Reduced baroreflex control of heart period after bed rest is normalized by acute plasma volume restoration

• DOI: 10.1152/ajpregu.00613.2002
• Publication Date: 2004-07-08T20:25:39Z
• Authors: Ken-ichi Iwasaki; Rong Zhang; Merja A. Perhonen; Julie H. Zuckerman; Benjamin D. Levine
• Keywords: Hypovolemia

Adaptation to spaceflight or head-down-tilt bed rest leads hypovolemia and an apparent abnormality of baroreflex regulation cardiac period. In a previous study, we demonstrated that both chronic (2 wk) acute induced led similar impairments in spontaneous control period, suggesting reduction plasma volume may be responsible for this after rest. Therefore hypothesized reduced "baroreflex function" could restored by intravenous infusion equivalent the Six healthy subjects underwent 2 wk -6 degrees head-down Beat-by-beat arterial blood pressure ECG were recorded during 6 min respiration fixed-rate breathing (0.2 Hz), transfer function analysis between systolic R-R interval was performed. Plasma measured with Evans blue dye, filling pressures directly (Swan-Ganz catheter). After rest, studies repeated before restoration, which left ventricular end-diastolic pre-bed levels dextran40 (288 +/- 31 ml). Transfer gain high-frequency range, used as index vagally mediated arterial-cardiac function, decreased significantly (13.4 3.1 8.1 2.9 ms/mmHg, P < 0.05) However, normalized level (12.2 3.6 ms/mmHg) precise restoration. This result confirms reductions volume, rather than unique autonomic nervous system adaptation are largely observed changes