Arterial pressure waveform analysis Flashcards
What does vasodilatation present as on the arterial waveform?
A lower systolic/diastolic pressure, wie pulse pressure and delayed dicrotic notch
How does vasoconstriction affect the pulse pressure?
Narrow pulse pressure
What are the components of the arterial waveform?
- steady component which is the mean pressure within the system (MAP)
- pulsatile component which oscillates around this value in a complex manner determined by
- SV
- vascular capacitance
- peripheral vascular resistance
- heart rate
What is systolic pressure?
The maximum pressure recorded in the arterial tree during ventricular ejection
What are the main influencers of systolic pressure?
Stroke volume
Vascular capacitance (how stuff or flexible the arteries are)
When vascular capacitance is contant, an increase in SV increases the systolic pressure.
Why do elderly people have a higher systolic pressure and lower diastolic pressure?
Because they have reduced vascular compliance due to ateriosclerosis so need a higher systolic to overcome this and also inability of the stiff arteries to recoil and maintain pressure within the compartment during diastole.
What effect does aortic cross clamping have on the brachial arterial pressure?
It causes an acute reduction in vascular compliance - so has an acute increase in the systolic pressure because the ability of the vascular tree to expand during ejection is decreased, and reduction in diastolic pressure due to reduced vascular volume so impairment of vascular tree to recoil
What is the dicrotic notch?
It’s the nadir point that occurs immediately after closure of the aortic valves and preceds the secondary dicrotic wave. It’s a marker of the end of the ventricular ejection period.
The secondary dicrotic wave occurs as the elastic recoil of the arterial tree pushes against a closed aortic valve causing a secondary pressure increase
Why is the dicrotic notch usually seen 1/3 of the way down the descending limb of the pressure wave?
This is when the pressure in the aorta > pressure left ventricle so the aortic valve closes
What causes a downward shift in the dicrotic notch?
- low systolic pressure
- low diastolic pressure
- widened pulse pressure
All of which are due to vasodilation and reduced peripheral vascular resistance (eg sepsis).
How does inspiration affect the arterial pressure waveform?
Inspiration increases intrathoracic pressure which will increase venous return to the LA due to squeezing of pulmonary capillaries.
This will increase the LV stroke volume and therefore the arterial pulse pressure
It will also cause a reduction in venous return to the right side of the heart and reduction in RV stroke volume will feed through to the left ventricle within 4-5 beats and therefore the LV SV and arterial PP will be gradually decreased after the transient increase.
What causes a swing in the arterial pressure waveform?
- the effects of intrathoracic pressure are amplified in hypovolaemia causing a “swing” in the pressure wave
- there’s also a beat-to-beat variation in SV (or PP) because the effects of intrathoracic pressure is exaggerated in hypovolaemia
- the extent of the swing is dependent on how much intrathoracic pressure is varying (eg tidal volumes, inspiratory pressure and PEEP)
- in patients with ARDS/very reduced lung compliance this may mask the swing because the intra-alveolar pressure fluctations may be poorly transmitted to the intra-pleural compartment
What is pulse contour analysis?
The indirect estimate of CO using parameters that are derived from a high fidelity arterial trace (usually the PP and Asys).
Only accurate as long as vascular capacitance/peripheral vascular resistance doesn’t change (eg in sepsis, use of vasopressors, regional blockade)
In this case - you’d need to recalibrate for results to be accurate
What are the two systems that use pulse contour analysis for estimating cardiac output?
- PiCCO - based on transpulmonary thermal dilution
- LiDCO - based on transpulmonary lithium dilution
Both use transpulmonary indicator dilution techniques to provide periodic calibration of the arterial trace before pulse contour analysis is used to derive CO
What would multiple wave reflections on the arterial waveform indicate?
Non-specific indicators of significant flow abnormalities within the arteries (eg significant small vessel disease such as SLE), and also may be evident during vasoconstriction associated with hypovolaemia
