Pulmonary mechanics

Question 1

What forces encourage the lungs to be small?

Answer 1

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

Question 2

To what extent does the chest wall intend to expand?

Answer 2

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

Question 3

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?

Answer 3

• at functional residual capacity

- negative 5 cm H2O

Question 4

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

Answer 4

It is the higher asymptote of the respiratory curve

Question 5

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

Answer 5

It is the y-intercept of the respiratory curve

Question 6

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

Answer 6

It is the lower asymptote of the respiratory curve

Question 7

What factors affect the total lung capacity?

Answer 7

Elastic recoil of the lung

Inspiratory muscle strength

Question 8

What are the primary muscles of inspiration?

Answer 8

The diaphragm–increases superior-inferior diameter

The external intercostals-increase anterior-posterior diameter

Question 9

What are the primary muscles of expiration?

Answer 9

None

Question 10

What are secondary muscles of inspiration?

Answer 10

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

Question 11

What are secondary muscles of expiration?

Answer 11

Internal intercostals, abdominal muscles

Question 12

What diseases reduce respiratory compliance?

Answer 12

Pulmonary fibrosis, pulmonary edema

Question 13

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

Answer 13

The curve will shift downward

Question 14

What diseases increase respiratory compliance?

Answer 14

Emphysema

Question 15

Why is increased respiratory compliance bad?

Answer 15

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

Question 16

What conditions can reduce chest wall compliance?

Answer 16

Obesity, abdomen distension, kyphoscoliosis

Question 17

What is hysteresis?

Answer 17

the lung is somewhat less compliant during inflation than during deflation

Question 18

Why does the lung exhibit hysteresis?

Answer 18

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

Question 19

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

Answer 19

In the apex due to gravity pulling the lungs downward

Question 20

Where are alveoli the largest?

Answer 20

In the apex of the lung

Question 21

Which alveoli are best ventilated?

Answer 21

In the bases of the lung

Question 22

Where is the resistance greatest in the airway?

Answer 22

In the trachea

Question 23

Where is air moving fastest in the airway?

Answer 23

In the trachea—lowest cross-sectional area

Question 24

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

Answer 24

L=small airways

T=trachea, bronchii

Question 25

How might turbulent flow in a small airway manifest?

Answer 25

Wheezing

Question 26

At what point to small airways start to collapse?

Answer 26

When the airway pressure is equivalent to the pleural pressure

Question 27

What is the main factor in increasing airway transmural pressure?

Answer 27

Elastic recoil of pressure (at high lung volumes)

Question 28

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

Answer 28

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

Question 29

What is the Bernoulli effect?

Answer 29

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

Question 30

What factors may increase airflow velocity in the periphery?

Answer 30

Tumors, mucus, or any other obstructions that introduce turbulence

Question 31

What control measures offset the pressure changes?

Answer 31

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

Question 32

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

Answer 32

Flow-volume loop | x= volume; y=rate of flow

Question 33

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

Answer 33

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)

Question 34

How would WOB relate to respiratory function?

Answer 34

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

Question 35

How does respiratory failure possibly develop?

Answer 35

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

Question 36

What is Dalton's Law?

Answer 36

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

Question 37

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

Answer 37

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

Question 38

What are the factors in gas diffusion?

Answer 38

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

Question 39

What does perfusion-limiting mean?

Answer 39

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

Question 40

What does diffusion-limiting mean?

Answer 40

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)

Question 41

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

Answer 41

High=150 mm Hg (PO2 in alveolus) | Low = 40 mm Hg (PO2 in periphery)

Question 42

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

Answer 42

VCO2/VO2 (production of CO2 to consumption of O2) | This number is usually 0.8

Question 43

What is the alveolar gas equation?

Answer 43

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

Question 44

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

Answer 44

Less than 10 mm Hg

Question 45

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

Answer 45

35%

Question 46

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

Answer 46

PCO2 is proportional to production/elimination

Question 47

How can hemoglobin carry CO2?

Answer 47

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

Question 48

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

Answer 48

Carbonic anydrase

Question 49

What is the chloride shift?

Answer 49

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

Question 50

How is the arterial oxygen content calculated?

Answer 50

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

Question 51

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

Answer 51

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