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Respiratory > Pulmonary mechanics > Flashcards

Pulmonary mechanics Flashcards

1
Q

What forces encourage the lungs to be small?

A

1) Surface tension of air-liquid at alveolar level (more important)
2) Elastic and collagen in the lungs that wants to recoil

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2
Q

To what extent does the chest wall intend to expand?

A

So long as total lung capacity is at or under 70%

The abdomen must also be compliant–if it cannot accept expansion of the diaphragm, the chest wall cannot expand

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3
Q

At what point are the contradicting desires of the lungs and the chest wall equally matched? What is the pressure of the pleural space at this point?

A
  • at functional residual capacity

- negative 5 cm H2O

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4
Q

In the respiratory pressure volume curves, how is total lung capacity noted?

A

It is the higher asymptote of the respiratory curve

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5
Q

In the respiratory pressure volume curves, how is functional residual capacity noted?

A

It is the y-intercept of the respiratory curve

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6
Q

In the respiratory pressure volume curves, how is residual volume noted?

A

It is the lower asymptote of the respiratory curve

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7
Q

What factors affect the total lung capacity?

A

Elastic recoil of the lung

Inspiratory muscle strength

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8
Q

What are the primary muscles of inspiration?

A

The diaphragm–increases superior-inferior diameter

The external intercostals-increase anterior-posterior diameter

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9
Q

What are the primary muscles of expiration?

A

None

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10
Q

What are secondary muscles of inspiration?

A

Scalenes, sternocleidomastoid, neck, back muscles, pectoralis minor, laryngeal and pharyngeal dilators

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11
Q

What are secondary muscles of expiration?

A

Internal intercostals, abdominal muscles

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12
Q

What diseases reduce respiratory compliance?

A

Pulmonary fibrosis, pulmonary edema

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13
Q

How would a decrease in respiratory compliance appear on a pressure/volume curve?

A

The curve will shift downward

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14
Q

What diseases increase respiratory compliance?

A

Emphysema

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15
Q

Why is increased respiratory compliance bad?

A

If the airways are opened too much, they can become floppy and collapse during exhalation

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16
Q

What conditions can reduce chest wall compliance?

A

Obesity, abdomen distension, kyphoscoliosis

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17
Q

What is hysteresis?

A

the lung is somewhat less compliant during inflation than during deflation

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18
Q

Why does the lung exhibit hysteresis?

A

The surface tension of the fluids in the lung makes it harder to open airways during initial inhalation

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19
Q

Where is transpulmonary pressure most negative in a standing person and why?

A

In the apex due to gravity pulling the lungs downward

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20
Q

Where are alveoli the largest?

A

In the apex of the lung

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21
Q

Which alveoli are best ventilated?

A

In the bases of the lung

22
Q

Where is the resistance greatest in the airway?

A

In the trachea

23
Q

Where is air moving fastest in the airway?

A

In the trachea—lowest cross-sectional area

24
Q

Where is air operating in laminar flow? Where is it operating in turbulent flow?

A

L=small airways

T=trachea, bronchii

25
Q

How might turbulent flow in a small airway manifest?

A

Wheezing

26
Q

At what point to small airways start to collapse?

A

When the airway pressure is equivalent to the pleural pressure

27
Q

What is the main factor in increasing airway transmural pressure?

A

Elastic recoil of pressure (at high lung volumes)

28
Q

What are factors that can decrease the airway transmural pressure? (promoting collapse)

A

1) The resistive pressure drop from the alveoli to the mouth
2) The reduction of airway pressure caused by the Bernoulli effect
3) Loss of mechanical tethering of the airways

29
Q

What is the Bernoulli effect?

A

The faster an air is moving, the lower the pressure it exerts (loss of potential energy)

30
Q

What factors may increase airflow velocity in the periphery?

A

Tumors, mucus, or any other obstructions that introduce turbulence

31
Q

What control measures offset the pressure changes?

A

Cartilage in the large airways, mechanical tethering in the small airways

32
Q

What is the main pulmonary function test and what are the axes of its graph?

A

Flow-volume loop

x= volume; y=rate of flow

33
Q

What is the work of breathing and how is it calculated?

A

The amount of work needed to be done by the lungs to overcome the tendency of the lung to stay deflated; measured as deltaPx deltaV (joules)

34
Q

How would WOB relate to respiratory function?

A

If WOB is high, muscles may not get demand to continue functioning and respiratory failure can occur

35
Q

How does respiratory failure possibly develop?

A

Too much load on respiratory system (resistor pressure, elastic pressure, minute ventilation [infection]), too little strength in nervous or muscular system

36
Q

What is Dalton’s Law?

A

The sum of all partial pressures of gas in an atmosphere is equal to the atmospheric pressure

37
Q

Why does the partial pressure of oxygen in the alveolus not equal the atmospheric partial pressure?

A

Water vapor in the lung is higher than the atmosphere (equal to about 47 mm Hg); it also has a higher CO2 concentration than the atmosphere itself

38
Q

What are the factors in gas diffusion?

A

The gradient of pressures for the gas
The cross sectional area of the membrane
Membrane thickness
Diffusivity (how well gas diffuses)

39
Q

What does perfusion-limiting mean?

A

Gases that do not interact with blood take the same amount of time to equibrilate regardless of their solubility (they need new aliquots of blood to get into blood); oxygen and carbon dioxide act this way

40
Q

What does diffusion-limiting mean?

A

The blood absorbs so much of a gas so quickly that its rate of absorption is dependent on the rate of diffusion (e.g. carbon monoxide)

41
Q

What are the highest and lowest possible values for the partial pressure of oxygen in arterial blood?

A

High=150 mm Hg (PO2 in alveolus)

Low = 40 mm Hg (PO2 in periphery)

42
Q

What is the respiratory exchange ratio and what is its average number?

A

VCO2/VO2 (production of CO2 to consumption of O2)

This number is usually 0.8

43
Q

What is the alveolar gas equation?

A

PaO2= Percentage of oxygen in atmosphere * (total atmospheric pressure-PH2O [47])-PCO2/R
R=respiratory exchange ratio

44
Q

What should the difference between arterial oxygen pressure and alveolar oxygen pressure be?

A

Less than 10 mm Hg

45
Q

About what percent of the lung is in a dead volume state at rest?

A

35%

46
Q

What is the relationship of carbon dioxide’s production, elimination, and partial pressure?

A

PCO2 is proportional to production/elimination

47
Q

How can hemoglobin carry CO2?

A

The amino groups in non-ionized alpha groups, can bind weakly to CO2. Since the bond is weak, it can release when PCO2 drops

48
Q

What enzyme catalyzes the production of bicarbonate from water and CO2?

A

Carbonic anydrase

49
Q

What is the chloride shift?

A

An antiporter permits chloride to enter red blood cells and bicarbonate will enter the blood stream

50
Q

How is the arterial oxygen content calculated?

A

CaO2 = (1.34 ml/g * [Hgb] * SaO2) + .003 ml/dL * PaO2
(where 1.34 ml/dl is the binding capacity of Hgb and SaO2 is the percent oxygen saturation). .003 is the total rate of dissolution of oxygen in blood

51
Q

What are factors that shift the decrease oxygen binding to hemoglobin? (i.e. a rightward shift of the curve)

A

↑ H+, PCO2, temperature, and 2,3‐bisphosphoglycerate

Respiratory (4 decks)

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