physics Flashcards

Question

phases of clinical trials

Answer 1

phase 1 - small no. healthy volunteers phase 2 - increase no. phase 3 - RCT phase 4 - product liscended and surviellence

Answer 2

cohort- group studied overtime to see who develops case control - look back at predisposing factors

Answer 3

used to represent meta-analysis data each rectangle = study , large lines = confidence interval - if they cross OR of 1 then not significant larger rectangle - larger no. of people in study the line in middle / OR of 1 = no significant difference. if diamond = the sum / average of all studies

Answer 4

qualitative review of data of all similar studies in response to a specifc Q (different from literature review as more random selection of studies)

Answer 5

quantitative review of data from all available primary studies (usually RCT) that are of similar nature to answer a specifc Q and reach a conclusion

Answer 6

- clearly defined Q for analysis - clear and reproducible methodology - clear inclusion/ exclusion criteria - avoid publication bias - random selection not just studies with positive outcome.

Answer 7

radio micro infrared visible light UV light Xrays gamma rays increased frequency and shorter wavelength e.g. gamma all transverse waves (sound waves are longitudanal)

Answer 8

400nm to 700nm

Answer 9

reflection - light bounces back at same angle it hit surface. angle of incidence = reflection refraction = when light travels from one medium to another, it bends because speed will vary in each medium. diffraction - disperses as it goes through narrowing

Answer 10

line of normal drawn. angle of incidence = the light coming through measured against normal angle of refraction - will be larger if travelling into a less dense medium. as angle of incidence increases so does angle of refraction - eventually > 90 degrees

Answer 11

thousands of glass fibres arranged in parrallel and tightly ordered to transmit light from one source to a distant source at the tip. work by total internal reflection - keeps light energy focused and prevents loss of energy each glass fibre is coated in cladding glass of lower density (lower refractive index) to allow total internal reflection.

Answer 12

pros - difficutl airway, visualise beyond glottis, pulmonary suction under vision cons - requires training , expensive and fragile, blood/secretions obsurce view, cork in wine bottle.

Answer 13

flash light / energy provided to lasing medium electrons elevated to higher energy level drop down and release photon - spontaneous emission photon hits another electron in exited phase = stimulated emission (same phase and same wavelegnth and in parralle) amplification of energy reflective ends - energy bouncing back and forth small hole in one end for it to escape

Answer 14

Light amplification by stimulated emission of radiation

Answer 15

stainless steal flexible spiral - cant burn non-combustable double cuff

Answer 16

turn off laser, call for help turn down O2 / cease ventilation remove ET tube flood with saline TIVA bronchoscopy reintubate HDU / ITU - ARDS / resp failure

Answer 17

H atoms have spin and charge and act like mini magnets placed in a magnet and align with the magnetic field - Radiofrequency magnetic filed energy is applied causing the H atoms to flip 90 degrees to the original field = higher energy state When RF turned off they relax back to original state and release energy Scanner picks up the energy released and compares different rates of relaxation/ excitation to determine type of body tissue.

Answer 18

1- 3 Tesla static magnet

Answer 19

T1 = water is black, fat white. T2 = water is white and fat white

Answer 20

Gadolinium used with T1 weighted MRI alters relaxation of H making the image more visible.

Answer 21

angiography GIT brain tumours that have crossed the BBB

Answer 22

non ionising better for soft tissues better for making 3D images.

Answer 23

cryogenic superconducting magnets the metal is cooled to close to absolute zero (0 K) by immersing in liquid helium this causes the metals resistance to become close to absolute zero meaning its current is v high allowing is to create a very strong magnetic field.

Answer 24

liquid helium heated rapidly vented from scanner no liquid helium to create a superconducting magnet no magnetic field

Answer 25

Practicalities for trust * Large * Expensive For patient: * Claustrophobia – trauma * Noisy – can cause damage to ears * Contraindicated for those with metal implants For anaesthetist: * Cant access patient * A lot of equipment incompatible * Far away from clinical area e.g. ITU * Availability of drugs and equipment is limited. * Interference with monitoring from magnet induced currents. Safety: * Risk of metal objects being projected and injuring patient * Radiofrequency energy causes induced current and heating of metals = may cause burns.

Answer 26

Unstable patient – intubated and ventilated Uncooperative patient – child, learning difficulties , Claustrophobia Intra op MRI – do surgery, check with MRI, do more surgery if needed

Answer 27

CTs take a series of X-ray images around a central axis

Answer 28

Any ferrous equipment E.g. laryngoscopes, stethoscopes, gas cylinders, drip stands, defibrillators Pulmonary artery catheter small bit of metal at tip – can get induced currents and cause microshock if put in a magnet.

Answer 29

Faraday cage - Entire room is coated with copper/ aluminium For monitoring – special MRI compatible equipment *e.g. ecg electrodes- carbon electrodes * e.g. graphite ecg leads. *e.g. nylon BP cuffs *e.g. special pulse oximeters – fibre optic cabling to prevent induced currents and burns wires should run down centre of patient - furthest from the walls of the doughnut.

Answer 30

can cause damage to scanner a lot of money to replace He risk of hypoxic area - designed to vent He externally however risk it gets into the MRI room, diluting O2

Answer 31

Magnetic field... * dangerous projectiles e.g. gas cylinders * ferromagnetic foreign bodies become dislodged e.g. metals in eye * pacemaker inactivated / reprogrammed dynamic magnetic field * induce currents - interference but also biological tissues patient * noise, claustrophobia radiofrequency heating * burns from any conducting material on patient hence ecg leads carbon fibre and pulse ox is fibre optic helium escape * hypoxic anaesthetist * unfamiliar environment with unfamiliar equiptment * away from patient

Answer 32

ferromagnetic object - loose coins/ keys in pockets accelarating and causing injury. more serious would be O2 cylinders, wheelchairs. may result in serious patient/ staff injury Cardiac arrest in MRI scanner- need to remove patient, cant take arrest trolley and defib into the room

Answer 33

MRI deactivating ICD paramagnetic O2 analyser

Answer 34

USS is a form of imaging relying on the use of sound waves in frequencies above that of human hearing (>20Hz)

Answer 35

It works via the piezoelectric effect. The USS probe contains multiple crystals that vibrate when current is applied and then produce sound. USS emits sound waves to tissue sound is reflected off tissue boundaries when there is a change in density of tissue. sound waves are detected by USS and again via piezoelectric effect transduced into current for interpretation. - The time taken for wave to be detected is determined by depth - The amount reflected is determined by tissue interfaces - The machine filters and processes the signals - Each wave creates a pixel on the screen to create an image

Answer 36

human hearing 20Hz to 20KHz USS anything above 20KHz however in **medical USS usually 5 to 15 MHz**

Answer 37

short wavelength, high frequency = lower depths, high resolution long wavelength, low freq = deeper but reduced resolution.

Answer 38

urine /fluid = black tissues = grey bone = white (strongly reflected sound waves)

Answer 39

the number of waves passing a point per second. measured in hertz inversely related to wavelength

Answer 40

the distance between 2 peaks of a wave or the length for one complete wave cycle.

Answer 41

v=λ×f v velocity λ wavelength f frequency the speed of sound in the body is constant and thus wavelength and frequency are inversely related.

Answer 42

improve contact between the probe and surface and reduce air in between these. air has high attenuation and thus will absorb sound waves and reduce image quality. gel is a low attenuation material - allows sound waves to pass through without loss of energy.

Answer 43

the ability to distinguish between 2 points hence improves quality of an image

Answer 44

sound waves are longitundal waves do not belong to EM spectrum (transverse waves)

Answer 45

A mode = amplitude - uses a single wave, assesses depth of tissue. no 2D image. e.g. opthal to look at globe size or bladder scanner B mode = brightness - linear array of waves to create 2D image. most common mode e.g. regional, vascular acsess M mode = motion - B mode used in series to look at changes to image and hence motion. used for heart valves / echo doppler mode = uses the doppler effect looking at a frequency shift in sound waves to determine velocity of a moving object e.g. blood.

Answer 46

The doppler effect is the phenomena whereby the sound of a moving object changes its frequency depending on if its moving towards or away from sound detector the shift in frequency is proportional to velocity of the moving object. can be used to quantify the direction and velocity of blood flow via the following formula

Answer 47

f0= original frequency c = speed of sound

Answer 48

if at 90 degres cos 90 = 0 so needs to be angulated and constant to measure velocity.

Answer 49

Frequency of waves - the higher frequency, the higher the resolution. hence to view deeper structures, this will have to be reduced which will reduce image quality. Attenuation of the material - low attenuation helps not loose energy from the sound waves hence use of gel to reduce attenuation (air has high attenuation) gain - increasing brightness to optimise the contrast seen at tissue bounfaries. type of probe - a linear probe creates higher frequency than curvilinear probe.

Answer 50

on modern USS machines you can select a mode which looks at blood flow via doppler effect red = blood moving towards probe blue = blood moving away from probe can help with vascular access

Answer 51

PROS: * safe , non ionising * cheap * relatively portable / more convienient * simple to use * many uses - cardiac output, regional, obstetrics cons: * not good for all tissue types e.g. bone * not good for deep structures * user dependant - requires some training

Answer 52

depth = how deep the sound waves go and image will show. lower frequency, longer wavelgnth gain = how bright image is - increases noise focus = increasing resolution - focal zone has highest resolution - can adjust where this is.

Answer 53

- Movement e.g. shivering - Obesity – difficult to view deep structures, increased fat results in attenuation of USS beam - Inability to position for certain scans

Answer 54

air is a poor absorber - so a lot is reflected at tissue / air interface

Answer 55

- Contact artefact – probe not in contact with skin e.g. need more gel - Acoustic shadowing – much of USS beam is reflected at interfaces between lesser and highly attenuating tissues. Tissues deep to these won’t be seen - Lateral shadowing/ refraction – USS hits curved structure and there is refraction - Poor resolution – USS wavelength is larger than size of structure - Anisotropy – image is dependent on the angle of USS to the structure

Answer 56

cannulation / CVC peripheral nerve blocks difficult airway assessment - cricothyroid membrane tracheostomy identifying pneumothorax oesophageal doppler FAST scan Transthoracic ECHO - Assessing degree of gastric emptying prior to induction

Answer 57

- Evidence of MI e.g. wall motion abnormalities - LV failure - Ejection fraction - valvular problems - Evidence of hypovolaemia – narrow and collapsing vena cava , small chambers, large EF - evidence of tamponade

Answer 58

1. flow through shunts 2. flow through valve / regurg fraction 3. LV function / aortic stenosis - velocity across valve 4. coronary artery flow

Answer 59

* oesophageal and CO monitoring * transthoracic - cardiac function e.g. velocity of blood, regurgitation * VTE assessment in peripheral limbs * transcranial doppler - cerebral blood flow * pulses in limbs in vascular patients

Answer 60

high frequency AC current = 0.5 - 1.5mHz applied over small area = high current density causes cutting and coagulation of tissues can be continous mode - sine wave Or pulsed or blend of the 2

Answer 61

monopolar = current between instument and plate. plate is large 10cm/10cm to allow low current density and no damage bipolar = current between 2 points of instrument, doesnt go through patient.

Answer 62

human tissue resonates at 50Hz well away from this so doesnt disrupt biolongical signals high frequnecy creates high energy for cutting/coag

Answer 63

pros = precise, reduces bleeding cons = interference with ECG, safety issues , pacemaker complications safety 1. burns - if pad not in good contact, high current density. OR no pad, current will go through ECG electrodes. OR ignition of skin preps 2. microshock - uses high freq current away from human tissue current. 3. interference with monitoring 4. interferes with pacemaker / ICD

Answer 64

diathermy currents picked up and pacing stops diathermy currents picked up and ICD activated - shock burns and damaged devices

Answer 65

1. assynchronous mode 2. innactivate ICD and attach external pads - can use magnet 3. use bipolar 4. monopolar - place plate away from pacaker 5. short bursts

Answer 66

current - movement of charge - measured in amperes. can be AC or DC . coulombs / second voltage = energy required to move charge between 2 points resistance = ability of material to resist current. ohms

Answer 67

50Hz 240 volts

Answer 68

a device that stores electrical charge = capacitor = farads. Capacitors prefer AC current - charge and discharge to allow them to continue 2 conducting plates either side of insultator inductor - component which opposes flow of current by creating backwards electromotive force to changes EMF decrease with direct current (as not changing) consists of coils of wire - increases inductance

Answer 69

energy used per unit time watts = joules / second

Answer 70

2 adhesive pads placed on patients chest with good contact 5000V batery - transformer and AC --DC conversion parrallel circuit capacitor inductor - slows current down to deliver charge over longer time. reduces risk of burns switch

Answer 71

resistance to flow of current Stroke volume - more impedance ventilation - more impedence shaving and skin prep = reduce impedence

Answer 72

synchronised to peak of R wave to prevent VF lower energies used.

Answer 73

risk of burns, fires risk of VF electrocution of staff interfer with pacemakers

Answer 74

voltage divider used to measure unknown resistance by comparing ratios of resistance when 2 voltage dividers are placed in parallel used for strain gauges in arterial BP monitoring

Answer 75

burns - depends on current density arrhtyhmias - depends on current density AND frequency tetany - cant let go phenomena

Answer 76

current type - AC / DC current frequency magnitude duration route taken conductivity of surface e.g. sole of foot vs wet skin

Answer 77

1mA = tingling 5mA = pain 15mA-30 = tetany 50mA = asphyxia 100mA = VF , burning

Answer 78

small amount of current but through a small area in close contact with myocardium e.g. guidewires, central lines, pacing lines. creates high current density

Answer 79

class 1 = earth casing class 2 = double insultated class 3 = safety extra low voltage - 24 V

Answer 80

- maintaince - use of eathing / double insulation - fuses - trained staff - correct shoes - avoid wet surface - anti-stratic surface - relative humidity > 50%

Answer 81

classed based on leakage current usually for equiptment inserted into the body and risk of microshocks B = max AC 500uA , DC 50uA - leakage current multiple circuits AC 100uA, DC 10uA BF = same as above but floating circuit i.e. isolated CF = cardiac floating max AC / DC 50uA, multiple 10uA

Answer 82

FGF --> PT --> expired air --> APL valve --> bag --> ventilator --> SL --> back to FGF closed - efficient / environment friendly CO2 needs to be reabsorbed one way waves wide bore tubes - minimise resistance

Answer 83

low FGF, less cost, less pollution , maintains humidity cons - high resistance, low FiO2 , risk of rebreathing, toxic products - compound A and CO

Answer 84

infra red spectrometry molecules with 2 dissimilar atoms absorb at particular wave length (4.3um) light passes throguh a sample beer and lambert law path of light is fixed conc of CO2 varies

Answer 85

LED emit these wavelength = 660nm and 940nm photodetect detect beer and lamberts oxyHb and deoxy Hb ratios compared only pulsatile blood looked at isobestic point is where the absorptions cross

physics Flashcards

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