title: Sustained mild hypergravity reduces spontaneous cardiac baroreflex sensitivity.
abstract: Head-to-foot gravitational force >1G (+Gz hypergravity) augments venous pooling in the lower body and reduces central blood volume during exposure, compared with 1Gz. Central hypovolemia has been reported to reduce spontaneous cardiac baroreflex sensitivity. However, no investigations have examined spontaneous cardiac baroreflex sensitivity during exposure to sustained mild +Gz hypergravity. We therefore hypothesized that mild +Gz hypergravity would reduce spontaneous cardiac baroreflex sensitivity, compared with 1Gz. To test this hypothesis, we examined spontaneous cardiac baroreflex sensitivity in 16 healthy men during exposure to mild +Gz hypergravity using a short-arm centrifuge. Beat-to-beat arterial blood pressure (tonometry) and R-R interval (electrocardiography) were obtained during 1Gz and 1.5Gz exposures. Spontaneous cardiac baroreflex sensitivity was assessed by sequence slope and transfer function gain. Stroke volume was calculated from the arterial pressure waveform using a three-element model. All indices of spontaneous cardiac baroreflex sensitivity decreased significantly (up slope: 18.6±2.3→12.7±1.6ms/mmHg, P<0.001; down slope: 19.0±2.5→13.2±1.3ms/mmHg, P=0.002; transfer function gain in low frequency: 14.4±2.2→10.1±1.1ms/mmHg, P=0.004; transfer function gain in high frequency: 22.2±7.5→12.4±3.5ms/mmHg, P<0.001). Stroke volume decreased significantly (88±5→80±6ml, P=0.025). Moreover, although systolic arterial pressure variability increased, R-R interval variability did not increase. These results suggest that even mild +Gz hypergravity reduces spontaneous cardiac baroreflex sensitivity, increasing the risk of cardiovascular disturbance during the exposure.
authors.affiliation: Division of Hygiene, Department of Social Medicine, Nihon University School of Medicine, Tokyo, Japan.
authors.forename: Ryo
authors.initials: R
authors.lastname: Yanagida
authors.affiliation: Division of Hygiene, Department of Social Medicine, Nihon University School of Medicine, Tokyo, Japan.
authors.forename: Yojiro
authors.initials: Y
authors.lastname: Ogawa
authors.affiliation: Department of Anesthesiology, Nihon University School of Medicine, Tokyo, Japan.
authors.forename: Kaname
authors.initials: K
authors.lastname: Ueda
authors.affiliation: Division of Hygiene, Department of Social Medicine, Nihon University School of Medicine, Tokyo, Japan.
authors.forename: Ken
authors.initials: K
authors.lastname: Aoki
authors.affiliation: Division of Hygiene, Department of Social Medicine, Nihon University School of Medicine, Tokyo, Japan. Electronic address: iwasaki.kenichi@nihon-u.ac.jp.
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Iwasaki
mesh_terms: D062186:Arterial Pressure / Q000502:physiology*; D017704:Baroreflex / Q000502:physiology*; D004562:Electrocardiography; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D018471:Hypergravity; D008297:Male; D008365:Manometry; D012119:Respiration; D013318:Stroke Volume / Q000502:physiology; D055815:Young Adult
keywords: Artificial gravity; Cardiovascular variability; Central hypovolemia; Centrifuge; Sequence method; Spontaneous cardiac baroreflex sensitivity; Transfer function analysis