GAS-EXCHANGE KINETICS DURING FUNCTIONAL ELECTRICAL-STIMULATION IN SUBJECTS WITH SPINAL-CORD INJURY

We examined the kinetics of VO2, VCO2, and V-E following the onset of unloaded leg cycling, and in recovery, in sis patients with spinal cor d injury (SCI). Exercise was produced by functional electrical stimula tion (FES) of the quadriceps, hamstrings, and gluteal muscles. End-exe rcise VO2 (1.03 +/- 0.16 l . min(-1)), VCO2 (1.20 +/- 0.22 l . min(-1) ) and V-E (41 +/- 10 l . min(-1)) were elevated compared to values typ ically seen in healthy ambulatory subjects performing similar unloaded cycling Mean response times for the on transients (MRT(on)) were both long and Variable across subjects for VO2 (165 +/- 62 s), VCO2 (173 /- 58 s), and V-E (202 +/- 61 s). Recovery kinetics showed much less i ntersubject variability, and for five of sis subjects were faster than the equivalent exercise MRT for all three variables (MRT(off) for VO2 of 103 +/- 28 s, VCO2 136 +/- 20 s, and V-E 144 +/- 34 s), but P > 0. 05 for all three. Size of the O-2 deficit (1.96 +/- 0.90 l) and end-ex ercise lactate (7.05 +/- 1.65 mmol . l(-1)) were similar to Values rep orted for healthy sedentary subjects performing maximal voluntary exer cise, but the end-exercise heart rate (102 +/- 16 bpm) was lower than expected for this intensity of exercise. Tn conclusion, FES-induced un loaded cycling leads to exaggerated responses of pulmonary gas exchang e and long time constants in patients with SCI. The delayed kinetics m ay be due in part to a blunted increase in heart rate in addition to s evere deconditioning.