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

Pathophysiology Respiratory Failure Oxygenation Failure Ventilation Failure

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 400-500mls.

What do we need for normal ventilation? 1 minute in pairs. Discussion to encourage delegate interaction

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.

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

Respiratory muscle strength 1 minute in pairs. Nerve NMJ Muscle

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

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

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

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

Factors affecting drive: Structural Lesions Trauma Vascular Depressants Drugs Sleep

Remember in MND A combination of factors may contribute to respiratory failure: Muscle weakness is the main cause: Increased load - airway collapse/obstruction (can also cause obstructive episodes with arousal) - obesity - lost compliance drugs, patients are often on opiates (compounding muscle weakness) aspiration may be involved. MND is a disease of middle and later years, there may be other respiratory pathology.

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

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.

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

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

Symptomatic effect of hypoventilation Less common symptoms morning headache poor concentration confusion poor appetite Breathlessness (This MND patient’s VC was only 400mls yet they didn’t feel breathless!)

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.

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

The inspiratory phase A period of rapid inhalation, caused by contraction of the diaphragm and accessory inspiratory muscles. Up to 85-90% total lung volume is inhaled.

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

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.

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

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. !

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.

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