Quantification and physiological significance of the rightward shift of the V-slope during incremental cardiopulmonary exercise testing

Abstract

BackgroundVentilatory anaerobic threshold (VAT) is frequently used as a measure of exercise tolerance, with the V-slope method being the standard; however, this needs to be visually determined. Over the years, we have observed that the V-slope itself often appears to shift rightward before the appearance of the VAT (RtShift: rightward shift of V-slope). This phenomenon has long been known to occur during the first 1–2 min of steady-state exercise and disappears thereafter; it is attributed to CO2 storage, presumably in active muscle. However, during incremental exercise, we have observed that the RtShift persists; furthermore, it seems to be related to the level of VAT. Therefore, we attempted to objectively quantify the RtShift, and to confirm its relationship to an index of exercise tolerance (VAT).MethodsThis study was based on a retrospective analysis of data from 100 cardiopulmonary ramp exercise tests (submaximal) performed by patients with cardiac disease. VAT was determined with the visual V-slope method. The horizontal distances between the diagonal R = 1 line and each data point on the V-slope plot to the right of R = 1 were measured; the average of these measurements was used as an objectively determined estimate of RtShift.ResultsThe predominant portion of RtShift occurred earlier than VAT. The mean RtShift was 33.9 ± 25.0 mL⋅min−1 VO2, whereas the mean VAT was 635 ± 220 mL⋅min−1. RtShift positively correlated with VAT (r = 718, p < 0.001), confirming previous visual observations. It also significantly correlated with ΔVO2/Δwork rate, a marker of oxygen uptake efficiency (r = 0.531, p < 0.001).ConclusionsWe identified that among patients with cardiac disease, V-slope is shifted rightward to varying degrees. The objectively quantified rightward shift of V-slope is significantly correlated with an index of exercise tolerance (VAT). Furthermore, it appears to occur at even lower work rates. This may offer a new objective means of estimating exercise tolerance; however, its exact biological basis still needs to be elucidated.Electronic supplementary materialThe online version of this article (doi:10.1186/s13102-017-0073-1) contains supplementary material, which is available to authorized users.

Constant Load Exercise at Gas Exchange Threshold is Accompanied by a Distinct Elevation in Blood Lactate Level

“…The GET was visually determined using the modi ed V-slope method, as described by Sue et al [10], which is a modi cation of the method described by Beaver et al [11]. The details of this method as practiced by us have been published previously [12,13]. In summary, this V-slope method (Fig.…”

“…This method xes the pre-GET slope as the baseline, making it easy to see a de ection. At the inception of Inc-Ex, the carbon dioxide production (VCO 2 ) increase in the blood and at the mouth is delayed against the VO 2 increase because of a larger CO 2 tissue storage capacity [12]. Therefore, the Vslope itself is shifted to the right [12].…”

“…At the inception of Inc-Ex, the carbon dioxide production (VCO 2 ) increase in the blood and at the mouth is delayed against the VO 2 increase because of a larger CO 2 tissue storage capacity [12]. Therefore, the Vslope itself is shifted to the right [12]. A line drawn parallel to the RER = 1 diagonal signi es a change in the rate of (delta VCO 2 /delta VO 2 ) of 1.0, in contrast to the conventionally calculated RER (simple division of moment-to-moment VCO 2 by VO 2 ) ( Fig.…”

“…The point at which this index begins to increase above 1.0 is the GET de ection point. A baseline representing a constant rate of change of 1.0 is often readily visible during the early stage of ramp exercise [12,13]. References 12 and 13 include as supplemental material readings of the GET for each case analyzed in each study.…”

“…Boehringer Ingelheim, Gaithersburg, MD) was applied to three ngers of the left hand (2nd, 3rd, and 4th ). After 10 min, the cream was removed and the entire left hand, including the distal part of the forearm, was placed in a water bath at 43-45 °C for 10 min [3,14]. BLa levels were determined using Lactate Pro LT-1730 (Arkray, Kyoto, Japan).…”