The Relationship Between Sleep-related Breathing Disorders And Chronic Mountain Sickness

The pathogenesis of chronic mountain sickness(CMS) is still not very clear, so there is no effective method for prevention and cure. Although it seems that sleep disorder is the risk factor for CMS, but the systemic studies are absent. We performed the case-control study to investigate if the sleep dysfunction and its associated factors are the risk factors for CMS. Polysomnography(PSG)was done in CMS patients with or without obesity at different altitudes in Q inghai- Tibetan plateau. We also observed the change of serum levels of dopamine in CMS patients. We hope these studies will helpful for understanding the relationship between sleep disorder and CMS and will useful for preventing and curing the CMS.The aim of the first part of our study was to investigate if the sleep dysfunction and its related factors such as obesity, smoking, drinking, occupation, the time living at high altitude were the risk factors for CMS. The case control study was applied at the altitude of 3780 m. CMS patients and controls were matched with age, gender and nationality in 1:2. The questionnaires for risk factors were performed in 67 CMS patients and 134 controls. Univariate analysis and multivariate logistic regression were applied to assess the investigative factors. The results showed that body mass index(BMI), smoking index and pittsburgh sleep quality index(PSQI) were the risk factors for CMS(BMI: OR=6.78,95%CI: 2.98~15.42; smoking index OR=2.26, 95%CI:1.03~4.97; PSQI: OR=12.91, 95%CI: 6.04~27.9.59).We did the second part of the study in order to know the sleep structure, sleep disorders and nocturnal oxygen saturation(Sa O2) in CMS patients and to confirm the difference of the sleep in obese and non-obese CMS patients. PSG was performed in Tibetan CMS patients(6 cases), obese and non-obese Han CMS patients(10 and 14 cases,respectively), Han controls with or without sleep disorder(4cases and 7cases, respectively) and Tibetan controls(10cases). Tibetan CMS patients were all obesity or overweight. The hemoglobin concentration and CMS score were significantly higher in Tibetan and obese Han CMS than other groups. The sleep efficiency decreased, arousal index increased and the apnea/hypopnea index(AHI) were significantly higher in Tibetan and obese Han CMS groups than other groups. The main type of apnea was obstructive apnea. Central apnea, mixture apnea, periodic breathing and hypopnea were also obse rved in these two groups. The mean and lowest sleep oxygen saturation(Sa O2) was significant lower in Tibetan and obese Han CMS groups than other groups. The hypopnea was the main type of sleep disorder in non-obese CMS patients and Sa O2 decreased during sleep. The waken Sa O2, mean and lowest sleep Sa O2 was negative correlated with CMS score. The AHI, average apnea time and the proportion of total sleep time of Sa O2 < 85% were significant positive correlated with CMS score. We concluded that obese CMS patients should diagnose as obstructive sleep apnea and hypopnea syndrome(OSAHS). These patients suffered from the hypoxia due to OSAHS and environment, so the disease was even more severe. Sleep disorder and nocturnal desaturation were contributed to CMS.We performed the third part of this study to compare the sleep structure, respiratory and Sa O2 in patients with CMS with or without obesity at different altitudes. We took the CMS patients with or without obesity(8 cases and 10 cases, respectively) from 3780 m who were received PSG in the second part of study and performed the PSG, tested hemoglobin concentration and CMS score after they stayed at 2260 m for two weeks. The results showed that non-obese CMS patients sleep disorder disappeared, Sa O2 significantly increased, the hemoglobin and CMS score significantly decreased. It was showed that high altitude hypoxia was important cause of sleep disorder for CMS patients. After the obese CMS patients decreased to lower altitude, the CMS score and hemoglobin also decreased relatively, but still higher than non-obese CMS patients. The Sa O2 of obese patients increased at lower altitude but still significantly lower than non-obese CMS patients. Although the central apnea of obese CMS patients at 2260 m were significantly lower than at 3780 m, the obstructive apnea didn’t show significantly change between two altitude. So this part of study further demonstrated that these obese patients should diagnose as OSAHS.In order to study the relationship between serum level of dopamine and Sa O2 in CMS patients, we tested the dopamine concentration of serum and recorded the Sa O2 before sleep, 2A.M. 4A.M. and woke up in parts of patients with CMS and controls when they received PSG at the second part of study. The dopamine concentration of CMS group at 2A.M. and 4A.M. were significantly lower than control group(all P < 0.05). The Sa O2 at four time point in CMS group were significantly lower than control group(all P < 0.05). In the control group, the dopamine concentration increased when Sa O2 decreased and dopamine concentrations decreased when Sa O2 increased. But there was no such correlation of dopamine concentration and Sa O2 in CMS group. This study indicated that the hypoxia sensitivity in patients with CMS decreased and this may be correlated with decreasing of the plasticity of carotid body.In conclusion, our study confirmed that hypopnea and hypoxia during sleep were correlated with CMS. The obese patients with polycythemia and pulmonary hypertension at high altitude should do PSG to distinguish OSAHS and CMS. The patients with OSAHS living at high altitude suffered from the hypoxia due to disease and environment, this made their conditions more seriously. It is important to diagnose and treat them timely. The function of carotid body in patients with CMS needs to do further research.