Extra Resp Phys Flashcards
What equation can be used to demonstrate resistance of an airway?
Poiseuille’s law: R = 8ƞl / πr^4.
ƞ = viscosity, l = length
Briefly describe inspiration.
Inspiration is an active process. The external intercostal muscles and diaphragm contract. The volume of the thoracic cavity increases and you get a negative intra-thoracic pressure; air is drawn in.
Briefly describe expiration.
Expiration is usually passive. The ribs move down and in, the diaphragm relaxes. The intra-thoracic volume decreases and the pressure increases.
The main driver is the by the elastic recoil of the internal intercostals
of the lungs
Air is forced out.
What is it called when you have a high V/Q ratio?
Dead space. Lots of ventilation but no perfusion.
Pulmonary Embolism
What is it called when you have a low V/Q ratio?
give example
Shunt. Lots of perfusion but no ventilation.
eg Pulmonary Oedema
Does the apex (top of lung) have a high or a low V/Q? Why?
High - effect of gravity, far more perfusion at the base of the lung.
Name 4 causes of hypercapnia
- Increased dead space ventilation; rapid, shallow breathing.
- V/Q mismatch.
- Increased CO2 production.
- Reduced minute ventilation.
Name 4 causes of hypoxia.
- Hypoventilation.
- V/Q mismatch.
- Diffusion abnormality.
- Reduced PiO2.
What is the alveolar gas equation?
PAO2 = PiO2 - (PaCO2/R)
r usually 0.8
What is Dalton’s law?
In a mixture of non reacting gases Ptotal = Pa + Pb. (P total is the sum of the pressures of individual gases).
What is Boyle’s law?
Pressure and Volume are inversely proportional:
P1V1 = P2V2.
What is Henry’s law?
THE SOLUBILITY of a gas is proportional to the partial pressure of the gas. S1/P1 = S2/P2.
At higher pressure, insoluble gasses are more likely to dissolve
E.g. nitrogen in joints whilst diving
What is the acid/base dissociation equation?
CO2 + H2O = H2CO3 = HCO3- + H+
What is Laplace’s law?
Whats the significance?
P = 2T/R.
(pleased 2Teach Rachel)
Small alveoli have greater pressure, more air will move from small to larger alveoli, = uneven aeration
When is surfactant produced?
It starts being produced from 34 weeks gestation and production increases rapidly 2 weeks before birth.
List 4 functions of surfactant.
- Prevents alveoli collapse.
- Allows homogenous aeration.
- Reduces surface tension.
- Maintains functional residual capacity.
What does the pneumotaxic area do and where is it located?
It switches off inspiratory neurones and so allows expiration. It is located in the upper pons.
What does the apneustic centre do and where is it located?
It inhibits expiration by activation inspiratory neurones. It is located in the lower pons.
Where are SASR (slow adapting stretch receptors) located?
What activates them?
Found in smooth muscle around airways.
Activated by lung distension
(to stop lungs from overstretching) Herring - Bruer Reflex)
How do SASR respond to activation?
They inhibit inspiration and so promote expiration. – Prevent overstretching
Where are RASR (rapidly adapting stretch receptors) located?
Between airway epithelial cells.
What activates RASR?
Respond by what?
Lung distension and irritants.
bronchoconstriction
What activates C fibres J receptors?
Increased interstitial fluid volume.
How do C fibres J receptors respond to activation?
They cause rapid, shallowing breathing. Bronchoconstriction and cardiovascular depression.
What do peripheral chemoreceptors detect?
Changes in ppO2 and H+ ion increase
(only activated when O2 is proper depleted, <90%
Carotid sinus there to detect O2 levels In the brain
They are faster, and less key for breathing (as O2 is
not the drive for respiration
What do central chemoreceptors detect?
Changes in ppCO2, through increase in H+ ions in brain
(small changes of CO2 result in change in respiratory rate to compensate)
H+ ions can’t cross Blood Brain barrier, CO2 can:
CO2 when crosses BBB reacts with water to form H2CO3 (carbonic acid, a weak acidic) (catalysed by carbonic anhydrase) , which dissociates into HCO3- (Bicarbonate) and H+ ions
The H+ ions are then detected as a decrease in pH
They are slower, and more key for breathing
o2 dissociation curve - What happens further left you go? (to a lower Pao2)
haemoglobin has More affinity to O2, picks up O2 easier, harder to dissociate O2
o2 dissociation curve - What happens further right you go? (to a higher Pao2)
haemoglobin has Less affinity for O2, dissociates more easily.
what are Factors that drive curve more left? More affinity for O2
Higher pH (More alkaline), Decrease in CO2, Decrease in Temperature, Foetal Haemoglobin, Carbon Monoxide
LEFT = LOCKS IN MORE
what are Factors that drive curve more right? Less affinity for O2
Decrease in pH (more acidic) , More CO2, Increase in Temperature
What is forced vital capacity?
Volume of air that can be forcibly exhaled after maximum inhalation.
How could you diagnose a patient with having an obstructive lung disease?
The FEV1/FVC ratio would be less than 70% predicted value.
FVC would be normal, but FEV1 would be low -
Making the FEV1/FVC ratio low
How could you diagnose a patient with having an restrictive lung disease?
The FEV1/FVC ratio would be normal but their FVC value would be very low.
How can you work out total lung capacity?
Add vital capacity to residual volume.
What is tidal volume?
The volume of air moved into or out of the lungs during normal, quiet breathing.
What changes are seen in an aging lung?
Decreased compliance, muscle strength, elastic recoil, immune function. Decreased response to hypoxia and hypercapnia. Impaired gaseous exchange.
What is the sympathetic neurotransmitter in the lungs?
Noradrenaline.
What is the effect of Ach on the pulmonary vessels?
Bronchoconstriction and vasodilation.
What is the effect of noradrenaline on the pulmonary vessels?
Bronchodilation and vasoconstriction.
Name 2 receptors for Ach.
Muscarinic (G protein coupled) and Nicotinic (ligand gated ion channels).
Host defense: What is innate immunity?
Immunity that doesn’t require prior exposure. It usually involves phagocytosis and inflammation.