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Flashcards in Pulmonary Mechanics II Deck (33)
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what does air's low viscosity mean for pressure needed for inhalation?

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


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

-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


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

chest pressure is equal to zero
lung pressure is equal to total pressure, and somewhat positive


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

expansive force of the chest wall


is intrapleural pressure positive or negative during inspiration and expiration

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


dynamic compliance (typical value)
-what does it do w/ small airway disease

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)


what does a discrepancy in static and dynamic compliance mean?

abnormal resistance


in small airway disease, what happens to:
-intrapleural pressure changes
-total volume
-respiratory rate
-airway resistance
-dynamic compliance

-dPpl changes are constant
-TV decreases
-RR increases
-AR increases
-Cdyn decreases


eddy and orifice flow

eddy - turbulent at bifurcation, laminar once through
orifice - turbulent in smaller opening, laminar once through


components of resistance to breathing

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


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

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


how does epinephrine decrease airway resistance in fight or flight?

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


5 factors affecting airway resistance and their receptors, if applicable

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


typical value for airway resistance

1.2 cm H2O/l/sec


is resistance greater when breathing through the nose or mouth?

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


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

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)


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

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


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

-peak expiratory flow
-forced vital capacity
-pulmonary compliance


what does pursed lips breathing do?

it increases pressure to keep airways open to decrease resistance


what does the MEFV curve show?

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


what is the MEFV curve used to diagnose?

obstructive and restrictive disease
-effort-independent (depends less on patient cooperation)
-less variable than IVPF and FEV1 tests


how can MEFV curves be constructed from IVPF curves?

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


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

1. lung elastic recoil pressure is abnormally low
2. airway dimensions are restricted abnormally


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?

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


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

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


pediatric MEFV loops

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


respiratory muscle disease MEFV loops

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


when is dynamic compression active; inspiration or expiration?



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

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

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


when does phrenic nerve spike frequency increase?

during inspiration

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