Chapter 8: Control of Ventilation Flashcards
Where does the normal rhythmic pattern of breathing originate?
Brainstem
When do expiratory neurons fire? Significantly, when do they not fire?
During forceful breathing. The expiratory area of the medulla is quiescent during quiet breathing.
Where is the pneumotaxic center located?
Upper pons
What facet of breathing does the pneumotaxic center regulate?
Appears to “switch off” or inhibit inspiration - this regulates inspiratory volume, and secondarily, respiratory rate
Where is the apneustic center located?
Lower pons
What is the apparent function of the apneustic center?
Impulses from the apneustic center have an excitatory effect on the inspiratory area of the medulla.
What happens to a person in whom the apneustic center is damaged?
Abnormal breathing pattern - prolonged inspiratory gasps (apneuses) interrupted by transient expiratory efforts
What part of the brain can override the respiratory center?
Cortex
Which is more difficult, voluntary hyperventilation or voluntary hypoventilation?
Voluntary hypoventilation
What nerves carry output from the respiratory center?
Phrenic nerves (C3-C5) control the diaphragm, other nerves from the spinal column carry signals to the intracostals, abdominals, and accessory muscles such as the SCM
Where are the central chemoreceptors located?
Ventral surface of the medulla
What medium surrounds the central chemoreceptors?
Brain ECF
To what stimulus are the central chemoreceptors responsive?
CO2, indirectly, but no O2. CO2 diffuses across the BBB all the way to CSF, pH in CSF goes down, H+ signal is then seen in the ECF, trigerring the central chemoreceptors.
How quickly do H+ and HCO3- diffuse across the BBB?
Not at all. pH response is modulated by CO2 diffusion only
Which is more pH-responsive to changes in [CO2], blood or CSF?
CSF - does not have nearly the buffering capacity that blood has
Describe the stimuli for the peripheral chemoreceptors
Carotid bodies - CO2, O2, and pH
Aortic bodies - CO2 and O2 (not pH)
Which chemoreceptors react more quickly to changes in PCO2?
Peripheral
Which receptors are more important for regulating ventilation in response to PCO2?
Central
How does ventilatory response to PCO2 change during sleep?
Decreases
In a patient with chronic hypoxia, how does ventilation response change?
In chronic hypoxia, compensation for abnormally high PCO2 through renal mechanisms (bicarb) means the central receptors are “tricked” into being comfortable with an abnormally high PCO2. Thus, hypoxia is the only stimulation to breathe. Treating this condition with oxygen results in a patient suffering from depressed ventilatory drive, despite high PCO2
What is the most important stimulus controlling the level of resting ventilation?
The pH of CSF on central chemoreceptors
What paradoxical conditions are observed during moderate exercise? Why is this paradoxical?
Arterial PO2 increases
Arterial PCO2 decreases
Arterial pH is normal
This is paradoxical b/c we’re not sure what is stimulating heavy breathing during exercise! Might be joint motion, lots of theories
What reflex helps to inflate the newborn lung?
Hering-Breuer inflation reflex
What condition may contribute to SIDS?
Uncoordinated respiratory muscle activity, especially during sleep, i.e., thoracic muscles try to inspire while the abdominal muscles expire
What is the Hering-Breuer inflation reflex?
Mechanism by which pulmonary stretch receptors in the smooth muscle of airways prevent over-inflation of the lungs during large inspirations
What nerve carries the signals of the Hering-Breuer reflex?
Large myelinated fibers in the vagus nerve
