Circulatory System Flashcards
Describe the auscultation of the heart
lower end of audible spectrum
- (20 to 500 Hz)
low freq (< 100 Hz)
- 3rd + 4th heart sound = diastolic murmur of mitral stenosis
high freq (> 400Hz)
- aortic regurgitation (blood falls back)
rests are in between (100 to 400 Hz)
Describe how to use a stethoscope
Bell (small side)
- used to listen to low-freq sound
(low-freq = sound diminished w/ extra pressure on bell)
Diaphragm (large side)
- used to listen to high-freq sound
(attenuates all sounds = makes low freq difficult to heart)
Errors
- loose-fitting earpieces
What is the relationship w/ blood pressure taking using invasive vs non-invasive techniques
No direct relationship:
non-invasive techniques
- (measure at the brachial artery)
- detect blood flow
ex. blood cuff
invasive techniques
- measure pressure
Describe the difference in pressure between the atriums and ventricles
Venctricle pressure > atrium pressure
(b/c ventricle needs lots of pressure to drive blood through the arteries and into the pulmonary / circulatory system)
! left ventricle pressure > right ventricle
(left–> rest of the body)
(right–> only to the lungs)
Explain the Non-invasive blood pressure technique
Materials
- sphygmomamometer (cuff, rubber bulb, mercury/aneroid mamometer)
- stethoscope
- increase blood cuff pressure until nothing can be heard from the stethoscope
- slowly the release cuff pressure
Korotkov Phase 1 (sharp sound)
- denotes systolic pressure
Korotkov Phase 2 - 3 (swishing sound)
Korotkov Phase 4 (faint sound)
- denotes diastolic pressure
What are 2 disadvantages of non-invasive blood pressure techniques?
- respiration and vasomotor waves
- introduces low-freq noise that decreases accuracy of readings - fails for infants and hypotensive patients
- blood pressure has to be around normal range in order for this technique to work
What are the 5 catheter sites for invasive blood pressure?
cannula needle is placed in an artery line:
- radial
- femoral
- dorsalis
- pedis
- brachial
What are some advantages of invasive blood pressure? (5)
- continuous beat-to-beat monitoring
- accurate readings at low pressures
- increased comfort for ICU patients
- convenient for blood sampling
- extra diagnosis based on trace
Describe the disposable sensors used in invasive blood pressure
Integrated silicon chip
- silicon diaphragm with four-resistor Wheatstone bridge diffused into it
Electrically isolated
- protected from saline by compliant silicone elastomer gel
Describe the catheter-sensor system used in invasive blood pressure?
Cathether + three-way stopcock + pressure sensor
Saline:
- system is filled with saline solution which is flushed every frew minutes to avoid blood clotting at tip
Insertion:
- inserted by surgical cut-down or use of a guided special needle
Describe the principles of strain gauge sensor (used in invasive blood pressure)
Fine wire (25 um) is strained (in its elastic limits) –> resistivity changes
- used to measure small displacements (nm)
[changing length –> changes resistance –> changes sensor reading]
Guage factor:
G = (dR / R) / (dL / L) = (1 + 2u) + (dp / p) / (dL / L)
Connections:
- unbonded strain-guage sensor connected by moving frame to diagram
- wires mounted under stress between fixed and movable frame (preload»_space; any expected load)
Measuring pressure
- increase in pressure –> increase strain on B and C + decrease strain on A and D
- wheatstone bridge: Rx and Ry balance the bridge at the start
- whatstone bridge output = dVo (measure of pressure)
Describe intravascular sensors used in invasive blood pressure measurment. Compare between catheter-tip and fiber-optic pressure sensors
Intravascular sensors:
Eliminates hydraulic connection
- enables high-freq response
- eliminates time delay
- has very little in
Catheter-tip pressure sensors:
- bonded strain-gauge sensors on the diagram
(F5 catheter: 1.67 mm outer diameter)
- expensive + breaks after few uses
Fiber-optic pressure sensors:
- measures displacement of the diagram by reflection of light
- lower cost
Which measurement provides the closest indirect measure of the amount of O2 in the blood cells?
A. [O2]
B. Blood flow
C. Blood pressure
D. ECG signal
E. none of the above
B. blood flow
(ECG would have more clinical preference if looking at how the heart works)
Describe the order of clinical preference for measuring the concentration of O2 and nutrients
- Concentration ‘
- Flow
- Pressure
- ECG
Explain why flow, despite being the closest indirect measure of [O2] does not have the highest clinical preference
Common flowmeters cannot be used
- requires cutting the blood vessel –> forms clots
Describe cardiac output, stroke volume, and their relationship to each other
Cardiac output:
- volume of blood the heart pumps per minute
Stroke volume:
- blood pumped by left venctricle in 1 contraction
(2/3 of blood in ventricle is expelled with each beat)
Cardiac output = (stroke volume)(heart rate)
Describe the method: Average flow by concentration
Calculates flow via change in concentration
[ ] = mass / volume
flow = dV / dt = (dm/dt) / dC
- Dye-dilution
- inject dye in pulmonary artery
- sample in artery
- compare change in color - Thermodilution
- inject cold saline in right atrium
- sample in pulmonary artery
- compare change in temp - Fick method
- Spirometer: measures O2 consumption
- blood samples (aortic and pulmonary artery)
F = (dm/dt) / (Ca - Cv)
Ca = [O2] atrial
Cv = [O2] venous
OR (if not using spirometer)
Cardiac output = 125(BSA) / (Ca - Cv)
BSA = body surface area
Describe the relationship between total peripheral resistance and cardiac output
TPR = resistance to blood flow
TPR = (AP - CVP) / CO
AP and CVP (units of mmHg)
CO (units of cc / min)
Describe electromagnetic flow sensors and their challenges (3)
- used in invasive surgeries where the blood vessel is exposed
- measures instantaneous aortal flow (good for monitoring flow in surgery)
- uses Farday’s law of induction b/ iron in hemoglobin can get magnetized
e = int[L,0] (u X B) * dL
e = BLu
u = blood flow velocity
B = magnetic field
Challenges
1. non-uniform flow
2. assymetric flow (near curve / branches of aorta
3. needs snug fit to artery (Expensive - $500 per probe)
Describe ultrasonic flow sensors
- measures instantaneous flow
- Uses piezo-electric transducer
- converts electricity to acoustic wave
- melted to desired shape, crystalized in strong electric field to polarize
- formed into disks, coated with metal electrodes
- driven by electric oscillator –> produces mechanical constrictions that generate longitudinal plane waves - Goal –> achieve near-field operation: higher freq and larger transducer
near-field distance
- portion of wave that goes straight before it pans outside
(increased sensor size = increased dnf)
(increased wavelength = decreased dnf)
Describe ultrasonic flow sensors: tranist-time flowmeters
- requires invasive surgery
- used to measure blood flow before, during, and after surgery
t = distance / conduction velocity = D / (c +- u*cos(0))
u –> avg blood velocity in arteries
measure time it takes ultrasonic waves to return to transducer
- US move faster along dir of blood, and slower against
- change in time can be used to find blood flwo
dT = 2Ducos(O) / c^2
Describe ultrasonic flow sensors: doppler flowmeters
Doppler effect:
Fd / Fo = u / c
Concept:
freq of US increases when exposed to moving flow of particles (blood)
- b/c scattered by RBC
Continuous-wave doppler flowmeter
- beamed through vessel wall
- backscattered by RBC
- received by piezeoelectrical signals
Describe thermal-convection flow sensor
Convective cooling of heated catheter-tip sensor due to local blood velocity
- thermistor is heated to temperature above blood temperature by power dissipated by current passign through thermistor
- non-linear methods w/ larger sensititive to lower velocities
W / dT = a + b logu
u = blood velocity
a, b = const
Describe venous-occlusion plehtymography
- measures change in volume due to arterial inflow
- cuff prevents venous blood from leaving the limb
adv
- non-invasive
applications
- used in extremities
Describe photoplethysmography (principle, adv, disadv, applications)
arterial pulsations change the volume of the vessels
- modifies absorption, reflection, and scattering of light
Adv
- simple
Applications
- timing of events such as heart rate
Disadv
- poor measure of volume change
- sensitive to motion artifacts
