The goal of this observational study is to learn how removing extra fluid from the body (diuresis) affects sleep apnea in adults hospitalized with heart failure.

The main questions it aims to answer are:

Does sleep apnea severity improve after fluid removal? Is the improvement in sleep apnea related to the amount of fluid removed? Do changes in neck size reflect changes in sleep apnea severity?

Participants admitted to the hospital with heart failure and fluid overload will take part in this study.

Participants will:

Use a wearable sleep monitoring device (WatchPAT) on the first night of hospitalization Use the device again after fluid removal, when the treating cardiologist determines that the patient is no longer fluid overloaded Have their neck circumference measured before and after fluid removal Have their weight and fluid balance recorded during hospitalization Have routine blood tests and clinical assessments as part of standard care

Researchers will compare each participant's results before and after fluid removal to see if sleep apnea improves and whether these changes are linked to fluid removal and changes in neck circumference.

Inclusion Criteria:

• Adults aged 18 years or older
• Hospitalized with decompensated heart failure and clinical evidence of fluid overload
• Diagnosis of heart failure (reduced or preserved ejection fraction)
• Clinically indicated for diuretic therapy
• Able to undergo sleep apnea assessment using the WatchPAT device
• Able to provide informed consent

Exclusion Criteria:

• Known central sleep apnea as the predominant sleep-disordered breathing type
• Current treatment with continuous positive airway pressure (CPAP)
• Acute respiratory failure requiring mechanical ventilation
• Conditions preventing proper use of the WatchPAT device (e.g., severe hand or finger injury)
• Hemodynamic instability precluding participation
• Pregnancy

Adults admitted with decompensated heart failure and clinical fluid overload, including both preserved and reduced ejection fraction. Participants will be recruited during hospitalization in a dedicated heart failure unit and followed prospectively with sleep monitoring and clinical assessments before and after achievement of clinical euvolemia.

Individual participant data (IPD) sharing is currently undecided. Any future data sharing will depend on institutional policies, ethical approvals, and applicable data protection regulations. If shared, only de-identified data will be made available to qualified researchers upon reasonable request.