1. Session 2: Respiratory and cough failure in MND – an overview

2. Normal ventilation
Ventilation is the movement of air between the environment and the lungs via inhalation and exhalation.
Normal ventilation ensures effective control of oxygen and carbon dioxide.
Normal tidal ventilation is around mls.

3. Normal Ventilation Normal Ventilation
Requires an effective respiratory muscle pump.
An appropriate load on those muscles.
Open upper airways.
A functioning control centre/normal drive.

4. Normal ventilation
Respiratory centre , regulates breathing and determines how often and deeply we breathe
Signal to breathe is carried to muscles via nerves
The nerve signal is then conveyed to the muscles via neural junction

5. Respiratory muscles
The respiratory muscles constitute the respiratory pump responsible for gas exchange
Respiratory muscle weakness leads to respiratory pump failure
Diseases that increase the load on pump or decrease its capacity or both, lead to breathlessness and eventually ventilatory failure
Anything that drives an increase in ventilation (hypoxia, hypercapnia) will increase ventilatory load
An increase in load: capacity ratio causes an increase in ventilatory drive (neural respiratory drive)
Respiratory muscle weakness often advanced before clinical symptoms occur
Cardinal symptom of respiratory muscle weakness is breathlessness

6. Muscular weakness Respiratory system
Inspiratory muscles (diaphragm, external intercostal, scalene, sternocleidomastoid and trapezium) responsible for ventilation
Expiratory muscles (internal intercostals and abdominal muscles) responsible for coughing
Glosso-pharyngeal muscles for airway protection
NMD involves all the respiratory muscles but mainly diaphragm and inspiratory muscles.
Increase in respiratory rate along with small tidal volumes may cause lung atelectasis and reduction of compliance, therefore increasing mechanical load on already weakened respiratory muscles.
This results in alveolar hypoventilation with increase in carbon dioxide

7. Hypoventilation
Anything which interferes with the fine balance between load, pump and drive will cause hypoventilation

10. Neuromuscular disorders affecting respiratory function
Neuropathic disease –
MND, poliomyelitis, Spinal muscular atrophy
Peripheral neuropathies – GBS, Critical illness polyneuropathy, Charcot –Marie-Tooth disease
Disorders of neuromuscular junction
Myasthenia Gravis, Botulism
Acquired myopathies – Critical illness myopathy
Inherited myopathy
Progressive muscular dystrophies (Duchenne, Becker, Myotonic)
Congenital muscular dystrophies (Ulrich congenital, Emery –Dreifuss)
Metabolic myopathies (mitochondrial)

11. Respiratory muscle strength 1 minute in pairs.
Nerve
NMJ
Muscle

12. Respiratory muscle strength
UMN: MND, MS
LMN: SCI, GBS, MND, Polio
Nerve
Myaesthenia, Botulism, drugs
NMJ
Congenital – muscle dystrophies, metabolic disorders
Acquired – endocrine, inflammatory
Muscle

13. Increased mechanical workload 1 minute in pairs
Upper airway
Chest wall
Lung compliance

14. Increased mechanical workload
Larynx
Upper airway
Pharynx
Scoliosis
Chest wall
Obesity
Atelectasis
Fibrosis
Lung compliance
Inflammation
Infection

15. Don’t forget the drive (1 minute in pairs)
Structural
Lesions
Depressants

16. Factors affecting drive:
Structural
Lesions
Trauma
Vascular
Depressants
Drugs
Sleep

17. Pathophysiology Respiratory Failure Oxygenation Failure
Ventilation Failure

19. Remember in MND Muscle weakness
Four factors may contribute to respiratory failure:
Muscle weakness
Increased load
Airway (can also cause obstructive episodes with arousal)
Obesity
Lost compliance
Drugs, patients are often on opiates
MND is a disease of middle and later years, there may be other respiratory pathology

20. Physiological effects of hypoventilation
Early effects
Falling VC,
Orthopnoea
Sleep disordered breathing, sleep fragmentation
Poor cough
Later Effects
*Hypercapnia PCO2>7.5 KPa
Hypoxaemia
*Tachypnoea
Death
*Poor prognostic signs if no treatment
with NIV

21. Muscle tone at night
If the diaphragm is damaged or weak or if there is increased load on the diaphragm then the patient will hypoventilate as no accessory muscles to support the diaphragm.

22. Sleep disordered breathing
Umbrella term for several chronic conditions
“partial or complete cessation of breathing occurs many times throughout the night, resulting in daytime sleepiness or fatigue that interferes with a person’s ability to function and reduces quality of life.” (BTS)
Includes:
Obstructive Sleep Apnoea
Central Sleep Apnoea
Nocturnal Hypoventilation

23. Symptomatic effect of hypoventilation
Common symptoms
fragmented sleep
orthopnoea
daytime somnolence
groggy
hangover
nightmares

24. Symptomatic effect of hypoventilation
Less common symptoms
Ls common sympommpto
morning headache
poor concentration
confusion
poor appetite
breathlessness

25. So what about the cough?
The function of cough is to clear inhaled foreign materials
captured in the mucociliary system, retained secretions
or excessive secretions associated with respiratory
infection or impaired mucociliary clearance, and aspirated
materials.

26. So what about the cough? Three (four) phases to a cough:
Phase 1: stimulation of cough receptors located primarily in the central airways or a voluntary initiation (trigger phase)
Phase 2 (1) The inspiratory phase
Phase 3 (2) The compression phase
Phase 4 (3) The expiratory phase

27. The inspiratory phase
A period of rapid inhalation, caused by contraction of the diaphragm and accessory inspiratory muscles.
Normal pre-cough inspiration : 85-90% of total
lung capacity

28. The compression phase The vocal cords close (0.2 secs)
Expiratory muscles of the rib cage and abdomen contract in a coordinated effort, compressing the alveolar gas volume.

29. The expiratory phase The vocal cord open abruptly.
The muscle of expiration continue to contract and air is exploded out of the airway.
Initial PCEF can be as high as 720LPM in
normal individuals.

30. Physiological effects of weak cough
Weakened inspiratory muscles
Reduced vital capacity
Weakened bulbar muscles
Weakened expiratory muscles
Reduced explosive phase
limited secretion clearance
Increased risk of pulmonary congestion, acute respiratory failure and death

31. Physiological effects of weak cough
Bulbar insufficiency, although important does not always cause a completely ineffective cough
Remember that trache patient who shot phlegm across the room!
Bulbar patients can be taught a huffing manoeuvre (forced exhalation through an open glottis)
Insidious weak cough, particularly due to weak expiratory muscles often goes unnoticed until it is too late. !

32. Symptomatic effect of weak cough
As well as increased significant complications and increased use of health care resources, weak cough causes:
difficulty clearing phlegm
choking, plugging and resultant anxiety
distress
decreased quality of life.

33. Summary Ventilatory Failure Cough Failure
Weak inspiratory respiratory muscles
Increased demand or load
Upper airway issues
Drugs
Often in combination in NMD cause Hypoventilation
Cough Failure
Weak inspiratory respiratory muscles
Weak expiratory muscles
Bulbar weakness
Often in combination cause weak cough