The Study Of The Influences Of High Altitude Induced Hypoxia On Left Ventricular Function

Research BackgroundHealthy individuals may have acute mountain sickness (AMS) after an acute exposureto high altitude environments or arrival in lower partial pressure of surroundings. Thesymptoms of AMS are usually mild and self-limiting but can become incapacitating. Insome cases, AMS progresses to high altitude cerebral edema (HACE) and high altitudepulmonary edema (HAPE), which are rare but life-threatening conditions. As we know, thebody reacts in many ways in attempt to adapt to its metabolic demands when acutelyexposed to a hypoxic environment. For example, obvious responses are associated withchanges in the cardiovascular system. The initial cardiac response to hypoxia ischaracterized by an increase in cardiac output with tachycardia，which helps maintainoxygen delivery. However, the effect of acute high altitude exposure upon left ventricularstroke volume is still a controversial problem. A previous study found that HAPE-resistantsubjects had a significantly augmented stroke volume, ejection fraction and cardiac indexand a sustained left ventricular Tei index during hypoxic breathing, while HAPE-susceptiblesubjects had no such changes. However, it is not clear whether high altitude-induced leftheart function alterations differ between subjects with AMS and those without AMS uponacute high altitude exposure. We explore objective diagnostic, therapeutic, prognosticparameters for AMS by examining the relationship between acute mountain sickness (AMS)and left ventricular function and with traditional echocardiography. Left ventricular masswould be decreased after short time high altitude exposure, some scholar suspected that itmay be due to myocardium autophagy similar to reduced skeletal muscle mass occurredwhen returned to sea level from high altitude. Respiratory chain complexⅠof skeletalmuscle cell down regulation and mitochondria density decreased with less production ofoxygen radical in human, in order to acclimatize well to high altitude environments. It is notclear about effect of staying at high altitude for a long time on left ventricular mass. In thepartⅡof this study, we investigate the effects of staying at high altitude for a long time onleft ventricular function and mass in young healthy males for purpose of providing advices to lowland residents whether they should be resided in high altitude for a long time.Part Ⅰ The influences of acute high altitude exposure on left ventricular function andthe association with acute mountain sicknessObjective The purpose of this study was to examine the influences of acute highaltitude exposure on left ventricular function, and aimed to look for objective diagnosticparameters for AMS by traditional echocardiography.Methods One hundred and sixteen Chinese healthy male servicemen participated inthe field trials. Structured case report form (CRF) questionnaires were used to recorddemographic data, physiological data, previous high altitude exposure and symptomsrelated to AMS. Heart rate (HR) were measured in116Chinese healthy lowlanders at sealevel; within24hours after arrival at3700m. By Doppler echocardiography, left ventricularfunctions were also examined in all subjects. AMS was diagnosed with Lake Louise score(LLS). Comparisons of the parameters were made between the subjects with and withoutAMS.Results Upon acute high altitude exposure,73of116(62.93%) subjects met thecriteria for AMS. Cardiac output (CO), ejection fraction (EF) and HR were significantlyincreased, but E/A ratio obviously decreased in the two groups after acute high altitudeexposure. The AMS group had remarkable shorter ejection time (ET), but higherleft ventricular myocardial performance index (LV Tei index) and HR than the non-AMSgroup. LV Tei index, HR showed significantly positive correlations with LLS, but ETnegatively correlated with LLS. In addition, ET cutoff value of274ms for diagnosis ofAMS was identified by receiver operating characteristic (ROC) curves analysis (area underthe curve (AUC),0.779;73.97%sensitivity;76.74%specificity). LV Tei index cutoff valueof0.463for diagnosis of AMS was identified (AUC,0.711;67.12%sensitivity;69.77%specificity).Conclusion Upon acute high altitude exposure, left ventricular systolic functionenhanced and diastolic dysfunction. LV Tei index and ET are significantly correlated withLLS and have relative accurateness in diagnosis of AMS by ROC analysis. Our findingswill provide novel parameters for objective diagnosis of AMS. Part Ⅱ The study of the influence of long time staying at high altitude on leftventricular function in young healthy malesObjective To assess the effects of long time staying at high altitude on leftventricular function and mass in young healthy males.Methods Fifty-one young healthy males living at the plain and53males living atan altitude of3700m for many years (group A) and another42men living at3700m plateaufor a long time and acclimatized in higher altitude of4400m for50days (group B) wereenrolled in this study. Blood pressure (BP), oxyhemoglobin saturation (SaO2) and heart rate(HR) were measured in all subjects, as well as Color Doppler Echocardiography wereperformed in each group.Results Left ventricular mass index (LVMI) and left ventricular end-systoledimension (LVESD) of the both groups staying at high altitude for a long time weresignificantly lower than the plain control group (P<0.05). Compared with the plain controlgroup, left ventricular end-systole volume (LVESV) of the group A was obviouslydecreased. Interventricular septum thickness (IVST) and left ventricular mass (LVM) ingroup B were also significantly lower than the control group (P<0.01). In addition, leftventricular ejection fraction (LVEF), fractional shortening (FS), stroke volume (SV),cardiac output (CO) of the both groups with sustained high altitude exposure weresignificantly higher than the subjects of plain control group (P<0.05). Furthermore, HR ofthe both groups was significantly higher than the plain control group (P<0.01). However,compared with the plain control group, both groups staying at high altitude had significantlyreduced SaO2(P<0.01) which was accordingly lower in group B than group A (P<0.01).Conclusion High altitude induced hypoxia increased HR although the subjectsacclimatized in plateau for many years and SaO2reduced with progressive altitude elevation.The left ventricular systolic function was significantly enhanced, but left ventricular massand afterload had not significant differences in healthy young males after staying at highaltitude for a long time compared with the plain control group.