FRCA Paper- Clinical Measurement MCQ: Part 1

Question 1

The following physical properties may be used in the measurement of pressure:

A. Change of electrical resistance in a wire
B. Variable inductance
C. Piezoelectric effect
D. Change in flow through a narrow tube
E. Torricellian vacuum

Answer 1

A. Change of electrical resistance in a wire (using a strain gauge)

B. Variable inductance– (The inductance of a coil can be varied by changing the position of the magnetic core within, which may be related to the application of pressure)

C. Piezoelectric effect– (Piezoelectric sensor: Converts pressure  electrical energy)

E. Torricellian vacuum (close ended manometer - vacuum above mercury- absolute pressure measurement)

Question 2

Non-invasive measurement of blood pressure comparison of systolic and diastolic values given compared to direct measurement?

Answer 2

Non-invasive techniques tend to under-read the systolic and over-read the diastolic

Question 3

What points in non-invasive BP measurement sounds do yo u get each value?

Answer 3

The systolic pressure is taken as the first time the sounds are heard as the cuff is deflated from a supra-systolic pressure.

There may then be muffling and resurgence of the sounds (Korotkoff’s second and third phase) before the sudden muffling of the sound (fourth phase) and then silence (fifth phase).

The latter two are both taken as diastolic pressures, though both are actually above the pressure recorded directly

Question 4

In non-invasive BP measurement how should cuff be sized to arm diameter?

Answer 4

The cuff should be 20% greater than the diameter of the arm

Question 5

The mean arterial pressure is the point ? in non-invasive BP monitoring.

Answer 5

The mean arterial pressure is the point of maximum oscillation in the cuff pressure

Question 6

What are the ideal features of an intravascular BP measurement device?

Answer 6

1. Resonant frequencies should be as high as possible to prevent resonance and ideally above the 10th harmonic of the highest frequency in the signal being transduced.
2. A damping coefficient of 0.64 is considered optimum producing a flat dynamic response up to the natural frequency of the system.
3. The transducer should be rigid (low displacement) so as not to take energy out of the system.
4. The manometer tubing should be short and stiff.

Question 7

Transducers commonly used in physiological monitoring include:

Select true or false for each of the following statements.

True		
False	
A.	Strain gauge				
B.	pH meter				
C.	Ear oximeter				
D.	ECG electrode				
E.	Galvanic fuel cell

Answer 7

Transducers commonly used in physiological monitoring include:

A.	Strain gauge			
B.	pH meter				
C.	Ear oximeter				
-		
E.	Galvanic fuel cell		

A transducer converts one type of energy to another so a strain gauge, pH meter, ear oximeter and fuel cell are all transducers while an ECG electrode is just a specialised conductor.

Question 8

in arterial BP measurement:
effect of underdamping?
D = ?

Answer 8

In an underdamped transducer system (D<0.5) significant overshoot and subsequent oscillation occurs.

Question 9

What is the overshoot limit in an optimally damped system?

D = ?

Answer 9

In an optimally damped system, (D=0.64) overshoot is limited to 6-7% of the initial pressure change and no oscillation will occur

Question 10

Overshoot in a critically damped system? D = ?

Answer 10

In a critically damped system (D=1.0) the change in mean pressure will be measured accurately with no overshoot.

Question 11

Response in an overdamped system? D = ?

Answer 11

In an overdamped system (D>1.0) the response is progressively slower.

Question 12

What is a fast flush used for?

Answer 12

A fast flush test can be used to assess the level of damping..

Question 13

What can cause increased distortion in an arterial trace?

Answer 13

-> bubbles, connections in the tubes, clots in the cannula.

Damping (a reduction of the speed in which changes in the input pressure are shown in the output) leads to distortion of the waveform if it is either too large or too small. Bubbles and clots in the cannula will cause over-damping. An optimally damped system is designed to dissipate energy and produce a flat dynamic response at driving frequencies up to the natural frequency of the system.

Question 14

How is thermodilution used to measure cardiac output?

Answer 14

The thermodilution technique using a pulmonary artery catheter gives an accurate, repeatable measurement of cardiac output. The cardiac output is assessed by measuring the area under the temperature change curve recorded at the distal end of the catheter by a thermistor..

Question 15

What can cause inaccuracies in measurement of CO by thermodilution?

Answer 15

1. Patient factors - including right heart valvular abnormalities, intracardiac shunts, arrhythmias and respiration.
2. Injectate factors - too little injectate will lead to an over-estimation, errors in injectate temperature measurement or prolonged injection duration.
3. Thermistor factors

Question 16

What thermistor factors can effect accuracy of CO measurement with the thermodilation method?

Answer 16

1. wedging or partial wedging of the catheter produces unreliable results as the cooled mixture does not make adequate contact with the thermistor.
2. looping of the catheter reduces the distance between the injection port and the thermistor so mixing of the injectate with blood may be incomplete.
3. Thrombi on the catheter will produce under-estimates of cardiac output.

Question 17

What methods can be used to measure cardiac output?

Answer 17

1. Lithium dilution
2. Indocyanine green indicator dilution
3. Impeaence cardiography
4. Aortic doppler ultrasound.

Question 18

How is impedance cardiography used to measure cardiac output?

Answer 18

Impedance cardiography detects voltage changes produced by the alteration in thoracic bioimpedance caused by ventricular ejection. Stroke volume is calculated from the magnitude of this voltage fluctuation.

Question 19

What is lithium dilution used for?

Answer 19

CO measurement.

Lithium dilution is a technique that does not require pulmonary artery catheterisation.

A bolus of lithium chloride is injected via a cvp line and the arterial concentration of lithium determined by a lithium sensitive electrode.

A dilution curve for lithium is plotted and the cardiac output derived.

Question 20

How can Doppler US be used to measure cardiac output?

Answer 20

Doppler ultrasound may be used at the suprasternal or oesophageal site to determine the velocity profile of the blood in the aorta from which cardiac output is estimated.

The cross-sectional area of the aorta must be known.

Question 21

What does an oesophageal doppler measure directly?

Answer 21

It is the velocity of blood in the descending aorta that is measured from which the volume is calculated using a nomogram for the cross sectional area of the aorta.

Question 22

How should the oesophageal probe be angled?

Answer 22

The angle of insonation between the ultrasound waves and blood stream must be known.

his is part of the Doppler equation and is 45 degrees due to the angulation of the tip of the probe.

Question 23

Does the probe in oesophageal doppler measure total cardiac output?

Answer 23

It measures cardiac output in the descending aorta which accounts for approximately 70% of total CO in healthy people.

It uses this assumption to calculate total cardiac output and so may be inaccurate in the presence of spinal or epidural anaesthesia when the proportion of blood flow in the descending aorta may be higher.