Physiology Flashcards
(21 cards)
What would be the value of the respiratory quotient if a patient was receiving an IV of glucose solution?
RQ = 1.0
What would be the value of the respiratory quotient if a patient was hypoglycemic or a diabetic relying on fatty acid metabolism?
RQ = 0.7
What is the value of the respiratory quotient when you consume a mix of fuels?
RQ = 0.8
What is the equation used to solve Alveolar O2 (PAO2)?
(PIO2)
PAO2 = Inspired O2 - O2 consumed
PAO2 = ((Patm - Ph2o) FiO2) - (PaCO2/RQ)
Patm = 760 mmHg at sea level Ph2o = 47 mmHg FiO2 = 21% (0.21) ALWAYS RQ = 0.8 (unless diet specified)
How do you calculate the Alveolar-Arterial O2 Gradient?
What does a high or low value indicate?
A-a O2 Gradient = PAO2 - PaO2
In a perfect world, a normal value would be zero as the PaO2 and PAO2 would be the same. However, a normal value is considered to either be <12 mmHg or 8+(20% of patient’s age)
High value indicates process of gas exchange is impaired by some disease process.
How does a decrease in V/Q ratio affect O2 and CO2 levels?
Ventilation is not keeping pace with perfusion
Alveolar O2 levels will decrease, which lead to a decrease in arterial O2 levels (PaO2)
Alveolar CO2 levels will increase (not getting rid of it as fast), also leading to an increase in arterial CO2 levels (PaCO2).
How does an increase in V/Q ratio affect O2 and CO2 levels?
An increase in V/Q ratio means that ventilation is in excess of the metabolic needs being met by perfusion.
We blow off CO2 (lower PaCO2) and increase our PAO2 and PaO2.
How does the apex of the lung compare to the other segments of the lung when it comes to ventilation, perfusion, and V/Q (when standing upright)?
Apex of the lung has the least amount of perfusion due to gravity.
Apex has relatively high ventilation.
V/Q ratio at the apex is high.
How does the base of the lung compare to the other segments of the lung when it comes to ventilation, perfusion, and V/Q (when standing upright)?
Base of the lung has the greatest amount of perfusion due to gravity.
Base of the lung has the least amount of ventilation
V/Q ratio is low in the base of the lung.
What happens when the V/Q ratio is infinity?
This occurs when there is nearly 0 perfusion occurring, most likely due to a pulmonary embolism blocking blood flow.
High ventilation with very low perfusion.
Any blood able to pass through will be very well oxygenated and have very low CO2.
Blood that can’t get to area affected by the embolism gets shunted to other parts of the lung (leading to a low V/Q ratio in those parts of the lung).
Energy is wasted bringing ventilation to part of lung that has now become Anatomic dead space.
What happens when the V/Q ratio is 0?
This occurs when there is 0 ventilation, likely due to inhalation of an object that blocks airway.
Causes blood to leave alveoli in exact condition as when it entered (resembling venous blood).
Wasted cardiac effort sending blood to lungs even though no gas exchange could occur. This is known as a PHYSIOLOGICAL SHUNT
Explain how Hypoxic vasoconstriction works to normalize V/Q ratio.
Hypoxic vasoconstriction occurs when the V/Q ratio is low (lots of blood, too little ventilation)
Hypoxic vasoconstriction causes blood coming into affected area to be directed to other parts of the lung
Decreased perfusion of hypoxic region will raise the V/Q ratio and bring arterial blood gas levels closer to normal.
Explain how Bronchoconstriction works to normalize V/Q ratio.
Bronchoconstriction occurs when the V/Q ratio is high (poor blood perfusion, high ventilation)
Bronchi constrict to increase airway resistance and decrease amount of ventilation coming into an area not well perfused (WILL NOT SHUT COMPLETELY)
Limits amount of alveolar dead space and minimizes “wasted” work that occurs within the alveolar dead space
How does COPD/Emphysema affect the V/Q ratio?
COPD/ Emphysema cause destruction of alveoli (creating large air spaces) and loss of capillaries in lungs
Large spaces = some air getting in does not get close to blood cells
Loss of capillaries = some areas of lung not getting much blood while other areas are getting too much blood
Some areas of lung will have HIGH V/Q ratio (good arterial blood gases; not enough perfusion to carry)
Some areas of lung will have LOW V/Q ratio (Poor supply of gases to blood cells; but lots of blood going to area)
This explains the hypoxia and hypercapnea seen in this disease
What is hypoxia?
INADEQUATE oxygen available for use BY THE TISSUES
What is Anoxia?
TOTAL ABSENCE of oxygen being delivered to the tissue
What is hypoxemia?
Low oxygen content in the BLOOD
What is Hypoxic Hypoxia?
PaO2 reduced due to PAO2 (alveolar) (e.g., high altitude)
OR blood is unable to equilibrium with alveolar air (diffusion impairment; e.g., emphysema or fibrosis)
What is Anemic Hypoxia?
Lungs are in perfect working condition
O2 carrying capacity of blood is reduced
Ex: Carbon Monoxide produces anemic hypoxia by binding to Hb strongly, preventing oxygen from binding
What is Circulatory Hypoxia?
Lungs are in perfect working condition and blood O2 carrying capacity is normal.
Heart cannot pump blood to tissues OR arteries leading to tissue are blocked by clots, etc..
Ex: Sickle Cell Anemia can cause blockage in arteries (can also cause Anemic Hypoxia due to destruction of sickle cells)
What is Histotoxic Hypoxia?
Lungs in perfect working condition, blood O2 carrying capacity normal, and no issues delivering blood to tissues
Cells are poisoned. The tissue itself is unable to use the oxygen delivered to it.
Ex: cyanide poisons systems that utilize O2 to create energy
