Resumo

RESNIK¹, Miguel et al. Double product breakpoint as an indicator of metabolic transition during exercise in coronary patients. Insuf. card. [online]. 2016, vol.11, n.4, pp.160-167. ISSN 1852-3862.

The anaerobic threshold has been used as a good indicator of functional capacity and prognostic implications in cardiac patients. The aim of our study was to evaluate an alternative and non invasive method like the double product break point (DPBP), as the point at which a clear and sustained increase in double product (DP) slope occurred during incremental exercise test. DP= heart rate (HR) x systolic blood pressure (SBP), that could be applied for physical training and prognosis information in patients with coronary heart disease (CHD). Material and methods. We evaluated 33 male and 9 female patients mean age 64.8 ± 7.6 years with documented CHD, clinically stables with medical treatment and sinus rhythm, in conditions to walk in a treadmill using an incremental test until exhaustion. The exercise consisted of an initial period of warm up (1 km/h) followed by the work rate being increased by 0.4 km/h each 1 minute stage to the limit of the subject’s tolerance. Oxygen consumption (VO2) was measured with a portable system (COSMED), HR trough a 12 lead ECG (SCHILLER) and blood pressure with sphygmomanometer each stage. Double product vs VO2 for each subject was submitted to 3 blind evaluators for visual determination of the ventilatory threshold (VT1) and DPBP, respectively. A Student t test was used to compare speed (km/h) at VT1 and DPBP and Pearson’s product-moment correlation to assess the relationship between both parameters (p<0.05). Results. Patients completed the evaluation without symptoms. We could determine VT1 and DPBP in all of them. Speed at DPBP was 2.6 ± 0.5 km/h and speed at VT1 2.6 ± 0.6 km/h, with no significant difference between both values. We found a positive linearship correlation comparing VT1 vs DPBP (r2=0.6). Conclusions. We could measure the DPBP in coronary patients with strong positive correlation with VT1, and could be used as effective variable in the prognosis of this disease and monitoring physical training, but it will require more subjects with different physical conditions to be analyzed as a relevant parameter.

Palavras-chave : Coronary heart disease; Double product break point; Ventilatory threshold; Exercise; Bruce ramp protocol.

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