A New Simple Method To Evaluate The Association Of Vascular Endothelial Function With Acclimatization And Acute Mountain Sickness

Acute mountain sickness?AMS?is characterized by the presence of headache and at least one of the following symptoms:loss of appetite,nausea,vomiting,fatigue/weakness,dizziness/light-headedness,and insomnia.It occurs when people arrive at an altitude above 2500 m,and can be classified into acute mild high-altitude sickness,high-altitude pulmonary edema,and high-altitude cerebral edema.It is well known that high-altitude residents have low susceptibility to AMS.The underlying mechanisms involve acclimatization,genetics,and other factors.such as the lower carotid wall/lumen ratio reported among highlanders relative to lowlanders in one study.Previous studies suggest an association between AMS and vascular endothelial dysfunction.The vasculature is the largest organ in the body and endothelial cells are important in regulating some key functions in hemostasis such as platelet aggregation,immune responses,and vascular permeability.Moreover,endothelium maintains vascular tone,thereby determining blood flow distribution to each tissue.The endothelium senses and responds to a myriad of internal and external stimuli through complex cell membrane receptors and signal transduction mechanisms,leading to the synthesis and release of various vasoactive,thromboregulatory and growth factor substances,including nitric oxide?NO??ET-1 and other factors.Many of the cardiovascular complication associated with endothelial dysfunction,particularly dysregulation of the vascular function associated with an imbalance in the close independent of NO and EF-1.Over the past decade,a noninvasive technique has evolved to evaluate flow-mediated vasodilation?FMD?,an endothelium-dependent function,in the brachial artery.This stimulus provokes the endothelium to release nitric oxide?NO?with subsequent vasodilation that can be imaged and quantitated as an index of vasomotor function.This technique is attractive because it is noninvasive and allows repeated measurements.At present,FMD is the most classical method of evaluating vascular endothelial function.A principal mediator of FMD is endothelium-derived NO.Endothelin-1?ET-1?was identified as the first endothelium–derived contracting factor and it is one of the most vasoconstrictors identified so far.The precise mechanisms for the acute detection of shear forces and subsequent signal transduction to modulate vasomotor tone are not fully understood.NO,however,strongly inhibits the release of ET-1 from native endothelium.For this reason,it has been suggested that NO and ET-1 regulate each other through an autocrine feedback loop.Flow-mediated vasodilation is typically expressed as the change in post-stimulus diameter as a percentage of the baseline diameter.Previous studies suggest an association between AMS and vascular endothelial dysfunction.In an experimental study,1hour of hypoxic exposure induced sustained reduction in flow-mediated dilatation among healthy lowlanders,While,FMD and endothelial–independent dilatation declined when a high altitude relative to sea level.Although FMD is the most commonly used method to evaluate vascular endothelial function,this method requires expensive equipment.The brachial diastolic blood pressure decline after 5 minutes of arm ischemia may provide a simple,inexpensive,and highly operational alternative as suggested by a study,in which it positively correlated with arterial dilatation??35?D/?35?D0?in the FMD test.In that study,Bilateral arm BPs were simultaneously measured with two automatic devices and right brachial artery diameter?D?was measured by ultrasound technique.Identification of practical means of AMS risk prediction assessment,which has been the focus of several studies,has important preventive value.This study therefore tested the hypothesis that post-ischemic DBP response differs between sea-level residents and moderate-altitude residents when exposed to high altitude,with post-ischemic DBP decline associated with AMS risk.Part I To investigate whether the ischemia-induced DBP decline and AMS score differs between moderate-altitude and sea level residents.ObjectiveIt is well known that high-altitude residents have low susceptibility to AMS,but no sufficient research was performed in whether acclimatization impacts on the ischemia-induced DBP decline and AMS score.This study tested the hypothesis that post-ischemic DBP response differs between sea-level and moderate-altitude residents when exposed to high altitude,with post-ischemic DBP decline associated with AMS risk.Methods42 healthy young males who had undergone physical,electrocardiographic and routine blood chemistry examination were enrolled and evenly assigned according to the original place of residence to either a sea-level group?i.e.,<400 meters above sea level?or a moderate-altitude?i.e.,1,000-2,000 meters above sea level?group.The young males in the two groups had similar age-and body mass index?BMI?distributions and all subjects had never been to 3200 meters before.All participants stayed at a station at an average altitude of 1,380 m for 4 days for acclimatization.On the day before transitioning to a training base at 3,200 meters,fasting venous blood was sampled for routine hematology,liver and renal function tests,lipid profiles,and levels of creatine kinase?CK?and its myocardial isozyme?CK-MB?.Body height and weight,BP and heart rate?HR?and oxyhemoglo-bin saturation were measured.Anxiety score was evaluated using a Self-Rating Anxiety Scale SAS,and BP examination was performed.BP examination was performed in a room at 22-24^o C.Before BP measurement,participants were asked to empty their bladder and to rest for 10 minutes.Bilateral brachial BP was measured twice and 2 minutes apart using two automated BP measurement devices,and their average was recorded as the baseline BP?BPb?.After BPb measurement,the cuff on the right arm was inflated to 50 mmHg above systolic BP?SBP?for 5 minutes to block blood flow to the right arm.This means that ischemia only developed in the right arm,and not in the left arm.The cuff then was rapidly deflated,and bilateral BP was measured at 1,5 and 10minutes?BPp1,BPp5 and BPp10?after cuff release.The differences between BPb and BPp at different time points were calculated as individual BPb-p.In the present study,the area between the BPb curve as reference and the BPp curve was calculated as the area between curves?AUC?-BP using the cubic spline interpolation method.The absolute value was expressed as the final value.For example,a DBP curve with more obvious DBP decline after arm ischemia had higher AUC-DBP.All subjects arrived at a training base located at an altitude of 3,200 m by automobile to conduct three-day physical training.During said period,subjects regularly received training on hand-to-hand combat for 5 hours daily and climbed a mountain up to 4,300 m with a 20 kg load for 20 minutes.At the afternoon of the third day,the subjects returned to the station by automobile.After arriving at the station,the plateau response scale?AMS score?was evaluated based on the classification and diagnostic criteria of high altitude disease in China.The Chinese AMS score was calculated as follows:according to their severity,headache was assigned 1,2,4 or 7 points and vomiting was assigned 2,4 or 7 points,respectively.Other symptoms,such as dizziness/light headedness,nausea,palpitation,shortness of breath,chest pain,blurred vision,sleeplessness?insomnia?,anorexia,abdominal distension,diarrhea,constipation,cyanosis of the lips,lethargy,and numbness of the extremities were assigned 1 point each if present.Based on total scores,4 grades of AMS were devised,namely normal?i.e.,no AMS;total score of1–4 points?;mild?total score of 5–10 points?;moderate?total score of 11–16 points?;and severe?total score of 16 points?.Results1.Before high altitude training,body mass index?BMI?,BP,heart rate?HR?,oxyhemoglobin saturation and Anxiety score of sea-level group and moderate-altitude group have no significant difference,p all?29?0.05.2.Before high altitude training,WBC?RBC?HGB?HCT?PLT?MPV?PCT?MCV?MCH?MCHC?N%?L%?M%?E%?BASO%?NEUT?LYM?MONO?EO?BASO?RDW-SD?RDW-CV?PDW?P-LCR of sea-level group and moderate-altitude group have no significant difference,p all?29?0.05.3.Before high altitude training,A/G of sea-level group is lower than moderate-altitude group?1.35±0.13?vs?1.44±0.12?,p=0.034)?ALT?AST?GGT?ALP?TBIL?DBIL?TP?ALB?GLO?BUN?CR?UA?CHOL?TR?HDL?LDL?GLU?AST?CK?CK-MB?LDH of the two groups have no significant difference,p all?29?0.05.4.The bilateral curves of SBP overlapped well,with no significant difference in AUC-SBP between sea-level and moderate-altitude groups.On the other hand,the DBP decline,and consequently AUC-DBP,for right arm ischemia was greater for the moderate-altitude group than the sea-level group.However,in the non-ischemia left arm,the DBP curves did not show a DBP decline and overlapped well with no significant difference in AUC-DBP between the two groups.5.After high altitude training,SBP of moderate-altitude group is lower than sea-level group[?111.86±6.15?mm Hg vs?116.90±9.10?mmHg,p=0.042]?heart rate?HR?,DBP,oxyhemoglobin saturation between the two groups have no significant difference,p all?29?0.05.6.After high altitude training,RBC?E%and EO of moderate-altitude group is higher than sea-level group:[?5.21±0.30?×10¹²/L vs?4.97±0.37?×10¹²/L,p=0.031],[?3.83±2.49?%vs?2.47±1.31?%,p=0.032]and[?0.215±0.14?×10⁹/L vs?0.14±0.06?×10⁹/L,p=0.031]respectively?WBC?HGB?HCT?PLT?MPV?PCT?MCV?MCH?MCHC?N%?L%?M%?BASO%?NEUT?LYM?MONO?BASO?RDW-SD?RDW-CV?PDW?P-LCR between the two groups have no significant difference,p all?29?0.05.7.After high altitude training,DBIL and GLO of sea-level group is higher than moderate-altitudegroup:[?2.81±0.91?umol/Lvs?2.31±0.64?umol/L,p=0.048]and[?34.24±3.22?g/L vs?31.57±2.89?g/L,p=0.007]respectively.While,A/G of sea-level group is lower than moderate-altitude group[?1.31±0.15?vs?1.45±0.15?,p=0.004].ALT?AST?GGT?ALP?TBIL?TP?ALB?BUN?CR?UA?CHOL?TR?HDL?LDL?GLU?AST?CK?CK-MB?LDH of the two groups have no significant difference,p all?29?0.05.8.The AMS score was lower in the moderate-altitude group than in the sea-level group?3.19±2.16 vs.5.52±4.58,respectively,P=0.043?.ConclusionModerate altitude relative to sea-level residents had a larger mean post-ischemic DBP and lower mean AMS score at 3200m.Part II: To investigate the level of NO and ET-1 between moderate-altitude and sea-level residents and identify rapidly AMS risk prediction assessment.It is well known that NO and ET-1 are sensitive indicators of vascular endothelial function.Identification of practical means of AMS risk prediction assessment,which has been the focus of several studies,has important preventive value.This study aim to investigate whether NO and ET-1 differs between moderate-altitude and sea-level residents and whether therefore tested the hypothesis that post-ischemic DBP response differs between sea-level residents and moderate-altitude residents when exposed to high altitude,with post-ischemic DBP decline associated with AMS risk.Objective42 healthy young men.Methods:fasting venous blood of 42 healthy young men was collected in serum separator tube.Allow samples to clot for two hours at room temperature or overnight at4?overnight before centrifugation for 20 minutes at approximately 1000×g,store samples in aliquot at-80?.Endothelin 1?ET-1?detection kit?enzyme linked immunosorbent assay?ELISA?sorption test?and nitric oxide?NO?kit were used to detect serum ET-1 and NO concentration of sea-level group and moderate altitude group respectively at 1380 m And 3200 m.The correlation between AUC-BP,NO,ET-1 and AMS score were analyzed by linear regression analysis using the Pearson coefficient.Results:1.The concentration of ET-1 of sea-level group and moderate altitude group are?222.40 ± 83.23?pg/ml and?239.11 ± 67.15?pg/ml respectively at 1380 m before altitude training.After altitude training,the concentration of ET-1 of the two groups are?129.47±64.88?pg/ml and?138.10±54.72?pg/ml respectively,p all <0.05.The concentration of ET-1 of the two group after altitude training all higher than before altitude training,p all <0.001.2.There is no significant difference in NO between sea-level and moderatealtitude groups before and after altitude training.The concentration of NO of sea-level group and moderate altitude group are?77.16±30.76?umol/L and?68.78±29.06?umol/L respectively at 1380 m before altitude training.After altitude training,the concentration of NO of the two groups are?89.35±62.85?umol/L and?80.46±34.06?umol/L respectively.There is no significant difference in NO level between before and after altitude training of the two groups.3.Body mass index?BMI?distributions,BP,heart rate?HR?,oxyhemog-lobin saturation and Anxiety score before high altitude training have no correlation with AMS score.Ischemia –induced DBP decline is in weak but significant association with lower mean AMS score at 3200m?r=-0.320,p=0.039?.4.WBC?RBC?HGB?HCT?PLT?MPV?PCT?MCV?MCH ?MCHC?N%? L% ?M%?E% ?BASO% ?NEUT?LYM ?MONO ?EO?BASO?RDW-SD? RDW-CV?PDW?P-LCR of the two groups before high altitude training have no correlation with AMS score,p all?29?0.05.5.ALT?AST?GGT?ALP?TBIL?DBIL?TP?ALB?GLO?A/G?BUN?CR?UA?CHOL?TR?HDL?LDL?GLU?AST?CK?CK-MB?LDH of the two groups before high altitude training have no correlation with AMS score,p all?29?0.05.6.Heart rate after altitude training of the two groups has significant association with mean AMS score at 3200m?r=0.437,p=0.048?.BP and oxyhemoglobin saturation after high altitude training have no correlation with AMS score.7.After high altitude training,BASO% and PDW of the two groups have significant correlation with AMS scores?r=-0.327,p=0.035?and?r=-0.318,p=0.040?respectively.WBC?RBC?HGB?HCT?PLT?MPV?PCT?MCV?MCH ?MCHC?N%?L% ?M%?E% ?NEUT?LYM ?MONO ?EO?BASO?RDW-SD?RDW-CV?P-LCR have no correlation with AMS score,p all?29?0.05.8.After high altitude training,DBIL of the two groups have significant correlation with AMS scores?r= 0.307,p=0.048?.9.NO and ET-1 of the two groups before and after high altitude training all have no correlation with AMS score.Conclusion:Despite a preacclimatization period of 4 days at 1380 m,moderate-altitude residents had a larger DBP decline after arm ischemia than sea-level residents,and DBP decline was negatively associated with lower AMS scores.These data suggest that differences in vascular endothelial function related to altitude of residence persist during travel to high altitude and might contribute to AMS risk.