Noninvasive ventilation improves the cardiovascular response and fatigability during resistance exercise in patients with heart failure

Participants attended the isokinetic strength testing laboratory on three different days, with a minimum interval of 72 hours between each visit. On the first day, the study participants were familiarized with noninvasive ventilation (BIPAP Sycnrony II, Respironics Inc, Murrysville, PA, USA) and the isokinetic dynamometer. To select the bi-level positive airway pressure intervention (BV) pressures during exercise, the best inspiratory and expiratory positive airway pressure (inspiratory positive airway pressure (IPAP) and expiratory positive airway pressure (EPAP) respectively) were evaluated. The IPAP was initially set at 10 cmH2O and increased gradually by 2 cmH2O every minute to a maximum of 14 cmH2O. The EPAP was set at 4 cmH2O and increased gradually by 1 cmH2O every minute to a maximum of 8 cmH2O. The pressure level was set to individual subject tolerance for all study participants. The sham intervention (SV) was applied with minimal pressure support (IPAP 4 cmH2O and EPAP 2cmH2O). All participants received noninvasive ventilation via a facial mask interface (Comfort full 2 Mask, Respironics Inc, Murrysville, PA, USA) during both BV and SV. On the second and third days, all subjects underwent a quadriceps isokineitc resistance exercise protocol utilizing both conditions of noninvasive ventilation (BV and SV). Subjects were randomly allocated to the BV or SV intervention before starting each procedure. First, all participants underwent 20 minutes of the allocated intervention (BV and SV) while at rest. During this initial period, the subjects sat on the isokinetic dynamometer (Biodex Medical System 2, Shirley, New York, USA). The resistance maneuver for this study was concentric knee extension, on the dominant side, at a speed of 60 degress per second. Five sets of 10 repetitions were performed during the two exercise bouts and each set was separated by two minutes of rest. Positioning and stabilization of each participant was standardized. Correction for the effect of gravity was made. Change in peak torque (PT, expressed in Nm), total work (TW, expressed in J) and Power (Pw, expressed in W) between the fifth and first sets were also measured to evaluate quadriceps fatigability by isokinetic dynamometer. Verbal encouragement and visual feedback using the computer screen were given in an attempt to achieve a maximum level of effort. All procedures were performed by the same investigator. The validity and reliability of this testing procedure have been previously described. At rest, during the resistance exercise protocol as well as during the recovery period, HR was continuously monitored (Polar model RS 800, Polar Electro Inc., Kempele, Finland). Systolic blood pressure (SBP) and diastolic blood pressure (DBP) were also measured using a calibrated oscilometric automatic device (OMROM MIT elite plus, OMROM Health Care Inc, Illinois, USA).