Ventilation: Diffusion, Common Lung Pathologies and Lung Function Tests Flashcards
Normal adult value for residual volume
1200ml (20-25ml/kg)
Normal adult value for expiratory reserve volume
1100mL in males
800mL in females
Normal adult value for tidal volume
500mL
Normal adult value for inspiratory reserve volume
1900-300mL
What does ventilation refer to?
Movement of air in and our of lungs
What are the two ways ventilation can be described as?
Pulmonary (minute) ventilation
Alveolar ventilation
Both measured in L/min
What is pulmonary ventilation?
Total air movement into/out of lungs
What is alveolar ventilation?
Volume fresh air getting to alveoli and available for gas exchange
What does Dalton’s Law state?
The total pressure of a gas mixture is the sum of the pressures of the individual gases
What is partial pressure?
The pressure of a gas in a mixture of gases is equivalent to the percentage of that particular gas in the entire mixture multiplied by the pressure of the whole gaseous mixture.
What is our air a mixture of?
Nitrogen (79%).
Oxygen (21%).
Negligible quantities of CO2 in the air (0.03%).
Why is there CO2 in our cells and blood?
We make CO2, we do NOT breathe it in.
Why would a patient’s CO2 be increased?
If a patient’s CO2 has gone up it is because they can’t get rid of CO2 in their body because they’ve got some kind of respiratory pathology blocking them from exhaling it.
What is PO2?
Partial pressure of oxgyegn
What is PCO2?
Partial pressure of carbon dioxide
How can alveolar PO2 and PCO2 vary?
Hyper and hypo ventilation
What is the normal value for alveolar partial pressure of 03?
100mmHg (13.3 kPa)
What is the normal value for alveolar partial pressure of CO2?
CO2 is 40mmHg (5.3kPa).
What does the pulmonary artery do?
Carries deoxygenated blood away from the heart to the lungs
What does the pulmonary vein do?
Carries oxygenated blood toward the heart
What supplies bronchial circulation?
Bronchial arteries arising from systemic circulation to supply oxygenated blood to lung tissues
Where does blood drain in bronchial circulation?
To left atrium via pulmonary veins
What % of left heart output is in bronchial circulation?
2%
What does pulmonary circulation consist of?
Left and right pulmonary arteries originating from the right ventricle
Where does the entire cardiac output come from?
Right ventricle
What does pulmonary circulation supply?
The dense capillary network surrounding the alveoli and returns oxygenated blood to the left atrium via the pulmonary vein
How can you describe pulmonary circulation?
High flow, low pressure
Pressure that is driving flow in pulmonary is much lower than the pressure that is driving flow in the systemic circulation.
What is partial pressure of gas?
The partial pressure of gas in the alveoli is the same as the partial pressure of gas in the systemic arteries providing we’ve got nice, healthy lungs
The rate of diffusion across the membrane is:
- directly proportional to the partial pressure gradient - bigger the gradient, the faster the gas will diffuse
- directly proportional to gas solubility - the more soluble the gas is, the easier it is to diffuse
- directly proportional to the available surface area
- inversely proportional to the thickness of the membrane
- most rapid over short distances - it doesn’t have so far to go
What has a larger partial pressure gradient? Carbon dioxide or oxygen?
Oxygen
What do the following abbreviations mean?
A
a
v~
PaO2
PaCO2
mmHg
kPa
A = alveolar
a = arterial blood
v~ (squiggly line on top) = mixed venous blood (eg in pulmonary artery.
PaO2 = partial pressure of oxygen in arterial blood
PACO2 = partial pressure of carbon dioxide in alveolar air
mmHg = millimetres mercury
kPa = kilopascals
What does reduction in surface area cause?
Less oxygen can enter that blood so blood flowing away from an emphysemic lung has a lower partial pressure of oxygen than normal.
Lower PO2 in the pulmonary vein and in the systemic arterial blood.
What is seen in both fibrosis and emphysema?
An increase in partial pressure of carbon dioxide
What does asthma cause?
No difficulty in gases diffusing between the alveoli and the blood.
Low partial pressure of oxygen in systemic arterial blood
To summarise:
What do emphysema, fibrosis, and oedema cause?
Emphysema - loss of surface area
Fibrosis - increased thickness of membrane
Oedema - increased diffusion distance
What are obstructive lung diseases?
Obstruction to air flow, especially on expiration (breathing out)
- Asthma
- Chronic bronchitis
- COPD
- Emphysema
What are examples of restriction of lung expansion?
Fibrosis
Infant respiratory distress syndrome
Pulmonary oedema
Pneumothorax
What is spirometry used for?
A technique commonly used to measure lung function
Measurements can be static or dynamic
What are static spirometry results?
Where the only consideration made is the volume exhales - for example, “exhaled five litres” end of story
What are dynamic spirometry results?
Where the time is taken to inhale or exhale a certain volume is what is being measured - more helpful - most clinical respiratory lung function testes work with expired air.
What can spirometry measure?
- Tidal volume
- Inspiratory reserve volume
- Expiratory reserve volume
- Inspiratory capacity
- Vital capacity
What is FEV1/FVC ratio?
Ratio of the forced expiratory volume in the first one second to the forced vital capacity of the lungs.
What is FEV1?
Measures how much air you can exhale in one second
What is FVC?
Total amount of air you can exhale forcefully in one breath
What is FEV1/FVC in a healthy adult?
80%
What would be seen in COPD spirometry?
- The rate at which air is exhaled is much slower
- Total expired volume (FVC) is also reduced (FRC may be increased)
- The major effect is on airways and so FEV1 is reduced to a greater extent than FVC
- Significant fall in ratio also reduced
What happens in spirometry in restrictive lung diseases?
Both FEV1 and FVC reduced in proportion and the ratio remains normal or may even increase.
