The six minute walk test accurately estimates mean peak oxygen uptake

<p>Abstract</p> <p>Background</p> <p>Both Peak Oxygen Uptake (peak VO2), from cardiopulmonary exercise testing (CPET) and the distance walked during a Six-Minute Walk Test (6 MWD) are used for following the natural history of various diseases, timing of procedures such as transplantation and for assessing the response to therapeutic interventions. However, their relationship has not been clearly defined.</p> <p>Methods</p> <p>We determined the ability of 6 MWD to predict peak VO2 using data points from 1,083 patients with diverse cardiopulmonary disorders. The patient data came from a study we performed and 10 separate studies where we were able to electronically convert published scattergrams to bivariate points. Using Linear Mixed Model analysis (LMM), we determined what effect factors such as disease entity and different inter-site testing protocols contributed to the magnitude of the standard error of estimate (SEE).</p> <p>Results</p> <p>The LMM analysis found that only 0.16 ml/kg/min or about 4% of the SEE was due to all of the inter-site testing differences. The major source of error is the inherent variability related to the two tests. Therefore, we were able to create a generalized equation that can be used to predict peak VO2 among patients with different diseases, who have undergone various exercise protocols, with minimal loss of accuracy. Although 6 MWD and peak VO2 are significantly correlated, the SEE is unacceptably large for clinical usefulness in an individual patient. For the data as a whole it is 3.82 ml/kg/min or 26.7% of mean peak VO2. Conversely, the SEE for predicting the mean peak VO2 from mean 6 MWD for the 11 study groups is only 1.1 ml/kg/min.</p> <p>Conclusions</p> <p>A generalized equation can be used to predict peak VO2 from 6 MWD. Unfortunately, like other prediction equations, it is of limited usefulness for individual patients. However, the generalized equation can be used to accurately estimate mean peak VO2 from mean 6 MWD, among groups of patients with diverse diseases without the need for cardiopulmonary exercise testing. The equation is:</p> <p><display-formula><graphic file="1471-2466-10-31-i1.gif"/></display-formula></p

Alterations in Adenosine Metabolism and Signaling in Patients with Chronic Obstructive Pulmonary Disease and Idiopathic Pulmonary Fibrosis

Background: Adenosine is generated in response to cellular stress and damage and is elevated in the lungs of patients with chronic lung disease. Adenosine signaling through its cell surface receptors serves as an amplifier of chronic lung disorders, suggesting adenosine-based therapeutics may be beneficial in the treatment of lung diseases such as chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF). Previous studies in mouse models of chronic lung disease demonstrate that the key components of adenosine metabolism and signaling are altered. Changes include an upregulation of CD73, the major enzyme of adenosine production and down-regulation of adenosine deaminase (ADA), the major enzyme for adenosine metabolism. In addition, adenosine receptors are elevated. Methodology/Principal Findings: The focus of this study was to utilize tissues from patients with COPD or IPF to examine whether changes in purinergic metabolism and signaling occur in human disease. Results demonstrate that the levels of CD73 and A2BR are elevated in surgical lung biopsies from severe COPD and IPF patients. Immunolocalization assays revealed abundant expression of CD73 and the A2BR in alternatively activated macrophages in both COPD and IPF samples. In addition, mediators that are regulated by the A 2BR, such as IL-6, IL-8 and osteopontin were elevated in these samples and activation of the A 2BR on cells isolated from the airways of COPD and IPF patients was shown to directly induce the production of these mediators. Conclusions/Significance: These findings suggest that components of adenosine metabolism and signaling are altered in

Expression of CD73 and the A_2BR in M2 macrophages.

<p>Lung sections from COPD or IPF patients were reacted with antibodies against CD73 (A, green) or the A_2BR (B, green) together with the M2 macrophage marker CD206 (red). In the merged images, yellow represents co-localization of CD73 or the A_2BR and the M2 marker, blue is dapi stained nuclei. Sections are representative of 10–14 different patients from each group. Scale bars = 100 µm.</p

Expression of components of adenosine metabolism and signaling.

<p>Transcript levels of various enzymes in adenosine metabolism, and adenosine receptors were quantified in lung RNA extracts from patients using quantitative RT-PCR. Shown are levels of (A) CD73, (B) ADA, (C) AK, (D) ENT1, (E) Adenosine receptors. Results are presented as mean percentage of 18sRNA transcripts ± SEM. *p≤0.05 versus Stage 0 COPD. #p≤0.05 versus Mild IPF. n = 4 (Stage 0 COPD), n = 10 (Mild IPF), n = 8 (Stage 4 COPD and Severe IPF).</p

Key components of adenosine metabolism and signaling.

<p>In response to cellular stress and damage, ATP is released into the extracellular space and is rapidly dephosphorylated by extracelluar nucleotidases. CD73 catalyzes the formation of extracellular adenosine from AMP. Extracellular adenosine can interact with seven-transmembrane adenosine receptors, A₁R, A_2AR, A_2BR, and A₃R, which are coupled by heterotrimeric G proteins to various second messenger systems, or it can be transported into cells via facilitated nucleoside transporters, such as ENT1. Both extracellular and intracellular adenosine can be deaminated to inosine by adenosine deaminase (ADA). Intracellular adenosine can be secreted or phosphorylated back to ATP. The first step in this process is catalyzed by adenosine kinase (AK).</p

A_2BR-dependent IL-8 and IL-6 expression in human primary alveolar macrophages.

<p>(A) Cells from an IPF patient were reacted with antibodies against CD73 (A, <i>upper panel</i>, green) or the A_2BR (A, <i>lower panel</i>, green) together with the M2 macrophage marker CD206 (red). In the merged images, yellow represents co-localization of CD73 or the A_2BR and the M2 marker, blue is dapi stained nuclei. (B) ELISA measurements of IL-8 and IL-6 production from macrophage cultures of IPF and COPD patients. Results are presented as mean concentrations of cytokines ± SEM. *p≤0.05 versus cells without any treatment. ^#p≤0.05 versus cells treated with NECA alone. n = 6.</p

Expression of pro-inflammatory mediators.

<p>Transcript levels of various cytokines and chemokines were quantified in lung RNA extracts from patients using quantitative RT-PCR. Shown are levels of (A) IL-6, (B) IL-8, (C) OPN. Results are presented as mean percentage of 18sRNA transcripts ± SEM. *p≤0.05 versus Stage 0 COPD. #p≤0.05 versus Mild IPF. n = 4 (Stage 0 COPD), n = 10 (Mild IPF), n = 8 (Stage 4 COPD and Severe IPF).</p

CD73 and ADA enzymatic activity.

<p>CD73 (A) and ADA (B) enzyme activity were quantified in lung protein extracts from patients. Reaction mixtures were separated, identified, and quantified by HPLC. Data are presented as mean nanomoles of substrate converted to product per min per milligram of protein ± SEM. *p≤0.05 versus Stage 0 COPD. #p≤0.05 versus Mild IPF. n = 4 (Stage 0 COPD), n = 10 (Mild IPF), n = 8 (Stage 4 COPD and Severe IPF).</p

Localization of the A_2BR.

<p>Lung sections were stained with antibodies against the A_2BR. (A) Lung section from a Stage 0 COPD patient. (B) Lung section from a Mild IPF patient. (C) Lung section from a Stage 4 COPD patient. (D) Lung section from a Severe IPF patient. Sections are representative of 10–14 different patients from each group. Scale bars = 100 µm. (E) A_2BR positive inflammatory cells were quantified in 20 images. Data are presented as mean number of positive cells per 10X field ± SEM. *p≤0.05 versus Stage 0 COPD. #p≤0.05 versus Mild IPF. n = 4 (Stage 0 COPD), n = 10 (Mild IPF), n = 8 (Stage 4 COPD and Severe IPF). (F) A_2BR expression in hyperplastic airway epithelial cells (blue arrow) and fibroblasts (red asterix). Scale bar = 200 µm.</p

Study population.

<p>Data are presented as median (interquartile range). M/F: male/female; FEV1: forced expiratory volume in one second; % pred: % predicted; FVC: forced vital capacity. ¹: Stage 0 COPD is defined as FEV1, % pred >80; ²: Mild IPF is defined as FVC, % pred >80; ³: Stage 4 COPD is defined as FEV1, % pred <50; ⁴: Severe IPF is defined as FVC, % pred <50; ^a: data available for 3/4 Stage 0 COPD patients; ^b: data available for 5/10 Mild IPF patients;^c: data available for 9/10 Stage 4 COPD patients;^d: data available for 4/10 Severe IPF patients;^e: data available for 9/10 Mild or Severe IPF patients. *: p<0.05 compared with Stage 0 COPD patients; ^#: p<0.05 compared with Mild IPF patients.</p