OXYGEN PULSE PREDICTS STROKE VOLUME DURING WHEELCHAIR RACING IN TRAINED MALES WITH QUADRIPLEGIA 484

Abstract

Oxygen pulse (O2 pulse), which is defined as the oxygen utilization per heart beat, is calculated as the product of cardiac stroke volume (SV) and mixed arteriovenous oxygen difference {(a-v)O2diff)}. The purpose of this study was to examine the inter-relationship among these variables during wheelchair racing in subjects with quadriplegia. Eight trained males (4 Class 1A, 2 Class 1B and 2 Class 1C, mean age = 31.8 ± 6.9 yr, peak VO2 = 19.8 ± 4.3 ml/kg/min) completed a 7.5km simulated wheelchair roller race in their personal racing wheelchairs. Cardiorespiratory and metabolic measurements were continuously monitored throughout the test. Cardiac output (Q) was measured by CO2 rebreathing at 3km and 6km of the race, from which SV and (a-v)O2diff were calculated. Reliability coefficients for the VO2, Q, HR, SV, and (a-v)O2diff between the two race stages were O.93, 0.91, 0.94, 0.92, and 0.87 respectively (p<.01). No significant differences (P>.05) were observed between the means for each of these variables at the two stages. At each stage of the race, O2 pulse was significantly related to the SV (0.84 and 0.88, P<.01) but not to the (a-v)O2diff (P>.05). As well, no significant correlations (-0.27 and -0.14 respectively, P>.05) were observed between SV and(a-v)O2diff. The regression equation for predicting SV from O2 pulse using the pooled means of the two race stages was: Y = 10.98X - 23.8, SEE = 12.1. These observations indicate that O2 pulse is a valid predictor of SV during wheelchair exercise in trained subjects with quadriplegia.