Vagal response during the immersion reflex vagal evaluare using a time-variant index [Respuesta vagal durante el reflejo de inmersión evaluada mediante un índice vagal variante en el tiempo]

In this paper the immersion reflex is explored at different water temperatures, considering that the maneuver is non-stationary. Given that this reflex produces a parasympathetic response and that the root mean of successive differences (rMSSD) of the beat-by-beat heart period is considered as a vagal index, a time variant rMSSD was proposed. To estimate this index an autoregressive model was fixed by adaptive filtering and non-differences were found when compared with conventional rMSSD for stationary maneuvers. The heart period records of eight subjects in prone position were obtained during a three stages protocol: one minute of control, 20s of maneuver and one minute of recovery. The maneuver consisted on apnea, without and with face immersion in water at temperatures of 19° C, 11° C and 2° C. Comparing the average of four beats at the end of each stage for time variant rMSSD and heart period, differences were observed for the thermal stimulus level (P<0.01) and among the stages (P<0.01). Apnea did not present differences among the stages (P>0.05), probably due to the position effort. After one minute of recovery, the rMSSD return close to control values while heart period did not. The time variant rMSSD estimation proposed allows reviewing the behavior of the non-stationary immersion reflex; using it we could observe the direct relation between the stimulus and vagal response magnitude. © Springer-Verlag Berlin Heidelberg 2007.

Biomedical engineering; Auto regressive models; Control values; Immersion in waters; Nonstationary; Prone position; Response magnitude; Thermal stimuli; Water temperatures; Heart

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