Table 1.

Normal and pathological IMR values in different studies

Reference	Disease	Number of subjects	Age (years)	Inclusion/exclusion standard	IMR measurement	Pathological IMR (mmHg·s)	Normal IMR (mmHg·s)	Control group
Melikian et al., 2010	Epicardial atherosclerosis	116	48±16 (15 subjects); 63±11 (101 subjects)	Exclusion: patients with diameter severity of >50% in left coronary artery, unstable coronary syndrome, left ventricular ejection fraction of <50%, previous coronary artery bypass surgery, impaired right ventricular function, elevated pulmonary pressures, and valvular heart disease.	Thermal dilution theory; $\mathrm{I}\mathrm{M}\mathrm{R}=P_{\mathrm{d}}\times T_{\mathrm{m}\mathrm{n}};$ a 6-F guide catheter; a pressure guide wire (Radi Pressure Wire® 5, Radi Medical Systems, Uppsala, Sweden)	25.0±13.0 (12.0‒38.0)	19.0±5.0 (14.0‒24.0)	15 subjects without coronary atherosclerosis
Luo et al., 2014	CSX	36	54.1±9.2 (18 subjects); 55.3±10.1 (18 subjects)	Inclusion: CSX patients with exertional angina, positive exercise treadmill test, and normal epicardial coronary arteries. Exclusion: patients with other coronary artery disease (variant angina, cardiomyopathies, and valvular or congenital heart disease), ejection fraction of <50%, atrial fibrillation or left bundle branch block, uncontrolled hypertension or diabetes mellitus, systemic disorders, and liver or renal insufficiency.	Thermal dilution theory; $\mathrm{I}\mathrm{M}\mathrm{R}=P_{\mathrm{d}}\times T_{\mathrm{m}\mathrm{n}}$ ; a coronary pressure wire (PressureWire-4; Radi Medical Systems, Wilmington, MA, USA)	33.1±7.9 (25.2‒41.0)	18.8±5.6 (13.2‒24.4)	18 subjects with normal coronary arteries at angiography
Solberg et al., 2014	Healthy subjects	20	47.0±5.5	Exclusion: patients with cardiopulmonary diseases, diabetes mellitus, atrial fibrillation or flutter, significant coronary atheromatosis, and atrial flutter.	Thermal dilution theory; $\mathrm{I}\mathrm{M}\mathrm{R}=P_{\mathrm{d}}\times T_{\mathrm{m}\mathrm{n}}$ ; a pressure guide wire (PressureWireTM CertusTM; St. Jude Medical, St. Paul, MN, USA)		12.6 (8.9‒22.7)
Lee et al., 2015	Stable angina and asymptomatic CAD	1096	61.1±9.7	Exclusion: patients with acute myocardial infarction and the postinterventional data.	Thermal dilution theory; $\mathrm{I}\mathrm{M}{\mathrm{R}}_{\mathrm{a}\mathrm{p}\mathrm{p}}=P_{\mathrm{d}}\times T_{\mathrm{m}\mathrm{n}}$ ; $\mathrm{I}\mathrm{M}{\mathrm{R}}_{\mathrm{c}\mathrm{o}\mathrm{r}\mathrm{r}}=P_{\mathrm{a}}\times T_{\mathrm{m}\mathrm{n}}\times (1.35\times P_{\mathrm{d}}/P_{\mathrm{a}}-0.32);$ a 5‍‒‍7-F guiding catheter; guide wire (St. Jude Medical, St. Paul, MN, USA)		Median IMRapp: 17.0 (13.0‒ 23.5); Median IMRcorr: 16.6 (12.4‒ 23.0)
Murai et al., 2016	Stable angina pectoris undergoing elective PCI	71	64.8±7.7	Inclusion: stable angina patients undergoing PCI and older than 20 years. Exclusion: patients with chronic total occlusion, congestive heart failure, myocardial infarction, arrhythmias, renal insufficiency, previous coronary artery bypass graft, extremely tortuous vessels or heavy calcification, significant valvular disease, and periprocedural myocardial necrosis.	Thermal dilution theory; $\mathrm{I}\mathrm{M}\mathrm{R}=P_{\mathrm{d}}\times T_{\mathrm{m}\mathrm{n}}$ ; a 6-F catheter; a coronary 0.014-inch pressure wire (St. Jude Medical, St. Paul, MN, USA)	Pre-PCI: 19.8 (14.6‒ 28.9); Post-PCI: 16.2 (11.8‒ 22.1); Follow-up: 14.8 (11.8‒ 18.7)
Lin et al., 2017	Renal microcirculation	96	56±12 (52 subjects); 56±11 (44 subjects)	Inclusion: epicardial stenosis patients with diameter severity from 50% to 70%. Exclusion: patients with diabetes, acute and chronic myocardial infarction or kidney diseases, uncontrolled heart failure, acute and chronic infection, chronic kidney diseases, asthma or smoke or cancer, collateral circulation, and connective tissue disease.	Thermal dilution theory; when FFR>0.80: $\mathrm{I}\mathrm{M}\mathrm{R}=P_{\mathrm{d}}\times T_{\mathrm{m}\mathrm{n}}$ ; when FFR≤0.80: $\mathrm{I}\mathrm{M}\mathrm{R}=P_{\mathrm{a}}\times T_{\mathrm{m}\mathrm{n}}\times [(P_{\mathrm{d}}-P_{\mathrm{w}})/(P_{\mathrm{a}}-P_{\mathrm{w}})]$ ; 6-F Judkins catheters; a pressure guide wire (St. Jude Medical, Inc., USA)	31.0±5.0	22.0±6.0	44 subjects with normal renal microcirculation
Long et al., 2017	CSX	40	53.6±9.8 (20 subjects); 54.7±10.0 (20 subjects)	Inclusion: CSX patients with exertional angina, positive exercise treadmill test, and normal epicardial coronary arteries. Exclusion: patients with other coronary artery diseases (angina, cardiomyopathies, valvular or congenital heart disease, regional wall motion abnormalities, atrial fibrillation or left bundle branch block), ejection fraction of <50%, hypertension or diabetes mellitus, and liver or renal insufficiency.	Thermal dilution theory; $\mathrm{I}\mathrm{M}\mathrm{R}=P_{\mathrm{d}}\times T_{\mathrm{m}\mathrm{n}}$ ; a coronary pressure wire (PressureWire-4, Radi Medical Systems, Wilmington, Mass., USA)	32.2±8.0 (24.2‒40.2)	19.5±5.5 (14.0‒25.0)	20 patients with normal coronary arteries at angiography
Murai et al., 2018	NSTE-ACS	83	63.7±9.7	Inclusion: patients with NSTE-ACS undergo PCI. Exclusion: patients with chronic total occlusion or visible side branch occlusion, congestive heart failure, significant valvular disease, myocardial infarction, arrhythmias, renal insufficiency, previous coronary artery bypass graft, significant arrhythmia, and multivessel PCI cases or ST segment elevation after PCI.	Thermal dilution theory; $\mathrm{I}\mathrm{M}\mathrm{R}=P_{\mathrm{d}}\times T_{\mathrm{m}\mathrm{n}}$ ; a 6-F system; a Certus coronary pressure wire (St. Jude Medical, St. Paul, MN, USA)	27.2 (22.9‒46.5)	16.3 (10.7‒29.2)
Rampat et al., 2019	Bifurcation disease of Medina (Medina type 1,1,0 or 1,0,0 or 0,1,0)	38	62.5±10.4	Inclusion: patients with ABSORB bioresorbable vascular scaffold implantation for coronary bifurcation disease. Exclusion: patients with false bifurcation disease, severe coronary stenosis with diameter severity of >70%.	Thermal dilution theory; Pre-PCI: $\mathrm{I}\mathrm{M}\mathrm{R}=P_{\mathrm{a}}\times T_{\mathrm{m}\mathrm{n}}\times [(P_{\mathrm{d}}-P_{\mathrm{w}})/(P_{\mathrm{a}}-P_{\mathrm{w}})]$ ; after PCI and at follow-up: $\mathrm{I}\mathrm{M}\mathrm{R}=P_{\mathrm{d}}\times T_{\mathrm{m}\mathrm{n}}$ ; a 0.014-inch pressure guidewire (St. Jude Medical Inc., MN, USA)	Pre-PCI: 27.7 (18.1‒37.6); Post-PCI: 17.9 (12.1‒29.3); Follow-up: 19.5 (15.7‒30.0)
Li Y et al., 2020	Coronary tortuosity without apparent coronary atherosclerosis	8	58±6	Inclusion: patients with coronary tortuosity and without coronary atherosclerosis. Exclusion: patients with acute coronary syndrome, previous myocardial infarction or coronary revascularization, myocardial diseases, tachycardia, diabetes, hypotension, or heart failure.	Thermal dilution theory; $\mathrm{I}\mathrm{M}\mathrm{R}=P_{\mathrm{d}}\times T_{\mathrm{m}\mathrm{n}}$ ; 0.014-inch coronary pressure	26.7±2.3 (24.4‒29.0)

Data are expressed as number, mean±SD (range), or median (range). $P_{\mathrm{a}}$ : aortic pressure; $P_{\mathrm{d}}$ : distal coronary pressure; $T_{\mathrm{m}\mathrm{n}}$ : mean transit time; $P_{\mathrm{w}}$ : coronary wedge pressure; IMR: index of microcirculatory resistance; $\mathrm{I}\mathrm{M}{\mathrm{R}}_{\mathrm{a}\mathrm{p}\mathrm{p}}$ : apparent IMR; $\mathrm{I}\mathrm{M}{\mathrm{R}}_{\mathrm{c}\mathrm{o}\mathrm{r}\mathrm{r}}$ : corrected IMR; SD: standard deviation; CSX: cardiac syndrome X; CAD: coronary artery disease; PCI: percutaneous coronary intervention; FFR: fractional flow reserve; NSTE-ACS: non-ST-segment elevation acute coronary syndrome. 1 mmHg=0.133 kPa; F: a worldwide standard for medical tubing outside diameter, 1 F=1/3 mm.