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Results for “Head-Down Tilt”

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At least 19 recordsLinked to original sources
PubMed1979

Comparison of physiological effects of head-down tilting and immersion on the human body.

Among the methods simulating weightlessness, effects on the human body, head-down tilting and water immersion are very useful. The purpose of the present investigation was to carry out a comparative study of water balance and water-protein composition of the blood using the above two methods to simulate the physiological effects typical of an acute stage of weightlessness adaptation. The results of the 7-d head-down tilting and immersion experiments allow the following conclusions: More pronounced changes in water balance and water-protein composition of the blood during immersion seem to indicate that immersion produces a greater effect on the human body; The pattern of changes during immersion and tilting suggests that the adaptation period to immersion takes a longer time; These findings give evidence that immersion, compared with head-down tilting, reproduces more closely effects of acute adaptation to simulated weightlessness.

Adaptation, Physiological↗
PubMed1979

Central and cerebral hemodynamics and metabolism of the healthy man during head-down tilting.

Experiments on six healthy test volunteers, who underwent simultaneous catheterization of different cardiovascular compartments, were carried out to study the effect of head-down tilting at an angle of -20 degrees on the central and cerebral hemodynamics and metabolism. By the third hour of exposure, the test subjects showed a decrease in the systolic arterial pressure and increases in the systolic pressure of the right ventricle, heart rate, cardiac output, and oxygen intake. They also displayed a trend for an increase in the content of adenosine triphosphate, a decrease in the content of pyruvic acid, and essentially no changes in the concentration of lactic acid and activity of lactate dehydrogenase in the arterial blood and in the blood flowing out from the brain. The oxygen arteriovenous difference for the systemic and cerebral circulation decreased by 24% and 13%, respectively. The above circulatory and metabolic changes seem to reflect processes of adaptation of the human body to functioning under conditions of cephalad fluid shifts.

Acid-Base Equilibrium↗
PubMedDate not supplied

[Change in human kidney activity in passive orthostatism and head-down tilting].

Changes in the natriuretic and water excretory renal functions of healthy people during tilt table tests--with the head-end lifted upwards at an angle of 45 degrees and lowered at an angle of -15 degrees--were investigated. The renal excretion of sodium, water and osmotically active substances decreased drastically during the first 20 min of the headdown tilting and continued to fall down during the next 20 min. These changes were induced by an increase in the rate of tubular reabsorption of filtrate, sodium and osmotically free water rather than by a significant decrease of glomerular filtration rate. After tilting to the horizontal position circulation and glomerular filtration parameters rapidly returned to the normal. However, sodium clearance, diuresis and osmolar clearance remained decreased till the end of the experiment due to the further increase in the tubular reabsorption rate of sodium and water. During head-down tilting an increase in natriuresis, diuresis and osmolar clearance was seen which was related to an increase in the glomerular filtration rate and a decrease in the tubular reabsorption rate of filtrate, sodium and osmotically free water.

Adult↗
PubMed1978

Regulation of arterial blood pressure in Australian tiger snakes.

1. Blood pressure was measured in the dorsal aorta of restrained, unanaesthetized tiger snakes (Notechis scutatus) at different body temperatures during graded, passive tilt. Aortic blood pressure in horizontal snakes showed no significant change over a range of body temperatures between 18 and 33 degrees C (mean of measurements on 16 snakes = 42.2 +/- I.98 mmHg), while heart rate increased logarithmically (Q10 approximately 2.5). Blood pressure was stable during heating and cooling between body temperatures of 15 and 30 degrees C, but the pressure was 10--50% higher during heating than during cooling. 2. Head-up tilt usually caused a brief fall in pressure at heart level followed by partial or complete recovery and tachycardia. At the cessation of tilt, there was a characteristic overshoot of the blood pressure followed by readjustment to control (pretilt) levels. Head-down tilt typically increased pressure which then either stabilized or returned toward pretilt levels. Heart rate changes during head-down tilt were not consistent in direction or magnitude. Stabilized pressures at mid-body usually increased following head-up tilt and decreased following head-down tilt, indicating physiological adjustment to posture change. Blood pressure control was evident at body temperatures ranging from 10 to 38 degrees C, but was most effective at the higher and behaviourally preferred temperatures. 3. Propranolol lowered heart rate but did not influence pressure in horizontal snakes. During head-up tilt propranolol eliminated or reduced tachycardia and sometimes reduced the efficacy of pressure compensation for tilt. Phentolamine increased heart rate, lowered blood pressure, and eliminated pressure regulation during tilt. The results suggest that sympathetically mediated reflexes assist central blood pressure regulation in the tiger snake, with vasomotor adjustments having greater importance than changes in heart rate.

Animals↗
PubMed1979

The Trendelenburg position: hemodynamic effects in hypotensive and normotensive patients.

The effect of the Trendelenburg position on systemic and pulmonary hemodynamics in critically ill patients is not generally appreciated. This study examined the hemodynamoc effect of 15-20 degrees head-down tilt in 61 normotensive and 15 hypotensive patients with acute cardiac illness or sepsis. In normotensive patients, the head-down tilt increased the preload of both right and left ventricles, increased cardiac output slightly, decreased systemic vascular resistance, and did not change the mean arterial pressure. This effect was probably mediated by baroreceptor stimulation. In hypotensive patients, the Trendelenburg position did not increase preload, slightly increased afterload, and decreased cardiac output. This study failed to document any beneficial hemodynamic effect of the Trendelenburg position in critically ill normo- or hypotensive patients.

Adult↗
PubMed1979

Forearm and finger blood flow responses to passive body tilts.

Ten to fifteen healthy subjects, ages 18--30 yr, were used to assess the correlation of forearm blood flow with graded passive body tilts and vascular resistance and also to discern the relative effects of body tilts on finger blood flow. In the head-up tilts forearm blood flow and arterial blood pressure fell progressively, whereas forearm vascular resistance and pulse rate increased. In the head-down tilts the forearm blood flow and the arterial blood pressure increased, whereas the forearm vascular resistance and pulse rate decreased. These changes were found to be significantly correlated with the different tilt angles and with one another. In a preliminary study it was found that infrared heating of the carpometacarpal region produced finger vasodilatation similar to the forearm vasodilatation observed by Crockford and Hellon (6). However, unlike forearm blood flow, finger blood flow showed no appreciable response to either the head-up or head-down tilts. This indicates that the sympathetic tone and the volume of blood in the finger are not appreciably altered by this test procedure at least 1 min after the body tilt is assumed.

Adolescent↗
PubMedDate not supplied

[Possibilities of preventing the adverse reactions in modeling the acute period of adaptation to weightlessness].

It has been shown that during head-down tilting at an angle of -30 degrees occlusion of the four limbs by 70 mm Hg relieved unpleasant symptoms. According to rheoencephalography, cerebral blood flow decreased to the level normally seen in the supine position. During a prolonged head-down tilting at an angle of -15 degrees intermittent occlusion of only lower limbs by 60--30 mm Hg proved more effective.

Adaptation, Physiological↗
PubMedDate not supplied

[Indices of human blood acid-base equilibrium and enzymatic activity in short-term antiorthostatic hypokinesia].

Before and after a 5 day head-down tilt of 4.5 degrees blood samples were withdrawn from different areas of the cardiovascular system of healthy male volunteers. Blood was sampled by means of selective catheterization. Parameters of acid-base equilibrium and activities of aminotransferases and alkaline phosphatase were measured. After immobilization the most significant changes were observed in the blood outflowing from the brain in which significant metabolic acidosis and increased activity of aspartate aminotransferase occurred. A slight increase in the activity of aspartate aminotransferase was also observed in the blood outflowing from the liver and kidneys. It is concluded that brain is the organ which is subjected to short-term simulated weightlessness in the highest degree.

Acid-Base Equilibrium↗
PubMedDate not supplied

[Use of electrical muscle stimulation for the prevention of neuormuscular disorders during 45 days' antiorthostatic hypokinesia].

Healthy test subjects exposed to a 45-day head-down tilting (- 6.5 degrees) showed a decline of the tone and strength of certain muscle groups, a decrease of leg circumference, a deterioration of the walking pattern, and a reduction of exercise tolerance (provocative tests with bicycle ergometry pedaling at a moderate and maximum rate). Electrostimulation of muscles applied by the Tonus-2 equipment for 30 min twice a day, 6 days a week helped to reduce the level of hypokinesia-induced disorders.

Adult↗
PubMedDate not supplied

[Antiorthostatic hypokinesia as an approximate model of weightlessness].

Eight test subjects were exposed to a five-day bed rest experiment in the recumbent and head-down position (at an angle of 0 degrees,--4 degrees,--8 degrees, and--12 degrees) to study the physiological effects of the exposure. The head-down tilting at--4 degrees and--12 degrees was shown to simulate physiological effects of real space flight better than bed rest at 0 degrees. The results made it possible to model an acute stage of weightlessness adaptation and to assay the contribution of gravity-induced blood redistribution to the physiological reactions.

Adult↗
PubMedDate not supplied

[Bioelectrical activity of the brain during 49-day antiorthostatic hypokinesia in persons with the early signs of autonomic vascular dysfunction].

Cerebral bioelectric activity of 18 male test subjects (9 test subjects with early manifestations of autonomic-vascular dysfunctions of the hypertensive, hypotensive or cardiac type, and 9 healthy test subjects), aged 25 to 42, was studied during their 49-day head-down tilting (-4 degrees) and during recovery. On the 5th experimental day their EEG showed signs of CNS irritation and increased excitation in response to photostimulation. That was very marked in the test subjects with autonomic-vascular dysfunctions. On the 15, 30 and particularly 45th experimental day their EEG showed both diffusion and paroxysmal slow activity; CNS excitability decreased significantly during rhythmic photostimulation. By the 20th--22nd day of recovery EEG parameters returned to normal. This indicates that the changes were reversible and that the therapeutic measures applied were effective.

Adult↗
PubMedDate not supplied

[Effect of short-term antiorthostatic hypokinesia on the pressure in various parts of the healthy human cardiovascular system].

Before and after 5-day head-down tilting (-4.5 degrees) blood pressure was measured in different cardiovascular compartments by the technique of selective catheterization: the upper bulb of the internal jugular vein, superior and inferior venae cavae, hepatic, renal and iliac veins, right atrium and right ventricle, coronary sinus, pulmonary and radial arteries. After exposure the pressure in extrathoracic vessels increased by 1.4 mm Hg on the average: in the internal jugular vein it rose by 1.7 mm Hg whereas in the iliac vein by 1.0 mm Hg. The blood pressure in the intrathoracic vessels of the systemic circulation increased, as a rule, by no more than 0.5--0.8 mm Hg. This elevation was characteristic of diastolic regions of the pressure curve (x- and y-collapse). The pressure in pulmonary vessels--pulmonary artery and left atrium--showed a trend for a decrease of 1.3 mm Hg. The factors that may be responsible for the dissimilar changes of pressure in different cardiovascular compartments under the influence of short-term simulated weightlessness are discussed.

Adult↗
PubMedDate not supplied

[Evaluation of the antiorthostatic reactions of the cerebral circulation].

On the basis of experiments on 122 healthy male test subjects the norms of reactions of cerebral circulation to antiorthostatic exposures, basic principles and evaluations of its antiorthostatic tolerance (AOT) were established. The level of AOT was found to increase in acrobats in the course of their training, in test subjects after 30-day head-down tilting, and in space crewmen postflight. This increase can be regarded as an adaptive reaction of cerebral circulation to the excess blood rush to the head both on the Earth and in weightlessness. The similarity of regulatory hemodynamic changes in the above groups shows the possibility and indicates approaches to the ground-based training of cerebral circulation aimed at facilitating and accelerating its adaptation to weightlessness.

Adaptation, Physiological↗
PubMedDate not supplied

[Clinical aspects of a change in the nervous system after 49-day head-down hypokinesis].

Clinical and neurological methods were used to investigate the state of the central nervous system of 9 healthy male test subjects during a 49-day head-down (at an angle of 4-6 degrees) bed rest experiment. Beginning with the 4-5th week polymorphic changes in the nervous state emerged and developed. They can be divided into three clinical syndromes: astheno-neurotic syndrome that of autonomic dysfunction and the syndrome of neuromuscular (trophic) and statokinetic disorders. In comparison with the clinostatic bed rest, head-down tilting brought about changes in the nervous system earlier and with a more distinct "acute" phase. This is in favour of the concept that hemodynamic changes in the brain and the upper body play a very important part in the pathogenetic mechanism that underlies most disorders accompanying bed rest.

Adaptation, Physiological↗
PubMedDate not supplied

[Kaliuretic function of the kidneys in humans with different degrees of motor activity and at bed rest].

The kaliuretic function of the kidneys was studied in 12 healthy test subjects during the 49-day head-down tilting (--4 degrees). The results suggest that the selection of optimal exercises and dietary potassium intake may prevent changes in the potassium metabolism and the renal kaliuretic function both during bed rest and weightlessness as well as facilitate a rapid recovery of potassium homeostasis on return to Earth.

Adult↗
PubMedDate not supplied

[Assessment of regional blood filling by using the rheoplethysmographic method combined with functional tests].

Vascular responses of fingers and toes to the occlusion test as well as fingers, head, lungs and liver to the Valsalva maneuver were studied. The responses to the tests depended on the initial level of blood filling. The different level of blood filling was induced by orthostatic, head-down tilt and LBNP tests. It is recommended to use rheography (slow and pulse components) in combination with the occlusion test and Valsalva maneuver in order to assess regional blood filling and venous tone of crew-members in space flights.

Adult↗
PubMed1979

Effect of posture on arterial pressures, timing of the arterial sounds and pulse wave velocities in the extremities.

We have recorded systolic and diastolic blood pressure, and the intervals between the QRS complex of the electrocardiogram and the Korotkoff arterial sound at systolic and diastolic pressure (QKs and QKd, respectively), at the brachial and posterior malleolar arteries, for normal subjects in the supine, standing, or head-down positions on a tilt table. These data make it possible to calculate an apparent mean pulse wave velocity. Results indicate: (1) when the subject is supine (0 degrees), brachial and posterior malleolar artery blood pressures are virtually identical; (2) upon standing (+90 degrees), both systolic and diastolic pressures in the foot are elevated by a mean of approximately 70 mm Hg, whereas brachial artery systolic pressure is unaffected and brachial diastolic pressure is raised 7 mm of mercury; (3) conversely, in the head-down (feet-up) position (-30 degrees) the blood pressure in the foot was decreased approximately 20 mm of mercury, whereas the brachial arterial pressure is again unaffected; (4) as one changes from the head-down to the supine to the standing positions, the mean QKs interval at the brachial artery was increased by 5 and 15 msec, respectively; (5) conversely, the arrival of the pulse wave in the leg was hastened, with QKd decreasing by 7 and then 18 msec. The effects of QKs were slightly smaller in the brachial artery but considerably larger in the malleolar artery, with a decrease of 16 msec and then 48 msec; (6) mean apparent pulse wave velocity increases from 9.1 to 10.9 to 17.6 m/sec, as one changes from -30 degrees to 0 degrees to +90 degrees.

Adolescent↗