Improvements in Aerobic Fitness are Correlated with Enhanced Cerebral Hemodynamics in Traumatic Brain Injured Patients

Abstract

Recent evidence has indicated that circuit training is effective in improving the peak cardiorespriatory fitness of patients with traumatic brain injury (TBI). However, it is not known whether these improvements enhance cerebral activation during exercise. Near infrared spectroscopy (NIRS) has been used as a diagnostic tool to evaluate regional changes in cerebral oxygenation (Cox) and blood volume (Cbv) responses in patients with severe TBI. PURPOSE: The purpose of this study was to examine the: (1) effects of circuit training on the peak values of the power output, oxygen uptake and Cox/Cbv responses in patients with moderate to severe TBI, and (2) interrelationship PMong the changes in these variables following training. METHODS: Fourteen in-patients with acquired TBI (Glasgow Coma Scale = 4.6 ± 1.4; time since injury = 17.2 ± 17 months) completed an average of 32 supervised circuit training sessions over 12 weeks. Training included exercises to improve muscle strength and endurance of the major muscle groups as well as aerobic fitness. During the aerobic phase, heart rate was maintained at 60% of the heart rate reserve calculated from the pre-training symptom limited incremental exercise test to volitional fatigue. Cox and Cbv were monitored from the left frontal lobe during the symptom limited tests using a dual wave near infrared spectrometer (MicroRunman, NIM Inc., PA). RESULTS: Training induced significant increases (p<.05) in the peak values of the power output (68.2 ± 50.1 to 99.2 ± 56.0 Watts), absolute oxygen uptake (1.29 ± 0.64 to 1.70 ± 0.80 L/min), relative oxygen uptake (17.3 ± 4.9 to 22.2 ± 7.4 ml/kg/min), Cox (0.023 ± 0.026 to 0.031 ± 0.073 OD units) and Cbv (0.073 ± 0.088 to 0.111 ± 0.109 OD units). Eight of the 14 patients showed increases in Cox and Cbv whereas in the remainder these variables were unchanged or showed a small decline. No significant correlations (p>.05) were observed between the NIRS and the exercise performance variables pre or post training. However, when the delta (post - pre) values were calculated for these variables, significant correlations (p<.05) were observed between absolute VO2 and: Cox (r2 = 0.56), Cbv (r2 = 0.57); relative VO2 and: Cox (r2 = 0.57), Cbv (r2 = 0.40). No significant correlations (p>.05) were observed between the delta values of the peak power output and Cox (r2 = 0.11) and Cbv (r2 = 0.08) following training. CONCLUSION: The improvement in aerobic fitness as a result of circuit training was associated with enhanced cerebral hemodynamics in patients with moderate to severe TBI. Funding: Alberta Heritage Foundation for Medical Research - Health Research Fund