title: Invasive assessment of the coronary microcirculation using the index of microcirculatory resistance: description and validation of an animal model.
abstract: BACKGROUND
  The index of microcirculatory resistance (IMR) enables/provides quantitative, invasive, and real-time assessment of coronary microcirculation status.
  
  
  OBJECTIVE
  The primary aim of this study was to validate the assessment of IMR in a large animal model, and the secondary aim was to compare two doses of intracoronary papaverine, 5 and 10 mg, for induction of maximal hyperemia and its evolution over time.
  
  
  METHODS
  Measurements of IMR were performed in eight pigs. Mean distal pressure (Pd) and mean transit time (Tmn) were measured at rest and at maximal hyperemia induced with intracoronary papaverine, 5 and 10 mg, and after 2, 5, 8 and 10 minutes. Disruption of the microcirculation was achieved by selective injection of 40-μm microspheres via a microcatheter in the left anterior descending artery.
  
  
  RESULTS
  In each animal 14 IMR measurements were made. There were no differences between the two doses of papaverine regarding Pd response and IMR values - 11 ± 4.5 U with 5 mg and 10.6 ± 3 U with 10 mg (p=0.612). The evolution of IMR over time was also similar with the two doses, with significant differences from resting values disappearing after five minutes of intracoronary papaverine administration. IMR increased with disrupted microcirculation in all animals (41 ± 16 U, p=0.001).
  
  
  CONCLUSIONS
  IMR provides invasive and real-time assessment of coronary microcirculation. Disruption of the microvascular bed is associated with a significant increase in IMR. A 5-mg dose of intracoronary papaverine is as effective as a 10-mg dose in inducing maximal hyperemia. After five minutes of papaverine administration there is no significant difference from resting hemodynamic status.
authors.affiliation: Serviço de Cardiologia, Hospital de Santa Marta, Centro Hospitalar de Lisboa Central, EPE, Lisboa, Portugal. Electronic address: antoniojosefiarresga@spc.pt.
authors.forename: António
authors.initials: A
authors.lastname: Fiarresga
authors.affiliation: Serviço de Cardiologia, Hospital de Santa Marta, Centro Hospitalar de Lisboa Central, EPE, Lisboa, Portugal.
authors.forename: Mafalda
authors.initials: M
authors.lastname: Selas
authors.affiliation: Serviço de Cardiologia, Hospital de Santa Marta, Centro Hospitalar de Lisboa Central, EPE, Lisboa, Portugal.
authors.forename: Eunice
authors.initials: E
authors.lastname: Oliveira
authors.affiliation: Instituto Nacional de Investigação Agrária e Veterinária, IP, Lisboa, Portugal.
authors.forename: Sandra
authors.initials: S
authors.lastname: Cavaco-Gonçalves
authors.affiliation: Serviço de Cardiologia, Hospital de Santa Marta, Centro Hospitalar de Lisboa Central, EPE, Lisboa, Portugal.
authors.forename: Duarte
authors.initials: D
authors.lastname: Cacela
authors.affiliation: Faculdade de Medicina Veterinária, Universidade Técnica de Lisboa, Lisboa, Portugal.
authors.forename: Belmira
authors.initials: B
authors.lastname: Carrapiço
authors.affiliation: Faculdade de Ciências Médicas, Universidade Nova de Lisboa, Lisboa, Portugal.
authors.forename: Nuno
authors.initials: N
authors.lastname: Cardim
authors.affiliation: Serviço de Cardiologia, Hospital de Santa Marta, Centro Hospitalar de Lisboa Central, EPE, Lisboa, Portugal.
authors.forename: Rui
authors.initials: R
authors.lastname: Cruz Ferreira
mesh_terms: D000818:Animals; D003326:Coronary Circulation; D003935:Diagnostic Techniques, Cardiovascular; D004195:Disease Models, Animal; D006940:Hyperemia / Q000139:chemically induced / Q000503:physiopathology*; D008833:Microcirculation; D010208:Papaverine / Q000008:administration & dosage; D013552:Swine; D014655:Vascular Resistance; D014665:Vasodilator Agents / Q000008:administration & dosage
chemical_list: D014665:Vasodilator Agents; D010208:Papaverine
keywords: Animal model; Coronary microcirculation; Index of microcirculation resistance; Microcirculação coronária; Modelo animal; Índice de resistência da microcirculação