Respiratory Mechanics II Flashcards
What is specific compliance?
Normalizes the compliance value to the FRC to account for volume differences when calculating compliance
SC = Compliance/FRC
What is the total pulmonary compliance?
Definecd as the sum of the lung and the chest wall compliance
1/total C = 1/lung compliance + 1/chest wall compliance
How is compliance measured?
Spirometry
What is the cause of emphysema?
Elastin is a prominent component of lung tissue and is degraded by elastase. Elastase is inhibited by alpha 1 - antitrypsin
Deficiency in a1-antitrypsin or inhibition by smoking will lead to widespread tissue destruction and cause emphysema
What is alveolar simplification?
Term used to describe the tissue destruction seen in emphysema
Refers to the loss of structure, entire alveoli are missing, replaced by big open spaces
Causes a larger than normal FRC
What is centrilobular emphysema?
Most common morphological subtype
Affects the central portion of secondary pulmonary lobules, around the central respiratory bronchioles, typically in the superior part of the lungs
Associated with long-standing cigarette smoking
What in panacinar emphysema?
Destroys the entire alveolus uuniformly and is predominant in the lower half of the lungs
Commonly associated with domozygous AAT deficiency or Ritalin-induced lung emphysema
What are some causes of decreased compliance?
Interstitial lung disease (fibrosis)
Loss of surfactant
What are some causes of increased compliance?
Emphysema
Age
Where is the largest airway resistance?
The largest airways
The smaller airways are incredibly numerous and arranged in parallel, therefore the they will have a much lower total resistance (because for parallel 1/Rt = 1/R1 + 1/R2…)
Where is the largest airflow velocity?
Largest airways
What value is the pleural pressure during normal exhalation and why is this significant
The Ppl always remains negative during a passive exhalation
This means that the air way is subjected to expansile forces along its length, these forces keep the airway open during normal passive exhalation
What is dynamic compression?
During forced exhalation, the pleural pressure becomes positive due to contraction of the extra muscles
At some point the pressure outside (pleural) the airway is greater than the pressure inside, causing the airway to collapse under the increased transmural forces.
More effort just causes the airways to collapse more and increase resistance
How does the Bernoulli Principle apply to the airway?
Applies to the inside of the airway; the faster the airflow, the lower the pressure exerted on the inside of the walls of the airway, promoting collapse
Largest airways have smallest side wall pressured due to highest velocity
This is why the large airways have cartilaginous rings, to prevent total collapse
What is radial traction?
Refers to the action of lung tissue on airway walls, tending to hold them open
Referred to as tethering of airways
How is radial traction implicated in emphysema?
Tissue damage makes their airways very soft and pliable
Forced exhalation causes increased velocity and therefore decreased pressure. Combined with the positive pleural pressure their is a high tendency for airway collpase and substantial increase in resistance
How is radial traction implicated in asthma?
Asthma causes airway constriction, meaning the same volume of air has to move through a narrower airway
This increases flow velocity and consequently lower pressure inside the airway, which promotes collapse and increase in airway resistance
Why is airway collapse a problem?
The collapsed units are not ventilated, but they are still being perfused
Meaning they act as right-to-left shunts impairing gas exchange
What is tethering of airways?
Refers to them being attached to their neighbors, promoting stability of alveoli and resist collapse
What happens to tethering forces in emphysema?
Tethering forces are reduced in emphysema due to tissue loss
What is tidal volume?
Volume of air inspired or expired with each breath
Normal value = 500mL
What is dead space volume?
Air which a person breathes bu is not used for gas exchange
Fills conducting pathways only (e.g. nose, pharynx, and trachea)
Normal value = 150mL
What is residual volume?
Amount of air in lungs which can’t be exhaled or pushed out
Normal value = 1-2 L
What is total lung capacity?
Volume of air in the lungs after a maximal inspiratory effort
Normal value = 6 L
