Impact of a four-day head-down tilt (-6 degrees) on lidocaine pharmacokinetics used as probe to evaluate hepatic blood flow.

The impact of a microgravity simulation using a head-down tilt (-6 degrees) on lidocaine pharmacokinetics used as a probe to evaluate hepatic blood flow is discussed. Eight healthy male subjects were selected for a 7-day study, including a 4-day head-down tilt from day 2 to day 5. Subjects were given 1 mg/kg of lidocaine on days 1 through 5 and 7. Blood sampling, cardiac output, and hepatic artery blood flow velocity measurements were done within 6 hours after administration. Cardiac output increased significantly during head-down tilt, and returned to basal values during the recovery period. Blood flow velocity in the hepatic artery increased during the first day of the down tilt. Slight side effects (buzzing noise in the ears and sleepy feeling) were reported within minutes after the injection of lidocaine. Lidocaine disposition was modified during head-down tilt: a significant decrease in maximal concentration (1.47 +/- 0.26 mg/L on day 1 and 0.96 +/- 0.30 mg/L on day 2); an increase in elimination clearance from 8.24 +/- 3.22 mL/kg.minutes-1 to 11.63 +/- 3.00 mL/kg.minutes-1; an increase in volume of distribution on day 2 and a decrease to lower than basal value on the other days (2.77 +/- 1.73 L/kg on day 1 and 2.33 +/- 0.48 L/kg on day 7). Half-life regularly decreased from 264 +/- 210 minutes to 160 +/- 60 minutes between day 1 and day 7.(ABSTRACT TRUNCATED AT 250 WORDS)

Psychomotor performance during a 28 day head-down tilt with and without lower body negative pressure.

Several factors may affect psychomotor performance in space: sensory-motor changes, sleep disturbances, psychological modifications induced by the social isolation and confinement. However, psychomotor performance is difficult to assess. A battery of standardized and computerized tests, so-called "Automated Portable Test System" (APTS) was devised to ascertain the cognitive, perceptive and motor abilities and their possible fluctuations according to environmental effects. Antiorthostatic bedrest, often used to simulate weightlessness, (particularly cardiovascular modifications) also constitutes a situation of social confinement and isolation. During two bedrest experiments (with head-down tilt of -6 degrees) of 28 days each, we intended to assess psychomotor performance of 6 males so as to determine whether: on the one hand, it could be altered by remaining in decubitus; on the other, the Lower Body Negative Pressure sessions, designed to prevent orthostatic intolerance back on Earth, could improve the performance. To accomplish this, part of the APTS tests as well as an automated perceptive attention test were performed. No downgrading of psychomotor performance was observed. On the contrary, the tasks were more accurately performed over time. In order to assess the experimental conditions on the acquisition phase, the learning curves were modelled. A beneficial effect of the LBNP sessions on simple tests involving the visual-motor coordination and attention faculties can only be regarded as a mere trend. Methods used in this experiment are also discussed.

Lower body negative pressure as a countermeasure against orthostatic intolerance for long term space flight.

NASA: The effectiveness of lower body negative pressure (LBNP) as a countermeasure against orthostatic intolerance associated with bed rest was investigated. Subjects were exposed to antiorthostatic bedrest at 6 degrees head down tilt, with some exposed to LBNP and some exposed to LBNP with exercise during the bedrest period. Tilt table tests were then performed on all subjects, with heart rate and blood pressure measurements taken. Exposure to LBNP seemed effective in preventing syncope in subjects exposed to bedrest. These results are discussed.^ieng