WISE-2005: prolongation of left ventricular pre-ejection period with 56 days head-down bed rest in women.
This study tested the hypothesis that prolonged physical deconditioning affects the coupling of left ventricular depolarization to its ejection (the pre-ejection period, PEPi) 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 PEPi 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, PEPi 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 PEPi. 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.
Hodges
Gary J
GJ
School of Kinesiology, University of Western Ontario, London, Ontario, Canada.
Mattar
Louis
L
Zuj
Kathryn A
KA
Greaves
Danielle K
DK
Arbeille
Phillipe M
PM
Hughson
Richard L
RL
Shoemaker
J Kevin
JK
D000328:Adult; D001510:Bed Rest; D001794:Blood Pressure / Q000187:drug effects; D018493:Cardiovascular Deconditioning; D004562:Electrocardiography; D005260:Female; D018475:Head-Down Tilt / Q000502:physiology*; D006352:Heart Ventricles / Q000187:drug effects / Q000503:physiopathology*; D006801:Humans; D007545:Isoproterenol; D008150:Lower Body Negative Pressure; D009638:Norepinephrine; D013318:Stroke Volume; D016683:Supine Position; D018544:Weightlessness Countermeasures; D018474:Weightlessness Simulation
D007545:Isoproterenol; D009638:Norepinephrine