Ventilation and Lung Volumes

Question 1

total lung capacity

-what are its components?

Answer 1

TLC - maximum volume of gas that lungs can contain

-divided into 4 non-overlapping volume components: TV (also VT), IRV, ERV, and RV

Question 2

tidal volume and normal value

Answer 2

VT - volume of gas that flows in and out of the lung in one normal breath

• usually 500-600 mL, and increases with exercise
• may be measured with spirometer

Question 3

inspiratory reserve volume

Answer 3

IRV - maximum volume of gas that can be inhaled from the end-tidal inspiratory position (if you inhaled as much as you could after a normal inhale)

Question 4

expiratory reserve volume

Answer 4

ERV - volume of gas that can be exhaled from the end-tidal expiratory position (if you exhaled as much as you could after a normal exhale)

Question 5

residual volume

Answer 5

RV - volume of gas contained in the lungs after maximal force expiration
-this CANNOT BE EXHALED

Question 6

vital capacity and equation

Answer 6

VC - maximum volume of gas that can be exhaled after a maximal inspiration
-VC = IRV + VT + ERV = TLC - RV

Question 7

inspiratory reserve capacity and equation

Answer 7

IC - maximum volume of gas that can be inhaled from resting expiratory position
-IC = VT + IRV = TLC - FRC

Question 8

functional residual capacity

Answer 8

FRC - volume of gas in lungs after a normal expiration, when diaphragm and chest muscles are relaxed (lungs and chest wall at mechanical equilibrium)

Question 9

effect of lung compliance on FRC

Answer 9

as lung compliance increases, FRC increases (such as in emphysema/hyperinflation and aging)
-vascular compliance may decrease, though

Question 10

3 methods to measure FRC

Answer 10

1. open circuit nitrogen washout
2. closed circuit helium dilution
3. body plethysmograph
   cannot use spirometer b/c FRC (and TLC) include RV, which cannot be exhaled

Question 11

open circuit nitrogen washout and corresponding equation

Answer 11

1. subject breathes normal air, and alveolar gas sample taken to measure initial N2 fraction
2. at the end of eupneic expiration, subject breathes in 100% O2 for at least 7 minutes to wash out all N2 from lung
3. expired gas collected in large spirometer, and volume expired and its N2 fraction are measured

FRC = (F of N2 * V)sp / F of N2 in original lung

this method underestimates FRC b/c there are regions of lung with trapped air

Question 12

body plethysmograph and corresponding equation

Answer 12

1. subject sits in gas-tight chamber and breaths out tube to outside
2. after equilibriation of temp and humidity w/in chamber, breathing line is closed by solenoid when lung is at FRC
3. subject makes expiratory effort against pressure transducer A, which measures change in P
4. transducer B measures decrease in pressure of box, giving the change in volume

V = FRC = (-Pt * dV)/dP

this method can be used to measure the “trapped air”

Question 13

normal values for dead space volume and alveolar volume and what this means for ventilation

Answer 13

if tidal volume = 500 mL
-dead space = 150 mL
-alveoli = 350 mL
so while total ventilation (if 12 breaths/min) = 6000 mL/min, the dead space gets 1800 mL of that, thus the alveoli get only 4200 mL

Question 14

effects of alveolar hypoventilation

Answer 14

alveolar hypercapnea (increased PACO2) and hypoxia (decreased PAO2)
-decreased pH thus acidosis

Question 15

effects of alveolar hyperventilation

Answer 15

alveolar hypocapnea (decreased PACO2) and hyperoxia (increased PAO2)
-increased pH thus alkalosis

Question 16

what are the normal PACO2 and PAO2

Answer 16

PACO2 = 40 mmHg
PAO2 = 100 mmHg

Question 17

why does PO2 decrease (and PCO2 increase) slightly in the beginning of inspiration?

Answer 17

there is still some CO2 trapped in the dead space

Question 18

Fowler Method

Answer 18

single breath analysis of dead space; principle is that expired CO2 comes exclusively from alveoli and not from anatomic dead space

1. subject breathes in air with negligible CO2, exhales into spirometer while F CO2 in expired gas is measured
2. use FECO2 to measure V of dead space
3. as exhales, FECO2 rises from low (from dead space) to plateau near 0.05 (due to mixing)