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HOM > Practicals > Flashcards

Practicals Flashcards

1
Q

What does lab tutor do

A

Receives input from a transducer, amplifies it and felt is it to give a smooth read out for sampling

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2
Q

Why is filtering necessary for the lab tutor

A

There is interference from surrounding electrical signals

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3
Q

What does interference from mains power line produce

A

A 50 Hz sinusoidal wave

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4
Q

What does the interference from surrounding traffic looks like

A

A low frequency interference

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5
Q

What does it mean if a filter is low pass

High pass?

A

It allows low frequencies to pass and attenuates higher frequencies

Attenuates lower frequencies while allowing higher ones to pass

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6
Q

What does a band pass filter do

A

Allows a distinct range of frequencies through

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7
Q

What does a faraday cage do

A

Eliminate electrical interference

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8
Q

What is aliasing and how do you avoid it

A

When a lower frequency signal is formed by the sample

It is avoided it by making the sample frequency twice the frequency of the original signal

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9
Q

How is the finger pulse measured

A

Through force changes in the tip of the finger during systole and diastole

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10
Q

Will compression of the radioulnar arteries stop the finger pulse signal

A

No it will only reduce it due to the anastomosis between them

Only blockage of the brachial artery will stop it

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11
Q

How can you reduce finger pulse amplitude

A

Immerse hand in cold water, causing vasoconstriction of the arterioles

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12
Q

Of the reference and test sides which is negative and positive

What is the voltage

What measures the potential difference

A

Ref: negative
Test: positive

Test - ref

Ag/AgCl electrodes either side of the artificial permeable membrane

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13
Q

What is the equation for τ

A

RC

τ= The time taken To charge the voltage to 63%

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14
Q

Why is there a discrepancy between the estimated voltage and the record one

A

Membrane is permeable to other ions

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15
Q

Describe the fibres in an earthworm

A

Has a median giant fibre and two lateral giant fibres in the dorsal cord

The median fibre is myelinated and 90 micro metres in diameter

Lateral chords conduct fibres to the head and the median conduct away from the head

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16
Q

Describe pin placement in the earthworm practical

A

The stimulating anode is superior/rostral To the stimulating cathode
The recording pins should be placed at the tail with the anode closer to the stimulating pins and the cathode

An earth pen is placed centrally, reducing stimulus artefact

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17
Q

Why will the stimulated AP in the earthworm practical be smaller than intracellular AP

A

The electrodes are placed away from the nerve fibre

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18
Q

What is the initial rapid artefact found in the earthworm action potential

A

This is due to the stimulating current itself which is muscle response following the AP

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19
Q

What is seen in the earthworm practical if the recording electrodes are swapped

A

And inverted AP will be produced

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20
Q

How will the action potentials change in the earthworm practical depending on whether it is high-voltage or low-voltage

A

At low voltage is only median fibre is recruited

At high voltages slower lateral fibres will be recruited as well

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21
Q

How can the refractory period be calculated in the earthworm practical

A

By reducing the delay between the two stimuli until only one AP is elicited

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22
Q

How can conduction velocity be calculated in the earthworm practical

A

By attaching to electrodes closer to the stimulating electrodes, eliminating the AP activation latency

The distance between these divided by the latency in APs gives the velocity of conduction

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23
Q

How would you increase the latency of AP generation

How is it eliminated

A

Reduced temperature

Bathing in Na+ free solution

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24
Q

What is measured in the electrical stimulation of muscle practical

A

The ulnar nerve stimulation of abductor digiti minimi, in terms of its EMG activity and it’s maximal force output

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25
Q

What does the trace show when the ulnar nerve is stimulated

What does the amplitude mean

How does the trace change when using a force transducer

A

An initial spike of the stimulus, followed by a biphasic wave form

The number variants of motor units recruited

The biphasic wave was followed by a prolonged increase in amplitude (meaning a delay between stimulating and contraction)

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26
Q

The P, are, and T waves are normally deflected upwards. What does it mean if they are inverted

A

If the leads are connected incorrectly

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27
Q

What happens to the duration of diastole and systole in exercise

What causes this

A

Duration of both decrease but diastole drops more

β1 stimulates reduction in pacemaker potential

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28
Q

How is systole estimated on an ECG

Diastole?

A

The QT interval (Start of QRS to end of T)

The converse

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29
Q

In an ECG, a) Lead I=? And b) lead III =?

c) will there be a difference in the timings

A

Lead I= horizontal (usually between wrists)

Lead III = vertical

c) no P, QRS, and T will all have the same timings, just different amplitudes

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30
Q

What does short PR interval mean

A

Wolff Parkinson White syndrome

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31
Q

What does a prolonged PR interval mean

A

Atrioventricular block

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32
Q

What does a prolonged QRS interval mean

A

Bundle branch block

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33
Q

What does a prolonged QT interval mean

A

Long QT syndrome e.g. Brugada

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34
Q

What is pulse pressure

A

Difference between systolic and diastolic pressure

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35
Q

Mean ABP=

A

D+pulse pressure/3

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36
Q

Which blood pressures are raised during exercise

A

Systolic BP and mean arterial BP rise

Diastolic often stays the same

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37
Q

Give the three reflexes that mean there is no change in BP on standing

A

Vino constructive, vasoconstrictive, cardiac accelerative

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38
Q

Standard pressure in STPD

Temp?

A

760mmHg

273K

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39
Q

How does PACO2 relate to ventilation rate

A

Inversely proportional

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40
Q

VA=? (Using VE CO2 and PACO2 and K)

A

(VE CO2/ PACO2) x K

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41
Q

What does it mean if experiments are done with spirometery apparatus

A

The air being respired is contained and preserved

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42
Q

What response do you get if you breathe normal air with a CO2 absorber

A

No hypercapnic hyperventilatory response to hypoxia

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43
Q

What is used as a CO2 absorber

A

Sodium and calcium hydroxide

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44
Q

What is seen in the experiment where you breathe normal and without a CO2 absorber

A

This results in hypercapnia and those hyperventilation

This experiment becomes unpleasant overtime

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45
Q

What is seen in the experiment where you breathe pure oxygen with a CO2 absorber

A

PO2 is maintained at 100% throughout the experiment, provided there is no external air entry

As the volume of O2 in the tank drops over time, it can be used to measure the O2 consumption rate

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46
Q

In the experiment when you breathe pure oxygen what can make it dangerous

A

If external enters through a misplaced noseclip or open valve: in the scenarios the experiment would be restarted as it is too dangerous

47
Q

What happens in the experiment when you breathe pure oxygen without a CO2 absorber

A

PCO2 will rise and a hyperventilatory response is elicited

As PO2 is maintained the response will be slightly less dramatic than breathing normal air without easier to absorb

48
Q

Which values can a spirometer be used to measure

A

Static lung volumes:

VT, IRV, ERV, IC, and VC

49
Q

Why can spirometer not be used to calculate FRC and TLC

A

RV cannot be measured

50
Q

What do peak flow meters measure

A

The maximum expiratory output a subject can produce

51
Q

What is the respiratory quotient

How can it be measured

A

The ratio of CO2 produced to O2 consumed

By comparing the fall in volume when breathing normal air without a CO2 absorber to the fall in volume when breathing pure O2 with a CO2 absorber

52
Q

The respiratory quotient can be measured By comparing the fall in volume when breathing normal air without a CO2 absorber to the fall in volume when breathing pure O2 with a CO2 absorber. What does it mean if the volume increases in the former experiment ?

A

Air leakage

53
Q

Work done =

A

Force x distance

54
Q

Power=

A

Force x velocity

55
Q

Efficiency=

But

A

Power out
—————-
Total power

We can’t account for the resting metabolic rate of energy consumption

56
Q

incremental efficiency equals?

Assuming?

A

0.3 x (Y1-Y2)/(X1-X2) %

Y= power output
X= O2 consumption

This is a normal person with an average diet just releasing 20 J/mL of oxygen

57
Q

What does the delay an increase of O2 consumption at the beginning of exercise represent

A

O2 debt

58
Q

What represents O2 repayment

A

Increased O2 consumption after exercise has finished

59
Q

How are O2 debt and repayment measured

A

By backwards extrapolation of the study O2 consumptions

60
Q

Why is 02 repayment necessary

A

To oxidise lactate and restore phosphocreatine supplies as well as supplying hyperactive tissue such as the heart and inspiratory muscles as their rate of activity declines

61
Q

Why is the O2 repayment higher than O2 debt

A

Oxygen must be consumed to supply hyperactive tissue during activity decline after exercise which is separate to O2 debt

62
Q

When is O2 consumption and work rate roughly proportional

A

During mild/moderate exercise as the respiration is mostly aerobic

63
Q

Give the Fick Principle

CO=

A

Rate of CO2 loss
————————————-
[Venous CO2]-[arterial CO2]

64
Q

How is the alveolar gas composition measured and adjusted

A

End expiratory sample

P gas= (P-47) x F gas

65
Q

What is nomogram used to do?

A

Translate PCO2 and PO2 into concentrations and vice versa

(Curved lines= conc; grid= partial pressure)

66
Q

What is a Douglas bag used for

A

To calculate venous concentration of CO2 and rate of CO2 production.

67
Q

How is the Douglas Bag used to find the concentration of Venus CO2

A

By sampling the change in CO2 in the alveoli in a set percentage of CO2, a plot of inspired CO2 minus alveolar CO2 against inspired CO2 can equal Lavina CO2 where there is no difference inspired and alveolar (Where y=0)

68
Q

How can you measure the rate of CO2 production using the Douglas bag

A

It is initially empty and a subject while wearing a noseclip breathes into the dog was back for a certain period of time with the number of breaths recorded

The gas is analysed and CO2 volume recorded (ATPS)

Once converted to STPD, a CO2 production rate in millilitres per minute can be calculated

69
Q

Why is the average respiratory quotient around 0.82

A

Due to the mixture of fat (0.7) and glucose (one) in our diet

70
Q

How to work out respiratory quotient

A

Rate of CO2 production
————————————
Rate of O2 uptake

71
Q

How does the respiratory quotient change from fasting to fed state

A

In fasting the quotient falls while after feeding it rises

72
Q

Which two chemicals are used in fingerprick glucose tests

A

Glucose oxidase

Ferricyanide

73
Q

What are the initial levels of blood glucose while fasting

After eating?

A

4mM

7mM

74
Q

When a muscle is stimulated quickly by a TENS machine what is observed

A

Frequency summation (15 Hz) and tetany (30 Hz)

75
Q

How is the heart a dipole

Why will different ECG leads pick up different voltage differences

A

It has areas of negativity (action potentials) and positivity (resting tissue)

They will record the difference according to the length of the vector in their orientation

76
Q

Which ECG lead is increased during inspiration

A

Lead III

The heart is rotated down and rate increases

77
Q

How does conduction in the squid giant axon differ from that of a mammal myelinated axon

A

Squid axons do not conduct as fast as the largest mammalian myelinated axons

78
Q

How are the anode and cathode arranged

A

The cathode must be closer to the nerves than the anode

79
Q

Define oxygen debt

A

The difference between the oxygen consumption from the onset of work until the steady-state is achieved and what would have been consumed during this period if the steady state had been reached immediately

80
Q

RBF =

A

ΔP
———
Reff + Raff

81
Q

Pc=

A

RBF x Reff + Pv

82
Q

Why might the earth worm in ethanol be less excitable than in vitro

A

Ethanol inhibits ca2+ entry, reduces transmitter release and can open K+ channels

This all results in hyperpolarising the cell

83
Q

How does the surrounding tissue affect the recorded AP in the earth worm

A

If the tissue between the recording electrodes has a low electrical resistance it will act as a short circuit, resulting in a smaller AP being recorded

84
Q

What is the stimulus artefact

A

The Stimulating current travelling directly to the recording electrode through the body of the worm or any liquid on its surface

85
Q

What would happen if you didn’t have the Earth electrode

A

Both stimulus artefact and electrical noise will be much larger

86
Q

Are you recording extracellular or intracellular APs in the Earth worm practical

A

Extracellular

87
Q

When might increasing the voltage of the second stimulus overcome the refractory period

A

If it is in the relative refractory period

88
Q

What is super excitability

A

This refers to a period ~20msec after the relative refractory period when the axon may be slightly depolarised and therefore closer to threshold

89
Q

What are the normal latency and firing threshold for median and lateral Earth worm fibres

A

Median:
Threshold: 0.3-0.6mV
Latency: 5-10msec

Lateral:
Threshold: 0.9-1.5mV
Latency: 10-18msec

90
Q

What is antidromic

A

When an AP travels in the opposite direction it’s meant to along the axon (usually when artificially stimulated in the middle)

91
Q

How does electrical systole and diastole change in exercise

What is the mechanism behind this

A

Both diastole and systole shorten (diastole>systole so time spent in systole increases with heart rate)

Stimulation of β1 adrenergic receptors increases current through VG K+ channels, resulting in a faster depolarisation of the cell in plateau phase and therefore a shorter cardiac AP

β1 also leads to the stimulation of Ca2+ pumps in the SR, leading to a faster removal of calcium and more rapid relaxation

92
Q

How does adrenaline affect the conduction in the heart

How can this be seen on an ECG

A

β1 stimulation shortens condition delays in the AVN

A reduced interval between P and QRS

93
Q

Why does cardiac output drop in supraventricular tachycardia

A

At pathologically high heart rate over 200 BPM the heart may not have enough time to relax for the ventricles to fill properly leading to a drop in cardiac output and low blood pressure

94
Q

How is the R wave technically defined

A

The first positive deflection of the ventricular depolarisation complex

95
Q

What is respiratory sinus arrhythmia

Discuss

A

Phenomenon on of an increase in heart rate on inspiration and a decrease on exploration

This is perfectly normal and there is more pronounced in younger fitter individuals

96
Q

What causes respiratory sinus arrhythmia

A

A signal passing from respiratory to cardiovascular centres in the hindbrain during deep breathing which results in a change in heart rate mediated primarily by the parasympathetic nervous system

97
Q

Describe how the electrical activity of respiratory sinus syndrome occurs

A

In deep inspiration, the diaphragm is lowered, resulting in the heart becoming more vertical position. If the electrical axis of the heart also becomes more vertical, the vertical component of electrical activity (lead three) is increased by the horizontal component (lead one) is reduced

98
Q

True or false

Arterial pressure in the brachial artery is effectively the same as aortic pressure

A

True

99
Q

How does arteriosclerosis affect systolic BP

A

Increases systolic pressures as the arteries harden and fail to accommodate extra blood effectively

100
Q

What does diastolic pressure depend on

A

The starting point (systolic pressure) and how easy it is for the blood to drain out of the arteries (TPR)

101
Q

What is the pressure of the left ventricle during diastole

Therefore how does ventricular diastolic pressure compare to that of the arterial system?

A

0mmHg (to allow filling from VR)

Ventricular Is much lower
this is possible because of the closure of the aortic valve

102
Q

How are MAP and pulse pressure meant to change in exercise

A

Expected to increase

103
Q

Why is it difficult to establish breathing rate using chest strap transducer

A

Many people breathe largely diaphragmatically resulting in a low signal to noise ratio

104
Q

How to calculate Va when you have tidal volume, expired %CO2 and alveolar %CO2

A

Va= Vt x expired %CO2/ alveolar %CO2

105
Q

How to convert pounds to Kg

A

Times lbs by 0.45

106
Q

Why may apparent RQ be greater than 1

A

Hyperventilating

This results in unloading of CO2 from stores in tissue. Steady state and therefore a more accurate RQ will appear once the CO2 stores have depleted

107
Q

What does mM mean

A

1 mmol per litre

108
Q

Which cells in the heart are the first to depolarise?

What does this mean for the ECG

A

Central heart
Ie septum and endocardial area
They are also the last to repolarise

Both R and T are positive Deflections

109
Q

Common Equation for maximum pulse rate

More accurate version

A

220 - age

208-(0.7 x age)

110
Q

Describe cell components as parts of an electrical circuit

A

PM- capacitor and resistor in parallel

111
Q

How to calculate average ventilation rate

A

Tidal volume x number of breaths per min

112
Q

What is a typical sampling rate

What is the signal input into Power Lab and what is the out put

What is the resolution of power lab

A

1kHz

Input: analogue; output: discrete

Can generate 2^24 levels between a specified range (v high resolution)

113
Q

Why must you integrate input voltage when finger pulse is measured

A

Voltage is proportional to force change over time not force itself

HOM (11 decks)

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