Fluid retention in the legs due to chronic heart failure (CHF) during the daytime may redistribute to neck when with supine positioning at night. A portion of the shifted fluid accumulates in the neck, and narrows the upper airway, predisposing the patient to obstructive sleep apnea (OSA) and central sleep apnea (CSA). However, the mechanism of overnight fluid shift on OSA and CSA remains unclear. The investigators pre-experiment demonstrated there may be a different mechanism of overnight fluid shift on OSA and CSA. The accumulation of water content in neck soft tissue increases neck circumference and leads to pharyngeal resistance, upper airway collapse and causes OSA. The effect of nocturnal fluid shift on CSA may be because of increasing of chemosensitivity (fluctuation of PaCO2), circulation delay and hemodynamic disordered. This study is aimed to explore the different mechanism of overnight fluid shift on OSA and CSA by comparing the changes of upper airway (inside diameter, water content, and pharyngeal resistance), PaCO2, circulation delay (lung-to-finger circulation time) and hemodynamic (loop gain).

Methods:

Between June 2015 and December 2017, 180 patients with chronic heart failure caused by rheumatic heart disease, cardiomyopathy and coronary heart disease (in Cardiology Department and Cardiothoracic Surgery Department of the First Affiliated Hospital of Nanjing Medical University), were screened for sleep apnea by polysomnography (PSG). Of them, 20 obstructive sleep apnea (OSA) and 20 central sleep apnea (CSA) were enrolled. Clinical evaluations including NYHA class, electrocardiographic, echocardiographic, arterial blood gas analysis findings, baseline medication, and 6-minute walk test (6MWT) were recorded.

The fluid index, head and neck CT and pharyngeal resistance were tested at 20:00. Then a full night PSG and percutaneous PaCO2 were performed. The fluid index, head and neck CT and pharyngeal resistance were repeated at 6:00 after PSG.

The volume of fluid shift from legs to head and neck,inside diameter of the upper airway, and water content of neck soft tissue were calculated. The lung-to-finger circulation time and loop gain were measured.

1. Mechanism of overnight fluid shift on OSA:

   Fluid shift volume from legs to head and neck,inside diameter of upper airway, water content of neck soft tissue, percutaneous PaCO2, severity of sleep apnea, minimum SP02, lung-to-finger calculation time and loop gain were measured at 22:00 and repeated at 6:00 next morning in patients with OSA.Correlations between changes of fluid shift volume and changes in diameter of upper airway, water content of neck soft tissue, PaCO2, minimum SP02, lung-to-finger calculation time and loop gain were analyzed.

2. Mechanism of overnight fluid shift on CSA:

Fluid shift volume from legs to head and neck,inside diameter of upper airway, water content of neck soft tissue, percutaneous PaCO2, severity of sleep apnea, minimum SP02, lung-to-finger calculation time and loop gain were measured at 22:00 and repeated at 6:00 next morning in patients with CSA.Correlations between changes of fluid shift volume and changes in diameter of upper airway, water content of neck soft tissue, PaCO2, minimum SP02, lung-to-finger calculation time and loop gain were analyzed.

Inclusion Criteria:

1. patients with chronic heart failure caused by rheumatic heart disease, cardiomyopathy and coronary heart disease
2. aged between 18 to 70 years
3. with symptomatic stable heart failure, New York Heart Association (NYHA) class >= II despite optimal drug therapy
4. patients combined with sleep apnea (apnea-hypopnea index >=10/h) according to the results of polysomnograph.

Exclusion Criteria:

1. history of stroke or clinical signs of peripheral or central nervous system disorders
2. chronic obstructive pulmonary disease or history of asthma
3. enrolment in another clinical study

patients with chronic heart failure caused by rheumatic heart disease, cardiomyopathy and coronary heart disease.