Optimal cardiorespiratory point of individuals with spinal cord injury

Abstract

Introduction: Spinal cord injury (SCI) is related to low cardiorespiratory fitness, which in turn increases the risk of cardiovascular morbidity and mortality. The maximum oxygen consumption (VO2max) is the variable that best describes the cardiorespiratory fitness of individuals, however, in individuals with functional limitations, obtaining it is not always possible due to early interruption of effort. Therefore, the analysis of variables in submaximal effort intensity can be advantageous and is necessary, such as the optimal cardiorespiratory point (POC), which is defined by the moment when the lowest value of the ventilatory equivalent is registered. Objective: The aim of the present study was to describe the exercise cardiorespiratory fitness, especially the POC, of individuals with high and low SCI and to compare them with individuals without SCI. Methods: Cross-sectional observational study with the participation of individuals with incomplete high SCI (from the fourth to the seventh cervical vertebra; TETRA group; n=09), complete low SCI (first thoracic vertebra to second lumbar vertebra; PARA group; n=08) and without SCI (n=10). Cardiorespiratory fitness was assessed by performing a progressive CPET on a cycle ergometer for upper limbs. Moments considered: Peak exercise, ventilatory threshold 1 (VT1) and POC. Results: Individuals with SCI had lower exercise tolerance and lower peak VO2 (TETRA = 0.8 (0.4 – 0.9) L/min; PARA = 1.2 (0.9 – 2.3) L /min) compared to individuals without SCI (peak VO2 = 2.9 (1.7 - 3.7) L/min), although all groups reached the end of exercise equally with a greater contribution of anaerobic metabolism in the energy production process (mean R of groups ≥1; P=0.725). Regarding the analyzes in submaximal effort intensities, the individuals with tetraplegia reached the maximum ventilatory efficiency, that is, the POC in higher percentages of the peak VO2, as well as the VT1. This difference was observed both in comparison to individuals with paraplegia and in relation to those without SCI. Conclusion: Individuals with SCI have lower cardiorespiratory fitness at different effort intensities than individuals without SCI. Specifically in relation to the POC, the higher the SCI height/level, the greater the ventilation for oxygen uptake and subsequent transport and delivery to active muscles during exercise.