Haemodynamic compensations for exercise tissue oxygenation in early stages of COPD: an integrated cardiorespiratory assessment study

Abstract

Background: Cardiovascular comorbidities are increasingly being recognised in early stages of chronic obstructive pulmonary disease (COPD) yet complete cardiorespiratory functional assessments of individuals with mild COPD or presenting with COPD risk factors are lacking. This paper reports on the effectiveness of the cardiocirculatory-limb muscles oxygen delivery and utilisation axis in smokers exhibiting no, or mild to moderate degrees of airflow obstruction using standardised cardiopulmonary exercise testing (CPET).

Methods: Post-bronchodilator spirometry was used to classify participants as 'ever smokers without' (n=88), with 'mild' (n=63) or 'mild-moderate' COPD (n=56). All underwent CPET with continuous concurrent monitoring of oxygen uptake (V'O₂) and of bioimpedance cardiac output (Qc) enabling computation of arteriovenous differences (a-vO₂). Mean values of Qc and a-vO₂ were mapped across set ranges of V'O₂ and Qc isolines to allow for meaningful group comparisons, at same metabolic and circulatory requirements.

Results: Peak exercise capacity was significantly reduced in the 'mild-moderate COPD' as compared with the two other groups who showed similar pulmonary function and exercise capacity. Self-reported cardiovascular and skeletal muscle comorbidities were not different between groups, yet disease impact and exercise intolerance scores were three times higher in the 'mild-moderate COPD' compared with the other groups. Mapping of exercise Qc and a-vO₂ also showed a leftward shift of values in this group, indicative of a deficit in peripheral O₂ extraction even for submaximal exercise demands. Concurrent with lung hyperinflation, a distinctive blunting of exercise stroke volume expansion was also observed in this group.

Conclusion: Contrary to the traditional view that cardiovascular complications were the hallmark of advanced disease, this study of early COPD spectrum showed a reduced exercise O₂ delivery and utilisation in individuals meeting spirometry criteria for stage II COPD. These findings reinforce the preventive clinical management approach to preserve peripheral muscle circulatory and oxidative capacities.

Keywords: Exercise; Pulmonary Disease, Chronic Obstructive; Respiratory Measurement.

Figure 1

Exercise-induced adjustments in Qc and systemic oxygen extraction across V’O2 isolines through near maximal cardiopulmonary exercise testing. Values are group means of Qc and a-vO2 ± their respective SEM. *Significant (p<0.05) difference in the Qc/a-vO₂ kinetics between the GOLD 2 COPD and the other groups. The boxed graph shows group mean values taken at the 1.5 L·min⁻¹ VO₂ isolines for a-vO₂ (upper) and Qc (lower). a-vO₂, systemic arterio-venous oxygen difference; GOLD, Global Initiative for Obstructive Lung Disease; Qc, cardiac output; V’O₂, rate of oxygen consumption.

Figure 2

Exercise-induced adjustments in Hr and SV across Qc isolines through near maximal cardiopulmonary exercise testing. Values are group means of Hr and SV ± their respective SEM. A leftward shift in the Hr×SV combination is seen for the GOLD 2 group resulting in a lower SV measured at the exercise endpoint. GOLD, Global Initiative for Obstructive Lung Disease; Hr, heart rate; Qc, cardiac output; SV, stroke volume.

Figure 3

Exercise-induced responses in V_T and in IC with respect to exercise-induced V’E responses. Values are mean±SEM. Significant differences between the GOLD 2 chronic obstructive pulmonary disease and the other two groups are shown for the exercise-induced changes to peak exercise in IC and in V_T. GOLD, Global Initiative for Obstructive Lung Disease; IC, inspiratory capacity; SV, stroke volume; VE, ventilation; V_T, tidal volume.

Figure 4

Concurrent cardiopulmonary exercise testing induced responses in SV and IC. Values are mean±SEM. Top bars indicates a significant (**p<0.001) difference in response curve between the GOLD 2 chronic obstructive pulmonary disease group and the two others. GOLD, Global Initiative for Obstructive Lung Disease; IC, inspiratory capacity; SV, stroke volume; V_T, tidal volume.