Cardiac atrophy in women following bed rest.
Level 2 - randomized trial
Randomized controlled trial of bed rest countermeasures in healthy volunteers.
PubMed 17379748 · doi:10.1152/japplphysiol.01162.2006
What was done
Twenty-four healthy young women (mean age 32.1 ± 4 years) underwent 60 days of 6-degree head-down tilt (HDT) bed rest. Participants were matched and randomized into three parallel groups (n = 8 each): sedentary bed rest (control), exercise training (supine treadmill running within lower-body negative pressure plus resistive training), or nutritional countermeasure (protein intake increase by 0.45 g·kg⁻¹·day⁻¹ plus 7.2 g/day branched-chain amino acids). Left ventricular (LV) and right ventricular (RV) volumes, masses, and morphology were measured via magnetic resonance imaging before and after bed rest.
What was found
In sedentary controls, 60 days of bed rest significantly reduced: - LV volume: 96 ± 26 to 77 ± 25 ml (P = 0.03) - RV volume: 104 ± 33 to 86 ± 25 ml (P = 0.02) - LV mass: 2.2 ± 0.2 to 2.0 ± 0.2 g/kg (P = 0.003) - RV mass: 0.8 ± 0.1 to 0.6 ± 0.1 g/kg (P < 0.001) - LV major-axis length: 90 ± 6 to 84 ± 7 mm (P < 0.001) In the exercise group, LV and RV volumes and axis length were preserved, while LV mass increased (1.9 ± 0.4 to 2.3 ± 0.3 g/kg; P < 0.001), RV mass increased (0.7 ± 0.1 to 0.8 ± 0.2 g/kg; P = 0.002), and mean wall thickness increased (9 ± 2 to 11 ± 1 mm; P = 0.02). In the protein/BCAA group, LV and RV masses were preserved without change, but LV volume decreased (103 ± 14 to 80 ± 16 ml; P = 0.02) and major-axis length shortened (91 ± 5 to 88 ± 7 mm; P = 0.003). Body mass loss was similar across all groups (control: 3.4 ± 0.2 kg; exercise: 3.1 ± 0.04 kg; protein: 2.8 ± 0.1 kg).
Why it matters
This study demonstrates that prolonged physical unloading causes significant biventricular cardiac atrophy in women at magnitudes comparable to men, and shows that concurrent exercise training prevents cardiac mass and volume loss.
Limits
The sample size is small (n = 8 per group). The study evaluated simulated microgravity via head-down tilt bed rest rather than actual spaceflight, and clinical endpoints such as orthostatic intolerance were not reported in the abstract.
Cited by
- supports The heart loses approximately 1% of its muscle mass per week during strict bed rest.