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

• Published in: BMC sports science, medicine & rehabilitation Vol. 9; no. 1; p. 9
• Main Authors: Nishijima, Hirotaka, Kondo, Kazuo, Yonezawa, Kazuya, Hashimoto, Hiroki, Sakurai, Masayuki
• Format: Journal Article
• Language: English
• Published: England BioMed Central 20-04-2017; BMC
• Subjects: Carbon dioxide; CO2 storage; Disease; Exercise tolerance; Fitness training programs; Heart rate; Hospitals; Metabolism; Patients; Rehabilitation; Ventilatory anaerobic threshold; CO2 storage; Ventilatory anaerobic threshold; Exercise tolerance
• ISSN: 2052-1847; 2052-1847
• DOI: 10.1186/s13102-017-0073-1

Ventilatory 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 CO
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).
This 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
 = 1 line and each data point on the V-slope plot to the right of
 = 1 were measured; the average of these measurements was used as an objectively determined estimate of RtShift.
The predominant portion of RtShift occurred earlier than VAT. The mean RtShift was 33.9 ± 25.0 mL⋅min
VO
, whereas the mean VAT was 635 ± 220 mL⋅min
. RtShift positively correlated with VAT (
 = 718,
 < 0.001), confirming previous visual observations. It also significantly correlated with ΔVO
/Δwork rate, a marker of oxygen uptake efficiency (
 = 0.531,
 < 0.001).
We 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.