Ventilation & Lung Volumes

Question 1

Describe how the functional residual capacity is measured by means of the open-circuit nitrogen washout method (give equation) and by using the body plethysmograph

Answer 1

FRC and TLC cannot be measured using only a simple spirometer because they include RV, which cannot be exhaled from the lung.

1) open-circuit nitrogen washout method: First, while the subject is breathing air, an alveolar gas sample is taken and the initial N2 fraction is measured. Then at the end of eupneic expiration, with the lung at FRC, the subject breathes 100% O2 for at least 7 min to wash out all of the N2 from the lung. The expired gas (with N2) is collected in a large spirometer. The volume expired and the N2 fraction in the collected gas are measured. A conservation of mass equation may be used to estimate FRC. The number of moles of N2 in the lung = number of moles of N2 in the lung.

Fraction (lung) x FRC Volume initial = Fraction (spirometer) x Volume (spirometer)

From ideal gas law, fraction, n, can be found in PV = nRT pr n = PV/RT

In practice, a correction is made for the amount of N2 brought to the lungs by the blood during the washout. If there are regions of the lung which contain trapped air, then this volume won’t be measured, and the method will underestimate FRC.

2) body plethysmograph: The subject breathes through a tube leading to the outside. After equilibration of temperature and humidity within the chamber, the breathing line is closed off when the lung is at FRC. The subject then makes an expiratory effort against a pressure transducer, which records the pressure within the lung. This method can measure total FRC including trapped air.

So if you subtract the result from the N2 washout from the Platysmograph, you get the volume of trapped air in the lung due to pathological processes.

We will get the formula on out list:

V = FRC = -(Ptotal)V/P(gas)

Question 2

Hyperinflation is characteristic of ________.

Answer 2

Hyperinflation is characteristic of Emphysema.

Question 3

Define Functional Residual Capacity (FRC). Can it be measured via spirometry?

Answer 3

Functional Residual Capacity (FRC) is the volume of air present in the lungs at the end of passive expiration when all of the muscles of respiration are relaxed. FRC occurs when the lungs and chest wall are at mechanical equilibrium.

FRC cannot be measured with a spirometer since this capacity includes RV.

FRC changes with compliance.

Question 4

Increased lung compliance ______ FRC, decreased lung compliance ______ FRC, & with increasing age, lung compliance & FRC both ______. With increasing age, vascular compliance ________. In fibrotic lung disease, the FRC _______.

Answer 4

Increased lung compliance increases FRC, decreased lung compliance decreases FRC, & with increasing age, lung compliance & FRC both increase (because protection against the proteases decreases). With increasing age, vascular compliance decreases. In fibrotic lung disease, the FRC decreases (since the compliance is decreased).

Question 5

Define total lung capacity & give its 4 equations. Can it be measured via spirometry?

Answer 5

The total lung capacity, or TLC, is the maximum volume of gas that the lungs can contain. TLC is normally about 6-7 L.

TLC cannot be measured with a spirometer since this capacity includes RV.

TLC = VC + RV

TLC = (IRV + ERV + TV) + RV

TLC = FRC + IC

TLC = FRC + TV + IRV

Question 6

Define tidal volume & give its 1 equation

Answer 6

The tidal volume, or TV, is the volume of gas which flows into and then out of the lung in one breath. TV is normally 500-600 ml, and increases with exercise. TV may be measured with a spirometer.

Question 7

Define inspiratory reserve volume & give its 1 equation

Answer 7

Inspiratory reserve volume, or IRV, is the maximum volume of gas that can be inhaled from the end-tidal inspiratory position.

Question 8

Define expiratory reserve volume & give its 1 equation

Answer 8

Expiratory reserve volume, or ERV, is the volume of gas that can be exhaled from the end-tidal expiratory position

Question 9

Define residual volume & give its 2 equations

Answer 9

Residual volume, RV, is the volume of gas contained in the lungs after a maximal forced expiration.

The residual volume cannot be exhaled; therefore, the lung always has a volume.

Question 10

Define vital capacity & give its 2 equations

Answer 10

Vital capacity, or VC, is the maximum volume of gas that can be exhaled after a
maximal inspiration.

VC = IRV + TV + ERV 
VC = TLC - RV

Question 11

Define inspiratory reserve capacity & give its 2 equations

Answer 11

Inspiratory reserve capacity, or IC, is the maximum volume of gas that can be inhaled from the resting expiratory position.

IC = TV + IRV 
IC = TLC - FRC

Question 12

Analyze spirogram figure in pg. 94

Answer 12

-

Question 13

Give the equation for total ventilation, VT =

Answer 13

VT = VD + VA

The trachea, bronchi, bronchioles, and terminal bronchioles comprise the conducting zone and make up the anatomic dead space. These passageways conduct the air into the lung but do not permit gas exchange.

The respiratory bronchioles, alveolar ducts and alveolar sacs comprise the respiratory zone where gas exchange occurs. Thus the last portion of each inspired breath does not participate in gas exchange because this air never reaches the respiratory zone.

Consequently, each tidal volume consists of air which flows into the anatomic dead space of volume VD, and into the alveolar volume, VA. Alveolar ventilation is what determines the steady state partial pressures of O2 & CO2 in the alveoli.

Question 14

Give the equation for ventilation, VE =

Answer 14

VE = f x TV

L/min = breath/min x L/ breath

Question 15

In hypoventilation, alveolar ______ (increased CO2) & ______ (decreased O2) occur. Furthermore, blood pH decreases = ______.

Answer 15

In hypoventilation, alveolar hypERcapnea (increased CO2) & hypoxia (decreased O2) occur. Furthermore, blood pH decreases = acidosis = acidemia.

Question 16

In hyperventilation, alveolar _______ (decreased CO2) & _________ (increased O2) occur. Furthermore, blood pH increases = ______.

Answer 16

In hyperventilation, alveolar hypOcapnea (decreased CO2) & hyperoxia (increased O2) occur. Furthermore, blood pH increases = alkalosis = alkalemia.

See figure pg. 100

Question 17

What are the normal partial pressures of O2 & CO2 in BOTH the alveolar compartment & arterial blood gases during normal ventilation?

Answer 17

Normal partial pressure of O2 = 100 mmHg & for CO2 = 40 mmHg @ equilibrium.

Values are DIFFERENT in venous blood

Question 18

In the steady state, you must _____ CO2 at the rate it is being _____ in the tissues. So flow in = flow _____.

Answer 18

In the steady state, you must exhale CO2 at the rate it is being produced in the tissues. So flow in = flow out.

Question 19

The alveolar gas equation for CO2 in the alveolar compartment: partial pressure CO2 or PACO2 =

Answer 19

PACO2 = (VCO2 x PT)/VA

PT = pressure total
V = Ventilation
Ventilation alveolar = VA

Note that many of the (difficult) equations will be on the list–so do not memorize them, know the difficult ones, like this one.

Question 20

For blood pressures:

Upper case “A” =

Lower case “a” =

Answer 20

Upper case “A” = Alveolar

Lower case “a” = arterial

Question 21

The 2 alveolar gas equations for O2 in the alveolar compartment: partial pressure O2 or PAO2 =

Answer 21

PAO2 = PIO2 - (PACO2/R)

PAO2 = PIO2 - (PT xVO2/VA)

PI = pressure inspired
R = VCO2/VO2

Question 22

Increasing alveolar ventilation ___ alveolar oxygen.

Increasing oxygen consumption _____ alveolar oxygen.

Increasing the partial pressure of oxygen in the inspired gas ________ alveolar oxygen.

Answer 22

Increasing alveolar ventilation increases alveolar oxygen.

Increasing oxygen consumption decreases alveolar oxygen.

Increasing the partial pressure of oxygen in the inspired gas increases alveolar oxygen. This is the basis for respiratory oxygen therapy when a patient is hypoventilating.

Question 23

Describe alveolar O2 & CO2 during a single breath

Answer 23

Since VT is only about 10% of TLC, the volume of air going into and out of the lung with each breath is a small fraction of the volume of air present in the lung. Consequently, alveolar gas composition does not change much with each breath.

The oscillations of PO2 and PCO2 in the alveoli are of the order of 1-2 mm Hg during eupnea. The large amount of air that is not exchanged acts as a buffer to minimize these oscillations.

See pg. 103

Question 24

What is the partial pressure of O2 & CO2 in the dead space (from the outside)?

Answer 24

O2 = 150 mmHg

CO2 = 0 mmHg

Question 25

Describe the single breath analysis of Anatomic dead space.

Answer 25

The principle of the Fowler method is that the expired CO2 comes exclusively from the alveoli and not from the anatomic dead space. CO2 is 0 in dead space & .05 in alveolar air.

The resultant value of VD (dead space) can then be used to estimate VA (alveolar ventilation)

As the subject exhales, the FECO2 rises from a negligibly low level to a plateau near 0.05. The first gas to be expired contains negligibly low CO2 because this gas comes from the anatomic dead space, VD. Due to mixing (diffusion), FECO2 rises in a sigmoid manner with time. The time of the midpoint of the rise of FECO2 defines the time at which all of the dead space air would be expired if there were a sharp boundary between dead space gas and alveolar gas. This therefore, gives a measure of the anatomic dead space.

See pg. 104

Question 26

Which of the following could produce a decrease in alveolar ventilation with no change in total ventilation?

Answer 26

An increased respiratory rate and decreased tidal volume

ventilation = freq x TV

An increase in the respiratory rate and a decrease in tidal volume indicate a pattern of rapid shallow breathing.

If the total ventilation does not change, alveolar ventilation will decrease because of the fact that the first 150 ml of each inspiration is dead-space

Question 27

The tidal volume is

Answer 27

the amount of air that normally moves into (or out of) the lung with each respiration.

Question 28

Alveolar ventilation =

Answer 28

Alveolar ventilation = (respiratory rate) X (tidal volume - dead air space)

Alveolar ventilation represents the amount of new fresh air that reaches the alveoli. For each inspiration it will be tidal volume minus dead space (anatomic). For alveolar ventilation per minute we must multiply by the respiratory rate.

Question 29

Can vital capacity be measured by spirometry? What cannot be measured by spirometry?

Answer 29

Yes

Residual volume (RV) cannot be measured by spirometry. Therefore, any lung volume or capacity that includes the RV cannot be measured by spirometry. Mesurements that include RV are functional residual capacity (FRC) and total lung capacity (TLC). Vital capacity (VC) does not include RV and is, therefore, measurable by spirometry. Physiologic dead space is not measurable by spirometry and requires sampling of arterial Pco2 and expired CO2.

Question 30

Which volume remains in the lungs after a tidal volume (TV) is expired during eupneic breathing?

Answer 30

Functional residual capacity (FRC)

During normal breathing, the volume inspired and then expired is a tidal volume (TV). The volume remaining in the lungs after expiration of a TV is the functional residual capacity (FRC).

Question 31

In a maximal expiration starting from total lung capacity the total volume expired is _____.

Answer 31

Vital capacity

The volume expired in a forced maximal expiration is forced vital capacity, or vital capacity (VC)

Question 32

A patient at rest is breathing at 12 breaths/min and has a total ventilation of 9.4 L/min, anatomic dead space of 200 ml, and a rate of production of CO2 of 300 ml/min. If barometric pressure is 747 mm Hg, using the alveolar gas equation for carbon dioxide what would be the partial pressure of CO2 in the functioning alveoli?

Answer 32

30 mm Hg

First compute the Alveolar ventilation: 9.4 - (12 x .2)

Convert CO2 production to .3L/min

Use dry gas pressure @ 700 mmHg

Question 33

At end-inspiration the anatomic dead space is filled with atmospheric air with a partial pressure of carbon dioxide ______. At end-expiration the anatomic dead space is filled with alveolar air with a partial pressure of ______ is a normal healthy individual.

Answer 33

At end-inspiration the anatomic dead space is filled with atmospheric air with a partial pressure of carbon dioxide near zero. At end-expiration the anatomic dead space is filled with alveolar air with a partial pressure of 40 mm Hg is a normal healthy individual.

Question 34

What is the equation for FRC from the body plethysmograph?

Answer 34

V = FRC = (Ptotal x ΔV)/Ptube

Question 35

In order to measure the functional residual capacity (FRC) with a body plethysmograph, a patient made an expiratory effort at the end of a normal eupneic expiration. A transducer connected to a tube leading to the subject’s mouth recorded an increase in pressure of 50 mm Hg while a second transducer in the chamber recorded a drop in pressure corresponding to an increase in volume of 200 ml. Anatomic dead space was 0.2 L and residual volume was 1.0 L. If the total dry gas pressure was 700 mm Hg, what was FRC?

Answer 35

2.8 L

V = FRC = (Ptotal x ΔV)/Ptube

Ptotal = 700mmHg

ΔV = .2L

Ptube = 50mmHg

Question 36

Pulmonary ventilation is defined to be

Answer 36

the flow of air into or out of the lung

Question 37

The open circuit N2 washout method was used to measure functional residual capacity (FRC). After initially breathing aire at 80% N2 (BTPS), the patient then breathed 100% O2 through a valve until FAN2 was zero. The expired gas was collected in a 20 L spirometer and was found to be 12% N2 (BTPS). The collection was started and ended at the end of a normal expiration. What was the patient’s FRC?

Answer 37

3.0 L

n1 x FRC = n2 x Vspirometer

n1 = 80

FRC =

n2 = 12

Vspirometer = 20 L

Question 38

What is the residual volume of a patient’s lung if the functional residual capacity (FRC) is 5 L, inspiratory reserve volume is 1 L, vital capacity is 2 L, and minute ventilation is 6 L/min at 20 breaths/min?

Answer 38

4.3 L

TLC = FRC + TV + IRV

TLC = VC + RV

We already have VC, find TLC by V = f x TV

6/20 = .3 L/ breath

Question 39

What is the total lung capacity of a patient’s lung if the functional residual capacity (FRC) is 3.3 L, inspiratory reserve volume is 2 L, vital capacity is 5 L, anatomical dead space is 0.2 L, and minute ventilation is 7 L/min at 10 breaths/min?

Answer 39

6.0 L

TLC = FRC + TV + IRV

ventilation = f x TV

TV = 7/10 = .7

minute ventilation is ventilation in a minute

Question 40

the volume of air expired in one breath =

Answer 40

is the tidal volume.

Question 41

the number of breaths per minute =

Answer 41

is the respiratory rate.

Question 42

the product of breathing frequency and total lung volume =

Answer 42

is the maximum ventilatory rate, not the definition of ventilation.