Control of Breathing

Question 1

Identify key structures responsible for automatic control of breathing rhythm and the sources of input to them.

Answer 1

Medulla: initiates breathing
- then, modified by higher structures in CNS and sensory input from central and peripheral chemoreceptors, mechanoreceptors in lung, chest wall etc.

DRG: main inspiratory neurons, drive inspiratory muscles. receive peripheral chemoreceptor/mechano input

VRG: main expiratory neurons, silent during quiet breathing
both in medulla

phrenic nerve supply motor output to diaphragm (c3,4,5)
intercostal nerves output to ab/intercostal muscles
CN supply UAW dilatory muscles

Stretch receptor in SM of airways respond to stretch in inflation, allows expiration to occur. Establish rhythm (CN 10)

Question 2

Specify the location of the central & peripheral chemoreceptors and describe their impact on ventilation in response to changes in arterial PCO2, PO2 and pH.

Answer 2

Peripheral chemoreceptors (carotid and aortic bodies)- respond to mainly decreased O2, also pH and CO2. ventilatory response is hyperventilation, lowers PaCo2 to below normal (hypocapnia) and raises O2

Central chemoreceptors (right below medulla)- respond to small changes PaCO2 via changes in [H+] in ECF. 
** arterial PCO2 = primary regulator of breathing

Question 3

Describe how metabolic acidosis accompanying intense exercise or diabetes impacts ventilation and arterial PO2 and PCO2

Answer 3

metabolic acids stimulate peripheral chemoreceptors increasing ventilation.
- lactic acid produced in skeletal muscle exercise
- diabetic ketoacidosis (Kussmaul breathing)
- ventilatory response = hyperventilation, ensuring hypocapnia and hyperoxia
(opposite effect if alkalosis)

Question 4

Specify the effect of hyperventilation and hypoventilation on
arterial blood gases (PCO2 and PO2).

Answer 4

hyperventilated- decrease in PCO2, increase in PO2

hypo=opposite

Question 5

Describe congenital hypoventilation syndrome, its treatment and
how it informs us about automatic versus the conscious/
voluntary control of breathing

Answer 5

breathing is adequate when awake (conscious), but not when sleeping
treatment: mechanical ventilation/diaphragm pacing
some have low ventilatory response to elevated CO2, low O2, acidosis