Hemodynamics and Hemodynamic Measurements - Quiz 4 Flashcards
Velocity
distance per unit of time
Velocity is ___________ related to the cross-sectional area
Inversely
Flow
volume per unit of time
How to measure Blood Flow
Velocity x Cross Sectional Area
In Ohm’s Law, what 2 factors determine blood flow through a vessel?
1) Difference in Pressure
2) Resistance
Flow (Q) = (PA - PV) / R
What is Blood Pressure
The force exerted by blood against the vessel wall
1 mmHg = ? cm-H2O
1 mmHg = 1.36 cm-H2O
What is Poiseuille’s Law?
Poiseuille’s Law
Flow is directly proportional to the pressure gradient
Flow varies directly as the fourth power of the radius
o Doubling the radius of a tube causes a 16-fold increase in flow
Flow is inversely proportional to the viscosity of the fluid
Flow is inversely proportional to the length of the tube
Resistance = the impediment to blood flow in a vessel and cannot be measured by any direct means
What is Cerebral Perfusion Pressure
Cerebral Perfusion Pressure = MAP - CVP or ICP (whichever higher)
What has greatest impact on rate of bloow flow through a vessel wall regarding Poiseuille’s Law?
Diameter of Blood Vessel
What is Resistance?
The impediment of blood flow in a vessel - cannot be directly measured
SVR Formula
SVR = [(MAP - CVP) / CO] X 80
Normal: 700-1600
PVR Formula
PVR = [(MPAP - PCWP) / CO] x 80
Normal: 100 - 300
Calculating resistance in blood vessels arranged in a series
Total Resistance = Sum of Resistance of Each Vessel
Rt = R1 + R2 + R3 + R4
Calculating blood vessel resistance in Parallel Arrangement?
1/Rt = 1/R1 + 1/R2 + 1/R3
Parallel Arrangement allows for Local Blood Flow Regulation
What happens to total resistance if you added another blood vessel in a parallel arrangement?
Total resistance would decreases - another channel for blood to flow through
What is Laminar Flow
Fluid particles following moving in smooth paths in layers in a parallel
What is Turbulent flow?
Turbulent flow occurs when it fluids make sharp turn or passes over rough surface, becoming disorderly.
Blood flows crosswise in vessel and form local eddies, increasing flow resistance due to friction.
Formula used to predict laminar vs turbulent flow
Reynold’s Number (NR)
NR = pDv / n
p = density D = tube diameter v = velocity n = viscosity
Relationship of Hematocrit to Blood Viscosity?
Increasing Hematocrit increases Viscosity
Why does an increase in Blood Pressure cause a much greater increase in Blood Flow
Autoregulation. It is the intrinsic ability of an organ to maintain a constant blood flow despite changes in perfusion pressure.
What is the mechanism that drives blood flow?
The difference in total energy between two points
What are the three primary factors that determine blood flow resistance in a single vessel?
- Vessel Diameter - most important
- Vessel Length
- Viscosity of Blood
Vessel resistance is ______ proportional to vessel length and blood viscosity
Directly Proportional
Vessel Resistance is _______ proportional to the radius to the fourth power
Inversely proportional
How does pulsatility effect flow resistance?
Increases flow resistance
Cororany Perfusion Pressure =
Diastolic Pressure - LVEDP
NR < 2000 = ?
NR: 2000-3000 = ?
NR > 3000 = ?
NR < 2000 = usually laminar
NR: 2000-3000 = variable
NR > 3000 = usually turbulent
For non-Newtonian fluids, like blood, a decrease in flow _____ viscosity
Increases viscosity
What is the most important monitor in the OR?
Eyes, Hands, and Ears of the Anesthetist
Return-To-Flow Techniques for measuring BP (3)
Palpation
Pulse Oximeter (Plethysmographic Waveform)
Arterial Catheter
Insertion Sites for Art Lines (6)
- Radial
- Brachial
- Ulnar
- Axillary
- Femoral
- Dorsalis Pedis
What happens to pulse pressure in the leg relative to the proximal aorta?
SBP rises and DBP falls, increasing pulse pressure
d/t
vessel branching and decreased arterial compliance
What is damping in an arterial line tracing?
The transducer is exposed to a high signal from the pressure bag by flushing, causing transducer to vibrate.
Damping is the speed at which the vibration stops and returns to normal transduction.
What is an overdamped art line?
Underestimation of SBP & overestimation of DBP (same MAP) due to frictional forces impeding wave form - wide, slurred wave
EX: Air bubbles, kink, stretchy tubing, low pressure bag, clots
What is an underdamped art line
Overestimation of SBP and underestimation of DBP (same MAP) due to reverberation in the tubing - Peak, narrow waves
EX: Long stiff tube, increased vascular resistance
3 Waves of CVP
A-Wave: Right Atrial Contraction (P-Wave on ECG)
C-Wave: Cusp of triscuspid valve - Right Ventricle Contraction (end of QRS)
V-Wave: Right Atrial Filling hitting triscuspid valve (After t-wave on ECG)
What does a huge V-Wave on a CVP tracing suggest?
Triscuspid Regurgitation
What are the waveforms seen when inserting a Swan-Ganz
- Right Ventricular Pressure
- Pulmonary Artery Pressure
- Wedge Pressure
What info can be Directly gathered from a Swan? (6)
- CVP
- Right Side Heart Pressures
- Pulmonary Arterial Pressure (PAP)
- Pulmonary Capillary Occlusion Pressure/Wedge Pressure
- Cardiac Output
- Mix Venous Oxyhemoglobin Saturation (SvO2)
What info can be Indirectly gathered by a Swan? (8)
- SVR
- PVR
- CI
- SVI
- Left Ventricular Stroke Work Index (LVSWI)
- RVSWI
- Oxygen Delivery (DO2)
- Oxygen Uptake (VO2)
Steps to inflating wedge?
Don’t inflate wedge > 15 seconds
Don’t Inflate with more than 1.5 mL of air
Steps to Zeroing Tranducer (4)
- Establish standard reference value, ambient atm. pressure = 0 mmHg
- Place transducer at vertical height relative to patient’s position
- upper most blood level in measured chamber
- 5 cm below left sternal border at the 4th intercostal space
Fick’s Principle
Cardiac Output =
O2 per minute absorbed by lungs (ml/min) / Arteriovenous O2 difference (mL/L blood)
Thermodilution Method for measure Cardiac Output
Inject room temp solution into right atrium, and measuring temperature over time at the tip of the catheter. The change over time is expressed as the area under the curve and is used to calculate cardiac output.
What is Pulsus Paradoxus?
A drop in BP > 10 mmHg on inspiration
The Reverse happens with Positive-Pressure Ventilation - treat with fluid
What is the Natural Resonant Freqency in an art line?
How fast the system vibrates in response to a pressure signal
What is the x-descent of the CVP tracing?
Downward movement of Right Ventricle as it contracts
(Happens before T-Wave)
What is the y-descent on a CVP tracing?
Pulse pressure decrease due to opening of tricuspid valve
(Happens before P-wave)
What does a loss of y-descent suggest?
Tamponade - restriction to RV filling
Large area under thermodilution curve = ?
Low Cardiac Output
Vice Versa
What is the most widely used method to determine Cardiac Output?
Thermodilution
What is the most common problem obtaining accurate Cardiac Output measurement?
Improper Injectate Adminstration
How to else to measure Cardiac Output other than Thermodilution?
- Ultrasound methods - Esophageal Doppler
- Bioimpedance
- Partial CO2 Rebreathing Fick method
- Lithium Dilution
- Pulse Countour
Poiseuille’s Equation
Flow inversely related : (radius4 x Change in Pressure) / (Viscosity x Length of Vessel)
Flow is ______ proportional to the Pressure Gradient
Directly Proportional
Flow is ________ proportional to Length of the Tube
Inversely Proportional
Pulmonary Artery Catheter Waves
What is Poiseuille’s Law?
the velocity of the steady flow of a fluid through a narrow tube (as a blood vessel or a catheter) varies directly as the pressure and the fourth power of the radius of the tube and inversely as the length of the tube and the coefficient of viscosity
