Ventilation Distribution Heterogeneity at Rest as a Marker of Exercise Impairment in Mild-to-Advanced COPD

Figures & data

Figure 1. Boxplot (median, interquartiles and range) of PCF in healthy controls and COPD patients according to GOLD grades.

Figure 2. Significant correlations between% predicted total lung capacity (TLC) (panel A) and alveolar volume (VA) (panel B) with PCF in COPD patients grades 1 to 4 (N = 276). Panel C shows the non-linear relationship (asymptotic regression) between%TLC-%VA differences and PCF.

Figure 3. Non-linear correlations of PCF with FEV₁, (panel A) and specific airway resistance (panel B) and linear correlations of PCF with residual volume (panel C) and lung diffusing capacity for carbon monoxide (panel D) in COPD patients grades 1 to 4 (N = 276). Lines represent the cutoffs for PCF tertiles.

Figure 4. Absolute frequency of the main symptom (leg effort or shortness of breath (SOB) reported at the end of progressive exercise in COPD patients separated by PCF tertiles.

Table 1. Selected resting and peak exercise variables in COPD patients separated by PCF tertiles

	“Mild” PCF (N = 92)	“Moderate” PCF (N = 92)	“Extensive” PCF (N = 92)
Rest
FEV1 (% pred)	83.4 ± 18.9	59.7 ± 19.6	39.2 ± 16.9
RV (% pred)	109.9 ± 26.7	144.9 ± 39.9	208.4 ± 62.9
IC (% pred)	103.1 ± 20.7	85.5 ± 19.3	66.8 ± 19.6
IC/TLC	0.47 ± 0.09	0.38 ± 0.08	0.28 ± 0.08
sRaw (cmH2O/L/s)/L)	10.7 ± 4.5	18.4 ± 8.7	30.8 ± 14.7
DLCO (% pred)	81.1 ± 21.7	66.5 ± 20.6	52.1 ± 18.8
Peak exercise
O2
% pred	86.4 ± 24.6	76.3 ± 21.9	56.1 ± 21.1
< 1 L/min	5.0	29.5	68.2
< 60% pred	13.2	26.4	60.4
E/CO2	34 ± 5	36 ± 7	39 ± 9
(EILV/TLC)/E	1.61 ± 0.49	2.31 ± 0.68	3.38 ± 1.23
(E/MVC)/ O2	0.50 ± 0.18	0.74 ± 0.29	1.17 ± 0.52
Dyspnea/E	0.09 ± 0.04	0.12 ± 0.06	0.19 ± 0.09

p < 0.05:

*vs. “moderate” and “extensive”;

^†vs. extensive. FEV₁: forced expiratory volume in 1 second; FVC: forced vital capacity; RV: residual volume; IC: inspiratory capacity; sRaw: specific airway resistance; DL_CO: lung diffusing capacity for carbon monoxide; O₂: oxygen uptake; E: minute ventilation; CO₂: carbon dioxide output; EILV: end-inspiratory lung volume; TLC: total lung capacity; MVC: maximal ventilatory capacity.

Table 2. Selected resting and peak exercise variables in controls and COPD patients separated by PCF tertiles within GOLD grades

		GOLD 1 (N = 78)		GOLD 2 (N = 95)			GOLD 3 (N = 75)		GOLD 4 (N =28)
	Controls (N = 64)	“Mild” PCF (N = 59)	“Moderate” PCF (N = 19)	“Mild” PCF (N = 33)	“Moderate” PCF (N = 40)	“Extensive” PCF (N = 22)	“Moderate” PCF (N = 33)	“Extensive” PCF (N = 42)	“Extensive” PCF
Rest
FEV1 (% pred)	115.9 ± 14.1	96.1 ± 13.7	86.5 ± 6.5	70.1 ± 8.8	61.3 ± 9.0	55.0 ± 3.5	42.5 ± 5.0	37.7 ± 6.3	23.6 ± 3.1
IC (% pred)	108.2 ± 16.4	107.5 ± 20.0	90.4 ± 22.6	94.7 ± 16.1	87.6 ± 19.2	76.5 ± 13.0	78.8 ± 14.7	71.1 ± 18.1	51.8 ± 11.6
IC/TLC	0.47 ± 0.07	0.47 ± 0.09	0.43 ± 0.10	0.43 ± 0.08	0.38 ± 0.08	0.35 ± 0.09	0.36 ± 0.07	0.28 ± 0.07	0.23 ± 0.07
RV (% pred)	86.1 ± 17.7	101.2 ± 23.3	105.1 ± 18.8	120.7 ± 28.9	137.4 ± 26.0	165.6 ± 30.2	167.0 ± 44.8	195.9 ± 48.0	261.6 ± 61.3
sRaw (abs)	5.29 ± 1.77	8.84 ± 2.80	8.70 ± 3.9	13.4 ± 5.0	17.4 ± 7.2	19.5 ± 8.5	17.7 ± 4.7	24.7 ± 6.7	43.5 ± 13.5
DLCO (% pred)	101.9 ± 21.8	85.9 ± 20.1	67.9 ± 23.4	76.4 ± 22.9	68.7 ± 20.1	54.2 ± 16.4	64.1 ± 21.0	53.2 ± 16.6	45.9 ± 17.2
Peak exercise
O2
% pred	122.3 ± 34.6	94.1 ± 16.0	90.9 ± 25.1	82.2 ± 25.6	75.4 ± 21.6	66.7 ± 12.5	67.5 ± 17.2	56.6 ± 16.9	39.5 ± 10.0
< 1 L/min (%)	0	6.8	55.4	12.5	37.5	66.7	37.5	64.3	85.2
< 60% pred (%)	0	5.2	43.8	9.7	19.6	66.7	41.4	68.1	85.2
E/CO2	33 ± 5	33 ± 5	39 ± 7	35 ± 4	37 ± 5	42 ± 6	35 ± 7	38 ± 11	40 ± 9
(EILV/TLC)/E	1.17 ± 0.35	1.51 ± 0.41	2.10 ±0.64	1.79 ± 0.57	2.23 ± 0.64	2.91 ± 0.97	2.56 ± 0.76	3.21 ± 0.98	4.48 ± 1.32
(E/MVC)/WR	0.28 ± 0.11	0.43 ± 0.14	0.58 ± 0.22	0.60 ± 0.18	0.72 ± 0.21	0.97 ± 0.32	0.75 ± 0.18	1.01 ± 0.36	1.57 ± 0.58
Dyspnea/E	0.05 ± 0.03	0.09 ± 0.05	0.09 ± 0.04	0.08 ± 0.04	0.12 ± 0.05	0.18 ± 0.05	0.14 ± 0.07	0.19 ± 0.10	0.23 ± 0.10
Dyspnea^3 Leg (%)	0	5.1	26.4	48.8	62.1	73.9	49.5	69.3	78.2

p < 0.05:

*vs. controls,

^†vs. “moderate”,

^‡vs. “moderate” and “extensive.” FEV₁: forced expiratory volume in one second; FVC: forced vital capacity; RV: residual volume; IC: inspiratory capacity; sRaw: specific airway resistance; DL_CO: lung diffusing capacity for carbon monoxide; O₂: oxygen uptake; E: minute ventilation; CO₂: carbon dioxide output; EILV: end-inspiratory lung volume; TLC: total lung capacity; MVC: maximal ventilatory capacity; WR: work rate.

Figure 5. Receiver operating characteristics curve of selected physiological variables to predict a severely reduced peak exercise capacity in COPD patients GOLD grades 1 to 4 (N = 276). The best PCF cutoff is also highlighted. Definition of abbreviations: AUC: area under the curve; CI: confidence interval; PCF: poorly communicant fraction; FEV: forced expiratory volume in 1 second; DL_CO: lung diffusing capacity for carbon monoxide; RV: residual volume.