Metabolic and cardiovascular responses during sub-maximal exercise in humans after 14 days of head-down tilt bed rest and inactivity

Abstract

VO(2), f (H), Q, SV, [Hb], C(a)O(2), QaO(2), MAP and R (P) were measured in 10 young subjects at rest and during exercise at 50, 100 and 150 W before and after 14 days of head-down tilt bed rest (HDTBR) and of ambulatory (AMB) control period. f (H) was 18 and 8% higher after HDTBR and AMB, respectively. SV dropped by 15% both after HDTBR and AMB, whereas Q did not change. After HDTBR, C(a)O(2) decreased at rest (-8%) and at 50 W (-5%), whereas QaO(2) did not change; MAP was 14 and 6% lower at rest and at 100 W and R (P) decreased by 23% only at rest. Changes in f (H) and SV were larger after HDTBR than after AMB. These results show that, notwithstanding the drop of SV, moderate-intensity dynamic exercise elicited a normal pressure response after 14 days of HDTBR.

Oxygen deficits and oxygen delivery kinetics during submaximal intensity exercise in humans after 14 days of head-down tilt-bed rest

“…Larger sympathetic output acting on the arterioles could therefore have increased their tone, causing a substantial drop in blood flow downstream from this section of the vascular tree. However, total peripheral resistance did not significantly increase during submaximal exercise after HDTBR, as reported in a previous paper on steady state metabolic and cardiovascular responses assessed in these same subjects after HDTBR (Capelli et al 2008). So the role of the augmented sympathetic tone in decreasing limb O 2 delivery after bed rest seems to be rather unlikely.…”

“…Q a O 2 measured before and after HDTBR at rest and during exercise at steady state. The values presented here are the same as those reported for the same subjects and conditions in a previous paper on cardiovascular and metabolic response to submaximal exercise after 14 days of HDTBR; the reader is referred to the earlier study for further detail (Capelli et al 2008). In brief, f H and Q H were significantly higher and lower after HDTBR both at rest and during exercise, respectively.…”

“…The workload was then increased by 50 W steps until the maximum; each step lasted 7 min with 5 min of rest in between. The present paper deals with the data obtained at the lowest workload of 50 W. The data concerning the other sub maximal workloads and maximal exercise have been presented elsewhere (Capelli et al , 2008.…”

“…Short-term head-down tilt-bed rest (HDTBR) is associated with clear signs of cardiovascular deconditioning leading to significant decrease in stroke volume (Q H ) and maximal cardiac output ( _ Q max ) (Capelli et al , 2008. Cardiovascular deconditioning is also characterized by a disregulation of the autonomic cardiovascular control system, decreased vagal activity (Pavy-Le Traon et al 1998), and impairment of the baroreceptor reflex (Linnarsson et al 2006).…”

“…Cardiovascular deconditioning is also characterized by a disregulation of the autonomic cardiovascular control system, decreased vagal activity (Pavy-Le Traon et al 1998), and impairment of the baroreceptor reflex (Linnarsson et al 2006). As a consequence, an elevated heart rate (f H ) is commonly observed at rest and a brisk tachycardic response occurs during exercise (Capelli et al 2008).…”