Ventilation and Compliance Flashcards
There is always residual air left in your lungs at the end of expiration. Why?
So patency of airways is maintained and smaller airways do not collapse, meaning the is less effort to inflate them.
What does TV stand for?
Tidal volume: volume of air breathed in and out of the lungs in each breath
What does ERV stand for?
Expiratory reserve volume: maximum volume of air that is expelled from the lungs at the end of a normal expiration
What does IRV stand for?
Inspiratory reserve volume: maximum volume of air which can be drawn into the lungs at the end of a normal inspiration
What does RV stand for?
residual volume: volume of gas at the end of a maximum expiration
what does VC stand for?
vital capacity: the volume of air a person can expire
tidal volume+inspiratory reserve volume+expiratory reserve volume
what does TLC stand for?
total lung capacity: vital capacity+residual volume
what does IC stand for?
inspiratory capacity: tidal volume+inspiratory reserve volume
what does FRC stand for?
functional residual capacity: expiratory reserve volume + residual volume
what does FEV1/FVC stand for?
fraction of forced vital capacity expired in one second
What does ventilation refer to?
the movement of air in and out of the lungs
what is alveolar ventilation?
fresh air getting to alveoli and available for gas exchange
what is pulmonary ventilation?
total air movement into and out of the lungs
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 happens to the PAO2 and PACO2 during hyper-ventilation?
PO2 rises (120mmHg) and PCO2 falls (2ommHg)
Describe changes of PAO2 and PACO2 in hypoventilation
PO2 falls (30mmHg) and PCO2 rises (100mmHg)
describe the role of surfactant
surfactant helps reduce the surface tension of the water in the alveoli which is directed inwardly tending to collapse the alveoli. this means small alveoli useful for their large SA do not collapse increasing lung compliance and reducing the recoil. makes breathing easier.
Describe infant respiratory distress disorder
premature babies have to battle collapsing alveoli with every breath as surfactant production does not start until 25 week of gestation and is only complete by week 36.
What is compliance?
the change in volume relative to change in pressure. this represents the Add to strechability of lungs (not the elasticity), there fore does not explain air leaving the lungs.
Describe what is meant by:
> High compliance
> Low compliance
> a large increase in lung volume for a small decrease in partial pressure
small increase in lung volume for a large decrease partial pressure
Why does it take greater change in pressure to reach a particular lung volume in inspiration than it does to maintain in during expiration?
this id due to elastic recoil and surface tension that has to be overcome
Why does expiration require a lot of work in emphysema?
due to loss of elastic tissues
Why does inspiration require more effort in fibrosis?
due to inert fibrous tissue instead of elastic tissue
Why does the pressure volume curve vary between the base and the apex of the lung?
The alveoli at the base of the lung are being squashed so have a higher compliance as can inflate more on inspiration. the alveoli at the top remain more inflated so the volume change is smaller for any given pressure change.
What is static spirometry reading?
the only consideration that is made is the volume exhaled
what is a dynamic spirometry reading?
where the time taken to exhale a certain volume is what is being measured
what are the affects of obstructive lung disease on the FEV and FVC?
rate at which air is exhaled is slower
total volume is also reduced
FEV is reduced to a greater extent than FVC
What are the affects of restrictive lung disease on FEV and FCV?
total volume is reduced due to limitations to lung expansion
ratio of FEV and FVC is constant of increases
where are the respiratory centres found?
in the pons and medulla
what does the dorsal respiratory group innervate?
inspiration
what does the ventral respiratory group innervate?
expiration via the pharynx, larynx and tongue
what modulates the rhythm of breathing?
> emotion, the limbic system
voluntary override by the cerebral cortex
mechano-sensory input from the thorax preventing over-inflation of the lungs stopping alveoli damage
chemical composition of the blood (PCO2, PO2, pH)
where are central chemoreceptors found?
in the medulla
what do central chemoreceptors respond to?
the H+ concentration in the CSF around the brain which directly reflecting the PCO2
what would a rise in [H+] in CSF cause?
a stimulation of ventilation as a rise of [H+] is driven by raised PCO2 (hypercapnia)
when is ventilation reflexly inhibited?
if there is a decrease in arterial PCO2 reducing CSF [H+]
what is the blood brain barrier permeable to?
gases (not ions)
what is the equation for carbon dioxide in the blood that the central chemoreceptors use to monitor PaCO2 ?
C02 +H2O = H2CO3 = H + HCO3
Where are peripheral chemoreceptors found?
carotid bodies where the carotid artery splits in the neck
aortic bodies in the aortic arch
what do the peripheral chemoreceptors respond to?
to the plasma [H+] and pO2 (less so to the pCO2)
What changes would occur to cause a stimulation of ventilation by the peripheral chemoreceptors?
a significant fall in arterial PO2
a rise in [H+], a fall in pH (acidosis)
what affect would alkalosis of plasma (pH increase) have on ventilation?
ventilation would be inhibited by the peripheral chemoreceptors
what can happen to chemoreceptors in chronic lung disease?
the chronic exposure to CO2 can lead to desensitisation of the receptors. the peripheral receptors are then used as the primary receptor but the peripherals can live with high levels of CO2 until ventilation changes. these circumstances are called hypoxic drive
what drugs can depress the respiratory centre?
barbiturates and opioids
in what cases can nitrous oxide be dangerous to a patient?
in patients with chronic lung disease who are in hypoxic drive as it blunts the peripheral chemoreceptors response to falling PaO2. administering oxygen to these individuals aggravates the situation as it reinforces the ide that everything is fine
