Abstract:Could the intrinsic characteristics of tolerance to hypoxia be retained in Tibetan high-altitude natives after they had migrated to a low altitude? To answer this question, we undertook a study of 33 healthy male adolescent Tibetans born and raised in a high plateau (3,700 m [12,140 ft] above sea level) who migrated to Shanghai (sea level) for 4 years. Ten agematched healthy male Han adolescents born and raised in Shanghai were regarded as the control group. Acute hypoxia was induced in a hypobaric chamber for 2 h to simulate the 3,700 m altitude. At sea level, maximal oxygen consumption (VO 2 max ) was not significantly different between the two groups. During acute hypoxia, the values of VO 2 max , tissue oxygen extraction, arterial oxygen pressure, and the arterial oxygen saturation showed markedly higher in Tibetan subjects than in Han subjects (1.41 ± 0.04 l/min/M 2 vs.1.25 ± 0.04 l/min/M 2 , 55.0 ± 4.2% vs. 47.3 ± 9.1%, 7.2 ± 0.6 vs. 5.5 ± 0.2 kPa, and 87.9 ± 3.3% vs. 78.2 ± 1.6%, respectively, P < 0.05). The calculated "oxygen reserve capacity" and "cardiac reserve capacity" were better in the Tibetans than in the Han natives (P < 0.05), which suggests that physical work capacity is greater in the Tibetan group. The sympathetic stimulation was less, and there was no noticeable change in cardiac function during acute hypoxia in the Tibetan group. The results indicate that the better tolerance to hypoxia in the Tibetans is retained during the 4-year stay at sea level, implying that the intrinsic hypoxic adaptation still exists in the Tibetan high-altitude natives.Key words: adaptation, high altitude, hypobaric chamber, oxygen transport, physical workload.For thousands of years, the overwhelming majority of Tibetans have been living at the roof of the world, characterized by an average altitude in excess of 4,000 m (13,123 ft). It is necessary that mechanisms be developed to compensate for low oxygen levels and to facilitate metabolism and other physiological functions in this hypoxic environment for both humans and animals.Our previous study has demonstrated that there exists a close relationship between the "cardiac pump function test" and hypoxic tolerance or climbing performance during a Mt. Everest expedition, and that Tibetans have a significantly better preservation of cardiac pump function [1]. We have also reported that compared to lowlanders, Tibetans have fewer incidents of excessive polycythemia, hypoventilation, and low pulmonary diffusion capacity than were observed in the lowlander's mountain sickness [2]. It is unclear whether the better hypoxic tolerance in the Tibetans is a result of the body's processes (physiological acclimatization) or of an intrinsic characteristic tolerance (genetic adaptation), or both. A comparison of the differences in the physiological responses to hypoxic stress in certain circumstances between Tibetans and lowlanders may reveal some essential facts about the possible mechanisms underlying the Tibetans' hypoxic tolerance.This study is one of our long-term...
SUMMARYAfter acclimatization to high altitude, the sea level haemorrhagic tolerance of rats was measured by determining the bleeding volume which resulted in death under anaesthesia following cannulation. For each animal this was recorded as a bleeding volume index (BVI), the total volume of blood lost per 100 g of body weight. The mean BVI of altitude acclimatized rats was greater than that for non-acclimatized rats (P < 0 001), showing that chronic exposure to altitude enabled the animals to tolerate more severe blood loss. Evidence is presented which suggests that the increased haemorrhagic tolerance resulted, in part, from an increased initial blood volume and an increased ability for arterial blood pressure regulation during haemorrhage.
In order to excel in sport, apart from the correct training, the genetic combination of an individual may also be a factor in making an elite athlete. Weightlifting, as a popular sport, has a unique bio-mechanism dealing with muscle performance. The current study investigated the polymorphisms of the angiotensin-converting enzyme (ACE), the a-actinin-3 (ACTN3), and the vitamin D receptor (VDR) genes (individually or in combination) in Thai weightlifters. A total of 117 male and female national and junior Thai weightlifters, and 99 healthy sedentary people were recruited for this study. Genotyping was analyzed by Polymerase Chain Reaction (PCR) and Polymerase Chain Reaction - Restriction Fragment Length Polymorphism (PCR-RFLP). When compared to the junior and non-athletes group, the genotype and allele frequencies of ACE (DD), ACTN3 (RR), and VDR (ff) were more frequent in both male and female national weightlifters. In addition, the genotype combinations between ACE (DD) + VDR (ff), ACE (DD) + ACTN3 RR, and ACTN3 RR + VDR ff presented highly in both genders of national weightlifters. Taken together, our results suggest that the ACTN3 and VDR genotype, individually or in combination, may influence muscle performance in weightlifters, appearing to significantly contribute to better weightlifting performance.
Acute exposure to high altitude for 1 day in rats caused an increase in hematocrit (Hct) with no change in mean arterial blood pressure (mABP) from the non-altitude control, whereas after prolonged exposure to altitude (5-6 weeks) there were increases in both Hct and mABP. No changes in total plasma protein (TPP) and plasma osmolality (POsm) from control rats were observed in all altitude-exposed animals. The ability of the acutely and chronically altitude and non-altitude exposed rats to resist hemorrhage was studied. Hemorrhage was standardized at mABP in the range of 30-35 mmHg. Chronic exposure to altitude increased the initial and maximum volume of blood withdrawn as well as the oligemic and survival times, whereas acute altitude exposure did not. The higher ability to resist standardized hemorrhagic shock of the chronically altitude exposed rats seemed to result, in part, from their greater hemodilution and better arterial blood pressure regulation. No difference in the rate of hemodilution as well as hemorrhagic tolerance was observed between the 1-day altitude and control rats. The difference in rate of hemodilution between the chronic altitude and control animals could not be due to arterial hyperosmolality since the magnitude of change in POsm during blood loss was the same for all animal groups.
This study aimed to test whether hypertonic sports drinks (SD) containing multiple types of carbohydrate (CHO) promote fluid absorption in healthy young men. Eight healthy males (20‐30 y old) were randomly infused with three SD containing multiple types of CHO (6‐13% total CHO, 336 ‐ 678 mOsm/kg) at a rate of 15 ml/min using a triple‐lumen nasojejunal tube. Fluid samples collected from the proximal and distal ports located at approximately 10 and 50 cm from the pyloric sphincter were analyzed for osmolality and concentrations of a non‐absorbable marker PEG, CHO, sodium and potassium. Infusion of SD with 6% CHO (336 mOsm/kg) resulted in net fluid absorption whereas SD with 11‐13% CHO (653‐678 mOsm/kg) induced fluid secretion in the test segment and reductions in luminal fluid osmolality towards isotonicity. Rates of CHO absorption were similar among, and net secretion of Na+ and K+ were observed in, all SD tested. SD having 11‐13% CHO induced a higher rate of electrolyte secretion than those with 6% CHO. Plasma glucose was doubled at 30 min after infusion of all test solutions. Thus, the presence of multiple types of CHO in the hypertonic test beverages could not offset the influence of hypertonicity on fluid absorption. Moreover, rates of CHO absorption seem independent of CHO concentrations in the SD (Gatorade Sports Science Institution, USA)
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