Cardiac atrophy after bed rest and spaceflight

Abstract

Cardiac muscle adapts well to changes in loading conditions. For example, left ventricular (LV) hypertrophy may be induced physiologically (via exercise training) or pathologically (via hypertension or valvular heart disease). If hypertension is treated, LV hypertrophy regresses, suggesting a sensitivity to LV work. However, whether physical inactivity in nonathletic populations causes adaptive changes in LV mass or even frank atrophy is not clear. We exposed previously sedentary men to 6 (n = 5) and 12 (n = 3) wk of horizontal bed rest. LV and right ventricular (RV) mass and end-diastolic volume were measured using cine magnetic resonance imaging (MRI) at 2, 6, and 12 wk of bed rest; five healthy men were also studied before and after at least 6 wk of routine daily activities as controls. In addition, four astronauts were exposed to the complete elimination of hydrostatic gradients during a spaceflight of 10 days. During bed rest, LV mass decreased by 8.0 +/- 2.2% (P = 0.005) after 6 wk with an additional atrophy of 7.6 +/- 2.3% in the subjects who remained in bed for 12 wk; there was no change in LV mass for the control subjects (153.0 +/- 12.2 vs. 153.4 +/- 12.1 g, P = 0.81). Mean wall thickness decreased (4 +/- 2.5%, P = 0.01) after 6 wk of bed rest associated with the decrease in LV mass, suggesting a physiological remodeling with respect to altered load. LV end-diastolic volume decreased by 14 +/- 1.7% (P = 0.002) after 2 wk of bed rest and changed minimally thereafter. After 6 wk of bed rest, RV free wall mass decreased by 10 +/- 2.7% (P = 0.06) and RV end-diastolic volume by 16 +/- 7.9% (P = 0.06). After spaceflight, LV mass decreased by 12 +/- 6.9% (P = 0.07). In conclusion, cardiac atrophy occurs during prolonged (6 wk) horizontal bed rest and may also occur after short-term spaceflight. We suggest that cardiac atrophy is due to a physiological adaptation to reduced myocardial load and work in real or simulated microgravity and demonstrates the plasticity of cardiac muscle under different loading conditions.

Altered left ventricular diastolic function in subjects with spinal cord injury

“…First, tissue Doppler imaging may be more sensitive than conventional echocardiography for detection of abnormalities in LV diastolic function in individuals with SCI. Second, our data showing lower Em and higher E/Em in subjects with SCI corroborate previous reports demonstrating impaired LV compliance in individuals subjected to prolonged bed rest and space flight, 7,8 thus indicating that physical inactivity may be associated with diastolic dysfunction. Nevertheless, this latter assumption is challenged by the lack of influence of injury level on LV diastolic function, as shown herein.…”

“…6 Similarly, the development of LV diastolic dysfunction has been reported in individuals subjected to prolonged physical inactivity, 7,8 thereby suggesting that patients with SCI might be at a higher risk of developing abnormalities in LV function. The aim of this study was to investigate cardiac functional and structural parameters in SCI and able-bodied subjects and evaluate the impact of clinical, hemodynamic, metabolic and inflammatory variables in this regard.…”

Resistance exercise combined with KAATSU during simulated weightlessness

“…In addition, supine exercise in a LBNP chamber (58 ± 2 mmHg LBNP) has been reported to maintain aerobic fitness and sprint speed during 15 d of 6˚head-down bed rest (Watenpaugh et al, 2000). Thus, exercise combined with LBNP appears to provide an effective procedure to stress the cardiovascular system (Hargens, 1994), and may be useful in maintaining upright exercise capacity and prevent orthostatic intolerance during longer bed rest periods or space-flight (Watenpaugh et al, 2000;Perhonen et al, 2001;Schneider et al, 2002). LBNP has been combined with many exercise modalities, e.g.…”

Hemodynamic and autonomic nervous responses to the restriction of femoral blood flow by KAATSU

“…Watenpaugh et al (2000) also reported that daily supine exercise in a LBNP chamber at 1.0-1.2 body weight (58 ± 2 mmHg LBNP) maintains aerobic fitness and sprint speed during 15 days of 6c head-down bed rest. Such preservation of submaximal responses after bed rest suggests that exercise combined with LBNP may be effective in maintaining upright exercise capacity during longer bed rest periods (Perhonen et al, 2001;Schneider et al, 2002). LBNP has been also used for preventing orthostatic intolerance and micogravity-induced cardiac remodeling/atrophy after space flight and for training astronauts (Watenpauch, 2001).…”