This study aims to investigate whether adjunctive hyperbaric oxygen therapy, compared to guideline-directed medical therapy with the "New Four Pillars" (ARNI/ACEI/ARB + β-blocker + MRA + SGLT2 inhibitor) alone, improves cardiac function in patients with chronic heart failure, and to evaluate its efficacy and safety.

1. Study Design This is a prospective, single-center, randomized controlled clinical trial designed to evaluate the efficacy and safety of hyperbaric oxygen therapy as an adjunctive treatment for chronic heart failure.

2. Randomization After confirming eligibility, participants will be randomized in a 1:1 ratio via a web-based randomization system into either the experimental group (hyperbaric oxygen therapy plus standard medication) or the control group (standard medication alone).

3. Treatment Protocol Patients diagnosed with chronic heart failure at the center, who meet the criteria and have no absolute contraindications for hyperbaric oxygen therapy, will be enrolled. Specifically, the study will enroll patients with Heart Failure with Reduced Ejection Fraction (HFrEF, EF ≤40%) as per the latest guidelines.

   Experimental Group: Participants will receive hyperbaric oxygen therapy in addition to stable, guideline-directed medical therapy based on the "New Four Pillars" (ARNI/ACEI/ARB + Beta-blocker + MRA + SGLT2 inhibitor).

   Control Group: Participants will receive only the standard guideline-directed medical therapy ("New Four Pillars" as above) for chronic heart failure. All other aspects of care are identical to the experimental group, except for the hyperbaric oxygen therapy.

   Given that chronic heart failure requires long-term management, the hyperbaric oxygen protocol is divided into three courses to consolidate and maintain efficacy, as well as to improve patients' oxygen reserve capacity and tolerance. Each course consists of 10 sessions, with a one-month interval between courses.

   The hyperbaric oxygen treatment will be administered in a multi-place chamber at a pressure of 0.2 MPa (2 ATA). The session protocol is as follows: 20 minutes of compression, followed by two 30-minute periods of oxygen inhalation via mask, separated by a 10-minute air break, and finally 20 minutes of decompression. The total duration per session is 110 minutes. Sessions are conducted 5 times per week, making the total duration of each treatment course 14 days.

4. Follow-up After randomization and initiation of treatment, clinical follow-up visits will be conducted to collect data. For the experimental group, follow-ups will occur one day after the completion of each hyperbaric oxygen course. All participants (both groups) will undergo additional follow-ups at 3 months, 6 months, and 12 months after the complete hyperbaric oxygen treatment regimen.

Inclusion Criteria:

1. Diagnostic Criteria

   Diagnosis of chronic heart failure according to the Chinese Guidelines for the Diagnosis and Management of Heart Failure (2024), and meeting the following conditions:

   1.1 Left Ventricular Ejection Fraction (LVEF) ≤ 40% (HFrEF group). 1.2 Presence of chronic HF symptoms (NYHA functional class II-IV) or objective evidence (e.g., elevated natriuretic peptides, structural cardiac abnormalities).

   1.3 Disease duration ≥ 3 months, with no adjustments to the foundational anti-heart failure regimen within the past month.

2. Age and Informed Consent 2.1 Aged 18 to 70 years (inclusive). 2.2 Understand the study purpose and provide signed informed consent.

3. Treatment Stability 3.1 Received guideline-recommended, standardized "New Four Pillars" anti-heart failure therapy (ARNI/ACEI/ARB + β-blocker + MRA + SGLT2 inhibitor) for at least 2 weeks prior to enrollment, with no changes in the past month.

3.2 No diuretic dose adjustments within the past 5 days and no clinical signs of fluid overload (e.g., weight gain of ≥ 2 kg/week, new-onset pulmonary edema).

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Exclusion Criteria:

• Absolute Contraindications

  1. Untreated pneumothorax or pneumomediastinum.

  2. Claustrophobia, agitation or inability to cooperate, or conditions unsuitable for HBOT such as angle-closure glaucoma or eustachian tube occlusion.

  3. Unstable vital signs.

  4. Concurrent intracranial hemorrhage, intracranial mass, malignant tumor, uncontrolled epilepsy, psychiatric disorder, coagulation dysfunction, or other severe uncontrolled comorbidities.

  5. Severe pulmonary bullae or emphysema.

  6. Active internal bleeding or coagulopathy.

  7. Uncontrolled hyperpyrexia (body temperature >38.0°C).

  8. Concurrent use of disulfiram, bleomycin, or cisplatin chemotherapy. Relative Contraindications

  9. Uncontrolled hypertension (systolic BP >160 mmHg or diastolic BP >100 mmHg).

  10. Severe cardiac arrhythmias (e.g., third-degree atrioventricular block without a pacemaker, frequent ventricular tachycardia).

  11. Chronic obstructive pulmonary disease (FEV1 <50% of predicted) or active asthma.

  12. Psychiatric or cognitive impairment preventing cooperation with the therapy. Comorbidity Restrictions

  13. End-stage renal disease (dialysis-dependent).

  14. Terminal malignancy (life expectancy <6 months).

  15. Pregnancy or lactation (a negative pregnancy test is required for women of childbearing potential).

      Recent Clinical Events

  16. Acute myocardial infarction or unstable angina within the past 4 weeks.

  17. Hospitalization or emergency department visit for acute heart failure within the past 2 weeks.

  18. Current use of intravenous positive inotropic agents.

  19. Within 6 months after cardiac surgery.

  20. Use of any mechanical circulatory support.

  21. Participants with a 6-minute walk test result exceeding 450 meters or who are unable to complete the test.

      Other Exclusion Conditions

  22. Inability to complete follow-up (e.g., planned relocation, non-compliance with follow-up assessments).

  23. Concurrent participation in any other clinical trial that may interfere with the outcomes of this study.

  24. Unforeseen circumstances judged by the investigators to be ineligible.