[Show abstract][Hide abstract] ABSTRACT: The aim of this study was to evaluate the temporal response of the sympatheticvagal balance during progressive exercise in healthy people by time-frequency analysis (TFA) of heart rate variability (HRV) and apply the parameters extracted from this to detect the anaerobic threshold (AT). RR series extracted from 26 athletes (22.2 ± 5.5 years, 74.1 ± 7.4 kg, 1.76 ± 0.07 m) during progressive maximal exercise were resampled (5 Hz) and filtered (band-pass Butterworth 4th order). The power spectral density of the bands of high (PSDHF) and low (PSDLF) frequency were extracted from three TFA techniques. The AT obtained by HRV (ThHRV) was compared with the gold standard. The dynamics of HRV obtained by TFA techniques revealed a predominance of sympathetic over the vagal activity (PSDLF / PSDHF) throughout the exercise (rest: 3.19 ± 4.47 n.u.; exercise: 3.97 ± 3.49 n.u.). The ThHRV presented errors of 23.1 to 80.8% using conventional methods, and from dynamic measurements, 2.8 to 18.2%, resulting in no significant differences between these (166 bpm [144-175]) and the ventilatory threshold (154.3 bpm [147 to 168 bpm]). In conclusion: Short-Time Fourier Transform was the best TFA alternative, the predominance of the sympathetic over the vagal activity during exercise was confirmed by the three TFA techniques employed and the ThHRV based on dynamic measurements showed acceptable agreement with AT obtained by ventilatory measurements, so that we can recommend its use for obtaining the AT.
[Show abstract][Hide abstract] ABSTRACT: The stability of arterial blood gas tensions and pH during steady-state moderate exercise has suggested an important humoral element of ventilatory control in humans. However, the involvement of central and peripheral chemoreflexes in this humoral control remains controversial. This reflects, in large part, technical and interpretational limitations inherent in currently used estimators of chemoreflex "sensitivity." Evidence suggests that the central chemoreceptors (a) contribute little during moderate exercise, given the relative stability of cerebrospinal pH, (b) constrain the hyperpnea of high-intensity exercise, consequent to the respiratory compensation for the metabolic acidemia, and (c) may play a role in the respiratory compensation during chronic metabolic acidemia. In contrast, the peripheral chemoreceptors appear to (a) exert considerable influence on ventilatory kinetics in moderate exercise, but are less important in the steady state, and (b) induce much of the respiratory compensation of high-intensity exercise.
Canadian journal of applied physiology = Revue canadienne de physiologie appliquée 10/1994; 19(3):305-33. · 1.30 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Models of the exercise hyperpnoea have classically incorporated elements of proportional feedback (carotid and medullary chemosensory) and feedforward (central and/or peripheral neurogenic) control. However, the precise details of the control process remain unresolved, reflecting in part both technical and interpretational limitations inherent in isolating putative control mechanisms in the intact human, and also the challenges to linear control theory presented by multiple-input integration, especially with regard to the ventilatory and gas-exchange complexities encountered at work rates which engender a metabolic acidosis. While some combination of neurogenic, chemoreflex and circulatory-coupled processes are likely to contribute to the control, the system appears to evidence considerable redundancy. This, coupled with the lack of appreciable error signals in the mean levels of arterial blood gas tensions and pH over a wide range of work rates, has motivated the formulation of innovative control models that reflect not only spatial interactions but also temporal interactions (i.e. memory). The challenge is to discriminate between robust competing control models that: (a) integrate such processes within plausible physiological equivalents; and (b) account for both the dynamic and steady-state system response over a range of exercise intensities. Such models are not yet available.
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