The Effects Of Gastrooesophageal Reflux To The Respiratory System Of Chronic Intermittent Hypoxic Rat

OBJECTIVE: Obstructive sleep apnea-hypopnea syndrome(OSAHS)mainly performs as upper airway obstruction during sleep,apnea and hypoventilation recurring constantly,causing sleep disturbances and chronic intermittent hypoxia(Chronic intermittent hypoxia,CIH).OSAHS patients had more heartburn and acid reflux symptoms at night than those in the general population,and CPAP treatment could reduce most symptoms of nighttime gastroesophageal reflux.Moreover,patients with gastroesophageal reflux disease(GERD)had a higher risk of OSAHS than normal people.Compared with non-GERD patients,GERD patients had higher AHI,a greater longest apnea time amd lower oxygen saturation.However,some studies suggested that OSAHS and GERD could only related through obesity,the commom risk factor of OSAHS and GERD,and AHI showed no significant association with the total number of acid reflux events within 24 hours.To sum up,there may be an association between OSAHS and GERD,but we haven't got any exact evidence.Therefore,this study aim to investigate the effects of acid reflux on airways of both normoxic and CIH conditions through models of rats.Methods: Forty SPF adult male Wistar rats(200-250g)were randomly divided into the normal saltine perfusion group under normixic condition(Air + NS group,n=10),the acid perfusion group under normoxic condition(Air + HCL group,n=10),the normal saline perfusion group under CIH condition(CIH+NS group,n=10)and acid perfusion group under CIH condition(CIH + HCL group,n=10).Acid was perfused into the distal part of the oesophagus once daily(20min / d,24 ml / h)for 21 consecutive days in Air+HCL group,NS was perfused in the same way in Air+NS group.Rats of CIH groups were exposed to CIH condition(8h / day,cycle of 180 s,hypoxia :5% O2 for 60 s,reoxygenation to 21% O2 for 60s)for 7 weeks.Rats of CIH + HCL group were perfused with acid in the same way 30 minutes later of the CIH exposure from the fifth week of CIH exposure,and rats of CIH + NS group were perfused with NS in the same way.Parameters of lung function were collected and 4 groups of rats were sensitized with increasing concentrations of ACh through the atomizing pump on day 0,day 7,day 14 and day 21 respectively to assess the airway responsiveness.Rats of each group were sacrificed,the hematoxylin-eosin(HE)staining was performed to the tissues of esophagus,bronchi and lung after the last time of acid or NS perfusion.The histopathological changes of those tissues were observed under the optical microscope.Blood were collected from heart and serum collection were performed by centrifugation.The total cell number and cell differential counts in bronchoalveolar lavage fluid(BALF)were determined.The level of CXCL1 and CRP in both BALF and serum were measured by enzyme-linked immunosorbent assay(ELISA).RESULTS: Histopathological results indicated that the acid reflux model was successful,and compared with the Air+NS group,the airway mucosal barrier was incomplete and lung inflammatory cells infiltrated in the Air +HCL group.CIH group perfused with acid showed a more severe trend of airway and lung injury than perfusing with NS.Compared with each NS perfusion group,the Penh value of both Air group and CIH group increased significantly on the 21 st day of acid perfusion(P <0.05),but compared with the Air group,the value of CIH group didn't have a significant icrease after acid perfusion(P> 0.05).Compared with the Air + NS group,the Air+ HCL group showed a significant increase in responsiveness to Ach on the 21 st day of acid perfusion(P <0.05),and compared with CIH + NS group,CIH + HCL group showed this significant increase on the 14 th day of acid perfusion(P<0.05).Compared with Air group,the rats in CIH group showed significantly higher responsiveness to Ach(P <0.05)and this kind of responsiveness appeared earlier.Compared with each NS perfusion group,the total cell number,neutrophils,and lymphocytes of BALF in Air group and CIH group increased significantly(P <0.05).Compared with Air group,the neutrophils and lymphocytes in BALF of CIH group increased significantly after acid perfusion(P <0.05),but the total cell number didn't increase significantly(P> 0.05).Compared with each NS perfusion group,the level of CXCL1 in serum of both Air group and CIH group didn't show a significant increase(P>0.05).Compared with each NS perfusion group,the level of CXCL1 in BALF of both Air group and CIH group increased significantly(P <0.05),and compared with Air group,the level of CXCL1 in BALF increased significantly by acid performed(P <0.05).Compared with NS perfusion,the level of CRP in both serum and BALF of Air group didn't show a significant increase after acid perfusion(P>0.05).The level of CRP in both serum and BALF of CIH group,hoverer,increased significantly(P<0.05).Conclusion: This study showed that acid reflux can cause airway and lung structural injury,leading to higher airway responsiveness,which may be related to the increase of inflammation level.This kind of airway responsiveness is higher and appears earlier with higher level of imflammation and injury under CIH condition.