Modelagem por partes da cinética da resposta cronotrópica cardíaca durante a caminhada em esteira ergométrica

Abstract

The objective of this study was to model the variations in the intervals between a R-peak and another (IRR) of the electrocardiogram (ECG) in response to walking steps through an exponential first order model. Twenty-five men, young and healthy, performed the test protocol comprised of: 1 min of rest, followed by 2 min of warming up at 3 km / h and four steps, with 4 min of duration at speeds of 5 km / h, 7 km / h, 5 km / h and 0 km / h. The IRR signal was acquired continuously by means of an electrocardiograph and a cardiofrequency meter. The Nelder Mead Simplex method was applied to adjust the time constant (τ) and the gain (k) of the model to the actual IRR values in each step, so that the subsequent steps curve were added to the previous ones. The adjustment obtained R2 = 0.9 (0.85-0.92) and statistically different values of τ and k between the steps, with p << 0.05. These results indicate that the model is able to describe the HR during walking at different speeds and that its dynamics, in submaximal exercise, is non-linear, since steps of same value presented different responses.