APK 2105C Lecture Notes - Lecture 28: Venae Cavae, Blood Pressure, Pressure Measurement
16 Jun 2018
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Chapter 14, Lecture 1
Vessels & Blood Pressure
• Stroke volume = blood flow from heart per cardiac cycle (heartbeat)
• Cardiac output = blood flow leaving per minute
o How quickly heart is beating, how strong heart is beating
o CO = HR x SV
o Regulation is both intrinsic and extrinsic
▪ Intrinsic = from within the organ
▪ Extrinsic = from the nerve system
• Physical laws of blood flow and BP
o Same laws that describe liquid flowing through pipes
o Flow = deltaP / R = (P1-P2)/R
▪ Delta P = pressure gradient = change in pressure
▪ R = resistance
• Any factors that hinder blood flow
▪ Flow is inversely proportional to resistance
▪ Flow is directly proportional to pressure gradient
▪ P1 = starting pressure, P2 = ending pressure
o How do you increase or decrease flow?
▪ Increase P1 to increase flow
▪ Decrease P2 to increase flow
▪ Decrease R to increase flow
▪ Inverse of above is true to decrease flow
• Pressure gradients in the CV system
o Bulk flow = regardless of the medium (gas, liquid, air), the driving force for bulk
flow is a pressure gradient—direction of flow is always down gradient
▪ High BP → low BP
o Rate of flow depends on pressure DIFFERENCE, not absolute pressure
▪ Without pressure gradient—no driving force
o DeltaP for systemic blood flow = MAP – CVP
▪ Difference between blood flow from aorta (right after it leaves the heart)
and other end of system before it comes back into the heart
▪ Aortic pressure = 85 mmHg (MAP) = P1
• Driving force for blood flow through system
• Very tightly regulated
▪ Pressure gets lower as it gets close to capillaries
▪ Vena cava pressure = 0 mmHg (dumping into RA—central venous
pressure = CVP) = P2
• CVP is actually 2-5 mmHg but is so low—negligible
o Pulmonary vs. systemic circuit flow
▪ Same in pulmonary AND systemic
• Pressure is maintained through
large arteries
o Falls off with smaller
arteries, arterioles
• Veins, vena cava have very low
pressure
▪ Pressure generated in pulmonary is
much lower than in systemic
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