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Respiratory Part 10

A-a gradient for O2 A-a gradient is used to distinguish whether it is pulmonary or non-pulmonary. Larger the A-a gradient, the larger the mismatch/shunt
Describe how the gas from the Alveolus with high PO2 mixes with gas from Alveolus with low PO2 The resultant gas mixture is the arithmetic mean.
Describe how blood with high PO2 mixes with blood with low PO2 The resultant blood mixture is less than the arithmetic mean.
What happens when blood leaves an alveolus with a low VA/Qc and mixes with blood from an alveolus with hihg VA/Qc? The mixture will have a lower PaO2 than the mixed alveolar gas from which those bloods originated.
True or False: A-a gradient is positional in a normal individual True. When a person lays down the A-a gradient will go away.
True or False: A-a gradient in individual with pulmonary disease is positional False. No matter how the person is positioned, the A-a gradient will be there.
True or False: A-a gradient is abnormal is individual with non-pulmonary disease False. A-a gradient is normal when individual has non-pulmonary disease
Dorsal Respiratory Group (DSG) DSG of neurons in the medulla contains cells that discharge in phase with inspiration. The Ventral Respiratory Group fires with inspiration and expiration
Mechanoreceptors in small airways 1. Small airways-stretch receptors stretched in inspiration leads to increase in afferent activity to DRG. Cease inspiration so that the lung limits is size.
Mechanoreceptors, free nerve endings (J-receptors) Pulmonary edema. Causes rapid, shallow breathing
Chemoreceptors (Peripheral) Aortic body: Aff 10 to DRG, increase in VA. Carotid body: Aff 9 to DRG, increase in VA.
Carotid body Per gm of tissue receives more blood than any other. All needs for O2 can be utilizing O2 dissolved in blood. Only responds to PO2, can do w/o hemoglobin. Stimulus: Drop in PaO2 at about 60mmHg. Not responsible for breath by breath. Does not Adapt.
What does a decrease in pH and fall in blood flow do to the carotid body? Decrease in pH will lead to extremely deep and rapid pattern of breathing. A drop in blood flow can compromise O2 delivery to the carotid body.
Central Chemoreceptors Located on the ventrolateral surface of the medulla in contact with CSF. Stimulus: CSF H+ (reflection of CO2). It is very sensitive & responsible to breath by breath control. System does adapt.
How does central chemorecptors adapt? Usually takes about 12-24 hours. It adapts by pumping HCO3 into or out of the CSF. HCO3 buffers the acidosis caused by the H+
Severe pulmonary disease Drop in PaO2 drives respiration. Increase in PaCO2 is adapted to. Peripheral chemoreceptors respond to hypoxia.
In Anemia will A-a gradient be in normal range? Yes
What does the presence of Carbon monoxide do to O2 affinity to hemoglobin? Makes O2 hang onto Hb much tighter.



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