207 -Obstructive Sleep Apnoea

Question 1

define obstructive sleep apnoea

Answer 1

the stopping or slowing of breathing during sleep due to closing of the upper airway. Sleep causes pharyngeal incompetence (muscles relax) causing a collapse of the upper airway. Incr. in PaCO2 causes the px to wake up causing broken sleep and daytime sleepiness.

Question 2

what are the risk factors for OSA?

Answer 2

• Obesity/lower facial shape *tonsil/nasal problems
• hypothyroidism *alcohol/sedatives *smoking
• being male *ty II DM *snorers *40-60 y/o

Question 3

how might a px with OSA present?

Answer 3

• Excessive daytime sleepiness - assess with Epworth Sleepiness scale
• snoring
• partner notices px stop breathing at night
• morning headaches, dry throat, anxiety, poor concentration, irritability
• sweats, reduced libido

Question 4

how would you investigate suspected OSA?

Answer 4

• overnight oximetry tracing - shows pattern of regular desaturation
• measure nasal flow
• measure throax/abdo movements

Question 5

how would you manage a px with OSA?

Answer 5

• treat underlying disorder - hypothyroidism, bariatric surgery
• lifestyle changes - smoking, alcohol in eve, weight, posture
• ventilation - Continuous positive airway pressure (CPAP) - continuously blows column of air down airway

Question 6

what can untreated OSA lead to?

Answer 6

• personality changes
• sleepiness at work/job problems
• relationship problems & sexual dysfunction
• risk of sudden death and cardiac problems
• commonest cause of 2ry hypertension
• poor diabetic control

Question 7

what ABG changes would you see in a px with type I respiratory failure?

Answer 7

• PO2 low
• PCO2 normal or low
• pH normal or alkalytic
• HCO3 normal or low

Question 8

what ABG changes would you see in a px with type II respiratory failure?

Answer 8

• PO2 low
• PCO2 high
• pH acidotic or normal
• HCO3 high or normal

Question 9

what FEV1 and FVC changes would you see in a px with restrictive lung disease

Answer 9

both FEV1 and FVC reduced and ration between them normal or incr. as full expiration achieved rapidly

Question 10

what ABG changes would you see in a px with respiratory acidosis and why?

Answer 10

caused by incr. in CO2 so incr. PaCO2, decr. pH & incr HCO3. Acute - slight incr. in HCO3 as more CO2 for dissociation. compensated - kidneys compensate over time gently incr. HCO3 retention

Question 11

what ABG changes would you see in a px with respiratory alkalosis and why?

Answer 11

caused by decr. in CO2 so decr. PaCO2, incr. pH & decr HCO3. Acute - slight decr. in HCO3 as more CO2 eliminated. compensated - kidneys compensate over time gently decr. HCO3 retention

Question 12

what ABG changes would you see in a px with metabolic acidosis and why?

Answer 12

caused by incr. in H+ due to incr. lactic acid production/decr. H+ elimination (renal failure) so normal/decr. PaCO2, decr. pH & decr HCO3. Acute - marked decr. in HCO3 as used to buffer acid. compensated - further decr. HCO3 due to hyperventilation

Question 13

what ABG changes would you see in a px with metabolic alkalosis and why?

Answer 13

caused by decr. in H+ due to loss of H+(vomit gastric acid)/excess bicarbonate infusion so normal/decr. PaCO2, incr. pH & incr HCO3. Acute - marked incr. in HCO3 as no acid to conjugate. compensated - further incr. HCO3 due to hypoventilation

Question 14

where does the automatic rhythm of breathing originate and what does it act upon?

Answer 14

the medulla oblongata (lowest segment of brainstem). Impulses are sent down the spinal cord to phrenic nerve & intercostals & via CN12 to the pharynx larynx. Compression of medulla causes respiratory depression

Question 15

what 3 medullary regions are responsible for impulses driving respiration?

Answer 15

• Parafacial Respiratory Group (PFRG) - originate action potentials just before inspiration
• Dorsal Respiratory Group (DRG) - action potentials during inspiration (stimulate muscles of insp)
• Ventral Respiratory Group (VRG) - mostly action potentials during expiration

Question 16

From where do the 3 medullary regions receive inputs from?

Answer 16

• chemoreceptors - via CN9/10 - monitor arterial blood gas/acid conc.
• higher CNS (cerebral cortex, hypothalamus) via Pontine Respiratory Group (PRG) in pons which fine tunes respiratory rhythm (sets vol when insp turns to exp)

Question 17

what ventilatory rhythm pacemaker models are there?

Answer 17

• distributed network model
• multiple oscillator models
• single oscillator models
• couple oscillator model - insp rhythm originates in pre botzinger complex (PBC) and exp in PFRG

Question 18

what is the group pacemaker hypothesis of signal generation?

Answer 18

• beginning of cycle - all neurones hyperpolarised
• recovery - some neurones recover and depolariseto cause Action potential
• recurrent excitation - AP stimulate other neurones to depolarise
• burst - incr. stimulation leads to all neurones to depolarise

Question 19

what innervates the muscles of respiration

Answer 19

• phrenic nerve supplies diaphragm for C3/4/5

* intercostals supplied by respective thoracic segments

Question 20

where in the brain does voluntary control originate?

Answer 20

from cerebral cortex via pyramidal tracts direct to effector muscles - voluntary control bypasses the medulla (Px can still breathe if medulla damaged)
reflexes can also modify resp rhythm via vagus (sneeze/cough in U/LRT, pulmonary stretch receptors, irritant receptors in epithelial cells, j-receptors in alveolar walls)

Question 21

why is chemoreception important?

Answer 21

maintains PaO2 to maintian O2 supply to tissue

maintains PaCO2 to keep pH of tissues constant

Question 22

how do chemoreceptors affect ventilation during exercise?

Answer 22

ventilation incr with work as chemoreceptors sense incr. in PaCO2 (due ro CO2 production in metabolism) to keep PaO2 and PaCO2 constant

Question 23

which chemoreceptors sense CO2 and O2?

Answer 23

CO2 - both central and peripheral (main stimulus for breathing)
o2 - peripheral only (stimulates breathing when PaO2 <60mmHg)

Question 24

where are central chemoreceptors located and what stimulates them?

Answer 24

• neurones on surface of ventro-lateral medulla (medullary raphe, retrotrapezoid)
• stimulated by [H+} in CSF that bathes medulla (indirectly determined by PaCO2 as CO2 diffuses from cerebral arteries to CSF and some [H+]blood - central more sensitive to resp acidosis than metabolic but slow acting due to diffusion

Question 25

where are peripheral chemoreceptors located and what stimulates them?

Answer 25

• carotid bodies
• stimulated by PaO2 when <60mmHg and some PaCO2 & [H+] - glomus cells sense blood gas levels and send to medulla via vagus. Fast acting due to thin membrane between blood and cells