Session 1 - Physics and Clinical Flashcards
State Boyles law
• Pressure is inversely proportional to volume for a fixed quantity of gas in a container of given size
State Charles law
• Pressure is directly proportional to absolute temperature for a fixed quantity of gas in a container of a given size (kelvin)
State the universal gas law
- 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)
What is STP?
• 273 deg K (0*C), 101.1 kPa (temperature sometimes corrected for body temperature)
Define the term partial pressure
- 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
Proportion of O2 in dry atmospheric air is 20.9% - what is the partial pressure of O2 if total atmospheric pressure is 101.1kPa
• pO2 = 101.1 x 0.209 = 21.1299 21l1 kPa
Define ‘vapour pressure’
• The pressure exerted by water vapour entering a gas
Define ‘saturated vapour pressure’
- 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
Define ‘tension’
- The partial pressure exerted by gas molecules entering a liquid
- Indicates how readily gas will leave the liquid
Define solubility
- The amount of gas that needs to enter a liquid in order to establish a given pressure
- Content/tension
Define ‘content’ of a gas in a liquid
• 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
Why is 13.3 kPa significant?
• The average kPa of O2 blood is exposed to
At normal levels, how many mmol.l-1 O2 are bound to haemoglobin per litre?
• 8.8 mmol.l-1
What’s the minimum amount of O2 that the body must pick up per minute per 5l of blood
• 12mmol
Define ‘tidal volume’
• The volume of air drawn into the lungs with each breath
Define the term ‘respiratory rate’
• Number of breaths per minute
Define the term ‘pulmonary ventilation rate’
• Tidal volume x respiratory rate
How can the larynx cause difficulty breathing?
• Laryngeal or vocal cord tumours • Laryngeal oedema due to ○ Allergic reactions ○ Severe infections such as croup or acute epiglottis • Bilateral vocal cord paralysis
How can problems in the nose cause difficulty breathing?
• Polyps, tumors
How can problems in the pharynx cause difficulty breathing?
- 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
How can viral URTIs spread to the sinuses and the middle ear?
Sinuses via opening into nasal cavity
Middle ear via eustachian tube, which connects nasopharynx to middle ear
What is emphysema caused by?
• Alpha-1-antitrypsin deficiency or smoking
What occurs in emphysema?
• 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.
What is pneumonia?
- Inflammation of the lung caused by bacteria
* The lungs fill with inflammatory fluid, increasing the difficulty of breathing
Give three different causative agents of pneumonia
- Streptococcus pneumoniae
- Mycoplasm pneumoniae
- Saphylococcus aureus
