Passage
In the event of end-stage heart failure, a left ventricular assist device (LVAD) can be used as a heart transplant bridge to keep a patient alive. The first iterations of LVADs were pulsatile and mimicked the physiological pumping action of the heart (Figure 1) .
Figure 1 A pulsatile-flow LVAD schematicA pulsatile-flow LVAD assists ventricular systole by mechanically pumping blood from a weakened left ventricle into the aorta through a pair of one-way valves. The pressure differential ΔP generated by the pump is related to cardiac output (CO) and vascular resistance (VR) :ΔP = CO × VREquation 1The efficiency and performance of the heart (or LVAD) can be determined by the patient's cardiac pressure-volume (PV) loop. A cardiac PV loop plots the pressure and volume of the blood in the left ventricle throughout a single cardiac cycle (Figure 2) .
Figure 2 Cardiac PV Loop of a pulsatile-flow LVADBlood pressure is often represented by only two numbers: arterial systolic and diastolic pressures. A more detailed representation of blood pressures is shown in a blood pressure profile, which graphs the blood pressure throughout the length of the different vessel groups (Figure 3) . Multiple pressure fluctuations are shown within a vessel because the pressure is traced across multiple cardiac cycles.
Figure 3 Blood pressure profile of the different vessels
-Which group of blood vessels is the main source of peripheral resistance?

Question

Passage
In the event of end-stage heart failure, a left ventricular assist device (LVAD) can be used as a heart transplant bridge to keep a patient alive. The first iterations of LVADs were pulsatile and mimicked the physiological pumping action of the heart (Figure 1) .

Figure 1 A pulsatile-flow LVAD schematicA pulsatile-flow LVAD assists ventricular systole by mechanically pumping blood from a weakened left ventricle into the aorta through a pair of one-way valves. The pressure differential ΔP generated by the pump is related to cardiac output (CO) and vascular resistance (VR) :ΔP = CO × VREquation 1The efficiency and performance of the heart (or LVAD) can be determined by the patient's cardiac pressure-volume (PV) loop. A cardiac PV loop plots the pressure and volume of the blood in the left ventricle throughout a single cardiac cycle (Figure 2) .

Figure 2 Cardiac PV Loop of a pulsatile-flow LVADBlood pressure is often represented by only two numbers: arterial systolic and diastolic pressures. A more detailed representation of blood pressures is shown in a blood pressure profile, which graphs the blood pressure throughout the length of the different vessel groups (Figure 3) . Multiple pressure fluctuations are shown within a vessel because the pressure is traced across multiple cardiac cycles.

Figure 3 Blood pressure profile of the different vessels
-Which group of blood vessels is the main source of peripheral resistance?

Quizplus · Accepted Answer

11ecba2d_12e9_0bfc_a3bf_29d1a6e7c7da_MD0008_00 Equation 1 is an example of Ohm law for flow, which states that the pressure drop (ΔP) across a pipe (or vessel) is directly proportional to its resistance (R): ΔP = Q × R where Q is the volumetric flow rate. In other words, a relatively high pressure is required to drive flow through highly resistive vessels. Therefore, the group of vessels that has the greatest pressure drop across its entire length has the greatest resistance and is the main source of peripheral resistance. From the blood pressure profile of different vessels (Figure 3), the greatest pressure drop is seen across the arterioles. In addition to having the greatest vascular resistance, the arterioles are also one of the main regulators of blood pressure. Unlike other vessels, the arterioles are very muscular and can significantly change their vessel radii. By constricting or relaxing, these vessels can change the total peripheral resistance to maintain blood pressures as necessary. (Choice A) These pressure fluctuations seen in the large arteries are not due to the resistance of the vessel. The pressure within the vessel fluctuates between its systolic and diastolic pressure depending on whether the heart is contracting or relaxing. (Choice C) Although the capillaries have the smallest vessel radii and high individual resistances, they are the most numerous and are in parallel with each other. Therefore, the equivalent resistance of the parallel network of capillaries is relatively small. (Choice D) Vascular resistance depends on the pressure drop across a vessel, not the pressure at its end. Educational objective: From Ohm law for flow (ΔP = Q × R), the pressure drop across a vessel is proportional to its resistance. Therefore, the group of vessels with the greatest pressure drop across its length, the arterioles, is the main source of peripheral resistance.

Passage In the Event of End-Stage Heart Failure, a Left Ventricular