Chronic Effort Dyspnea Explained by Lung Function Tests and by HRCT and CRX Radiographic Patterns in COPD: A Post-Hoc Analysis in 51 Patients

Figures & data

Figure 1 High-resolution computed tomography (HRCT) scans at the carina level, out of the 3 selected lung levels, spirometrically gated: (A) at 10% of vital capacity, (B) at 90% of vital capacity.

Figure 2 HRCT scan at the carina level, at 10% of vital capacity. Lung parenchyma contours are outlined; the 3 HU frequency functions represent distribution of lung density for both lungs (A), right (B), and left ones (C), respectively, and are used to compute Mean CT exp (HU) (ME in the picture = − 787.9 HU for both lungs); the vertical line represents − 910 HU threshold, and it is used to compute RAE₉₁₀ (% lung area) (corresponding to % AR in the picture = 16,8 for both lungs). Other figures in the picture are not used in the analyses.

Table 1 Univariate analysis of Medical Research Council (MRC) dyspnea score association with lung function, Chest X-Ray (CXR) findings and High- Resolution Computed Tomography (HRCT) density in 51 patients with COPD

Explanatory variables	Correlation coefficients	p value	Nature of explanatory variables
Lung function
DLCO (% pred.)	−0.60	< 0.0001	Lung parenchymal loss
FEV1/VC (%)	−0.57	< 0.0001	Expiratory flow obstruction/limitation
FEV1 (% pred.)	−0.55	< 0.0001	″ ″ ″ ″
FRC (% pred.)	0.55	< 0.0001	Lung hyperinflation
RV (% pred.)	0.54	< 0.0001	″ ″ ″ ″
RV/TLC (%)	0.53	< 0.0001	″ ″ ″ ″
TLC (% pred.)	0.42	= 0.0023	″ ″ ″ ″
PaO2 (mmHg)	−0.37	= 0.0076	Pulmonary gas exchange
PaCO2 (mmHg)	0.29	= 0.0368	″ ″ ″ ″
CXR findings
Increased vessels branching angles	0.28	< 0.05	Pulmonary changes of emphysema
Attenuation of vessels	0.32	< 0.05	Vascular changes of emphysema
Pulmonary hypertension features	0.37	< 0.01	Vascular changes of chronic bronchitis
Enlarged right heart sections	0.38	< 0.01	Cardiovascular changes of chronic bronchitis
Increased lung volumes	0.42	< 0.01	Pulmonary changes of emphysema
Small vertical heart	0.44	< 0.01	Cardiovascular changes of emphysema
HRCT lung density
RAE910 (% lung area)	0.61	< 0.0001	Expiratory lung density
Mean CTexp (HU)	−0.59	< 0.0001	″ ″ ″ ″
RAI950 (% lung area)	0.47	< 0.0005	Inspiratory lung density
Mean CTinsp (HU)	−0.44	< 0.0010	″ ″ ″ ″

*Lung function, CXR findings and HRCT lung density explanatory variables are listed according to the decreasing value of their correlation coefficients. DL_CO: single-breath diffusing capacity for carbon monoxide; FEV₁: forced expiratory volume in the 1st second; VC: vital capacity; FRC: functional residual capacity; RV: residual volume; TLC: total lung capacity; PaO₂: O₂ partial arterial tension; PaCO₂: CO₂ partial arterial tension; RAE₉₁₀ (% lung area): relative lung area with attenuation values below –910 Hounsfield Unit (HU) for scans at 10% of VC; mean CT_exp: mean computed tomography lung attenuation for scans at 10% of VC; RAI₉₅₀ (% lung area): relative lung area with attenuation values below –950 HU for scans at 90% of VC; mean CT_insp: mean computed tomography lung attenuation for scans at 90% of VC.

Table 2 Multivariate analysis of separate MRC dyspnea score association with lung function and HRCT density in 51 patients with COPD, respectively

Explanatory variables	Number of variables	Correlation coefficients	p value	Nature of explanatory variables
Direct regression
Lung function	9	0.73	< 0.0001
Stepwise regression
Lung function	3	0.71	< 0.0001
DLCO (% pred.)		0.71	< 0.0001	Lung parenchymal loss
PaCO2 (mmHg)		0.60		Pulmonary gas exchange
FRC (% pred.)		0.67		Lung hyperinflation
Direct regression
HRCT lung density	4	0.63	< 0.0001
Expiratory variables	2	0.62	< 0.0001
Inspiratory variables	2	0.47	< 0.0001
Stepwise regression
HRCT lung density	1	0.61	< 0.0001
RAE910 (% lung area)				Expiratory lung density

See Table 1 for abbreviations.

Table 3 Multivariate analysis of combined MRC dyspnea score association with lung function and HRCT density in 51 patients with COPD

Explanatory variables	Number of variables	Correlation Coefficients	p value	Nature of explanatory variables
Direct regression
Lung function	9	0.75	< 0.001
HRCT lung density	4
Stepwise regression forward
Lung function	3	0.69	< 0.0001
HRCT lung density	1
RAE910(% lung area)		0.61		Expiratory lung density
FRC (% pred.)		0.65		Lung hyperinflation
PaCO2 (mmHg)				Pulmonary gas exchange
Stepwise regression backward
Lung function	3	0.71	< 0.0001
HRCT lung density	0
PaCO2 (mmHg)				Pulmonary gas exchange
DLCO (% pred.)				Lung parenchymal loss
FRC (% pred.)				Lung hyperinflation

See Table 1 for abbreviations.

Table 4 Multivariate analysis of separate MRC dyspnea score association with 6 CXR findings in 51 patients with COPD

Explanatory variables	Number of variables	Correlation coefficients	p value	Nature of explanatory variables
Direct regression
CRX findings	6	0.57	< 0.0030
Pulmonary hypertension features				Vascular changes of chronic bronchitis
Attenuation of vessels				Vascular changes of emphysema
Increased lung volumes				Pulmonary changes of emphysema
Small vertical heart				Cardiovascular changes of emphysema
Increased vessels branching angles				Pulmonary changes of emphysema
Enlarged right heart sections				Cardiovascular changes of chronic bronchitis
Stepwise regression
CXR findings	2	0.54	< 0.0001
Small vertical heart		0.44	< 0.0001	Cardiovascular changes of emphysema
Increased lung volumes				Pulmonary changes of emphysema

*The 6 CXR findings as explanatory variables of MRC score of dyspnea were selected from a list of 14 CXR findings, proposed to distinguish chronic bronchitis from emphysema ([6]). See Table 1 for abbreviations.

Table 5 Multivariate analysis of combined MRC dyspnea score association with lung function, HRCT density, and CXR findings in 51 patients with COPD

Explanatory variables	Number of variables	Correlation coefficients	p value	Nature of explanatory variables
Direct regression
Lung function	9	0.81	< 0.001
HRCT lung density	4
CXR findings	5
Stepwise regression forward
Lung function	1	0.70	< 0.0001
HRCT lung density	1
CXR findings	1
RAE910(% lung area)		0.61		Expiratory lung density
Increased lung volumes		0.66		Pulmonary changes of emphysema
PaCO2 (mmHg)				Pulmonary gas exchange
Stepwise regression backward
Lung function	3	0.76	< 0.0001
HRCT lung density	0
CXR findings	1
Pulmonary hypertension features				Vascular changes of chronic bronchitis
FRC (% pred.)				Lung hyperinflation
PaCO2 (mmHg)				Pulmonary gas exchange
DLCO (% pred.)				Lung parenchymal loss

See Table 1 for abbreviations.

Milne E NC, Pistolesi M. Reading the Chest Radiograph. A Physiologic Approach. Mosby, St Louis 1993; 267–310

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