BP stuff Flashcards
What is the test called that assesses the damping coefficient?
“square wave”
“fast flush test”
Fill in the blanks
What determines the diastolic arterial pressure?
- blood viscosity
- arterial distensibility (i.e., compliance)
- length of the cardiac cycle
What determines the systolic arterial pressure?
- stroke volume
- arterial compliance
- ejection velocity of the LV
- SVR
- left ventricular preload
Explain what causes the dicrotic notch
elastic recoil of the arteries after the aortic valve closes causes the upspike
In what condition can the dicrotic notch dissapear?
vasoconstriction (i.e., arterial elasticity will go down)
overdamping
How does the pressure waveform change when arterial BP is measured further away from the center?
- upstroke becomes steeper
- higher SAP
- dicrotic notch appears later in the downstroke
- lower DAP
i.e., underdamping
e.g., long tubing
How does the MAP change when moving the dABP measurement more peripherally?
does not change, even though pulse pressure increases, MAP remains fairly constant
How does the SAP change during inspiration and expiration in mechanical ventilation
remember overall: decreased BP
BUT:
* inspiration –> increased intrathoracic pressure –> increased LV preload and decreased afterload –> increased LV SV and SAP
* expiraiotn –> decreased SV –> decreased SAP
How much is the pulse pressure variation from inspiration and expiration normally?
5 mm Hg difference - not clinically significant
What are the 2 ways to obtain MAP?
- machine averages the area under the pressure waveform from several beats
- MAP = DAP + (SAP-DAP)/3
In what situation does the traditional MAP equation underestimate MAP?
tachycardia
–> less diatolic filling time
MAP is closer to SAP in this scenario
Name the systolic pressure variation equation
What systolic pressure variation indicates volume responsiveness?
over 10 mm Hg in people
over 4.5 mm Hg in dogs
i.e., check for hypovolemia or pericardial effusion
What is the equation for pulse pressure variation?
What pulse pressure variation cutoff indicates fluid responsiveness in dogs?
PPV > 11-16%
How does pulse contour analysis work?
Measurement for cardiac output
computation of the area under the systolic portion of the arterial waveform
need initial calibration to a known cardiac output (e.g., thermo or lithium dilution)
Note: not correlating well in veterinary patients compared to other CO measurement techniques
What are causes of overdamping? What pathophysiology can look like overdamping?
- air bubbles
- too compliant tubing
- line occlusion from kinking or clotting
Hypotension if significant –> decreased SV and vasoconstriction
List potential causes for tall and narrow blood pressure waveforms? “waterhammer pulse”
- decreased blood viscosity (e.g., dilutional anemia)
- peripheral vasodilation (e.g., sepsis)
- hypertension
- aortic regurgiation
- PDA
Explain how doppler BP measurements works
- doppler probe with piozoelectric crystals –> placed over artery
- emits ultrasonic wave and tissue reflects it back –> probe converts this frequency shift into an audible sound
- sphygmomanometer proximal to the doppler probe
- inflate cuff until no sound is heard –> gradually deflate until sound returns = SAP
What are the advantages and disadvantages of Doppler BP readings
Advantages:
* cheap
* relatively easy to set up and perform
Disadvantages:
* cannot determine DAP or MAP
* poor agreement with iBP in dogs < 5jg –> poor sensitity to detect hypotension
* cats: SAP correlates better with MAP or callibration adjustment SAP read + 14 mm Hg
Explain how oscillometric BP measurements work
cuff over artery connected to a device sensing oscillations causing by blood flowing through vessel
cuff is inflated –> occludes blood flow –> deflated –>
* SAP: oscillations start increasing
* MAP: oscillations the strongest
* DAP: oscillations start decreasing
What are advantages and disadvantages of oscillometric BP measurements?
Advantages:
* faster than doppler
* less technical skills needed than doppler
Disadvantages
* DAP and SAP may not be as reliable because calculated from algorithm from MAP
