Session 3: Assessing weak cough and testing respiratory muscle strength

Why respiratory muscle testing? Are the respiratory muscles weak? How severe is the weakness? Is the extent of the muscle weakness clinically important? Are all the respiratory muscles affected equally? Is the weakness deteriorating or improving over time? (ARTP 2005) Are the respiratory muscles weak? – how do they compare to reference values, are they within normal limits? How severe is the weakness? – What it the pecent below LLN Is the extent of the respiratory muscle weakness clinically important? Are all respiratory muscles affected equally? – are there tests for specific respiratory muscles – yes we’ll descuss these further on in the presentation. Is the weakness deteriorating over time? – Its important to trend patients results, we often find that there are hight correlations between a patient VC and SNIP pressure measurements and bith may have a equall decline as the patient begins to deteriorate.

Vital capacity (VC) (Hough 2001) Volumes Vital capacity (VC) (Hough 2001) Lung function should be within a predicted range based on: Age - Height - Gender - ethnicity Normal VC = 3 – 6 L. Or 80% of TLC For adequate cough: >1L.

Why vital capacity (VC)? Measures ventilatory reserve in a Indicates ability to breathe deeply and cough. Reflects inspiratory and expiratory muscles strength. VC is sometimes reduced in obstructive disorders. VC is always reduced in restrictive disorders. Malnourished and obese. patients.

Assessing cough effectiveness Inspiratory phase: vital capacity Sniff nasal inspiratory pressure Maximum inspiratory pressure Glottic closure: Staccato expiration from Maximum inspiratory capacity? Expiratory phase: Peak cough flow Maximum expiratory pressure Audible cough

Respiratory muscle function tests Volitional (Used Frequently) Vital Capacity Mouth pressure (Pe max and Pi max) Sniff pressures Cough PEF Invasive – Volitional Methods (Infrequent use) Sniff oesophageal pressure Cough gastric pressures Non – Volitional Electrical stimulation Magnetic stimulation So here is a list of the tests that can be conducted to test respiratory muscle strength. Most laboratories will test muscle strength using non-invasive volitional tests. Mainly because these are less invasive and simple and providing you have a trained/competent practitioner results will be sound.

Vital capacity Simple Widely available Non-invasive Advantages Simple Widely available Non-invasive Serial measurements easy Disadvantages Volitional Non-specific Insensitive in mild/moderate disease Vital Capacity. A test to assess how much air the patient can breath in and out the lungs in one long breathe from a position of full inspiration. Advantages/Disadvantages VC measures can be done in a sitting a supine position to detect abnormalities within the diaphragm. In normal subjects the decline is less that 10% whilst in patients with diaphragmatic paralysis the difference may be more that 25%. (ARTP 2005)

Sniff pressures non–invasive widely available and inexpensive Advantages non–invasive widely available and inexpensive serial measurements easy high pressures exclude significant respiratory muscle weakness reference values available Disadvantages Volitional Difficult with bulbar disease Impaired transmission of pressure in COPD Normal values SNIP >60(F) - >70(M) Sniff pressure offers a simples non invasive alternative to mouth pressures. Advantage being that this is a familiar manoeuvre. Inserting a plug containing a pressure catheter into one nostril so that its distal end is within the nose opening. Patient then required to perform maximal sniff (From FRC) through the contralateral nostril whilst keeping the mouth closed. This generate a negative pressure in the nasopharynx that is similar to oesophageal pressure as an indication of global inspiratory muscle strength. In patients with COPD the transmission of the negative intrathoracic pressure to the nose is dampened so that the sniff is less negative, underestimating muscle strength. Hand-held device for measuring sniff nasal inspiratory pressure (SNIP). (ARTP 2005)

Don’t forget the PCEF (more this afternoon)

Patient example SNIF 05/07/2012 84cmH2O 15/08/2013 44cmH2O 21/11/2013 34cmH2O 09/01/2014 23cmH2O 20/02/2014 22cmH2O This data demonstrates the fall in vital capacity and corresponding fall in VC of a patient with MND over 4 years

Signs of respiratory compromise for those without access to spirometry, PEF or SNIPS increased respiratory rate shallow breathing recurrent chest infections weak cough quiet voice weak sniff abdominal paradox use of accessory muscles of respiration reduced chest expansion on maximal inspiration drop on usual sPO2 <94%.

Lung volumes