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Randomized Controlled Trial
. 2012 May;112(10):1735-43.
doi: 10.1152/japplphysiol.00019.2012. Epub 2012 Feb 16.

Effect of rowing ergometry and oral volume loading on cardiovascular structure and function during bed rest

Jeffrey L Hastings  1 , Felix Krainski, Peter G Snell, Eric L Pacini, Manish Jain, Paul S Bhella, Shigeki Shibata, Qi Fu, M Dean Palmer, Benjamin D Levine
Affiliations
Randomized Controlled Trial

Effect of rowing ergometry and oral volume loading on cardiovascular structure and function during bed rest

Jeffrey L Hastings et al. J Appl Physiol (1985). 2012 May.

Abstract

This study examined the effectiveness of a short-duration but high-intensity exercise countermeasure in combination with a novel oral volume load in preventing bed rest deconditioning and orthostatic intolerance. Bed rest reduces work capacity and orthostatic tolerance due in part to cardiac atrophy and decreased stroke volume. Twenty seven healthy subjects completed 5 wk of -6 degree head down bed rest. Eighteen were randomized to daily rowing ergometry and biweekly strength training while nine remained sedentary. Measurements included cardiac mass, invasive pressure-volume relations, maximal upright exercise capacity, and orthostatic tolerance. Before post-bed rest orthostatic tolerance and exercise testing, nine exercise subjects were given 2 days of fludrocortisone and increased salt. Sedentary bed rest led to cardiac atrophy (125 ± 23 vs. 115 ± 20 g; P < 0.001); however, exercise preserved cardiac mass (128 ± 38 vs. 137 ± 34 g; P = 0.002). Exercise training preserved left ventricular chamber compliance, whereas sedentary bed rest increased stiffness (180 ± 170%, P = 0.032). Orthostatic tolerance was preserved only when exercise was combined with volume loading (-10 ± 22%, P = 0.169) but not with exercise (-14 ± 43%, P = 0.047) or sedentary bed rest (-24 ± 26%, P = 0.035) alone. Rowing and supplemental strength training prevent cardiovascular deconditioning during prolonged bed rest. When combined with an oral volume load, orthostatic tolerance is also preserved. This combined countermeasure may be an ideal strategy for prolonged spaceflight, or patients with orthostatic intolerance.

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Figures

Fig. 1.
Fig. 1.
Study design: 5 wk of 6 degree head down tilt bed rest and the following two countermeasures: 1) rowing ergometry and resistance training and 2) oral volume loading. Exercise (n = 18) depicts the exercise training countermeasure. Following the 5 wk of exercise countermeasure, the exercise group was split into ExVol (n = 9), who received the oral volume load, and ExNoVol (n = 9), who did not receive volume expansion. Sedentary (n = 9; Sed) depicts sedentary bed rest without any countermeasures. Testing scheme and schedule were matched pre- and postbed rest. Testing days 1 and 2 were separated by at least 72 h.
Fig. 2.
Fig. 2.
Exercise subject's training schedule: a comprehensive periodized competitive-style training program with biweekly resistance training is shown in black. Rowing intensity prescription as: “base” training, “recovery” training, and “interval” training, with 6 repetitions of 3 min followed by 3 min of recovery. Exercises are preceded and followed by appropriate warm-up and cool-down periods.
Fig. 3.
Fig. 3.
Left ventricular pressure-volume curves: pre- and postbed rest in exercise and sedentary groups. Six data points correspond to 2 degrees of lower-body negative pressure (LBNP), 2 baselines, and 2 saline infusions. PCWP, pulmonary capillary wedge pressure; LVEDV, left ventricular end-diastolic volume; BSA, body surface area.
Fig. 4.
Fig. 4.
Myocardial compliance curves: estimated transmural pressure (PCWP, right atrial pressure) and LVEDV for pre- and postbed rest in exercise and sedentary subjects.
Fig. 5.
Fig. 5.
Starling curves: before (pre) and after (post) bed rest in the exercise and sedentary groups. Shown are mean group data ± SE for stroke volume (SV) at given PCWP. Six data points correspond to 2 degrees of LBNP, 2 baselines, and 2 saline infusions. Curves were drawn by second linear regression based on mean values for each condition.
Fig. 6.
Fig. 6.
A: peak work rate: pre- and postbed rest in ExVol, ExNoVol, and in the sedentary group without exercise or volume loading (Sed). B: maximal oxygen uptake (V̇o2): pre- and postbed rest in ExVol, ExNoVol, and Sed groups.
Fig. 7.
Fig. 7.
Orthostatic tolerance: maximal LBNP tolerance pre and post head down tilt bed rest in ExVol, ExNoVol, and Sed groups.
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