Acute Effects of High-flow Nasal Cannula and Non-invasive Ventilation on Constant-load Exercise Tolerance in Patients With Moderate to Severe Chronic Obstructive Pulmonary Disease

The patients underwent an initial clinical examination, with anthropometric evaluation, blood gas analysis, pulmonary function tests and measurement of maximum respiratory pressures. The exercise protocol started in the sector of Ergometry and Cardiopulmonary Exercise Testing. After completing the maximum incremental cardiopulmonary exercise test, two additional visits were scheduled for the three constant load tests. All patients studied underwent an evaluation of cardiopulmonary exercise testing (CPET). During maximum-incremental CPET, breath by breath: oxygen consumption (V̇O2, mL/min), carbon dioxide production (V̇CO2, mL/min), respiratory exchange rate (RER), minute ventilation VE (L/min), respiratory rate (bpm), equivalent ventilation for O2 and CO2 (V̇E/V̇O2 and V̇E/V̇CO2). In addition, cardiac monitoring was performed by 12-lead electrocardiogram (ECG) throughout the procedure. On the day of the experiment, the patients underwent two cardiopulmonary exercises with constant-load at 90% of the previously determined peak, separated by an interval of at least 1 hour.

The NIV parameters were adjusted for each patient with Trilogy 100 (Philips™). Spontaneous ventilation mode was set before the protocol for all patients, and a previous period of NIV adaptation was performed to titrate the inspiratory and expiratory pressures. The adaptation period started with the minimum Inspiratory Positive Airway Pressure (IPAP) value of 15cmH2O, and, every 2 minutes, increasing the pressure every 2 cmH2O according to the patient's tolerance.16 The Expiratory Positive Airway Pressure (EPAP) was programmed to vary between 4 and 6 cmH2O. Before the start of the examination, an adaptation was performed with the selected mask and initial ventilator settings for 20 min. No additional oxygen was offered.

The high flow system used was Optiflow® (Fisher & Paykel Healthcare, Auckland, New Zealand). Before the test, flow titration was performed for the patient, which started with the administration of a minimum gas flow of 30L/min and, every 2 minutes, the flow was increased by 5L/min according to patient tolerance. The test only started after 20 minutes of adaptation.