207- OSA

Question 1

What is OSA?

Answer 1

Obstructive sleep apnoea

Stopping or slowing of breathing during sleep due to obstruction or narrowing of the upper airway

Question 2

What is the incidence of OSA in the UK?

Answer 2

Men - 3-5%

Women - 1-2%

Question 3

What are the risk factors for OSA?

Answer 3

Obestiy
Smoking
Nasal problems
Tonsils
Hypothyroid
Facial shape
Alcohol use
Menopause
Neuromuscular diseases
Stoke

Question 4

What is the peak age of presentation of OSA?

Answer 4

40-60s

Question 5

What are the usual presenting symptoms of OSA?

Answer 5

Daytime = sleepiness, mornign headaches, dry throat, poor concentration, irritability, loss of libido

Nighttime = Snoring, Choking, Apnoeas, sweats, restlessness, vivid dreams, nocuria

Question 6

What tests can be done in OSA?

Answer 6

Overnight oximetry (look for o2 drops)
Sleep studies - limited channel embletta, visilab

Question 7

What is the management of OSA?

Answer 7

Treat underlying cause - loose weight, stop smoking

Gum Shields, CPAP

Question 8

How does CPAP work?

Answer 8

Blows air into airway to keep it constantly slightly open, wear it overnight
80% who try it carry on
Improves BP and diabetes too?!

Question 9

What are the consequences of OSA?

Answer 9

Untreated - increased mortality (46% risk of sudden death compared to 16%)
Snoring - impact for partner
Sleepiness - VERY DANGEROUS

Question 10

What type of respiratory failure does hypoventilation cause?

Answer 10

Type 2 - Low pO2, High pCO2, Low PH, High or normal HCO3

Question 11

What are the causes of hypoventilation?

Answer 11

CNS depression (drug OD)
Neuromuscular junction (snake bites, anaesthesia)
Chest Wall (broken ribs, TB distortion, weak resp muscles, phrenic nerve palsy)
Lung (massive ascites, obesity, COPD)

Question 12

What symptoms might be seen in type 2 resp failure/hypoventilation?

Answer 12

Sleepiness
Headaches
Ankle swelling

Question 13

What treatment is available for hypoventilation/type 2 resp failure?

Answer 13

Negative pressure (used to use iron lungs for TB)
Positive pressure (CPAP + BiPAP)

Question 14

What evidence showed that the origin of respiratory rhythm is outside the thorax?

Answer 14

Galen (2nd century AD)
Sword cuts
Cut below C3 - Paralyses limbs but breathing controlled ok
Cut above C3 - Paralyses limbs and stops breathing control

Question 15

What evidence showed that the origin of respiratory rhythm is in the medulla oblongata?

Answer 15

Limbar trasections in 1920’s

Cut base of medulla - stops breathing (can still detect resp rhythm via CNXII but can’t act)

Cut Top of medulla - breathing ok - resp rhythm able to act

So must be controlled in medulla

Question 16

What do respiratory neurones in the medulla control?

Answer 16

Breathing - inspiration and expiration

Question 17

Which resp neurones in the medulla control inpiratory firing?

Answer 17

DRG - Doral resp group

• also inhibit expiration

Question 18

Which resp neurones in the medulla control mostly expiration?

Answer 18

VRG - Ventral resp group

• in vigarous exercise they also help inspiration

Question 19

How do the respiratory neurones generate the resp rhythm?

Answer 19

Group pacemaker hypothesis

- A combination of membrane properties of the individual neurones + connections betweem them, cause rhythmic firing.

Question 20

Where are the exact locations of respiratory central pattern generators?

Answer 20

Unknown - lots of research
? Distributed
? single oscillator in the PBC - Pre-Botzinger complex

Question 21

What 3 factors can modify the respiratory rhythm?

Answer 21

CNS
Chemoreceptors
Airway + lunch reflexes

Question 22

How does the CNS modify respiratory rhythm?

Answer 22

PRG neurones (pontine respiratory group) fine tunes the rhythm -> lumsden transections evidence - if you cut between medulla and pons then the breathing continues but it becomes gasping/abnormal rhythm

Voluntary control possible from the cerebral cortex, via pyramidal tracts - corticospinal tracts

Question 23

How do chemoreceptors modify resp. rhythm?

Answer 23

They constantly adjust Va to match changes in VCO2 and VO2, which allows pCO2 and pO2 to be kept normal

Question 24

What is the main stimulus for chemoreceptors?

Answer 24

CO2

At low pO2, O2 can be used to stimulate breathing
Acidosis also can be used

Question 25

Where are the central chemoreceptors?

Answer 25

Medulla

Question 26

What do central chemoreceptors respond to?

Answer 26

Best to PaCO2 + pH, not to paO2

Question 27

What % of resp drive comes from PaCO2?

Answer 27

80%

Question 28

Where are the peripheral chemoreceptors?

Answer 28

Int he carotid bodies

Question 29

What do peripheral chemoreceptors respond to? What are they particularly good at?

Answer 29

Best to PaO2 + 20% to PaCO2

They are good at matching Va when PaCO2 changes rapidly

Signal to medulla via CNIX

Question 30

Name 4 locations/types of receptors that are involved in airway/lung reflexes of resp rhythm

Answer 30

Nose + upper airways irritant receptors
Pulmonary stretch receptors
Irritant receptors
J receptors

Question 31

What nerve carries signals from airway receptors to the respiratory control centers?

Answer 31

Vagus CNX

Question 32

Where are J receptors?

Answer 32

In alveolar walls

Question 33

What do J receptors monitor?

Answer 33

Engorged capillaries - Increase in interstitial fluid - cause dyspnoea

Question 34

What do pulmonary stretch receptors monitor?

Answer 34

Lung distention - cause reduced resp frequency

Question 35

What is the Hering-Bruer inflation reflex?

Answer 35

As the lung expands the pulmonary stretch receptors are activated and prevents overinflation by stoping inspiration and activating expiration

eg. in exercise