Microvascular responses to (hyper-)gravitational stress by short-arm human centrifuge: arteriolar vasoconstriction and venous pooling.
OBJECTIVE
We hypothesized that lower body microvessels are particularly challenged during exposure to gravity and hypergravity leading to failure of resistance vessels to withstand excessive transmural pressure during hypergravitation and gravitation-dependent microvascular blood pooling.


METHODS
Using a short-arm human centrifuge (SAHC), 12 subjects were exposed to +1Gz, +2Gz and +1Gz, all at foot level, for 4 min each. Laser Doppler imaging and near-infrared spectroscopy were used to measure skin perfusion and tissue haemoglobin concentrations, respectively.


RESULTS
Pretibial skin perfusion decreased by 19% during +1Gz and remained at this level during +2Gz. In the dilated area, skin perfusion increased by 24 and 35% during +1Gz and +2Gz, respectively. In the upper arm, oxygenated haemoglobin (Hb) decreased, while deoxy Hb increased with little change in total Hb. In the calf muscle, O2Hb and deoxy Hb increased, resulting in total Hb increase by 7.5 ± 1.4 and 26.6 ± 2.6 µmol/L at +1Gz and +2Gz, respectively. The dynamics of Hb increase suggests a fast and a slow component.


CONCLUSIONS
Despite transmural pressures well beyond the upper myogenic control limit, intact lower body resistance vessels withstand these pressures up to +2Gz, suggesting that myogenic control may contribute only little to increased vascular resistance. The fast component of increasing total Hb indicates microvascular blood pooling contributing to soft tissue capacitance. Future research will have to address possible alterations of these acute adaptations to gravity after deconditioning by exposure to micro-g.
Institute of Physiology, Charité-University Medicine Berlin, Charitéplatz 1, 10117, Berlin, Germany. helmut.habazettl@charite.de.|German Heart Institute Berlin, Berlin, Germany. helmut.habazettl@charite.de.|Center for Space Medicine Berlin, Berlin, Germany. helmut.habazettl@charite.de.
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Habazettl
Institute of Physiology, Charité-University Medicine Berlin, Charitéplatz 1, 10117, Berlin, Germany.|Center for Space Medicine Berlin, Berlin, Germany.
Alexander
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Stahn
Institute of Aerospace Medicine, German Aerospace Center, Cologne, Germany.
Andrea
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Nitsche
Institute of Physiology, Charité-University Medicine Berlin, Charitéplatz 1, 10117, Berlin, Germany.|Center for Space Medicine Berlin, Berlin, Germany.
Michael
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Nordine
Institute of Physiology, Charité-University Medicine Berlin, Charitéplatz 1, 10117, Berlin, Germany.|Center for Cardiovascular Research, Charité-University Medicine Berlin, Berlin, Germany.
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Pries
Institute of Physiology, Charité-University Medicine Berlin, Charitéplatz 1, 10117, Berlin, Germany.|Center for Space Medicine Berlin, Berlin, Germany.
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HC
Gunga
Institute of Physiology, Charité-University Medicine Berlin, Charitéplatz 1, 10117, Berlin, Germany.|Center for Space Medicine Berlin, Berlin, Germany.
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Opatz
D000328:Adult; D001132:Arm / Q000098:blood supply*; D001794:Blood Pressure / Q000502:physiology*; D002498:Centrifugation; D005260:Female; D006112:Gravitation; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D018471:Hypergravity; D007866:Leg / Q000098:blood supply; D008297:Male; D008833:Microcirculation / Q000502:physiology*; D012039:Regional Blood Flow / Q000502:physiology; D013312:Stress, Physiological; D014655:Vascular Resistance / Q000502:physiology*; D014661:Vasoconstriction / Q000502:physiology*; D014680:Veins / Q000502:physiology; D055815:Young Adult
Hypergravitation; Laser Doppler imaging; Microcirculation; Near-infrared spectroscopy; Skin perfusion