control of breathing

Question 1

respiratory centre input

Answer 1

reflex/automatic brainstem only (not voluntary behavioural motor cortex or emotional limbic system, which are only when awake);uses bulbospinal pathway from respiratory neurones of medulla

Question 2

what is the PreBotzinger complex

Answer 2

network of cells (not pacemaker) in medulla brainstem which reciprocally inhibit each other to generate rhythm; close to surface of medulla to detect pH in CSF based on CO2 levels

Question 3

change in minute ventilation and SaO2

Answer 3

breathing becomes more shallower in sleep but at same rate (hypoventilation); minute ventilation decreases (lower tidal volume); SaO2 decreases very slightly but barely changes as on flat of oxygen-dissociation curve

Question 4

changes in PaO2 with sleep

Answer 4

PaO2 reduces but saturation stays high (oxygen saturation curve); if lower PaO2 when awake, much lower saturarion when asleep (as curve)

Question 5

changes in PaCO2 with sleep

Answer 5

PaCO2 increases slightly when asleep as tidal volume decreases; if it doesn’t you won’t breathe as no change in pH detected

Question 6

hypercapnia: ventilatory sensitivity to CO2

Answer 6

when asleep less sensitive to CO2 hence bigger increase in PaCO2 when asleep to breathe

Question 7

apnoeic sleep threshold and central sleep apnoea

Answer 7

PaCO2 threshold at which you don’t breathe by reducing tidal volume - must exceed to stimulate breathing; central sleep apnoea is the failure of tidal volume to decrease due to issue in medulla or muscles controlled by medulla (stroke or central congenital hypoventilation syndrome), so no effort made to breathe

Question 8

obstructive sleep apnoea

Answer 8

upper airway above trachea (no cartilage) becomes obstructed when asleep (obesity, size of jaw), so effort to breathe but ineffective (thorax and abdomen still work when airflow ceases)

Question 9

causes of occlusion of phalangeal airway in obstructive sleep apnoea

Answer 9

reduced upper airway muscle activity as loses tone and becomes floppy; negative intra-luminal pressure during inhalation can force shut rather than allow air to enter - exacerbated by excess adipose tissue in tongue and neck as applies external positive pressure

Question 10

obstructive sleep apnoea cycle

Answer 10

effort to breathe against closed airway → arousal → increased ventilation → sleep restarts → decreased accessory muscle function leads to hypercapnia and return of apnoea; can lose emotional intelligence due to being very tired as no deep sleep

Question 11

how is COPD exacerbated by sleep

Answer 11

further left on SaO2 curve so less SaO2 (accessory muscles paralysed so worse)

Question 12

effect of heart failure on central sleep apnoea

Answer 12

causes pulmonary congestion, which irritates receptors, causing hyperventilation; this lower PaCO2 below apnoeic threshold, causing cessation of breathing due to central sleep apnoea