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Physiology > The lungs/pulmonary mechanics > Flashcards

The lungs/pulmonary mechanics Flashcards

1
Q

What are the two primary functions of the respiratory system?

A

To deliver oxygen from the atmosphere to the tissues of the body and to remove carbon dioxide produced by metabolism

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2
Q

Define: ventilation. What is a typical resting value for ventilation? During exercise?

A

The flow of air into and out of the lungs. 7.5 L/min at rest. Up to 120 L/min during exercise

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3
Q

How would you calculate ventilation mathematically?

A

Multiply frequency of breathing (breaths/min) x Tidal Volume (volume of air moving into or out of the lung in one breath in L/breath)

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4
Q

What is a typical value for frequency of breathing at rest? Tidal volume at rest?

A 
frequency= 15 breaths/min
TV= .5 L/breath
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5
Q

What is ATPS? Where might this be found?

A

Ambient Temperature and Pressure, Saturated
Room temp (25C), 760 mm Hg, Water vapor pressure of 24 mm Hg
In a spirometer

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6
Q

What is BTPS? Where might this be found?

A

Body Temperature and Pressure, Saturated
37C, 760 mm Hg, Water vapor pressure of 47 mm Hg
In the body (i.e. in the lungs)

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7
Q

What is the ideal gas law for a dry gas? How does this change calculations for the body?

A

PV=nRT or PV/T= constant

To do calculations for the body, must subtract P(water vapor pressure) from P(dry gas)

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8
Q

What is the water vapor pressure in the human body?

A

47 mm Hg

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9
Q

What is the conductive zone? What is a nickname for this area? What is its function?

A

The first 16 branches of the lung (i.e. trachea, bronchi, bronchioles, terminal bronchioles). Called anatomical dead space b/c no gas exchange occurs here. Conveys the air to the respiratory zone

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10
Q

What is the ventilatory apparatus? What is its function?

A

It is the conductive and respiratory zones. It allows you to breathe

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11
Q

____ line the epithelium of the conducting zone and _____ produce mucus. Both act to trap and expel inhaled particles.

A

Cilia; goblet cells

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12
Q

What is the respiratory zone? What is it’s function?

A

The last 7 branches of the ventilatory apparatus including respiratory bronchioles, alveolar ducts and alveolar sacs. Gas exchange

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13
Q

Why do the airways branch?

A

To increase the surface area available for gas exchange

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14
Q

What do type 1 alveolar cells do? Type 2?

A

Type 1- line the alveoli (gas exchange occurs across them)

Type 2- make surfactant

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15
Q

What is surfactant? What does it do?

A

It is DPPC (dipalmitoylphosphatidylcholine). It coats alveoli, lowering surface tension, making inhalation easier and preventing collapse

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16
Q

How does gas exchange occur across the alveoli?

A

By diffusion. Total alveolar surface area is huge so velocity (Q=Av) is minimal and diffusion, rather than bulk flow, carries the gas across type 1 cells to the capillaries.

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17
Q

What gasses make up atmospheric air? What are their relative mole fractions?

A

Nitrogen- .78
Oxygen- .21
CO2- .0003
Argon- .01

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18
Q

How would you calculate partial pressure of a gas? Of a wet gas?

A

Partial pressure dry gas = (mole fraction of gas) x (total pressure)
Partial pressure wet gas = (mole fraction) x (total pressure- water vapor pressure)

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19
Q

What is Henry’s law? What implications does it have?

A

Concentration of dissolved gas= (proportionality constant) x (partial pressure of dissolved gas)

  • Dissolved gasses don’t contribute to blood volume or blood pressure (i.e. transported O2, CO2)
  • If a gas and it’s dissolved gas are in equilibrium, they will have equal partial pressures
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20
Q

What happens if we do not breathe in enough oxygen? Breathe out enough CO2?

A

Not inhale enough O2- become hypoxic and may pass out (b/c brain doesn’t get the O2 it needs)
Not exhale enough CO2- CO2 builds up in the blood, forms H+ and HCO3- which reduces blood pH leading to acidemia and acidosis

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21
Q

What should the flow of O2 into the body be equal to?

A

Rate of consumption of O2 by tissues and flow of O2 out of the body

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22
Q

Normal inspiration is driven by (positive/negative) pressure. Inspiration while on a ventilator is driven by (positive/negative) pressure.

A

Normally- (-) pressure

Ventilator- (+) pressure

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23
Q

What is the main muscle for inspiration? What other muscles participate?

A

The diaphragm. It contracts to increase the volume of the chest cavity.
External intercostals also participate during active breathing

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24
Q

What muscles are involved in expiration?

A

Internal intercostals and 4 abdominal muscles (transversus abdominus, rectus abdominus, internal and external obliques). Only involved in active respiration

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25
Q

Define: eupnea. Is inspiration active or passive? How about expiration? What muscles are involved?

A

Quiet breathing. Active inspiration (only the diaphragm involved) with passive expiration driven by the elastic recoil of the chest wall and lungs

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26
Q

Define: hyperpnea. Is inspiration active or passive? How about expiration? What muscles are involved?

A

Active breathing during exercise. Inspiration is active (diaphragm and external intercostals) and expiration is active (internal intercostals and 4 abd muscles). Accessory muscles of the chest and neck (sternocleidomastoid, scalene) may also be used to aid inspiration in strenuous exercise

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27
Q

Define: tachypnea

A

Breathing more rapidly, but not necessarily more deeply than normal

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28
Q

Define: hypoventilation. When might this occur?

A

When the respiration rate is insufficient for normal oxygen consumption of the tissues, leading to an accumulation of CO2 in the tissues and the blood (with a corresponding decrease in pH) causing respiratory acidemia and acidosis. DMD, other pathologies

29
Q

Define: hyperventilation. When might this occur?

A

When RR is greater than required for metabolic needs. Causes respiratory alkalosis and alkalemia (b/c decreased CO2 in blood so increased pH). In anxiety or a panic attack

30
Q

During inspiration, P(alv) is (greater/less than) P(atm). During expiration, P(alv) is (greater/less) than P(atm).

A

inspiration- P(alv) < P(atm)

Expiration- P(alv) > P(atm)

31
Q

How would you calculate transmural chest wall pressure? What does that mean physiologically?

A

P(C)= P(intrapleural)- P(atmospheric)

The degree of inflation of the chest wall

32
Q

How would you calculate transmural lung pressure? What does that mean physiologically?

A

P(L)= P(alveolar)- P(pl)

The degree of inflation of the lung

33
Q

How would you calculate total transmural pressure?

A

P(T)= P(alv)-P(atm)= P(L)+P(C)

34
Q

How would one obtain the data needed to calculate compliance in the pulmonary system?

A

Using a weighted spirometer. A person inspires then holds their breath with the glottis open and relaxes their chest wall muscles. The weight on the spirometer maintains lung inflation allowing us to measure P(alv) in the lungs, P(pl) in the esophagus at the level of the lungs and P(atm) outside of the body.

35
Q

How would you calculate total pulmonary compliance?

A

C(t)= (change in V)/(change in P)= (change in V)/P(T) where P(T)= P(L)+P(C) = P(alv)- P(atm)

36
Q

How would you calculate lung compliance?

A

C(L)= (change in V)/(change in P)= (change in V)/P(L) where P(L)= P(alv)- P(pl)

37
Q

How would you calculate chest wall compliance?

A

C(C)= (change in V)/(change in P)= (change in V)/P(C) where P(C)= P(pl)- P(atm)

38
Q

Define: Functional Residual capacity. What is the value of P(T) at this point? What about P(C) and P(L)? What does this mean physiologically?

A

The lung volume at which P(T)=0, thus P(C)= -P(L)

The outward elastic recoil of the chest wall is equal to the inward elastic recoil of the lungs

39
Q

Define: vital capacity

A

All of the air you can breathe out at once

40
Q

Describe the static compliance curve for the chest wall. Describe the curve for the lung. For total pulmonary compliance.

A

Chest wall- has greater compliance at greater pressures (inflate chest cavity a lot, it wants to come in. Inflate a little, wants to inflate more)
Lung- has less compliance at greater pressures (lungs are stiffer when more stretched out)
Total compliance is about constant

41
Q

What drives air out in forced expiration?

A

Chest wall recoil drives volume towards FRC

42
Q

What drives air out after a big inspiration?

A

Both chest wall and lung elastic recoil (both inwardly directed)

43
Q

How does intrapleural pressure change to allow for a big inspiration? What about after the big inspiration?

A

It becomes more negative so you can take a big breath then becomes more positive after the big inflation

44
Q

How is lung compliance altered in patient’s with emphysema? Why does this occur? What about in patients with fibrosis?

A

It is increased in emphysema b/c cigarette smoke damages alpha1-antitrypsin which normally inhibits proteases from digesting the lungs. Proteases digest the lung CT, inhibiting elasticity and increasing compliance.
Compliances decreases in fibrosis

45
Q

How does tissue elasticity influence compliance?

A

Elastance= 1/compliance. Anything that increases elasticity will decrease compliance (and emphysema, which decreases elasticity has increased compliance)

46
Q

How does surfactant influence compliance?

A

Surfectant reduces surface tension. Increased surface tension decreases compliance. So, surfactant increases compliance of lungs (think of surfactant as decreasing the decrease in compliance)

47
Q

How does surfactant stabilize alveoli?

A

Using LaPlace’s Law (pressure= (2x surface tension)/radius), two alveoli of different sizes with the same amount of surfactant will have different amounts of surface tension. The bigger alveolus has greater radius thus will have more surface tension b/c the surfactant is spread more thinly. This will make pressure higher in the bigger alveolus and allow air to move to the smaller alveolus (down the pressure gradient)

48
Q

On inspiration, what happens to thoracic volume? Intrapleural pressure? Transmural lung pressure?Flow? Alveolar pressure?

A

For inspiration to occur, the diaphragm contracts, increasing the volume of the thoracic cavity. This makes intrapleural pressure more negative and transmural lung pressure (P(alv)- P(pl)) more positive. This allows the lung to expand and P(alv) becomes a little negative and air flows into the lung.

49
Q

On expiration, what happens to thoracic volume? Intrapleural pressure? Transmural lung pressure?Flow? Alveolar pressure?

A

The diaphragm begins to relax so intrapleural pressure starts becoming less negative. This causes a decrease in transmural lung pressure and thus a decrease in lung volume. The corresponding positive values for P(alv) drive flow out of the lungs.

50
Q

Define: dynamic lung compliance. How is it calculated?

A

The compliance of the lung during breathing

C(dyn)= tidal volume/ (P(alv)-P(pl))

51
Q

How is C(dyn) related to C(static) in a normal person? How does this change with an increased respiration rate?

A

C(dyn) is a little less than or equal to C(static)

Does not change with increased RR

52
Q

How is C(dyn) related to C(static) in a someone with small airway disease? How does this change with an increased respiration rate? Why does this happen?

A

C(dyn) is less than C(static) at normal RR and becomes increasingly less than C(static) as RR increases). In small airway disease, the resistance in the lungs is increased so TV is smaller at a greater RR.

53
Q

What type of flow is expected when auscultating the lungs?

A

Laminar with some turbulence due to surface roughness (ciliated epithelium) in the conducting zone

54
Q

What makes up more of the resistance to breathing: tissue or airway resistance? Define each type of resistance

A

Airway (80%)- resistance due to the motion of air

Tissue (20%)- due to the motion of tissues (i.e. chest size)

55
Q

How does resistance change as air moves through the lungs? Why is this important?

A

Resistance increases during the 1st three branches (til the bronchi). This slows flow allowing air to be warmed and cleansed. Then resistance decreases with the increased branching of the airways, quickly delivering the air to the alveoli for gas exchange

56
Q

What are some factors that increase airway resistance (may cause bronchoconstriction)? What factors decrease airway resistance (may cause bronchodilation)?

A

Increased resistance- Parasympathetic innervation (weakly), certain stimuli (i.e cold, smoke), histamine, mucosal swelling
Decreased resistance- sympathetic innervation (via norepi on B2 receptors), positive end-expiratory pressure for those on ventilators

57
Q

What relationship does an isovolume pressure-flow (IVPF) curve describe? What information does the slope give you?

A

IVPF curves plot the change in flow with changing alveolar pressure at constant volume. The slope is change in flow/change in pressure or 1/resistance

58
Q

How do inspiration IVPF curves change with changing volume? How do expiration curves change?

A

Inspiration- all curves look basically the same. Pressure doesn’t affect flow
Expiration- Greater flow occurs at greater lung volumes for the same pressure. Also, the curves tend to plateau

59
Q

Why do IVPF expiration curves differ for different lung volumes?

A

At smaller lung volumes, the lungs are more compliant and airway resistance is greater than expected. Dynamic compression occurs.
At larger lung volumes, the lungs are less compliant and resistance is constant following Ohm’s law (P= QR)

60
Q

Define: dynamic compression

A

It is when the airway partially collapses during forced expiration (P(pl) is positive) at a point distal (closer to the mouth) of the point where P(pl) = P(airway) (the equal pressure point)

61
Q

How does dynamic compression change with increased effort? With increased compliance of the lungs (as in a person with emphysema)?

A 
Increased effort means increased P(pl) which shifts EPP closer to the lungs
increased compliance (less stiff lungs) allows more of the airway to close during forced expiration, creating the plateaus seen in the expiratory IVPF curves at low volumes
62
Q

What machine is used to create a maximal expiratory flow-volume (MEFV) curve? What must a patient do for this test?

A

A spirometer. Inhale fully then exhale to his/her residual volume with a maximum force

63
Q

Why are expiratory curves not perfectly symmetrical to inspiratory MEFV curves?

A

Dynamic compression occurs for expiratory curves, even in healthy individuals

64
Q

Peak expiratory flow is effort (independent/dependent) while mid-expiratory flow is effort (independent/dependent)

A

Peak- depends on effort

Mid- independent

65
Q

How is forced vital capacity (FVC) measured on a MEFV curve? What can it be used to calculate?

A

FVC is the total volume expired. The ratio of forced expiratory volume in 1 second (FEV1) to FVC should be around .8 in a normal, healthy individual. A ratio of less than that indicates increased airway resistance characteristic of small lung disease such as bronchitis

66
Q

How does the shape of an expiratory MEFV curve change with increased compliance (i.e. emphysema)? How about with restrictive airway disease (i.e. fibrosis)?

A

Emphysema- more dynamic compression makes the expiratory curve more concave
Fibrosis- the curve is less concave. FVC is also reduced b/c of the increased resistance

67
Q

How would a respiratory muscle disease (i.e. DMD) change the shape of the MEFV curve?

A

PEF would be less b/c they don’t have the muscular strength to blow out the air. The curve would also look atypical with plateaus on both inspiration and expiration

68
Q

How does pursed-lip breathing help patients with emphysema?

A

It works to maintain P(airway) by increasing resistance at the lips so pressure doesn’t drop as much in the airway so the EPP is closer to the mouth and there is less opportunity for dynamic compression

Physiology (13 decks)

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