26-05-2012, 02:03 PM
change over time and value as a predictor of survival in severe COPD
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Material and methods
Patients with COPD, referred to the pulmonary departments
at St Elizabeth9s Medical Center and Bay Pines Veterans
Administration Hospital, were prospectively enrolled. The
protocol was approved by the institutional review board of
both hospitals. Primary care physicians referred patients
or pulmonologists to perform pulmonary function tests,
assess their performance status and evaluate requirement
for oxygen therapy during physical activity.
The 6-min walk distance test
Patients completed two 6MWD tests per evaluation of
o30 min apart, following a modified protocol [14, 19]. The
modifications included the use of a 36 m long corridor,
encouragement of the patient, oxygen saturation monitoring
and oxygen provision to the patients whose oxygen saturation
decreased to v85%. The respiratory therapist carried the
oxygen tank. The longest of the two walk distances was used
in analysis. The same respiratory nurse on each site performed
the evaluations during the time span of the study. For all the
patients, the minimal time between two evaluations was 1 yr.
This minimised the possible influence of pulmonary rehabilitation
on the walked distance in the nine patients who enrolled
in pulmonary rehabilitation.
Physiological and anthropometric measurements
Pulmonary function tests were performed following the
ATS standards [22]. Weight and height were measured and
the BMI was calculated. The degree of comorbidity was
assessed using the validated Charlson Index [23].
The Charlson comorbidity index was designed to classify
prognostic comorbidity in longitudinal studies. It has been
used in several studies to stratify patients in order to control
for the confounding influence of comorbid conditions on
overall survival. It combines the risk from age and the risk
from comorbid disease into a single variable, estimating the
risk of death. The conditions have a specific weight. A higher
Charlson comorbidity score indicates an increased severity of
condition and a higher relative risk of death.
Statistical analysis
Descriptive data for continuous variables are presented
as mean¡SD and percentages are presented for categorical
variables. T-tests were used to compare changes between
the baseline and subsequent measurements for each group.
Pearson9s correlation was used to describe the association
between continuous variables. A Chi-squared test was used to
compare the difference in mortality according to the categorised
distance walked.