Cardiorespiratory problems associated with sleep

Question 1

Define sleep

Answer 1

Sleep is a natural, recurring state of relatively suspended sensory and motor activity in animals.
It is characterised by:
- total or partial unconsciousness
- nearly complete inactivity of voluntary muscles
It is:
- easily reversible and self-regulating
- essential for survival
- occurs in all living animals

Quality as well as quantity of sleep is essential.
Sleep disorders affect quality.

Question 2

Describe function of sleep

Answer 2

Many proposed theories, with no clear answer.
- restoration
- memory
- immune
- energy conservation
- circadian homeostasis
- prevention

Question 3

List the centres of the brain regulating wake and sleep

Answer 3

• Wake
  
  • Reticular formation
• Sleep
  
  • Thalamic relay ^[i.e. not a uniform event]

Question 4

List and describe the types of sleep

Answer 4

When awake, brain waves are fast and have low amplitude.
As sleep gets deeper, waves get slower and deeper, with higher amplitudes.
There are four stages of sleep. 4 is the deepest.

Note that REM is an active stage of sleep.

Different stages have different functions:
- deep sleep has a pruning function
- REM aims to refresh networks

Question 5

List the drivers of sleep

Answer 5

• Sleep debt
• Circadian “body clock”

Question 6

Describe the roles of sleep debt and body clock

Answer 6

Sleep debt
- Paid with slow wave sleep
- Mostly first half of the night

Body clock
- Regulates cycle of sleep
- Influences REM sleep
- REM mostly second half
- note also that the duration of REM increases in the second half

Question 7

Explain why REM induces hypotonia

Answer 7

To prevent us from acting out our dreams during sleep, REM induces hypotonia.
Hypotonia exacerbates sleep-disordered breathing.

Question 8

Describe the hypercapnoiec ventilatory response

Answer 8

• CO2 response alters depending on sleep state
• Drive to breathe is protected in slow-wave (N3) sleep - because this stage of sleep is very important
• Most blunted in REM sleep – hypoventilation most likely to occur. Sleep apnoea can start here and then progress to other stages of sleep

REM and breathing
- Hypotonia
- Effect on upper airway
- Blunted response to CO2 compared with other sleep stages

Question 9

Describe nervous activity and sleep

Answer 9

• Sympathetic nervous system
  
  • Progressive reduction in SNS activity from stage 1 to 4 - this trade-off does not necessarily occur in disorders
• Parasympathetic nervous system
  
  • Increased activity
  • Vagal tone

Question 10

List the types of sleep apnoea and their characteristics, and how to distinguish them

Answer 10

• Obstructive sleep apnoea - overwhelmingly more common compared to CSA
  
  • Apnoea – cessation of airflow from obstruction; increased respiratory effort
• Central sleep apnoea; no respiratory effort
  
  • Apnoea – cessation of airflow from reduced drive

Ways to differentiate OSA and CSA include: oesophageal probe - to measure respiratory effort, or respiratory bands to measure activity.

Question 11

Describe OSA

Answer 11

• Chest pump - effect on upper airway
• Balance of forces – forces promoting closure succeed
• Arousal from apnoea – resumption of airflow; disrupted sleep
  
  • this is good, essentially the brain rescues the body from apnoeic episode

Question 12

Describe risk factors for OSA

Answer 12

• Craniofacial
• Nose - resistance
• Mouth - large tongue, soft palate, retrograde mandible and overbite
• Jaw
• Tonsils
• General
  
  • Muscle tone - impacted by alcohol and hypothyroidism, obesity, especially central obesity

Question 13

Describe typical patient with OSA

Answer 13

• 45 years old
• Heavy snoring
• Witnessed apnoea
• Unrefreshing sleep
• Daytime sleepiness
• Recent car crash
• 3 antihypertensives ^[over two is associated with high risk of OSA]
• Obese
  
  • 130kg
  • BMI 40.7
• Crowded airway
• Polysomnography Summary
  
  • Obstruction
    
    • 68 times an hour
  • Arousals
    
    • 76 an hour (15-20 per hour is normal)

Question 14

Describe how the risk profile for CSA differs from OSA

Answer 14

CSA has a different risk profile to OSA. It is usually found in patients with:
- HF and Cheyne-Stokes respiration
- side effects of drugs e.g. respiratory depressants
It is largely characterised by a lack of effort.

Question 15

Describe the effects of OSA

Answer 15

• cardiac problems - MI, HF, arrhythmia
• snoring
• memory problems and inability to think correctly
• stroke
• hormone disruption
• increased traffic and workplace accidents
• death
• increased insulin resistance due to elevated SNS - even in no-diabetic patients
• high blood pressure
• depression

Question 16

Describe the consequences of sleep disordered breathing

Answer 16

Consequences can be the result of multiple pathways:
- Arousal - sleep disruption
- Sympathetic NS stimulation
- Hypoxaemia
- Deox-reox flux - reactive oxygen species
- Cardiovascular effects
- Neurohormonal effects
- Airway, chest pump effects
- Inflammatory effects

Question 17

Describe the cardiovascular pathophysiology of sleep disordered breathing

Answer 17

• Intermittent hypoxia
• Arousal response
  
  • Oscillation of:
    
    • systemic and pulmonary arterial blood pressures
    • Heart rate
    • Cardiac function

Question 18

Descrube the realtionship between hypertension and sleep apnoea

Answer 18

This graph represents the relationship between hypertension and sleep apnoea.
Mild sleep apnoea is associated with an increased odds ratio 1.8-2.
It is slightly elevated in patients with snoring and no sleep apnoea.

Question 19

Describe the management of sleep disordered breathing

Answer 19

• Behavioural e.g. weight loss, alcohol consumption, regular sleep schedule
• Splinting therapies
  
  • Pressure devices
  • Mouth guards
• Surgery- more of a paediatric option e.g. to remove tonsils
• CPAP (Continuous Positive Airway Pressure)
• Bilevel PAP (Non-invasive Ventilation) - issues of ventilation as opposed to obstruction