bpm), while left ventricular diastolic dimension (49 +/- 1 to 45 +/- 1 mm), systolic blood pressure (137 +/- 5 to 116 +/- 4 mmHg), cardiac output (6.2 +/- 0.3 to 5.4 +/- 0.3 1.min-1), abdominal aortic flow (4.1 +/- 0.4 to 3.1 +/- 0.3 1.min-1), femoral artery flow (0.66 +/- 0.07 to 0.33 +/- 0.04 1-min-1), and lower body negative pressure test tolerance time (750 +/- 71 to 582 +/- 48 s) decreased significantly (p < 0.05). However, common carotid artery flow (0.97 +/- 0.09 to 1.03 +/- 0.08 1.min-1) did not change. Although no significant changes in systemic vascular resistance, lower body vascular resistance or head vascular resistance were observed, leg vascular resistance increased significantly after 20 days of bed rest (6933 +/- 2905 to 13221 +/- 2606 dyn.s.cm-1) (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Effect of 20 days bed rest upon peripheral capillary filtration rate, venous compliance and blood flow in arms and legs.
Capillary filtration rate, venous compliance and blood flow in arms and legs were measured during bed rest by strain gauge plethysmography using a liquid metal alloy in silastic tubes. Furthermore orthostatic tolerance to lower body suction was recorded. Six young healthy males and three young healthy females participated in the 20 days bed rest study. Neither arm nor leg blood flow was changed by bed rest. Arm blood flow varied between 2.18 +/- 0.30 and 3.03 +/- 0.35 vol%.min-1 and leg blood flow between 1.42 +/- 0.12 and 1.76 +/- 0.40 vol%.min-1. The capillary filtration rate tended to decrease in the arms from 0.27 +/- 0.07 vol%.min-1 at day 0 to 0.17 +/- 0.03 vol%.min-1 at day 3 and a tendency to an increase in filtration rate in the legs from 0.16 +/- 0.06 at day 0 to 0.56 +/- 0.21 vol%.min-1 at day 3 but both of these changes had recovered from day 10 on. There was a steady state in venous compliance of the forearm between 1.31 +/- 0.20 and 1.50 +/- 1.13 vol% during the first two weeks of the bed rest period but the values tended to increase to 1.75 +/- 0.16 and 1.89 +/- 0.22 vol% at days 16 and 19, respectively, while leg venous compliance showed a transient tendency to increase at day 3 (from 0.83 +/- 0.08 at day 0 to 1.30 +/- 0.32 vol% at day 3) to attain control values from day 5. Orthostatic intolerance measured during lower body suction decreased in the present subjects.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Health care during prolonged weightlessness in humans.
The demands for accumulation of knowledge about the human adaptation to weightlessness of long duration and the implications for the health and well-being of the astronaut have become increasingly important also for the international space programmes which are under development. The health care during long duration space-flights starts already with the selection where professional, psychological and medical criteria are considered. Space flights in low earth orbit have not been extended beyond 1 year, so the predictable value for long term space flights is limited, because e.g. Mission to Mars will last from 1.5 to 3 years, depending on the position of the planets, the space vehicle etc. The long duration and the enormous distance covered will induce very special and until now unknown effects on the human psychology which might be seen as the one single major factor which might be prohibitive for such long duration flights. The Moon base will bring further knowledge useful for long duration space flights in the field of medical care in general, but also with regard to the development of countermeasures against the adverse effects of weightlessness on the human body. The Moon's gravitational field of 0.16 G makes it possible to study this as a threshold in the adaptation processes.
Aerospace Medicine↗
Peripheral and central blood flow in man during cold, thermoneutral, and hot water immersion.
Cardiovascular reflexes were studied during immersion in water to the chest. Cardiac output (CO) was determined by acetylene rebreathing; forearm muscle and subcutaneous blood flow by 133Xe-clearance; and cutaneous blood flow by laser Doppler. Measurements were taken in a) control situation (CTR) (subject sitting dry); b) immersed in thermoneutral (NWI); c) in cold (CWI); and d) in hot water (HWI). The overall trend was that water immersion per se increased stroke volume (SV), but mostly during NWI and CWI, where heart rate (HR) was decreased by 15%; during HWI, HR increased by 32%, the temperature effect evidently overriding the immersion effect. Insignificant increases in CO were seen in NWI and HWI (18% and 44%), and no effect in CWI. Arterial pressure and total peripheral resistance (TPR) increased significantly in CWI due to an increase in peripheral vascular resistance, while significant decreases in TPR and CPR were observed in HWI and tendencies to decreases were found in NWI.
Adolescent↗
Influence of the renin-angiotensin system on human forearm blood flow.
Although angiotensin II is a potent vasoconstrictor agent in all tissues, including the human forearm, equivocal effects on forearm blood flow (FBF) have been found after angiotensin blockade. In 13 healthy Na(+)-depleted subjects FBF was measured by the 133Xe washout technique; subcutaneous and muscle blood flows were determined separately. FBF was measured during supine rest, after the arm was lowered, and during lower body negative pressure (LBNP). The measurements were repeated during intra-arterial saralasin infusion in six subjects and after intravenous administration of enalapril in seven subjects. FBF decreased and forearm vascular resistance (FVR) increased during arm lowering and LBNP, as the result of local and central adrenergic reflexes, respectively. We observed similar FBF and FVR values after both saralasin and enalapril, except for a decrease in FVR at rest after enalapril. It is concluded that, in the human forearm, angiotensin II is not necessary for sympathetic vasoconstrictor reflexes but may, through a central effect, have some influence on arteriolar tone at rest.
Adult↗
Catecholamines, circulation, and the kidney during water immersion in humans.
Because results in literature are discrepant with regard to the effects of water immersion (WI) on the release of norepinephrine (NE) in humans, the following study was performed. Simultaneous measurements of plasma NE, central cardiovascular variables, and renal sodium excretion were conducted in eight normal male subjects on 2 study days; 6 h of thermoneutral (35.0 degrees C) WI to the neck were preceded and followed by 1 h in the seated posture outside the water and 8 h of a seated control period. During the control period, the subjects wore a water-perfused garment (water temperature 34.6 degrees C) to obtain the same skin temperature as during WI. The subjects were fluid restricted overnight and kept in this condition throughout the study. Compared with the prestudy, post-study, and control periods, plasma NE decreased significantly by 61% during WI. Simultaneously, central venous pressure, cardiac output, stroke volume, systolic arterial pressure, and arterial pulse pressure increased, whereas heart rate decreased. Renal sodium excretion and urine flow rate increased. In conclusion, the release of NE is suppressed in humans during immersion. This decrease probably reflects a decrease in sympathetic nervous activity initiated by stimulation of low- and high-pressure baroreceptors. It is possible that the decrease in NE acts as one of several mechanisms of the natriuresis and diuresis of immersion in humans.
Adult↗
Effects of angiotensin blockade on the splanchnic circulation in normotensive humans.
The effects of angiotensin-converting enzyme inhibition (ACE-I) by enalapril on splanchnic (n = 10) and central hemodynamics (n = 9) were examined in moderately salt-depleted healthy volunteers, at rest and during 15-20 min of lower body negative pressure (LBNP), reducing mean arterial pressure by 10 mmHg. During LBNP before ACE-I, both splanchnic and total peripheral vascular resistances increased. During ACE-I, splanchnic and total peripheral vascular resistances decreased. After enalapril administration, splanchnic vascular resistance did not increase during LBNP. Total peripheral vascular resistance still increased but not to the same extent as during LBNP before ACE-I. The increases in heart rate and plasma norepinephrine during LBNP were attenuated after ACE-I compared with LBNP before ACE-I. The effectiveness of the ACE-I was clearly demonstrated by unchanged and low plasma angiotensin II levels during ACE-I. We conclude that, in normal sodium-depleted humans, acute ACE-I decreases splanchnic vascular resistance at rest and abolishes splanchnic vasoconstriction during LBNP. Furthermore, it may interfere with autonomic nervous system control of the circulation.
Adult↗
Central venous pressure in humans during short periods of weightlessness.
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Central Venous Pressure↗
Human cardiovascular reactions to simulated hypovolaemia, modified by the opiate antagonist naloxone.
Six healthy males were exposed to 20 mm Hg lower body negative pressure (LBNP) for 8 min followed by 40 mm Hg LBNP for 8 min. Naloxone (0.1 mg.kg-1) was injected intravenously during a 1 h resting period after which the LBNP protocol was repeated. Systolic, mean, and diastolic arterial blood pressures (SAP, MAP, DAP), and central venous pressure (CVP) were obtained using indwelling catheters. Cardiac output (CO), forearm blood flow (FBF), heart rate (HR), left ventricular ejection time (LVET), and electromechanical systole (EMS) were measured non-invasively. Pulse pressure (PP), stroke volume (SV), total peripheral resistance (TPR), forearm vascular resistance (FVR), systolic ejection rate (SER), pre-ejection period (PEP), PEP/LVET and indices for the systolic time intervals (LVETI, EMSI, PEPI) were calculated. During the second LBNP exposure, only two parameters differed from the pre-injection values: DAP at LBNP = 40 mm Hg increased from 60.0 +/- 4.8 mm Hg to 64.8 +/- 4.1 mm Hg (N = 4, p less than 0.02) and LVETI at LBNP = 20 mm Hg increased from 384.4 +/- 5.2 ms to 396.8 +/- 6.2 ms (N = 6, p less than 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Hypovolemic stimuli and vasopressin secretion in man.
Different non-hypotensive hypovolemic stimuli were applied to 21 healthy and 20 uremic dialysis patients. The purpose was to study the effect on plasma arginine-vasopressin concentration, using orthostasis as a reference model. Orthostasis increased the plasma AVP level in healthy subjects as well as in uremic dialysis patients. In healthy subjects plasma AVP increased both when they were normohydrated and after they had been water-depleted. Lower body negative pressure (LBNP, -40 mmHg) was applied to 11 healthy males to induce a central blood volume decrease, equal to that induced by orthostasis. The plasma AVP increased in two subjects only who became hypotensive during the investigations. Ten hemodialysis patients were volume-depleted by isolated ultrafiltration. A flow directed Swan-Ganz catheter was used to measure the central intravascular pressures. Pulmonary capillary wedge pressure was reduced to normal or subnormal values during 1-2 h of ultrafiltration, without any significant changes in plasma AVP. Plasma AVP increased only in 2 patients, who became hypotensive during the investigations. Thus, of the present non-hypotensive volume stimuli only orthostasis was able to stimulate AVP secretion. Equal or even greater reductions in central blood volumes by other stimuli had no effect on AVP secretion. The results demonstrate that isolated stimulation of low-pressure volume receptors has no effect on the secretion of AVP in humans.
Adult↗
Central venous pressure in humans during short periods of weightlessness.
Central venous pressure (CVP) was measured in 14 males during 23.3 +/- 0.6 s (mean +/- SE) of weightlessness (0.00 +/- 0.05 G) achieved in a Gulfstream-3 jet aircraft performing parabolic flight maneuvers and during either 60 or 120 s of +2 Gz (2.0 +/- 0.1 Gz). CVP was obtained using central venous catheters and strain-gauge pressure transducers. Heart rate (HR) was measured simultaneously in seven of the subjects. Measurements were compared with values obtained inflight at 1 G with the subjects in the supine (+1 Gx) and upright sitting (+1 Gz) positions, respectively. CVP was 2.6 +/- 1.5 mmHg during upright sitting and 5.0 +/- 0.7 mmHg in the supine position. During weightlessness, CVP increased significantly to 6.8 +/- 0.8 mmHg (P less than 0.005 compared with both upright sitting and supine inflight). During +2 Gz, CVP was 2.8 +/- 1.4 mmHg and only significantly lower than CVP during weightlessness (P less than 0.05). HR increased from 65 +/- 7 beats/min at supine and 70 +/- 5 beats/min during upright sitting to 79 +/- 7 beats/min (P less than 0.01 compared with supine) during weightlessness and to 80 +/- 6 beats/min (P less than 0.01 compared with upright sitting and P less than 0.001 compared with supine) during +2 Gz. We conclude that the immediate onset of weightlessness induces a significant increase in CVP, not only compared with the upright sitting position but also compared with the supine position at 1 G.
Adult↗
Plasma arginine vasopressin during neck suction in upright sitting man.
In order to examine the influence of carotid baroreceptor stimulation on arginine vasopressin secretion, 8 normal healthy males were subjected to static neck suction of -3.3 kPa for 20 min in the upright sitting position after overnight food and fluid restriction. The plasma concentration of arginine vasopressin did not change significantly during neck suction. However, in 3 subjects the termination of neck suction induced large increases in plasma arginine vasopressin from 1.8 to 63.7 ng/l, from 0.7 to 34.3 ng/l and from 2.1 to 19.0 ng/l, respectively. Two subjects experienced symptoms such as nausea and paleness during neck suction. Systolic arterial pressure increased slightly but significantly during neck suction from 15.3 +/- 0.3 to 15.7 +/- 0.4 kPa (N = 7, P less than 0.05), whereas mean arterial pressure, diastolic arterial pressure, central venous pressure, heart rate, plasma osmolality, plasma sodium and potassium were unchanged. Haemoglobin concentration in blood and haematocrit increased significantly during and after neck suction, whereas plasma volume decreased. We conclude that neck suction with a negative pressure of 3.3 kPa in upright sitting man does not significantly affect plasma arginine vasopressin. However, termination of the stimulation induces large increases in some subjects. This may be explained by a direct effect on the vagus nerve or by a selective deloading of carotid baroreceptors.
Adult↗
Cardiovascular reflexes during isometric exercise--role of muscle mass and gravitational stress.
Six healthy males performed sustained static contractions of five arm- and leg muscle groups for 2 min at 40% maximum voluntary contraction (MVC) sitting and supine. Delta heart rate, blood pressure, forearm vascular resistance, and cardiac output increased during contraction incrementing increasingly in the following order: dorsi flexion of ankle, plantar flexion, third finger flexion, handgrip, and knee extension. Muscle ischemia during recovery did not change this order. The cardiovascular responses to static contraction did not relate to muscle mass involved in a simple rectilinear manner. The increments in cardiovascular responses were not reduced in the supine position, although the values were at a lower level, probably due to the combination of a decreased sympathetic nervous activity in the supine position and an increased aortic baroreceptor stimulation induced by the increased stroke volume.
Adult↗
Central transmural venous pressure and plasma arginine vasopressin during negative pressure breathing in man.
After overnight food and fluid restriction, 8 normal healthy males were examined in the upright sitting position before (prestudy), during and after (recovery) negative pressure breathing (NPB) with a pressure (P = difference between airway pressure and barometric pressure) of -9.6 +/- 0.5 to -10.4 +/- 0.4 mm Hg for 30 min. Plasma arginine vasopressin (pAVP) did not change significantly comparing prestudy with 10 and 30 min of NPB or comparing recovery with NPB at 10, 20 or 30 min. However, at 20 min of NBP, pAVP was slightly lower than at prestudy (p less than 0.05). Central venous pressure (CVP) decreased significantly during NPB, and central transmural venous pressure (CVP-P) increased significantly from -0.9 +/- 0.8 mm Hg to 3.8 +/- 0.7, 4.3 +/- 0.7 and 4.5 +/- 0.6 mm Hg (p less than 0.001) after 10, 20 and 30 min, respectively. Systolic, diastolic and mean arterial pressure and heart rate did not change significantly during NPB. Diuresis, natriuresis, kaliuresis, osmotic excretion and clearance were slightly increased during the recovery hour after NPB compared to prestudy, while urine osmolality decreased during NPB (n = 6). However, none of these changes were significant. There was no significant correlation between CVP-P and pAVP. In conclusion, -10 mm Hg NPB for 30 min in upright sitting subjects did not change pAVP consistently, while CVP-P was significantly increased and HR and arterial pressures were unchanged. This lends support to the concept that arterial baroreceptors and not cardiopulmonary mechanoreceptors are of importance in regulating AVP secretion in man.
Adult↗
Central venous pressure and plasma arginine vasopressin in man during water immersion combined with changes in blood volume.
To investigate the influence of central venous pressure (CVP) changes on plasma arginine vasopressin (pAVP), 8 normal male subjects were studied twice before, during and after immersion to the neck in water at 35.1 degrees +/- 0.1 degrees C (mean +/- SE) for 6 h. After 2 h of immersion, blood volume was either expanded (WIEXP) by intravenous infusion of 2.0 1 of isotonic saline during 2 h or reduced by loss of 0.5 1 of blood during 30 min (WIHEM). The two studies were randomised between subjects. WIEXP increased CVP, systolic arterial pressure (SAP), diuresis, natriuresis, kaliuresis and osmolar clearance compared to WIHEM while haematocrit, haemoglobin concentration and urine osmolality decreased. Heart rate, mean arterial (MAP) and diastolic arterial pressure, plasma osmolality, plasma sodium, plasma potassium and free water clearance did not differ significantly in the two studies. pAVP was significantly higher after 6 h in WIHEM than after 6 h in WIEXP (2.0 +/- 0.2 vs. 1.6 +/- 0.2 pg X ml-1, mean +/- SE; P less than 0.05). pAVP values were corrected for changes in plasma volume due to infusion in order properly to reflect AVP secretion. In conclusion, there was a weak, but significant, negative correlation between CVP and pAVP during the two studies, while during recovery from WIHEM and WIEXP decrements in SAP and MAP correlated significantly and strongly with increases in pAVP. It is therefore concluded that it is the arterial baroreceptors rather than the cardiopulmonary mechanoreceptors which are of importance in AVP regulation in man.
Adult↗
Arginine vasopressin, circulation, and kidney during graded water immersion in humans.
Ten normal males rested sitting upright at an air temperature of 28 degrees C for 5.5 h (control, C) and underwent 4 h of graded water immersion (WI) to the umbilicus (UI), to the chest (CI), and to the neck (NI), respectively (water temperature = 34.5 degrees C), on different experimental days. Plasma arginine vasopressin (PAVP) was suppressed during WI compared with C and maximally so during NI. However, there was no change in PAVP comparing CI with UI even though central venous pressure (CVP) increased. CVP increased during CI and NI compared with C but was unchanged during UI, whereas cardiac output (rebreathing method), stroke volume, and plasma volume increased to approximately the same level during all three steps of WI compared with C. Heart rate and total peripheral vascular resistance decreased during UI, CI, and NI. Systolic arterial pressure (SAP) and pulse pressure (PP) were increased gradually from prestudy related to the degree of WI. Also diuresis, natriuresis, kaliuresis, osmotic excretion, and clearance were increased gradually compared with C, whereas free water clearance (CH2O) gradually decreased. There were weak negative but statistically significant correlations between PAVP and CVP and between changes in PAVP from prestudy and corresponding changes in SAP and PP. Furthermore, a statistically significant and negative correlation between CH2O and natriuresis could be established. We conclude that graded immersion gradually increases central blood volume and decreases PAVP. However, not only cardiopulmonary mechanoreceptors but also arterial baroreceptors may play a role in AVP suppression during WI in humans. In hydropenic subjects the suppression of PAVP during WI is apparently not effective in counteracting the decrease in CH2O induced by increased solute excretion.
Adult↗