Blood Pressure Flashcards
What do we refer to when speaking of BP?
Systemic arterial blood pressure
What are some vital signs?
- BP (Systemic arterial blood pressure)
- Heart rate
- Temperature
- Respiratory rate
How does the pressure fluctuate in the left ventricle and how does this affect aortic pressure?
Left ventricular pressure = LVP
The pressure in the ventricle is nearly 0, very low, in the diastolic period, this is the resting pressure.
The pressure in the aorta is higher than the pressure in the ventricle at this point and the valve is closed
When the ventricle contracts, the LVP is higher than aortic pressure, the valve opens and the pressure keeps increasing as the ventricle contracts. The ventricular muscle relaxes and the pressure quickly falls such that the aortic pressure becomes higher and the valve closes
The pressure in the aorta falls but very slowly and remains mostly high the whole time
Why do we care about aortic pressure?
It is the BP, the pressure in the aorta corresponds to the BP
What is the ejection phase?
Period between which LVP is higher than aortic pressure due to contraction, valve is open, blood flows from the ventricle into the aorta. When the muscle relaxes and the LVP falls just below the aortic pressure such that the valve closes, this is the end of the ejection phase.
What is the arterial systolic pressure?
Peak of pressure around 120 mmHg
What is the arterial diastolic pressure?
Minimum pressure in the artery around 80 mm Hg
How do we denote BP?
120/80 mmHg (max over min)
What is arterial pulse pressure?
- Amplitude of pulse (max-min)
- around 40 mmHg (cuz 120-80)
What is the mean arterial pressure?
MAP is around equal to diastolic pressure + 1/3 (pulse pressure) or around equal to 100 mmHg
What is the windkessel effect (firefighter example)?
Two teams are taking turns pushing on a pump to generate pressure so that the water flows and pushes the air in an air chamber
When they stop pushing and stop generating pressure, well the compressed air expands and generates a pressure on the water maintaining flow
- generated pressure (input pressure) from the teams is high and falls to 0 and high and falls to 0 but the output pressure (pressure on the flowing water) never falls to 0 because of the pressure from the air, so the graph looks more zig zag up and down never reaching 0
How does the Windkessel effect translate to the CVS?
- The heart is like the firefighter pump and does turn on for 1/3 of a second and off for 2/3 of a second and dumps stroke volume into the aorta but does not immediately flow because of the resistance of all organs (“afterload”)
- Pressure in the aorta increases proportional to the volume being dumped and then blood can flow, because pressure increases when volume increases in this compliant structure (2/3 of a second), when the heart is not pumping, energy to floe comes from the elasticity of arteries, analogous to air, as it comes back to its OG form pushes a bit on the blood during diastole, pressure is about 80 mm Hg, as volume is flowing and decreasing in the aorta, pressure falls but not too much thanks to the elasticity, so it can accumulate blood and then push as it relaxes and keeps organs perfused at all points of the cardiac cycle
How is the flow into the aorta during the cardiac cycle?
Only flows in for 1/3 of cardiac cylcle
How is the pressure in the aorta vs the ventricle during the cardiac cycle?
- Pressure only high in ventricle for 1/3 of a second then falls to zero
- Aortic pressure is really high for 1/3 of a second and falls slowly after but stays high so that organs are always perfused not just 1/3 of a second
How quickly does pressure fall in the aorta and what determines this using principles of the Windkessel effect?
- If compare to a circuit with a resistor and a capacitor, we see that although voltage goes up and down to 0 very quickly, the actual voltage measured goes up and falls slowly as an exponential curve because the capacitor charges up and how quickly voltage falls depends on a time constant determined by the product of resistance and capacitance
- In the aorta, the product of the resistance from organs and compliance of the vessel will give a time constant that will determine how quickly pressure in aorta falls during that 2/3 of a second
- Luckily that product of resistance and compliance gives quite a high time constant, so aortic pressure falls quite slowly and organs can remain perfused for the whole cardiac cycle
What are the different methods to measure BP?
Direct: arterial puncture, think horse :(, 1st ever method to measure arterial bp
Indirect: palpation, auscultation and oscillometry
What is an important component of the three indirect method of bp measurement?
All indirect methods need an aneroid (without liquid to contrast with Hg sphygmomanometer) sphygmomanometer
- There is a cuff that goes around the patient’s arm
- Bladder, thick part of the cuff, a rubber sack that fills with air by the
- tube
- Aneroid gauge that shows measurement of pressure
- Inflating bulb to pump air into cuff
- Needle valve to slowly release air, when turned all the way clockwise, pump air into cuff and increase pressure in cuff
What are the important parts of the aneroid gauge, how does this allow us to measure pressure?
- Pointer, Spindle, vacuum chamber, lever
- When air gets pumped and goes back to the aneroid gauge, the air in it gets pressurized and pushes on the vacuum chamber (pressure is 0) which moves the lever which is attached to the spindle through a cord, the spindle will then spin, moving the pointer, indicating the pressure, still mm Hg grading
Difference between a Hg sphygmomanometer and aneroid sphygmomanometer?
Basically the same as the aneroid, but replace the Hg column with an aneroid gauge since Hg is a neurotoxin
Describe the method of palpation for BP measurement.
- By touch, feeling the radial pulse which is easily felt with fingers
- pump up air in cuff, very high pressure, artery will close and cannot feel the pulse then open the valve a bit so air leaks out slowly and pressure in cuff falls slowly
- Can only measure systolic, no measure diastolic
We measure the systolic pressure when we can feel pulse again because that means that pressure in the artery is finally higher than in the cuff, has reopened, this is systolic
What are the parts of the stethoscope?
- Earpiece, bell, diaphragm
Describe the method of auscultation for BP measurement.
- Listen
- Can measure systolic and diastolic pressure
- If place stethoscope on the inside of the elbow, cannot hear anything because smooth flow since laminar/parabolic
=> pump up until high cuff pressure and allow to fall slowly by opening valve - When start hearing sound => systolic pressure (Korotkoff sounds), cuff pressure so strong that the artery is closed, but when the pressure is just below systolic, artery sort of opens, so from completely closed to completely open, flow expansion, turbulent flow does make sound, squirting blood
- When stop hearing sound bcs pressure in cuff is lower than pressure in artery at all points of cardiac cycle, no compression of artery, fully open, no sound, restore laminar flow
Describe the oscillometric method for BP measurement.
- Look at oscillations
- Pump inflates cuff and then allows air to leak out, computer does not get sounds, it gets pressure in cuff
- Oscillations in cuff pressure starts right before reaching systolic pressure and persists until reach diastole, machine computes slopes of oscillations to determine systolic (seeing how it rises)/diastolic (seeing how quickly it falls)
What generates the BP?
- Left ventricle contracts around 1/second and then aorta basically the sequence of events of variation in aortic pressure and left ventricular pressure
- The combination of contraction, relaxation, opening/closing of valves and winkessel effect that keeps aortic pressure high
