Pulmonary mechanics

From Iusmphysiology

  • started here on 02/09/11 at 9AM.


Contents

[edit] Pulmonary mechanics

  • FRC set by expansion and contraction
  • trans pulmonary pressure determines degree of how fast air gets in and out.
    • That is, flow is dependent on the pressure gradient.
  • The pleural pressure is negative.
    • If you get stabbed, the air flows down it's pressure gradient and fills that side of the thorax.
    • So pressure in the lung on stabbed side will go to atmospheric pressure
    • pneumothorax
  • Then there will even be pressre on the mediastinum because of the increased pressure as pressure gets above the atmospheric pressure
  • Interpleural pressure is very important for the lung function

[edit] Pressure during breathing cycle

  • Alveolar pressure at fu
  • Solid line is from normal tidal volume breath.
    • Gives an estimate of the resistance to air flow and the resistance to tissue being expanded (elastic recoil).
  • Dashed line is taken very slowly.
    • Resistance to airflow goes away
    • So this line represents just resistance to recoil.

[edit] Compliance

  • Defined as a change in volume over a change in pressure.
  • Normal is 200 ml / cm of H20.

[edit] Elastance

  • The inverse of the compliance.
  • Can hold a lot of volume at a low pressure.

[edit] Static vol-pressure relationship

  • Volume on y, pressure on x; opposite of the heart!
  • Residual volume is where you've blown out all you can blow out.
  • Transpulmonary (pleural) pressure has to go up for lungs to get air.
    • The more air you want to take in, the more this has to increase.
    • So degree of inflation of the lungs is determined by transpulmonary pressure.


  • Historesis is due to variable surface tension in the lung.
  • It is easier for the lung to expel air than to inhale air.
    • You need a higher transpulmonary pressure to get air in than to get it out.

[edit] Compliance masurement

  • To measure, as one exhales, we measure the pressure; the slow of the curve is the compliance.

[edit] Pulmonary compliance

  • What are the factors?
  • Lung size
  • Lung volume
  • Elastic / fibrous tissues
  • Alveolar surface tenstion
  • What decreases?
    • high lung volume
      • fill a balloon and it gets harder to put air in
    • fibrotic disease
      • alveolar membranes become thickened and fibrous
      • harder to inflate them
    • alveolar edema
      • surfactant reduced
    • vascular congestion
  • what increases?
    • COPD
      • emphasyma: elastic tissue destroyed

[edit] Compliance and pulmonary disease

  • So more or less compliance changes the volume-pressure relationship.
  • More compliant means more volume held at a lower pressure.
  • Less compliant means less volume held at a higher pressure.

[edit] Compliance respiratory system

  • Take the lungs out, look at chest wall and lungs, separately.
  • Measure how their volume changes relative to pressure.
  • Chest wall by itself is close to that of the lung by itself.
  • But together, the slope is lower, so the compliance of the two together is lower than each alone.
  • Why?
    • FRC is from chest wall expansion and elastic recoil.
    • As you inspire, these two factors work together to increase pressure (?) of the system.

[edit] Surface forces and lung recoil

  • 300 million alveoli
  • Each has a radius of 110 micrometers (at FRC)
  • We want the air to transfer through watery surface to the blood.
  • The size of the alveoli is determined by the translung pressure.

[edit] Surface tension (laplace's law)

  • Note that the wall pressures of these two alveoli are the same because pressure is higher in the smaller alveoli.
  • Air will flow from higher pressure (little alveolus) to higher and the little will collapse.
  • Bad! this is why we need surfactant.

[edit] Pulmonary volume-pressure relationship hysteresis

  • We use submersion in saline to reduce air-surface tension.
  • With lower surface tension the lung is much more compliant (more volume at lower pressures).
  • It is the variable surface tension during inspiration that is responsible for the hysteresis seen in the volume-pressure relationship.


  • hysteresis: "he lagging of an effect behind its cause; especially the phenomenon in which the magnetic induction of a ferromagnetic material lags behind the changing magnetic field" per wordent

[edit] Surfactant

?

[edit] Surfactant

  • The smaller the alveolus, the closer together are the surfactant molecules so the more effect they have on pushing outward.
    • They resist compression.
  • As they are spread out, elastic recoil increases.

[edit] Advantages of surfactant

  • Wall tension in larger alveolus is lower than in the small alveolus.
  • Surfactant, then, causes the pressures to equalize.
  • Thus the alveoli do not collapse.
  • Advantages of Surfactant:
    • Stabilizes alveoli that tend to deflate at different rates.
    • Lowers elastic recoil and thus helps prevent alveolar collapse.
      • Reduces the work of breathing.
    • Decreases muscular effort needed to expand the lungs.
      • compliance
      • work of breathing
    • Plays a role in host defense.

[edit] Respiratory Distress Syndrome

  • In this case, there is no surfactant.
    • Perhapse Type 2 alveolar epithelial cells do not secrete surfactant.
  • Means that greater pressures will have to be generated to get air in.
  • This will shift the volume-pressure relationship to the right.
    • Need higher pressures to get air into the lungs.

[edit] Infant respiratory distress syndrome

  • Two surfactant treatments help baby off vent.

[edit] Dynamic Volume-Pressure Relationship

  • The dotted curve is the max.
  • Green is where healthy humans live.
  • Red arrows with strenuous exercise.

[edit] Airway resistance

  • We have to make negative pressures and there is resistance to the airflow caused by the negative pressure.
  • Resistance factors:
    • size of airways
    • smooth muscle tone of airway
    • density of gas you choose to inhale
    • dynamic compression
  • Airway resistance is highest at the medium size bronchii.
  • Airway resistance can be calculated by ohm's law.

[edit] Airway size and patterns of airflow

  • Laminar: in small peripheral flow
  • Turbulant flow: high flow rates in trachea and larger aiways
    • Resistance is higher
  • Transitional flow – occurs in larger airways (branches).

[edit] Lung volume and airway resistance

  • The resistance to airflow goes down as the tubes get bigger because the lung is filling with air.

[edit] Control of bronchial smooth muscle

  • Controled by lots of things.
  • Dilation
    • Sympathetic stimualation
      • Primariliy betas, especially beta2
      • epinephrine
    • NO
    • Increased Pco2 in the small airways
    • Decreased PO2 in the small airways
      • These happen when pt isn't breathing well.
  • Constriction:
    • Parasymp
      • contstricts
      • causes mucus production
      • Alpha adrena receptors
      • Ache
      • Noreepie
    • Decreased Pco2
  • Parasympathetics > sympathetics

[edit] Dynamic airway compression

  • -8 is the interpleural pressure.
    • At the end of a normal inspiration.
  • +10 is wall tension or recoil of the lung.
  • +2 is the transpulmonary pressure
    • 10-8 = 2
  • Because recoil pressure is > interpleural pressure is the air goes out.
  • As we expire forcefully, the interpleural pressure is made very positive to push air out.
    • Inter pleural pressure is +28
    • Note that pressures decrease from the alveoli to the outside.
    • There is apoint where the pressure is equal.
    • So the airway closes. 
Why would the tube collapse when pressures are equal.

[edit] Dynamic airway compression

  • In emnphysema...
  • Was thinking too hard to type.

[edit] flow-volume relationship

  • Small circle is normal tidal breathing.
  • Big line is total inhale with fast, forceful exhale.

[edit] flow-volume relationship

  • A is healthy
  • Note that they all fall onto the "effor independent" portion of the curve.
    • This is the location of the dynamic comnpression's effect.

[edit] Flow-volume relationship

  • This is used clinically to diagnose COPD.
  • The scoop on the right (red) shows that the pt is having a hard time expelling air.
  • Emphysema:
    • Recoil is high
    • Total lung capacity is reduced.

[edit] Flow-volume relationship

  • Guarenteed test quation on this.

[edit] Lung volume and pulmonary disease

  • See cartoon.

[edit] Work of breathing

  • read on own

[edit] Efficiency of breathing

  • Read it.


  • stopped here on 02/09/11 at 10AM.
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