Dynamic physiological responses in obese and non-obese adults submitted to cardiopulmonary exercise test

Abstract

Purpose: Obese individuals have reduced performance in cardiopulmonary exercise testing (CPET), mainly considering peak values of variables such as oxygen uptake ([Formula: see text]), carbon dioxide production ([Formula: see text]), tidal volume (Vt), minute ventilation ([Formula: see text]) and heart rate (HR). The CPET interpretation and prognostic value can be improved through submaximal ratios analysis of key variables like [Formula: see text], [Formula: see text], [Formula: see text] [Formula: see text] and oxygen uptake efficiency slope (OUES). The obesity influence on these responses has not yet been investigated. Our purpose was to evaluate the influence of adulthood obesity on maximal and submaximal physiological responses during CPET, emphasizing the analysis of submaximal dynamic variables.

Methods: We analyzed 1,594 CPETs of adults (755 obese participants, Body Mass Index ≥ 30 kg/m2) and compared the obtained variables among non-obese (normal weight and overweight) and obese groups (obesity classes I, II and III) through multivariate covariance analyses.

Result: Obesity influenced the majority of evaluated maximal and submaximal responses with worsened CPET performance. Cardiovascular, metabolic and gas exchange variables were the most influenced by obesity. Other maximal and submaximal responses were altered only in morbidly obese. Only a few cardiovascular and ventilatory variables presented inconsistent results. Additionally, Vtmax, [Formula: see text], Vt/Inspiratory Capacity, Vt/Forced Vital Capacity, Lowest [Formula: see text], [Formula: see text], and the y-intercepts of [Formula: see text] did not significantly differ regardless of obesity.

Conclusion: Obesity expressively influences the majority of CPET variables. However, the prognostic values of the main ventilatory efficiency responses remain unchanged. These dynamic responses are not dependent on maximum effort and may be useful in detecting incipient ventilatory disorder. Our results present great practical applicability in identifying exercise limitation, regardless of overweight and obesity.

Fig 1. Procedure used to establish the dynamic physiological responses.

(A) Cardiovascular efficiency ($\mathrm{\Delta HR}/\mathrm{\Delta }\dot{V}{\mathrm{O}}_2$). (B) Ventilatory efficiency ($\mathrm{\Delta }\dot{V}\mathrm{E}/\mathrm{\Delta }\dot{V}\mathrm{C}{\mathrm{O}}_2$). (C) Oxygen uptake efficiency slope ($\mathrm{\Delta }\dot{V}{\mathrm{O}}_2/\mathrm{\Delta log}\dot{V}\mathrm{E}$). (D) Ventilatory pattern ($\mathrm{\Delta Vt}/\mathrm{\Delta ln}\dot{V}\mathrm{E}$).

Fig 2. Flowchart.

Fig 3. Differences in obesity-related physiological responses in the cardiopulmonary exercise test obtained by using multivariate analysis of variance (n = 1,594).

^a p ≤ 0.05 vs. Normal weight; ^b: p ≤ 0.05 vs. Overweight; ^c: p ≤ 0.05 vs. Obesity Class I; ^d p ≤ 0.05 vs. Obesity Class II; and ^e p ≤ 0.05 vs. Obesity Class III. N: normal weight; O: overweight. (A) graphical representation of respiratory pattern; (B) graphical representation of y intercept of respiratory pattern; (C) graphical representation of cardiovascular efficiency; (D) graphical representation of y intercept of cardiovascular efficiency; (E) graphical representation of respiratory efficiency; (F) graphical representation of y intercept of respiratory efficiency. Models adjusted for age, sex, arterial hypertension, diabetes, dyslipidemia, and physical inactivity through self-report. $\dot{V}{\mathrm{O}}_2$: pulmonary oxygen uptake; $\dot{V}\mathrm{C}{\mathrm{O}}_2$: carbon dioxide production; $\dot{V}\mathrm{E}$: minute ventilation; Vt: tidal volume; Rf: respiratory frequency; HR: heart rate; bpm: beat per minute; $\ln \dot{V}\mathrm{E}$: linearized ventilation; OUES: oxygen uptake efficiency slope.