The respiratory system of a normal person undergoes a series of changes during sleep, especially a decline in respiratory function. When the lungs are diseased, breathing during sleep is bound to be more severely affected. By studying the pathophysiology of the sleep period, we have gained a deeper understanding of diseases such as chronic obstructive pulmonary disease, interstitial fibrosis and asthma. Overlap syndrome Sleep apnea hypoventilation syndrome and chronic obstructive pulmonary disease are both common diseases, the two combined with the existence of more opportunities, when the two diseases coexist in the same patient, the medical term “overlap syndrome”. Patients with overlap syndrome may have multiple manifestations of both COPD and sleep apnea syndrome, making diagnosis complicated and treatment more difficult. Patients often have difficulty in falling asleep, frequent awakening, obvious headache in the morning, and sleep inversion; they have no clear history of chronic bronchitis and emphysema, but they have the manifestation of pulmonary heart disease in a very short period of time; their condition worsens in a short period of time on the basis of their existing pulmonary heart disease, and is accompanied by weight gain, nocturnal snoring, and apnea; and they have frequent respiratory failure, cardiac insufficiency, and intractable hyperviscosity in patients with chronic bronchitis. The patients with chronic bronchitis frequently suffer from respiratory failure, cardiac insufficiency and stubborn hyperviscosity. Second, sleep breathing disorder and bronchial asthma The bronchial asthma mentioned here mainly refers to nocturnal asthma, which means that most of the untreated patients are aggravated at night or early in the morning, or wheezing symptoms occur only at night. Nocturnal asthma is not an isolated phenomenon; virtually all asthmatics have a tendency to narrow their airways at night. In recent years, studies have shown that there is a relationship between sleep and nocturnal asthma, due to the slowing down of airflow at night, airway resistance fluctuates significantly during sleep, and snoring can make the upper airway vibration and spasm, which significantly aggravates the airway resistance at night and triggers nocturnal asthma attacks. Typical nocturnal asthma often has the following characteristics: 1, a clear history of asthma; 2, appear in the asthma attack period; 3, also have more obvious asthma symptoms during the daytime; 4, nocturnal asthma attacks and sudden changes in temperature and humidity; 5, female patients often have attacks before and after menstruation 3, sleep apnea and interstitial lung disease interstitial lung disease patients with reduced lung capacity, increased pulmonary elastic resistance and extrapulmonary structures congenital When the patient falls asleep, the prone position makes the lung capacity of the existing interstitial lung disease further reduced, and at the same time, the ventilatory response is suppressed during sleep, coupled with the weakening of intercostal muscles and other auxiliary respiratory muscle groups will aggravate the hypoxemia, and is accompanied by a decrease in oxygen saturation and more pronounced hypercapnia during sleep. The patient develops severe true erythrocytosis, pulmonary hypertension, and pneumogenic heart disease as a result of prolonged hypoxemia and hypoventilation. In acute respiratory failure, patients show restrictive ventilatory dysfunction, increased dead space ventilation, and in order to increase the tidal volume, they may show shortness of breath; at the same time, they may be accompanied by obvious symptoms of sleep apnea hypoventilation syndrome. Through the above introduction, it is not difficult to find sleep apnea hypoventilation syndrome and many respiratory diseases and the development of the disease are inextricably linked, it directly affects the development of a variety of diseases and prognosis, and even directly affects the choice of treatment.