Biomedical subjects

F Baisch

Publications and source records attributed to F Baisch.

At least 19 recordsLinked to original sources

PubMed2000

Increased hypoxic ventilatory response during hypovolemic stress imposed through head-up-tilt and lower-body negative pressure.

The aim of this study was to quantify the influence of head-up-tilt (HUT) on the isocapnic hypoxic ventilatory response (HVR) in man, and to investigate the effect of orthostatic blood shifts separately from other gravitational effects by the application of lower-body negative pressure (LBNP) with subjects in a horizontal position. HVR was measured in 15 subjects during passive HUT from 0 degrees to 85 degrees as well as during -7 degrees head-down-tilt and while they were in a sitting position. In a subgroup of eight subjects the effect of 85 degrees HUT was compared to a corresponding LBNP of -70 mbar on HVR. Moreover, by imposing graded HUT (7 degrees, 15 degrees, 30 degrees, 50 degrees) and LBNP (-15, -30 mbar) we studied the effect of low-level orthostatic stress on HVR. Ventilation, end-tidal partial pressure of CO2, heart rate and blood pressure were recorded continuously for 1 min before, and during HVR. HVR was significantly increased by approximately equal to 50% through both 85 degrees HUT and -70 mbar LBNP as compared to 0 degrees and 0 mbar, respectively, at unchanged mean arterial pressure. Low-level HUT and LBNP had no effect on HVR. It was concluded that the orthostatic HVR increase may be attributable to caudal blood shifts (i.e., central hypovolemia). This HVR increase requires a pronounced hypovolemic stress but no decrease in arterial blood pressure. It is suggested that a central interaction of arterial and cardiopulmonary baroreceptors is underlying this response. Their separate contribution remains to be assessed.

Adult↗

PubMed2000

Body fluid regulation in micro-gravity differs from that on Earth: an overview.

Similar to the response to central hypervolemic conditions on Earth, the shift of blood volume from the legs to the upper part of the body in astronauts entering micro-gravity should, in accordance with the Henry-Gauer mechanism, mediate diuresis and natriuresis. However, fluid balance and kidney function experiments during various space missions resulted in the surprising observation that the responses qualitatively differ from those observed during simulations of hypervolemia on Earth. There is some evidence that the attenuated responses of the kidney while entering weightlessness, and also later during space flight, may be caused by augmented fluid distribution to extravascular compartments compared to conditions on Earth. A functional decoupling of the kidney may also contribute to the observation that renal responses during exposure to micro-gravity are consistently weaker than those during simulation experiments before space flight. Deficits in body mass after landing have always been interpreted as an indication of absolute fluid loss early during space missions. However, recent data suggest that body mass changes during space flight are rather the consequences of hypocaloric nutrition and can be overcome by improved nutrition schemes. Finally, sodium-retaining humoral systems are activated during space flight and may contribute to a new steady-state of metabolic balances with a pronounced increase in body sodium compared to respective conditions on Earth. A revision of the classical "micro-gravity fluid shift" scheme is required.

Body Fluids↗

PubMed2000

Cardiovascular response to lower body negative pressure stimulation before, during, and after space flight.

BACKGROUND: It is well known that space travel cause post-flight orthostatic hypotension and it was assumed that autonomic cardiovascular control deteriorates in space. Lower body negative pressure (LBNP) was used to assess autonomic function of the cardiovascular system. METHODS: LBNP tests were performed on six crew-members before and on the first days post-flight in a series of three space missions. Additionally, two of the subjects performed LBNP tests in-flight. LBNP mimics fluid distribution of upright posture in a gravity independent way. It causes an artificial sequestration of blood, reduces preload, and filtrates plasma into the lower part of the body. Fluid distribution was assessed by bioelectrical impedance and anthropometric measurements. RESULTS: Heart rate, blood pressure, and total peripheral resistance increased significantly during LBNP experiments in-flight. The decrease in stroke volume, the increased pooling of blood, and the increased filtration of plasma into the lower limbs during LBNP indicated that a plasma volume reduction and a deficit of the interstitial volume of lower limbs rather than a change in cardiovascular control was responsible for the in-flight response. Post-flight LBNP showed no signs of cardiovascular deterioration. The still more pronounced haemodynamic changes during LBNP reflected the expected behaviour of cardiovascular control faced with less intravascular volume. In-flight, the status of an intra-and extravascular fluid deficit increases sympathetic activity, the release of vasoactive substances and consequently blood pressure. Post-flight, blood pressure decreases significantly below pre-flight values after restoration of volume deficits. CONCLUSION: We conclude that the cardiovascular changes in-flight are a consequence of a fluid deficit rather than a consequence of changes in autonomic signal processing.

Adult↗

PubMed2000

Water and sodium balances and their relation to body mass changes in microgravity.

BACKGROUND: Since the very beginning of space physiology research, the deficit in body mass that is often observed after landing has always been interpreted as an indication of the absolute fluid loss early during space missions. However, in contrast to central hypervolemic conditions on Earth, the acute shift of blood volume from the legs to the upper part of the body in astronauts entering microgravity (microG) has neither stimulated diuresis and natriuresis nor resulted in negative water-and sodium-balances. DESIGN: We therefore examined the kinetics of body mass changes in astronauts (n = 3) during their several weeks aboard the space station MIR. A continuous diet monitoring was performed during the first mission (EuroMIR94, 30 days). The second mission (MIR97, 19 days) comprised a 15-day metabolic ward period (including predefined constant energy and sodium intake). Water and sodium balances were calculated and the kinetic of changes in basal concentrations of fluid-balance-related hormones during flight were determined. CONCLUSION: The data suggest firstly that loss of body mass during space flight is rather a consequence of hypocaloric nutrition. Secondly, microG provokes a sodium retaining hormonal status and may lead to sodium storage without an accompanying fluid retention.

Astronauts↗

PubMed2000

High dietary sodium chloride consumption may not induce body fluid retention in humans.

A commonly accepted hypothesis is that a chronically high-sodium diet expands extracellular volume and finally reaches a steady state where sodium intake and output are balanced whereas extracellular volume is expanded. However, in a recent study where the main purpose was to investigate the role of natriuretic peptides under day-to-day sodium intake conditions (Heer M, Drummer C, Baisch F, and Gerzer R. Pflügers Arch 425: 390-394, 1993), our laboratory observed increases in plasma volume without any rise in extracellular volume. To scrutinize these results that were observed as a side effect, we performed a controlled, randomized study including 32 healthy male test subjects in a metabolic ward. The NaCl intake ranged from a low level of 50 meq NaCl/day to 200, 400, and 550 meq/day, respectively. Plasma volume dose dependently increased (P < 0.01), being elevated by 315 +/- 37 ml in the 550-meq-NaCl-intake group. However, in contrast to the increased plasma volume, comparable to study I, total body water did not increase. In parallel, body mass also did not increase. Mean corpuscular volume of erythrocytes, as an index for intracellular volume, was also unchanged. We conclude from the results of these two independently conducted studies that under the chosen study conditions, in contrast to present opinions, high sodium intake does not induce total body water storage but induces a relative fluid shift from the interstitial into the intravascular space.

Adult↗

PubMed2000

Regulation and distribution of body fluid during a 6-day head-down tilt study in a randomized cross-over design.

Head down tilt (-6 degrees HDT) examinations are commonly used simulation models for various microgravity induced changes in body functions. Body fluid distribution (by means of dye dilution and two independent multifrequency impedance techniques), water- and sodium-handling, and the plasma/serum concentrations of fluid balance related hormones have been determined in a randomized, controlled, cross-over study in 8 healthy test subjects. The comparison of responses to HDT and an upright control position with respective experiences from space shows some similarities but also various discrepancies between the terrestrial simulation and real microgravity.

Bed Rest↗

PubMed1999

Effects of an antihypertensive medication on functional capacity under simulated flight-typical stress-conditions.

A model to investigate the functional capacity (psychomental performance) under stressful conditions was developed. Twenty eight patients with mild hypertension receiving Nitrendipine (20 mg) for 30 days were tested under hypoxic (16% oxygen) and/or orthostatic (-30 mmHg lower body negative pressure) conditions using a subset of the AGARD battery. The main effect was a decreasing performance of the grammatical reasoning task (GRT) under hypoxia or the combination of hypoxia and orthostasis. A simultaneous application of stressors while performing psychometric test batteries may be useful to reveal pharmaceutical influences on human performance and may help to recommend the use of drugs in occupational medicine.

Aerospace Medicine↗

PubMed1997

Shifts in blood volume alter the perception of posture.

Recent experiments have shown that somatic graviceptors exist in humans. Traditionally, extravestibular gravity information has been thought to originate from mechanoreceptors in the joints, muscles and skin. Experiments with normal, paraplegic and nephrectomized subjects revealed that the kidneys and the cardiovascular system are involved in providing truncal gravity information. The present study intends to determine the influence of shifts in body fluid, especially of the distribution of blood along the subjects' spinal (Z-) axis, on the perception of posture. To this end, the distribution of body fluids was altered by means of the technique of lower body negative and positive pressure (LBNP and LBPP). LBNP leads to venous pooling of blood in the legs, whereas LBPP prevents venous blood from pooling, increasing central volume. Changes in blood distribution were measured by segmental impedance cardiography for four body segments: the upper torso (thoracic cavity), lower torso (abdominal and pelvic region), thigh and calf. Seventeen healthy subjects (mean age: 27.3 years) participated in the experiment. They were positioned on the side (right-ear-down head position) on a tilt table which the subjects and the experimenter could tilt via remote control around an axis parallel to the subjects' visual (X-) axis. The experimenter set the initial tilt in total darkness to arbitrary angles while strictly alternating between head-up and head-down tilts. Subjects were then asked to rotate the board until they felt they were in a horizontal posture. Means and variances of eight pairs of settings were taken as a measure of the subjective horizontal posture (SHP). During LBNP (-30 mmHg), subjects perceived being tilted head-up, whereas LBPP (+30 mmHg) led them to feel tilted head-down. The results corroborate the hypothesis of an effect of the blood's mass on graviception and also indicate supplementary contributions of other visceral afferences.

Adult↗

PubMed1997

Cardiovascular regulation: a modelling approach.

A detailed analysis of autonomic cardiovascular control (ACVC) may provide a key to a better understanding of the mechanisms underlying postflight orthostatic hypotension. The central substrate of human ACVC is not directly accessible to measurements and observation in space research. Modelling--supporting inference and physiological reasoning--is a valuable tool to disclose its involvement We are currently determining the suitability of artificial neural networks (ANN's) as a model of the central substrate of ACVC. Having conducted a number of experiments with simulated tilt test data to clarify the choice of input coding and of architectural biases in network training we will now report on the approximation of data obtained from human subjects during preparation of the German MIR'97 and D-2 missions.

Adaptation, Physiological↗

PubMed1995

Changes in the thoracic impedance distribution under different ventilatory conditions.

The present study was performed with the aim of checking the suitability of EIT in imaging regional thoracic impedance variations during lung ventilation under predefined conditions and to compare EIT with established reference techniques. A new technique of functional EIT imaging designed to visualize physiologically relevant information from the sequentially registered series of thoracic distributions was introduced. Experiments were performed on five spontaneously breathing healthy subjects and on 12 anaesthetized supine pigs. 16 electrodes were placed around the thorax and consecutive transthoracic impedance distributions were measured at a rate of 1 Hz (Sheffield APT system mark I, IBEES, Sheffield, UK). Several voluntary breathing manoeuvres were performed in human subjects and the tracings of local impedance were compared with standard spirometry. In animal experiments EIT was applied during artificial ventilation at different ventilation rates and during stepwise passive emptying and filling of either one or both lungs while the respiratory muscles were relaxes. Further, selective blockade of lung regions resulting in regionally reduced ventilation was performed and the capability of EIT to follow and differentiate local ventilatory disturbances was checked by reference techniques (x-ray and staining methods). The experiments revealed an overall agreement between the spirometric and impedance data in all breathing patterns performed. A linear relationship between changes of the air content of the lungs and the regional thoracic impedance was shown (intraindividual correlation coefficient range, 0.986-0.999; n = 12 animals). The functional images of the impedance distribution across the thorax reproduced adequately the typical anatomical characteristics of the pig and the human thorax. The spatial resolution of EIT functional images was sufficient to differentiate lung areas corresponding to approximately 20 ml tissue volume. EIT with the additional evaluation procedure of functional imaging was shown to be a suitable and reliable method of imaging different ventilatory conditions with the potential to become a useful tool for monitoring respiratory function.

Adult↗

PubMed1993

Long-term elevations of dietary sodium produce parallel increases in the renal excretion of urodilatin and sodium.

The effects of dietary sodium intake on the renal excretion of urodilatin and of sodium were examined in six healthy male subjects. The 24-day study period was divided into three phases of 8 days each. Subjects ingested 2.8 mequiv sodium (kg body weight)-1 day-1 during the first phase, 5.6 mequiv (kg body weight)-1 day-1 during the second phase, and 8.4 mequiv (kg body weight)-1 day-1 during the third phase. The excretion of both sodium (P < 0.002) and urodilatin (P < 0.006) increased in response to the increasing dietary sodium, while urine flow did not change. Urinary urodilatin excretion correlated closely with renal sodium excretion (P < 0.001). Serum aldosterone levels (P < 0.01) as well as serum renin levels (P < 0.05) significantly decreased with increasing sodium intake. Plasma [Arg]vasopressin levels increased significantly (P < 0.05). Plasma atrial natriuretic factor and cGMP levels as well as urinary cGMP excretion rates were unaltered by the changes in sodium intake. We conclude from these results that the renal natriuretic peptide, urodilatin, but not the main cardiac member of the natriuretic peptide family may be involved in the regulation of day-to-day sodium balance.

Adult↗

PubMed1993

Noninvasive cardiac output measurement by arterial pulse analysis compared with inert gas rebreathing.

Noninvasive cardiac output (CO) measured by arterial pulse analysis was compared with that measured by inert gas rebreathing in six healthy male volunteers. Pulse contour analysis was applied to the pressure wave output of a Finapres, which noninvasively measures continuous arterial pressure in a finger. Data were collected before, during, and after a 10-day 6 degrees head-down tilt experiment. Intravenous saline loading and lower body negative pressure stimuli varied CO over 2.8-9.6 l/min, as measured by the rebreathing technique. Because pulse contour provides only relative changes in CO, to obtain absolute values it must be calibrated against another measurement. Pulse contour data were calibrated every measurement day against the mean of two to four control rebreathing CO measurements before the lower body negative pressure or intravenous saline loading stimuli. Using one averaged calibration factor per subject for a total of 27 days, we compared the results of both methods. The linear regression between pulse contour (Pc CO) and rebreathing CO (Rebr CO) was Pc CO = 0.15 + 0.98(Rebr CO) (r = 0.96). The standard deviation of the difference of the two methods was 0.5 l/min (n = 205), excluding data used for calibration. By monitoring pulse contour CO before and during rebreathing, the rebreathing maneuver itself was shown to produce a substantial increase in CO that was mainly related to an increase in heart rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1992

Effects of simulated microgravity (HDT) on blood fluidity.

Exposures to microgravity and head-down tilt (HDT) produce similar changes in body fluid. This causes an increase in hematocrit that significantly affects hemorheological values. Lack of physical stimulation under bed rest conditions and the relative immobility of the crew during spaceflight also affects the blood fluidity. A group of six healthy male subjects participated as volunteers, and blood samples were collected 10 days before, on day 2 and day 9, and 2 days after the HDT phase. Blood rheology was quantified by plasma viscometry, red cell aggregability, and red cell deformability. A reduced red cell deformability, an indication of the diminished quality of the red blood cells, was measured under HDT conditions that finally led to the so-called "space flight anemia." Enhanced red cell membrane fragility induced by diminished physical activity and an increase in hemoglobin concentration are responsible for this effect. Plasma viscosity is reduced as a result of diminished plasma proteins. However, despite the reduction in plasma proteins, including fibrinogen, alpha 2-macroglobulin, and immunoglobulin M, red cell aggregation was enhanced, principally because of the increase in hematocrit. Our results of hemorheological alterations under HDT conditions may help to elucidate the formerly documented hematologic changes during spaceflight.

Adult↗

PubMed1992

Diuresis and natriuresis following isotonic saline infusion in healthy young volunteers before, during, and after HDT.

In the present study the response to acute saline loading was investigated. During a 24-day study period six male subjects followed a standardized diet including a daily intake of 40 ml water and 125 mg NaCl per kg body weight. Before, during, and after a ten-day period of 6 degrees head down tilt (HDT) each volunteer received an intravenous 0.9% saline infusion of 22 ml/kg body weight over 20 minutes. HDT produced significant losses in body weight and in blood volume, but the responses to saline loading were similar during all phases of the study. Plasma levels of atrial natriuretic peptide (ANP) did not increase, while plasma levels of cyclic GMP increased by about 40% 90 minutes after each infusion. Urine flow nearly doubled during second hour post-infusion. Sodium excretion showed a 3-fold increase and remained elevated during the third hour, while potassium excretion was significantly reduced. Urinary excretion of cyclic GMP reached a peak during the second hour post-infusion. At the end of these short-term periods the cumulative water- and sodium-balance data disclosed that only about 20% of the infused water and less than 15% of the infused sodium was excreted during each experiment. In addition to the short-term renal response, urine flow and sodium excretion remained significantly elevated for more than 48 hours after each saline load. The long-term renal response was paralleled by an increased excretion of urinary cyclic GMP. HDT produced significant changes in body fluid distribution, but only minor changes in the regulatory responses to an acute saline load. We conclude from these data that the excretion of an acute isotonic saline load requires several days and that the renal response appears to be independent of the secretion of ANP from the heart.

Adult↗

PubMed1992

Response of adrenergic receptors to 10 days head-down tilt bedrest.

Adrenergic receptor responses to 10 days head-down tilt (HDT) bed-rest were measured in six healthy young males. The densities of alpha 2-receptors on platelets, beta 2-receptors on lymphocytes, and the responsiveness of beta 2-receptors to isoproterenol stimulation were assessed, as were the urinary catecholamine excretion rates. The densities of alpha 2- and beta 2-receptors were low before HDT, and were high during HDT. While the density of alpha 2-receptors decreased after HDT, that of beta 2-receptors remained high. No changes in the responsiveness of beta 2-receptors were observed. The urinary catecholamine levels were high before HDT, decreased during the bedrest period. After HDT urinary norepinephrine excretion increased significantly. It is likely that the receptors were down-regulated before HDT in response to a situation that was perceived as being stressful. There were no changes in receptor characteristics specifically attributable to HDT.

Adult↗

PubMed1992

Head-down tilt bedrest. HDT'88--an international collaborative effort in integrated systems physiology.

An international collaborative project, initiated by the DLR-NASA Life Sciences Working Group, led to the performance of a head-down tilt bedrest (HDT) study at the DLR Institute for Aerospace Medicine. Scientific and operational questions were addressed in preparation for the D-2 Spacelab mission. Principal areas of interest were cardiovascular regulation and fluid/electrolyte metabolism. The results are detailed in a series of 13 reports to which the present paper serves as an introduction.

Adaptation, Physiological↗

PubMed1992

Effect of head-down bedrest on blood/plasma density after intravenous fluid load.

Using the mechanical oscillator technique, the mass density of antecubital venous blood and plasma samples was measured in 6 men before and after infusion of 22 ml/kg isotonic NaCl solution before, on day 7 during, and on day 3 after ten days of 6 degrees head-down bedrest. We studied 1) the distribution volumes of the infused NaCl solution, 2) the magnitude and time-course of induced fluid shifts to the extravascular spaces after rapid volume expansion, and 3) the protein concentration of the translocated fluid. The NaCl distribution volume was 16.7 +/- 2.9% body weight (BW) before, 15.0 +/- 3.0% BW during (P less than 0.05) and 13.0 +/- 1.3% BW after the head-down tilt (HDT) period (P less than 0.01). The volume of fluid shifted 120 min after infusion was not different in the control (12.9 +/- 7.4% plasma volume and 8.3 +/- 3.2% blood volume), during HDT (14.7 +/- 3.8% plasma volume and 7.4 +/- 5.6% blood volume), during HDT HDT conditions (14.6 +/- 2.2% plasma volume, and 8.2 +/- 1.3% blood volume, respectively). The density of the shifted fluid which reflects protein concentration was also unchanged (1004.2 +/- 4.2 g/l, 1002.6 +/- 4.3 g/l and 1003.9 +/- 8.2 g/l in the control, during, and after HDT periods, respectively). The mass density of red cells did not change with any condition. It is concluded that the distribution volume of isotonic saline solution decreases with diminished body mass. Densitometry provides a means of monitoring volume changes and protein shifts under the circumstances of our study.

Adult↗

PubMed1992

The effects of a 10-day period of head-down tilt on the cardiovascular responses to intravenous saline loading.

We tested the hypothesis that adaptation to microgravity, simulated by a 10-day period of head-down tilt (HDT), alters the responses to an intravenous fluid load by causing a larger fraction of the infused volume to be retained and magnifying the acute hemodynamic effects. HDT caused a significant (p less than 0.01) decrease in blood volume (-0.72 liters) and weight (-1.6 kg). Rapid infusion (22 ml/kg over 20 min.) of isotonic saline before, during, and after HDT produced a transient blood volume expansion with 18% of the infusate retained intravascularly after 2 hours. HDT had no effect on this response. Control hemodynamics were significantly different with lower cardiac output and higher total peripheral resistance (TPR) during and after HDT. Saline caused significant increases in cardiac output, heart rate, and stroke volume and a decrease in TPR. The magnitude and time course of these changes were not altered by HDT. The results refute the hypothesis and suggest that during HDT new set points or operating points were established for the control of intravascular volume and hemodynamic state.

Adult↗