Exercise capacity and breathing pattern in patients with chronic obstructive pulmonary disease. Predictors and longitudinal changes

<p>Chronic obstructive pulmonary disease (COPD) is a progressive lung disease
characterized by expiratory flow limitation. The knowledge about factors contributing
to the long-term changes in exercise capacity and breathing pattern in terms of the
relationship between tidal volume (VT) and minute ventilation (V̇ E) in COPD is
scarce. This thesis deals with issues related to long-term changes in exercise capacity
and breathing pattern in COPD and potential predictors for the changes. The thesis is
based on three studies.</p>
<p>Study I was a 3-years prospective cohort study, including 389 patients with COPD in
Global Initiative for Chronic Obstructive Lung Disease (GOLD) stages II-IV. We
examined predictors for the longitudinal change in six-minute walking distance
(6MWD). Study II was a cross-sectional study, including 63 COPD patients
performing a cardiopulmonary exercise test (CPET) on treadmill. We aimed to study
if a quadratic equation (VT = a + b·V̇ E + c· V̇ E
2) could describe the breathing pattern
in terms of the relationship between V̇ E and VT during incremental exercise in COPD.
Study III was a longitudinal cohort study, were the 63 COPD patients performed two
CPETs with a mean time of 4.5 years between the tests. The longitudinal changes in
peak oxygen uptake (V̇O2peak) and breathing pattern as well as potential explanatory
variables of change were examined.</p>
<p>The 6MWD decreased significantly during the observation period in GOLD stage III
(B= −36, 95 % Confidence Interval (CI): -51 to -7, p=0.009) and IV (B= −79, 95 %
CI: −125 to −20, p=0.007), while patients in GOLD stage II maintained their walking
distance. Predictors for the longitudinal change in 6MWD were self-reported hard
physical activity and FEV1. The fraction of subjects performing hard physical activity
at three years was higher in those who had participated in a pulmonary rehabilitation
program during the observation period, odds ratio 2.4 (95 % CI 1.4−4.2, p=0.001).</p>
<p>In Study II we found that a quadratic model could describe the relationship between
V̇
E and VT in 59 of 63 COPD patients (p&lt;0.05) and the linear coefficient (b) was
negatively (p=0.001) and the quadratic coefficient (c) positively (p&lt;0.001) related to
FEV1.</p>
<p>In Study III, V̇O2peak and FEV1 deteriorated significantly during follow-up. The
reduction in V̇O2peak was related to baseline V̇O2peak (p&lt;0.001), the changes in resting
inspiratory capacity (IC) (p=0.005) and FEV1 (p=0.031), age (p=0.023) and smoking
during follow-up (p=0.021). A higher baseline V̇O2peak, a larger decrease in IC and
FEV1 and higher age were associated with a larger reduction in V̇O2peak. The
quadratic model described the relationship between V̇ E and VT in 61 of 63 patients at
CPET1 and at 59 of 63 patients at CPET2. The linear coefficient (b) increased
(p=0.007) and the quadratic coefficient decreased significantly (p=0.002) from
CPET1 to CPET2. Maximal VT was achieved at a lower V̇ E. The changes in the curve
parameters were all related to the change in FEV1.</p>
<p>We have concluded that exercise capacity deteriorates over time in COPD, and that
the longitudinal change is related to the decline in lung function. Persistent smoking is
associated with a larger decline, while high habitual physical activity is associated
with a lower decline in exercise capacity. The longitudinal change in breathing pattern
is associated with the reduction in lung function. Any relationships between
exertional dyspnea and changes in breathing pattern need further studies.</p