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Biomedical subjects

F Baisch

Publications and source records attributed to F Baisch.

At least 37 records · Page 2Linked to original sources
PubMed1992

Effects of head-down tilt and saline loading on body weight, fluid, and electrolyte homeostasis in man.

We studied the effects of head-down tilt bedrest (HDT) on body weight, fluid and sodium homeostasis. A fluid load session with rapid intravenous infusion of 22 ml/kg body weight (BW) isotonic saline was performed before, during and after HDT. During the pre- and post HDT periods the test subjects were given a diet containing 2600 kcal/day. The energy intake was reduced to 2000 kcal/day during HDT. Water intake was kept constant at 40 ml/kg BW, sodium intake was 2.2 mmol/kg BW and protein intake was 1.4 g/kg BW, while the daily fat and carbohydrate intake was reduced during the HDT period. As expected plasma volume and BW changed rapidly in the beginning of HDT and during early recovery. A total body water loss of 0.6 l was observed within the second day after tilting. Plasma volume was reduced by 16% during HDT-bedrest. The time course of the body fluid loss paralleled a decrease in body sodium that then remained fairly constant during the HDT-bedrest period (except for the interference caused by the fluid loading on day S06). A restoration of body fluid and body sodium content occurred early in the recovery period. Fluid loading caused a negative fluid balance of 0.6-0.9 l over a 48 hr period following infusion regardless of the phase of the HDT study. These results demonstrate that under our strictly controlled conditions 1) HDT alters body fluid and sodium balances, 2) a standard fluid loading causes a net negative 3-day fluid balance during all phases of the study.

Adult↗
PubMed1992

Effect of head-down tilt bedrest (10 days) on lymphocyte reactivity.

Immunological responses of six healthy males to 10 days of head-down tilt bedrest (HDT) were assessed. Lymphocyte responsiveness was severely reduced immediately before, during, and immediately after the HDT, even though the lymphocyte numbers did not change. By contrast, delayed-type hypersensitivity was not affected. No dramatic changes were found in WBC counts and lymphocyte subpopulations, with the only exception of natural killer (NK) cells which transiently decreased immediately after HDT. Plasma cortisol levels were elevated above normal immediately before and during the HDT. The data suggest that the mitogenic response of lymphocytes was affected by psychological and fluid shift stress. These results are compared with data obtained during and after spaceflight. We conclude that the stress of HDT induces changes in immunological responsiveness that are strikingly similar to those arising from the stress of spaceflight.

Adult↗
PubMed1992

Cardiopulmonary function during 10 days of head-down tilt bedrest.

Pulmonary and cardiovascular responses to simulated weightlessness, i. e. 6 degrees head-down tilt bedrest (HDT) were investigated in six healthy male volunteers (mean age 26 yrs). Pulmonary diffusing capacity, functional residual capacity, pulmonary capillary blood flow, and lung tissue volume were measured by inert gas rebreathing. Heart rate and mean arterial blood pressure were obtained from finger blood pressure readings using a plethysmographic technique (Finapres). The short-term (20 min) response to HDT consisted of a 22% increase in pulmonary blood flow, and 13% and 31% falls in blood pressure and heart rate relative to standing. Functional residual capacity fell by 33%, while lung tissue volume increased insignificantly. Subsequent measurements during 10 days of HDT and 5 days of recovery revealed no further changes in lung volume, lung tissue volume, or blood pressure. However, diffusing capacity fell gradually and remained 4%-5% below baseline values after the 7th day of bedrest and during recovery (p less than 0.05). Pulmonary blood flow decreased by 16% during head-down bedrest and recovered partially within the following 5 days (p less than 0.05). We conclude that during and after simulated weightlessness marked alterations in cardiovascular function and marginal affections of gas exchange can be demonstrated already at rest. They may be considered as contributing factors to orthostatic and exercise intolerance observed after space flight.

Adult↗
PubMed1992

Pulmonary responses to lower body negative pressure and fluid loading during head-down tilt bedrest.

Exposure to microgravity redistributes body fluids with important secondary effects on cardiovascular function. We tested the hypothesis that the fluid shifts also affect pulmonary gas exchange. Microgravity was simulated in six male volunteers by a 10-day period of bedrest at 6 degrees head-down tilt (HDT). Lower body negative pressure (LBNP) and intravenous saline loading superimposed acute changes in fluid distribution on the prolonged effects of HDT. HDT produced relative dehydration and hypovolemia with decreased pulmonary blood flow and diffusing capacity. Before bedrest, pulmonary blood flow decreased by 24% during LBNP and diffusing capacity by 7%, while functional residual capacity increased by 14% (p less than 0.05). Intravenous saline loading caused a 24% increase in pulmonary blood-flow (p less than 0.05). Functional residual capacity decreased by 10% and diffusing capacity by 6% (p less than 0.05). Lung tissue volume did not change significantly. Head-down tilt had only minor effects on the responses to LBNP and saline loading. We conclude that LBNP and intravenous saline loading produce major changes in pulmonary blood-flow and minor effects on pulmonary gas exchange, and that the response to acute changes in fluid distribution is not significantly altered during simulated microgravity.

Adult↗
PubMed1992

Cardiovascular response to lower body negative pressure before, during, and after ten days head-down tilt bedrest.

The haemodynamic response to lower body negative pressure (LBNP) was studied in 6 test subjects before (baseline), during, and after (recovery) ten days of 6 degrees head-down bedrest. The LBNP protocol consisted of a 35 min control period, application of a staircase differential pressure profile (15 min at -15 mmHg; 5 min at -30 mmHg; 15 min at -40 mmHg), and a 10 min post-stress observation period. Cardiac output was measured by a foreign gas rebreathing technique. Finger plethysmographic arterial blood pressure (BP), ECG, and heart rate (HR), lower limb crossectional area, and the electrical impedance of three body segments were recorded continuously. As expected, HDT caused a decrease in plasma volume and total body fluid volume. Resting CO at the end of HDT was 16% below the baseline level and similar to CO in the upright position before HDT. Stroke volume (SV) was also reduced, but there were no significant changes in control HR or BP. Absolute changes in CO and SV during LBNP were similar at baseline and during HDT, but the relative changes were larger during HDT. HR and vasoconstriction responses were enhanced, but presyncope occurred in two subjects. Reduced cardiac filling with decreased stroke volume at rest is the apparent primary cause of the altered LBNP response during HDT.

Adult↗
PubMed1992

Effects of head-down tilt for 10 days on the compliance of the leg.

The purpose of this investigation was to measure lower leg compliance before, during and after a 10-day period of bedrest at head-down tilt to test the hypothesis that leg compliance and the capacity for venous pooling is increased by the adaptation to stimulated microgravity. Venous occlusion plethysmography with multiple proximal occlusion pressures was used to obtain compliance measurements in six male subjects. Calf circumference decreased significantly during the tilt (corresponding to a decrease in cross sectional area of 7%) and had not returned to baseline seven days after the end of tilt. Compliance post-tilt was significantly greater than pre-tilt, probably mainly due to a reduction in muscle mass. This study supports the need for investigations to define: (a) the degree of protection against orthostatic hypotension that can be achieved by maintaining leg muscle mass and tone, and (b) efficient and specific exercise programs to prevent loss of muscle mass and function-particularly during spaceflight.

Adaptation, Physiological↗
PubMed1992

Increased orthostatic blood pressure variability after prolonged head-down tilt.

The effect of simulated weightlessness on orthostatic blood pressure regulation was evaluated with passive 70 degrees head-up tilt (HUT) after 10 days 6 degrees head-down tilt (HDT). Six healthy male volunteers were studied. Continuous recording of finger blood pressure (BP) was obtained non-invasively with a FinapresTM device. Instantaneous heart rate (HR) was derived from the electrocardiogram. To quantify orthostatic BP variability, a fast fourier transform (FFT) of the beat-by-beat BP- and RR-interval values was performed. Control HR before HUT after the 10-day HDT period was increased, probably due to an arousal state of the test subjects. The change in BP induced by HUT was not influenced by 10 days' HDT, in contrast to the HR rise which increased from 24 +/- 2 beats/min to 41 +/- 7 beats/min (P less than 0.05). After HDT the total variance in orthostatic BP almost doubled. FFT indicated that this increase in variance can be ascribed to BP oscillations with a frequency of around 0.1 Hz. In three subjects transient HR decelerations during HUT after HDT were observed. Analysis of the relationship between BP and HR in the transients showed that each HR decrease was preceded by a BP increase above normal. These HR decelerations seemed, therefore, to be an effect of the vagal part of the arterial baroreflex and did not necessary signal an impending vasovagal syncope. The present study indicates that although 10 days' HDT do not influence absolute BP responses to 70 degrees HUT BP was maintained by an increased sympathetic activity, reflected by an increased HR response and an augmented variance in BP around 0.1 Hz.

Adult↗
PubMed1991

Effects of 10 days 6 degrees head-down tilt on the responses to fluid loading and lower body negative pressure.

In an international collaborative project six normal male subjects were studied before, during and after 10 days 6 degrees HDT. Fluid intake was controlled at 40 ml/(kgbw day). Urine volume and body weight were determined daily. Fluid loading and LBNP were performed in all three phases of the study. Body weight diminished by 2.6% because of fluid loss. Blood volume diminished by 13%. The responses to fluid loading were similar in the three phases of the study. Sixty minutes after end of infusion only 5.5% of the infused saline remained in the intravascular compartment. Excess interstitial fluid was eliminated in the next 24 hs but a negative balance was recorded also in the following day. The compliance of the lower limbs expressed as the rate of limb volume change/unit LBNP change was increased at the end of the HDT phase and during the post HDT phase. The set point of intravascular volume was defended, as shown by the response to FL. HDT increased the compliance of the lower limbs.

Adult↗
PubMed1991

Effects of saline loading during head down tilt on ANP and cyclic GMP levels and on urinary fluid excretion.

In the present study the renal and humoral effects of acute saline infusions were investigated in six healthy male volunteers before, during and after a ten day period of -6 degrees head-down-tilt (HDT). During the whole 23-day study period the subjects received a standardized diet including 40 ml water and 125 mg NaCl per kg body weight per day. After the infusion of 0.9% saline (22 ml/kg within 20 minutes) plasma atrial natriuretic peptide (ANP) levels were only slightly increased (not significant) at the end of the infusion, while plasma cyclic GMP levels were significantly increased by about 40% (p<0.05) one hour later. No difference was observed in the plasma ANP and cyclic GMP changes between the pre-HDT, the HDT and the post-HDT infusion experiment. Urine flow, sodium excretion and urinary cyclic GMP excretion were significantly increased (p<0.05 and below) by 100 to 300% during the second and third hour after each saline infusion. However, during these short-term periods only 20% of the infused water and less than 20% of the infused sodium were excreted. Furthermore, a significantly increased volume, sodium and cyclic GMP excretion was observed for over 48 hours after each fluid load experiment. These data suggest that HDT does not induce major alterations in the regulation of an acute saline infusion and plasma ANP does not play a major role in the diuretic/natriuretic effects of volume loading.

Adult↗
PubMed1991

Classification of the free fluid reservoir in the calf by electrical impedance tomography.

The Electrical impedance tomography computes images of resistivity distribution which allow to analyse the body fluid content. The Sheffield system, Applied Potential Tomography (APT) was chosen to examine fluid shifts in the calf following body postural change, saline infusion (FL), and lower body negative pressure stress (LBNP). The APT allows the detection of differently reacting regions in the tomogram. The overall images of APT showed an exponential resistivity increase after the body position change from upright to 6 degrees head down tilt (HDT). During LBNP the pattern of the APT images looked the same as during FL. Both showed a resistivity decrease in the overall images. The outer surface showed a different magnitude of resistivities compared to the inner region in all experiments. A comparison of the overall APT images with the tomograms simultaneously obtained by NMR in one test subject showed the same tendency. This leads to the conclusion that the changes in the fluid reservoir of the calf may be classified by electrical impedance tomography.

Adult↗