Respiratory Physiology Flashcards
Which Lung Volumes can be measured with the spirometer
Tidal Volume and Vital Capacity
Which lung Volumes cannot be measure with the spirometer
Total Lung Capacity (TLC), FRC and RV
How are TLC, FRC and RV measured
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
What is Boyle’s law?
PV = K, at constant temperature, used in the body plethysmograph
Tidal Volume
500ml
Anatomical dead space
150ml
total ventilation =
VT x breaths/min; 500 x 15 = 7500ml/min
alveolar ventilation =
(500 - 150) x 15 = 350 x 15 = 5250ml/min
How to calculate alveolar ventilation by measuring the concentration of CO2 in expired gas
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
The Alveolar Ventilation Equation
VA = VCO2 / FCO2
FCO2 is proportional to PCO2 by a constant K, therefore
VA = VCO2 / PCO2 x K
Why is the relationship between alveolar ventilation and PCO2 of crucial importance?
According to the Alveolar Ventilation Equation, if alveolar ventilation halves then the alveolar (and therefore the arteria)l pressure of CO2 will double!
How can anatomical dead space be measured?
Fowlers method using nitrogen concentration following a single inspiration of oxygen
How is physiological dead space measured?
Bohrs method. It measures the volume of the the lung that does not eliminate CO2 by using arterial and expired CO2
What is the difference between anatomical and physiological dead space?
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.
What does inhalation of radioactive xenon gas demonstrate?
Demonstrates that the lower regions of the lung ventilate better than the upper regions.
what is the anatomical unit of the lung distal to the terminal bronchiole
the acinus
what demarcates the conducting zone from the transitional zone
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.
alveolar volume is
2.5 - 3 Litres
diameter of a pulmonary capillary
7 - 10 um, just enough for a RBC
mean pulmonary artery pressure
15mmHg
how thick is the blood gas interface?
extremely thin, 0.2 - 0.3um
What is the surface area of the blood gas interface?
enormous, 50 - 100m2 obtained by having about 500 million alveoli
What is a consequence of large increases in capillary pressure or lung volume
can damage the blood gas barrier with bleeding and leakage of fluid
how long does a RBC spend in the pulmonary capillary network?
0.75 seconds
The lung has 2 different circulations?
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.
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?
Cells lining the alveoli secrete Surfactant which acts to lower the surface tension inside the alveoli, helping to prevent collapse.
which cells secrete the mucous of the mucocillary escalator
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.
What happens to inhaled particles in the alveoli?
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.
How does air flow differ from in the upper conductive zones to the lower respiratory zones?
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.
