Effect of High-Flow Nasal Cannula Use on Exercise Tolerance and Physical Performance in Heart Failure Patients Enrolled in a Cardiac Rehabilitation Program: A Randomized Crossover Trial

Heart failure is a chronic syndrome characterized by reduced cardiac output, exercise intolerance, and dyspnea. Despite the well-established benefits of cardiac rehabilitation, many HF patients have severely limited exercise capacity, which restricts the intensity and duration of training they can safely perform.

High-flow nasal cannula (HFNC) delivers heated, humidified air at flow rates of 50-60 L/min. Its physiological effects include reduction of inspiratory work, washout of nasopharyngeal dead space, generation of positive end-expiratory pressure, and improved mucociliary transport. These mechanisms may facilitate exercise in patients with cardiorespiratory limitations.

STUDY DESIGN. Randomized crossover trial. Each participant acts as their own control, completing two incremental treadmill tests in random order, separated by a washout period of 48-72 hours: Condition A (experimental): HFNC via AIRVO 2™ device (Fisher & Paykel Healthcare) with asymmetric nasal cannula at 50-60 L/min, FiO₂ 0.21, temperature 34-37°C. Condition B (control): no ventilatory support device. Randomization will be performed using randomizer.org. Before the experimental condition, participants will undergo an acclimatization period in which flow is increased by 10 L/min every 5-10 minutes until reaching the target flow or maximum tolerated flow.

EXERCISE PROTOCOL. An incremental protocol will be used on the treadmill, which will consist of incline and a progressive increase in speed and grade. The test ends at voluntary exhaustion or when predefined safety stopping criteria are met.

SAFETY. The test will be stopped if any of the following occur: chest pain, severe dyspnea (Borg ≥8), nausea or presyncope, cyanosis, SpO₂ below 90%, or heart rate above 85% of age-predicted maximum. The testing site will be equipped with automated external defibrillator, bag-valve mask, emergency oxygen, and at least one team member certified in advanced life support. Direct transfer to the hospital emergency service is available on-site (Complejo Hospitalario San José).