Reliability and validity of the test of incremental respiratory endurance measures of inspiratory muscle performance in COPD

Figures & data

Table 1 Demographic characteristics and inspiratory muscle performance of the psychometric testing samples

Variables	Test–retest reliability (n=21)		Known-groups validity (n=81)		Convergent validity: 6MWT (n=47)		Convergent validity: mMRC (n=53)
	Mean	SD	Mean	SD	Mean	SD	Mean	SD
Age (years)	68.7	6.2	69.9	5.7	70.3	5.5	69.5	5.2
Height (cm)	173.9	8.1	175.5	7.7	175.3	8.1	176.1	8.3
Weight (kg)	83.7	26.2	80.9	19.2	79.0	19.4	80.9	21.0
Post-BD FEV1 (% predicted)	48.1	21.2	46.5	16.9	43.5	16.4	47.3	16.7
MIP (cmH2O)	78.1	25.4	77.5	23	74.8	17.9	75.8	19.7
SMIP (PTU)	387.3	160.7	403.8	135.5	392.9	115.2	410.6	117.9
ID (seconds)	9.6	3.7	10	2.8	43.5	2.4	10.5	2.5

Abbreviations: 6MWT, 6-minute walk test; ID, inspiratory duration; MIP, maximal inspiratory pressure; mMRC, modified Medical Research Council dyspnea scale; Post-BD FEV₁, post-bronchodilator forced expiratory volume in the first second; PTU, pressure time units; SMIP, sustained maximal inspiratory pressure.

Figure 1 Graphic representation of an inspiratory effort performed using the PrO2 device software.

Abbreviations: FIT, Fatigue Index Test; ID, inspiratory duration; MIP, maximal inspiratory pressure; PTU, pressure time units; SMIP, sustained maximal inspiratory pressure.

Table 2 Test–retest reliability of MIP, SMIP and ID measurements in COPD

Variables	Mean±SD		ICC	95% CI	SEM
	Test	Retest
MIP (cmH2O)	78.1±25.4	76.2±24	0.979	0.947–0.991	3.477
SMIP (PTU)	387.3±160.7	385.2±154	0.994	0.986–0.998	11.928
ID (seconds)	9.6±3.7	9.7±3.2	0.975	0.940–0.990	0.505

Abbreviations: ICC, intraclass correlation coefficient; ID, inspiratory duration; MIP, maximal inspiratory pressure; PTU, pressure time units; SEM, standard error of measurement; SMIP, sustained maximal inspiratory pressure.

Figure 2 Bland–Altman plot highlighting test–retest agreement in MIP (A), SMIP (B), and ID (C) values obtained using the TIRE method.

Note: The middle line indicates the mean difference between testing sessions, and the upper and lower lines indicate the 95% confidence limits for these measurements calculated as mean difference±(SD×1.96).
Abbreviations: ID, inspiratory duration; MIP, maximal inspiratory pressure; SMIP, sustained maximal inspiratory pressure; TIRE, Test of Incremental Respiratory Endurance.

Table 3 Known-groups validity of maximal and sustained inspiratory muscle measurements in different airflow limitation groups

Variables	GOLD I–II (n=29)		GOLD III–IV (n=52)		Significance	Effect size
	Mean	SD	Mean	SD	p-value	Hedge’s g
MIP (cmH2O)	84.2	29.0	73.7	18.0	0.024	0.466
SMIP (PTU)	460.0	117.7	373.0	135.7	0.003	0.671
ID (seconds)	11.2	1.9	9.4	3.0	0.003	0.676

Abbreviations: GOLD, the Global Initiative for Chronic Obstructive Lung Disease classification; ID, inspiratory duration; MIP, maximal inspiratory pressure; PTU, pressure time units; SMIP, sustained maximal inspiratory pressure.

Figure 3 Scatter plots with lines of best fit on the relationships between MIP (left), SMIP (middle) and ID (right) with the 6MWT distance in the study sample.

Note: Only SMIP and ID were significantly associated with the 6MWT distance (n=47).
Abbreviations: 6MWD, 6-minute walk distance; 6MWT, 6-minute walk test; ID, inspiratory duration; MIP, maximal inspiratory pressure; SMIP, sustained maximal inspiratory pressure.

Figure 4 Scatter plots with lines of best fit on the relationships between MIP (left), SMIP (middle) and ID (right) with degrees of dyspnea in the study sample.

Note: Only SMIP and ID were significantly associated with shortness of breath (n=53).
Abbreviations: ID, inspiratory duration; MIP, maximal inspiratory pressure; SMIP, sustained maximal inspiratory pressure.