Ventilation and Lung Mechanics

Question 1

47 mm Hg

Answer 1

vapor pressure at body temperature (37C)

Question 2

Dalton’s Law

Answer 2

the pressure exerted by one gas in a gas mixture is the same pressure it would exert if it occupied the volume alone

Question 3

fractional concentration of atmospheric O2

Answer 3

.21

Question 4

fractional concentration of atmospheric N2

Answer 4

.79

Question 5

fractional concentration of atmospheric CO2

Answer 5

0

Question 6

VC

Answer 6

Vital Capacity- the max V that can be exhaled after max inspiration

VC= IRV + TV + ERV

Question 7

FRC

Answer 7

Functional Residual Capacity- gas V in lungs at the resting expiratory level

Measured by one of three methods:

1) nitrogen washout
2) helium dilution
3) blody plethysmography

Question 8

TV

Answer 8

Tidal Volume- volume of gas inspired/exhaled during normal breathing

Question 9

RV

Answer 9

Residual Volume- volume of gas in the lungs at the end of maximal expiration

RV= FRC-ERV

Question 10

TLC

Answer 10

Total Lung Capacity- volume of gas in the lungs at end of max inspiration

TLC= VC + RV

Question 11

IC

Answer 11

Inspiratory Capacity- max V that can be inspired from the resting expiratory level

Question 12

IRV

Answer 12

Inspiratory Reserve Volume- max V that can be inspired from end-tidal inspiration

Question 13

ERV

Answer 13

Expiratory Reserve Volume- max V that can be exhaled from the resting expiratory level

Question 14

volumes a spirometer can’t measure

Answer 14

1) RV
2) FRC
3) TLC

Question 15

Lung Volume Relationships

Answer 15

For Age Range 15-34 (calculated by Fowler in 1950s)
RV/TLC= .2
RV=VC(.25)
TLC= VC(1.25)

FRC is .4-.5 TLC

Question 16

FVC

Answer 16

Forced Vital Capacity- The volume of air exhaled during the forced expiration maneuver.

assume same as vital capacity

Question 17

FEV 0.5

Answer 17

Forced Expiratory Volume- The volume of gas exhaled during the first 0.5 sec of a forced expiration.

Question 18

FEV 1.0

Answer 18

The volume of gas exhaled during the first 1.0 sec of a forced expiration.

Question 19

FEF 25-75

Answer 19

Forced Expiratory Flow- The average rate of gas flow measured between 25% and 75% of the forced vital capacity.

Question 20

obstructive ventilatory defect

Answer 20

• FVC most often (but not always) less than 70% of the predicted value
• The value of FEV(1.0) divided by the FVC is less than 0.75 “disproportionate reduction of maximal airflow”
• The other lung volumes, such as total lung capacity, are normal or above normal.

Question 21

restrictive ventilatory defect

Answer 21

• The forced vital capacity is always less than 70% of the predicted value
• The value of FEV1.0 divided by the FVC is 0.75 or greater
• Other lung volumes, in particular the total lung capacity, are less than 70% of the predicted value

Question 22

normal ventilatory pattern

Answer 22

• FVC greater or equal to 70% predicted FVC for that person’s sex, age and height
• FEV(1.0)/FVC > 0.75
• TLC (calculated by 1.25 x FVC) greater or equal to 70% predicted

Question 23

flow-volume loop

Answer 23

tracing air flow in liters/sec (y-axis) as a function of volume in liters (x-axis)

• The difference in volume between the left and right side of the loop is the forced vital capacity
• FEF(50) or V(.)50- the forced expiratory flow at 50% of the vital capacity is the index of expiratory flow commonly obtained from a flow-volume loop

Question 24

anatomic dead space

Answer 24

volume of air in the conducting airways

equal to weight in mL

Question 25

physiologic dead space

Answer 25

anatomic dead space, plus any alveolar regions of the lung that, due to disease, have lost their ability to perform gas exchange with the blood VC - PhDS = max V air that can reach functioning alveoli with a single breath measured by determining the partial pressure of CO2 in expired gas and comparing it to the partial pressure of CO2 in the blood

Question 26

dead space equation

Answer 26

VD = VT x (PaCO2 - PECO2)/PaCO2

Question 27

pressure difference

Answer 27

dP = P(in) - P(out)

Question 28

transpulmonary pressure

Answer 28

PA - Ppl

Question 29

dP across chest wall

Answer 29

Ppl - Patm -> Ppl bc Patm = 0

Question 30

dP across resp. system

Answer 30

PA - Patm -> PA bc Patm = 0

Question 31

ERlung

Answer 31

Elastic Recoil Pressure = PA - Ppl when glottis is open and no air flow occurs, PA = 0 ERlung = -Ppl working to collapse the lung at a given lung volume same as transpulmonary pressure Ptp

Question 32

ERcw

Answer 32

Elasticity of the chest wall = Ppl - Patm = Ppl

Question 33

lung compliance

Answer 33

how easy or difficult it is to inflate the lung = dV/dP (L/cmH20)

Question 34

LaPlace equation

Answer 34

P = 2y/r derived from: (pressure volume work) = (surface tension work) ->(P x d(4/3PIr^3)) = (y x d(4PIr^2) ->(P x (4PIr^2)) = (y x (2PIr)

Question 35

PA

Answer 35

``` Alveolar Pressure determines air flow PA = ERlung + Ppl 0 = no flow neg = flow into the lung pos = flow out of lung ```

Question 36

V(.)

Answer 36

``` rate of flow V(.)= dP/R where V(.) = airflow (L/sec) dP = (PA -Patm) (cm H20) R = airway resistance in cm (H20/(L/sec)) normal resistance is .5-2 (H20/(L/sec)) ```

Question 37

Poiseuille equation

Answer 37

laminar: R = 8ηl/PIr^4 turbulent: R = 8ηl/PIr^5 η is the viscosity of the gas, l is the length of the airway, and r is the radius of the airway

Question 38

laminar flow

Answer 38

Laminar flows are linearly related to the driving pressures, such that V(.) = ΔP/R resistance to flow is dependent upon the gas viscosity, and independent of gas density

Question 39

turbulent flow

Answer 39

resistance developed by the gas in a given airway is not constant, but increases as the rate of flow increases resistance developed by the gas in the airway is dependent upon the density of the gas, rather than the viscosity V(.) = ΔP^.5/K where K is a constant that if flow is turbulent, in order to increase flow rate two-fold, driving pressure must increase four-fold.

Question 40

equal pressure point

Answer 40

as air flows from the alveoli to the mouth, the air pressure in the airway will change from alveolar pressure (greater than pleural pressure) to atmospheric pressure (less than pleural pressure). Somewhere along the way, the air pressure in the airway will be equal to the pleural pressure, and this is called the equal pressure point

Question 41

dynamic compression

Answer 41

only occurs during forced expiration major cause of flow limitation due to compression of the airways when the airway pressure is less than the surrounding pleural pressure beyond (~10cm H20) no further increase in flow rate is possible