Peak and kinetic cardiorespiratory responses during arm and leg exercise in patients with spinal cord injury

Abstract

Study design: A paired comparison of the peak and submaximal responses of oxygen uptake and heart rate in patients with spinal cord injury (SCI) performing voluntary arm cycle exercise and functional electrical stimulation (FES) leg cycling exercise. Objectives: To test if the blunted heart rate response and slower rate of adjustment of oxygen uptake seen in patients with SCI performing FES leg cycle exercise are also characteristic of arm exercise in these patients. Methods: Eight paraplegics performed incremental and constant work rate (CWR) exercise with the legs and arms. Mean response times (MRT) for Vo 2 during exercise (on) and in recovery (o ) were calculated from the breath-by-breath Vo 2 pro®le. Results: Peak heart rate was higher during incremental arm exercise, and uncorrelated with that observed during incremental FES leg cycling. For the same increase in Vo 2 , constant work rate arm exercise was associated with faster (and normal) Vo 2 kinetics, greater increase in heart rate, and lower end-exercise blood lactate, compared to FES leg cycling. Conclusions: The consistently higher peak heart rate and Vo 2 , and faster Vo 2 kinetics, for voluntary arm compared to FES leg cycle exercise suggest no intrinsic dysfunction of heart rate control in these paraplegics. Rather, these data suggest that during FES leg cycling the changes seen are due to some characteristic speci®c to the injury, such as reduced muscle mass and/or deconditioning of the remaining muscle.

Kinetics and steady-state of V̇O2 responses to arm exercise in trained spinal cord injury humans

“…O 2 kinetics in the present study became much faster as compared with that during arm cranking exercises in an upright posture in some previous studies. 5,7,8,10 Our observation of similar t 1/2 HR on-and okinetics in both groups suggests that the V . O 2 kinetics was not matched to the HR kinetics, at least during 31 NMR in persons with paraplegia following 3 min of tetanic isometric contraction of the quadricepts.…”

Comparison of stimulation patterns for FES-cycling using measures of oxygen cost and stimulation cost

“…We chose to switch each pattern every 6 minutes because we wished to ensure that each stage was of sufficient duration that a true steady-state was attained; we estimated that this was the minimum time necessary for the respiratory responses to reach a steady state, based on the knowledge that SCI subjects typically have prolongedVO 2 kinetics [2,27]. On the other hand, it was desirable to make the duration of each stage as short as possible to allow a greater number of pattern repetitions within a given test period.…”

Can the efficacy of electrically stimulated pedaling using a commercially available ergometer BE improved by minimizing the muscle stress–time integral?

“…Also, 3 subjects were unable to pedal beyond 5 minutes during the first 7-minute period for at least one of the testing sessions. Previous research 26,43 and examination of the data indicate that the metabolic responses of these subjects had not yet reached steady state. As such, these subjects were omitted from the metabolic data analysis.…”

“…The 7-minute time step was chosen to account for the mean response time of oxygen uptake kinetics ( _ VO 2 ) to reach steady state. 26,43 Data Processing and Analysis. The respiratory and pedaling data recorded from each of the subjects were time synchronized.…”

“…Similarly, the resting blood lactate concentration was subtracted from the values collected while the subject actively pedaled. The recorded pedaling rate and external applied flywheel resistance data were combined with the internal friction of the ergometer 43 to calculate the instantaneous pedaling work rate (i.e., power). The pedaling work rate data were averaged over the same 1-minute period as the respiratory data.…”