Assessing Ventilatory Threshold in Individuals With Motor-Complete Spinal Cord Injury

OBJECTIVE: To assess the feasibility of measuring ventilatory threshold (VT) in higher-level motor-complete spinal cord injury (SCI) using 4 different analysis methods based on noninvasive gas exchange. DESIGN: Observational. SETTING: Laboratory testing. PARTICIPANTS: Individuals with C4-T6 motor-complete SCI (16 paraplegia, 22 tetraplegia; American Spinal Injury Association Impairment Scale A/B; 42±10 years old). INTERVENTIONS: Not applicable. MAIN OUTCOME: VT from a graded arm cycling test to volitional exhaustion using 4 methods: ventilatory equivalents, excess CO₂, V-slope, and combined method. RESULTS: VT could be identified in all individuals with paraplegia, but in only 68% of individuals with tetraplegia. Individuals without observable VT completed the graded exercise test with lower ventilatory rate, peak power output, and peak oxygen consumption (Vo₂peak) (all P<.05), compared to those with a detectable VT. Bland-Altman plots indicate minimal bias between methods (range: 0.01-0.03 L/min), with 95% limits of agreement of the difference within 0.25 L/min. Absolute V.o₂ at VT with individual methods were all correlated to peak power output (r>0.74; P<.01) and Vo₂peak (r>0.91; P<.01), with negligible differences between methods. CONCLUSIONS: The assessment of VT is a feasible alternative to peak exercise testing for aerobic fitness in individuals with higher-level, motor-complete SCI, although care should be taken when interpreting VT in individuals with tetraplegia who have lower cardiorespiratory fitness and lower peak power outputs.