Metabolic Testing During Overground Exoskeleton Assisted Walking After Chronic Spinal Cord Injury

HISTORY: A 28-year-old male (BMI 16.7) 12 years post complete (AIS A) spinal cord injury (SCI) at C5-C6 presented to an outpatient rehabilitation program to participate in his third overground exoskeleton assisted walking (EAW) session. Physical Exam: He presented with decreased bilateral lower extremity passive range of motion [hip extension = 10 degrees, knee extension = 0, dorsiflexion = 0] and strength [biceps = 3/5, triceps = 0/5, lower extremity muscle groups = 0/5] with minimally increased spasticity [Modified Ashworth Scale = 1]. He required minimal assist for level surface transfers, was independent with power assist manual wheelchair mobility, and demonstrated intact skin integrity and cognitive function. He reported participating in a standing program with a standing frame 1-2x/week. DIFFERENTIAL DIAGNOSIS Deconditioning TESTS AND RESULTS Autonomic dysfunction and the non-linear relationship between heart rate (HR) and oxygen consumption (VO2) with cervical SCI suggests HR alone may be inadequate to estimate exercise intensity (EI). Metabolic testing was indicated in addition to HR to measure EI during EAW. The participant completed a single EAW session [up time 37.65 min, walk time 28.9 min, step count 1,047 (0.76 km)] with a HR monitor and portable metabolic cart. Reduced pulmonary capacity was observed at rest and exercise. Peak HR (133 bpm) reached 70% of age-predicted and mean HR (112 bpm) reached 60% age-predicted throughout, consistent with moderate EI. However, VO2 was reduced (7.7 mL/min/kg at peak and 6.23 mL/min/kg on average) achieving light EI when adjusted for SCI (2.3-2.9 METs). FINAL/WORKING DIAGNOSIS Cardiopulmonary impairment TREATMENT AND OUTCOMES The EAW session was tolerated well and no adverse responses to exercise were observed. The discrepancy between EI measured by HR (moderate) and METs (light) may be partially explained by the significant loss of fat free mass over time reducing VO2 and reduced sympathetic cardiac innervation associated with cervical SCI. This population is at high risk for developing chronic health conditions related to insufficient levels of activity and this case supports the use of direct metabolic testing concurrent with HR to accurately prescribe EI recommendations.