Direct Comparison Of Tilt Test And Lower Body Negative Pressure Effects On Human Hemodynamics And Baroreflex Regulation After Dry Immersion Доклады на конференциях
Язык | Английский | ||
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Тип доклада | Стендовый | ||
Конференция |
42nd Annual the International Society of Gravitational Physiology Meeting 02-07 июн. 2023 , Антверпен |
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INTRODUCTION Head-up tilt test (HUT) and its spaceflight equivalent lower body negative pressure test (LBNP) are widely used in space medicine as cardiovascular system (CVS) stress tests. Both tests cause blood redistribution towards lower body but differ in cardiovascular outcomes due to differences in regulatory mechanisms involved (Kitano A. et al., 2005 and Tanaka, K., et al., 2009). Dry immersion (DI) as model of gravitational unloading impairs CVS regulation (Eckberg D.L., 2003 and De Abreu S. et al., 2017), which may alter these outcome differences. The analysis of low frequency (LF) heart rate (HR) and mean arterial pressure (MAP) waves including α-coefficient estimation (Pagani M., et al., 1988) is widely used to assess the state of CVS baroreflex control. Thus, we decided to use such analysis during short-term (3 min) HUT and LBNP in the same subjects before and after DI. Exposure durations were set to 3 min, to address short-term hemodynamic responses mediated mostly by the autonomic nervous system and to minimize the possibility of pre-syncope manifestations after DI. Aim To compare the responses of MAP, HR and their LF spectral characteristics in 3-min HUT and LBNP before and after 7-day DI. METHODS Nine healthy men (age 30.8±4.8 yrs., BMI 22.9±2.3 kg/m2) were exposed to 7-day DI. HUT (65°, 3 min) and LBNP (Chibis suit, -35 mm Hg, 3 min) were performed before and on the first day after DI. ECG (NVX52, MCS, Russia), blood pressure and stroke volume (SV) (Finometer, Finapres Medical Systems, the Netherlands) were continuously recorded; HR and MAP were calculated for every cardiac cycle. Amplitudes of HR (aHR) and MAP (aMAP) waves in LF (0.06-0.13 Hz) band were calculated using continuous wavelet transform. Each test was repeated 5 times alternating with 3-min rest. SV, MAP and HR were averaged for the last 30 sec while aHR, and aMAP were averaged for the last 70 sec of test and rest intervals in all repetitions. LF α-coefficient was calculated as aHR/aMAP. Percent differences between parameters in rest state and HUT/LBNP state are reported as reactions to test. Two-factor ANOVA with Sidak's multiple comparisons test was used to examine influence of DI and Test factors on hemodynamic parameter reactions. RESULTS In both SV and HR the only source of variation was DI factor (p=0.001). SV reduction was similar in both HUT and LBNP pre-DI, and was more pronounced after DI (Fig.1). HR increased in similar fashion: HUT and LBNP reactions did not differ pre-DI and were more pronounced after DI. MAP reaction was influenced by both DI (p=0.04) and Test (p<0.0001); DI decreased the difference in MAP reactions between the tests (p=0.001 for interaction of two factors). MAP remained the same in HUT pre-DI and decreased post-DI, while it decreased in LBNP both pre- and post-DI. LF aHR didn’t change in HUT and LBNP neither pre- nor post-DI (Table 1). LF aMAP increased similarly in both tests only after DI. LF α-coefficient did not change in HUT and LBNP performed pre-DI. Post-DI, α-coefficient decreased in HUT (p = 0.02) but not in LBNP. Table 1. Amplitudes of LF HR and MAP oscillations and α-coefficient during HUT and LBNP before and after dry immersion. * - p<0.05 between rest and HUT/LBNP state (Sidak’s multiple comparisons test). Pre dry immersion Post dry immersion HUT LBNP HUT LBNP Rest Test Rest Test Rest Test Rest Test aHR, bpm 1.32±0.64 1.48±0.29 1.43±0.68 1.41±0.37 1.2±0.44 1.23±0.43 1.14±0.32 1.38±0.42 aMAP, mmHg 1.17±0.37 1.67±0.46 1.18±0.31 1.55±0.57 1.10±0.25 1.95±0.57* 1.02±0.23 1.79±0.56* α, bpm/mmHg 1.1± 0.39 0.93±0.22 1.2±0.46 0.97±0.31 1.1±0.33 0.65±0.24* 1.12±0.27 0.83±0.31 CONCLUSION Before DI MAP decreases during LBNP but not in HUT. DI influence dimmed this contrast: it didn’t change MAP reaction to LBNP but was associated with MAP decrease in HUT in similar fashion to LBNP. Effect of DI on LF α was also evident only in HUT but not in LBNP. These observations suggest the DI-induced changes in CVS regulation mechanisms which involved mostly during orthostasis, such as vestibulosympathetic reflex (Tanaka, K. et al., 2009) or myogenic constriction of lower limb vasculature (Rodionov I.M. et al., 1999). It seems that short-term HUT may be more sensitive test then LBNP to assess unloading-induced CVS deconditioning. The results of this study may help to interpret spaceflight LBNP and pre-/postflight HUT data. FUNDING Cardiovascular studies were performed under the State Program of Basic Research (64.1) and a grant from the Russian Foundation for Basic Research (20-015-00536). REFERENCES Kitano A. et al., 2005, Journal of Applied Physiology, 98(6), 2081-2086. Tanaka K. et al., 2009, Autonomic Neuroscience, 148(1), 90-96. Eckberg D.L., 2003, Acta Physiologica Scandinavica, 177, 299–311. De Abreu S. et al., 2017, Frontiers in physiology, 8, 799. Pagani M. et al., 1988, Hypertension, 12(6), 600-610. Rodionov I.M. et al., 1999, Environmental Medicine, 43(1), 1-9.
Библиографическая ссылка:
Zhedyaev R.Y.
, Tarasova O.S.
, Tomilovskaya E.S.
, Semenov Y.S.
, Vinogradova O.L.
, Borovik A.S.
Direct Comparison Of Tilt Test And Lower Body Negative Pressure Effects On Human Hemodynamics And Baroreflex Regulation After Dry Immersion
42nd Annual the International Society of Gravitational Physiology Meeting 02-07 Jun 2023
Direct Comparison Of Tilt Test And Lower Body Negative Pressure Effects On Human Hemodynamics And Baroreflex Regulation After Dry Immersion
42nd Annual the International Society of Gravitational Physiology Meeting 02-07 Jun 2023