Abstract 3160: Measurement of Pulmonary Flow Reserve and Pulmonary Index of Microcirculatory Resistance for Detection of Pulmonary Microvascular Obliteration

Abstract

BACKGROUND: Early pulmonary vascular disease (PVD) is often clinically silent, as initial pulmonary microvascular loss does not lead to significant pulmonary artery pressure rise. Assessment of peak hyperemic flow using thermodilution derived mean transit-time (Tmn) facilitates accurate evaluation of the coronary microcirculation, but is unvalidated in lung. We therefore aimed to:

1. validate Tmn as surrogate of pulmonary blood flow;

2. measure the novel indices Pulmonary Flow Reserve [PFR=(maximum hyperemic)/(basal flow)] and Pulmonary Index of Microcirculatory Resistance [PIMR=(maximum hyperemic distal pulmonary artery pressure)*(maximum hyperemic Tmn)], and;

3. study the effect of pulmonary microvascular obliteration on PFR and PIMR.

METHODS: Temperature- and pressure-sensor guidewires were placed in segmental pulmonary arteries (SPA) of 12 baboons and intravascular temperature measured. Tmn and hemodynamics were recorded at rest and following intra-SPA adeno-sine(10 – 400μg/kg/min) and papaverine(3–24mg). PFR and PIMR were calculated before and after intra-SPA microsphere administration.

RESULTS: Temperature did not vary with intra-SPA sensor position (0.010±0.009 v 0.010±0.009°C; distal v proximal; p=0.1), validating Tmn use in lung. Adenosine(to 200μg/kg/min) & papaverine(to 24mg) induced dose-dependent flow augmentations (40±7% & 35±13% Tmn reductions v baseline, respectively; p<0.0001). Cumulative microvascular obliteration progressively reduced PFR (1.41±0.06, 1.26±0.19, 1.17±0.07 & 1.01±0.03; for 0, 10^4, 10^5 & 10^6 microspheres; p=0.009) while increasing PIMR (5.7±0.6, 6.3±1.0, 6.8±0.6 & 7.6±0.6mmHg.sec; p=0.0048).

CONCLUSIONS: Tmn is a valid surrogate of pulmonary flow. PFR and PIMR can be assessed using sensor-guidewires and adenosine or papaverine as hyperemic agents. These novel indices detect progressive pulmonary microvascular obliteration with potential implications for the diagnosis of early PVD.