Acute Responses of Functional Electrical Stimulation Cycling on the Ventilation-to-CO2 Production Ratio and Substrate Utilization After Spinal Cord Injury.
BACKGROUND
Ventilation-to-carbon dioxide ratio is comparable with peak oxygen uptake in the prognosis of cardiovascular disorders. Currently, there are no established indices to determine the submaximal effects of functional electrical stimulation on cardiovascular performance in persons with spinal cord injury.


OBJECTIVE
To determine the effects of an acute bout of functional electrical stimulation-lower extremity cycling on ventilation, carbon dioxide production, ventilation-to-carbon dioxide ratio, and substrate utilization in people with motor complete spinal cord injury.


METHODS
Observational cross-sectional design.


METHODS
Clinical laboratory setting.


METHODS
Ten individuals with motor complete spinal cord injury.


METHODS
Participants were allowed to cycle until fatigue. The effects of functional electrical stimulation on ventilation, carbon dioxide production, ventilation-to-carbon dioxide ratio, and substrate utilization were measured with a portable metabolic cart (COSMED K4b2). Body composition was determined with bioelectrical impedance.


RESULTS
Resting and warm-up ventilation were 8.15 ± 3.5 L/min and 8.15 ± 2.8 L/min, respectively. Functional electrical stimulation increased ventilation significantly (14.5 ± 6.4 L/min), which remained significantly elevated (13.3 ± 4.3 L/min) during the recovery period. During resting and warm-up phases, the ventilation-to-carbon dioxide ratios were 41 ± 4.8 and 38 ± 5.4, respectively. Functional electrical stimulation decreased the ventilation-to-carbon dioxide ratio significantly to 31.5 ± 4, which remained significantly reduced during the recovery period (34.4 ± 3). Functional electrical stimulation relied primarily on carbohydrate utilization (188 ± 160 g/day to 574 ± 324 g/day; P = .001) with no changes in fat utilization (77.5 ± 28 g/day to 93.5 ± 133.6 g/day; P = .7) from resting to exercise periods. Significant relationships were noted between carbohydrate utilization during functional electrical stimulation and carbon dioxide (r = 0.98; P = .00010) production. The percentage whole body fat-free mass was negatively related to the exercise ventilation-to-carbon ratio (r = -0.66; P = .045).


CONCLUSIONS
An acute bout of functional electrical stimulation resulted in a significant drop in the ventilation-to-carbon ratio, accompanied with a reliance on carbohydrate utilization and a diminished capacity to utilize fat as a substrate. Fat-free mass may be associated with a decrease in ventilation to carbon dioxide ratio and an increase in carbohydrate utilization in persons with spinal cord injury.
Spinal Cord Injury and Disorders Center, Hunter Holmes McGuire VAMC, 1201 Broad Rock Boulevard, Richmond, VA 23249; and Department of Physical Medicine and Rehabilitation, Virginia Commonwealth University, Richmond, VA(∗). Electronic address: ashraf.gorgey@va.gov.
Ashraf S
AS
Gorgey
Spinal Cord Injury and Disorders Center, Hunter Holmes McGuire VAMC, and College of Health and Human Performance; Virginia Commonwealth University, Richmond, VA(†).
Justin
J
Lawrence
D000293:Adolescent; D000328:Adult; D000368:Aged; D002245:Carbon Dioxide / Q000378:metabolism*; D003430:Cross-Sectional Studies; D004599:Electric Stimulation Therapy / Q000379:methods*; D005081:Exercise Therapy / Q000379:methods*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D035002:Lower Extremity / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption; D012121:Respiration, Artificial / Q000379:methods*; D013119:Spinal Cord Injuries / Q000378:metabolism / Q000503:physiopathology / Q000534:rehabilitation*; D055815:Young Adult
D002245:Carbon Dioxide