Part 2: Physics & Equipment Flashcards

Question

Describe the **fire triangle** with examples from the theatre environment.

Answer 1

* Oxidiser (oxygen or nitrous oxide) * Fuel source (such as surgical drapes or alcohol-based preparations) * Ignition (like electrosurgical units or laser beams)

Answer 2

Higher frequencies provide better resolution, but at the expense of penetration depth, making them less suitable for deep structures.

Answer 3

Simulated moving bed chromatography

Answer 4

Measures blood pressure through the mechanical expansion and contraction of bellows, which moves a pointer across a calibrated scale to indicate pressure changes.

Answer 5

Freezing point osmometer ## Footnote Determined concentration by measuring the freezing point of the solution as depression of the freezing point is directly correlated with concentration.

Answer 6

A resistor used in pressure transducers. ## Footnote A diaphragm moves as the pressure changes which changes the tension in the resistance wire, making it longer and thinner and INCREASING its resistance.

Answer 7

% vaporiser output = % calibrated x (calibrated pressure/ambient pressure)

Answer 8

Gas analysis technique based on the Raman effect. ## Footnote Light scatters **inelastically** off gas molecules resulting in a frequency shift - this is specific to each gas. Can be affected by extreme temperatures.

Answer 9

* Bicarbonate * Base Excess * Oxygen Saturation

Answer 10

**Clark Electrode (Polarographic)** * Requires external voltage and measures oxygen via an electrochemical reaction where O2 is reduced at the platinum cathode, generating a current proportional to pO2. Used in blood gas analysers. **Galvanic Fuel Cell** * Self-powered and uses spontaneous redox reaction where the anode is consumed over time. Simpler and cheaper and used in anaesthetic machines.

Answer 11

Ethylene oxide sterilisation

Answer 12

**Coherence** between high- and low-frequency EEG components. This reflects consistency of phase relationships across different EEG frequencies. In deeper anaesthesia, EEG signals become more synchronised leading to higher coherence (and lower BIS number).

Answer 13

**DIAGNOSTIC**: 0.05-150 Hz & 0.1-4 mV **MONITORING**: 0.5-50 Hz

Answer 14

Mapleson A Including Lack (coaxial)

Answer 15

200 mL/kg/min

Answer 16

* Improved humidity and temperature of inspired gases (as it has passed through the respiratory tract) * Minimises consumption of volatile agents

Answer 17

Coulomb’s Law states that the electric force between two charges is inversely proportional to the square of the distance between them. In the context of **nerve stimulation**, this means the threshold current required to stimulate a nerve increases in proportion to the square of the distance between the stimulating electrode and the nerve.

Answer 18

**Yes** The Tec 6 vaporiser is designed to deliver a controlled **VOLUME PERCENT** of desflurane vapour. This will vary depending on the ambient pressure. The partial pressure of the drug is responsible for its effect. ## Footnote NOTE: Goes in 1% gradations from 1-10%, then 2% up to 18%.

Answer 19

15-20% ## Footnote NOTE: Can get up to 60 degrees celsius.

Answer 20

At least 7 seconds 60 dB at 1 metre

Answer 21

1 kPa = 0.145 psi

Answer 22

Surgical instrument used to **freeze** and destroy tissue. Works by rapidly cooling its tip using compressed gases (like nitrous oxide or carbon dioxide), which expand and cool (Joule-Thomson effect), freezing adjacent tissue on contact.

Answer 23

**Ostwald**: The ratio of the volume of a gas dissolved in a liquid to the volume of the gas at the same temperature and pressure. (Dimensionless - more commonly used) **Bunsen**: The volume of a gas, corrected to 0 °C and 1 atm, that dissolves in a unit volume of liquid at a given temperature.

Answer 24

Formed from the orbit of electrons round an atom at high speeds creating spontaneous dipole charges influencing the neighbouring dipole.

Answer 25

* Ionic * Covalent * Hydrogen * Dipole-Dipole * Van Der Waals'

Answer 26

The partial pressure of the anaesthetic vapour in the gas **equals the SVP** of the agent at a given temperature. The rest of the gas is made up of carrier gas (e.g. oxygen or air) making up the rest of the 760 mm Hg.

Answer 27

It is the **minimum angle of incidence** at which light is completely reflected within a denser medium when it strikes the boundary with a less dense medium, enabling total internal reflection, as used in fibreoptics. ## Footnote Total internal reflection occurs when the angle of incidence is greater than the critical angle.

Answer 28

200 micrometres

Answer 29

Venous congestion | (first wave is arterial pulsation, second wave is venous) ## Footnote This can happen in fluid overload, tricuspid regurgitation, right-sided heart failure and high ventilatory pressures - because these increase venous pressures and it becomes pulsatile. NOTE: The pulse oximeter will under-estimate arterial oxygen saturations because it is also reading the venous saturation.

Answer 30

**Optimally Damped**: 2-3 **Under-damped**: > 3

Answer 31

Membrane covering the electrode

Answer 32

860 L ## Footnote NOTE: stored at -150 degrees at 7-10 bar

Answer 33

* Alcohol * Mercury * Dial (bimetallic strip or bourdon gauge)

Answer 34

Polio Macintosh

Answer 35

Miller Straight blades with curved tips ## Footnote NOTE: used for floppy airways in paediatrics

Answer 36

McCoy ## Footnote Features a hinged, lever-controlled tip on the blade that allows for elevation of the epiglottis

Answer 37

* pCO₂ * pO₂ * pH

Answer 38

Pass through a 4-mesh (4 openings per inch). Retained by 8-mesh (8 openings per inch). This is a granule size of 2.38 mm to 4.75 mm in diameter.

Answer 39

Calcium hydroxide is the main reactant. Sodium hydroxide is a CATALYST.

Answer 40

Arterial pulsation **changes path length** causing changes in absorption (as per Beer-Lambert law). ## Footnote This means that it will only assess the saturations of that component (i.e. excluding tissue and venous blood).

Answer 41

3 x 10^8 m/s

Answer 42

* **Collimated**: parallel rays * **Coherent**: consistent phase * **Monochromatic**: single wavelength * **High intensity**: concentrated energy

Answer 43

10^-5 Newtons

Answer 44

+/- 0.1 degrees centigrade

Answer 45

0.5-10 MHz

Answer 46

Unit of capacitance ## Footnote 1 Farad is the capacitance of a capacitor that stores one coulomb of charge when one volt is applied across it.

Answer 47

Twice the average speed.

Answer 48

1. Step-up transformer increases 240 to 5000 V 2. Capacitor needs DC to charge so rectifier (diode) converts AC to DC 3. Switch charges and discharges capacitor 4. Inductor smooths the current delivered to the defibrillator pads ## Footnote NOTE: A smoother discharge means that heart is depolarised more effectively and safely, it reduces tissue damage and minimises electrical stress on the device.

Answer 49

The partial vapour pressure of a component in a solution equals the vapour pressure of the pure component multiplied by its mole fraction in the solution. ## Footnote **EXAMPLE** In a 1:1 mole ratio mixture of ethanol (SVP 44 mmHg) and water (SVP 24 mmHg), the total vapour pressure = (0.5 × 44) + (0.5 × 24) = 34 mmHg.

Answer 50

* 75%: 2500 m * 50%: 5500 m * 25%: 11,000 m

Answer 51

Permittivity = how easily it allows an electric field to pass through it.

Answer 52

Insulating material that, when placed in an electric field, becomes polarised, allowing it to **support the field** and store electrical energy without conducting current. ## Footnote Used in capacitors.

Answer 53

ETT: 15 mm Catheter Mount: 22 mm

Answer 54

Aortic arch pathology ## Footnote Because the Doppler relies on the assumption that 70% of cardiac output enters the descending aorta. It also assumes that the cross-section of the descending aorta can be assumed based on demographic data.

Answer 55

0.2 microns

Answer 56

**HIGH USAGE** (also cold weather): decrease in oxygen temperature and pressure, at 1000 kPa, the pressure raising valve opens allowing liquid oxygen to shunt through a pressure-raising vaporiser and allow environmental heat to enter. **LOW USAGE** (hot weather): temperature of liquid oxygen increases and pressure increases, blow off valve opens to allow vapour into the environment.

Answer 57

* 110 cm with 5 lumens * Proximal lumen is 30 cm from tip and sits in right atrium * Balloon at tip is filled with 1.5 mL of air and floated through the circulation whilst observing the pressure trace * Thermistor 3.7 cm from tip

Answer 58

Thermistor

Answer 59

Transfers energy to the volatile agent to prevent it from cooling down due to latent heat of vaporisation. ## Footnote This maintains a stable SVP and is particularly important with high fresh gas flows.

Answer 60

The Doppler equation describes the change in frequency or wavelength of a wave in relation to an observer moving relative to the wave source. ## Footnote It is commonly used in physics and astronomy to explain phenomena such as the redshift and blueshift of light from stars and galaxies.

Answer 61

* Use circle system * Lowest possible FGF * Lowest possible FiO2 * Check FiO2 alarms

Answer 62

Bicarbonate ## Footnote It is measured based on the pCO2 and the Henderson-Hasselbalch equation.

Answer 63

1-15 MHz ## Footnote NOTE: Speed of sound in tissues at body temperature is 1540 m/s.

Answer 64

* **Anaesthetic Gases**: 8-9 µm * **Nitrous Oxide**: 4.6 µm * **Carbon Dioxide**: 4.3 µm

Answer 65

**Lead Anode**: electrons are lost in an oxidation reaction **Gold Cathode**: electrons are gained in a reduction reaction

Answer 66

* **Position I**: chamber(s) paced – V (ventricle), A (atrium), D (ventricle and atrium), O (none). * **Position II**: chamber(s) sensed – V (ventricle), A (atrium), D (ventricle and atrium), O (none). * **Position III**: mode of response – T (triggered), I (inhibited), D (triggered or inhibited), O (none). * **Position IV**: programmable functions – R (rate modulated), O (none). * **Position V**: multi-site pacing – O (none), A (atria), V (ventricles), D (dual).

Answer 67

* **Method of cycling**: volume, time, pressure * **Inspiratory phase gas control**: volume, pressure * **Source of power**: electric, pneumatic * **Suitability of use**: operating theatre, ICU * **Paediatric use**: yes, no * **Method of operation:** pressure generator, flow generator * **Sophistication**: SIMV, PS, CPAP etc. * **Function**: minute volume divider, bag squeezer, intermittent blower

Answer 68

Size of the main working channel

Answer 69

* Pair of voltage dividers. * Designed to measure an unknown resistance by balancing two limbs of a bridge circuit so that the voltage between them is 0. ## Footnote Has 2 fixed resistors (R1 and R2), a variable resistor (R3) and the resistance to be measured (Rx). To produce a voltage of 0, R3:R1 and Rx:R2 must be the same. R3 is altered until the voltmeter reads 0.

Answer 70

A capacitor with capacitance of 1 Farad will store 1 Coulomb of charge when 1 Volt (not Amp) is applied across it.

Answer 71

Newton valve affords the user **greater control over tidal volume**, and thus reduces the risk of volutrauma in paediatric patients. ## Footnote It can deliver up to 300 mL of tidal volume.

Answer 72

* **Oxygen**: 2, 5 * **Medical Air**: 1, 5 * **Carbon Dioxide**: 1, 6 * **Nitrous Oxide**: 3, 5 * **Entonox**: 7

Answer 73

A **pencil-point needle** (e.g., Whitacre or Sprotte) has a rounded, non-cutting tip with a side hole for drug delivery. It spreads dural fibers rather than cutting them, reducing the risk of post-dural puncture headache (PDPH). A **cutting needle** (e.g., Quincke) has a sharp, beveled tip that slices through tissues, making dural puncture easier but increasing the risk of PDPH due to greater dural trauma.

Answer 74

HMEFs can achieve a relative humidity of **60-70%**. At 37ºc the maximum absolute humidity of air is 44 g/m³. ## Footnote 60-70% of 44 g/m³ is 26.4 – 30.8 g/m³

Answer 75

When a gas contains two or more dissimilar atoms. The bond between the atoms can absorb energy at specific wavelengths leading to absorption spectra that can be used to identify and quantify the gas. ## Footnote E.g. N₂O can be detected but not O₂.

Answer 76

When two conductors made from dissimilar materials are joined together, a potential difference is produced at the point of contact, the magnitude of which depends on the temperature.

Answer 77

At the junction of two dissimilar metals, a voltage will be produced in **direct proportion to the temperature difference between two such junctions**. Typically copper and constantan are the metals used. The response is nearly linear and passes through the origin as a temperature difference of 0 produces 0 output voltage. ## Footnote Uses the Seebeck effect.

Answer 78

**Relative humidity** refers to the amount of water vapour in a gas sample relative to the mass if the gas sample was fully saturated. It is measured in %. **Absolute humidity** refers to the total mass of water within a given volume of gas, and is measured in g/m3.

Answer 79

Mass spectrometer

Answer 80

Designed for occupational safety - all gases are eventually vented into the atmosphere. * Collecting system * Transfer system * Interface (allows pressure to be vented so that it is not transmitted to the patient) * Disposal system

Answer 81

The **absolute humidity** is the mass of water vapour in a given volume of gas at a given temperature and pressure and is often expressed in g/m³. The **relative humidity** is the ratio of the actual mass of water vapour compared to the maximum amount of water vapour the gas could contain at the same temperature and pressure.

Answer 82

The temperature to which a given volume of gas must be cooled for water vapour to condense. This occurs when the **relative humidity is 100%**. If air has a lower humidity therefore a greater temperature drop is required to reach the dew point.

Answer 83

* Angle of incident ray * Refractive index of air * Refractive index of material * Speed of light in material

Answer 84

Calibrate daily using a two point method with 21% (room air) and 100% oxygen.

Answer 85

**Good muscle bulk** and **blood supply** means better conductivity and less heat generation. ## Footnote Proximal to operating site means lower chance of current division, reduced impedance and less power needed.

Answer 86

Reduces respiratory and body movement artefacts. ## Footnote NOTE: High-pass is the same as low-frequency because signals ABOVE a certain frequency (i.e. 0.5 Hz) are allowed to pass.

Answer 87

**H = Wb/A** ## Footnote H = Henry (unit of inductance) Wb = Weber A = Ampere NOTE: To get a value for self-inductance, you need to multiply by the number of turns in the coil.

Answer 88

Sensitive piece of equipment that monitors the current flowing through the live and neutral wires and, if there is any discrepancy, it will break the circuit. ## Footnote This can happen with even very small discrepancies.

Answer 89

Breaks a circuit when it detects small leakage currents. ## Footnote Live and neutral wires are wound round a transformer with the same number of windings. There is a third winding attached to a circuit breaker. When there is a difference between the live and neutral wires, it produces a magnetic field which induces a current in the third winding which breaks the circuit.

Answer 90

Sampling error where an insufficient frequency of pulses relative to the velocity of blood flow being measured results in the system not being able to determine the direction of blood flow correctly.

Answer 91

* Aortic cross-section provided by normogram * Probe position unchanged with fixed angle between probe and aorta * Flow is laminar * 70% of LV output going into descending aorta

Answer 92

* **SUCTION**: collects blood using heparin or citrate to prevent clotting * **RESERVOIR**: stores and roughly filters blood, removing large clots * **CENTRIFUGE**: separates red cell from plasma and contaminants * **WASHING**: isotonic saline removes free haemoglobin, activated clotting factors and anticoagulants * **FILTRATION**: leukocyte depletion filter to remove white cells and microaggregates * **REINFUSION BAG**: stores concentrated clean red cells for transfusion

Answer 93

Both are co-axial. **Lack** behaves like a Mapleson A (FGF on outside). **Bain** behaves like Mapleson D (FGF on inside). Can be very long without much issue because FGF delivered right to patient.

Answer 94

**High Pass** (low frequency): better assessment of ST segment, P wave and T wave . **Low Pass** (high frequency): good for QRS and tachyarrhythmias.

Answer 95

Measures the potential difference between two leads and eliminated inputs that are common (common mode rejection). This helps remove background noise.

Answer 96

* Technique to measure regional blood flow (usually cerebral). * Inert, diffusible tracer gas like nitrous oxide is used. * Blood and tissue tracer concentrations are measured over time and flow is calculated based on tracer uptake.

Answer 97

1.3-1.63 mm | (14-16 G)

Answer 98

Intersection of 4th intercostal space and mid-axillary line (this is where the right atrium is).

Answer 99

* Method of measuring the concentration of an inhalational agent. * Measures the extent to which light is bent when it moves from air into a sample gas.

Answer 100

* **Schrader Sockets**: unique diameter index collar matches the relevant socket * Flexible, kink-proof **colour-coded pipe** (blue for nitrous, white for oxygen, black for air) * **Non-Interchangeable Screw Thread**: nut and probe with unique profile for each gas, unidirectional valve ## Footnote NOTE: Pin index is for the cylinders that are mounted on the back of the machine.

Answer 101

Dumbbell of nitrogen is aligned perpendicular to a magnetic field and balanced on a suspending filament. Oxygen will be attracted to the magnetic field causing a deflection in the dumbbell. Photocells are used to control a variable current that induces a magnetic field that exactly offsets movement due to oxygen - the current is used to calculate oxygen concentration.

Answer 102

**ACTIVE**: generate electric current or voltage directly in response to environmental stimulation (e.g. thermocouple) **PASSIVE**: change in passive electrical quantity such as resistance, capacitance or inductance (e.g. strain gauge, thermistor)

Answer 103

Steel alloy (manganese molybdenum steel, chromium molybdenum steel or nickel chromium molybdenum steel).

Answer 104

WEIGHT of cylinder contents divided by WEIGHT of water it could hold.

Answer 105

100 microamps

Answer 106

II, III and aVF V1

Answer 107

An element that tends to lose electrons to form positive ions and has characteristic properties such as high electric and thermal conductivity, malleability, ductility and a shiny appearance due to free-moving electrons in a metallic bond.

Answer 108

Thermal energy that flows from one body in contact with another when they are at different temperatures.

Answer 109

Mean kinetic energy of molecules within a body.

Answer 110

Occurs via direct collisions between atoms and molecules of warmer and cooler regions and the resultant transfer of kinetic energy. ## Footnote Unit of conductivity is W/K/m.

Answer 111

Transfer of heat from a body by the liquid or gas that surrounds it. ## Footnote Passive: still air Active: moving air (e.g. bear hugger)

Answer 112

Hot bodies emit thermal energy in the form of electromagnetic radiation resulting in heat transfer.

Answer 113

Radiation energy per unit time from a black body is proportional to the **fourth power of the absolute temperature**.

Answer 114

Is a dimensionless quantity which quantifies the ability of a body to radiate heat. ## Footnote This is expressed as a comparison to a perfect black body surface at the same temperature (a black body has a value of 1).

Answer 115

A body that absorbs all radiation that falls upon it.

Answer 116

* Radiation: 40% * Convection: 30% * Evaporation: 20% * Respiration: 10% ## Footnote NOTE: Average emission is 50 watts per square metre.

Answer 117

Energy cannot be created or destroyed, only transformed from one form to another. ΔU = Q − W ## Footnote ΔU = change in internal energy of a system Q = heat added to the system W = work done by the system

Answer 118

In any natural thermodynamic process, the total entropy of a system and its surroundings always increases. ΔS = ΔQ/T ## Footnote ΔS: change in entropy ΔQ: heat entering the system T: temperature

Answer 119

As the temperature of a system approaches absolute zero (0 K), the entropy of a perfect crystalline substance approaches zero. ## Footnote The temperature absolute zero is unattainable.

Answer 120

Thermodynamic process in which a gas expands without exchanging heat with its surroundings. Any change in internal energy comes solely from work done by the gas. It usually leads to a drop in temperature, since the gas does work but receives no heat to compensate.

Answer 121

A gas changes temperature when it moves from a higher pressure to a lower pressure and for most gases, they cool.

Answer 122

Series of repeating disturbances that propagates in space and time. ## Footnote **Longitudinal Waves**: oscillations occurring in the direction of travel (e.g., sound waves) **Transverse Waves**: oscillations perpendicular to the direction of travel (e.g., Mexican wave)

Answer 123

Velocity = Frequency x Wavelength

Answer 124

20-20,000 Hz 170 mm to 0.17 mm

Answer 125

Speed of light travels faster through less dense materials. Sound travels faster through more dense material.

Answer 126

Characterised by periodic oscillation about the equilibrium position and each oscillation is one cycle. The acceleration of an object is proportional and in opposition to its displacement from the equilibrium position. ## Footnote Example: child on a swing

Answer 127

When the system oscillates with maximum amplitude. ## Footnote This occurs when the external driving frequency equals the natural frequency of the material.

Answer 128

Frequency at which a system oscillates when displaced from its equilibrium position and allowed to vibrate freely without any external forces acting on it.

Answer 129

Tendency to resist oscillation.

Answer 130

Most oscillators resonate at multiple frequencies. The lowest is the natural frequency, and integer multiples of this are called harmonics.

Answer 131

Mathematical model for analysing a periodic waveform to find its component frequencies. It will plot a spectrum of frequencies (amplitude against frequency). In the context of invasive blood pressure monitoring: enables detection of oscillatory patterns, filtering of noise, and precise assessment of heart rate and waveform features.

Answer 132

Number of joules of energy emitted each second - expressed in watts.

Answer 133

Describes how much energy falls on a surface and is measured in watts per square metre.

Answer 134

**I = P/4πr²** ## Footnote P = total power output from light (watts)

Answer 135

Measures pressure in a gas by vertical displacement of a liquid in a tube If the density of the liquid is known, the difference in column height can be used to calculate the hydrostatic pressure of the displaced column which is equal to the gas pressure. ## Footnote Derivation P = F/A P = mg/A P = ((Density x Area x Height) x Gravity)/Area Gauge Pressure = Density x Gravity x Height

Answer 136

Consists of a C-shaped hollow spring-like tube that extends outwards at the sealed end when pressure rises in the tube. The expansion and contraction is relayed to a pointer that indicates the pressure on a calibrated dial.

Answer 137

It measures absolute atmospheric pressure. A sealed, liquid-filled tube is inverted into a reservoir (Torricellian vacuum) Atmospheric pressure pushes on the reservoir, balancing the column of liquid. The height of the liquid column is proportional to atmospheric pressure. ## Footnote NOTE: Mercury is used due to its high density, keeping the column height manageable.

Answer 138

Relieves pressure beyond a specified limit and re-closes upon return to the normal pressure range.

Answer 139

Turning a screw raises or lowers the spring and diaphragm. When lowered, more pressure is required to raise the diaphragm enough for gas to escape through the apertures. The diaphragm is pushed upwards and reaches a point where the gas can escape. The adjustable pressure limit valve allows the blow-off pressure to be adjusted by turning a screw that raises or lowers the spring and diaphragm. When the spring is lowered, the spring must be compressed further so more pressure is needed to raise the diaphragm enough for the gas to escape.

Answer 140

Used to supply a flow of gas to an outlet (e.g. facemask) at a much lower pressure than the supply (e.g. cylinder). Gas flows into a chamber via an aperture around a piston If the chamber pressure gets too high, the diaphragm and piston rise to narrow the aperture. This restricts gas flow into the chamber, thereby reducing outflow pressure.

Answer 141

Physical phenomenon where a liquid is drawn from a higher container to a lower one through a tube, with the liquid flow maintained by gravity and hydrostatic pressure differences, once the tube is initially filled.

Answer 142

The subatmospheric pressure created in the bottle as liquid flows from the bottle to the vein would mean that the pressure will equilibrate with the pressure in the vein, thereby stopping drug delivery. A vent in the bottle enables air to replace the liquid so the pressure in the bottle remains atmospheric.

Answer 143

If a syringe driver is placed at a significant height above the patient, the weight of the column of fluid (hydrostatic pressure) could overcome the friction between a plunger and the barrel, thereby making the syringe empty faster.

Answer 144

Instrument for measuring the changes in pulsations in the arteries, especially of the extremities. The cuff is inflated and slowly deflated through a valve whilst a sensor monitors the cuff pressure and the small oscillations which begin as soon as cuff pressure drop below the systolic. Max amplitude occurs when the cuff pressure is equal to the mean pressure.

Answer 145

Monitors arterial blood volume via light absorption (photoplethysmography). Increased blood volume → more light absorbed → less detected. A cuff inflates until blood volume is constant—this occurs at mean arterial pressure. A feedback system adjusts cuff pressure in real time to maintain constant arterial volume, approximating MAP. ## Footnote NOTE: Only works in vasodilated patients

Answer 146

Uses a pressure transducer with strain gauges in a Wheatstone bridge to detect small pressure changes. A fluid-filled catheter (saline-heparin) transmits arterial pressure to the transducer. Sensor is placed at cannula level and zeroed to atmospheric pressure by exposing it briefly to air. Continuous saline flush (3–5 mL/hr) prevents clotting and maintains patency.

Answer 147

Systolic: overestimated Diastolic: underestimated

Answer 148

Under-estimates systolic Over-estimates diastolic

Answer 149

* Long catheter * Narrow catheter * Air bubble (compressible meaning that a lot of the pressure change is absorbed by the bubble and not transmitted to the transducer)

Answer 150

Sun heats water → evaporation increases water vapor Water vapor displaces heavier gases → air becomes less dense and rises Rising air expands and cools (adiabatic expansion) → condensation occurs Condensation forms clouds and leads to rise in air density

Answer 151

Mass of water molecules per unit volume (grams per metre cubed).

Answer 152

Uses two thermometers: a dry bulb to measure ambient temperature, and a wet bulb wrapped in a water-saturated wick. The rate of evaporation from wick depends on relative humidity of surrounding air. Evaporation from wick causes a drop in temperature on the wet bulb. Temperature difference correlates to relative humidity.

Answer 153

Hair contains cytokeratin molecules linked by disulphide bridges and hydrogen bonds. H bonds absorb moisture from the air, causing the hair to lengthen. The degree of lengthening depends on relative humidity and can be calibrated to give a humidity reading.

Answer 154

Air is passed through ether in a silver tube, causing it to evaporate and cool the tube via latent heat loss. Condensation on the tube’s surface marks the dew point temperature. Modern versions use a chilled mirror and electronic sensors to detect condensation.

Answer 155

44 g/m3 Gives a partial pressure of around 6.3 kPa

Answer 156

Calcium chloride or silica

Answer 157

Exhaled warm, moist air condenses on the material, releasing latent heat and warming it. On the next inhalation, dry gas passes over the warm, moist material, becoming warmed and humidified. Approx. 80% efficient in conserving heat and moisture. A 0.2 µm filter can be added to block bacteria/viruses, preventing circuit contamination.

Answer 158

100 mL in adults Up to 2 cm H₂O resistance ## Footnote NOTE: It can get blocked with secretions which increases the resistance.

Answer 159

**Active**: Use heating elements and thermostats to reach up to 100% efficiency, but are bulky—used mainly for long-term ventilation. **Passive**: Bubble inspired gas through water to saturate it with humidity.

Answer 160

Water temperature limits humidity; evaporation cools the bath (latent heat loss). ## Footnote Active systems maintain temperature (typically 40–60°C) with a thermostat. 40°C: Less scald risk, more microbial growth. 60°C: More scald risk, lower infection risk.

Answer 161

* < 3 µm: enter the alveoli and THERAPEUTICALLY BENEFICIAL * 1 µm = ideal * 5-10 µm: deposit in the upper airways

Answer 162

High-pressure gas flows over a capillary tube immersed in fluid. Gas passes through a small orifice, creating negative pressure via the Bernoulli principle. This draws fluid up and converts it into an aerosol mist.

Answer 163

A ceramic piezoelectric transducer converts electrical energy into mechanical vibrations (~1.5 MHz). Vibrations pass through water to a flexible diaphragm. The diaphragm vibrates the solution, breaking it into fine aerosol particles. The particle size is more consistent.

Answer 164

The movement of a gas or liquid through a tube or other system (volume passing a point per unit time).

Answer 165

Smooth, orderly movement of fluid in parallel layers.

Answer 166

In laminar flow, flow is directly proportional to driving pressure. Q = ΔP/R

Answer 167

A mathematical formula that describes the **flow rate of a fluid** through a cylindrical pipe, given by the equation: **Q = (πΔPr^4) / (8ηL)** ## Footnote This equation illustrates how flow rate is influenced by pressure difference, pipe radius, fluid viscosity, and length of the pipe.

Answer 168

A chaotic, irregular fluid motion characterised by swirling eddies and vortices, where layers of fluid mix unpredictably.

Answer 169

Re = (Velocity x Radius x Density)/Viscosity ## Footnote Interpretation < 2000 = Laminar 2000-4000 = Transitional > 4000 = Turbulent

Answer 170

Q ∝ √ΔP Q² ∝ ΔP The gradient is resistance which increases with flow rate

Answer 171

Fluid moving rapidly (e.g. through a constriction) exerts less pressure than a static fluid.

Answer 172

As velocity increases at a constriction, the kinetic energy increases and, for the total energy within the system to remain constant, the potential energy must decrease. The potential energy of a gas is proportional to the pressure it exerts, so the pressure exerted on the walls of the tube will decrease with increased velocity.

Answer 173

If the Bernoulli principle is used to create an area at subatmospheric pressure, it will **entrain air**.

Answer 174

Rate of entrainment (determined by the size of the holes) Rate of flow of oxygen (to a lesser extent) Entrainment Ratio = Entrained Flow/Driving Flow

Answer 175

A fluid or gas stream will hug a convex contour when directed at a tangent to that surface.

Answer 176

A fast-moving fluid jet generates a region of lower pressure around it, entraining surrounding fluid into the stream. When the jet encounters a nearby surface, entrainment is reduced on the side facing the surface, leading to a local drop in pressure. This pressure differential causes the jet to be drawn toward and follow the contour of the adjacent surface.

Answer 177

* It is a tapered vertical tube with a bobbin that rises as gas flow increases. * The bobbin equilibrates when the upward force of gas balances its weight. * The conical shape allows more air around the bobbin at higher gas flows. * It is calibrated for specific gases due to viscosity/density.

Answer 178

It is the time-integral of the flow rate. ## Footnote I.e. flow is volume passing a certain point per unit time, the area under the curve will be the lung volume

Answer 179

It is the differential of the volume-time curve.

Answer 180

Measures gas flow using a small turbine that spins with the flow. Interruptions of a light beam by the turbine generate a voltage proportional to flow rate. Most accurate at low respiratory flows due to turbine inertia.

Answer 181

It measures airflow by detecting the pressure difference across a fine mesh in a tube (fixed resistance). This **pressure difference**, sensed by pressure sensors, is proportional to flow rate (per Ohm’s law) under laminar conditions. A widened tube ensures laminar flow by reducing velocity and the Reynolds number.

Answer 182

Measures flow by comparing pressure in two sealed tubes—one facing into the airflow and one facing away. The flow-facing tube compresses air, creating a pressure increase. The pressure difference reflects the square of the flow velocity (kinetic energy = 1/2(mv^2)), which is assumed proportional to flow rate. Unlike pneumotachometers, they use no flow resistor.

Answer 183

It measures peak expiratory flow by using exhaled air to push a diaphragm against a spring. As the diaphragm moves, it opens a narrow slot for air to escape, reducing pressure. A sliding marker is pushed by the diaphragm and stops when the spring force balances the airflow pressure, indicating the peak flow rate.

Answer 184

It measures lung volume by collecting exhaled gas in a sealed, movable bell chamber. As air enters, the bell rises or falls, with its displacement proportional to the volume of air exhaled. A water seal ensures airtight movement, and the motion is recorded—traditionally on a rotating drum. It may underestimate volume due to air cooling and condensation inside the chamber.

Answer 185

* Molecules are so far apart that there is no attraction between them. * Volume of the molecules themselves is negligible. * Molecules are in random motion, obeying Newton's laws of motion.

Answer 186

Temperature of 273.15 K (0 degrees) Atmospheric pressure of 101.3 kPa = 760 mm Hg

Answer 187

Equal volumes of gases, at the same temperature and pressure, contain the same number of molecules.

Answer 188

A unit of measurement that is the amount of a pure substance containing the same number of molecules as there are atoms in exactly 12 grams of carbon-12 (i.e., 6.022 x 10^23).

Answer 189

Quantifies how many molecules make up one mole. | (6.02 x 10^23 per mole)

Answer 190

22.4 litres

Answer 191

For a gas, the total pressure is simply all the partial pressures added together.

Answer 192

The volume of a gas is inversely proportional to its pressure at a fixed temperature. P α 1/V

Answer 193

At a given pressure, the absolute temperature (in kelvin) is directly proportional to the volume of the gas.

Answer 194

The pressure of a gas is directly proportional to its temperature within a fixed volume.

Part 2: Physics & Equipment Flashcards

Apply principles of physics and measurement to anaesthesia, including pressure, flow, gas laws, vaporizers, electrical safety, and monitoring. (227 cards)