TY - JOUR
T1 - Diastolic suction is impaired by bed rest
T2 - MRI tagging studies of diastolic untwisting
AU - Dorfman, Todd A.
AU - Rosen, Boaz D.
AU - Perhonen, Merja A.
AU - Tillery, Tommy
AU - McColl, Roderick W
AU - Peshock, Ronald M
AU - Levine, Benjamin D
PY - 2008/4
Y1 - 2008/4
N2 - Bed rest deconditioning leads to physiological cardiac atrophy, which may compromise left ventricular (LV) filling during orthostatic stress by reducing diastolic untwisting and suction. To test this hypothesis, myocardial-tagged magnetic resonance imaging (MRI) was performed, and maximal untwisting rates of the endocardium, midwall, and epicardium were calculated by Harmonic Phase Analysis (HARP) before and after -6° head-down tilt bed rest for 18 days with (n = 14) and without exercise training (n = 10). LV mass and LV end-diastolic volume were measured using cine MRI. Exercise subjects cycled on a supine ergometer for 30 min, three times per day at 75% maximal heart rate (HR). After sedentary bed rest, there was a significant reduction in maximal untwisting rates of the midwall (-46.8 ± 14.3 to -35.4 ± 12.4 °/s; P = 0.04) where untwisting is most reliably measured, and to a lesser degree of certainty in the endocardium (-50.3 ± 13.8 to -40.1 ± 18.5 °/s; P = 0.09); the epicardium was unchanged. In contrast, when exercise was performed in bed, untwisting rates were enhanced at the endocardium (-48.4 ± 20.8 to -72.3 ± 22.3 °/ms; P = 0.05) and midwall (-39.2 ± 12.2 to -59.0 ± 19.6 °/s; P = 0.03). The differential response was significant between groups at the endocardium (interaction P = 0.02) and the midwall (interaction P = 0.004). LV mass decreased in the sedentary group (156.4 ± 30.3 to 149.5 ± 27.9 g; P = 0.07), but it increased slightly in the exercise-trained subjects (156.4 ± 34.3 to 162.3 ± 40.5 g; P = 0.16); (interaction P = 0.03). We conclude that diastolic untwisting is impaired following sedentary bed rest. However, exercise training in bed can prevent the physiological cardiac remodeling associated with bed rest and preserve or even enhance diastolic suction.
AB - Bed rest deconditioning leads to physiological cardiac atrophy, which may compromise left ventricular (LV) filling during orthostatic stress by reducing diastolic untwisting and suction. To test this hypothesis, myocardial-tagged magnetic resonance imaging (MRI) was performed, and maximal untwisting rates of the endocardium, midwall, and epicardium were calculated by Harmonic Phase Analysis (HARP) before and after -6° head-down tilt bed rest for 18 days with (n = 14) and without exercise training (n = 10). LV mass and LV end-diastolic volume were measured using cine MRI. Exercise subjects cycled on a supine ergometer for 30 min, three times per day at 75% maximal heart rate (HR). After sedentary bed rest, there was a significant reduction in maximal untwisting rates of the midwall (-46.8 ± 14.3 to -35.4 ± 12.4 °/s; P = 0.04) where untwisting is most reliably measured, and to a lesser degree of certainty in the endocardium (-50.3 ± 13.8 to -40.1 ± 18.5 °/s; P = 0.09); the epicardium was unchanged. In contrast, when exercise was performed in bed, untwisting rates were enhanced at the endocardium (-48.4 ± 20.8 to -72.3 ± 22.3 °/ms; P = 0.05) and midwall (-39.2 ± 12.2 to -59.0 ± 19.6 °/s; P = 0.03). The differential response was significant between groups at the endocardium (interaction P = 0.02) and the midwall (interaction P = 0.004). LV mass decreased in the sedentary group (156.4 ± 30.3 to 149.5 ± 27.9 g; P = 0.07), but it increased slightly in the exercise-trained subjects (156.4 ± 34.3 to 162.3 ± 40.5 g; P = 0.16); (interaction P = 0.03). We conclude that diastolic untwisting is impaired following sedentary bed rest. However, exercise training in bed can prevent the physiological cardiac remodeling associated with bed rest and preserve or even enhance diastolic suction.
KW - Bed rest deconditioning
KW - Cardiac atrophy
KW - Exercise
KW - Magnetic resonance imaging with myocardial tagging
KW - Spaceflight
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U2 - 10.1152/japplphysiol.00858.2006
DO - 10.1152/japplphysiol.00858.2006
M3 - Article
C2 - 18239079
AN - SCOPUS:41949097232
SN - 8750-7587
VL - 104
SP - 1037
EP - 1044
JO - Journal of applied physiology
JF - Journal of applied physiology
IS - 4
ER -