Definitions Flashcards
What is CT?
Coupled rotational source + detector; tangential beams across body to target specific structures, whereby beam rotates and patient advances through scanner.
What is contrast?
Exogenous agents that are radiodense and usually iodine-based. Administered at time convenient to scan to fit perfusion phase of structure
What are Hounsfield units?
Quantitative measure of radiodensity to differentiate structures on CT.
What units are used to differentiate radiodensity of structures on CT? What are the limits of these?
Hounsfield units
-1000 = air
0 = water
+3000 = bone
What unit is the measure for radiation dose?
Gray - mGy.
What is the usual ionizing background radiation known as?
Sievert (SV)
What is clinical ultrasound?
Oscillating waves of frequency outside range for human hearing
What is the frequency of diagnostic ultrasound?
1-18Hz
What is the Doppler effect/shift?
Change in frequency of wave for observer moving relative to source
What is Addison’s Disease?
Failure of adrenal glands to produce sufficient glucocorticoid hormones (and often also mineralocorticoid) due to immune destruction of adrenal cortex by autoantibodies
What is cardiopulmonary exercise testing?
Non-invasive simultaneous measurement of CV and respiratory system during exercise to assess capacity and by proxy fitness for elective surgery
What is VO2Max?
Max rate of O2 consumption
What is a phaeochromoctyoma?
Catecholamine producing tumour derived from chromaffin cells of adrenal medulla
What is pulse oximetry?
Light source LED and photodetector - 2 wavelengths of light emitted which pass through tissue (red visible/infrared) and absorbed by oxy and deoxyHb
What is the Hering-Breur reflex?
When lung inflated, stretch receptors in airways send vagal impulses to respiratory neurones in response to tidal volume over 800ml (during exercise) - this shortens inspiratory time and so increases respiratory rate
What reflex speeds up respiratory rate in response to increased tidal volume? How does it work?
Hering-Breur reflex - via vagus nerve triggered by stretch receptors in lungs
What are inotropes? How do they work generally?
Agents which affect contractility of myocardium via increasing intracellular Ca levels
What is transplantation?
Transposition of tissue from one anatomical region to another
What is allograft?
Organ or tissue from one non-related individual to another of same species
Organ or tissue from one non-related individual to another of same species?
Allograft
What is isograft?
Organ or tissue from a genetically identical individual
Organ or tissue from a genetically identical individual?
Isograft
What is autograft?
Organ or tissue from same individual to different site
Organ or tissue from same individual to different site?
Autograft
What is xenograft?
Organ or tissue from different species
Organ or tissue from different species?
Xenograft
What is HLA? What are the main subtypes?
Human leucocyte antigen - protein expressed on all tissue, forming basis of immune system. MHC 1 = A, B and C, MHC2 = DR (also DP and DQ)
What is the central role of HLA?
Identifying tissues as ‘self’ by immune system
What equation is used to calculate bicarbonate from known parameters on ABG?
Henderson-Hasselbach
What is cryoprecipitate? What are the 5 constituents?
Blood product obtained by centrifugation of plasma, containing: fibrinogen, fibronectin, factor 8, factor 13 and vWF
What is primary haemorrhage in tonsillectomy?
Haemorrhage as direct result of primary vascular injury or clot dislodgement
What is secondary haemorrhage in tonsillectomy?
Delayed 7-14 days post-op, due to infection and sloughing of vascular walls
What is an open fracture?
Disruption of bony cortex in association with breach in overlying skin and/or viscera
What is neurogenic shock?
Form of distributive shock characterised by hypotension due to loss of systemic vascular resistance due to sympathetic outflow tract damage, usually following spinal cord injury
What defines a massive haemothorax?
Draining over 1500ml of blood on insertion of chest drain, or 200ml per hour for at least 4 hours (or one third of patient’s circulating volume)
What is a tension pneumothorax? What causes it?
Pneumothorax in association with shock resulting in shift of midline structures (tracheal deviation). Due to positive pressure in pneumothorax throughout respiratory cycle - one way valve into intrapleural space.
What is haemoglobin?
Globular protein consisting of one haem moiety (ferrous ion plus protoporphyrin ring) and globin chain (in adults 2 alpha and 2 beta)
What is the oxygen dissociation curve?
Describes relationship between percentage of saturated Hb and partial pressure of oxygen in blood
What is Courvoisier’s Law?
States that a distended palpable gallbladder in presence of jaundice is unlikely to be gallstones, because chronic inflammation due to gallstones causes wall thickening/fibrosis which precludes distension
