Central venous pressure in humans during short periods of weightlessness

Abstract

Central venous pressure (CVP) was measured in 14 males during 23.3 +/- 0.6 s (mean +/- SE) of weightlessness (0.00 +/- 0.05 G) achieved in a Gulfstream-3 jet aircraft performing parabolic flight maneuvers and during either 60 or 120 s of +2 Gz (2.0 +/- 0.1 Gz). CVP was obtained using central venous catheters and strain-gauge pressure transducers. Heart rate (HR) was measured simultaneously in seven of the subjects. Measurements were compared with values obtained inflight at 1 G with the subjects in the supine (+1 Gx) and upright sitting (+1 Gz) positions, respectively. CVP was 2.6 +/- 1.5 mmHg during upright sitting and 5.0 +/- 0.7 mmHg in the supine position. During weightlessness, CVP increased significantly to 6.8 +/- 0.8 mmHg (P less than 0.005 compared with both upright sitting and supine inflight). During +2 Gz, CVP was 2.8 +/- 1.4 mmHg and only significantly lower than CVP during weightlessness (P less than 0.05). HR increased from 65 +/- 7 beats/min at supine and 70 +/- 5 beats/min during upright sitting to 79 +/- 7 beats/min (P less than 0.01 compared with supine) during weightlessness and to 80 +/- 6 beats/min (P less than 0.01 compared with upright sitting and P less than 0.001 compared with supine) during +2 Gz. We conclude that the immediate onset of weightlessness induces a significant increase in CVP, not only compared with the upright sitting position but also compared with the supine position at 1 G.

Manned Space Flight and the Kidney

“…It was further postulated that the central blood vol ume expansion would initiate a diuresis early in flight [7,11,16]. Indeed, some have speculated on the possibility that the increase could be of sufficient magnitude that pulmonary congestion or even edema would develop [17,18]. Today after 3 decades of manned space flights there is no indication whatsoever that pulmonary edema develops during weightlessness.…”

“…During such a maneuv er, weightlessness can be attained for 20-30 s. Imme diately prior to the weightless period, an increased G load of +2 Gz (foot-to-head direction of acceleration; seated subjects) is imposed on the subjects. Norsk et al [30] measured changes in CVP utilizing long, intratho racic catheters introduced through cubital veins. The fluid-filled catheters were connected to pressure trans ducers which were placed at the subjects' right midatrial level.…”

Efeitos cardiovasculares agudos da exposição ao ambiente microgravitacional

“…No caso da manobra HDT, os valores da pressão venosa central durante a inclinação foram iguais ou maiores do que os obtidos na posição supina horizontal [21][22][23][24] contrariando, portanto, a tendência predominante no ambiente espacial. No que tange ao vôo parabólico, o mesmo grupo de fisiologistas relatou tanto aumento (+2,4cmH 2 O) 25 , quanto redução (-2,0cmH 2 O) 20 dos valores da pressão venosa central, o que foi creditado a diferenças metodológicas: enquanto na segunda investigação os indivíduos estudados permaneceram o tempo todo deitados, na primeira eles alternaram entre a posição supina (medidas controles em 1G) e a sentada (medidas realizadas durante a manobra parabólica). No modelo de imersão em água, os resultados imediatos mostraram nítido aumento da pressão venosa central 26 .…”

Prolonged water immersion. Effects on blood pressure maturation in normotensive rats.

“…The effects of microgravity 89 can be studied on Earth by several models such as the free fall phase of parabolic flight in jet aircraft, 10 head down" 12 and horizontal bed rest, 13 -15 and head out water immersion. 16 " 19 The latter technique, based on the principle of Archimedes, assumes that when a body is placed in a fluid of about its density, the force acting in the opposite direction to gravity is proportional to the mass of the displaced fluid and that the loss of weight of the submerged object is equal to the weight of the fluid displaced by the object itself.…”