Respiratory Physiology

Question 1

Which Lung Volumes can be measured with the spirometer

Answer 1

Tidal Volume and Vital Capacity

Question 2

Which lung Volumes cannot be measure with the spirometer

Answer 2

Total Lung Capacity (TLC), FRC and RV

Question 3

How are TLC, FRC and RV measured

Answer 3

Helium dilution technique or the body plethysmograph. Helium is used because of low solubility in the blood - i.e. it will not absorb from the lungs

Question 4

What is Boyle’s law?

Answer 4

PV = K, at constant temperature, used in the body plethysmograph

Question 5

Tidal Volume

Answer 5

500ml

Question 6

Anatomical dead space

Answer 6

150ml

Question 7

total ventilation =

Answer 7

VT x breaths/min; 500 x 15 = 7500ml/min

Question 8

alveolar ventilation =

Answer 8

(500 - 150) x 15 = 350 x 15 = 5250ml/min

Question 9

How to calculate alveolar ventilation by measuring the concentration of CO2 in expired gas

Answer 9

VCO2 = VA x %CO2/100

%CO2/100 is called the FCO2, therefore

VA = VCO2 / FCO2

Thus VA can be obtained by dividing the CO2 output by the alveolar fractional concentration of the gas

Question 10

The Alveolar Ventilation Equation

Answer 10

VA = VCO2 / FCO2

FCO2 is proportional to PCO2 by a constant K, therefore

VA = VCO2 / PCO2 x K

Question 11

Why is the relationship between alveolar ventilation and PCO2 of crucial importance?

Answer 11

According to the Alveolar Ventilation Equation, if alveolar ventilation halves then the alveolar (and therefore the arteria)l pressure of CO2 will double!

Question 12

How can anatomical dead space be measured?

Answer 12

Fowlers method using nitrogen concentration following a single inspiration of oxygen

Question 13

How is physiological dead space measured?

Answer 13

Bohrs method. It measures the volume of the the lung that does not eliminate CO2 by using arterial and expired CO2

Question 14

What is the difference between anatomical and physiological dead space?

Answer 14

anatomical dead space is the volume of the conducting airways = 150ml. Physiological dead space is the volume of gas that does not eliminate CO2. In normal subjects these two volumes are almost the same. The physiological dead space is increased in many lung diseases.

Question 15

What does inhalation of radioactive xenon gas demonstrate?

Answer 15

Demonstrates that the lower regions of the lung ventilate better than the upper regions.

Question 16

what is the anatomical unit of the lung distal to the terminal bronchiole

Answer 16

the acinus

Question 17

what demarcates the conducting zone from the transitional zone

Answer 17

The conducting zone includes the trachea, bronchi, bronchioles down to the terminal bronchioles. The transitional and respiratory zones begin where the terminal bronchioles become the respiratory bronchioles. The respiratory bronchioles are those which first have some alveoli budding off of them.

Question 18

alveolar volume is

Answer 18

2.5 - 3 Litres

Question 19

diameter of a pulmonary capillary

Answer 19

7 - 10 um, just enough for a RBC

Question 20

mean pulmonary artery pressure

Answer 20

15mmHg

Question 21

how thick is the blood gas interface?

Answer 21

extremely thin, 0.2 - 0.3um

Question 22

What is the surface area of the blood gas interface?

Answer 22

enormous, 50 - 100m2 obtained by having about 500 million alveoli

Question 23

What is a consequence of large increases in capillary pressure or lung volume

Answer 23

can damage the blood gas barrier with bleeding and leakage of fluid

Question 24

how long does a RBC spend in the pulmonary capillary network?

Answer 24

0.75 seconds

Question 25

The lung has 2 different circulations?

Answer 25

yes the pulmonary and the bronchial circulations. The bronchial circulation does not participate in gas exchange, it supplies the conducting airways down to about the terminal bronchioles. The blood flow through this circulation is a mere fraction of that through the pulmonary and in fact the lung can function without it as in the case of lung transplants.

Question 26

Imagine 500million bubbles, each 0.3mm in diameter all sitting on top of each other. This structure is inherently unstable i.e. prone to collapsing down. Liquids that line the alveoli produce surface tensions that develop large collapsing forces. How is this problem mitigated?

Answer 26

Cells lining the alveoli secrete Surfactant which acts to lower the surface tension inside the alveoli, helping to prevent collapse.

Question 27

which cells secrete the mucous of the mucocillary escalator

Answer 27

mucous glands and goblet cells secrete the mucous which is then propelled by millions of tiny cilia. These cilia can be paralysed by some inhaled toxins.

Question 28

What happens to inhaled particles in the alveoli?

Answer 28

They are gobbled up by macrophages that wander about. There are no cilia down that far. The macropharges then are removed by the lymphatics or the blood flow.

Question 29

How does air flow differ from in the upper conductive zones to the lower respiratory zones?

Answer 29

convective flow takes the air down to about the terminal bronchioles after that all movement of gasses is by simple diffusion because the air flow has slowed down by this point.