Practicals Flashcards
What does lab tutor do
Receives input from a transducer, amplifies it and felt is it to give a smooth read out for sampling
Why is filtering necessary for the lab tutor
There is interference from surrounding electrical signals
What does interference from mains power line produce
A 50 Hz sinusoidal wave
What does the interference from surrounding traffic looks like
A low frequency interference
What does it mean if a filter is low pass
High pass?
It allows low frequencies to pass and attenuates higher frequencies
Attenuates lower frequencies while allowing higher ones to pass
What does a band pass filter do
Allows a distinct range of frequencies through
What does a faraday cage do
Eliminate electrical interference
What is aliasing and how do you avoid it
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
How is the finger pulse measured
Through force changes in the tip of the finger during systole and diastole
Will compression of the radioulnar arteries stop the finger pulse signal
No it will only reduce it due to the anastomosis between them
Only blockage of the brachial artery will stop it
How can you reduce finger pulse amplitude
Immerse hand in cold water, causing vasoconstriction of the arterioles
Of the reference and test sides which is negative and positive
What is the voltage
What measures the potential difference
Ref: negative
Test: positive
Test - ref
Ag/AgCl electrodes either side of the artificial permeable membrane
What is the equation for τ
RC
τ= The time taken To charge the voltage to 63%
Why is there a discrepancy between the estimated voltage and the record one
Membrane is permeable to other ions
Describe the fibres in an earthworm
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
Describe pin placement in the earthworm practical
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
Why will the stimulated AP in the earthworm practical be smaller than intracellular AP
The electrodes are placed away from the nerve fibre
What is the initial rapid artefact found in the earthworm action potential
This is due to the stimulating current itself which is muscle response following the AP
What is seen in the earthworm practical if the recording electrodes are swapped
And inverted AP will be produced
How will the action potentials change in the earthworm practical depending on whether it is high-voltage or low-voltage
At low voltage is only median fibre is recruited
At high voltages slower lateral fibres will be recruited as well
How can the refractory period be calculated in the earthworm practical
By reducing the delay between the two stimuli until only one AP is elicited
How can conduction velocity be calculated in the earthworm practical
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
How would you increase the latency of AP generation
How is it eliminated
Reduced temperature
Bathing in Na+ free solution
What is measured in the electrical stimulation of muscle practical
The ulnar nerve stimulation of abductor digiti minimi, in terms of its EMG activity and it’s maximal force output
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
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)
The P, are, and T waves are normally deflected upwards. What does it mean if they are inverted
If the leads are connected incorrectly
What happens to the duration of diastole and systole in exercise
What causes this
Duration of both decrease but diastole drops more
β1 stimulates reduction in pacemaker potential
How is systole estimated on an ECG
Diastole?
The QT interval (Start of QRS to end of T)
The converse
In an ECG, a) Lead I=? And b) lead III =?
c) will there be a difference in the timings
Lead I= horizontal (usually between wrists)
Lead III = vertical
c) no P, QRS, and T will all have the same timings, just different amplitudes
What does short PR interval mean
Wolff Parkinson White syndrome
What does a prolonged PR interval mean
Atrioventricular block
What does a prolonged QRS interval mean
Bundle branch block
What does a prolonged QT interval mean
Long QT syndrome e.g. Brugada
What is pulse pressure
Difference between systolic and diastolic pressure
Mean ABP=
D+pulse pressure/3
Which blood pressures are raised during exercise
Systolic BP and mean arterial BP rise
Diastolic often stays the same
Give the three reflexes that mean there is no change in BP on standing
Vino constructive, vasoconstrictive, cardiac accelerative
Standard pressure in STPD
Temp?
760mmHg
273K
How does PACO2 relate to ventilation rate
Inversely proportional
VA=? (Using VE CO2 and PACO2 and K)
(VE CO2/ PACO2) x K
What does it mean if experiments are done with spirometery apparatus
The air being respired is contained and preserved
What response do you get if you breathe normal air with a CO2 absorber
No hypercapnic hyperventilatory response to hypoxia
What is used as a CO2 absorber
Sodium and calcium hydroxide
What is seen in the experiment where you breathe normal and without a CO2 absorber
This results in hypercapnia and those hyperventilation
This experiment becomes unpleasant overtime
What is seen in the experiment where you breathe pure oxygen with a CO2 absorber
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
In the experiment when you breathe pure oxygen what can make it dangerous
If external enters through a misplaced noseclip or open valve: in the scenarios the experiment would be restarted as it is too dangerous
What happens in the experiment when you breathe pure oxygen without a CO2 absorber
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
Which values can a spirometer be used to measure
Static lung volumes:
VT, IRV, ERV, IC, and VC
Why can spirometer not be used to calculate FRC and TLC
RV cannot be measured
What do peak flow meters measure
The maximum expiratory output a subject can produce
What is the respiratory quotient
How can it be measured
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
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 ?
Air leakage
Work done =
Force x distance
Power=
Force x velocity
Efficiency=
But
Power out
—————-
Total power
We can’t account for the resting metabolic rate of energy consumption
incremental efficiency equals?
Assuming?
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
What does the delay an increase of O2 consumption at the beginning of exercise represent
O2 debt
What represents O2 repayment
Increased O2 consumption after exercise has finished
How are O2 debt and repayment measured
By backwards extrapolation of the study O2 consumptions
Why is 02 repayment necessary
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
Why is the O2 repayment higher than O2 debt
Oxygen must be consumed to supply hyperactive tissue during activity decline after exercise which is separate to O2 debt
When is O2 consumption and work rate roughly proportional
During mild/moderate exercise as the respiration is mostly aerobic
Give the Fick Principle
CO=
Rate of CO2 loss
————————————-
[Venous CO2]-[arterial CO2]
How is the alveolar gas composition measured and adjusted
End expiratory sample
P gas= (P-47) x F gas
What is nomogram used to do?
Translate PCO2 and PO2 into concentrations and vice versa
(Curved lines= conc; grid= partial pressure)
What is a Douglas bag used for
To calculate venous concentration of CO2 and rate of CO2 production.
How is the Douglas Bag used to find the concentration of Venus CO2
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)
How can you measure the rate of CO2 production using the Douglas bag
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
Why is the average respiratory quotient around 0.82
Due to the mixture of fat (0.7) and glucose (one) in our diet
How to work out respiratory quotient
Rate of CO2 production
————————————
Rate of O2 uptake
How does the respiratory quotient change from fasting to fed state
In fasting the quotient falls while after feeding it rises
Which two chemicals are used in fingerprick glucose tests
Glucose oxidase
Ferricyanide
What are the initial levels of blood glucose while fasting
After eating?
4mM
7mM
When a muscle is stimulated quickly by a TENS machine what is observed
Frequency summation (15 Hz) and tetany (30 Hz)
How is the heart a dipole
Why will different ECG leads pick up different voltage differences
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
Which ECG lead is increased during inspiration
Lead III
The heart is rotated down and rate increases
How does conduction in the squid giant axon differ from that of a mammal myelinated axon
Squid axons do not conduct as fast as the largest mammalian myelinated axons
How are the anode and cathode arranged
The cathode must be closer to the nerves than the anode
Define oxygen debt
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
RBF =
ΔP
———
Reff + Raff
Pc=
RBF x Reff + Pv
Why might the earth worm in ethanol be less excitable than in vitro
Ethanol inhibits ca2+ entry, reduces transmitter release and can open K+ channels
This all results in hyperpolarising the cell
How does the surrounding tissue affect the recorded AP in the earth worm
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
What is the stimulus artefact
The Stimulating current travelling directly to the recording electrode through the body of the worm or any liquid on its surface
What would happen if you didn’t have the Earth electrode
Both stimulus artefact and electrical noise will be much larger
Are you recording extracellular or intracellular APs in the Earth worm practical
Extracellular
When might increasing the voltage of the second stimulus overcome the refractory period
If it is in the relative refractory period
What is super excitability
This refers to a period ~20msec after the relative refractory period when the axon may be slightly depolarised and therefore closer to threshold
What are the normal latency and firing threshold for median and lateral Earth worm fibres
Median:
Threshold: 0.3-0.6mV
Latency: 5-10msec
Lateral:
Threshold: 0.9-1.5mV
Latency: 10-18msec
What is antidromic
When an AP travels in the opposite direction it’s meant to along the axon (usually when artificially stimulated in the middle)
How does electrical systole and diastole change in exercise
What is the mechanism behind this
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
How does adrenaline affect the conduction in the heart
How can this be seen on an ECG
β1 stimulation shortens condition delays in the AVN
A reduced interval between P and QRS
Why does cardiac output drop in supraventricular tachycardia
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
How is the R wave technically defined
The first positive deflection of the ventricular depolarisation complex
What is respiratory sinus arrhythmia
Discuss
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
What causes respiratory sinus arrhythmia
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
Describe how the electrical activity of respiratory sinus syndrome occurs
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
True or false
Arterial pressure in the brachial artery is effectively the same as aortic pressure
True
How does arteriosclerosis affect systolic BP
Increases systolic pressures as the arteries harden and fail to accommodate extra blood effectively
What does diastolic pressure depend on
The starting point (systolic pressure) and how easy it is for the blood to drain out of the arteries (TPR)
What is the pressure of the left ventricle during diastole
Therefore how does ventricular diastolic pressure compare to that of the arterial system?
0mmHg (to allow filling from VR)
Ventricular Is much lower
this is possible because of the closure of the aortic valve
How are MAP and pulse pressure meant to change in exercise
Expected to increase
Why is it difficult to establish breathing rate using chest strap transducer
Many people breathe largely diaphragmatically resulting in a low signal to noise ratio
How to calculate Va when you have tidal volume, expired %CO2 and alveolar %CO2
Va= Vt x expired %CO2/ alveolar %CO2
How to convert pounds to Kg
Times lbs by 0.45
Why may apparent RQ be greater than 1
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
What does mM mean
1 mmol per litre
Which cells in the heart are the first to depolarise?
What does this mean for the ECG
Central heart
Ie septum and endocardial area
They are also the last to repolarise
Both R and T are positive Deflections
Common Equation for maximum pulse rate
More accurate version
220 - age
208-(0.7 x age)
Describe cell components as parts of an electrical circuit
PM- capacitor and resistor in parallel
How to calculate average ventilation rate
Tidal volume x number of breaths per min
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
1kHz
Input: analogue; output: discrete
Can generate 2^24 levels between a specified range (v high resolution)
Why must you integrate input voltage when finger pulse is measured
Voltage is proportional to force change over time not force itself
