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Physiology > Pulmonary Mechanics II > Flashcards

Pulmonary Mechanics II Flashcards

1
Q

what does air’s low viscosity mean for pressure needed for inhalation?

A

since air < water in terms of viscosity, a lower pressure is needed for inhalation into the lung

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2
Q

how are flow, alveolar pressure, and interpleural pressure related during inspiration and expiration?

A
  • flow and alveolar pressure are closely related (decrease to negative in inspiration, then increase to positive in expiration)
  • interpleural pressure is linearly following, but will have more negative/positive curves that match flow and Palv to overcome friction and other resistances to get more air in and out
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3
Q

what happens to pressure (of chest and lung) at end inspiratory volume?

A

chest pressure is equal to zero

lung pressure is equal to total pressure, and somewhat positive

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4
Q

what is the dominant driving force for return of the lung to FRC during forced expiration?

A

expansive force of the chest wall

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5
Q

is intrapleural pressure positive or negative during inspiration and expiration

A

it’s negative during inspiration, but positive in expiration and while measuring chest wall compliance (chest muscles are resting)

  • the pressures recorded during measurement of compliance are not the same as during breathing
  • the values will be more positive/negative with greater inspiration/expiration
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6
Q 
dynamic compliance (typical value)
-what does it do w/ small airway disease
A

dV/dP at end-inspiration and end-expiration, when Palv = Patm (usually 0.1 L/cm H2O)
-falls b/c increased resistance (like if there are mucous plugs or inflammatory swelling)

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7
Q

what does a discrepancy in static and dynamic compliance mean?

A

abnormal resistance

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8
Q

in small airway disease, what happens to:

  • intrapleural pressure changes
  • total volume
  • respiratory rate
  • airway resistance
  • dynamic compliance
A
  • dPpl changes are constant
  • TV decreases
  • RR increases
  • AR increases
  • Cdyn decreases
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9
Q

eddy and orifice flow

A

eddy - turbulent at bifurcation, laminar once through

orifice - turbulent in smaller opening, laminar once through

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10
Q

components of resistance to breathing

A

20% due to tissue resistance (depends on the size of the chest)
80% due to airway resistance
-10% small airways
-15% trachea and bronchi (bronchioles not normally main site of resistance, but can become so in bronchitis)
-25% glottis
-50% nose or mouth

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11
Q

how does airway resistance increase/decrease from conduction to respiratory areas

A

resistance increases in the conduction area (first 3 airway generations, b/c humidifies, warms, filters, and cleanses air), then falls as X-sectional area increases

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12
Q

how does epinephrine decrease airway resistance in fight or flight?

A
  1. E binds with high affinity B2 receptors
  2. increased cAMP stimulates PRO kinase A
  3. PKA phosphorylates MLCK
  4. decreased sensitivity of MLCK for Ca-calmodulin
  5. inhibits binding of myosin cross-bridges to actin
  6. dilates bronchi and bronchioles; reduces resistance
  7. enhances breathing
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13
Q

5 factors affecting airway resistance and their receptors, if applicable

A
  1. neural innervation of bronchial smooth muscle in humans is sparse, but:
    - sympathetic dilation of bronchial smooth muscle by E acting on B2 receptors
    - parasympathetic constriction through vagus nerve (cholinergic) on muscarinic receptors
  2. reflex constriction (smoke particles, noxious gases, extreme cold)
  3. histamine is a potent bronchoconstrictor and vasodilator (H1 receptor)
  4. inflammatory swelling of bronchial mucosa increases Raw in asthma
  5. PEEP decreases Raw in patients on respirators
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14
Q

typical value for airway resistance

A

1.2 cm H2O/l/sec

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15
Q

is resistance greater when breathing through the nose or mouth?

A

resistance is greater when breathing through the nose than through the mouth

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16
Q

what do isovolume pressure-flow (IVPF) curves tell you? what is this due to?

A

resistance to expiration increases at low lung volumes (as in, maximal effort that exhales everything out)

  • this is due to dynamic compression of airways (deviates from Ohm’s laws)
  • during inspiration, no plateau is reached (only slight curvature is seen in dependence of flow on pressure)
17
Q

how does dynamic compression relate to quiet VS forced expiration, and what does that mean for the equal pressure point (EEP)?

A

in forced expiration, dynamic compression partially collapses airways and moves the EEP closer to the alveoli, which compresses more of the airway to increase resistance
-this is because the pleural pressure is -5 in quiet expiration, but +10 in forced; alveolar pressure is +5 in quiet, but +20 in forced

18
Q

what does the maximal effort flow volume (MEFV) loop measure?

A
  • peak expiratory flow
  • forced vital capacity
  • pulmonary compliance
19
Q

what does pursed lips breathing do?

A

it increases pressure to keep airways open to decrease resistance

20
Q

what does the MEFV curve show?

A

it shows the maximal flow that can be attained at each lung volume
-max flow is greater at greater lung volume b/c the airways are distended and the resistance to flow is less

21
Q

what is the MEFV curve used to diagnose?

A

obstructive and restrictive disease

  • effort-independent (depends less on patient cooperation)
  • less variable than IVPF and FEV1 tests
22
Q

how can MEFV curves be constructed from IVPF curves?

A

takie points off of the plateaus of the flow pressure curves at each lung volume, and re-plot max flow versus volume expired

23
Q

what are 2 reasons why maximal expiratory flow rate would be low?

A
  1. lung elastic recoil pressure is abnormally low

2. airway dimensions are restricted abnormally

24
Q

how are MEFV loops measured? what is normal vital capacity, and at what percent VC does peak expiratory flow occur? when is 100% VC exhaled?

A

flow and volume are recorded simultaneously with a spirometer during as forceful and rapid an expiration as possible, after a maximal inspiration

  • normal VC is 4.75 L
  • PEF occurs at 75-80% VC
  • 100% VC exhaled slightly over 1 sec with maximal effort
25
Q

how does the MEFV loop change in obstructive (emphysema VS bronchitis) VS restrictive (fibrosis) lung diseases?

A

emphysema: peak expiratory flow is normal
-at low lung volumes, elevated compliance causes abnormally low mid-expiratory values (quickly has low flow rates)
bronchitis: steadily decreasing flow rate, similar to normal
both obstructive have increased expiration times, but normal inspiration

fibrosis: decreased vital capacity (can’t inspire much), and expiration is likewise shortened

26
Q

pediatric MEFV loops

A

smaller chest size, so it just looks like a smaller version of the normal MEFV
-still normal developing

27
Q

respiratory muscle disease MEFV loops

A

the peak expiratory flow is lower and hits a plateau until it reaches max volume at the end of expiration

  • inspiration is likewise affected
  • curve is independent of effort b/c of dynamic compression
28
Q

when is dynamic compression active; inspiration or expiration?

A

expiration

29
Q

when do intrapleural pressure, alveolar pressure, and flow attain their most negative values?

A

Ppl - at end-inspiration
Palv and flow - at mid-inspiration

they reach their most positive values at end-expiration and mid-expiration, respectively

30
Q

when does phrenic nerve spike frequency increase?

A

during inspiration

31
Q

how does intrapleural pressure change in eupneic breathing?

A

it is always negative, but is most negative at end-inspiration, and least negative at end-expiration

32
Q

what can drive intrapleural pressure positive?

A

during vigorous expiration, contraction of internal intercostals can drive it positive

33
Q

in forced expiration, when is airway resistance larger?

A

airway resistance is less at the beginning than at the end of forced expiration (narrowing of diameters)
-airway resistance is treater than tissue resistance, and greater in nose and mouth than bronchioles

Physiology (60 decks)

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