1. Session 3: Assessing weak cough and testing respiratory muscle strength

2. 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 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.

3. 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-ivasive volitional tests. Mainly because these are less invasive and simple and providing you have a trained/competent practitioner results will be sound.

4. 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 BTS guidelines (2009) critical level of 1.5l /min or <50% predicted <20% difference from sitting to supine indicates diaphragmatic weakness (Bourke 2014) <20% decrease from sitting to supine indicates diaphragmatic weakness (Bourke, 2014) <<20% decrease from sitting to supine indicates diaphragmatic weakness (Bourke, 2014) 20% decrease from sitting to supine indicates diaphragmatic weakness (Bourke, 2014)

5. Lung volumes

6. Why vital capacity (VC)?
Measures ventilatory reserve in a co-operativ
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.

7. 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 Capaciy. 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/Disadvanages
VC measures can be done in a sitting a supine position to detect abornamilities 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)

8. 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
(AJRCCM 2002, Vol 166: )
SNIP >60(F) - >70(M)
Sniff pressure offers a simples non invasive alternative to mouth pressures. Advantage being that this is a familiar manoeuvre.
Instering a plug containing a pressure catheter into one nostril so that its distall 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 nasaopharynx that is similar to oesophageal pressure as an indication of global inspiratory muscle strength.
In patients with COPD the transmission of the negative intrathrorcic 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)

9. 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

10. Don’t forget the PCEF (more this afternoon)

11. Patient example SNIF 05/07/2012 84cmH2O 15/08/2013 44cmH2O

12. 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%