Relationship between ventilation and predicted arterial CO2 pressure during recovery from an impulse-like exercise without metabolic acidosis

Effect of work intensity on time delay in mediation of ventilation by arterial carbon dioxide during recovery from impulse exercise

Time delay in the mediation of ventilation (V(.)E) by arterial CO(2) pressure (PaCO(2)) was studied during recovery from short impulse-like exercises with different work loads of recovery. Subjects performed two tests including 10-s impulse like exercise with work load of 200 watts and 15-min recovery with 25 watts in test one and 50 watts in test two. V(.)E, end tidal CO(2) pressure (PETCO(2)) and heart rate (HR) were measured continuously during rest, warming up, exercise and recovery. PaCO(2) was estimated from PETCO(2) and tidal volume (V(T)). Results showed that predicted arterial CO(2) pressure (PaCO(2 pre)) increased during recovery in both tests. In both tests, V(.)E increased and peaked at the end of exercise. V(.)E decreased in the first few seconds of recovery but started to increase again. The highest correlation coefficient between PaCO(2 pre) and V(.)E was obtained in the time delay of 7 s (r=0.854) in test one and in time delays of 6 s (r=0.451) and 31 s (r=0.567) in test two. HR was significantly higher in test two than in test one. These results indicate that PaCO(2 pre) drives V(.)E with a time delay and that higher work intensity induces a shorter time delay.

Higher ventilatory responses during and after passive walking-like leg movement in older individuals

Background

Minute ventilation (V·E) during walking has been shown to be higher in older individuals than in young individuals, but the mechanisms underlying the higher ventilatory response is unclear. Central command and peripheral neural reflex are important neural control mechanisms underlying ventilatory response during exercise. Passive leg movement has been used to exclude the influence of central command due to the lack of voluntary activation of muscles. The aim of the present study was to compare the ventilatory response during and after passive walking-like leg movement (PWM) in young and older individuals.

Methods

Eight young subjects (20 ± 2 years) and seven older subjects (70 ± 1 years) participated in this study. Subjects spent 7 minutes in a quiet standing (QS) position. Thereafter, they performed 14-minute rhythmic PWM at 1 Hz and this was followed by 7 minutes of QS.

Results

V·E values during pre-PWM QS were calculated as 1-minute averages using data obtained between 5 and 6 minutes. V·E values at pre-PWM QS in the young and older groups were 8.4 ± 2.1 and 7.5 ± 1.2 l/minute, respectively. V·E values increased significantly at the first minute of PWM to 11.4 ± 2.2 and 10.4 ± 2.5 l/minute in the young and older groups, respectively (P <0.001). In the young group, V·E at the last minute of PWM (9.2 ± 2.0 l/minute) was not significantly different from that at pre-PWM QS due to a decline in V·E, whereas V·E at the last minute of PWM in the older group (9.4 ± 2.2 l/minute) was still significantly higher (P <0.01). On the other hand, V·E at the first minute of post-PWM QS (7.2 ± 1.8 l/minute) was significantly lower than that during pre-PWM QS in the young group (P <0.05) but not in the older group.

Conclusions

Ventilatory response during and after PWM is higher in older individuals than in young individuals. This may be associated with a mechanism(s) other than central command. Our findings may explain part of the higher V·E response while walking in older individuals.