Flow reserve in the coronary circulation and vascular reserve and reactivity in the cutaneous microcirculation

Flow and vascular reserves are important concepts for assessing the functional consequences of changes to a circulation as a result of alterations in vessel geometry, wall properties and overall hemodynamics. To investigate factors that affect vascular reserve, two special circulations, namely the coronary and cutaneous circulations, were selected based on their high degree of clinical relevance. For the coronary circulation, experiments were performed on the left anterior descending coronary artery (LAD), which is one of the principal arteries in the coronary circulation perfusing the myocardium. For the cutaneous circulation, microcirculatory vascular reserve and its hyperemic responses were studied.; Pressure waveforms obtained in the LAD coronary artery, during stenosis and following cardiological interventions were analyzed in order to quantify vascular reserve. For the latter, a popular index known as the Fractional Flow Reserve (FFR) was calculated, following pressure gradient estimation. Modeling of a tapered artery with stenosis was then carried out to study the local hemodynamic effects of a geometric stenosis. Increases in phase velocity, characteristic impedance and local reflection coefficients were demonstrated as the principal hemodynamic consequences of stenosis.; Temporary ischemia and heat were used to test the Laser Doppler-measured flow response of the microcirculation. The peak response of reactive hyperemia following ischemia was shown to be higher in the arm than in the foot, although the foot had a more prolonged response. The foot response was significantly muted in smokers. Diabetics had demonstrably lower vascular reserve in response to heating as estimated by the Microvascular Perfusion Reserve (MPR) index.; An important contribution of this study was the use of a second-order system to simulate and predict the vasodilatory response to temporary ischemia. It was shown that the amplitude and time course of reduced hyperemia in smokers could be simulated when the microcirculation was considered to be less compliant and more resistant to increases in blood flow. This could, for example, explain changes in the coronary flow reserve as a result of altered properties of the distal coronary vasculature.