Ventilation and Lung Compliance

imissyou419's version from 2017-02-01 03:50


Question Answer
Ventilation definitionprocess by which air moves in and out of the lung
Inspiration, active or passive, what muscles?active process,
diaphragm (abdominal contents pushed downward and forward) and external intercostals (ribs are pulled upward and forward), increase volume of thoracic cavity causes negative intrapleural pressure to be even more negative, as a consequence the lung expands slightly subatm (-1 mmHg) [increases pressure gradient b/w lung (intrapulmonary pressure) and intrapleural space]
Expiration, active or passive, what muscles?normally passive (lung and chest wall return to their equilibrium position),
active process during exercise or spontaneous hyperventilation, muscles of abdominal wall (pushes diaphragm upward) and internal intercostals (pull ribs downward and inward)
Pulmonary compliance (equation)Compliance = delta V/ deltaP; ability of the lung to inflate due to relatively small increase in pressure gradient between lung and intrapleural space (from contracting the diaphgram and external intercostals) due to distensibility of the lung
What are the 2 properties of the lung that influence compliance?1. elasticity of lung tissue, 2. surface tension forces of alveolar lining fluid
How is PV curve obtained?inflation of an isolated lung in 2cm H2O pressure intervals and determining corresponding volume at each pressure; deflated in similiar function
PV Curve 3 features (Hint: curve type, high pressure/low pressure, hysteresis)1. non-linear, during the initial inflation steps smaller volumes are sufficient to increase the pressure by 2 cm H2O whereas at higher pressures (10-20 cm H2O), larger volume can be inflated for a similar pressure changes. Therefore, the lung is more compliant at higher pressures.
2. At high pressure (>20 cm H2O), the lung becomes once again less compliant.
3. At the same pressure the lung has more volume during deflation compared to inflation. This difference between inflation and deflation is called hysteresis (consequence of phenomenon of surface tension and surfactant)
Fluid (saline) inflation/deflationtake out surface tension (no air-liquid interface anymore) so do not need to include forces needed to expand the air-liquid interphase, takes less pressure to expand lung than with air + shows no hysteresis
How much of pressure is required to overcome the elastic properties of the lung and surface tension properties?1/3 of pressure to fill up the lung with air is needed to overcome elastic force and 2/3 is needed to overcome surface tension properties at air-liquid interface
What causes the elasticity of the lung?fibers of elastin (easily stretched) and collagen (rigid structure) present on alveolar wall and throughout lung, the specific geometric arrangement of these fibers is responsible for elasticity
Surface tensionattractive forces between molecules within a liquid. Molecules within the bulkphase of the liquid are attracted to molecules surrounding it. Molecules at the surface of the liquid experience a force into the bulk of liquid since there are no attractive force above these molecules (net inward force)
Examples of surface tension effectsdroplets, glass plates, bubbles (sphere is least SA for a given volume)
Laplace's law (with water)deltaP = 2(surface tension)/r; when surface tension is high (i.e. water), alveoli will collapse, especially when the radius of bubble is small (air will flow from smaller bubble to larger bubble b/c 1 big bubble has less SA, air will flow into larger bubble - large bubbles inflate and smaller ones will collapse), it will take a lot of pressure to inflate a bubble b/c need to overcome all surface tension forces
Pulmonary surfactantreduces surface tension of alveolar lining so reduces the pressure to inflate the line && allow for even inflation of different size alveoli (by forming a lipid film with polar head interacting w/ water and hydrophobic part sticking out at air-liquid interface which eliminate water molecules from the surface)
Babies born pre-maturehave little surfactant; air-liquid interphase is just water so high surface tension = detrimental to lungs, need high pressure to inflate lungs
What gives rise to hysteresis?expansion of surfactant film during inflation, compression of film during deflation
What does pulmonary surfactant consists of?lipids and surfactant associated proteins (these proteins are responsible for generating and maintaining the surfactant film)
What synthesize and secrete surfactant?both surfactant lipids and surfactant proteins are synthesized and secreted by alveolar type II cells

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