Equações de predição da frequência cardíaca máxima com adequada aplicabilidade clínica para prescrição do exercício aeróbio em indivíduos pós-acidente vascular encefálico

Abstract

For adequate prescription of aerobic exercise intensity for individuals after stroke it is necessary to obtain the maximum heart rate (HRmax). This measurement is ideally obtained through a maximal exercise test, such the Cardiopulmonary Exercise Test (CPET). However this test has low clinical applicability. Alternatively, several age-based HRmax prediction equations have been developed, none of them specific for individuals after stroke. This dissertation aimed: 1-to investigate the validity of six age-based prediction equations to predict the HRmax of individuals after stroke; 2-to develop two specific equations for individuals after stroke; and 3-to investigate the validity of the developed equations. This is a cross-sectional study. Individuals after stroke in the chronic phase were recruited. To answer objective-1, 60 individuals (54±12 years; 64±69 months after stroke) were included. Six HRmax prediction equations were selected for the investigation of validity: 1- 220-age, 2- 206.9 – (0.67 x age), 3- 208 – (0.7 x age), 4- 216.6 – (0.84 x age) (all designed for able-bodied individuals); 5- 164 – (0.72 x age) and 6- 200 – (0.92 x age) (both developed for individuals with coronary heart disease. The agreement between the HRmax obtained by the CPET and the HRmax predicted by the equations was analyzed using the intraclass correlation coefficient (ICC) with a 95% confidence interval (95%CI) and the Bland-Altman method (α=5%). There was no significant agreement for equations 1-5 (-0.18≤ 95%CI ≤0.79) and there was significant agreement (95%CI= 0.05-0.75), but of moderate magnitude (ICC=0.51) for equation-6. The Bland-Altman method showed that equations 1-4 and 6 overestimated the HRmax obtained by the CPET, and equation-6 had the lowest mean difference (2.4 beats per minute (bpm)). Therefore, the equations tested were not considered valid to predict the HRmax of individuals after stroke. To answer objective-2, two multiple regression analyzes were performed. The following regression models were obtained: Equation-1 (Six-minute Walking Test (6MWT)): HRmax= 87.655 + 0.726 (HRpeak in 6MWT) – 0.386 (age) (R²=0.58, p<0.001) and Equation-2 (Incremental Shuttle Walking Test (ISWT)): HRmax= 96,523 + 0.681 (HRpeak in ISWT) – 0.039 (walking distance on ISWT) – 0.400 (age). (R²=0.58, p<0.001) To answer objective-3, 20 individuals were included (58±8 years; 60±46 months after stroke.) The agreement between the HRmax obtained by the CPET and the HRmax predicted by the new equations was analyzed using the ICC with 95%CI and by the Bland-Altman method (α=5%). Equation-1 showed significant agreement (95%CI= 0.63 – 0.94) with a high magnitude (ICC=0.85), and a mean difference of 3.2 bpm. Equation-2 showed significant agreement (95%CI= 0 .29 – 0.89) with a high magnitude (ICC=0.72), and a mean difference of – 1.3 bpm. In conclusion, previously developed equations that are not valid for individuals after stroke should not be used to determine the HRmax of these individuals. The use of one of the two equations specifically developed for these individuals is recommended, as they have adequate validity and can be easily used in clinical practice to predict the HRmax, requiring only age and HRpeak measurement and/or walking distance obtained with one of the clinical tests: 6MWT or ISWT.