Flashcards in Cremo 2: Factors that control CO2 and O2 in alveoli and blood Deck (46)
Sensors of blood CO2 levels
1. Central chemoreceptors in medulla
2. Peripheral chemoreceptors in carotid and aortic bodies
Arterial CO2 is controlled by two rates. What are they?
1. Metabolic production of CO2 (VCO2)
2. Alveolar ventilation (VA)
PCO2 ventilation equation
PaCO2 = VCO2 * 0.863 / VA
H-H equation (acid-base)
pH = 6.1 + log [HCO3-]/0.03(PaCO2)
Alveolar gas equation (oxygenation)
PAO2 = PIO2 - 1.2(PaCO2)
What is a buildup of CO2 in the blood due to?
A failure in some component of the respiratory system (not an increase in metabolic CO2 production)
What is VCO2?
Rate of CO2 production by metabolism
What two rates control PaCO2?
VA: rate of alveolar ventilation by lung
VCO2: rate of CO2 production by metabolism
Alveolar ventilation and CO2 production double during moderate exercise in a 24-year old man. What is the effect on PaCO2?
No effect! Both variables change together!
Clinical definition of hypercapnia or hypoventilation.
PaCO2 of >45mmHg
Clinical definition of hypocapnia or hyperventilation.
PaCO2 of <35mmHg
Normal PaCO2 levels
A 32 year old male has just run into the classroom after being late for class. He can be considered to be hyperventilating if his PaCO2 is at what level?
The only physiologic reason for elevated PaCO2
A level of alveolar ventilation inadequate for the amount of CO2 produced and delivered to the lungs.
What does VA refer to in the PCO2 equation?
VA = VE - VD = total volume of lung - dead space
What is the equation for VE, or total ventilation rate?
VE = Total ventilation rate (L/min) = respiratory rate · tidal volume
Is dead space ventilated? Is it perfused?
Anatomic dead space + all other dead space
Physiologic dead space
3 processes required for gas exchange
1. Gas entering and leaving
2. Blood flow = perfusion
3. Diffusion of gases across capillary membrane
What is another way to think of VA?
VE - VD
Level of VE needed to keep PaCO2 constant
Minute ventilation requirement
In a normal lung, what is PACO2? What is PaCO2?
In a normal lung, what is PvCO2?
What is a typical PAO2 for a normal lung?
Is the PAO2 equal to the PaO2 in a normal lung?
No, PaO2 is slightly lower
PO2 at sea level
159mmHg = 0.21 * 760mmHg
PO2 at the trachea
PaO2 at the terminal respiratory units
Anatomic unit used by pathologists
10 to 12 terminal respiratory units