Blood Flow, Pressure and Resistance AND BP measurement

What part of the blood system receives the MOST blood

Systemic 84% → VENOUS is 64%

What is the relationship between velocity, force and surface area

Velocity is directly proportional to force and indirectly proportional to surface area

In which area of the circulatory system has the highest pressure

LV → Decreases as the blood moves from systemic to pulmonary circulation

How does Ohm’s law apply to blood

Force is directly proportional to the pressure difference and inversely proportional to resistance

What is laminar flow

Blood flowing at a steady rate through smooth blood vessel

What is parabolic profile (laminar flow)

In laminar flow the velocity of flow is greater in the center than the edge

What is turbulent flow

Blood flow becomes turbulent from obstruction, sharp flow etc

What factors are related to turbulent flow

Increase with velocity, diameter and density; decrease with higher viscosity

What is the resistance in systemic vascular resistance

1 PRU

What is the normal pulmonary vascular resistance value

0.14 PRU

What is the equation for conductance

Conductance = 1/Resistance

What factor greatly influences conductance

Diameter → Conductance ∝ Diameter^4

What factors are DIRECTLY proportional to rate of blood flow in Poiseuille’s law

Pressure difference and radius 

What factors are INDIRECTLY proportional to rate of blood flow in Poiseuille’s law

Length of vessel, viscosity of blood

What determines the viscosity of blood

Amount of RBC → Measured by hematocrit

What is the effect of sympathetic system on blood flow and arterial pressure

Inhibit decrease both blood flow and arterial pressure; stimulate increase both

What does BP depend on

HR, preload, caadiac contractility, SVR

Do all BP machines give the same measurement

No, the values differ from invasive, mercury and automated

What are the conditions needed for BP measurement

NO smoking, caffeine, food, exercise 30 min BEFORE; quiet room, comfortable temperature, 3-5 minute rest, no talking 

How should the patient sit during a BP measurement

Back against chair, elbow and arm on table, foot on the floor

What value would correlate to hypertension

ESC cutoff at >130, ACC/AHA cutoff >140

What is masked hypertension

High home BP, normal office BP

What is white coat hypertension

High office BP, normal home BP

What is sustained hypertension

Both home and office BP high 

If a patient has already done office BP, is home BP necessary

Yes; patient may have underlying masked hypertension therefore home BP MUST be done WITH office BP