Session 1 - Physics and Clinical

Question 1

State Boyles law

Answer 1

• Pressure is inversely proportional to volume for a fixed quantity of gas in a container of given size

Question 2

State Charles law

Answer 2

• Pressure is directly proportional to absolute temperature for a fixed quantity of gas in a container of a given size (kelvin)

Question 3

State the universal gas law

Answer 3

• Pressure is inversely proportional to volume for a fixed quantity of gas and directly proportional to absolute temperature
• PV = nRT (n = number of molecules of gas in moles) (R = the universal gas constant)

Question 4

What is STP?

Answer 4

• 273 deg K (0*C), 101.1 kPa (temperature sometimes corrected for body temperature)

Question 5

Define the term partial pressure

Answer 5

• Provided the constituents of a gas mixture do not combine chemically, each component of a gas mixture can be said to exert a partial pressure
• Same proportion of the total pressure as the volume fraction of the gas in the mixture

Question 6

Proportion of O2 in dry atmospheric air is 20.9% - what is the partial pressure of O2 if total atmospheric pressure is 101.1kPa

Answer 6

• pO2 = 101.1 x 0.209 = 21.1299 21l1 kPa

Question 7

Define ‘vapour pressure’

Answer 7

• The pressure exerted by water vapour entering a gas

Question 8

Define ‘saturated vapour pressure’

Answer 8

• If a gas mixture is in equilibrium (molecules enter and leave water at same rate) with water, then the vapour pressure is maximum - the saturated vapour pressure
• 6.28 kPa at 37*C

Question 9

Define ‘tension’

Answer 9

• The partial pressure exerted by gas molecules entering a liquid
• Indicates how readily gas will leave the liquid

Question 10

Define solubility

Answer 10

• The amount of gas that needs to enter a liquid in order to establish a given pressure
• Content/tension

Question 11

Define ‘content’ of a gas in a liquid

Answer 11

• The amount of gas in a liquid
• Total content of gas = reacted gas (O2 bound to haem) + dissolved gas (O2 free in plasma)
Content = solubility x tension

Question 12

Why is 13.3 kPa significant?

Answer 12

• The average kPa of O2 blood is exposed to

Question 13

At normal levels, how many mmol.l-1 O2 are bound to haemoglobin per litre?

Answer 13

• 8.8 mmol.l-1

Question 14

What’s the minimum amount of O2 that the body must pick up per minute per 5l of blood

Answer 14

• 12mmol

Question 15

Define ‘tidal volume’

Answer 15

• The volume of air drawn into the lungs with each breath

Question 16

Define the term ‘respiratory rate’

Answer 16

• Number of breaths per minute

Question 17

Define the term ‘pulmonary ventilation rate’

Answer 17

• Tidal volume x respiratory rate

Question 18

How can the larynx cause difficulty breathing?

Answer 18

• Laryngeal or vocal cord tumours
• Laryngeal oedema due to
	○ Allergic reactions
	○ Severe infections such as croup or acute epiglottis
• Bilateral vocal cord paralysis

Question 19

How can problems in the nose cause difficulty breathing?

Answer 19

• Polyps, tumors

Question 20

How can problems in the pharynx cause difficulty breathing?

Answer 20

• Tumours
• Airway of an unconscious person may become blocked if their tounge falls backwards into their pharynx
• Sleep apnoea syndrome - loss of tone in pharyngeal muscles during sleep can cause them to become floppy and obstruct airways

Question 21

How can viral URTIs spread to the sinuses and the middle ear?

Answer 21

Sinuses via opening into nasal cavity

Middle ear via eustachian tube, which connects nasopharynx to middle ear

Question 22

What is emphysema caused by?

Answer 22

• Alpha-1-antitrypsin deficiency or smoking

Question 23

What occurs in emphysema?

Answer 23

• Aveolar walls normally hold bronchioles open - however, when they are damaged bronchioles collapse and air becomes trapped, making it difficult for the lungs to empty.

Question 24

What is pneumonia?

Answer 24

• Inflammation of the lung caused by bacteria

* The lungs fill with inflammatory fluid, increasing the difficulty of breathing

Question 25

Give three different causative agents of pneumonia

Answer 25

• Streptococcus pneumoniae
• Mycoplasm pneumoniae
• Saphylococcus aureus