Clinical Measurement

Question 1

What is humidity?

Answer 1

This is the amount of water vapour in the atmosphere.

Question 2

What is absolute humidity?

Answer 2

Total mass of water vapour present in the atmosphere per unit volume. Measured in kg.m-3 or g.m-3

Question 3

What is relative humidity?

Answer 3

This is the ratio of the amount of water vapour in air compared to the amount it would contain at the same temperature if the air was fully saturated. RH %

Question 4

What is dew point?

Answer 4

This is the temperature at which the relative humidity of air exceeds 100% and water condenses out of vapour phase to form a liquid.

Question 5

How is humidity measured?

Answer 5

The hygrometer

Question 6

What does the humidity graph try to explain?

Answer 6

How a fixed amount of water vapour in the atmosphere can leave to variable RH depending on the current temperature.

Also explains the importance of the upper airway in a room fully humidified by the addition of 27g.m-3 of water vapour

Question 7

Formulas for calculating heat loss during humidifying dry air or warming cold air?

Answer 7

See image attached

Question 8

What is more relevant in the respiratory tract; Heat loss or drying of airway?

Answer 8

Heat loss is minimal but drying of airway is more relevant

Question 9

What are the mechanisms of heat loss during surgery ?

Answer 9

Radiation (40 - 60%)
Convection (25 - 30%)
Conduction (5%)
Evaporation (15 - 50%)
Respiration (5 - 10%)

Question 10

Energy consumed by the patient’s airway for warming and humidifying cold, dry gases?

Answer 10

About 10 Watts

Question 11

Mechanism of heat loss via Radiation?

Answer 11

• Transfer of infrared radiation
• No direct contact with the cold body
• Proportional to the 4th power of temperature difference

Question 12

Mechanism of heat loss via Convection?

Answer 12

• Loss via air movement across an exposed surface
• Warmed air is replaced with un-warmed air

Question 13

Mechanism of heat loss via Conduction?

Answer 13

• Direct transfer of energy to an adjacent body
• Both bodies are in contact

Question 14

Mechanism of heat loss via Evaporation?

Answer 14

• Loss of heat via latent heat of vaporization
• Liquid from body moves to vapor phase

Question 15

Mechanism of heat loss via Respiration?

Answer 15

• Heat loss by humidification (8%)
• Heat loss by warming (2%)

Question 16

Heat loss during surgery?

Answer 16

• Phase 1 - 37 - 35.5 degrees
• Phase 2 - 35 - 34 degrees
• Phase 3 - 34 degrees

Question 17

Phase 1 - 37 - 35.5 degrees - Properties?

Answer 17

• Over a course of 1 hour
• Loss of core - periphery temperature gradient
• Redistribution of heat

Question 18

• Phase 2 - 35 - 34 degrees - Properties?

Answer 18

• Over 2.5 hours
• Actual heat loss from body
• The slope may be altered by active or passive warming

Question 19

• Phase 3 - 34 degrees - Properties?

Answer 19

• Thermo-regulatory mechanisms act

Question 20

CVS implications of hypothermia?

Answer 20

• Arrhythmia
• Direct myocardial depressant effect
• Hypotension
• Peripheral vasoconstriction

Question 21

Respiratory implications of hypothermia?

Answer 21

• Hyperventilation
• Respiratory alkalosis
• Left shift of the OHDC

Question 22

Haematological implications of hypothermia?

Answer 22

• Coagulopathy

Question 23

Renal implications of hypothermia?

Answer 23

• Increased renal blood flow
• Diuresis

Question 24

Neurological implications of hypothermia?

Answer 24

• CNS depressant effect

Question 25

GI implications of hypothermia?

Answer 25

- Impaired liver function - Pancreatitis - Ileus

Question 26

Metabolic implications of hypothermia?

Answer 26

- Increased due to shivering - Decreased metabolic rate with further decrease in temperature

Question 27

What is the Bernoulli principle?

Answer 27

Decrease in pressure will lead to increase in flow velocity of a perfect fluid

Question 28

What is the venturi effect ?

Answer 28

Introduction of constriction to fluid with increase of velocity. Pressure of the fluid falls

Question 29

Define the law of conservation of energy ?

Answer 29

Energy cannot b created or destroyed but can only be changed from one form to another.

Question 30

What is the Coanda effect ?

Answer 30

This is the tendency of a stream of fluid flow in proximity to a convex surface, to follow the line of the surface rather than its original course

Question 31

What is Henry’s law?

Answer 31

The amount of gas dissolved in a liquid is directly proportional to the partial pressure of the gas in equilibrium with the liquid.

Question 32

What is Fick’s law of diffusion ?

Answer 32

The rate of diffusion of a gas across a membrane is proportional to the membrane area and concentration gradient across the membrane and inversely proportional to its thickness.

Question 33

What is Boyle’s law (1st gas law)?

Answer 33

At constant temperature the volume of a fixed amount of perfect gas varies inversely with its pressure PV=K

Question 34

What’s is Charles’ law (2nd gas law)?

Answer 34

At constant pressure the volume of a fixed amount of perfect gas varies in proportion to its absolute temperature V/T =k

Question 35

What is Gay-Lussac’s law (3rd gas law)?

Answer 35

At constant volume the pressure of a fixed amount of perfect gas varies in proportion to its absolute temperature. P/T =k

Question 36

What is the perfect gas ?

Answer 36

- It obeys all three gas laws - infinitely small in size - Occupies no volume - No force of attraction - Hydrogen is the closest to a perfect gas

Question 37

What is Avogadro’s hypothesis?

Answer 37

Equal volumes of gases at the same temperature and pressure contain equal numbers of molecules

Question 38

What is the universal gas equation?

Answer 38

PV=nRT

Question 39

Properties of Hagen-Poiseuille equation?

Answer 39

- Flow is proportional to the 4th power of the radius. - Doubling radius is 2(4) - 16 fold increase in flow

Question 40

What is turbulent flow?

Answer 40

- Fluid flow is unpredictable - Multiple eddy currents - Not parallel to side of tube

Question 41

Calculation of Reynold’s number ?

Answer 41

Re=pvd/n P = Density of fluid V = Velocity of fluid d = Diameter of tube n = Viscosity of fluid < 2000 laminar > 2000 turbulent

Question 42

What is surface tension?

Answer 42

Tendency of liquid surfaces to shrink into the minimum surface area possible

Question 43

What is the clinical application of surface tension?

Answer 43

- Surface tension decrease the size of alveoli. Alveolar collapse following expiration

Question 44

whats cells produce surfactant?

Answer 44

Type II pneumocytes

Question 45

Whats is the chemical name of surfactant?

Answer 45

Dipalmitoylphosphatidylcholine (DPPC)

Question 46

Whats is the function of surfactant?

Answer 46

Decreases the pressure applied to the alveoli thus decreasing surface tension

Question 47

what is the LaPlace law for surface tension?

Answer 47

P = 4T/r Pressure, Tension and radius