Past Paper questions Flashcards
(32 cards)
Outline the concept of 3 orthogonal lead ECG
It was first thought that the hearts electrical activity could be summed up in one vector, who’s magnitude is proportional to the EMF strength and direction represents the mean electrical activity. Therefore it was thought to record in 3 perpendicular directions.
X - direction measures activity in right - left direction across thorax.
Y - head to foot
2 - front to back of chest.
Most common form is the Frank Lead ECG system
How is a Vendocardiogram derived from a 3 orthogonal lead ECG
The Vendocardiogram shows the resultant cardiac vector in space throughout the cardiac cycle. Using the 3 leads it is possible to produce a 3D diagram showing the direction at each point however it is more common just to use the 2D vector movement between two of the electrodes.
Describe in broad terms how a 12 led ECG recording with the patient at rest is interpreted by a computer
ECG is electrical therefore first step is to converted the signal from analogue to digital form, with fs = 1000. 10s recording of all leads simultaneously.
Locate QRS complexes of ECG, by summing all 12 leads into a single function then searching for areas of high amplitude(peaks). Approximate onset and offset of QRS complexes are then found.
Noise reduction techniques should also be used such as removal of baseline drift, mains, AC interference.
Briefly explain exercise electrocardiography
Record ECG when subject is either using cycle machine or treadmill. Use standard 12-lead ECG, however place lib=mb electrodes on the torso to minimise artefacts caused by movements during exercise.
ECG is monitored on an oscilloscope or ECG paper and any changes in waveforms (like abnormal ST-T o unusual cardiac rhythms) can be detected. The speed of treadmill or bike resonates can be changed to reflect the fitness level of the subject.
Define
Electrocardiogram
A recording of the electrical activity of the heart
Define
Electrocardiograph
The machine used to record an electrocardiogram
What is tomato-sensory evoked potential
It measures the integrity of the sensory pathways i.e. muscle afferents and associated dermatomes
In SENIAM both electrodes should have the same surface area
The surface conductive areas should be the same so the impedance to each imput to the measuring amplifier are similar
What are the differences between non-parametric and parametric methods to calculate power spectral density in EEG
Non-parametric methods calculate frequency response of a signal based in Fourier transformation and a parametric method uses Z transform and autoregressive modeling
For EEG sequences of short duration should parametric or non-prametric methods be used and why?
Parametric - Because Frequency resolution does not depend on the Fs as it does in Fourier transformation which requires a high Fs. Also it is not required to smooth the Power Spectrum density by averaging over smaller EEG subsequences taken from original EEG (welsh) like in the non-parametric method.
How is similarity analysed in frequency domain between two channel of EEG signal.
Coherence is a measure of similarity between 2 sequences across different frequencies.
Explain Bi-polar measurement
Out gives the potential difference between two electrodes which have the same noise cancellation. If electrodes are placed along the muscle they will pick up the action potentials at different time points, therefore noise will not be cancelled.
They have a ground electrode in common for the body and device.
what are the 5 SEMG electrode properties
Size, Shape, distance between electrodes, material, construction
what is Rolandic rhythm recorded by EEG
Related to activity of motor cortex, 8-12Hz, Not easily observed in every adult. Event related synchronisation and desynchronisation can be seen in 90% of adults. During motor action of a certain part of the body the mu rhythm drops as compared to the relaxed state (ERde-S) however at the same time it can increase (ERS)
Explain why either montage, monopoly or bipolar produce EEG with larger amplitude
Monopolar has the largest amplitude since it measures the difference in potential between active electrode and a distant ground electrode. Bipolar records EEG signal between two different locations in which both record brain activity and are typically placed close to each other, therefore all components of EEG signal which are picked up by both electrodes will be cancelled out therefore EEG will have a lower amplitude
Explain, mobility, activity and complexity in EEG
They are three parameters which describe EEG signal in time domain. Relate Variance (activity), first derivative (mobility)(standard deviation of the slope) and second derivative (complexity) and are used to describe the dynamics of the signal without analysing frequency content. (equation)
Provide clinical reasons for the ambulatory (Holter) ECG recording
Investigation of Palpataions & Syncope. Assessment of antirhythmicc therapy, Ischemic ECG change, Event recording, Heart rate variability
Describe what correlation is and the differences between autocorrelation and cross correlation
Cross Correlation shows the similarity between two signals in the time domain, E.g. EEG recording of different areas of the brain.
Autocorrelation shows how a dynamic signal changes over time. E.G. when the subject closes their eyes.
it has values between 0 & 1 with 0 meaning no similarity and 1 being identical.
What is coherence
Is the similarity between 2 signals in the frequency domain
Define Power Spectrum Density and what is its application in biological signals
The distribution of power into its frequency components
Analyse frequency shift left to right during muscle fatigue, allowing one to obtain information and how much effort someone is using
Which method of calculating Power Spectrum density is best for high frequency sampling
2 methods. Short time Fourier transformation and wavelet transformation. Wavelet is best as it’s time-frequencyresolution can be adapted to different frequencies. By modelling signals as the weighted sum of signals of a finite duration in both time and frequency domain therefore solving the issue of FT method of having choose good resolution in time or frequency domain. Some model examples are the Mexican hat and morels wavelet.
In EEG what is the beta wavelength and what are the 4 spatially distinctive components
13-30Hz
Frontal Beta: Fairly common, not very fast, increased with increased concentration
Central Beta - Partly but not generally the basis of Mu rhythm
Posterior Beta - Fast, alpha equivalent, reactive to closing eyes
Diffuse beta - No link to any physiological rhythm
What do the letters mean in EEG setup
Frontal lobe, Temporal Lobe, Pariatal lobe, Occipital Lobe
What are the two methods of generating synchronous rhythms in EEG
Central clock Pacemaker (thalamus) Voltage gated ion channels allow each thalamic cell to generate self-sustaining discharge patterns, a synaptic connection between thalamic cells for synchronisation of the rhythm of the group.
- Distributed timing function - cells in the cerebral cortex excite & inhibit each other. Repeating of synchronous excitation of a number of cells results in large rhythmic waves.
