Table 5. Correlations among mMRC grade, CAT score, CPET parameters, and FEV₁.

Variables	mMRC grade			CAT score
	ρ†	P value		ρ†	P value
VO2 max, L/min	−0.295	<0.001		−0.297	<0.001
VO2 max, mL/kg/min	−0.282	<0.001		−0.252	<0.001
FEV1	−0.387	<0.001		−0.299	<0.001
O2 pulse	−0.195	0.006		−0.142	0.047
Anaerobic threshold	−0.135	0.07		−0.194	0.009
Breathing reserve	−0.108	0.13		−0.122	0.089
ETCO2	−0.131	0.068		−0.145	0.043
VE max	−0.248	<0.001		−0.232	0.001
VD/VT peak	0.256	<0.001		0.271	<0.001

^†, Spearman’s correlation coefficient. VO₂ max, maximal oxygen uptake; mMRC, modified Medical Research Council; CAT, chronic obstructive pulmonary disease Assessment Test; CPET, cardiopulmonary exercise testing; FEV₁, forced expiratory volume in 1 s; V_E, minute ventilation; V_D, dead space volume; V_T, tidal volume.