Effects of Intermittent Hypoxic Exercise Training on Hemodynamics and Erythrocyte Rheology

• Main Authors: Tso-Yen Mao, 毛祚彥
• Other Authors: Li-Lan Fu
• Format: Others
• Language: en_US
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/88653562951641546302

博士 === 國立體育大學 === 體育研究所 === 100 === Hypoxic exercise training is a good strategy for enhancing endurance athletes’ performance. Recently, lots of evidences indicated intermittent and chronic hypoxia exposures have similar advantages in increasing physical fitness. However, whether the physiological acclimatization induced by different interventions might cause further questions need further exploration. Compared with chronic hypoxia, intermittent hypoxia has more impact on pulmonary, circulatory and metabolic functions. Long-term intermittent hypoxia exposure changes respiratory pattern, cardiac functions and vessel adjustment. These further affect tissue oxygen delivery and utilization by hemodynamic pathways. Moreover, whether intermittent hypoxia combined with exercise regimen cause similar pathological symptoms, what’s the ideal hypoxic exercise prescription, require further investigation. Opposite to chronic hypoxia, intermittent hypoxia acclimatization didn’t induce erythrocytosis. Most stresses occurred at hypoxic environment, which affect rheological properties of non-renewed RBC and further molecular mechanisms are still unknown. Two parts of studies were designed in order to investigate the effects of intermittent hypoxia on hemodynamics and RBC rheology, and try to find a safe and efficient hypoxic exercise prescription. The research purpose of part 1 study was to compare the effects of different normoxic with/without hypoxic exercise regimens on cardiopulmonary fitness, physical performances and hemodynamic parameters. Sixty healthy male subjects were recruited and random assigned to hypoxic absolute exercise (H-AE, n=12), hypoxic relative exercise (H-RE, n=12), normoxic exercise (NE, n=12), hypoxic control (H-C, n=12) and normoxic control (N-C, n=12). Exercise groups were trained at 50% maximal work rate (Wmax), 30 min/day, and five days/week on stationary bicycle for 4 weeks. Hypoxic and normoxic conditions were set at 12% to 21% oxygen concentrations. Graded exercise test (GXT), normoxic and hypoxic submaximal continuous test (N&HECT), vessel functional test (VFT), and blood sample were collected before and after interventions. Cardiopulmonary fitness was measured by exercise physiological systems. Cardiac functions were evaluated by non-invasive cardiac output monitor system. Cerebral and muscular hemodynamics were assessed by near-infrared spectroscopy. Basic hematological parameters, ions and acid-base balance were detected from blood samples. The research purpose of part 2 study was to compare the effects of normoxic and hypoxic exercise on RBCs rheology and to explore underlying mechanisms. Twenty-four healthy male subjects were recruited and random assigned to H-AE (n=12) and NE (n=12). Both groups were trained at 50%Wmax, 30 min/day, 5days/week, for 5 weeks on stationary bicycle with 21% or 15% oxygen concentration conditions. Similarly, GXT, HCET, and blood samples were collected before and after experiments. RBCs rheology (deformability) was detected by ektacytometer. Cell volume, membrane stability, cytoskeleton protein levels were measured and evaluated by flow cytometer. In order to explore the further molecular RBCs mechanisms, the eryptosis and rheological properties under oxidative stress and Gardos channels regulation in vitro were tested. All data was presented as mean±SE. Normal distribution of data was examined by Shapiro-Wilk test. Nonparametric results were inspected by Kruskal-Wallis test and Wilcoxon matched pairs test. Parametric results were tested by repeated measurement ANOVA and Tukey post hoc test. Statistical significant level was p＜0.05. The part 1 results demonstrated that the H-AE group had a larger improvement in aerobic capacity compared with the N-E group. Both H-RE and H-AE ameliorated the suppression of cardiac stroke volume and the GN hyperemic response (Δtotal Hb/min) and reoxygenation rate by acute 12% O2 exposure. Simultaneously, the two hypoxic interventions enhanced perfusion (Δtotal Hb) and O2 extraction [Δdeoxy Hb] of the VL muscle during the 12% O2 exercise. Although acute 12% O2 exercise decreased oxygenation (ΔO2Hb) of the FC, none of the 4-wk interventions influenced the cerebral perfusion and oxygenation during normoxic/ hypoxic exercise tests. The results of part 2 demonstrated that HE (i) down-regulated CD47 and CD147 expressions on erythrocyte, (ii) decreased actin and spectrin contents in erythrocyte, (iii) reduced erythrocyte deformability under shear flow, and (iv) diminished erythrocyte volume changes under hypotonic stress. Treatment of erythrocytes with H2O2 that mimicked in vivo pro-oxidative status resulted in the cell shrinkage, rigidity, and phosphatidylserine exposure, whereas HE enhanced the eryptotic responses to H2O2. However, HE decreased the degrees of clotrimazole to blunt ionomycin-induced shrinkage, rigidity, and cytoskeleton breakdown of erythrocytes, referred to as Gardos effects. Reduced erythrocyte deformability by H2O2 was inversely related to the erythrocyte Gardos effect on the rheological function. Conversely, NE intervention did not significantly change resting and exercise erythrocyte rheological properties. Therefore, we concluded that moderate hypoxic exercise training improves cardiopulmonary fitness and increases resistance to disturbance of cardiac hemodynamics by severe hypoxia, concurred along with enhancing O2 delivery/utilization in skeletal muscles but not cerebral tissues. However, HE rather than NE reduces erythrocyte deformability and volume regulation, accompanied by an increase in the eryptotic response to oxidative stress. Simultaneously, this intervention depresses Gardos channel-modulated erythrocyte rheological functions. Results of this study provide further insight into erythrocyte senescence induced by HE. Finally, we stated that if exercise training for only enhancing aerobic fitness, the prescription of hypoxic related-exercise can enhance physical fitness and anoxic tolerance simultaneously. But, if exercise training for strength sports performance, the prescription of hypoxic absolute-exercise can be used to enlarge exercise capacity. However, to supply anti-oxidant during training prevented the senescence and rheological dysfunctions of erythrocyte induced by oxidative stress.