Peak oxygen uptake and breathing pattern in COPD patients – a four-year longitudinal study

Activities of daily living in patients with chronic obstructive pulmonary disease (COPD) are limited by exertional dyspnea and reduced exercise capacity. The aims of the study were to examine longitudinal changes in peak oxygen uptake (V̇O_2peak), peak minute ventilation (V̇_Epeak) and breathing pattern over four years in a group of COPD patients, and to examine potential explanatory variables of change.

This longitudinal study included 63 COPD patients, aged 44-75 years, with a mean forced expiratory volume in one second (FEV₁) at baseline of 51 % of predicted (SD = 14). The patients performed two cardiopulmonary exercise tests (CPETs) on treadmill 4.5 years apart. The relationship between changes in V̇O_2peak and V̇_Epeak and possible explanatory variables, including dynamic lung volumes and inspiratory capacity (IC), were analysed by multivariate linear regression analysis. The breathing pattern in terms of the relationship between minute ventilation (V̇_E) and tidal volume (V_T) was described by a quadratic equation, V_T = a + b∙V̇_E + c∙V̇_E², for each test. The V_Tmax was calculated from the individual quadratic relationships, and was the point where the first derivative of the quadratic equation was zero. The mean changes in the curve parameters (CPET2 minus CPET1) and V_Tmax were analysed by bivariate and multivariate linear regression analyses with age, sex, height, changes in weight, lung function, IC and inspiratory reserve volume as possible explanatory variables.

Significant reductions in V̇O_2peak (p < 0.001) and V̇_Epeak (p < 0.001) were related to a decrease in resting IC and in FEV₁. Persistent smoking contributed to the reduction in V̇O_2peak. The breathing pattern changed towards a lower V_T at a given V̇_E and was related to the reduction in FEV₁.

Increasing static hyperinflation and increasing airway obstruction were related to a reduction in exercise capacity. The breathing pattern changed towards more shallow breathing, and was related to increasing airway obstruction.