Quantitative Computed Tomography Assessment of Pectoralis and Erector Spinae Muscle Area and Disease Severity in Chronic Obstructive Pulmonary Disease Referred for Lung Volume Reduction

Figures & data

Figure 1. Representative computed tomography (CT) scans at thoracic level used to determine muscle area in chronic obstructive pulmonary disease (COPD). (A) CT image used for pectoralis muscle imaging shaded in light blue. (B) CT image for erector spinae muscle imaging shaded in light blue. Label delineates the designated Hounsfield units for skeletal muscle from –50 to 90, the percentage of skeletal muscle mass, and the CSA measured in cm².

Table 1. Baseline clinical and demographic characteristics of lung cancer screening (LCS) control subjects and chronic obstructive pulmonary disease (COPD) case subjects.

	LCS, n = 41	COPD, n = 117	p
n	41	117
Demographics
Age (in years) (SD)	65.39 (5.72)	64.01 (6.86)	0.249
Female sex (%)	17 (41.5)	57 (48.7)	0.536
Height (cm) (SD)	167.72 (8.28)	167.90 (10.39)	0.92
Weight (kg) (SD)	80.99 (18.39)	73.71 (17.77)	0.027
BMI (kg/m^2) (SD)	28.70 (6.37)	26.27 (4.98)	0.014
Race (%)			<0.001
African American	20 (48.8)	10 (8.5)
Caucasian	21 (51.2)	107 (91.5)
Other	0 (0.0)	0 (0.0)
Smoking status (%)			<0.001
Current	20 (48.8)	1 (0.9)
Former	21 (51.2)	114 (97.4)
Never	0 (0.0)	1 (0.9)
Pack years (SD)	50.40 (22.05)	52.88 (30.74)	0.635
Oxygen therapy (%)	0 (0.0)	85 (72.6)	<0.001
FEV1%	98 (13)	31 (10)	<0.001
FEV1/FVC ratio	74.42 (5.03)	32.12 (7.04)	<0.001
Outcomes
Pectoralis muscle area CSA (cm^2) (SD)	33.92 (10.71)	29.00 (8.82)	<0.001
Erector spinae muscle area CSA (cm^2) (SD)	33.53 (9.72)	35.20 (10.47)	0.380

Notes: P-values represent chi-square tests for categorical variables and t-tests for continuous variables. FEV₁ = forced expiratory volume in one second; FEV₁/FVC = FEV₁ divided by forced vital capacity.

Table 2. Clinical characteristics of patients with COPD.

	COPD, n = 117
Long term oxygen therapy (%)
Continuous^a	62 (53.0)
With exertion	20 (17.1)
Nocturnal	3 (2.6)
None	32 (27.4)
Prior exacerbation history^b	76 (65.0)
BODE (mean (SD))	6.27 (1.47)
mMRC dyspnea scale score (mean (SD))	3.01 (0.76)
CAT (mean (SD))	22.58 (7.15)
Charlson comorbidity index (mean (SD))	3.61 (1.25)
GOLD stage (%)
II	5 (4.3)
III	50 (42.7)
IV	62 (53.0)
GOLD grade (%)
B	40 (34.2)
C	2 (1.7)
D	75 (64.1)
Emphysema score (n = 97)	16.11 (4.65)
Axial distribution of emphysema (n = 89)
Peripheral predominant	7 (7.7)
Central/axial predominant	46 (50.5)
Evenly distributed	36 (39.6)
Craniocaudal distribution of emphysema (n = 90)
Diffuse	9 (9.8)
Lower lobe predominant	1 (1.1)
Upper lobe predominant	80 (87.0)
Mortality (%)	14 (12.0)
Proceeded with surgical LVRS (%)	15 (12.8)
Proceeded with bronchoscopic LVR (%)	4 (3.4)
Underwent lung transplant (%)	7 (6.0)

Note: GOLD = Global Initiative for Chronic Obstructive Lung Disease; mMRC = modified Medical Research Council. The continuous variables are presented as mean±SD (range).

^aContinuous oxygen defined as 2 L or greater continuous oxygen.

^bPrior exacerbation history defined as either ≥2 in the prior year or ≥1 leading to a hospital admission.

Table 3. Spirometric measures and AATD testing of patients with COPD.

	COPD, n = 117
FEV1% (mean (SD))	31 (10)
FVC L (mean (SD))	2.63 (0.82)
FVC % (mean (SD))	73 (16)
FEV1/FVC ratio (mean (SD))	32.12 (7.04)
DLCO ml/min/mm Hg (mean (SD))	9.04 (3.55)
DLCO % (mean (SD))	37 (13)
VC L (mean (SD))	2.72 (1.20)
VC % (mean (SD))	73 (18)
RV L (mean (SD))	4.46 (1.37)
RV % (mean (SD))	210 (55)
TLC L (mean (SD))	7.11 (1.73)
TLC % (mean (SD))	123 (19)
RV /TLC ratio (mean (SD))	62.23 (9.02)
FRC L (mean (SD))	5.21 (1.34)
FRC % (mean (SD))	1.66 (0.34)
IC (mean (SD))	1.90 (0.67)
6 min walk test meters (mean (SD))	270.23 (77.07)
6 min walk test % (mean (SD))	53 (15)
Alpha-1 antitrypsin level, mg/dl (mean (SD)), n = 72	142.30 (30.71)
Alpha-1 antitrypsin genotype (%), n = 39^a
MM	29 (74.4)
MS	2 (5.1)
MZ	3 (7.7)

Notes: AAT = alpha-1 antitrypsin deficiency; DLCO = diffusing capacity of carbon monoxide; FEV₁ = forced expiratory volume in one second; FEV₁% = FEV₁ percent predicted; FVC = forced vital capacity; FVC % = FVC percent predicted; TLC = total lung capacity; FRC = functional residual capacity; IC = inspiratory lung capacity; RV = residual volume. The continuous variables are presented as mean+SD (range).

^aGenotype cases that represented only 1 case (2.6%) include FM, GM, MI, SZ, and ZZ.

Figure 2. Muscle area in COPD patients and smoking controls. (A) Distribution of pectoralis muscle area (in cm²) stratified by GOLD stage compared to current and former smoking controls. †<p < 0.01, ‡p < 0.05 for Tukey’s test for intergroup differences. (B) Distribution of erector spinae muscle area (in cm²) stratified by GOLD stage compared to current and former smoking controls. Tukey’s test did not show significant intergroup differences.

Table 4. Bivariate assessment of covariates with pectoralis muscle (PM) area in COPD subjects.

Predictor	Mean difference in PM area (cm^2)	95% CI	p Value
Age (per year)	0.01	–0.18 to 0.20	0.908
Female sex	–7.99	–10.62 to −5.36	<0.001
Race (Caucasian vs AA)	–5.01	–9.65 to −0.38	0.034
BMI (kg/m^2)	0.62	0.36–0.89	<0.001
Pack year of smoking	–0.01	–0.06 to 0.03	0.507

Notes: R² 0.39, model p < 0.001. AA = African Americans.

Table 5. Bivariate assessment of covariates with Erector Spinae muscle (ESM) area in COPD subjects.

Predictor	Mean difference in ESM area (cm^2)	95% CI	p Value
Age (per year)	–0.11	–0.36 to 0.13	0.360
Female sex	–7.88	–11.22 to −4.54	<0.001
Race (Caucasian vs AA)	–2.79	–8.67 to 3.09	0.349
BMI (kg/m^2)	0.82	0.49–1.15	<0.001
Pack year of smoking	–0.01	–0.06 to 0.04	0.703

Notes: R² 0.32, model p < 0.001. AA = African Americans.

Table 6. Relationship between PM CSA and physiologic parameters/clinical traits.

Predictor	Mean difference in PM area (cm^2)	95% CI	p Value	R^2 value
Lung function
FEV1%	0.11	0.06–0.17	<0.001	0.08
FEV1 (per ml)	4.01	2.10–5.91	<0.001	0.32
FVC %	6.23	–2.51 to 15.0	=0.437	0.01
FVC (per ml)	2.36	0.36–4.36	=0.021	0.24
FEV1/FVC ratio	0.18	0.09–0.26	<0.001	0.33
DLCO ml/min/mm Hg^a	0.32	0.002–0.65	=0.049	0.23
DLCO %^a	–0.01	–0.11 to 0.08	=0.771	0.02
TLC^a (per ml)	0.17	–1.11 to 1.44	=0.796	0.22
TLC %^a	–0.01	–0.11 to 0.08	=0.772	0.02
RV/TLC^a	–0.10	–0.24 to 0.05	=0.196	0.23
Clinical traits^a
Exacerbations	–1.08	–4.12 to 1.97	=0.485	0.22
mMRC	–0.09	–0.41 to 0.23	=0.577	0.21
CAT	–0.47	–0.35 to 0.25	=0.757	0.28
Charlson	–0.21	–1.40 to 0.98	=0.724	0.23
6 min walk test	0.00	–0.02 to 0.02	=0.896	0.22
Mortality	–2.62	–10.31 to 5.07	=0.502	0.21
Emphysema scoring	–0.39	–0.75 to −0.04	=0.030	0.27
ESM CSA cm^2	0.49	0.36–0.61	<0.001	0.43

Notes: Models with PM area were adjusted for age, sex, height, smoking status, pack years, and race. Models with % predicted were adjusted only for smoking status and pack years, as these parameters are already adjusted for age, height, sex, and race.

Bold p values denote statistical significance.

^aFull lung volumes and clinical traits only available in COPD cohort. FEV₁%, FEV₁L, FVC%, FVCL, and FEV₁/FVC ratio available for both the LCS and COPD cohort. Charlson comorbidity index was not adjusted for age as age is already included in the index.

Table 7. Relationship between ESM CSA and physiologic parameters/clinical traits.

Predictor	Mean difference per cm^2 increment in ESM area	95% CI	p Value	R^2 value
Lung function
FEV1%	0.04	–0.02 to 0.11	=0.223	0.03
FEV1 (per ml)	1.37	–0.80 to 3.54	=0.214	0.22
FVC %	3.07	–6.35 to 12.50	=0.520	0.02
FVC (per ml)	1.57	–0.63 to 3.76	=0.161	0.23
FEV1/FVC ratio	0.06	–0.04 to 0.15	=0.221	0.23
DLCO ml/min/mm Hg^a	0.39	0.01–0.77	=0.044	0.22
DLCO %^a	–0.06	–0.18 to 0.05	=0.278	0.01
TLC^a (per ml)	0.22	–1.34 to 1.77	=0.782	0.21
TLC %^a	–0.02	–0.14 to 0.10	=0.702	0.02
RV/TLC^a	–0.21	–0.38 to −0.03	=0.022	0.24
Clinical traits^a
Exacerbations	1.32	–2.41 to 5.05	=0.485	0.20
mMRC	–0.61	–3.04 to 1.83	=0.622	0.22
CAT	–0.04	–0.38 to 0.31	=0.833	0.21
Charlson	1.21	–0.23 to 2.66	=0.099	0.21
6 min walk test	0.01	–0.02 to 0.03	=0.658	0.21
Mortality	2.67	–5.70 to 11.04	=0.529	0.22
Emphysema scoring	–0.45	–0.88 to −0.027	=0.037	0.22
PM CSA cm^2	0.57	0.42–0.72	<0.001	0.43

Notes: Models with PM area were adjusted for age, sex, height, smoking status, pack years, and race. Models with % predicted were adjusted only for smoking status and pack years, as these parameters are already adjusted for age, height, sex, and race.

^aFull lung volumes and clinical traits only available in COPD cohort. FEV₁%, FEV₁L, FVC%, FVCL, and FEV₁/FVC ratio available for both the LCS and COPD cohort. Charlson comorbidity index was not adjusted for age as age is already included in the index.

Figure 3. Survival analysis of patients with COPD. (A) and (B) Receiver operating characteristic curves to determine the optimum cutoff value for ESM and PM CSA and the event (death, bronchoscopic or surgical lung volume reduction surgery, or lung transplant). Area under the curve was 72.2 for ESM CSA and 78.5 for PM CSA. (C) Kaplan–Meier survival curves stratified by ESM CSA. The cutoff value corresponds to greater than or equal to the mean ESM CSA and less than the mean ESM CSA (≥ 35.2 cm² and <35.2 cm², respectively). The solid line indicates event-free survival probability. The crosses indicate censoring. The steps down indicate events (mortality, lung volume reduction surgery, or lung transplant). There was no significant difference for patients with COPD who had lower ESM CSA values in terms of event-free rates (p = 0.5 by log rank test). (D) Kaplan–Meier survival curves stratified by PM CSA. The cutoff value corresponds to greater than or equal to the mean PM CSA and less than the mean PM CSA (≥ 29 cm² and <29 cm², respectively). The solid line indicates event-free survival probability. The crosses indicate censoring. The steps down indicate events. The patients with COPD and lower PM CSA values exhibited significantly worse event-free rates (p = 0.04 by log rank test).

Data availability statement

A data availability statement provided by the authors is available upon request.