The nocturnal short-term BPV induced by sleep-breathing events is affected by many factors. The purpose of the study is as follows: (1) to explore the relationship between nocturnal short-term BPV and vascular endothelial function and sympathetic activity in patients with OSA respectively, (2) to explore which play the key role in BP fluctuation, (3) how to prevent the frequent BP fluctuation and arrive at a safe point.

It has been known that nocturnal short-term blood pressure variability (BPV) is a special phenomenon in obstructive sleep apnea (OSA) patients. Nocturnal short-term BPV is a quantitative measure that describes the BP fluctuation over a period of seconds to minutes. It is significantly associated with target organ injury, increased risk of cardio-cerebrovascular events, and increased mortality, independent of mean BP level. Our prior study found that nocturnal BP will temporarily reach the peak during one OSA episode and come to decline rapidly. However, this phenomenon does not occur in all OSA patients. In some severe OSA patients with severe hypoxemia, their BP can still maintain a relatively stable level when one OSA episode. The specific mechanism is still unclear. In physiological conditions, the BP fluctuation caused by each cardiac cycle is affected by vascular function, central sympathetic, arterial reflex, cardiopulmonary reflex, elastic properties of arteries, humoral, and even emotional factors. Therefore, the purpose of the study is as follows: (1) to explore the relationship between nocturnal short-term BPV and vascular endothelial function and sympathetic activity in patients with OSA respectively, (2) to explore which play the key role in BP fluctuation, (3) how to prevent the frequent BP fluctuation and arrive at a safe point.

First, about 300 suspected OSA and 50 healthy subjects under full-night polysomnography (PSG) will be recruited in the sleep medicine center of The Affiliated Huai'an No. 1 People's Hospital of Nanjing Medical University and The First Affiliated Hospital with Nanjing Medical University. All the participants complete the questionnaire which includes clinical medical history, sleep habits, general health, smoking and drinking history, and anthropometric data. When PSG worked, BP was calculated by pulse transit time (PTT) simultaneously and continuously. The electrocardiography data extracted from the entire overnight PSG recordings are visually inspected for accuracy and quality and used for heart rate analysis (HRV) analysis. The next day, 4-5 mL peripheral venous blood samples are obtained from participants in the morning after an overnight fast and used for biochemical analysis. The sympathetic activity could be represented by HRV and Norepinephrine detected by enzyme-linked immunosorbent. Then, brachial artery diameter will be measured after the reactive hyperemia (called flow-mediated dilation, FMD) and nitroglycerin stimulus (called nitroglycerin-mediated dilation, NMD). The FMD and NMD could represent the vascular function. About 80 patients will be in the next plan. On the second day, under patient safety, Phentolamine will be pumped into the OSA patients equipped with PSG and ECG monitoring in a safe dose to prevent sympathetic overactivity. On the third day, under patient safety, Nitroglycerin will be pumped into the OSA patients equipped with PSG and ECG monitoring in a safe dose to prevent endothelial dysfunction. The parameters before and after medicine will be analyzed and compared.

Hypothesis: The investigator predicted that patients who received phentolamine and nitroglycerin injections would lower nocturnal short-term BPV measured by polysomnography

Inclusion Criteria:

• medium to severe OSA (apnea-hypopnea index, AHI≥15 events/h) and patients without OSA (AHI<5 events/h)
• age from 18 to 65 years old.

Exclusion Criteria:

• combined with other sleep disorders
• patients with comorbidities, such as hypertension, diabetes, cardiovascular diseases, and cerebrovascular diseases etc
• conditions that potentially affect the accuracy of BPV and endothelial function
• ever-received the treatment of constructive positive airway pressure (CPAP)
• who refuse to participate in the study.