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CardioPulmonary Class > Mechanics of Breathing Lecture 2 > Flashcards

Mechanics of Breathing Lecture 2 Flashcards

1
Q

Discuss the mechanism behind air flow during negative pressure ventilation

A
  • Muscles of inspiration contract
  • Alveolar pressure is lowered below atmospheric pressure
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2
Q

Describe the mechanical interaction of the lungs and chest wall and its relationship to negative intrapleural pressure

A
  • Lung volume tends to decrease due to elastic recoil
  • Chest wall tends to increase volume due to outward recoil
  • Pleural pressure is usually negative (-5cm H20) due to interaction between chest wall and lung
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3
Q

Describe the relationship between the change in transmural pressure and the change in lung volume

A
  • Muscles of inspiration contract to increase the volume of the thoracic cavity and outward stress on the lung
  • The intraplueral pressure becomes more negative
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4
Q

Identify the muscles of inspiration and their effect on negative pressure ventilation

A
  • During inspiration, external intercostal contract, causing elevation of ribs and expansion of thoracic diameter.
  • Muscles of inspiration contract to increase the volume of the thoracic cavity and outward stress of the lung
  • The intrapleural pressure becomes more negative
  • Alveoli enlarge passively (interdependent)
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5
Q

Identify the muscles of expiration and their role in active and passive exhalation

A
  • During expiration, the abdominal muscles contract and push the diaphragm up
  • During exhalation, internal intercostals contract and have the opposite effect
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6
Q

Define resistance as it applies to pulmonary mechanics

A

​Resistance is the change in FLOW along a tube in relationship to pressure change

  1. Elastic resistance
  • Elastic fibers within alveoli
  • Surface tension
  • Lung compliance
  1. Noneleastic resistance
  • Airway resistance
  • Airway collapse
  • Tissue resistance
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7
Q

Define compliance as it applies to pulmonary mechanics

A
  • The change in pressure in relationship to a change in volume.
  • Movement of gas depends on the elastic resistance of the tissues (including compliance) and nonelastic resistance to gas flow
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8
Q

Describe the components creating the elastic forces within the lungs

A
  • Determined by elastin and collagen fibers interwoven amount the lung parenchyma
  • Fibers are contracted in deflated lung and stretched in expanded lung
  • Elastic force is always exerting force to return to deflated state
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9
Q

List three functions of surfactant

A
  1. Surfactant acts as a detergent to Decrease the surface tension
  2. Promote alveolar stability
  3. Compliance is increased and work of breathing is reduced.
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10
Q

List two factors maintaining alveolar stability

A
  1. Surfactant decreases surface tension of fluid

When surface tension is reduced by surfactant, smaller alveoli tend to expand due to lower surface tension

  1. Alveolar interdependency

Mechanically interdependent polygons with flat walls shared with adjacent alveoli

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11
Q

Describe the pressure volume curve for the human lung

A
  • As transpulmonary pressure increases, lung volume increases
  • Pressure - Volume curve is not linear (distends easiliy at low volumes, very little change at high volumes)
  • Slope between two points on a curve is the compliance defined as change in volume divided by change in pressure.
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12
Q

List five factors affecting lung compliance

A
  1. Pulmonary blood volume
  2. Lung volume
  3. Bronchial smooth muscle tone
  4. Disease (asthma, emphysema)
  5. Age
  6. Position
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13
Q

Describe the effect of the thorax on lung compliance and provide examples

A
  1. Compliance of lungs alone is 200 ml per cmH20 pressure change
  2. Compliance of the combined lung-thorax system is one-half of the lungs alone, or 110 mL per cmH20 pressure change
  3. When thorax is compressed the compliance can be one-fifth that of the lungs alone (variable compliance)
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14
Q

Compare compliance in upper regions of the lung to lower regions of the lung

A
  • Lower dependent regions of the lung receive more VENTILATION than upper regions
  • Lower regions are MORE COMPLIANT as volume changes more than pressure
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15
Q

Describe the effect of position changes such as trendelenberg and semi-recumbent positions on compliance and FRC

A
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16
Q

Describe the effect of positive pressure ventilation and anesthesia on lung compliance

A
  • Lung compliance decreases with general anesthesia
  • Muscle relaxant does not decrease compliance but may cause higher diaphragm
  • Position
  • Other surgical factors include position and retractors, as during abdominal retraction pneumopeitoneum and sternal retractor.
17
Q

List three factors affecting airway resistance

A
  1. Radius
  2. Turbulent flow (Density)
  3. Length of airway
18
Q

Identify the airways which have the most resistance and why

A
  • Medium airways (3rd-7th generation)
  • Highest resistance
  • Large airways have larger radius
  • Smaller airways have larger cross-sections
19
Q

Define Reynold’s number and its relationship to resistance during anesthesia

A
  • Measure of density
  • Gasses with a low Reynold’s number have less resistance duing turbulent flow
  • Laminar flow will be established more quickly after bifurcations and obstructions
  • Values greater than 2000 are associated with turbulent flow (<1000 laminar)
20
Q

Identify the roles of PSNS and SNS in regards to determination of airway resistance

A

PNS

  • Major importance with afferent and efferent innervation via the vagus
  • Afferents arise from bronchial epithelium and respond to noxious stimulation or cytokines from mast cells
  • Efferents release acetylcholine at muscarinic receptors resulting in bronchoconstriction.

SNS

  • Efferents may produce some opposition to acetylcholine but are weak
  • Balances cholinergic effect of bronchoconstriction
  • Bronchial smooth muscle have plentiful B2 adrenergic receptors, which are sensitive to circulating adrenaline.
21
Q

Describe the role of VIP in airway resistance

A

Vasoactive intestinal polypeptide

  • Produces nitric oxide
  • Activates guanylate cyclase to produce cyclic GMP and muscle relaxation
  • Sensory fibers of this system also react to smoke and other irritants and secrete substance P, neurokinin A, which are potent bronchoconstrictors.
22
Q

Describe how mechanical stimuli may elicit bronchospasm

A

Direct stimulation activates the PARASYMPATHETIC reflex

  1. Laryngoscopy
  2. Foreign bodies
  3. Chemicals such as gastric acids
23
Q

Identify the MOA of alupent, albuterol, atrovent, and cromolyn

A
  • Alupent : Symp/ B2
  • Albuterol: Symp/ B1/B2
  • Atrovent : Parasym/cholinergic
  • Cromolyn: Antihistamine
24
Q

Describe the effect of volatile anesthetics on airway resistance

A
  • Bronchodilating properties offset decrease in FRC’s effect on airway resistance
  • May cause posterior displacement of tongue, laryngospasm, secretions (subsequent bronchoconstirciton)
    • Dose dependent and similar decrease in airway resistance
  • Relaxant effect due to decrease in vagal activity (B2- agonist effect is additive)
    • Sevo > Halo> Iso
25
Q

Describe the relationship between lung volume and airway resistance

A
  • When lung volume is reduced, airway resistance increases
  • At very low lung volumes airways collapse
26
Q

Define closing capacity

A
  • Smaller airways lack cartilaginous support and are dependent on lung volume
  • The volume at which these airways close is called closing capacity
  • Closing capacity is usually less than funcitonal residual capcity but becomes closer wtih age and certain conditions.
27
Q

Describe the benefit of PEEP in optimizing FRC and closing capacity

A

Keeps small airways open and prevents collapse.

28
Q

List four factors decreasing FRC during abdominal surgery

A
  1. Supine position
  2. Induction of anesthesia
  3. Paralysis
  4. Surgical position and displacment
29
Q

Define flow related airways collapse as it relates to resistance in the asthmatic

A
  • During forced exhalation REVERSAL of the normal intrapleural airway pressure (-5 to +5) may occur due to positive pleural pressure as with valsalva
  • Resistance increases due to alveolar collapse as intrapleural pressure is greater than alveolar pressure
  • Examples include asthma and emysema.
30
Q

Describe the effect of anesthesia on tissue resistance

A
  • Tissue resistance is usually nominal in the spontaneously breathing patient
  • In anesthetized patients or paralyzed patients it may represent half of the respiratory system resistance
  • Tissue resistance ORIGINATES from both lung and chest wall tissues, with most originating in the chest wall
31
Q

Describe the effect of increasing respiratory rates in patients with obstrucive lung disease

A
  • Slow and deep pattern
  • Closer to 10 BPM
32
Q

Identify the effect of COPD on work of breathing

A

CardioPulmonary Class (6 decks)

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