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Define Compliance
  • Measure of distensibility of the chest and/ or lungs
  • Expressed as change of volume produced by a unit pressure change
  • The compliance of the pulmonary system can be divided into 2 parts
Two parts of pulmonary system compliance
  • CL = Lung compliance = 0.2 L/cm H20
  • CT = Thorax compliance = 0.2 L/cm H2O
  • There is a reciprocal relationship
  • 1   =  1  +  1
  • _       __  ___
  • CLT   CL     CT
  • Total lung compliance is less than individual parts
Define Transairway pressure
  • The difference between barometric (atmospheric) pressure and the alveolar pressure.
  • The pressure gradient difference between the mouth pressure (atmospheric) and alveolar pressure
Define Transpulmonary pressure
  • The difference between the alveolar pressure and the pleural pressure
Define Transthoracic pressure
  • The difference between body surface pressure and pleural pressure
Methods of measurement of CLT
  • Iron lung- by reducing pressure in chamber & measuring volume inspired
  • Intubating and measuring changes in pressure for given volume delivered
  • Pt inspires known volumes while measuring changes via nasal plug
  • All of these methods are affected by skeletal muscle contraction
Methods of measurement of CL
  • Via esophageal balloon
  • Only measures changes in pleural pressure
Define Hooke's Law

  • When a truly elastic body is acted on by one unit of force it will stretch one unit of length.

  • When acted on by two units of force it will stretch two units of length and so on.

  • This is only true within the elastic body's functional range.

  • When apllied to the elastic properties of the lung, volume and pressure replace length and force.

Define Law of LaPlace
  • Calculates the amount of pressure generated inside a drop or bubble as a result of surface tension
                                   
Law of LaPlace applied to a drop
P= Pressure difference
r= radius

P = 2 ST
      ____
         r

Law of LaPlace applied to a bubble
P = 4 ST
      ____
        r

P= Pressure difference
r= radius
Law of LaPlace

Bubble tendencies
  • As the ST (surface tension) increases or the r (radius) decreases the P (pressure difference) increases.
  • The smaller the bubble the greater the tendency to collapse.
  • Given two bubbles with the same ST but different r the bubble with the smaller radius will empty into the larger bubble
Determinants of Compliance
  • ST
  • Surfactant
  • Lung elasticity
Define surfactant
  • Chemical substance in alveolar lining that varies ST w/alveolar vol changes
  • Produced in Type II pneumocytes
  • Fatty acds incorporated nto phospholipids
  • Dipalmitoyl lecithin- highest concentration
  • Has hydrophobic and hydrophilic ends
  • Disrupts the mutual attraction of liquid molecules
 
There is a ____ # of molecules per unit area when volumes are decreased thus ST is ______.
  • Increased
  • Decreased
There is a ______ # of molecules per unit area when volumes are increased thus ST is ______.
  • Decreased
  • Increased
The greater surface density of surfactant at smaller volumes also offers greater resistance to further ________.
  • Compression
  • This promotes alveolar stability
Symptoms of surfactant deficiency
  • WOB increases
  • Alveolar hypoventilation develops
  • V/Q mismatch increases
  • Hypoxemia and respiratory acidosis develop
  • Severe hypoxemia may lead to metabolic acidosis
Conditions that cause suractant deficiancy
  • Hypoxia
  • Hyperoxia
  • Acidosis
  • Vascular congestion
  • Pulmonary embolism
  • Pulmonary edema
  • Atelectasis
  • Drowning
Conditions with decreased lung compliance
  • Pulmonary interstitial fibrosis
  • Sarcoidosis
  • Pulmonary edema
  • Atelectasis
  • Pneumonia
  • Neoplasms
The difference in P-V curves from inspiration to expiration is called lung hysterisis
Conditions w/increased CL
  • Emphysema- loss of elasticity
  • Reduces transpulomary pressure
  • Causes reduced airway caliber
  • Distribution of ventilation is altered
  • Increased V/Q mismatch
  • Also limits expiratory flowrates
Gas moves from one point to another in response to a _____ ______.
Pressure gradient
The rate at which it flows depends on :
  • The magnitude of the pressure gradient
  • The resistance to gas flow
  • the density and viscosity of the gas
  • The type of flow: Laminar or Turbulent
Poiseulles Law for Flow

Flow will _____ in response to decreased P and tube radius.
  • decrease
 
Poiseulles Law for Flow

Flow will _____ in response to decreased tube length and viscosity.
  • Increase
Flow will ____ in response to increased tube length and viscosity
  • decrease
When gas flowing through a tube reaches a critical linear velocity the _______ of the ____ changes.
  • character
  • flow
The Reynold's number is used to predict _________.
  • The character of flow through a tube.
Reynolds number formula
NR = (v) (d) (D)
         _________
             (n)
- v= velocity
- d= diameter
- D= density of gas
- n= viscosity of gas
NR > than 2000 generally indicates _______
Turbulent flow
For turbulent flow to double a given flowrate the driving pressure must be increased by a factor of ___.
  • 4
  • For Laminar flow use factor of 2
Three components of Nonelastic resistence to gas flow.
  • Inertial forces- contributes very little
  • Viscous resistance- tissue friction caused by nonelastic tissue 15-20%
  • Airway resistance- Viscosity friction between gas molecules and walls of airways plus gas molecules themselves. 80-85%. Most occurs in nose and upper airway.
Airway resistence formula (Raw)
Raw = Pm - Palv
          ________
            Flow

Pm- mouth
Palv- alveolar
Define airway resistence
  • The pressure differance required for a unit flow change.
  • Normal Raw 0.6-2.4 cmH2O/L/sec
  • More than 60% of normal Raw is the result of turbulent gas flow through the nose.
  • Desirable so gas gets heated, humidified and filtered.
Define Gaw (Conductance)
  • Reciprocal of Raw
  • The ease with which fluid flows through a tube
  • Linear relationship between Gaw and volume
Physiologic Factors Affecting Raw

  • The number of airways

  • Airway length

  • Lumen diameter

  • Airway length increases during inspiration

  • Airway length dcreases during expiration

Factors that decrease airway caliber can increase Raw dramatically.

  • Bronchoconstion

  • Secretions

  • Edema

  • Vascular congestion

  • Loss of traction on airway

Define EPP
(Equal Pressure Point)
The point where intraairway pressure equals the pleural pressure is the equal pressure point (EPP)
Define Time Constant
 of the volume that wouldThe time in seconds required for inflation to 63% of the volume that would be achieved for any given pressure
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