Clinical Correlations to Hypercapnia/ Hypoxemia Flashcards
What cells make up the carotid body? What do they do?
Glomus cells- sense chemicals in the blood and associate with the Glossopharyngeal nerve
Sheath cells- surround the glomus cells to maintain and support them
How does the body control respiration? Where are these controls?
Chemoreceptors
Central-Pons, Medulla
Peripheral-Carotid, Aortic Bodies
Mechanoreceptors
Lung, Nose, GI tract
Emotional
Hypothalamus
What do chemoreceptors sense?
PaO2, PaCO2, [H+]
Which has the dominant CO2 response: peripheral or central chemoreceptors?
Central (70% response)
How are hydrogen ions produced? How are they measured?
Produced during metabolic processes (mainly oxidative phosphorylation)
Measured as pH (negative log of concentration)
What is the response to increased PaCO2?
Increased breathing rate and volume
What is special about the peripheral receptors?
They can measure Oxygen (central chemoreceptors can’t)
What determines PaO2?
P_O2
Other factors contribute, but are far less important
How can the blood be oxygenated?
Oxygen bound by hemoglobin
Dissolved oxygen
What do chemoreceptors sense for oxygen?
They sense dissolved oxygen only
How can dissolved oxygen be calculated?
P_O2*0.003
This is Henry’s law.
Does hypoxia always trigger a ventilation response?
No, if dissolved oxygen is normal, but bound oxygen is low, there will be no ventilation response.
How does the abdomen move in normal respiration?
How does it move in respiratory distress?
Outwards on inhalation, inwards on exhalation
Inwards on inhalation, outwards on exhalation
What controls phrenic nerve firing?
What spinal levels make up the phrenic nerve?
Central chemoreceptors
C3, C4, C5
What are symptoms of hypercapnic respiratory failure?
Somnolent (drowsiness)
Asterixis (hand tremor on wrist extension)
Hypo-motile chest wall
What is disease typically has hypercapnic respiratory failure? Why?
COPD
Air- trapping leads to long-term chemoreceptor adaptation to hypercapnia
Why is giving oxygen to someone with long-term hypercapnia adaptation a bad idea?
Long-term hypercapnia adaptation means that the ventilation drive is controlled by oxygen only. When oxygen is given, it suppresses ventilation.
What is hypoxic vasoconstriction?
Shunting blood away from hypoxic areas of the lung (and presumably shunting more blood to highly oxygenated areas)
Why can hypoxic vasoconstriction cause problems when giving oxygen to diseased patients?
Giving oxygen will divert blood to the lung, but the lung may still be unable to diffuse the oxygen into the blood.
Paradoxically, less blood is getting oxygenated!
What is the Haldane effect?
Deoxygenated hemoglobin can bind CO2 to act as a buffer.
