Respiratory mechanics Flashcards
In order for respiration to occur, how must the pressure of the air in the alveoli relate to atmospheric air?
Must by slightly lower
What is the relationship between transmural pressure and elastic recoil of the lung?
The larger the difference in transmural pressure, the more elastic recoil in the lungs (bigger the gradient to drive expansion)
When is transpulmonary pressure highest?
Full inspiration
How is Hooke’s Law described?
For an elastic structure, the increase in length (or volume) varies directly with the increase in force (or pressure) until the elastic limit is reached (concept of compliance)
What is lung compliance?
Extent to which the lungs will expand for each unit increase in transpulmonary pressure
What determines observed compliance curves in an air filled lung?
Intrinsic compliance of the lung, and the surface tension at the liquid-air interface
What is represented between the expiration and inspiration compliance curves?
Recoil due to surface tension forces
What is the law of Laplace (qualitatively)?
Pressure tending to collapse an alveolus is directly proportional to the surface tension generated by the molecules of liquid lining the alveolus and inversely proportional to alveolar radius
What is the Laplace equation for pressure tending to collapse an alveolus?
P = 2T / r
How does the collapsing pressure of a small alveolus relate to its pressure to keep it open?
High collapsing pressure / more pressure to keep it open (dilemma is solved by surfactant)
What marker signifies an 80% risk of respiratory distress syndrome in infants?
Lecithin / sphingomyelin ratio less than 1.5
What is the most influential factor in determining airflow resistance?
Airway radius
What does parasympathetic activation do to airway resistance?
Increase
What does sympathetic activation do to airway resistance?
Decrease
What does high lung volume do to airway resistance?
Decrease
