De-adaptation change in cardiac function of laborers engaged in physical labor at high altitude after returning to lower altitude

Objective　To assess the effects of physical labor on cardiac function of laborers at high altitude and changes in cardiac function after returning to lower altitude. Methods　According to symptomatic scores on Chinese acute high altitude reaction (AHAR), 96 male officers and soldiers, who rapidly entered high altitude areas (3700m altitude)，and engaged in heavy physical work for 50 days, were be scored and graded. Levels of creatine kinase isoenzymes -MB (CK-MB) and lactic dehydrogenase isoenzyme -1 (LDH-1) in the serum, Tei index, left ventricular ejection fraction (LVEF), and left ventricular fractional shortening (LVFS) were measured in the 96 servicemen at the 50th day of residing at high altitude, and the 2nd and 15th day after returning to lower altitude (1500m altitude), and the results were compared with that of 50 healthy controls residing at 1500m. Results　 Among the 96 male servicemen, 71 developed AHAR, and 24 of them had severe AHAR, 47 mild to moderate AHAR, and the rest 25 had no AHAR. Levels of serum CK-MB, LDH-1 and Tei index were higher in the severe AHAR group than in the mild to moderate AHAR group, higher in the mild to moderate AHAR group than in the no AHAR group and higher in the no AHAR group than in the healthy group. As far as the values of LVEF and LVFS were concerned, the severe AHAR group < mild to moderate AHAR group < no AHAR group < control group. Significant difference was found in these levels between every two successive groups (P < 0.01). Linear correlation analysis showed that levels of CK-MB and LDH-1 of persons staying at 3700m altitude for 50 days were positively correlated with Tei index (r= 0.625, 0.598, respectively, P＜0.01), and negatively correlated with LVEF(r=－0.716, －0.658, respectively, P＜0.01), and also negatively correlated with LVFS (r=－0.639, －0.727, respectively, P＜0.01). Level of serum CK-MB, LDH-1 and Tei index at 3700m altitude for 50 days were significantly higher than those 2 days and 15 days after returning to 1500m altitude and those in control group (P＜0.01), and were significantly higher on the 2th day than on the 15th day. Moreover, the values of LVEF and LVFS were significantly lower than those at 2 and 15 days after returning to 1500m altitude and those in control group (P＜0.01), and significantly lower on the 2th day than on the 15th day. All parameters after 15 days returning to low altitude showed no significant difference compared with control group (P＞0.05). Conclusion　Heavy physical work at high altitude could obviously impair human cardiac function. The impairment may aggravate along with increase in severity of AHAR. However, cardiac function may be improved significantly after returning to low altitude for 2 days, and recover to normal status 15 days later.