The Variation Of Left Ventricular Function And EPO Concentration And Their Relevance With AMS Occurrence Under Acutely High Altitude Exposure

Research backgroundAMS(acute mountain sickness) is one the syndrome that may happen to people who quickly access to high altitude environment without the tolerance of hypoxia and therefore cause symptoms such as headache and etc. If not been treated in time, it may further get worse to become high altitude pulmonary edema or high altitude cerebral edema. The occurrence mechanism of AMS is not finally concluded, but there is no doubt that the effect of the change of the cardiovascular system is important in this process. Although there are many researches related to the change of cardiac function in high altitude have been published, there is no consistent result and conclusion. In addition, despite the left ventricular dysfunction of the high altitude pulmonary edema patients has been pointed out, researches are rarely focus on the difference of left ventricular function between AMS patients and healthy people. Therefore it is important to the prevention and treatment of AMS that to discuss the change of left ventricle function in high altitude hypoxia.Nowadays people considered that the regulation of cardiac function under hypoxia stress is mainly affected by sympathetic nervous system. But researchers also discovered that some circulating hormones affect cardiac functions as well. Erythropoietin(EPO) is an important hematopoiesis-improving hormone that regulated by hypoxia. Recently people discovered that the EPO receptor not only expresses and works in classical hematopoietic system, but also has been found in some non-hematopoietic tissues and organs. In modern researches, it has been proved that EPO has the positive effect on inotropic increase on myocardium, also researchers pointed out EPO increasing dramatically in post-hypoxia mice and the positive correlation between the changes of left ventricular systolic function and concentration of EPO in plasma. So this article infers that the change of endogenous EPO caused by high altitude hypoxia is an important factor of compensatory increase of the left ventricular function.Object:1) To observe the changes of left ventricular function under acute high altitude hypoxia exposure, and the relevance between of that and AMS occurrence.2) To observe the varying pattern of plasma EPO concentration of subjects at different altitude on plateau and its influence to left ventricular function. Further to consider the relevance of the change of EPO concentration and AMS occurrence.Method:Following strictly the inclusion and exclusion criteria, 422 Han nationality Chinese males(ages from 18 to 33) are chosen as subjects from the sample(501 males included). Data were collected separately according to experimental designs by following conditions: ① Low altitude subjects; ①Subjects 24 h after acutely access to high altitude area(3700m); ③ Subjects 24 h after acutely access to high altitude(4400m) after acclimation at 3700 m for 1 week; ④Long time(>a year) high altitude(3700m) migration subjects; ④Subjects migrated to 4400 m for 50 days after long time(>a year) acclimation at 3700 m.Testing parameters include baseline demographic data(age, weight, height, etc.), vital signs index(blood pressure, oxyhemoglobin saturation, heart rate, etc.), the observation of left ventricular function by echocardiography, and Lake Louise Scoring System to estimate the occurrence of AMS.Result:1) After acutely get into high altitude(3700m), stroke volume, ejection fraction and cardiac output of subjects was increased clearly(P<0.05). stroke volume of subjects that get into high altitude(4400m) after 7 days acclimation was observably decreased(P<0.05). but ejection fraction and cardiac output changed rarely(P>0.05). Compared with at low altitudes, although stroke volume of healthy people that get into 3700 m acutely is remarkably increased(P<0.05), no such change is observed in AMS group(P>0.05). Further after short-term acclimation healthy people get into high altitudes(4400m), they have higher stroke volume than AMS patients(P<0.05).2) After going up to high altitudes acutely, people’s EPO concentration run up. Compared with low altitudes, plasma EPO concentration of acutely high altitude exposure people and acutely high altitude exposed people after short-term acclimation are outstanding(P<0.05). EPO concentration comparing between of either immigrants or exposed immigrants and low altitude subjects make no sense statistically(P>0.05). EPO concentration of acutely exposed people is observed positive correlated to left ventricular function parameters such as left ventricular diastolic diameter, stroke volume, E/A(R=0.236, R=0.278, R=0.293,respectively, P<0.05) and negative correlated to AMS score(R=- 0.249,P<0.05).Conclusion:1) Not only left ventricular systolic function of people who get into high altitude acutely is significantly enhanced and also their cardiac output adapt hypoxia condition.2) After acutely high altitude exposure, stroke volume of AMS- people are considered greater than it at low altitude. Further they go up to higher altitude, their stroke volume are still outstanding to AMS+ people. Depend on this, it can be inferred that AMS- people have stronger left ventricular functional adaption to lower AMS risk in hypoxia at high altitudes.3) Plasma EPO concentration of people who get into high altitude acutely is raised. But migration to plateau has no apparent influence on EPO concentration.4) For people acutely getting into plateau, their plasma EPO concentration shows positive correlated to left ventricular function parameters(stroke volume, left ventricular diastolic diameter and E/A) evidently, and negative correlated to AMS score. EPO can improve left ventricular function by the enhancement of positive inotropic effect, which may contributes to a lower risk of AMS.