Volumes and pressures Flashcards
What are the units of pressure?
Pressure in kPa in the respiratory system.
Pressure in mmHg in the cardiovascular system.
What is the abbreviation for pressure in inspired air?
PIO2 = partial pressure of oxygen in inspired air.
PICO2 = partial pressure of carbon dioxide in inspired air.
What is the abbreviation of pressure in the alveoli?
PAO2 = partial pressure of oxygen in alveolus.
PACO2 = partial pressure of carbon dioxide in alveolus.
What is the abbreviation of pressure in arteries?
PaO2 = partial pressure of oxygen in arterial blood.
PaCO2 = partial pressure of carbon dioxide in arterial blood.
What is the abbreviation of pressure in veins?
PvO2 = partial pressure of oxygen in venous blood.
PvCO2 = partial pressure of carbon dioxide in carbon dioxide.
What is Charles’s Law?
Volume is proportional to temperature at constant pressure.
As temperature increases, the gas molecules move faster and spread out, causing the gas volume to increase.
What is Boyle’s Law?
Pressure is proportional to 1/volume (inversely proportional) at constant temperature.
If volume increases, the pressure decreases because gas molecules have more space to move and collide less frequently with container walls.
What is partial pressure?
The pressure exerted by a gas, either alone or in a mixture, and depends upon the number of molecules of that gas in the given volume and temperature.
What is Dalton’s law of Partial pressures?
Each gas exerts its own partial pressure.
Total partial pressure is the sum of each of the gases individual partial pressure.
In atmospheric air, the total pressure = PN2, PO2, PCO2, and PH2O.
What is the calculation for partial pressure?
Partial pressure = fractional concentration x total pressure of gas.
e.g. 21% x 101kPa = 21.2 kPa PIO2.
How does PIO2 change if a patient was given 100% O2 to breathe?
100% O2 = 101pKa,
Will increase the inspired oxygen of the patient.
How would PIO2 change if exposed to high altitude?
O2 decreases, so PIO2 decreases, and partial pressure gradient is less.
It changes how much oxygen is available for diffusion into the blood.
What is the importance of partial pressures?
They are important because diffusion occurs down partial pressure gradients.
How does the PO2 change from the atmosphere to the mitochondria?
PIO2 in air is 20pKa.
To alveolus, PAO2 drops to 13kPa.
The PaO2 is very similar to PAO2.
Tissue PaO2 drops to less than 7pKa, so there is a very large pressure gradient between the blood and the tissue, so diffusion is rapid.
What would be the effects of low PAO2?
e.g. in respiratory disease, have low PAO2 and therefore PaO2.
The pressure gradient will be reduced, so perfusion of oxygen is impaired.
What are the functions of the upper airways?
Filtering
Warming
Humidifying
Why is air mostly breathed through the nose?
The nasal hairs filters dirt.
They warm the air as it passes by the blood in the nasal cavity.
It also humidifies the air, which increases the water vapour of the gas, so the gas and lungs are wet - gases diffuse better across a wet surface.
What are dry gases?
Dry atmospheric gases contain O2, N2 and CO2.
When air enters the lungs, it contains O2, N2, CO2, and water vapour.
Gas laws apply to dry gas only.
How does water vapour affect pressure?
The total pressure remains at 101kPa, but water vapour pressure in the lungs is 6kPa.
This means the available pressure for O2 and other gases is reduced.
PH2O displaces gas molecules equally so must be subtracted to calculate dry gas pressure.
What is the equation for water affecting oxygen pressure?
PIO2 = 21% x 101-6 kPa = 19.95kPa.
This is important because it changes how much oxygen is available for diffusion into the blood.
What are BTPS conditions?
In the lungs, gases are at Body Temperature, body Pressure and fully Saturated with water vapour at that temperature.
What are ATPS conditions?
Volumes collected are usually at Ambient Temperature, ambient Pressure and saturated with water vapour at that temperature.
What is the Boyle-Charles formula?
P1V1/T1 = P2V2/T2
Converts atmospheric conditions (ATPS) to body conditions (BTPS).
What are the gas values around the body?
PAO2 = 13pKa
PACO2 = 5kPa
Blood coming back from heart has low oxygen, high CO2.
So there is a gradient between venous blood and air in alveolus, drives diffusion.
Big O2 partial pressure gradient between venous blood and alveolus
Small CO2 partial pressure gradient.
What are the conditions for low tidal volume and high respiratory frequency?
e.g. 150ml tidal volume, 40 RF, minute ventilation 6000, anatomic dead space 6000ml, alveolar ventilation 0.
Hypoventilation
Hypoxia - low oxygen
Hypercapnia - high carbon dioxide and therefore respiratory acidosis.
What are the conditions for high tidal volume and low respiratory frequency?
e.g. 1000ml VT, 6 RF, minute ventilation 6000ml, anatomic dead space 900ml, alveolar ventilation 5100ml/min.
Hyperventilation
Hypocapnia - low carbon dioxide, and therefore respiratory alkalosis.
What are the advantages of anatomical dead space?
Carbon dioxide is retained, resulting in bicarbonate-buffered blood and interstitium.
Inspired air is raised or lowered to body temperature, increasing the affinity of haemoglobin for O2, and improving O2 uptake.
Particulate matter is trapped in the mucus that lines the conducting airways, allowing it to be removed by mucociliary transport.
Inspired air is humidified, so improves the quality of airway mucous.
How are oxygen levels increased using a ventilator?
It is more efficient to increase the tidal volume rather than the respiratory frequency.
