Correlation of a decline in aerobic capacity with development of emphysema in patients with chronic obstructive pulmonary disease: a prospective observational study

Diaphragm dome height on chest radiography as a predictor of dynamic lung hyperinflation in COPD

Background and objective

Dynamic lung hyperinflation (DLH) can play a central role in exertional dyspnoea in patients with COPD. Chest radiography is the basic tool for assessing static lung hyperinflation in COPD. However, the predictive capacity of DLH using chest radiography remains unknown. This study was conducted to determine whether DLH can be predicted by measuring the height of the right diaphragm (dome height) on chest radiography.

Methods

This single-centre, retrospective cohort study included patients with stable COPD with pulmonary function test, cardiopulmonary exercise test, constant load test and pulmonary images. They were divided into two groups according to the median of changes of inspiratory capacity (ΔIC=IC lowest - IC at rest). The right diaphragm dome height and lung height were measured on plain chest radiography.

Results

Of the 48 patients included, 24 were classified as having higher DLH (ΔIC ≤-0.59 L from rest; -0.59 L, median of all) and 24 as having lower DLH. Dome height correlated with ΔIC (r=0.66, p<0.001). Multivariate analysis revealed that dome height was associated with higher DLH independent of % low attenuation area on chest computed tomography and forced expiratory volume in 1 s (FEV₁) % predicted. Furthermore, the area under the receiver operating characteristic curve of dome height to predict higher DLH was 0.86, with sensitivity and specificity of 83% and 75%, respectively, at a cut-off of 20.5 mm. Lung height was unrelated to ΔIC.

Conclusion

Diaphragm dome height on chest radiography may adequately predict higher DLH in patients with COPD.

Resting Dead Space Fraction as Related to Clinical Characteristics, Lung Function, and Gas Exchange in Male Patients with Chronic Obstructive Pulmonary Disease

Background

Measures of forced expired volume in one second % predicted (FEV₁%), residual volume to total lung capacity ratio (RV/TLC) and diffusing capacity for carbon monoxide measurements (D_LCO) are the standard lung function test for evaluating patients with chronic obstructive pulmonary disease (COPD). The dead space fraction (V_D/V_T) has been shown to be a robust marker of gas exchange abnormality. However, the use of V_D/V_T has gradually become less common. As V_D/V_T measured at rest (V_D/V_TR) has been successfully used in non-COPD conditions, it was hypothesized that in COPD the V_D/V_TR was more sensitive than the standard lung function test in correlation with clinical characteristics and gas exchange. This study aimed to test the hypothesis and to identify the variables relevant to V_D/V_TR.

Methods

A total of 46 male subjects with COPD were enrolled. Clinical characteristics included demographic data, oxygen-cost diagram (OCD), and image studies for pulmonary hypertension. The standard lung function was obtained. To calculate V_D/V_T, invasive arterial blood gas and pulmonary gas exchange (PGX) were measured. The variables relevant to V_D/V_TR were analyzed by multiple linear regression.

Results

Compared to lung function, V_D/V_TR was more frequently and significantly related to smoking, carboxyhemoglobin level, pulmonary hypertension and P_aCO₂ (all p <0.05) whereas FEV₁% was more related to lung function test, P_aO₂ and OCD score. V_D/V_TR and FEV₁% were highly related to resting gas exchange but RV/TLC and D_LCO% were not. Cigarette consumption, the equivalent for CO₂ output, arterial oxyhemoglobin saturation, and the product of tidal volume and inspiratory duty cycle were identified as the parameters relevant to V_D/V_TR with a power of 0.72.

Conclusion

Compared to lung function test, V_D/V_TR is more related to clinical characteristics and is a comprehensive marker of resting gas exchange. Further studies are warranted to provide a noninvasive measurement of V_D/V_TR.

Registration Number

MOST 106-2314-B-040-025 and CSH-2019-C-30.

Impact of pulmonary emphysema on exercise capacity and its physiological determinants in chronic obstructive pulmonary disease

Exercise limitation is common in chronic obstructive pulmonary disease (COPD). We determined the impact of pulmonary emphysema on the physiological response to exercise independent of contemporary measures of COPD severity. Smokers 40–79 years old with COPD underwent computed tomography, pulmonary function tesing, and symptom-limited incremental exercise testing. COPD severity was quantified according to the Global Initiative for Chronic Obstructive Lung Disease (GOLD) by spirometry (GOLD 1–4); and symptom burden and exacerbation risk (GOLD A-D). Emphysema severity was quantified as the percent lung volume <−950 Hounsfield units. Regression models adjusted for age, gender, body size, smoking status, airflow limitation, symptom burden and exacerbation risk. Among 67 COPD subjects (age 67 ± 8 years; 75% male; GOLD 1–4: 11%, 43%, 30%, 16%), median percent emphysema was 11%, and peak power output (PPO) was 61 ± 32 W. Higher percent emphysema independently predicted lower PPO (−24 W per 10% increment in emphysema; 95%CI −41 to −7 W). Throughout exercise, higher percent emphysema predicted 1) higher minute ventilation, ventilatory equivalent for CO₂, and heart rate; and 2) lower oxy-hemoglobin saturation, and end-tidal PCO₂. Independent of contemporary measures of COPD severity, the extent of pulmonary emphysema predicts lower exercise capacity, ventilatory inefficiency, impaired gas-exchange and increased heart rate response to exercise.

The features of AECOPD with carbon dioxide retention

Background

Chronic obstructive pulmonary disease (COPD) with carbon dioxide retention is associated with a worsening clinical condition and the beginning of pulmonary ventilation decompensation. This study aimed to identify the factors associated with carbon dioxide retention.

Methods

This was a retrospective study of consecutive patients with COPD (meeting the Global Initiative for Chronic Obstructive Lung Disease diagnostic criteria) hospitalized at The Ninth Hospital of Xi’an Affiliated Hospital of Xi’an Jiaotong University between October 2014 and September 2017. The baseline demographic, clinical, laboratory, pulmonary function, and imaging data were compared between the 86 cases with carbon dioxide retention and the 144 cases without carbon dioxide retention.

Results

Compared with the non-carbon dioxide retention group, the group with carbon dioxide retention had a higher number of hospitalizations in the previous 12 months (p = 0.013), higher modified Medical Research Council (mMRC) dyspnea scores (p = 0.034), lower arterial oxygen pressure (p = 0.018), worse pulmonary function (forced expiratory volume in one second/forced vital capacity [FEV₁/FVC; p < 0.001], FEV₁%pred [p < 0.001], Z5%pred [p = 0.004], R5%pred [p = 0.008], R5-R20 [p = 0.009], X5 [p = 0.022], and Ax [p = 0.011]), more severe lung damage (such as increased lung volume [p = 0.011], more emphysema range [p = 0.007], and lower mean lung density [p = 0.043]). FEV₁ < 1 L (odds ratio [OR] = 4.011, 95% confidence interval [CI]: 2.216–7.262) and emphysema index (EI) > 20% (OR = 1.926, 95% CI: 1.080–3.432) were independently associated with carbon dioxide retention in COPD.

Conclusion

Compared with the non-carbon dioxide retention group, the group with carbon dioxide retention had different clinical, pulmonary function, and imaging features. FEV₁ < 1 L and EI > 20% were independently associated with carbon dioxide retention in AECOPD.

Trial registration

ChiCTR-OCH-14004904. Registered 25 June 2014.

Electronic supplementary material

The online version of this article (10.1186/s12890-018-0691-8) contains supplementary material, which is available to authorized users.

Nitrogen single-breath washout test for evaluating exercise tolerance and quality of life in patients with chronic obstructive pulmonary disease

Pulmonary function tests (PFTs) traditionally used in clinical practice do not accurately predict exercise intolerance in patients with chronic obstructive pulmonary disease (COPD). The aim of this study was to assess whether the nitrogen single-breath washout (N₂SBW) test explains exercise intolerance and poor quality of life in stable COPD patients. This cross-sectional study included 31 patients with COPD subjected to PFTs (including the N₂SBW test) and a cardiopulmonary exercise test (CPET). Patients were also evaluated using the following questionnaires: the COPD assessment test (CAT), the 36-Item Short Form Health Survey (SF36) and St. George's Respiratory Questionnaire (SGRQ). Peak oxygen uptake (peak VO₂) was negatively correlated with the phase III slope of the N₂SBW (SIII_N2) (r=-0.681, P<0.0001) and positively correlated with forced expiratory volume in one second (FEV₁; r=0.441, P=0.013). Breathing reserve was negatively correlated with SIII_N2, closing volume/vital capacity, and residual volume (RV) (r=-0.799, P<0.0001; r=-0.471, P=0.007; r=-0.401, P=0.025, respectively) and positively correlated with FEV₁, forced vital capacity (FVC) and FEV₁/FVC (r=0.721; P<0.0001; r=0.592, P=0.0004; r=0.670, P<0.0001, respectively). SIII_N2 and CAT were independently predictive of VO₂ and breathing reserve at peak exercise. RV, FVC, and FEV₁ were independently predictive of the SF36-physical component summary, SF36-mental component summary, and breathing reserve, respectively. The SGRQ did not present any independent variables that could explain the model. In stable COPD patients, inhomogeneity of ventilation explains a large degree of exercise intolerance assessed by CPETs and, to a lesser extent, poor quality of life.

Emphysema on Thoracic CT and Exercise Ventilatory Inefficiency in Mild-to-Moderate COPD

There is growing evidence that emphysema on thoracic computed tomography (CT) is associated with poor exercise tolerance in COPD patients with only mild-to-moderate airflow obstruction. We hypothesized that an excessive ventilatory response to exercise (ventilatory inefficiency) would underlie these abnormalities. In a prospective study, 19 patients (FEV₁ = 82 ± 13%, 12 Global Initiative for Chronic Obstructive Lung Disease (GOLD) stage 1) and 26 controls underwent an incremental exercise test. Ventilatory inefficiency was assessed by the ventilation ([Formula: see text]E)/CO₂ output ([Formula: see text]CO₂) nadir. Pulmonary blood flow (PBF) in a submaximal test was calculated by inert gas rebreathing. Emphysema was quantified as % of attenuation areas below 950 HU. Patients typically presented with centrilobular emphysema (76.8 ± 10.1% of total emphysema) in the upper lobes (upper/total lung ratio = 0.82 ± 0.04). They had lower peak oxygen uptake ([Formula: see text]O₂), higher [Formula: see text]E/[Formula: see text]CO₂ nadir, and greater dyspnea scores than controls (p < 0.05). Lower peak [Formula: see text]O₂ and worse dyspnea were found in patients with higher [Formula: see text]E/[Formula: see text]CO₂ nadirs (≥30). Patients had blunted increases in PBF from rest to iso-[Formula: see text]O₂ exercise (p < 0.05). Higher [Formula: see text]E/[Formula: see text]CO₂ nadir in COPD was associated with emphysema severity (r = 0.63) which, in turn, was related to reduced lung diffusing capacity (r = -0.72) and blunted changes in PBF from rest to exercise (r = -0.69) (p < 0.01). Ventilation "wasted" in emphysematous areas is associated with impaired exercise ventilatory efficiency in mild-to-moderate COPD. Exercise ventilatory inefficiency links structure (emphysema) and function (D_LCO) to a key clinical outcome (poor exercise tolerance) in COPD patients with only modest spirometric abnormalities.