Lecture 21: Quantitative Respiratory Mechanics Flashcards
is surface tension higher during inflation or deflation
higher during inflation
what factors DECREASE lung compliance
- pulmonary fibrosis
- pulmonary congestion
- surfactant deficiency
- edema
factors that INCREASE lung compliance
-loss of elastic lung elements
-advancing age
what is airway resistance
- frictional resistance caused by the airway that opposes airflow
- at rest, the upper airways provides about 60% of the resistance
-during exercise, nares dilate and vascular tissue constricts, decreasing mucousal thickness and decreasing resistance
what has the greatest affect on airway resistance
radius of airway
how can airway resistance be reduced
increasing lung volume increases alveolar volume which stretches the airway walls and reduces resistance
what can cause an increase in airway resistance
activation of the parasympathetic system
- releases ACh that acts on muscarinic receptors, causes contraction and bronchoconstriction
- inflammatory mediators like histamine or leukotrienes
sympathetic activation of the airway
causes relaxation of smooth muscles –> dilation
causes release of Epi that activates B2 adrenergic receptors on smooth muscle
what are the 3 types of dead space
anatomical, alveolar, physiological
what is anatomical dead space
the volume of gas contained in conducting airways
what is alveolar dead space
pulmonary capillaries are not open at a given time, so some alveoli are ventilated but not perfused
what is physiological dead space
anatomical dead space + alveolar dead space
what is ‘alveolar ventilation’
the amount of ‘fresh’ air that reaches the lung per minute
what does it mean if PaCO2 is high
hypoventilation
what does it mean if PaCO2 is low
hyperventilating
what would the effects of decreased alveolar ventilation (hypoventilation) be on PaO2 and PaCO2
decreased PaO2 (hypoxemia)
increased PaCO2 (hypercapnia)
what would the effects of increased alveolar ventilation (Hyperventilation) be on PaO2 and PaCO2
PaO2 - increase
PaCO2 - decrease (hypocapnia)
what is the PO2 of Alveolar gas
100mmHg
what is the PCO2 of alveolar gas
40mmHg
what is the PO2 in cells, interstitial fluid
<40mmHg
what is the PCO2 in cells, interstitial fluid
> 46mmHg
gas exchange across alveolar membranes occurs entirely by ____
diffusion
diffusion rate depends on…
membrane area
thickness
solubility of diffusing molecule in membrane
The pressure gradient for O2 is 10x that of CO2 yet CO2 diffuses twice as fast as O2 why/how??
Diffusivity (D) for CO2 is 20x that of O2
CO2 is much more soluble than O2 in water and lipid membranes
