Greater exercise tolerance in COPD during acute interval, compared to equivalent constant‐load, cycle exercise: physiological mechanisms

Louvaris, Zafeiris, Chynkiamis, Nikolaos, Spetsioti, Stavroula, Asimakos, Andreas, Zakynthinos, Spyros, Wagner, Peter D. and Vogiatzis, Ioannis (2020) Greater exercise tolerance in COPD during acute interval, compared to equivalent constant‐load, cycle exercise: physiological mechanisms. Journal of Physiology, 598 (17). pp. 3613-3629. ISSN 0022-3751

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Official URL: https://doi.org/10.1113/JP279531

Abstract

The relative importance of ventilatory, circulatory and peripheral muscle factors in determining tolerance to exercise in patients with COPD is not known. In twelve COPD patients (FEV1 :58 ± 17%pred.) we measured ventilation, cardiac output, dynamic hyperinflation, local muscle oxygenation, blood lactate and time to exhaustion during a) interval exercise (IE) consisting of 30 s at 100% peak work-rate alternated with 30 s at 50% and b) constant load exercise (CLE) at 75% WRpeak, designed to produce the same average work rate. Exercise time was substantially longer during IE than CLE (19.5 ± 4.8 versus 11.4 ± 2.1 min, p = 0.0001). Total work output was therefore greater during IE than CLE (81.3 ± 27.7 versus 48.9 ± 23.8 kJ, p = 0.0001). Dynamic hyperinflation (assessed by changes from baseline in inspiratory capacity-ΔIC) was less during IE than CLE at CLE exhaustion time (isotime, p = 0.009), but was similar at exhaustion (ΔICCLE : -0.38 ± 0.10 versus ΔICIE : -0.33 ± 0.12 l, p = 0.102). In contrast, at isotime, minute ventilation, cardiac output and systemic oxygen delivery did not differ between protocols (p>0.05). At exhaustion in both protocols, vastus lateralis and intercostal muscle oxygen saturation were higher in IE than CLE (p = 0.014 and p = 0.0002, respectively) and blood lactate concentrations were lower (4.9 ± 2.4 mmol/l versus 6.4 ± 2.2 mmol/l, p = 0.039). These results suggest that 1) exercise tolerance in COPD is limited by dynamic hyperinflation; and 2) cyclically lower (50%) effort intervals in IE help preserve muscle oxygenation and reduce metabolic acidosis compared to CLE at the same average work rate, but these factors do not appear to determine time to exhaustion.

Item Type: Article
Uncontrolled Keywords: cardiac output, COPD, exercise, limb muscles, NIRS. respiratory muscles
Subjects: B100 Anatomy, Physiology and Pathology
C600 Sports Science
Department: Faculties > Health and Life Sciences > Sport, Exercise and Rehabilitation
Depositing User: Rachel Branson
Date Deposited: 16 Jun 2020 12:56
Last Modified: 17 Sep 2020 14:45
URI: http://nrl.northumbria.ac.uk/id/eprint/43474

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