Physiology Terms Flashcards
2 causes of Hypoxemia with a normal A-a difference.
Decreased PiO2 (Inspired oxygen) - altitude
Hypoventilation - drugs/head injury
3 causes of Hypoxemia with a widened A-a difference.
Diffusion limitation
R-to-L shunt
Ventilation/ Perfusion (V/Q) mismatch.
What does a normal A-a difference tell you about the origin of the Hypoxemia?
It’s not a lung problem - originates elsewhere.
A widened A-a difference indicates an intrinsic lung disease.
Why do higher altitudes cause hypoxemia?
Barometric pressure decreases with altitude but the fractional concentration of each gas remains the same. Still, there is less pressure at high altitudes, so you inspire less oxygen overall, so the partial pressure of alveolar and arterial oxygen decreases.
Describe the relationship between the partial pressure of Alveolar CO2 and the ventilation rate.
Inversely proportional.
ventilation decreases, and partial pressure of CO2 in the alveoli increases.
This is how hypoventilation causes hypoxemia.
Which is more common: hypoxemia with a normal or widened A-a difference?
Widened.
How do you differentiate between the 3 causes of Widened A-a Hypoxemia?
Apply 100% O2.
Hypoxemia due to diffusion limitation and V/Q mismatch will be eliminated, but there will be no improvement if the source is an intrapulmonary shunt.
FEV1/FVC ratios are useful for differentiating between what types of lung disease?
Restrictive and Obstructive.
In both diseases, FEV1 and 2 are reduced, but in obstructive diseases (asthma), FEV1 is reduced MORE, causing the FEV1/FVC ratio to lower. The ratio increases with restrictive lung disease.
What do FVC and FEV stand for, respectively?
FVC - forced vital capacity ( the volume of air that can be forcibly expired after max inhalation)
FEV - the amount of air that can be forcibly expired in 1 second.
What is FEV1 for a normal person?
One with asthma?
One with fibrosis?
Normal - 0.8
Means that a person can expel 80% of their max breath in the first second.
Asthma (obstructive) 0.8
When is the compliance of the lungs the greatest: Inspiration or Expiration?
Why?
Expiration, due to the heavy amount of surfactant present on the surface of the alveoli. - REDUCES SURFACE TENSION
Surfactant initially is secreted when the alveoli begin to expand during inspiration. The lungs expand faster than surfactant can be created, so the intermolecular forces between the liquid molecules lining the lung are strong. There isn’t enough surfactant to break them up.
During exhalation, there is high lung volume and stretch, so intermolecular forces are low, and plenty of surfactant is present. The density of surfactant increases as the lung shrinks, contributing further to the elasticity.
What type of drug is atropine? What effect does it have on the lungs?
Atropine is a muscarinic antagonist, so it lets the sympathetic nervous system override the parasympathetic.
BRONCHODILATION.
What type of drug is Albuterol? What effect does it have on the lung?
Albuterol is a B2 selective agonist. It causes bronchodilation.
What type of drug is Muscarine?
Muscarine is a neurohormone that activates muscarinic receptors (parasympathetic).
Parasympathetic activity in the lung causes BRONCHOCONSTRICTION.
