Respiratory Muscle Strength Testing

Respiratory muscle strength is important for breathing, speaking, coughing, and swallowing. When impaired, it can contribute to impairments in speech and airway protection. This may lead clinicians who are working with people with speech and airway protective disorders to potentially recommend some form of respiratory muscle strength training - including both Expiratory Muscle Strength Training (EMST) or Inspiratory Muscle Strength Training (IMST). However, before EMST or IMST are recommended, it is important to first assess respiratory muscle strength in order to develop of a sense if a person is presenting with reduced strength when compared to age- and sex-based normative reference values.

The goal of this tutorial is to teach you how various methods for assessing respiratory muscle strength in clinical practice. 

Three reasons I think it can be important to include objective assessment of respiratory muscle strength as part of a standardized clinical swallow evaluation are:

(1) To develop an educated hypothesis on the role that respiratory muscle strength may or may not be playing on a person's speech, cough, or swallow impairment.

(2) To provide rational support for the potential recommendation of EMST or IMST (i.e., recommending it if strength measures are reduced and you think these reductions in strength are contributing to functional impairments in cough, swallowing, or speech).

(3) To personalize the delivery of a person's EMST or IMST protocol.

The methods outlined in this tutorial are based on guidelines outlined by the American Thoracic Society. In clinical practice, two measures of respiratory muscle strength are typically assessed:

1. Maximal expiratory pressure ('MEP' or 'PEmax') 

2. Maximal inspiratory pressure ('MIP' or 'PImax) 

MEP is assessed by having a person inhale to the top of vital capacity, then gently biting and wrapping their lips around the respiratory filter's mouth piece, and then exhaling with maximum effort for ≥ 2 seconds. 

MIP is assessed by having a person exhale to the bottom of vital capacity, then gently biting and wrapping their lips around the respiratory filter's mouth piece, and then inhaling with maximum effort for ≥ 2 seconds. 

The maximum of 3 trials that vary by ≤ 20% should be recorded and used for MEP and MIP.

Note: For both MEP and MIP, it is critical that no air leakage occurs through the nose. For that reason, a nose clip should be placed. It is also critical that no air leakage occurs around the respiratory filter's mouth piece. For that reason, the clinician should help the patient to secure a tight lip seal - this will likely mean the clinician will apply manual pressure circumferentially around the mouth piece to ensure no air leakage.

There are no standardized verbal instructions for MEP or MIP proposed by the American Thoracic Society. Therefore, the verbal instructions outlined below are the ones that I use for MEP and MIP: 

MEP: "Breathe in as much air as possible until you can't breathe in anymore, then gently bite on this mouthpiece and seal your lips tightly around the mouthpiece to make sure no air leaks out of the side, then blow out as hard as possible until I tell you to stop.”

MIP: "Blow out as much air as possible until you can't breathe out anymore, then gently bite on this mouthpiece and seal your lips tightly around the mouthpiece to make sure no air leaks out of the side, then suck in as hard as possible until I tell you to stop.”

MEP and MIP are assessed by using a manometer and a respiratory bacteria filter. A manometer is a pressure reading device and is used for respiratory muscle strength testing to obtain objective measurements of positive (expiratory) and negative (inspiratory) pressures. A respiratory bacteria filter is attached to the manometer and is the place through which a person forcefully exhale or inhale for MEP and MIP. The respiratory bacteria filter should get disposed of and replaced between people. Below, I will show you three potential setups that can be used clinical for respiratory muscle strength assessments.

Once you have obtained a valid and reliable measure of MEP and MIP, you can compare to age- and sex-based norms to estimate how normal or abnormal a person is presenting. The norms I use as a reference are from the article below: 

Lista-Paz, A., Langer, D., Barral-Fernández, M., Quintela-del-Río, A., Gimeno-Santos, E., Arbillaga-Etxarri, A., ... & González-Doniz, L. (2023). Maximal respiratory pressure reference equations in healthy adults and cut-off points for defining respiratory muscle weakness. Archivos de Bronconeumologia, 59(12), 813-820

This articles presents normative data three ways:

1. Means and Standard Deviations by age and sex

   1. • Norms are grouped between men and women for the age groups of 18-29, 30-39, 40-49, 50-59, 60-69, 70-80

      • Recall that, clinically, 1-2 standard deviations (SD) from the mean is considered 'mildly atypical' (could be normal, could be abnormal), and ≥ 2 SD from the mean is 'Very Atypical' (unlikely to be normal - is likely abnormal and a sign of impairment)

2. Predicted value reference equations, by age, sex, and body mass index (BMI)

   1. • Entering age, sex, and BMI into the reference equation, you can identify what the person's MEP or MIP should be. 

      • From there, divide expected MEP or MIP from what the person is currently presenting with. This will give you '% predicted'.

      • This is the most accurate prediction of what the person's respiratory strength should be, and how normal/abnormal they are - but is the most difficult to calculate 

3. Binary Cut-Offs

   1. • This is the least accurate prediction of what the person's respiratory strength should be, and how normal/abnormal they are - but is the easiest to calculate