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.
Why assess respiratory muscle strength?
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.
How to assess respiratory muscle strength?
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:
Maximal expiratory pressure ('MEP' or 'PEmax')
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.
Verbal Instructions for MEP and MIP
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.”
Devices for MEP and MIP Testing
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.
The MicroRPM Respiratory Pressure Manometer (MicroRPM; MD Spiro) is the 'industry standard' for assessment of respiratory muscle strength. It was designed specifically for MEP and MIP, and has been used in clinical and research practices for decades.
The MicroRPM costs ~$1500. The MicroRPM is typically sold with expiratory (blue) and inspiratory (pink) flanged mouth piece respiratory filters - each costing ~$4.30 per filter. However, the round respiratory filters also attach to the MicroRPM, cost ~$1.82 per filter, and may also be suitable for testing.
See below video demonstrations of MEP and MIP with the MicroRPM.
Generic, Low-Cost Manometers
Many generic low-cost manometers/pressure gauges are commercially and readily available. One such manometer is the Leaton Digital Manometer. This manometer was developed for generic pressure testing purposes. Our recent research demonstrated near-perfect relationship in pressure readings between the MicroRPM industry standard and the Leaton Digital Manometer, suggesting it may be a valid substitute to the MicroRPM.
The Leaton Digital Manometer is just one of many models available on popular online shopping platforms (e.g., Amazon), and costs ~$40. In order to attach the round respiratory filters to this manometer, you will need to purchase 4 mm inner diameter food grade silicone tubing (~$2.13 per foot), and attach to that a 6 mm x 22 mm adaptor (~$0.43 each), and attach to that a 22 mm x 22 mm adaptor (~$0.50). From there you, can you attach and replace disposable respiratory filters. Depending on infection control, they may be okay with not using the respiratory filter and only replacing the tubing between patients.
See below video demonstrations of MEP and MIP using the Leaton Digital Manometer.
Pressure Threshold Training Devices (e.g., EMST150)
Both manometers described above provide precise measurements of maximal expiratory and inspiratory pressures and are the ideal instruments of choice for MEP and MIP. However, in certain circumstances, you may be interested in estimating MEP and MIP using one of the devices a person may be using for their EMST and IMST practice.
Pressure threshold devices are one type of device use for EMST and IMST. Pressure threshold devices require a person to generate sufficient pressure to open the one-way spring-loaded valve contained within the training device. The amount of pressure required to open the one-way valve is adjusted using a knob at the top of the device. A color-coded label next to the knob label shows the approximate amount of pressure required to open the valve. If the person does not generate enough pressure to open the valve, then the device will be silent and it will feel as if the person is trying to exhaling/inhaling while holding their breath. If the person generate enough pressure to open the valve, then the person will feel themselves able to exhale/inahle and an air release/hissing sound will be heard from the device.
While there are several pressure threshold training devices available, the devices I am most familiar with are the EMST150, EMST75 Lite, and the Inspiratory Adaptor - all by Aspire Products. With pressure devices, a person will exhale forcefully into the device.
In order to measure MEP and MIP using these devices, a person will typically start at the lowest pressure setting and attempt to exhale/inhale forcefully. If they open the valve, then the pressure should get manually increased, and the person should perform another MEP/MIP trial. This gets repeated continuously until the point is found just before the person can no longer exhale/inhale and open the valve. Use the table outlined in the 'Calibration Instruction' files seen here, to determine how estimated pressure levels on the EMST150 device.
American Thoracic Society. (2002). ATS/ERS Statement on respiratory muscle testing. American Journal Respiratory Critical Care Medidicine, 166, 518-624.
Curtis, J. A., Mocchetti, V., & Rameau, A. (2023). Concurrent Validity of a Low‐Cost Manometer for Objective Assessments of Respiratory Muscle Strength. The Laryngoscope.