Ventilation and Lung Volumes

Question 1

describe the total lung capacity and name its components.

Answer 1

the max volume of gas that the lungs can contain.

tidal volume, inspiratory reserve volume, expiratory reserve volume and residual volume.

Question 2

what is the tidal volume?

Answer 2

the volume of gas that flows into and out of the lung in one breath

Question 3

what are the inspiratory reserve volume and expiratory reserve volume?

Answer 3

IRV- max gas that can be inhaled from end tidal inspiratory position
ERV- max gas that can be exhaled from the end titdal expiratory position

Question 4

what is the residual volume?

Answer 4

the volume of gas contained in the lungs after a max forced expiration

Question 5

what is the vital capacity? what is it made up of?

Answer 5

the max volume of gas that can be exhaled after max inspiration
IRV+ERV+tidal volume

Question 6

what is the inspiratory reserve capacity? what is it made up of?

Answer 6

the max volume of gas that can be inhaled from resting position
tidal volume+IRV

Question 7

what is the functional residual capacity?

Answer 7

the volume of gas in the lungs when the diaphragm and chest muscles are relaxed

Question 8

why can’t FRC be measured with a spirometer?

Answer 8

because it is impossible to exhale the residual capacity

Question 9

what effect does compliance have on FRC? how does this change during aging?

Answer 9

increased compliance increases FRC (decrease resistance of lung to pull of chest)
compliance and FRC increase during aging

Question 10

what does the open-circuit nitrogen washout test measure?

Answer 10

the FRC

Question 11

what is the equation that is used by the open circuit nitrogen washout test?

Answer 11

FRC=(fraction N2 sp x volume sp)/ fraction N2 lung

sp->spirometer

Question 12

how are the values for the nitrogen washout test collected?

Answer 12

fraction N2 lung=0.8 (same as in atmosphere)
V sp-> measure of all of the air expired in the test
fraction N2 sp-> measured from the expired gas

Question 13

how is the nitrogen washed out of the lung in the open circuit nitrogen washout test?

Answer 13

the patient breathes in 100% oxygen for at least 7 min and all of the expired gas from the test is collected.

Question 14

in practice, what is different about the equation compared to the fractional equation?

Answer 14

there is a correction made for the amount of nitrogen brought to the lungs from the blood during the washout

Question 15

what would not be measured during the nitrogen washout test? what would this due to the result?

Answer 15

any regions of the lung that contain trapped air, underestimating the actual FRC

Question 16

describe the initiation of use for a body plethysmograph.

Answer 16

the subject sits in a gas tight chamber and breathes through a tube leading outside until temp and humidity are equilibrated

Question 17

during testing for FRC using a body plethysmograph, what is the protocall?

Answer 17

the breathing line is closed when the lung is at FRC and the subject makes an expiratory effort against a pressure transducer

Question 18

what is measured while in the body plethysmograph?

Answer 18

the pressure transducer blocking expiration measures the lung pressure and there is a second transducer records the pressure change of the box.

Question 19

what equation is employed when calculating the FRC from values measured in the plethysmograph?

Answer 19

FRC= -Pt (deltaV/deltaP)

Question 20

what happens to the pressure in the lungs and in the plethysmograph with the forced expiration?

Answer 20

the pressure in the lungs increases because the volume is being compressed. this compression of volume increases the volume within the plethysmograph, decreasing the pressure

Question 21

what makes up the anatomic dead space?

Answer 21

the conducting zone

Question 22

why does the last portion of each inspired breath not participate in gas exchange?

Answer 22

because the last amount of air only interacts with the anatomic dead space and never reaches the respiratory zone

Question 23

what is the alveolar ventilation?

Answer 23

total ventilation - dead space ventilation

frequency of breathing x (total volume-dead space volume)

Question 24

what is the rough approximation for anatomic dead space volume in an individual?

Answer 24

1 lb body weight=1 ml dead space (used in clinical practice)

Question 25

what is the result of hypoventilation?

Answer 25

alveolar hypercapnea and hypoxia (decreased O2 and increased CO2)

Question 26

why does hyperventilation result in alveolar hypocapnea and hyperoxia?

Answer 26

because the rate of gas diffusion into and out of the capillaries is small compared to the rate of influx of oxygenated air and efflux of CO2 containing air

Question 27

what is the equation for CO2 ventilation at steady state?

Answer 27

ventilation of CO2= alveolar ventilation x alveolar fraction of CO2

Question 28

what is the equation for alveolar partial pressure of CO2? based on this equation what happens if the alveolar ventilation is increased?

Answer 28

P CO2 alveolar= (ventilation CO2 x total pressure)/ alveolar ventilation
ventilation increased, alveolar CO2 partial pressure decreases

Question 29

based on the equation for partial pressure of CO2, what two factors would increase the partial pressure of CO2 in the alveoli at steady state?

Answer 29

increasing CO2 production and decreasing alveolar ventilation

Question 30

based on the equation for partial pressure of O2 in the alveoli, what three factors would increase alveolar oxygen?

Answer 30

increasing alveolar ventilation, decreasing oxygen consumption and increasing the partial pressure of oxygen in the inspired gas

Question 31

what is the equation for partial pressure of O2 in the alveoli?

Answer 31

P O2 alveoli= (P O2 inspired- P CO2 alveoli)/ R

R= ventilation of CO2/ ventilation of O2

Question 32

what percentage of total lung capacity does the tidal volume represent? what does this imply?

Answer 32

only ~10%
implies that the volume going in and out of the lung in each breath is a small fraction of the volume of air present in the lung

Question 33

what is the magnitude of the partial pressure differences of CO2 and O2 during inspiration and expiration in the alveoli?

Answer 33

1-2 mmHg

Question 34

why does the partial pressure of O2 fall and the partial pressure of CO2 rise during the beginning of inspiration?

Answer 34

because there is still gas transfer in the alveoli while air is traveling through the dead space to the alveoli

Question 35

describe the protocall for using the single breath analysis of anatomic dead space.

Answer 35

a subject inspires air (negligible CO2) and then exhales into a spirometer while the fraction of CO2 is being measured

Question 36

what is the principle of the fowler method of single breath analysis of anatomic dead space?

Answer 36

that expired CO2 comes exclusively from the alveoli and not from the anatomic dead space

Question 37

on the fraction of CO2 graph, what point reveals the time when all of the dead space air would be expired if there was a sharp boundary between alveolar and dead space air?

Answer 37

at the point of concavity change in the sigmoidal shaped curve. the volume of expired air at this time corresponds to the volume of dead space

Question 38

why is the curve of fraction of exhaled CO2 sigmoidal?

Answer 38

because there is a mixing of air free of CO2 from the dead space and air with a considerable amount of CO2 in the alveoli