Abstract 9157: Rightward Shift Of V-slope In Cardiopulmonary Exercise Testing (CPX) As A Marker Of Increased Exercise Tolerance

Abstract

INTRODUCTION: A new method to detect change in exercise tolerance is presented. It is based on our observation that rightward shift of the v-slope relative to the R=1 line, due to exercise-induced increased tissue CO2 store, correlated with increased anaerobic threshold (AT) and VO2 max.

METHODS: The records of 166 patients who underwent CPX during cardiac rehabilitation (CR, 3-6 months) were retrospectively reviewed. The mean age was 64(SD:11) with 143 males and 23 females. The underlying heart disease was ischemic. CPX using upright bicycle was submaximal, mostly terminated with the appearance of AT. CR was hospital (mean 3.1 visits/month) and home based. The mean time between the 1st and 2nd tests was 135(29) days. AT was determined blind by an experienced evaluator. Pre and post CR v-slope data sets were plotted together. Exercise data points in the pre-post shared range were selected. Each v-slope was regressed for the quadratic equation. At the y-axis mid-point (line A-B) the distance between R=1 and each regression line was read off (Rightward Shift: RS, ml/min VO2).

RESULTS: The changes in basic exercise variables were as follows: highest HR (b/min), from 111(22) to 117(18) (ns); highest VO2 (ml/min/kg), 14.6(3.5) to 17.0(4.1) (p<0.001), and body weight (kg), 66.1(10.9) to 66.7 (10.9)(p<0.006). AT (ml/min VO2) increased from 670(217) to 721(251) (p<0.0004). RS increased from 35(61) to 49(60) (p<0.0003). Also, the baseline RS significantly correlated with AT (r=0.68, p<0.001).

CONCLUSION: A completely new method to detect changes in exercise tolerance is described. It calculates a shift in 2 v-slopes. At baseline the degree of rightward shift was associated with an increase in AT. After cardiac rehabilitation v-slope shifted further rightwards as AT increased. The shift method was as sensitive as AT to detect changes in exercise tolerance. There is no need for maximal exercise or an evaluator to read a v-slope. The procedure can be automated.