Temperature & Humidity Flashcards
Define heat
The form of kinetic energy that passes between 2 substances
Define temperature
The property of a substance that determines whether it will transfer or receive heat to/from another substance.
What does the amount of heat depend on?
The mass of the substance
Define specific heat capacity
The amount of heat required to raise the temp of a unit of mass of substance by 1K
What is the triple point?
The temp & pressure at which solid, liquid, gas phases of a substance exist in equilibrium
273K
What is STP?
Standard temperature & pressure
What is critical temperature?
The temp above which a vapour cannot be liquefied by any amount of pressure
What is latent heat?
The energy required to change the state of a substance without changing its temperature
What are the types of latent heat?
- Latent heat of vaporisation
- Latent heat of fusion
What are the 3 scales used for measuring temperature?
- Fahrenheit
- Celsius (273K)
- Kelvin
What is 1K equal in magnitude to?
1 degree celsius
What does doubling the kelvin do to a volume of gas
Double the volume
What does a resistance wire temperature graph look like?
Linear - as temp increases (Y axis) so does resistance (X axis)
What does a thermistor temperature graph look like?
Inverse exponential graph. As temp falls so does resistance exponentially
What does a thermocouple temperature graph look like?
Linear graph- as temp difference increases so does potential difference
What are the advantages/ disadvantages of each type of graph?
Wire: Very accurate but fragile and slow
Thermistor: Cheap, small, fast but calibration error & deteriorates over time
Thermocouple: Tough, cheap, small but needs signal amplification
What are non-electrical methods of measuring temperature?
- Liquid expansion: Mercury expands with heat
- Dial: Metal coil that turns pointer as heated up
- Tympanic/infrared: Emit electromagnetic radiation. Intensity & wavelength for max radiation is detected
- Chemical: Plastic strip containing colour changing crystals
How is heat transferred/lost?
- Radiation - MOST
- Convection
- Evaporation
- Conduction
How does hypothermia affect the body systems?
-CVS: VasoC, inc blood viscosity, reduced CO
- Resp: Reduced O2 demand & CO2 production
- Neuro: Confusion
- Anaesthetics: Reduced MAC, prolongs NM blockers
- Other: Reduced metabolism, diuresis, coagulopathy, metabolic acidosis
What does hypothermia do to the O2 dissociation curve?
Shifts to the left - reduced O2 tissue delivery
What makes a patient high risk for perioperative hypothermia?
- ASA 2 +
- Pre-op temp <36
- Combined RA & GA
- At risk of CVS complications
- Intermediate/major surgery
What is the Seebeck effect?
The production of voltage at the junction of 2 different conductors.
Magnitude is proportional to temp.
What is absolute humidity?
A fixed amount of water vapour in the atmosphere per unit vol at a give temp/pressure
Which holds more water warm or cool air?
Warm- increasing amount of H2O is required to saturate a gas as temp increases
What is humidity?
The amount of water present in the atmosphere
What is relative humidity?
The ratio of the mass of water vapour in a given vol of air compared with the mass required to saturate that vol of air
What is a dew point?
The temp at which the relative humidity of the air exceeds 100% and water condenses out as liquid
What is a hygrometer?
Instrument for measuring humidity
What is hygroscopic material?
Material that attracts moisture from the atmosphere
What are the humidity values for room, alveoli & trachea, soda lime?
Air at room temp: 17
Air at body temp/alveoli : 44
Air in upper trachea: 34
Soda lime: 29
What problems can dry air cause to airways?
- Drying of resp mucosa
- Thickening of mucus causing plugging
- Reduced ciliary activity
- Keratinisation & ulceration
What are the different mechanisms to humidify air?
1) Cold water bath - least effective
2) HME
3) Hot water bath
4) Bernoulli neb
5) USS neb - most effective
Where are the different sized droplets in a nebuliser deposited?
20um = tubing/upper resp tract
2-5um = trachea-bronchial tree
1um = alveoli
<1um = no deposit, inhaled & exhaled
How are absolute and relative humidity measured?
Absolute: Regnault’s hygrometer
Relative: Hair hygrometer, Wet & dry bulb hygrometer, Regnault’s hygrometer
