<unk>  <unk>  is a diagnostic technique used in coronary catheterization to measure pressure differences across a coronary artery stenosis (narrowing, usually due to atherosclerosis) to determine the likelihood that the stenosis impedes oxygen delivery to the heart muscle (myocardial ischemia).<unk>  is defined as the pressure after (distal to) a stenosis relative to the pressure before the stenosis. The result is an absolute number; an<unk>  of 0.80 means that a given stenosis causes a 20% drop in blood pressure. In other words,<unk>  expresses the maximal<unk>  down a vessel in the presence of a stenosis compared to the maximal<unk>  in the hypothetical absence of the stenosis.
Fractional flow reserve
Coronary flow reserve
Pressure reactivity index
Instantaneous wave-free ratio
Impedance cardiography
Arterial resistivity index
Tissue Doppler echocardiography
Intracoronary optical coherence tomography