Premium
WISE‐2005: prolongation of left ventricular pre‐ejection period with 56 days head‐down bed rest in women
Author(s) -
Hodges Gary J.,
Mattar Louis,
Zuj Kathryn A.,
Greaves Danielle K.,
Arbeille Phillipe M.,
Hughson Richard L.,
Shoemaker J. Kevin
Publication year - 2010
Publication title -
experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0958-0670
DOI - 10.1113/expphysiol.2010.054254
Subject(s) - head down tilt , bed rest , cardiology , medicine , deconditioning , afterload , ventricle , supine position , stroke volume , qrs complex , ejection fraction , heart failure
This study tested the hypothesis that prolonged physical deconditioning affects the coupling of left ventricular depolarization to its ejection (the pre‐ejection period, PEP i ) and that this effect is minimized by exercise countermeasures. Following assignment to non‐exercise (Control) and exercise groups (Exercise), 14 females performed 56 days of continuous head‐down tilt bed rest. Measurements of the electrocardiogram (ECG) and stroke volume (Doppler ultrasound) during supine rest were obtained at baseline prior to (Pre) and after (Post) the head‐down tilt bed rest (HDBR) period. Compared with Pre, the PEP i was increased following head‐down tilt bed rest (main effect, P < 0.005). This effect was most dominant in the Control group [Pre = 0.038 ± 0.06 s ( s.d. ) versus Post = 0.054 ± 0.011 s; P < 0.001]. In the Exercise group, PEP i was 0.032 ± 0.005 s Pre and 0.038 ± 0.018 s Post; P = 0.08. Neither the QRS interval nor cardiac afterload was modified by head‐down tilt bed rest in Control or Exercise groups. Low‐dose isoprenaline infusion reversed the head‐down tilt bed rest‐induced delay in the PEP i . These results suggest that head‐down tilt bed rest leads to a delayed onset of systolic ejection following left ventricular depolarization in a manner that is affected little by the exercise countermeasure but is related to β‐adrenergic pathways. The delayed onset of systole following head‐down tilt bed rest appears to be related to mechanism(s) affecting contraction of the left ventricle rather than its depolarization.