Ventilation & Lung Volumes Flashcards by Captain Wayne

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

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)

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Hyperinflation is characteristic of ________.

Hyperinflation is characteristic of Emphysema.

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

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.

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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 _______.

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).

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

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

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Define tidal volume & give its 1 equation

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.

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Define inspiratory reserve volume & give its 1 equation

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

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Define expiratory reserve volume & give its 1 equation

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

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Define residual volume & give its 2 equations

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.

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Define vital capacity & give its 2 equations

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

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Define inspiratory reserve capacity & give its 2 equations

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

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Analyze spirogram figure in pg. 94

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Give the equation for total ventilation, VT =

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.

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Give the equation for ventilation, VE =

VE = f x TV

L/min = breath/min x L/ breath

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

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

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

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

See figure pg. 100

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

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

Values are DIFFERENT in venous blood

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

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

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

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.

For blood pressures:

Upper case “A” =

Lower case “a” =

Upper case “A” = Alveolar

Lower case “a” = arterial

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

PAO2 = PIO2 - (PACO2/R)

PAO2 = PIO2 - (PT xVO2/VA)

PI = pressure inspired
R = VCO2/VO2

Increasing alveolar ventilation ___ alveolar oxygen.

Increasing oxygen consumption _____ alveolar oxygen.

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

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.

Describe alveolar O2 & CO2 during a single breath

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

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

O2 = 150 mmHg

CO2 = 0 mmHg

Describe the single breath analysis of Anatomic dead space.

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

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

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

The tidal volume is

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

Alveolar ventilation =

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.

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

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.

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

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).

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

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

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?

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

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.

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.

What is the equation for FRC from the body plethysmograph?

V = FRC = (Ptotal x ΔV)/Ptube

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?

2.8 L V = FRC = (Ptotal x ΔV)/Ptube Ptotal = 700mmHg ΔV = .2L Ptube = 50mmHg

Pulmonary ventilation is defined to be

the flow of air into or out of the lung

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?

3.0 L n1 x FRC = n2 x Vspirometer n1 = 80 FRC = n2 = 12 Vspirometer = 20 L

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?

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

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?

6.0 L TLC = FRC + TV + IRV ventilation = f x TV TV = 7/10 = .7 minute ventilation is ventilation in a minute

the volume of air expired in one breath =

is the tidal volume.

the number of breaths per minute =

is the respiratory rate.

the product of breathing frequency and total lung volume =

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