L44 - Blood Pressure Flashcards
What are factors that determine the flow through a tube?
- pressure
- flow
- resistance
What is flow like?
- proportional to pressure gradient (deltaP)
- inversely proportional to resistanve (R)
What is Poiseuille’s law?
- flow is directly proportional to pressure gradient (P) vessel and radius (r^4) of tube
- flow is inversely proportional to length (L) of vessel and viscosity (n, eta) of fluid
What is Poiseuille’s law eqn for flow?
Q = deltaP x pi.r^4 / 8.L.n
What is the flow eqn like in cardiovascular system?
Q = deltaP / R
Q - cardiac output (L/min)
deltaP - Blood pressure (mmHg)
R - peripheral resistance
What way is blood flow?
Always from region of high pressure to low pressure
What are problems encountered during blood flow?
- pressure difference is needed to allow blood flow
- length - the longer - the more R - the less flow
- viscosity - the more viscous - the more R - the less flow
What is viscosity related to?
- hematocrit (RBCs/erythrocytes)
- dehydration
- high altitude
- Erythropoietin (EPO)
What is the most important factor in determining resistance?
- radius
- caused by friction of fluid against vessel vall
- effect of changes ^4
- possible to regulate r of blood vessel using smooth muslce
What is total peipheral resistance?
The sum of the resistance of all blood vessels and determine blood pressure
What is blood flow like in veins?
- thin compliant walls with large diameter and valves
- large blood vlo with low R and valves aid return to heart
What is blood flow like in arteries?
- thick muscular walls
- pressure reservoir
What is blood flow like in arterioles?
- thin muscular walls
- regulate blood pressure and flow to organs
What is blood flow like in capillaries?
- single layer of endothelial cells with small diameter and large SA
- site of gases, nutrient and waste exchange
What is total peripheral resistance primarily regulated by?
arterioles
What do arterioles determine?
- blood flow to individual organs
- resistance
What do you measure for blood pressure?
- systolic to diastolic difference
How do you measure BP directly?
- cannulate artery measure pressure with transducer
- very accurate
How do you measure arterial BP?
- cuff (arm or wrist)
- stethoscope
- sphygmomanometer
What are korotkoff sounds?
- no sounds (artery closed)
- cuff pressure < systolic pressure, first sounds heard, soft, tapping and intermittent
- low muffed sound continuously (artery opens and closes)
- cuff pressure < diastolic pressure, vessel always open so no sound
What is a pulse?
- vibration of arteries
- caused by ejection of blood from heart into systemic circulation
What is pulse pressure?
Difference between systolic and diastolic pressure
What is mean arterial pressure?
- avg pressure over cycle (diastole twice as long as systole)
- DP + 1/3 PP
What is BP like when standing?
- inc pressure of mean arterial BP in legs
- = pooling of blood in veins
What is hypertension associated with?
- inc mortality
- stroke
- myocardial infarction
- heart failure
- chronic kidney failure
