TIPHEMODYNAMIC.pdf.pdf

 Δ Δ Δ Δ Functional murmurs (also called physiologic murmurs) can occur in the absence of valvular pathology. An example would be an aortic systolic ejection murmur caused by a high cardiac output state. Very high flow velocities in the aorta can lead to turbulent...

 Δ Δ Δ Δ Functional murmurs (also called physiologic murmurs) can occur in the absence of valvular pathology. An example would be an aortic systolic ejection murmur caused by a high cardiac output state. Very high flow velocities in the aorta can lead to turbulent flow which will result in a murmurs during the ejection phase of the cardiac cycle. Examples of this include high cardiac outputs in trained athletes and high output states during anemia. Another example is pregnancy where the increase in cardiac output especially when coupled with anemia can result in physiologic ejection murmurs. Δ Δ Δ STRUCTURE OF MICROCIRCULATION  RT = RA + Ra + Rc + Rv + RV (A artery; a arterioles; c capillary; v venules; V vein) The resistance of each segment relative to the total resistance of all the segments determines how changing the resistance of one segment affects total resistance. To illustrate this principle, assign a relative resistance value to each of the five resistance segments in this model. The relative resistances are similar to what is observed in a typical vascular bed. Assume RA =1 , Ra = 70 , Rc = 20 , Rv = 8 , RV = 1 ; Therefore, RT =1 + 70 +20 +8 +1 = 100 If RA (Resistance of Artery) were to increase four-fold (to a value of 4), what would be the RT (Resistance Total)?  RT = RA + Ra +Rc +Rv + RV RA = 4-fold increase RX = Remainder of the resistance elements (Ra+Rc+Rv+RV) Normally, RL = 0.01(RA) and RX =0.99(RT) (if the large artery (RL) resistance is normally 1% of the total resistance) RA = 4(0.01)RT or RA= 0.04(RT) RT=0.04(RT) + 0.99 (RT) = 1.03 (RT) Total coronary resistance increase by only 3 %  If Ra were to increase four-fold (to a value of 280 (70X4)), the RT would increase to 310, a 210% increase Changes in large artery resistance have little effect on total resistance, whereas changes in small artery and arteriolar resistances greatly affect total resistance. This is why small arteries and arterioles are the principal vessels regulating organ blood flow and systemic vascular resistance. The above analysis explains why the radius of a large, distributing artery must be decreased by more than 60% or 70% to have a significant effect on organ blood flow Blood Flow to Organs Runs in Parallel Δ Shear Stress = viscosity X Shear rate (The ratio of the velocity of one layer of fluid to that of the adjecent layers) Shear Rate Distribution (greater at the edges!) Shear stress values in various vessels according to data reported by Lipowsky Differential distribution of shear stress in an arterial segment with lumen-protruding plaque with necrotic core (NC) The viscosity of Blood as a function of the shear rate Compliance Compliance describes the distensibility of blood vessels. Vascular compliance (C) is the slope of the relationship between a rise in volume in the vessel and the rise in pressure produced by that rise; hence, C = ΔV ΔP The compliance of combined veins is about 19 times greater than the compliance found in the combined arteries. Systolic pressure is a function of the stroke volume (preload and contractility) and compliance. Diastolic pressure is a function of the heart rate and the arteriolar resistance, which determines run-off into the veins. Diastolic area accounts for afterload.  Myocardial compliance refers to the ventricle’s ability to stretch to receive a given volume of blood If comliance is low, small changes in volume will result in large changes in pressure within ventricle If the ventricle cannot stretch, it will be unable to increase cardiac output with increased preload