IJCS | Volume 31, Nº2, March / April 2018

144 Teixeira et al. Gas Analysis in the 6-MinuteWalkTest in HFNEF Int J Cardiovasc Sci. 2018;31(2)143-151 Original Article The aim of this study was to describe and analyze the kinetic behavior at each minute of hemodynamic, ventilatory, and metabolic variables in patients with HFNEF during the 6MWT using a portable gas analyzer, and to compare the findings with those obtained during a cardiopulmonary exercise test (CPET). Methods Prospective, analytical study with a non-probabilistic, intentional, and convenience sample, as set by the adopted criteria, carried out at the Hospital Universitário Antônio Pedro (HUAP) of the Universidade Federal Fluminense (UFF) between March 2010 and July 2013. The study project was approved by the Ethics Research Committee at HUAP under the number 152A/2010, and all participants signed an informed consent form. The inclusion criteria adopted to characterize HFNEF were those described by Paulus et al., 11 in addition to the following factors: (A) complaints suggestive of HF (dyspnea, fatigue, and/or edema); (B) report of prior hospitalization due to decompensated heart disease, but at the moment of the test presenting with a functional class II to III according to the NewYorkHeart Association (NYHA); (c) age > 18 years; (d) disease duration greater than 6months; (e) use ofmedication; and (F) stable disease. The exclusion criteria adopted were: (A) chronic obstructive pulmonary disease (COPD) based on clinical criteria, (B) functional class IV or other criteria contraindicating the CPET, 12 and (C) participation in supervised cardiac rehabilitation programs. The patients were instructed to maintain the current medications. The tests comprised three moments: conventional 6MWT (6MWT1), 6MWT coupled to a portable gas analyzer (6MWT2), andCPET on a treadmill. Due to a matter related to the hospital's flow, some patients were first assigned randomly to the 6MWT and others to the CPET. The 6MWT was performed in a hallway with an extension of 30 meters. The first 6MWT (6MWT1) had a learning effect as objective, as recommended in the literature. 6 The second 6MWT (6MWT2) was performed at least 3 days and no more than 3 weeks after the first, when the patients repeated the 6MWT, but this time they were connected to a portable gas analyzer. Themaximum interval between the 6MWT and the CPET was also 3 weeks. Both the 6MWT and the CPET were scheduled by the same evaluator and applied by the same team to avoid application variability . We used for the assessments the metabolic analyzer MedGraphics (MGC) VO2000 (Imbrasport, Porto Alegre, RS, Brazil), the system Ergo PC Elite 13, and the treadmill Centurion 300 (MicroMed , Brasília, DF, Brazil). The gas analyzer was calibrated before each test by the autocalibration system in a ventilated environment. The biological control of the calibrationwas performed monthly and the control by the equipment's representative (CAEL, Rio de Janeiro, RJ, Brazil) was conducted every 3 months. In the CPET, each patient underwent a 2-minute baseline collection followed by a 1-minute warm-up at 1 km/h and 0º slope before starting the ramp protocol. In order to analyze and assess the CPET variables, we used the software ErgoPCElite for Windows 13W (MicroMed, Brasília, DF, Brazil). The perceived exertion (PE), assessed by the Borg scale (variation 0-10), and the hemodynamic and electrocardiographic variables were recorded at every minute. During the recovery phase, the patient remained seated. Two referees analyzed the report of the test to obtain the following information: VE/VCO 2 slope value, presence of oscillatory breathing (OB), and establishment of the ventilatory threshold I, referred from now on as the anaerobic threshold (AT). In order to determine the AT, we used the curves of the ventilatory equivalents of the VO 2 and VCO 2 , in addition to the curves of VO 2 and VCO 2 expired fractions, as recommended by the CPET guideline of the American Heart Association (AHA). 13 The evaluations were performed while the patients maintained the use of their usual medications, during the same time of the day, and at least 2 hours after the last meal. Peak VO 2 was defined as the highest VO 2 value obtained up to the final 30 seconds or 10 seconds into the immediate recovery. In order to determine the occurrence of OB and the value of the VE/VCO 2 slope, we followed the AHA guideline 13 and the recommendations by Guazzi et al. 14 Since spirometry was not performed, the ventilatory reserve was not considered in the analysis. Only one CPET was performed, as recommended by Scott et al. 15 The maximum estimated heart rate (HR) was obtained using the formula by Tanaka et al. 16 and was used to calculate the chronotropic index. During the 6MWT, we recorded the HR (Polar monitor, model T31, Oulu, Finland) at each minute, along with the PE according to the Borg scale and the capillary O 2 saturation using a pulse oximeter (Onyx, Minneapolis, MN , USA ).