The control of ventilation is dissociated from locomotion during walking in sheep

Abstract

This study was designed to test the hypothesis that the frequency response of the systems controlling the motor activity of breathing and walking in quadrupeds is compatible with the idea that supra-spinal locomotor centres could proportionally drive locomotion and ventilation. The locomotor and the breath-by-breath ventilatory and gas exchange (CO 2 output (V CO 2 ) and O 2 uptake (V O 2 )) responses were studied in five sheep spontaneously walking on a treadmill. The speed of the treadmill was changed in a sinusoidal pattern of various periods (from 10 to 1 minute) and in a step-like manner. The frequency and amplitude of the limb movements, oscillating at the same period as the treadmill speed changes, had a constant gain with no phase lag (determined by Fourier analysis) regardless the periods of oscillations. In marked contrast, when the periods of speed oscillations decreased, the amplitude (peak-to-mean) of minute ventilation (V E ) oscillations decreased sharply and significantly (from 6.1 ± 0.4 l min −1 to 1.9 ± 0.2 l min −1 ) and the phase lag between ventilation and treadmill speed oscillations increased (to 105 ± 25• during the 1 min oscillation periods). V E response followedV CO 2 very closely. The drop inV E amplitude ratio was proportional to that inV CO 2 (from 149 ± 48 ml min −1 to 38 ± 5 ml min −1 ) with a slightly longer phase lag for ventilation than forV CO 2 . These results show that beyond the onset period of a locomotor activity, the amplitude and phase lag of theV E response depends on the period of the walking speed oscillations, tracking the gas exchange rate, regardless of the amplitude of the motor act of walking. Locomotion thus appears unlikely to cause a simple parallel and proportional increase in ventilation in walking sheep.

Control of Breathing During Exercise

“…20). In other words, when conditions are created where work rate changes with no concurrent change inV O 2 andV CO 2 ,V E follows factors related to gas exchange rate and not to the motor activity (151,154).…”

Control of arterial PCO2 by somatic afferents in sheep

“… Δ versus Δ relationship for all the tests (•) when c P was maintained constant The open symbols are mean values from previous studies from our laboratory: □, mean value obtained in spontaneously walking sheep (Haouzi et al 2004 a ); ○, mean value obtained during ERC in the sheep, but with an ‘intact’ cephalic circulation (Haouzi et al 1997). …”

Dynamic Characteristics of Ventilatory and Gas Exchange during Sinusoidal Walking in Humans

“…Haouzi et al . [16] also reported that parallel adjustments of the locomotor activity and V̇ E were observed during treadmill walking in the sheep. Wells et al .…”

“…Second, following 5 min of walking at constant speed at the midpoint of the sinusoidal walking speed (4.5 km·h -1 ), the treadmill speed was changed with a sinusoidal pattern from 3 km·h -1 to 6 km·h -1 at a period ( T ) of 10, 5, 2 and 1 min and in a stepwise manner (steady-state) at the speeds of 3 km·h -1 and 6 km·h -1 for each 5 min [4,16–18]. The sinusoidal loading was repeated for five cycles at 1 min periods and continued three cycles at 2 min periods following warming up at a constant work load at the midpoint between the maximum and minimum.…”

“…All the data were analyzed using Fourier analysis as previously reported [2–7,16–19]. The variation in the treadmill speed or work rate was regarded as the input function.…”