Aortic, cerebral and lower limb arterial and venous response to orthostatic stress after a 60-day bedrest

Abstract

The objective of this study is to assess by echography and Doppler the Cerebral (Vmca), Aortic (Vao) and Femoral (Vfem) arterial flow velocity and calf vein (Tibial, Gastrocnemius) section (Tib, Gast) during orthostatic intolerance (OI) test after a 60-day, head down tilt bed rest (HDBR). Twenty-four women (25-40 years) underwent a 60-day HDBR at -6°: eight as control (Con), eight with exercise against lower body negative pressure (Ex-Lb) and eight with nutrition supplement (Nut). Before and after (R0) HDBR, all subjects underwent a 10-min, 80° tilt followed by progressive LBNP until presyncope. After the post-HDBR Tilt + LBNP test, two groups were identified: finishers (F, n = 11) who completed the Tilt and non-finishers (NF, n = 13). A higher percentage decrease in Vao flow, higher percentage distension of Tib vein and a lack of increase in Vmca/Vfem ratio during the post-HDBR Tilt + LBNP compared to pre-HDBR were correlated to OI, but not all of these abnormal responses were present in each of the NF subjects. Abnormal responses were more frequent in Con and Nut than in Ex-Lb subjects. (1) HDBR did not affect the cardiac, arterial and venous responses to the orthostatic test to the same extent in each subject. (2) Exercise within LBNP partially preserved the cardiovascular response to Tilt, while Nutrition supplementation had no efficacy. (3) Cerebral/femoral flow ratio and aortic flow were the parameters most closely related to OI. (4) Reduction in aortic flow was not the major hemodynamic change preceding syncope.

Peripheral Arterial and Venous Response to Tilt Test after a 60-Day Bedrest with and without Countermeasures (ES-IBREP)

“…FEM systolic velocity dropped similarly in all 3 groups during the tilt test (Figure 6), which meant that stroke volume also dropped in all groups [22].…”

“…Changes in femoral systolic peak velocity (FEM S) were similar in the three groups, so the changes in SV were also similar [22]. Thus, neither of the 2 CMs had a significant impact on the change in FEM S (i.e., stroke volume) during the tilt test even though RVE and Herb contributed to reduce the loss of left ventricular volume.…”

Temporal Artery Doppler Spectrum Morphology Responses to Tilt and LBNP as an Early Indicator of Syncope

“…This is also in agreement with other studies which suggested that one of the primary mechanism underlying syncope should be a fall in cardiac output ( 9 , 17 ). However, the drop in stroke volume is not observed systematically or at the same time before presyncope in all subjects ( 5 ). It seems that even with a continuous decrease in stroke volume, the last hemodynamic changes, happening at the leg level [drop in vascular resistance ( 14 ) or drop in venous return], or at the splanchnic level, contribute to further reduce cardiac output.…”

“…In these cases the reverse fl ow, present since the start of tilt, became greater when approaching syncope. Another study performed, also using the tilt plus LBNP stress, demonstrated that not all of arterial and venous territories showed vasoconstriction simultaneously, or to the same extent during the test ( 5 ). Therefore, this might suggest that in the second profi le where temporal artery negative velocity was seen early in the test, vasoconstriction of the area supplied by the temporal artery, or cutaneous vascular beds were not the last to be recruited for vasoconstriction.…”

Effects of real and simulated weightlessness on the cardiac and peripheral vascular functions of humans: A review

“…increased carotid resistance index in 2 of 3 astronauts during a 237-day spaceflight on Salyut [55]. And Zhang reported a decreased femoral vascular resistance and an insignificant change in the cerebral vascular resistance during a 6-month spaceflight [56].…”