Effects of chronic intermittent hypoxia on left ventricular myocardial contractibility in a rabbit model of obstructive sleep apnea

Abstract

Objective: To explore the effects of chronic intermittent hypoxia (CIH) on left ventricular myocardial contractibility in a rabbit model of obstructive sleep apnea (OSA). Methods: Based on random number table, twenty-four rabbits were randomly divided into three groups: operation, sham, and control groups, each with 8 rabbits. The rabbit model for OSA in operation group was established by repeatedly closing the airway and then reopening it. Upper airway obstructions were conducted on rabbits every day, which were alternately closed for 15 s and then reopened for 75 s in a 90 s-long cycle, for 8 h each day over 3 months. The sham rabbits were subjected to the same surgical procedure but no airway obstructions were applied. The control animals were subjected to no intervention. The blood pressure, left ventricular function parameters were assessed before and after the experiment. And the relative expressions of myosin heavy chain α/β (α-MHC and β-MHC) mRNAs in myocardium were observed for all rabbits by real time fluorescent quantitative polymerase chain reaction 3 months later. Results: After 3 months, all rabbits in the operation group manifested sleepiness and the blood pressure rose gradually [(114.25±4.20) vs (93.88±2.10) mmHg, P<0.01]. Compared with the sham operation and the control groups, the left ventricular end-systolic volume [(6.05±1.62) vs (2.83±0.49) and (2.74±0.32) ml, P<0.001] and the left ventricular end-diastolic volume [(1.61±0.78) vs (0.83±0.13) and (0.82±0.10) ml] in operation group were obviously higher, the left ventricular ejection fraction [(63.9±4.2) % vs (74.3±2.5) % and (75.8±3.8) %], left ventricular fractional shortening [(32.2±2.1) % vs (41.8±1.8) % and (42.1±1.8) %] and stroke volume [(1.46±0.13) vs (1.93±0.21) and (1.98±0.24) ml/s] were decreased (all P<0.001). Besides, the maximal rate of the increase of left ventricular pressure [(4 154±360) vs (6 802±492) and (6 759±206) mmHg/s], the maximal rate of the decrease of left ventricular pressure [(4 994±621) vs (6 330±314) and (6 591±225) mmHg/s] in the operation group decreased markedly, left ventricular end diastolic pressure (LVEDP) increased [(6.5±1.6) vs (3.3±0.8) and (3.2±0.9) mmHg] (all P<0.001). The relative expression of α-MHC mRNA in left ventricular myocardial tissue was lower and the relative expression of β-MHC mRNA was higher in operation group than those in the sham operation and the control groups (P<0.05). There were no significant difference in the relevant indicators of cardiac function, and in the relative expressions of α-MHC mRNA and the β-MHC mRNA between the control group and the sham operation group (P>0.05). Conclusions: Repeated intermittent hypoxia can induce hypertension and myocardial contractibility damage in OSA model rabbit simulating upper airway obstruction.