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QUIZ20thMay2020(answersbelow)
1. Whatisthedifferencebetweenincidenceandprevalence?
2. Whatisxanthochromia?
3. Whatistheprevalenceofasymptomaticcerebralaneurysminthegeneralpopulation?
4. Whatisulnarvariance?
5. DescribeandinterpretthefollowingECG.
QUIZanswers20thMay2020
1. Whatisthedifferencebetweenincidenceandprevalence?Prevalence is the proportion of existing cases of the disease/condition in a given
populationataspecifictimewhereasincidenceisthenumberofnewcasesinagiven
populationoveraspecificperiodoftime.
2. Whatisxanthochromia?XanthochromiareferstotheyellowdiscolourationofCSFduetobilirubin.Theword
xanthochromiaisfromtheGreekxanthos(yellow)andchroma(colour).
DetectingxanthochromiaintheCSFtwelvehoursafterheadacheonsetcandiagnose
subarachnoid haemorrhage as opposed to a bloody tap. Blood in the CSF releases
oxyhaemoglobin, which is then converted into bilirubin. This process is time
dependentanditmaytakeupto12hoursforbilirubintobedetectable.Bilirubincan
thenremaindetectableformorethan2weeks.Oxyhaemoglobinisdetectablefora
fewdaysafterableedbeforeitisallconvertedtobilirubin.
Bilirubin can also be detected in the CSFwhen CSF total protein is raised orwhen
serum bilirubin is raised. This may be indicated by a raised CSF bilirubin but no
oxyhaemoglobin. Inthefirst fewdaysafterableed,oxyhaemoglobinshouldstillbe
detectable. Raised total CSF protein can occur when there is a breakdown in the
blood-brainbarrier(suchasmeningitis)andsothatishowCSFbilirubincanalsobe
detected.
Xanthochromiacanbedetectedbytwomethods.Thefirst isbyvisual inspectionof
the centrifuged sample next to a water sample and against a white background.
Secondly, and more reliably, xanthochromia is detected by spectrophotometry as
bilirubin has a very narrow absorption wavelength of 440 – 460nm.
Spectrophotometrydistinguishesbilirubinfromoxyhaemoglobin,redcells,andother
proteinsorpigmentsanddetectsverylowconcentrationsofbilirubin.
3. Whatistheprevalenceofasymptomaticcerebralaneurysminthegeneralpopulation?
Theworldwideprevalanceof cerebral aneurysms is estimated tobeapproximately
3.2%withameanageof50.
4. Whatisulnarvariance?
Ulnarvarianceistherelativelengthsofradiusandulnaatthewrist.Itismeasuredas
thedistancebetweentwoparallel linesdrawnperpendiculartothe longaxisofthe
radiusatthedistalarticularsurfaceoftheulnaandtheulnarcornerofthesigmoid
notch(orcentralreferencepoint)oftheradius.Normalmeasurementis0to2mm.
5. DescribeandinterpretthefollowingECG.
Rate Regularlyirregularat88/min
Atrialtrigemenyasincompletecompensatorypause(c/wventricular)
Pwaves UprightinIIandnormalmorphologysolikelysinusinorigin
NoPwaveprecedingtheprematurebeat,likelytobeintheQRS-T
PRinterval Normal
QRS WidewithRBBBmorphology
PathologicalqwavesV1-4
Leftaxisdeviation-60
STsegment GrosselevationV1-4(concordant)
STelevation1-2mminaVLandI
InferiorSTdepressionII,IIIandaVf
è AcuteanteriorandhighlateralSTEMIwithinferiorreciprocalchanges RBBBandleftanteriorhemiblockwithatrialtrigemeny