Pulmonary Vascular Volume by Quantitative CT in Dyspneic Smokers with Minor Emphysema

Figures & data

Table 1. Subjects general and resting functional characteristics.

Variable	Trace-E (LAA: 1.3 ± 0.6%)		Mild-E (LAA: 5.7 ± 4.2%)		p value
	Preserved DLCO (n = 16)	Reduced DLCO (n = 16)	Preserved DLCO (n = 16)	Reduced DLCO (n = 16)
Demographic/Anthropometric
Age, years	63 ± 8	68 ± 8	69 ± 7	66 ± 10	NS
Gender (M: F)	11:5	6:10	13:3	11:5	NS
Height, cm	173 ± 12	167 ± 11	174 ± 8	172 ± 9	NS
Body mass, Kg	86 ± 10	83 ± 18	92 ± 17	83 ± 20	NS
BMI, Kg/m^2	29 ± 4	30 ± 6	30 ± 5	28 ± 5	NS
Clinical
Pack-year smoking history	39 ± 30	45 ± 15	35 ± 20	33 ± 18	NS
MRC dyspnea score (1-5)	1.38 ± 0.51	1.64 ± 0.67	1.79 ± 0.97	1.93 ± 0.70	NS
CAT score (0-40)	10.5 ± 6.4	12.4 ± 4.8	10.3 ± 6.4	11.2 ± 5.9	NS
SGRQ total score	17.5 ± 15.0	24.7 ± 14.3	18.8 ± 17.0	18.0 ± 13.5	NS
Spirometry
FEV1/FVC (no. <LLN)	0.65 ± 0.09 (9)	0.68 ± 0.07 (7)	0.60 ± 0.05 (12)	0.61 ± 0.08 (11)	NS
FEV1, %predicted (no. <LLN)	87 ± 14 (3)	85 ± 11 (3)	82 ± 12 (2)	83 ± 15 (4)	NS
FVC, %predicted	103 ± 12	97 ± 11	104 ± 14	107 ± 17	NS
Lung volumes
IC, L (%predicted)	3.10 ± 0.79 (100 ± 18)	2.75 ± 0.59 (104 ± 16)	3.11 ± 0.73 (101 ± 19)	2.96 ± 0.94 (97 ± 19)	NS
FRC, L (%predicted)	3.27 ± 1.19 (95 ± 22)	2.60 ± 0.53 (84 ± 17)	3.81 ± 0.93 (106 ± 20)	3.33 ± 0.93 (99 ± 27)	NS
TLC, L (%predicted)	6.37 ± 1.83 (95 ± 15)	5.35 ± 0.88 (93 ± 10)	7.10 ± 1.37 (106 ± 11)	6.29 ± 1.37 (98 ± 15)	NS
RV/TLC, %predicted	100 ± 23	99 ± 19	115 ± 21	96 ± 28	NS
Lung diffusing capacity
DLCO, %predicted	99 ± 51^a	63 ± 13^d	92 ± 12^c	59 ± 15	0.02
VA, %predicted	96 ± 12	87 ± 9^d	100 ± 11^c	91 ± 11	0.01
DLCO /VA, %predicted	108 ± 23^b	91 ± 18^d	123 ± 37^c	78 ± 25	<0.001
VA/TLC	0.90 ± 0.06	0.80 ± 0.23	0.85 ± 0.08	0.85 ± 0.07	NS
Selected quantitative CT scan measurements
LAA <-950 HU, %	1.25 ± 0.62^b	1.36 ± 0.65	5.92 ± 4.48^d	5.38 ± 4.09	<0.001
TPVV, cc	157 ± 49^a	124 ± 31	174 ± 38 ^c,d	146 ± 26	0.01
TPPV/height	0.90 ± 0.24^a	0.74 ± 0.16	0.93 ± 0.31^c,d	0.80 ± 0.24	0.03
TAC, n	273 ± 125	292 ± 120	272 ± 75	288 ± 84	NS
Mean AW wall thickness, mm	1.18 ± 0.12	1.19 ± 0.15	1.16 ± 0.09	1.17 ± 0.16	NS
Mean inner lumen area, m^2	6.80 ± 1.94	7.25 ± 1.89	6.82 ± 1.55	7.26 ± 1.72	NS

Values are mean ± SD, unless otherwise specified.

^ap < 0.05 Trace-E preserved DL_CO vs. Trace-E reduced DL_CO.

^bp < 0.05 Trace-E preserved DL_CO vs. Mild-E reduced DL_CO.

^cp < 0.05 Mild-E preserved DL_CO vs. Mild-E reduced DL_CO.

^dp < 0.05 Trace-E reduced DL_CO vs. Mild-E preserved DL_CO.

Abbreviations: BMI, body mass index; CAT, COPD assessment test; DL_CO, single breath diffusing capacity of the lung for carbon monoxide; F, female; FEV₁, forced expired volume in 1 s; FRC, functional residual capacity; FVC, forced vital capacity; IC, inspiratory capacity; LAA, low attenuation area of the lung below -950 HU as a percentage of the total lung area; LLN, lower limit of normal; M, male; Mild-E, mild emphysema; MRC, Medical Research Council; NS, non significant; RV, residual volume; TAC, total airway count; TLC, total lung capacity; TPVV, total pulmonary vascular volume; Trace-E, trace emphysema; V_A, alveolar volume measured by single breath gas dilution; AW, airway.

Figure 1. Selected measurements of chest quantitative computed tomography: (a) percentage of emphysema as assessed by low attenuation area (LAA) <-950 HU (LAA_<-950HU), and (b) total pulmonary vascular volume (TPVV) in smokers separated by emphysema burden and DL_CO. Boxes depict the first to third quartiles; central lines denote the median. Whiskers range from the 5^th to the 95^th percentiles. Panels (c) and (d) show Pearson’s correlations between DL_CO and both LAA_<-950HU (panel c) and TPVV (panel d) where dotted lines represent the 95% confidence interval (CI) for the slope of the regression line. Abbreviations: DL_CO, single breath diffusing capacity of the lung for carbon monoxide.

Table 2. Results of the multiple linear regression models predicting DL_CO and exertional dyspnea.

Dependent variable	Model	Coef.	Std. Error	t	p value
DLCO (%predicted)	Constant	95.95	83.66	1.147	0.26
	TPVV	0.28	0.14	2.06	0.04
	LAA<-950HU	−1.12	0.99	−1.13	0.27
	Height	−0.17	0.54	−0.32	0.75
	Age	−0.39	0.42	−0.92	0.36
	Model summary: F = 2.65, p = .04, r = 0.39, R^2 = 0.16
Dyspnea/V.EE slope	Constant	0.04	0.06	0.71	0.48
	TPVV	−0.001	0.0002	−3.00	0.004
	LAA<-950HU	−0.0003	0.0017	−0.22	0.83
	Age	0.002	0.001	2.15	0.04
	Model summary: F = 5.535, p = .002, r = 0.48, R^2 = 0.23
Dyspnea/WR slope	Constant	0.04	0.03	1.27	0.21
	TPVV	−0.0003	0.0001	−3.19	0.002
	LAA<-950HU	0.001	0.001	1.31	0.19
	Age	0.001	0.001	1.31	0.19
	Model summary: F = 4.844, p=.01, r = 0.45, R^2= 0.20

Abbreviations: DL_CO, signle breath diffusing capacity of the lung for carbon monoxide; LAA_<-950HU, low attenuation area of the lung below -950 HU as a percentage of the total lung area; TPVV, total pulmonary vascular volume; WR, work rate; V._E, minute ventilation.

Figure 2. Selected ventilatory and sensory parameters during incremental cardiopulmonary exercise test at the highest equivalent work rate of 60 watts in smokers separated by emphysema burden and DL_CO. (a) ventilatory equivalent for carbon dioxide output (V._E/V.CO₂), (b) end-tidal CO₂ (P_ETCO₂), (c) breathing frequency/tidal volume ratio (Fb/V_T), (d) V_T/inspiratory capacity (IC), (e) dyspnea Borg ratings and (f) leg discomfort Borg ratings. Boxes depict the first to third quartiles; central lines denote the median. Whiskers range from the 5^th to the 95^th percentiles. Abbreviations: DL_CO = single breath diffusing capacity of the lung for carbon monoxide.

Table 3. Selected physiological and sensory responses at peak and submaximal exercise in smokers separated by emphysema burden and DL_CO.

Variable	Trace-E		Mild-E		p value
	Preserved DLCO	Reduced DLCO	Preserved DLCO	Reduced DLCO
Power/metabolic
Peak WR, W	116 ± 46	88 ± 33^d	118 ± 32	103 ± 35	0.04
Peak WR, % predicted	70 ± 24	66 ± 24	70 ± 19	66 ± 21	NS
Peak V.O2, L/min	1.76 ± 0.62	1.43 ± 0.46	1.88 ± 0.60	1.66 ± 0.56	NS
Peak V.O2, %predicted	78 ± 28	71 ± 13	79 ± 20	73 ± 19	NS
Cardiovascular
Peak HR, % predicted	75 ± 13	74 ± 9	67 ± 12	71 ± 12	NS
Peak O2 pulse, mL/min/beat	15.3 ± 4.6	13.3 ± 5.5	14.3 ± 4.6	13.4 ± 4.5	NS
Ventilatory/mechanical
V.E at the HEWR, L/min	28.7 ± 6.2^a, b	33.9 ± 5.0	32.3 ± 5.2^c	36.9 ± 7.4	0.003
VT at the HEWR, L	1.29 ± 0.31	1.24 ± 0.12^d	1.51 ± 0.07	1.45 ± 0.28	0.02
Fb at the HEWR, breaths/min	23 ± 4^a	28 ± 4^d	22 ± 5^c	26 ± 4	0.002
IRV at the HEWR, L	1.80 ± 0.68	1.54 ± 0.66	2.04 ± 0.76	1.72 ± 0.82	NS
EILV/TLC at the HEWR	72 ± 8	72 ± 9	70 ± 13	73 ± 10	NS
Pulmonary gas exchange
Peak SpO2, %	95 ± 2	96 ± 2	94 ± 2	93 ± 5	NS
V.E/V.CO2 at its nadir	28.6 ± 2.3^a, b	31.6 ± 3.8	30.1 ± 2.9^c	34.5 ± 5.4	0.01
PETCO2 at the V.E/V.CO2 nadir, mmHg	38.7 ± 4.4^a, b	35.2 ± 4.8	38.5 ± 3.3^c	33.9 ± 4.5	0.01
RER at the V.E/V.CO2 nadir	0.96 ± 0.08	1.02 ± 0.12	0.96 ± 0.10	1.00 ± 0.11	NS
Sensory
Dyspnea at the HEWR, Borg units	0.60 ± 0.87^a, b	2.44 ± 2.2^d	0.72 ± 0.60^c	1.88 ± 1.81	0.005
Dyspnea-V.E slope, Borg/L/min	0.06 ± 0.05^a	0.11 ± 0.06	0.06 ± 0.03	0.08 ± 0.05	0.04
Dyspnea-WR slope, Borg/W	0.03 ± 0.02^a	0.06 ± 0.03	0.03 ± 0.02	0.05 ± 0.04	0.03

Values are mean ± SD. Values are mean ± SD.

^ap < 0.05 Trace-E preserved DL_CO vs. Trace-E reduced DL_CO.

^bp < 0.05 Trace-E preserved DL_CO vs. Mild-E reduced DL_CO.

^cp < 0.05 Mild-E preserved DL_CO vs. Mild-E reduced DL_CO.

^dp < 0.05 Trace-E reduced DL_CO vs. Mild-E preserved DL_CO.

Abbreviations: DL_CO, single-breath diffusing capacity of the lung for carbon monoxide; Fb, breathing frequency; HEWR, highest equivalent work rate; HR, heart rate; IC, inspiratory capacity; IRV, inspiratory reserve volume; Mild-E, mild emphysema; O₂ pulse, oxygen pulse; P_ETCO₂, partial pressure of end-tidal carbon dioxide; NS, non significant; RER, respiratory exchange ratio; SpO₂, arterial oxygen saturation measured by pulse oximetry; TLC, total lung capacity; Trace-E, trace emphysema; V._E, minute ventilation; V._E/V.CO_2, ventilatory equivalent for carbon dioxide output; V.O₂, oxygen uptake; V_T tidal volume; WR, work rate.