Comparison Of Effects Of Chronic Intermittent Hypoxia And Chronic Continuous Hypoxia On Vascular Endothelial Function And Myocardial Contractility

General BackgroundObstructive sleep apnea syndrome(OSAS)is a type of disordered breathing during sleep and is basically characterized by chronic intermittent hypoxia(CIH).Repetitive hypoxia-reoxygenation in OSAS can cause systemic damage to the vascular endothelium,which leads to endothelial dysfunction,platelet activation,coagulation and imbalance of fibrinolysis systems,and subsequent dysfunction of the coagulation and fibrinolysis system,and increase the tendency of thrombosis.A long term of intermittent hypoxia can lead to a decrease in cardiac systolic function.Patients with severe chronic obstructive pulmonary disease may have changes of hemorheology,endothelial function,coagulation and fibrinolytic system,and myocardial contractility,which caused probably by chronic continuous hypoxia(CCH).Both CIH and CCH can cause cardiovascular events.It may be related to abnormal hemorheology,endothelial dysfunction,dysfunction of coagulation and fibrinolytic system,and changes in myocardial contractile function.However,there is no comparative study so far about the effects of the two hypoxic models,whether they have the same effects or not.This study is divided into five parts to explore the mechanism of cardiovascular events caused by two hypoxic patterns and compare the effects of the two.Part ? Making Animal Models of CIH and CCHObjective:Establish animal models of CIH and CCH to further explore whether the mechanisms of cardiovascular events caused by the two hypoxic patterns are the same.Method:Forty-five adult Sprague-Dawley(SD)rats were randomly divided into noroxic control(NC)group(n=15),CCH group(n=15),and CIH group(n=15).The NC group was placed in a normoxic animal chamber while the rats in the CIH group were placed in an intermittent hypoxia chamber for 8 hours per day(from 8:00 to 16:00)and the rats in the CCH group were placed in a continuous hypoxia chamber for 8 hours per day(from 8:00 to 16:00).The animal chambers in our laboratory have been built in which rats can be housed and stimulate the condition of cyclic hypoxia and continuous hypoxia as planned,and the experiment runs continuously for 3 weeks.Result:Animals in the NC group showed no abnormal symptoms.Animals in the CIH and CCH groups showed symptoms similar to the patient of OSA and COPD.Conclusion:Animal models of CIH,CCH have been successfully established.Part ? Effect of CIH and CCH on HemorheologyObjective:The pathophysiological mechanism of CIH which leads to cardiovascular disease,may be related to hemorheology.CCH can increase blood viscosity,fibrin and other hemorheological factors.This section investigates whether there are differences in the effects of CIH and CCH on hemorheology.Method:After establishment of animal models,collect blood samples from three groups.Test the following indicators:whole blood surface viscosity,plasma viscosity,red blood cell rheology,hematocrit,platelet aggregation,and fibrinogen levels.Result:1.Compared with NC group,CIH and CCH group can both increase the surface viscosity and plasma viscosity of whole blood.The blood viscosity index of CCH group is higher than CIH group.2.The hematocrit,erythrocyte aggregation index and electrophoretic index in CIH and CCH groups were significantly higher than those in NC group.The hematocrit index was higher in CCH group than in CIH group.No statistical difference of the red blood cell deformability and rigidity index among three groups.No statistical difference in hemorheology between CCH and CIH groups.3.The platelet aggregation rate in CIH and CCH groups was significantly higher than that in NC group,so was the fibrinogen level.The platelet aggregation rate and fibrinogen levels in CCH group were significantly higher than those in CIH group.Conclusion:Both CIH and CCH can cause increased blood viscosity,increased platelet aggregation,and impaired red blood cell function.There was no significant difference in the hemorheological effect between the CIH and CCH groups.Probably due to longer duration and greater intensity of hypoxic stimulation,continuous hypoxia has a greater effect on the blood viscosity index,the platelet aggregation rate and the fibrinogen level.Hypoxia causes change in blood viscosity,which probably leads to cardiovascular events.Part ? Effect of CIH and CCH on Endothelial FunctionObject:Hypoxia can induce impaired endothelial function,and endothelial dysfunction is associated with the occurrence of cardiovascular events.CIH and CCH can both cause endothelial dysfunction,but it is unclear whether the severity and mechanism are the same.This section investigates the effects of CIH and CCH on endothelial function and whether there are differences in their effects.Method:After successful modeling,collect blood and tissue samples to detect the following indicators:serum NO concentration,ET-1,ICAM-1,vWF levels,endothelial cell COX-2,eNOS,P-eNOS expression,NF-?B nuclear translocation,Transmission electron microscopy was used to observe the ultrastructural changes of endothelial cells.Result:1.Compared with NC group,the NO concentration in CIH and CCH groups was significantly reduced,and the ET-1 level was significantly increased;the ET-1 level in CIH group was higher than that in CCH group,and the NO concentrations in CCH and CIH groups were not statistically different.2.The levels of vWF in CIH and CCH groups were significantly higher than those in NC group.The levels of vWF in CIH group were higher than those in CCH group.The levels of ICAM-1 in CIH group were significantly higher than those in NC group and CCH group.There was no statistical difference in the level of ICAM-1 between CCH group and NC group.3.The expression of COX-2 and NF-?B activity in endothelial cells of CIH and CCH groups were significantly higher than those in NC group.There was no significant difference in COX-2 expression and NF-?B activity between CCH and CIH groups.4.Compared with NC group,the expression of eNOS and P-eNOS in endothelial cells was significantly decreased in CIH and CCH groups.There was no significant difference in the expression of eNOS and P-eNOS in endothelial cells between CCH and CIH groups.5.Transmission electron microscope observation showed that the mitochondrial morphology and ultrastructure of thoracic aorta endothelial cells in NC group were normal,while the mitochondrial ultrastructure of thoracic aorta endothelial cells in CIH and CCH groups was damaged.Conclusion:Both CIH and CCH can cause damage to vascular endothelial function and cause ultrastructural damage to endothelial cells.There is no significant difference in the effects of CIH and CCH on the endothelial eNOS and its synthesis product NO,which indicates no difference in the effects of the two hypoxia models on endothelial cell diastolic function.There is no significant difference in the effect of CIH and CCH on NF-?B inflammation pathway and its downstream product COX-2.CIH has a greater effect on vasoconstriction and vascular endothelial cell adhesion,and has a stronger procoagulant effect.Both two types of hypoxia can cause endothelial dysfunction,but their severity are not the same.Hypoxia causes endothelial dysfunction and is likely to be one of those responsible to cardiovascular events.Part IV Effect of CIH and CCH on Coagulation and Fibrinolytic SystemObject:Hypoxia can cause endothelial injury,followed by coagulation and fibrinolytic disorders.This section investigates the effects of the two hypoxic models(CIH and CCH)on coagulation and fibrinolytic system and whether the mechanism and severity are the same.Method:After successful modeling,blood samples were collected and tested for the following indicators:platelet activation index CD62p,CD63;coagulation index FIB,F?,AT-?;fibrinolytic system index t-PA,PAI-1.Result:1.The expression of CD62p:CCH group was significantly higher than that in NC group and CIH group.No significant difference in CD62p expression between CIH group and NC group.The expression of CD63:three groups were the same.2.Compared with NC group,FIB and FVIII in CIH and CCH groups were significantly increased,and AT-? was significantly decreased;FIB,FVIII,and AT-?levels in CCH and CIH groups were not statistically different.3.Compared with NC group,PAI-1 in CIH and CCH groups increased significantly,and t-PA in CIH group decreased significantly.There was no significant difference in t-PA level between CCH group and NC group.The level of t-PA in CIH group was significantly lower than that in CCH group.There was no significant difference in PAI-1 between CIH and CCH groups.Conclusion:Both CIH and CCH can induce hypercoagulability and reduce the function of fibrinolytic system,but the effect on platelet activation is not clear.Further study are needed.Hypoxia causes dysfunction of coagulation and fibrinolysis system,leads to thrombosis and early changes in atherosclerosis,which may be one of the mechanisms that cause cardiovascular events.Part ? Effect of CIH and CCH on Myocardial Contractile FunctionObject:Hypoxia can cause cardiac function changes,but there is no direct comparison study on the effect of CIH and CCH models of cardiac function,and in this section the effect of CIH and CCH will be investigated on myocardial contractility and compares the effects.Method:Before and after the modeling,ultrasound cardiogram was used to measure myocardial contractility related indicators:effective cardiac output(CO),heart index(CI),left ventricular ejection fraction(LVEF),left ventricular short axis shortening rate(FS).Result:1.Before and after the modeling,there was no significant difference in the indexes of myocardial contractility such as CO,CI,LVEF and FS in the control group;2.After modeling,the indicators of myocardial contractility such as CO,CI,LVEF,and FS in CIH and CCH groups were significantly lower than those before modeling.3.Comparison between groups after modeling.Compared with NC group,the indexes of myocardial contractility such as CO,CI,LVEF and FS of CIH and CCH groups were significantly decreased,and there was no statistical difference between CIH group and CCH group.Conclusion:The two hypoxia models(CIH and CCH)can cause the reduction of myocardial contractile function,but there is no significant difference in the severity of their effects.Hypoxia may be an independent risk factor for the decrease of myocardial contractile function.General ConclusionHypoxia can cause changes in blood rheology,vascular endothelial function,coagulation and fibrinolytic system function,and myocardial contractile function.Continuous hypoxia has a greater effect on the blood viscosity index,the platelet aggregation rate and the fibrinogen level,while intermittent hypoxia has a greater effect on vasoconstriction and adhesion of vascular endothelial cells,and a stronger procoagulant effect.Hypoxia causes OSA and COPD and may be one of the causes of cardiovascular events.