Modeling human orthostatic responses on the Moon and on Mars.

Purpose: Since manned missions to the Moon and Mars are planned, we conducted active standing tests with lunar, Martian, terrestrial, and 1.8 loads of inertial resistance (+G) modeled through defined parabolic flight maneuvers. We hypothesized that the cardiovascular response to active standing is proportional to the +G load.

Increased salt consumption induces body water conservation and decreases fluid intake.

Background: The idea that increasing salt intake increases drinking and urine volume is widely accepted. We tested the hypothesis that an increase in salt intake of 6 g/d would change fluid balance in men living under ultra-long-term controlled conditions.

Methods: Over the course of 2 separate space flight simulation studies of 105 and 205 days' duration, we exposed 10 healthy men to 3 salt intake levels (12, 9, or 6 g/d).

EMG and heart rate responses decline within 5 days of daily whole-body vibration training with squatting.

In this study, we examined the acute effects of a 5-day daily whole-body vibration (WBV) training on electromyography (EMG) responses of the m. rectus femoris and m. gastrocnemius lateralis, heart rate (HR, continuously recorded), and blood lactate levels.

Pulse contour methods to estimate cardiovascular indices in micro- and hypergravity.

Background: The importance of noninvasive health monitoring in space increased as a result of the long-duration missions on the International Space Station (ISS). In order to monitor changes in cardiovascular indices such as cardiac output (CO) and total peripheral resistance (TPR), many methods have been developed using signal processing and mathematical modeling techniques. However, their performance in various gravitational conditions has not been known.

Long-term space flight simulation reveals infradian rhythmicity in human Na(+) balance.

The steady-state concept of Na(+) homeostasis, based on short-term investigations of responses to high salt intake, maintains that dietary Na(+) is rapidly eliminated into urine, thereby achieving constant total-body Na(+) and water content. We introduced the reverse experimental approach by fixing salt intake of men participating in space flight simulations at 12 g, 9 g, and 6 g/day for months and tested for the predicted constancy in urinary excretion and total-body Na(+) content. At constant salt intake, daily Na(+) excretion exhibited aldosterone-dependent, weekly (circaseptan) rhythms, resulting in periodic Na(+) storage.

Upright cardiac output measurements in the transition to weightlessness during parabolic flights.

Objective: Aims of this study were: 1) to determine cardiac output by inert gas rebreathing (CO(reb)) during transition into 0 Gz in the standing position; and 2) to compare impedance cardiography (ICG) and pulse contour method (PCM) with CO(reb) as a reference method.

Methods: We measured baseline CO(reb) and heart rate (HR) on the ground, and CO(reb), CO(pcm), CO(icg), and HR in standing and supine positions in the transition to weightlessness in six subjects. We conducted repeated measures ANOVA, Bland and Altman analysis, and analysis of percentage error of each data set.

Increasing sodium intake from a previous low or high intake affects water, electrolyte and acid-base balance differently.

Contrasting data are published on the effects of high salt intake (between 300 and 660 mmol/d) on Na balance and fluid retention. In some studies high levels of NaCl intake (400, 440, 550 and 660 mmol/d) led to positive Na balances without fluid retention. To test the relevance of different baseline NaCl intake levels on changes in metabolic water, Na, K, chloride and acid-base balance, a 28 d clinical trial ('Salty Life 6') was carried out in a metabolic ward.

Effect of change in intrathoracic pressure on thermoregulatory responses during -6 degree head-down bed rest.

We investigated the effect of change in intrathoracic pressure by total body negative pressure (TBNP) or positive pressure (TBPP) on thermoregulatory responses during -6 degree head-down bed rest (HDBR). Eight healthy male subjects participated to three of the following interventions in a randomised sequence: 1) HDBR, 2) HDBR with TBNP of -15 cmH2O, 3) HDBR with TBPP of +15 cmH2O. A rapid decrease of cutaneous blood flow occurred after the start of TBNP.

Influence of salt intake on renin-angiotensin and natriuretic peptide system genes in human adipose tissue.

We tested the hypothesis that changes in sodium intake modulate adipose-tissue renin-angiotensin and natriuretic peptide system gene expression in humans. We studied 9 healthy young men in a metabolic ward at constant room temperature, humidity, and water, potassium, and calcium intake. Subjects were submitted to 4 different periods of sodium intake, and blood samples, microdialysis samples (interstitial fluid), and biopsies from subcutaneous abdominal adipose tissue were obtained at the end of the low-sodium period (0.