Lungs (HLB) Flashcards
What is VE?
Minute ventilation - the amount of air entering or exiting the lung each minute
What is the A-a gradient?
Alveolar and arterial O2 gradient - difference between the O2 in the alveoli and the arteries.
What is the V/Q ratio?
Ventilation / Perfusion
What happens when there is reduced O2 available?
Hypoxic pulmonary vasoconstriction - constriction of the pulmonary arteries in the presence of alveolar hypoxia = redirects blood to areas that are poorly ventilated to areas which are more O2 rich & better ventilated.
Hypoxic pulmonary vasoconstriction (HPV) is a homeostatic mechanism that is intrinsic to the pulmonary vasculature. Intrapulmonary arteries constrict in response to alveolar hypoxia, diverting blood to better-oxygenated lung segments, thereby optimizing ventilation/perfusion matching and systemic oxygen delivery.
What is the definition of respiratory failure?
Hypoxaemia with PaO2 <8.0kPA
What is the difference between T1 and T2 respiratory failure
T1 = hypoxaemia with normal CO2
T2 = hypoxaemia with high CO2
What causes acute upon chronic respiratory failure?
Acute worsening of existing abnormalities (e.g. infection on top of COPD)
What are the two mechanisms behind respiratory failure?
Lung failure = hypoxaemia
Pump failure - hypercapnoea
What causes T1 RF?
Disease of the lungs - preventing adequate oxygenation of the blood = low O2 but normal or low CO2.
PaO2 = <8 with normal or low CO2
What are the 5 mechanisms of hypoxaemia in T1RF?
Hypoventilation
Low FIO2
Diffusion Impairment
Shunt
V/Q Mismatch
How does hypoventilation cause respiratory failure?
What causes hypoventilation?
Inadequate ventilation = low PaO2 and high CO2
Can cause T1 or T2 failure
Hypoventilation - caused by head injury, respiratory centre depression, respiratory muscle weakness, COPD, NMD, MSK disease
Why is high altitude a problem for FiO2?
How do we treat this?
Higher altitudes - the atmospheric pressure decreases = this decreases the partial pressure of O2 in blood
Treatment = supplemental O2
How does diffusion impairment cause respiratory failure?
Disease or damage to the basement membrane in alveoli & capillaries = reduces the amount of O2 that can cross = hypoxaemia.
How can we measure diffusion across the intersitium of the alveoli?
Measured by diffusing capacity called Transfer Factor = measures how much CO can pass over.
The Alveolar - arterial gradient can also tell us if there is a problem.
What factors can cause impaired diffusion of gases across the alveolar membrane?
Decreased SA (emphysema)
Inc thickness of membrane (pulmonary fibrosis)
Diffusion coefficient
pp & gradient of the gas
How is diffusion impairment treated?
Why do shunts cause hypoxaemia?
Because the arterial and venous bloods can mix - thereby reducing the amount of oxygenated blood to travel around the body.
What is a pulmonary shunt?
A shunt of deoxygenated blood from the RHS of the heart to the LHS without participating in gas exchange in the lungs
What is a physiological shunt?
Can happen with consolidation (causing hypoxia pulmonary vasoconstriction) or an AVM - causes hypoxaemia.
What is the normal V/Q ratio?
0.8
What is ventilation?
Volume of gas inhaled and exhaled over a given time period
What is perfusion?
Total blood vol reaching the pulmonary capillaries in a given time period
Complete the following for ventilation and perfusion in the lung:
Apex - V Q
Middle - V Q
Base - V Q
Apex = V > Q (over ventilated)
Middle = V = Q
Base = V < Q (over perfused)
In healthy lungs, what is VQ mismatch minimised by?
Minimised by hypoxic vasoconstriction - this directs blood away from poorly ventilated areas.