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Frequency-domain characteristics and filtering of blood flow following the onset of exercise: implications for kinetics analysis

¹Department of Anatomy and Physiology and ²Department of Kinesiology, Kansas State University, Manhattan, Kansas

Submitted 24 August 2005 ; accepted in final form 19 October 2005

We examined the validity and usefulness of a low-pass filter (LP_FILTER) to reduce point-to-point variability and enhance parameter estimation of the kinetics of blood flow (BF). Computer simulations were used to determine the power spectrum of simulated responses. Moreover, we studied the leg BF response to a single transition in four subjects during supine knee-extension exercise using three methods of data processing [beat-by-beat, average of 3 cardiac cycles (AVG_{3 BEATS}), and LP_FILTER]. The power spectrum of BF containing the kinetics information (0.2 Hz) did not overlap with the oscillations due to muscle contraction and cardiac cycle (simulations and Doppler measurements). There were no significant differences between the parameter estimates for a two-exponential model using Beat-by-Beat, AVG_{3 BEATS}, and LP_FILTER (P > 0.05; n = 4). However, LP_FILTER (cutoff = 0.2 Hz) resulted in a significantly lower standard error of the estimate for all parameters (P < 0.05). The means ± SD for the standard error of the estimate for Beat-by-Beat, AVG_{3 BEATS}, and LP_FILTER were, respectively, time constant-phase 1 = 5.0 ± 1.1 s, 4.5 ± 2.1 s, and 0.3 ± 0.2 s; time delay-phase 2 = 17.8 ± 7.9 s, 12.8 ± 7.5 s, and 1.4 ± 1.4 s; time constant-phase 2 = 15.8 ± 4.6 s, 9.9 ± 2.9 s, and 1.1 ± 0.5 s. In conclusion, LP_FILTER appeared to be a valid procedure providing a high signal-to-noise ratio and data density and thus LP_FILTER resulted in the smallest confidence interval for parameter estimates of BF kinetics.

low-pass filter; Doppler ultrasound; signal processing; knee-extension exercise

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