Blood pressure (L18) Flashcards
Laminar vs Turbulent flow
Laminar flow should be silent, when liquid is flowing in one direction.
Turbulent flow is not silent and layers are not moving in a homogenous direction, meaning there is a lot of mixing of layers. The way you would switch from laminar to turbulent flow is based on reynold’s number.
What is reynold’s number?
A dimensionless number which will indicate the propensity of a liquid to switch to turbulent flow. Greater density, diameter, and velocity of liquid will tend to make to more likely to be turbulent,
however he more viscous a liquid is the less likely it will be to become turbulent.
What are Korotkoff sounds?
The sound of mixing blood in turbulent flow
What is the sound of mixing blood in turbulent flow?
Korotkoff sounds
What is an example of a pathological situation you may hear turbulent flow in this way, and why?
Anemia.
This is because you have reduced hematocrit. Hematocrit is directly proportional to viscosity so by decreasing hematocrit you have decreased viscosity. This means that as you become anemic your reynold’s number is increasing making it more likely for turbulent flow to exist in a given vessel.
What would the effect of anemia be on cardiac output?
Cardiac output would be positively affected by anemia because of a decreased resistance
How does a blood pressure cuff work?
By measuring Korotkoff sounds.
Basically, you squeeze down the vessel by increasing pressure until it overcomes it. Then you slowly release the pressure. When you start hearing noise, this is turbulent flow (remember, the diameter of the vessel is small now but the pressure and velocity is extremely high). So you begin counting here. The laminar flow will continue until the diastolic pressure has also been passed because at this point the transmural pressure is not great enough to beat against the vessel. This is where you stop counting.
This happens because you have decreased diameter, but not velocity. Velocity is related to cross-sectional area, so the relative contribution of velocity has increased a lot (CSA would be calculated by pi*r^2). So you’re still doubling reynold’s number and propensity for turbulence.
What subsystem of the circulation tube set contains the largest CSA space?
Capillaries
What subsystem of the circulation tube set contains the most amount of blood
Veins (~64%) - remember these are capacitance vessels that act as partly filled sacks.
Why is the relative volume in capillaries so small compared to veins when the cross-sectional area is huge?
This is because the capillaries are short and you want blood to be moving slowly and deliberately through it.
Mean Arterial Pressure
Can be used to describe the overall pressure of the system, specifically looking at the aorta, and can be approximately calculated by 1/3 systolic pressure, 2/3 diastolic pressure.
Pressure changes during the cardiac cycle: Where does the greatest pressure drop happen?
Due to the precapillary sphincters and the thick arterioles, this happens in the muscular arteries and arterioles.
pressure in larger arteries is higher than that of aorta. Why is this?
The aorta is extremely compliant, more so than the subsequent arteries. This means i will have a comparatively lower higher systolic pressure (not stretchy) and a lower diastolic pressure (not storing energy, not bouncing back, not producing pressure in diastole), leading to a larger pulse pressure in these vessels.
What two physiological parameters determine arterial pressure
Cardiac output and total peripheral resistance of the vascular system
How does cardiac output influence arterial pressure?
If you increase the blood volume you eject you’re putting more pressure on the aorta.
How does resistance of peripheral vascular system affect arterial pressure?
Total peripheral resistance is the summation of all resistance downstream of aorta and large arteries. Also, during diastole, the blood is flowing toward the periphery. So if you’re altering the resistance of the peripheral vascular system, you’re affecting diastolic BP.
What two physical factors affect arterial pressure?
changes of arterial blood volume (can overstretch aorta) Arterial compliance (compliance of a vessel affects systolic and diastolic bp)
4 things that can alter the physiological and physical aspects of arterial pressure
Baroreceptor (affects both CO and peripheral resistance)
Metabolic activity (local changes can override CNS)
Exercise, systolic pressure increases and diastolic pressure drops or remains the same, widens pulse pressure and MAP goes up
Disease (CHF, for instance)
SNS stimulation of heart and how it affects heart rate
SNS stimulation on the heart increases heart rate, which will increase cardiac output, which increases blood pressure
SNS stimulation of the heart also increases the contraction strength, which increases stroke volume (which is essentially an increase in volume being ejected), so this thus increases blood pressure
SNS stimulation of veins and how it affects blood pressure and how it affects BP
SNS will stimulate veins to venoconstrict (squeeze blood like toothpaste) which will lead to increased venous return which leads to increased preload which increases stroke volume and leads to an increase in blood pressure
SNS stimulation of arteries and arterioles and how it affects BP
Sns stimulation of arteries and arterioles leads to vasoconstriction of these vessels, subsequent increase in peripheral resistance will then lead to an increase in blood pressure
PSNS activity on heart and how it affects BP
Decrease in heart rate leading to a decrease in cardiac output which means you have a decrease in overall blood pressure (less blood getting into aorta)
What are the two things that primarily affect total peripheral resistance
Radius of the vessel (primary contributor)
Viscosity
What are some ways the radius of a vessel can change?
Vasoconstriction and vasodilation from things like RAAS and NO
