cv wk 4 hemodynamic measurements Flashcards
what is the most important monitor in the operating room?
the anesthetist
Name a return-to-flow technique of blood pressure measurement
palpation,
pulse oximeter (plethysmographic),
indwelling arterial catheter
name several insertion sites for arterial catheters
radial, brachial, femoral, dorsalis pedis, axillary, ulnar artery
In a healthy individual with disease-free arteries, does systolic blood pressure increase or decrease in the leg relative to the proximal aorta?
systolic BP increases while diastolic BP decreases, creating an increase in pulse pressure. This occurs because of reflective waves from vessel branching, and from decreased arterialcompliance(increased vessel stiffness) as the pressure pulse travels from the aorta into systemic arterie. MAP only slightly decreases
3 waves of CVP
a) wave- atrial contraction
c) RV begins to contract CUSP of tricuspid valve protrudes backwards through RA
v) as blood fills the right atrium, it hits the tricuspid valve and this the back-pressure wave.
- What are the different waveforms that would be encountered when inserting a Swan-Ganz catheter from its insertion in the right jugular vein to its final position in a pulmonary artery?
- CVP
- Right ventricle
- pulmonary artery
- wedge
what are direct measurements that can be gathered by a swan ganz
CVP, Right-sided intracardiac pressures, pulmonary arterial pressures, wedge pressure, mixed venous oxyhemoglobin saturation
what are measurements that a swan ganz or pac indirectly measure
SVR, PVR, CI, Stroke volume index, Right ventricular stroke work index, LV stroke work index, oxygen delivery, oxygen uptake
First step to zero transducer
Establishing a standard reference value, ambient atmospheric pressure, which is assigned the value of 0 mm Hg and used as the reference point for all subsequent intravascular pressure measurements
second step to zero transducer
The second step in transducer setup involves placing the transducer at the appropriate vertical height relative to the patient’s position.
Fick measurement equation for CO
O2 per minute absorbed by the lungs (ml/min) / Arteriovenous O2 difference (mL/ L of blood)
what is the thermodilution method for measuring CO?
Based on the indicator dilution technique and utilizes temperature as the indicator
A known amount of indicator (saline) at a known temperature (lower than blood) is injected into the right atrium
This indicator mixes with blood lowering its temperature
The temperature is measured near the tip of the catheter; the change over time expressed as the area under the curve is planimetered to calculate the cardiac output
how is the velocity of blood flow related to the cross-sectional area of a blood vessel or group of blood vessels?
Velocity is inversely related to cross-sectional area.
according to ohm’s law what 2 factors determine blood flow through a blood vessel?
I (current flow) = V (voltage drop, apressure-vpressure) / R (resistance)
Define blood pressure
Blood pressure is the force exerted by the blood against any unit area of the vessel wall
conversion factor from mmHg to cmH2O
1.36
What is cerebral perfusion pressure?
MAP-CVP or ICP (whichever is higher)
Poiseuille’s law
Q = Pie(Pi-Po)r^4 / 8nL
n=viscosity
Poiseuille’s what factor has the greatest impact on the rate of blood flow through a vessel?
Flow varies directly as the fourth power of the radius
What is resistance?
Resistance is the impediment to blood flow in a vessel and cannot be measured directly
SVR=
(MAP-CVP)80/CO
PVR=
(MPAP-MCWP)80/CO
How would you calculate resistance when blood vessels are arranged in series?
R1+R2+R3…
Resistance=
Pi-Po / Q
Flow =
(Pa-Pv) / R
How would you calculate resistance when blood vessels are arranged in parallel?
1/ (1/R1 + 1/R2 + 1/R3)…
- If you added another blood vessel in a parallel arrangement, would total vascular resistance increase or decrease? Why?
Decrease, dividing 1 by Rtotal, as total increases, fraction becomes smaller 1/4 vs 1/5
what is laminar flow?
fluid particles following smooth paths in layers, with each layer moving smoothly past the adjacent layers with little or no mixing.
what is turbulent flow?
flow in which the fluid undergoes irregular fluctuations, or mixing
what formula can you sue to predict laminar vs turbulent flow?
Reynolds number. NR=(density x tube diameter x mvelocity) / viscosity
what is the relationship of hematocrit to blood viscosity?
Directly proportional, As hct increases, viscosity increases
- As blood pressure increases within a vessel why does blood flow increase much greater than one would expect?
Flow=Pressure/Resistance, sympathetic stimulation?
- What is damping in an arterial line tracing?
how quickly the vibrations come to a rest
what is ringing in an arterial line tracing?
Ringing” or oscillations below and above the baseline. This leads to false-high systolic
pressures and false-low diastolic pressures. Peak systolic tracings may show more than
one sharp upstroke and diastolic points are hard to differentiate. The MAP is usually
accurate.