Comparison of CPAP and Bi-level Effects on Exercise Tolerance and Cardiorespiratory Responses in Individuals With Chronic Heart Failure.

This study is a randomized controlled trial, double-blind and cross-over, to be composed of 45 volunteers of both genders, aged between 30 and 80 years, with CHF will be selected from a specialized outpatient clinic with medical consent. Patients should have symptoms of compensated CHF; presenting functional capacity II and III (New York Heart Association), with left ventricular ejection fraction <50%; not participating in cardiac rehabilitation programs; and clinical stability in the last three months, with no history of angina or coexistence of obstructive pulmonary disease (Tiffeneau-Pinelli index> 70% in spirometry). In addition, they should not present any osteoarticular or neurological disease would prevents them from performing the proposed tests, as well as having a score higher than 22 in the Leganés cognitive test (20). In the case of NIV or exercise intolerance, as well as in case of non-attendance to the experiments on the scheduled days, subjects will be excluded from the study.

The sample will be the result of a non-probabilistic sampling process, calculated based on the magnitude of the effect of the main variable (distance traveled) after the use of NIV therapy, obtained in a pilot study. In addition, this protocol was aproved by the institution's Ethics Committee on Human Research (CAAE: 49324415.0.000.5537).

Experimental procedure The experimental protocol will occur in three visits, one per day, with a minimum interval of 48 hours between them. On the first visit, the volunteers will undergo a screening that consists of clinical evaluation (assessment sheet) and cognitive (Leganéscognitive test), as well as evaluation of lung function (spirometry) and QoL (Minnesota Living with Heart Failure Questionnaire). Next, the Shuttlel Walking Test (SWT) control (T-Co) will be performed, without previous use of NIV, in order to determine the distance traveled and other physiological variables in the absence of interventions. Finally, during the initial visit, a preliminary NIV session will be held to adjust the interface and adapt the volunteer to the therapy.

At each subsequent visit, volunteers will perform a SWT immediately after 30 minutes of NIV, one day in Bi-level mode and one in CPAP mode, following a randomized sequence. Thus, all volunteers will perform one SWT after CPAP (T-CP) and one SWT after Bi-level (T-Bi). In the experiment, the CPAP pressure will be maintained at 6 cmH2O, while at the Bi-level an expiratory pressure (EPAP) of 6 cmH2O and an inspiratory pressure (IPAP) of 12 cmH2O will be defined.