Dynamics of ventilation, heart rate, and gas exchange: sinusoidal and impulse work loads in man

Abstract

Dynamic characteristics of ventilation, heart rate, and gas exchange in response to sinusoidally varying work loads were analyzed in four male subjects, exercising in the upright position on a bicycle ergometer. Mean work-load and sinusoidal amplitude were about 1.5 and 0.9 W/kg, fat-free mass), respectively. Seven different frequencies were used, the periods ranging from 12 to 0.75 min. To further investigate the linearity of the variables under study, 10-s impulse loads were also applied to three of the four subjects. Harmonic analysis of the sine-wave data and comparison of the sine-wave fundamental responses with the impulse frequency responses showed that only O2 uptake behaves in a linear fashion. Ventilation and CO2 production showed quasi- to nonlinear behaviors, whereas the responses of heart rate and alveolar partial pressures were clearly dependent on the type of forcing used. By means of mathematical parameter identification techniques, it was found that the individual frequency responses of O2 uptake could be almost completely described by a four-parameter transfer function with parameter values showing second-order underdamped to critically damped dynamics.

Cardiorespiratory dynamics during sinusoidal and impulse exercise in man.

“…In Fig. 6, the relationship between the mean-to-peak amplitudes of VE and Vco2 responses to sinusoidal forcings are given on the basis of integrated data of ours and two other investigator groups', i.e., CASABURI et al (1977) andBAKKER et al (1980). Despite the differences among subjects and techniques, the correlation coefficient between both the variables was excellent (r=0.994).…”

“…Under the same condition, VE correlated to a less extent to Vo 2 and PETco 2 with the correlation coefficients of 0.951 and 0.688, respectively. Correlations between the mean-to-peak amplitudes of response sinusoids to impulse stimuli were also examined using the data given in Table 3 and the mean values for the same parameters given in Table 5 of BAKKER et al (1980). Correlation coefficients were determined to be: VE .…”

“…WIGERTZ (1970) investigated the dynamic characteristics of heart rate and ventilation. CASABURI et al (1977) and BAKKER et al (1980) compared the kinetics of heart rate, ventilation, and gas exchange parameters to define the interrelationship among variables during exercise. Other investigators used impulse forcings which differ from sinusoidal work in that a scale of frequencies can be given simultaneously (BAKKER et a!.,1980;BENNETT et a!., 1981;FUJIHARA et al, 1973a, b).…”

“…However, in a nonlinear system such as in most of the biological control systems, discrepancies would usually appear. For example, the heart rate and ventilatory responses to sinusoidal forcings have been described by a single exponential function with a very small time delay (CASABURI et a!.,1977), while the responses to impulse forcings have been generally represented by a second-order model in which fast and slow response components were connected in parallel (BAKKER et al, 1980;FUJIHARA et al, 1973b). Since the first rapid component occurs before metabolites from the exercising limbs reach to known chemoreceptor sites, this has been attributed to a neural reflex, most probably due to afferent discharges from the muscle spindles.…”

“…From another point of view, sinusoidal forcing is superior to impulse forcing since its possible influence of the cerebral activity can be avoided. Although simultaneous analyses of cardiorespiratory dynamics to sinusoidal and impulse forcings have been made by BAKKER et al (1980), these authors gave their mathematical analysis no physiological interpretation. Furthermore the present work differs from the previous one in such a way that transient changes in cardiac output were directly determined by using a new instrument recently developed by MIYAMOTo et al (1981b).…”