Regional blood flow in microgravity: adaptation and deconditioning.

The objectives were to evaluate cardiac and peripheral changes induced by microgravity with and without countermeasures (CM), to assess the peripheral response to orthostatic tests (tilt, LBNP). Inflight or HDT, we used echography and Doppler to assess the left heart function and the peripheral arteries. We studied the cardiovascular system during 1) 21-d and 25-d spaceflights without CM, 2) 14.d spaceflight with "bracelets" CM, 3) 28-d HDT with and without LBNP, and 4) 30-d HDT with and without Exercise+LBNP. Similar peripheral circulation changes were noticed in both astronauts and HDT subjects without CM. There was a decrease in renal, cerebral, and femoral vascular resistances and maintenance of cerebral flow at rest, and a lack of increase in lower limb vascular resistance and abnormal flow redistribution during orthostatic tests. Conversely, with CM at rest, cerebral and renal vascular resistances stayed elevated and femoral resistance decreased, but less than without countermeasures. Lower limb vascular resistance increased normally, peripheral flows were adequately redistributed during orthostatic tests, and no orthostatic intolerance was observed. This confirms the efficiency of countermeasures (LBNP, exercise, cuffs) in preserving the vasomotor tone in most peripheral areas at rest and reducing the development of orthostatic intolerance.

Cardiac and vascular adaptation to 0g with and without thigh cuffs (Antares 14 and Altair 21 day Mir spaceflights).

UNLABELLED: Cardiovascular adaptation was evaluated on 2 astronauts: one wearing thigh cuffs from flight day 1 to 8 (14d flight), the second without cuffs (21d flight). Ultrasound investigations were performed at rest and during LBNP. RESULTS: Without thigh cuffs the cardiovascular adaptation consists in (1) the development of a hypovolemia with an increase of the heart rate and the cardiac output, (2) the decrease of the vascular tone in the deep (mesenteric and splanchnic) and peripheral (Lower limbs) vascular areas. The use of thigh cuffs maintains the volemia and the cardiac output at the preflight level (without heart rate increase) and prevents the loss of vascular tone in the deep and peripheral areas. Moreover the adaptative process changes since the cuffs are removed and even the volemia seems to be unaffected at this stage the vascular tone decreases to a comparable extend as during the flight without cuffs. Nevertheless during the flight without cuffs or 3 days after removing the cuffs hemodynamic signs of decreased orthostatic tolerance are present during the inflight and the 3 days post flight LBNP. Presently the possible contribution of the thigh cuffs to the reduction of the vascular deconditioning has not been tested yet.

Vascular resistance quantification in high flow resistance areas using the Doppler method.

The objective of the present study is to define and validate on an animal model (ewe) a new Doppler parameter for the assessment and monitoring of the vascular resistances in high resistance to flow areas (lower limbs, placenta with vascular disease). The high resistance index (HRI) was derived from the transmission line theory and defined as: HRI = D/S with S the amplitude of the systolic peak and D that of the diastolic reverse flow. Validation of the HRI was performed on adult ewes. Distal lower limb vascular resistances were evaluated from the Doppler femoral waveform (HRI) and compared with the classic vascular resistances (Rv), calculated from pressure and flow (mmHg/mL/min). The femoral flow variations were measured by duplex (echo-Doppler) method and the mean pressure through an arterial catheter inserted into the abdominal aorta. Two tests were used in this study: (1) A calibrated venous compression of the lower limbs extremity: The femoral flow dropped by 29%, the pressure and heart rate did not change, the HRI increased by 37% (p < 0.01), and the vascular resistance (Rv) by 46% (p < 0.01). (2) The intravenous injection of 1 mg adrenaline: The arterial pressure increased by 70% (p < 0.001), the heart rate and femoral flow dropped by 50% (p < 0.001), and 35% (p < 0.001), the HRI increased by 70% (p < 0.01) and the vascular resistances (Rv) by 140% (p < 0.01). During the two tests, the HRI changed in proportion with the "classic" vascular resistances.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of the thigh cuffs countermeasure on the cardiovascular adaptation to 0.g (14 and 21 day Mir spaceflights).

Assess the 0.g induced cardiac and vascular changes at rest on two cosmonauts: one using thigh cuffs from flight day 1 to 8 (Mir 14d flight) the second one not using thigh cuffs (Mir 21d flight). Both were not using intensively any other countermeasure. The ultrasound device onboard Mir with Echo, Doppler, and TM, modes was used.