Adaptation of the left heart, cerebral and femoral arteries, and jugular and femoral veins during short- and long-term head-down tilt and spaceflights

Abstract.

The objective of this investigation was to identify the major cardiovascular changes induced by exposure to real or simulated 0g (spaceflights: 6, 14, 21 and 25 days, and 6 months; head down tilt, HDT: 10 h, 4, 5, 7, 30 and 42 days), with a minimum of countermeasures. The following cardiovascular data were measured by echocardiography and Doppler ultrasonography: left ventricle end-diastolic volume (LVDV), stroke volume (SV), cardiac output (CO), ejection fraction (EF), middle cerebral artery flow velocity (% MathType!MTEF!2!1!+- % feaaeaart1ev0aqatCvAUfKttLearuavP1wzZbqedmvETj2BSbWexL % MBbXgBcf2CPn2qVrwzqf2zLnharyWqVvNCPvMCG4uz3bqee0evGueE % 0jxyaibaieYlf9irVeeu0dXdh9vqqj-hEeeu0xXdbba9frFj0-OqFf % ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr % 0-vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaiqbdgfarzaaca % WaaSbaaSqaaiabbogaJjabbggaHbqabaaaaa!38E6! $\dot Q_{{\rm ca}}$ ), femoral artery flow velocity (% MathType!MTEF!2!1!+- % feaaeaart1ev0aqatCvAUfKttLearuavP1wzZbqedmvETj2BSbWexL % MBbXgBcf2CPn2qVrwzqf2zLnharyWqVvNCPvMCG4uz3bqee0evGueE % 0jxyaibaieYlf9irVeeu0dXdh9vqqj-hEeeu0xXdbba9frFj0-OqFf % ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr % 0-vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaiqbdgfarzaaca % WaaSbaaSqaaiabbAgaMjabbggaHbqabaaaaa!38EC! $\dot Q_{{\rm fa}}$ ), cerebral vascular resistance (R _ca), femoral vascular resistance (R _fa), jugular vein cross-sectional area (A _jv), femoral vein cross-sectional area (A _fv), heart rate (HR), and mean blood pressure (MBP). LVDV remained decreased compared to pre-HDT or pre-flight levels after 1 week of spaceflight or HDT (–8 to –13%, P<0.05), EF did not change. HR tended to increase (5–10%) during spaceflight and HDT, whereas MBP tended to decrease during flight, but did not change in HDT. These findings are consistent with the existence of a moderate and stable hypovolemia. % MathType!MTEF!2!1!+- % feaaeaart1ev0aqatCvAUfKttLearuavP1wzZbqedmvETj2BSbWexL % MBbXgBcf2CPn2qVrwzqf2zLnharyWqVvNCPvMCG4uz3bqee0evGueE % 0jxyaibaieYlf9irVeeu0dXdh9vqqj-hEeeu0xXdbba9frFj0-OqFf % ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr % 0-vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaiqbdgfarzaaca % WaaSbaaSqaaiabbogaJjabbggaHbqabaaaaa!38E6! $\dot Q_{{\rm ca}}$ and R _ca fluctuated between +10 and –10% from pre-HDT or pre-flight values, and always showed opposing variations. There was no significant decrease in cerebral perfusion. Lower-limb resistance (R _fa) remained decreased (–5% to –18%, P<0.05) throughout the flights or HDT after week 1. A _jv remained significantly enlarged (+40% P<0.05) after 1 week in spaceflight or in HDT. A _fv was enlarged in spaceflight after week 1 (+15% to +35%, P<0.05), whereas it decreased after 4–5 days of HDT (–20% to –35%, P<0.05). The cardiovascular system reached a new and stable equilibrium during flight and HDT within less than 1 week. With the exception of the femoral vein, there was no significant difference in either the amplitude or the time course of the cardiovascular changes in both situations after 1 week.