The minimal important difference for target lobe volume reduction after endoscopic valve therapy

Figures & data

Figure 1 Calculation of the TLVR based on thin-section MDCT scan analysis using quantitative imaging software (Apollo; VIDA Diagnostics, Coralville, IA, USA).

Notes: LLL as targt lobe with an emphysema index of 53.7%. Reduction in LLL volume of 2.120 mL after treatment (100% reduction).
Abbreviations: LAC, low attenuation cluster; LLL, left lower lobe; MDCT, multidetector computed tomography; TLVR, target lobe volume reduction.

Table 1 Patient characteristics

Clinical parameter	n	Mean	SD	Min	Max
FEV1 (L)	119	0.77	0.23	0.39	1.62
FEV1 (%)	119	30.1	7.3	13.8	54.4
RV (L)	118	5.83	1.3	3.6	9.1
RV (%)	118	270.5	54.6	166.1	450.2
Δ6-MWD (m)	108	281	99.9	80	490
TLV (mL)	119	1,817.02	456.33	1,027.08	3,066.69

Abbreviations: 6-MWD, 6-minute walk distance; FEV₁, forced expiratory volume in 1 second; RV, residual volume; TLV, target lobe volume.

Table 2 Descriptive statistics for changes from baseline to 3 months after valve implantation

Clinical parameter	n	Mean	SD	Min	Max	% (≥MID)
TLVR (mL)	119	944.79	718.38	−353.9	2,842.8
TLVR (%)	119	54.44	39.94	−12.74	100
ΔFEV1 (L)	119	0.11	0.18	−0.37	0.72	44
ΔRV (L)	118	−0.51	1.03	−3.39	2.06	57
Δ6-MWD (m)	98	43.98	60.4	−105	235	61
ΔmMRC (pts)	89	−0.7	1.3	−4	2

Abbreviations: 6-MWD, 6-minute walk distance; FEV₁, forced expiratory volume in 1 second; MID, minimal important difference; mMRC, modified Medical Research Council; RV, residual volume; TLVR, target lobe volume reduction.

Figure 2 (A and B) Scatter plots.

Note: Pearson’s correlation coefficients for TLVR (mL [A] and % [B]) versus changes in anchor variables.
Abbreviations: 6-MWD, 6-minute walk distance; FEV₁, forced expiratory volume in 1 second; RV, residual volume; TLVR, target lobe volume reduction.

Table 3 MID estimates for TLVR (mL)

		MID estimate (95% CI), mL	n (%) responders (≥MID of TLVR) (n=119)	Sensitivity (%)	Specificity (%)
Anchor-based method using linear regression (MID)
ΔFEV1	(0.1 L)	929 (822, 1,035)	57 (48)	79	76
ΔRV	(−0.31 L)	891 (769, 1,013)	57 (48)	64	73
	(−0.37 L)	909 (788, 1,029)	57 (48)	62	72
	(−0.43 L)	926 (806, 1,046)	57 (48)	65	72
Δ6-MWD	(24 m)	939 (785, 1,093)	57 (48)	57	63
	(26 m)	941 (789, 1,094)	57 (48)	56	64
	(28 m)	944 (793, 1,095)	57 (48)	57	63
Anchor-based method using ROC method (MID)
ΔFEV1	(0.1 L)	1,020–1,070	55 (46)	79	79
ΔRV	(−0.31 L)	960–1,010	56 (47)	62	74
	(−0.37 L)	960–1,010	56 (47)	64	75
	(−0.43 L)	960–1,010	56 (47)	65	74
Δ6-MWD	(24 m)	610–620	67 (56)	66	58
	(26 m)	610–620	67 (56)	65	55
	(28 m)	610–620	67 (56)	65	55
Distribution-based method
½ SD		228	97 (82)	–	–
Cohen’s effect size (0.2)		91	111 (93)	–	–

Abbreviations: 6-MWD, 6-minute walk distance; FEV₁, forced expiratory volume in 1 second; MID, minimal important difference; ROC, receiver operating characteristics; RV, residual volume; SD, standard deviation; TLVR, target lobe volume reduction.

Table 4 MID estimates for TLVR (%)

		MID estimate (95% CI), %	n (%) responders (≥MID of TLVR) (n=119)	Sensitivity (%)	Specificity (%)
Anchor-based method using linear regression (MID)
ΔFEV1	(0.1 L)	54 (48, 60)	55 (46)	79	79
ΔRV	(−0.31 L)	51 (45, 58)	55 (46)	62	77
	(−0.37 L)	52 (46, 59)	55 (46)	64	76
	(−0.43 L)	53 (47, 60)	55 (46)	65	75
Δ6-MWD	(24 m)	53 (45, 62)	55 (46)	53	66
	(26 m)	54 (45, 62)	55 (46)	55	66
	(28 m)	54 (46, 62)	55 (46)	55	64
Anchor-based method using ROC method (MID)
ΔFEV1	(0.1 L)	49–54	55 (46)	79	79
ΔRV	(−0.31 L)	49–54	55 (46)	62	77
	(−0.37 L)	49–54	55 (46)	64	76
	(−0.43 L)	49–54	55 (46)	65	75
Δ6-MWD	(24 m)	41–46	59 (50)	60	64
	(26 m)	47	58 (49)	60	66
	(28 m)	47	58 (49)	60	66

Abbreviations: 6-MWD, 6-minute walk distance; FEV₁, forced expiratory volume in 1 second; MID, minimal important difference; ROC, receiver operating characteristic; RV, residual volume; TLVR, target lobe volume reduction.

Figure 3 (A and B) ROC curves.

Note: Estimated MIDs for TLVR (mL [A] and % [B]) using MID estimates of anchor variables as gold standard.
Abbreviations: 6-MWD, 6-minute walk distance; FEV₁, forced expiratory volume in 1 second; MID, minimal important difference; ROC, receiver operating characteristic; RV, residual volume; TLVR, target lobe volume reduction.