High-Flow Nasal Cannula on Exercise Tolerance in Heart Failure Patients Undergoing Cardiac Rehabilitation.

Heart failure (HF) 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).

OUTCOMES Primary outcomes are maximum treadmill test duration (seconds) and perceived exertion (Modified Borg Scale, 0-10), measured immediately after each test. Secondary outcomes - blood pressure, heart rate, SpO₂, respiratory rate, and rate-pressure product - are measured at baseline and immediately post-test.

STATISTICAL ANALYSIS Data normality will be assessed using the Shapiro-Wilk test (n<50). Paired t-test or Wilcoxon signed-rank test will be applied depending on data distribution. Sample size was calculated for a crossover design (two-tailed, α=0.05, power=80%, dz=0.8), yielding 23 participants; 28 will be recruited assuming 20% dropout.

CO-INVESTIGATORS:

Monserrat Delgado Valverde, Monserrat Orellana Morales, Emily Quiñileo Riffo, and Sergio Silva Valverde (Escuala de Kinesiología, Universidad de Santiago de Chile). Claudia Román Ureta, Paulina Castro Olivares (Complejo Hospitalario San José).

SETTING Cardiovascular rehabilitation program, Complejo Hospitalario San José, Independencia, Santiago, Chile.