Lecture 21: Ventilation/Gas Laws

Question 1

Know which muscles are inspiratory:

Answer 1

• Respiratory diaphragm
• External intercostal muscles (limited)
• sternomastoids
• serratus anterior muscles
• scalene muscles

Question 2

Know which muscles can be used for forced expiration:

Answer 2

Abdominal muscles

Internal intercostals

Inspiration is passive at rest*

Question 3

Distinguish btw volume and capacity

Answer 3

Volume: distinct, non-overlapping sub-compartments

Capacity: combinations of lung volumes (2 or more volumes)

Question 4

Know the definition of each volume and each capacity and the approximate normal volumes.

Answer 4

Total lung capacity: maximum volume of gas the lungs can hold.

Tidal volume: volume of air that is inspired or expired w/ each breath at rest-500mL

Inspiratory reserve volume: volume of air that can be inspired in addition to tidal volume w/ forceful inspiration-3000mL

Expiratory reserve volume: additional volume of air that can be expired at end of tidal volume by forceful expiration-1100mL

Residual volume: volume of air remaining in lungs after forceful expiration-1200mL

Vital capacity: the sum of all volumes inspired or exhaled(max.)-4600mL

Total lung capacity: sum of all the volumes: vital capacity + residual volume-5800mL

Inspiratory capacity: sum of volumes above resting capacity=tidal volume + inspiratory reserve volume-3500mL

Functional residual capacity: the sum of volumes below resting capacity=expiration reserve volume+residual volume-2300mL

Functional residual capacity:

Question 5

Know definitions of and how to calc minute ventilation, alveolar ventilation and dead space

Answer 5

Minute ventilation: total volume of gases moved into or out of the lungs /min. [breaths/min x tidal volume(.5)]=

Alveolar ventilation: total volume of gases that enter spaces participating in gas exchange /min= [breaths/min x (tidal volume-dead space)]

Dead space:

• anatomic dead space: places that do not participate in gas exchange.
• Physiologic: anatomical dead space+ventilated alveoli w/ poor or absent perfusion-0.15L
• Calc: there is a formula for indirect calc.

Question 6

Know definitions of pleural pressure, alveolar pressure, and transpulmonary pressure and know how to calculate transpulmonary pressure

Answer 6

Pleural pressure: pressure of the fluid btw parietal pleura and the visceral pleura.

Alveolar pressure:pressure of the air inside the alveoli

Transpulmonary pressure: difference btw the alveolar pressure and the pleural pressure.
-Calc: alveolar pressure - pleural pressure = (-5–7.5)

Question 7

Know definition of compliance as it applies to the lungs and compare it w/ elastance

Answer 7

The extent (volume) to which lungs will expand for each unit increase in the transpulmonary pressure= increase in volume/ increase in Pressure.

Compliance is the measure of the expansibility of the lungs and trachea

Compliance and elastance are reciprocal.
Elastance is a measure of the tendency of a hollow viscus to recoil toward its original dimensions upon removal of a distending or collapsing force.

Question 8

Relate pressure to alveolar surface tension and alveolar radius and compare when surfactant is present and when it is not present.

Answer 8

Alverolar surface tension/
Alveolar radius= surrface tension

Surfactant contains phospholipids , produced by type 2 alveolar cells. THis reduces surface tension.
Normal: 4 cm of water pressure (3 mmHg)
W/o surfactant= 18 cm of water pressure (about 4.5 as great)

Question 9

List the major components of air and know their relative [ ] ‘s

Answer 9

78% N
21% O2
1% Ar
0.03% CO2

Question 10

Know the three gas laws described here and know how they r/t pulmonary function.

Answer 10

Dalton’s: total pressure exerted by the mixture of non-reactive gases is = to the sum of the partial pressures of individual gases.

Boyle’s: for a fixed amt. of an ideal gas kept at a fixed TEMP, pressure and volume are inversely proportional.

Henry’s: at a constant TEMP, the amt. of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium w/ that liquid.

Question 11

List the variables and constants that determine partial pressure

Answer 11

Atmospheric pressure (760)x partial pressure (0.197 O2) =
 150 mmHg

Question 12

Be able to calculate partial pressures of a gas given percentage of the gas in the atmosphere or under other circumstances.

Answer 12

Partial pressure= dissolved gas / sol. Coefficient

Question 13

Compare solubility coefficients of oxygen and carbon dioxide and explain the effect on partial pressures.

Answer 13

O2: 0.024
CO2: 0.57 –more soluble in water than O2. It will exert a partial pressure that is less than 1/20th that of O2.

Question 14

Define water vapor pressure and explain its relationship to temperature

Answer 14

Vapor pressure of water is the partial pressure exerted to escape from the liquid phase to the gas phase.

Temp increases=vapor pressure increases.

Question 15

List factors that affect rate of gas diffusion in a fluid

Answer 15

• Solubility of gas in the fluid
• cross-sectional area of the fluid
• distance through which the gas must diffuse
• molecular weight of the gas
• temp of the fluid(body)