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. 2020 Dec;52(12):2515-2521.
doi: 10.1249/MSS.0000000000002417.

Reference Values for Chronotropic Index from 1280 Incremental Cycle Ergometry Tests

Worawan Sirichana, Eric V Neufeld  1 , Xiaoyan Wang  2 , Scott B Hu  1 , Brett A Dolezal  1 , Christopher B Cooper  1
Affiliations

Reference Values for Chronotropic Index from 1280 Incremental Cycle Ergometry Tests

Worawan Sirichana et al. Med Sci Sports Exerc. 2020 Dec.

Abstract

Purpose: Clinical cardiopulmonary exercise testing can determine causes of exercise limitation. The slope of heart rate (fC) versus oxygen uptake (V˙O2), which we call the chronotropic index (CI), can help identify cardiovascular impairment. We aimed to develop a reference equation for CI based on a large number of subjects considered to have normal exercise responses.

Methods: From a database of 13,728 incremental cycle ergometry exercise tests, we identified 1280 normal tests based on the absence of a clinical diagnosis, normal body mass index, and normal aerobic performance plus absence of cardiovascular disease, medications, or ventilatory limitation. A linear mixed-model approach was used to analyze the relationship between CI and other variables.

Results: Subjects were age 18-84 yr, and 693 (54.1%) were men. Mean ± SD CI in men was lower than in women, 41.2 ± 9.3 beats per liter versus 63.4 ± 15.7 L. Age (in years), sex (0, male; 1, female), height (in centimeters), and weight (in kilograms) were significant predictors for CI:CIi = 106.9 + 0.16 × agei + 14.3 × sexi - 0.31 × heighti - 0.24 × weighti. The SE of estimates ranged from 10.6 to 11.2 L (median of 10.7 L).

Conclusions: We report a reference equation for CI derived from normal subjects. The CI can be used in conjunction with V˙O2max to interpret maximal cardiopulmonary exercise tests. We consider a high CI to be cardiovascular impairment and a low CI plus low V˙O2max to be chronotropic insufficiency.

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Comment in

  • Incorrect Terminology Confuses Article's Purpose and Usefulness.
    Zavorsky GS. Zavorsky GS. Med Sci Sports Exerc. 2021 Jun 1;53(6):1315. doi: 10.1249/MSS.0000000000002650. Med Sci Sports Exerc. 2021. PMID: 33986232 No abstract available.
  • Response.
    Sirichana W, Neufeld EV, Wang X, Hu SB, Dolezal BA, Cooper CB. Sirichana W, et al. Med Sci Sports Exerc. 2021 Jun 1;53(6):1316. doi: 10.1249/MSS.0000000000002651. Med Sci Sports Exerc. 2021. PMID: 33986233 No abstract available.

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