Physiology 3 Flashcards
What is anatomical dead space?
The volume of inspired air that remains in the conducting airways where it cannot be involved in gas exchange (it is expired unchanged)
What does pulmonary ventilation (L/min) =?
Tidal volume (L/breath) X respiratory rate (breath/min)
Why is alveolar ventilation?
The volume of air that is going to exchange gases with the blood
Approximately how much of the airway is dead-space?
150ml
What is the equation for alveolar ventilation?
(Tidal volume - dead space) X respiratory rate
What 2 types of dead space can you get?
Anatomical/ airway dead space (air left in airways which doesn’t reach alveoli and therefore doesn’t take part in gas exchange)Alveolar dead space (alveoli not perfused)
What is pulmonary ventilation?
The volume of air breathed in and out per minute
What 2 things can be done to incase pulmonary ventilation e.g. during exercise?What way is more advantageous?
Increase depth (tidal volume)Increase breathing rateIncreasing depth of breathing (due to dead space)
What does the transfer of gases between the body and atmosphere depend upon?
Ventilation (rate at which gas is passing through the lungs)Perfusion (rate at which blood is passing through the lungs)
What is the V/Q ration?
Measurement used to assess the efficiency and adequacy of the matching of two variables: “V” – ventilation – the air that reaches the alveoli. “Q” – perfusion – the blood that reaches the alveoli.
V/Q ratio at the bottom of the lungs?
Less than 1 (higher blood supply)
V/Q ratio at the top of the lungs?
more than 1 (higher ventilation)
How well does ventilation and perfusion in the lung normally match?
Not exactly the same but usually does matter except sometimes in disease (where the alveolar dead space could increase significantly)
What is alveolar dead space?
Ventilated alveoli which are not adequately perfused with blood
What is the physiological dead space?
Anatomical dead space + alveolar dead space
What normal happens regarding ventilation perfusion match in the lungs?
Local controls act on the smooth muscles of airways and arterioles to match airflow to blood flow
What does the accumulation of CO2 in the alveoli cause?
Due to increased perfusion = decreases airway resistance leading to increased airflow
What does an increase in alveolar O2 conc. lead to?
Due to increased ventilation therefore causes pulmonary vasodilation increasing blood flow to match larger airflow
What does decreased O2 cause pulmonary arterioles and systemic arterioles to do?
Pulmonary = vasoconstrictionSystemic = vasodilation
What does increased O2 cause pulmonary arterioles and systemic arterioles to do?
Pulmonary = vasodilationSystemic = vasoconstriction
What are the 4 factors that influence the rate of gas exchange across the alveolar membrane?
Partial pressure gradient of O2 and CO2Diffusion coefficient for O2 and CO2Surface area of alveolar membraneThickness of alveolar membrane
What is the total pressure exerted by a gaseous picture =? (Dalton’s law of partial pressures)
The sum of the partial pressures of each individual component of the gas mixture
What causes a gas to move across the cell membrane?
A pressure gradient
What determines the pressure gradient for a particular gas?
Its partial pressure
What is the partial pressure of a gas in a mixture of gases that don’t react with each other?
The pressure the gas would exert if it occupied the total volume for the mixture in the absence of other components
What is the partial pressure gas 1 which makes up half of the picture of a gas mixer of 100kPa?
50kPa
What is the partial pressure of Oxygen?
160mmHg (total atmospheric pressure = 760mmHg, 21% air is O2)
What is the respiratory exchange ratio for someone eating a balance diet?
Ratio of CO2 produce/ O2 consumed 0.8
What is the air in the respiratory tract saturated with?
Water
How much does the water vapour pressure contribute to the total pressure in the lungs?
47mmHg
What does the pressure of inspired air=?Normal values?
Atmospheric pressure - water vapour pressure760 - 47 = 713mmHg
What does PiO2 = ?
713-0.21 = 150mmHg
What does PAO2 = at a normal arterial PCO2 of 40mmHg?
100mmHg at see level
What unit for pressure is used in the UK?
kPa (US uses mmHg)
How to convert from mmHg to kPa?
Divide mmHg by 7.5
What is the diffusion coefficient?Does O2 or CO2 have a higher diffusion coefficient?
The solubility of the gas in membranesCO2 has a higher diffusion coefficient (more soluble in membranes)
Why is there a small difference between alveolar PO2 PAO2) and arterial PO2 (PaO2)?
Ventilation perfusion match is usually not perfect
What does a big gradient between PAO2 and PaO2 indicate?
Problems with gas exchange in the lungs or a right to left shunt in the heart
What is Flick’s law of diffusion/
The amount of gas that moves across a sheet of tissue in unit time is proportional to the area of the set but inversely proportional to its thickness (lung has a very large surface area with thin membranes
What are alveoli made up from?
A single layer of flattened type 1 alveolar cells
What circles each alveolus?
Pulmonary capillaries
What happens to the rate of gas transfer as the partial pressure gradient increases?
Rate of transfer increases
What happens to the rate of gas transfer as the partial pressure gradient increases?
Rate of transfer increases
Why does alveolar surface area increase during exercise?
More pulmonary capillaries open up when the cardiac output increase Alveoli expand as the breathing becomes deeper
what happens to the rate of transfer as the thickness of the alveoli increases?
Rate decreases
What happens to the rate of transfer as the diffusion coefficient increases?
Rate of transfer increases
Despite the diffusion coefficient for CO2 being 20 times greater than that of O2, why are are approximately equal amounts of CO2 and O2 transferred across the membrane?
It offsets the smaller partial pressure gradient for CO2
