Cardiac atrophy after bed rest and spaceflight.
Level 3 - non-randomized controlled study
Non-randomized prospective controlled physiological study with parallel controls and an uncontrolled spaceflight cohort
PubMed 11457776 · doi:10.1152/jappl.2001.91.2.645
What was done
Sedentary men underwent horizontal bed rest for 6 weeks (n = 5) or 12 weeks (n = 3). Five healthy men maintaining routine daily activities served as non-bed-rest controls. In addition, four astronauts were assessed before and after a 10-day spaceflight. Left ventricular (LV) and right ventricular (RV) mass and end-diastolic volume were measured with cine magnetic resonance imaging (MRI) at 2, 6, and 12 weeks of bed rest, before and after at least 6 weeks of normal activity in controls, and pre- and post-spaceflight.
What was found
- LV mass in bed-rest subjects decreased by 8.0 ± 2.2% at 6 weeks (P = 0.005), with an additional atrophy of 7.6 ± 2.3% in those remaining bedridden for 12 weeks; control subjects showed no change (153.0 ± 12.2 vs. 153.4 ± 12.1 g, P = 0.81). - Mean LV wall thickness decreased by 4 ± 2.5% after 6 weeks of bed rest (P = 0.01). - LV end-diastolic volume decreased by 14 ± 1.7% after 2 weeks of bed rest (P = 0.002) and changed minimally thereafter. - At 6 weeks of bed rest, RV free wall mass decreased by 10 ± 2.7% (P = 0.06) and RV end-diastolic volume decreased by 16 ± 7.9% (P = 0.06). - In astronauts, LV mass decreased by 12 ± 6.9% after 10 days of spaceflight (P = 0.07).
Why it matters
This study provides direct MRI evidence that human cardiac muscle undergoes rapid, reversible atrophy and volume reduction in response to reduced myocardial loading from physical unloading or microgravity.
Limits
Sample sizes were very small in all groups (3 to 5 subjects per condition), leaving several comparisons marginally powered (P = 0.06 to 0.07). The study was non-randomized, included only men, and lacked an active flight control group for astronauts. Clinical or functional recovery post-reloading was not reported in the abstract.
Cited by
- supports The heart loses approximately 1% of its muscle mass per week during strict bed rest.