Lung volume augmentation

In summary, these changes collectively lead to reduced ventilation and secretion clearance, along with an increased work of breathing.

For an acute, motor-complete NLI at T6 or above, but especially at C5 and above, significant respiratory function changes occur due to neuromuscular weakness and paralysis, compounded by the presence of spinal shock, as well as autonomic nervous system (ANS) disruption. Key respiratory muscles affected include the intercostal, abdominal and diaphragm muscles.

At this time, weakened or paralysed respiratory muscles present with flaccidity and increased compliance due to spinal shock. This affects diaphragm positioning and function, as well as breathing mechanics. Ultimately, this results in reduced ventilation and secretion clearance. Paradoxical breathing can also develop, which is very inefficient and increases the work of breathing.

For more information on respiratory function changes following SCI, refer to Respiratory changes.

Without adequate and timely intervention, the combination of hypoxaemia, hypercapnia and respiratory fatigue is a key precursor to the onset of respiratory failure. In addition to this, chronic hypoventilation also contributes to sleep-disordered breathing, compounded by any other obstructive and central factors.

Many lung volume augmentation techniques are clinically practised today by physiotherapists. They have evolved over decades, in the treatment of post-surgical and neuromuscular conditions, including SCI. While there is considerable clinical experience in the use of these interventions, there has been limited scientific study of their efficacy in the management of SCI respiratory dysfunction.

In 2022, The Australian and New Zealand Clinical Practice Guidelines: For Physiotherapy Management of People with Spinal Cord Injury were developed, providing evidence-based recommendations where possible, or consensus-based opinion statements.

The process completed systematic reviews and SCI professional peer consultation to address physiotherapy enquiry questions, presented in a PICO (Participant, Intervention, Comparison and Outcome) format. The outcomes are presented as either evidence or consensus statements and form the new clinical practice guidelines. Those which are relevant to the management of respiratory function following SCI, have been incorporated into the “Lung Volume Augmentation” and “Secretion Management” sections. They will be presented using the following colour variations banners.

The Australian and New Zealand Physiotherapy Guidelines for people with SCI states:

Evidence: Weak for recommendation

Guideline

The Australian and New Zealand Physiotherapy Guidelines for people with SCI states:

Consensus: Weak for recommendation

The Australian and New Zealand Physiotherapy Guidelines for people with SCI states:

Consensus: Strong for recommendation

Guideline

The Australian and New Zealand Physiotherapy Guidelines for people with SCI states:

Consensus: Weak against recommendation

Guideline

Beyond the acute management phase after a SCI, any respiratory muscle recovery and strengthening which occurs due to neural plasticity and rehabilitation will ultimately enhance respiratory function. As spinal shock resolves over weeks to months, intercostal and abdominal muscle flaccidity may transition to spasticity. Combined with any chronic chest wall immobility, the tendons, ligaments and joints of the rib cage stiffen.

This typically:

• reduces excessive chest wall and abdominal compliance
• helps correct a paradoxical breathing pattern
• decreases the work of breathing.

Typically, there is also some partial rebalancing of ANS disruption and a reduction in vagal overactivity. Negative cardiovascular and respiratory effects slightly diminish, and respiratory function improves further.

With these adjustments, weaning from ventilation supports and progression to sitting may be introduced. However, weaning from ventilation support and the introduction of graduated sitting should be carefully planned by the multidisciplinary team, with appropriate timing and staging to promote success.

Inclining the bedhead introduces gravitational load, increasing the ventilatory demand on the diaphragm to maintain tidal volumes—this increases the work of breathing. An additional and significant concern is the impact of prolonged upright bed positioning on skin integrity.

The preferred method for introducing sitting is to use a recliner or tilt-in-space wheelchair, with an appropriate pressure-relieving cushion, headrest, and if required, elevating leg rests. These wheelchairs enable a controlled sitting orientation between supine and upright sitting, for immediate repositioning if necessary e.g. hypotensive episode.

This approach is particularly useful to:

• manage the initial risk of respiratory fatigue, due to increased ventilatory demand on the diaphragm
• manage the risk of hypotension, associated with ANS disruption
• optimise skin care for seating, as sitting time gradually increases.

Once upright sitting is well tolerated for at least 6–8 hours, transition to a fully upright wheelchair can be considered. Adequate postural supports should be incorporated, including a solid backrest with appropriate height and contour, armrests and a chest strap to minimise the risk of falls.

These seating supports aim to:

• achieve postural symmetry at the pelvis and trunk
• promote thoracic extension with optimal head alignment
• assist sitting balance and upper limb function for activities of daily living (ADLs)
• optimise respiratory function, including periods of rest.

The Australian and New Zealand Physiotherapy Guidelines for people with SCI states:

Evidence: Weak for recommendation

Abdominal binders in sitting may be provided to improve lung volume in people with SCI who have abdominal muscle weakness or paralysis.

If abdominal muscle paralysis or significant weakness is present, the use of an abdominal binder is recommended when sitting—and possibly standing.

A well-fitted abdominal binder helps counteract the loss of normal abdominal muscle tone and increased abdominal compliance, when changing position from supine (where gravity is providing positioning assistance). It applies pressure across the abdomen onto the abdominal contents to support:

• venous return in the inferior vena cava, to maintain blood pressure
• dome-shaping of the diaphragm, to improve its position for efficient contraction
• passive and forced expiration.

Overall, the abdominal binder is clinically used in the management of orthostatic hypotension, along with the use of compression stockings and pharmacological interventions.

Due to respiratory changes following SCI, the abdominal binder is also used to enhance lung volumes and reduce the work of breathing in sitting, while improving coughing. One study reported that use of an abdominal binder in sitting for people with a complete SCI above T1, improved maximal inspiratory pressure (MIP), vital capacity (VC), forced expiratory volume in 1 second (FEV₁) and peak expiratory flow (PEF). It also increased the time for sustained voice.

Anecdotal evidence suggests that an abdominal binder may also assist with balance and postural cueing during early rehabilitation.

For more information about the prescription and application of an abdominal binder, refer to Abdominal binder.

Effect of an abdominal binder on abdominal compliance in sitting following high-level SCI
Image source QSCIS

1. An IPPB device uses compressed air +/- oxygen and is typically flow-controlled, but pressure-cycled.
2. The operator sets the maximum inspiratory pressure, flow rate, and inspiratory trigger sensitivity.
3. The user initiates a spontaneous breath by generating negative inspiratory pressure against the IPPB interface via an appropriate circuit and interface attached to the user. Device sensitivity can be further adjusted to better detect the user’s effort, and flow rate can be tuned to match the user’s breathing pattern.
4. A positive-pressure breath is delivered by the device (typically starting at 10–15 cmH₂O, increasing up to a maximum of 40cmH₂O), supporting lung volume augmentation with minimal effort from the user.
5. Expiration occurs passively through the attached circuit inclusive of an exhalation valve/leak port.
6. The user completes a pre-determined series of IPPB-assisted breaths.
7. Following the final breath, a manual assisted cough (MAC) can be applied to facilitate a strong cough. This requires coordinated effort between the user and the operator.

Additional features include:

• attachment options such as a non-vented mask, mouthpiece, or tracheostomy connector
• aerosolised medication, including saline
• ambient air or supplemental oxygen via an air-mix system
• parameter variations such as inspiratory pressure, flow rate and trigger sensitivity.

Recommendations for use include:

• a mouthpiece is often more comfortable and successful than a mask for triggering inspiration
• an increase in maximum inspiratory pressure and a decrease in flow rate will promote a longer and deeper breath, and vice versa
• IPPB may be an option for ventilated users with tracheostomy who are conscious, medically stable and are assessed to be ready for weaning, but extreme caution is required to reduce the risk of volutrauma/barotrauma. In these cases:
  • it may be safer to leave the invasive airway cuff deflated and permit some leakage, rather than inflating to maximise pressure delivery to the lung periphery
  • inspiratory pressure settings may need to be carefully increased to account for increased airway resistance, dead space and leakage.

1. The MI-E device uses compressed air +/- oxygen and is typically pressure-controlled, but time-cycled.
2. The operator sets various parameters including whether treatment will be insufflation +/- exsufflation, as well as the maximum pressures and time for insufflation +/- exsufflation, the insufflation flow rate or rise time and inspiratory trigger sensitivity.
3. The operator initiates mechanical insufflation using the device toggle switch (on the device, hand remote or foot pedal) via an appropriate circuit and interface attached to the user.
4. A positive pressure breath is delivered by the device (typically 20 to 40 cmH₂O), up to the user’s maximal insufflation capacity (MIC). This supports lung volume augmentation with minimal effort from the user.
5. Expiration occurs passively through the attached circuit with nil exhalation valve/leak port (unless using the following other non-MI-E modes on the same device).
6. A series of insufflation breaths is delivered for lung volume augmentation and sputum mobilisation; a mechanical assisted cough can then be triggered by rapidly reversing airflow to generate negative pressure (typically –20 to –40 cm H₂O). This sudden shift in pressure simulates a cough, without requiring active effort from the user. The effectiveness of the cough is enhanced by increasing the pressure gradient between insufflation and exsufflation, thereby increasing forced tidal volume and peak expiratory flow. A manual assisted cough (MAC) can be applied simultaneously to further improve cough effectiveness.
7. While optimal MI-E dosage and frequency has not been determined yet, a typical MI-E treatment session may be repeated cycles of 3 pre-therapy breaths, 2 exsufflations, 2 post-therapy breaths. Other treatment approaches may consist of cycling between insufflation and exsufflation, with a exsufflation cough as needed.

Modes may include:

• manual– allows the operator greater control over insufflation and exsufflation timing and pressures
• automatic– enables pre-programmed cycle for consistent, repeatable therapy—suitable for unsupervised use by trained clinicians and carers
• IPPB– supports programmed lung volume recruitment initiated by the user when needed
• burst NIV– provides EPAP typically used before or after treatment for respiratory rest, while maintaining any lung volume recruitment; it is not intended for continuous ventilatory support and will be time limited e.g. <15 minutes; it is not for users with a tracheostomy or endotracheal tube
• Intrapulmonary Percussive Ventilation (IPV) or “Percussor Mode”– provides airway percussion therapy with settings for frequency (e.g. 10-780 CPM), pressure (e.g. 0-70 cmH₂0) and I:E ratios (e.g. 1:5 to 5:1)
• High Frequency Chest Wall Oscillations (HFCWO)– typically using an inflatable chest wrap to provide external chest wall percussion with settings for frequency (e.g. 50-900 bpm), pressure (e.g. 5-70 cmH₂0) and I:E ratios (typically 1:1).

Circuit design must be appropriate to the mode, as well as the actual device.

• Most MI-E devices use a single lumen circuit, although dual lumen may be required, ensuring there is no contamination between insufflation and exsufflation debris
• Manual and automatic MI-E modes use standard MI-E circuits which have no exhalation valve/leak ports, to allow for delivery of negative pressure delivered in short treatment sessions (disconnect user from MI-E device when each short treatment session is complete)
• In contrast, IPPB, NIV and IPV modes require a circuit with an exhalation valve/leak port, to prevent CO₂ rebreathing during longer use (disconnect user from MI-E device when treatment is complete).
  • Some circuits have the exhalation valve/leak port as an extra attachment (it is normally preferable to operate with 2 circuits: 1 circuit dedicated to MI-E and another circuit dedicated to the other modes)
  • Some circuits have a switch valve on the circuit to open or close when changing between modes (MI-E mode (closed) and IPPB, NIV, IPV (open)).

Additional features may include:

• interface options such as a non-vented mask (preferred) versus mouthpiece, and sometimes a tracheostomy or endotracheal tube connector
• options for ambient air, and sometimes supplemental oxygen via an entrainment port and/or humidification
• recorded measures of volume and exsufflation flow rate, pulse oximetry for monitoring during treatment sessions
• real time pressure wave and bar graphs for feedback during treatment sessions
• real time capacity to record or adjust treatment sessions
• parameter variations may include
  • insufflation and exsufflation pressures and time ratios, with some providing an option for stepped insufflation
  • pause time between insufflation and exsufflation/cough
  • flow rate or rise time options for each insufflation
  • sensitivity trigger options for insufflation
  • synchrony options for insufflation or exsufflation/cough
  • airway oscillations on insufflation, exsufflation or both with a selection range for frequency (e.g. 4-20 Hz) and amplitude (e.g. 1-10 cmH₂0)
  • EPAP on pause breath
  • options for pre-therapy and post-recruitment breaths
  • number of pre-save programs for different types of therapies, including when well and unwell.

Additional accessories may include:

• option of a stand as well as mask holders
• internal battery (e.g. 3-4 hr capacity) in addition to external power supply
• hand remote or foot pedal
• pulse oximeter.

Additional variations may include:

• overall weight of device
• device handle, carry bag etc.
• customisation of screen colours, or orientation of screen for visualisation
• touch screen versus button operation, including varying sensitivity and ease of navigation
• connectivity e.g. ethernet, USB, USB C, HDMI port, flash drive, wifi, bluetooth
• remote control access e.g. app to adjust device settings via a mobile phone
• data download processes i.e. simple vs multi-stage
• access to compliance summary/user log
• safety prompts about correct circuit +/- external valve/leak port
• terminology and use of positive (+) and negative (-) numbers for insufflation and exsufflation
• provision of user quick reference guides and online resources.

Recommendations for use include:

• during the initial use of MI-E carefully monitor oxygen and heart rate settings to ensure safety; if there is a high sputum load, it may be advisable to have suction and resuscitation equipment ready
• start pressure settings low and seek user feedback, while monitoring chest wall expansion to determine adequacy of pressure settings; typically start insufflation with 15 cmH₂0 and increase in 5 cmH₂0 increments (unless the user is also accessing NIV, then start insufflation NIV IPAP +5 cmH₂0 and increase in 5 cmH₂0 increments)
• keep exsufflation pressure 5-10 cmH₂0 more negative than insufflation pressure to maintain a pressure gradient that biases sputum mobilisation
• progressively increase pressures until efficacy is achieved, remembering the delivered tidal volume varies depending on airway resistance, lung compliance, and circuit integrity
• individually adjust inspiratory and expiratory time/rise/pressures for each user, matching their normal breathing pattern and optimising comfort
• if adding oscillations, adjust insufflation and exsufflations pressures to factor in the additional pressure overlay; however, there is little evidence this is a useful feature when compared to options with percussor modes
• if there are concerns about chest wall and spine bone mineral density, or chest wall and lung compliance, start with lower flow rates and pressures; also opt for IPV mode rather than use HFCWO
• measures of volume and peak flow rate are not always accurate and represent gas decompression in the device circuit, so also compare to pressure-wave forms as well as observations of the chest wall and sound of the cough effectiveness
• when the user is spontaneously breathing, use of a non-vented face mask is preferable to a mouthpiece
• MI-E use may be an option for ventilated users, but extreme caution is required to reduce the risk of volutrauma/barotrauma. In these cases:
  • it may be safer to leave the invasive airway cuff deflated and permit some leakage, rather than inflating to maximise pressure delivery to the lung periphery
  • inspiratory pressure settings may need to be carefully increased to account for increased airway resistance, dead space and leakage.

_{(LVR= lung volume recruitment; AS = air stacking; GBP = glossopharyngeal breathing; MAC = manual assisted cough, MI-E = mechanical insufflation-exsufflation)}.

The following are examples of published flowcharts for the safe introduction and titration of basic MI-E parameters in adults with neuromuscular disease, including SCI. It is also important to note that device pressure and volume readings may not accurately indicate the lung volume augmentation or peak cough flow achieved. Rather subjective reports from the user and objective assessment of chest wall expansion and the sound of the cough should also inform titration.

A video demonstrating MI-E therapy is here.

A video with MI-E therapy FAQ is here.

A LVR kit consists of a manual resuscitator bag with a general pressure gauge, modified with a one-way valve, a flexible tubing piece, via a mouthpiece and nose clip. A bacterial filter may also be included in the circuit to support airway hygiene. The LVR bag does not deliver aerosolised medications and typically operates using room air only.

The one-way valve alters the function of the resuscitator bag by allowing airflow only in the direction of insufflation and preventing leakage between stacked insufflations. As a result, the LVR bag is no longer suitable for resuscitation, and exhalation into the circuit is contraindicated due to the risk of barotrauma. Instead, the interface must be detached from the user once the final insufflation volume is reached, prior to their exhalation.

1. The user first takes a deep breath, according to their maximal inspiratory capacity.
2. The user then closes their glottis to hold their inspiratory volume, while being connected to the LVR bag.
3. The user then reopens their glottis, to allow the LVR bag to deliver additional air volume—this is stacked onto their own maximal inspiratory capacity by a series of squeezes, until the user’s MIC/comfort limit is reached and they signal to cease insufflation (typically up to five small squeezes of the LVR bag).
4. The user then closes their glottis to hold the stacked inspiratory capacity, while being disconnected from the LVR bag.
5. The user then opens their glottis to exhale, cough (+/- manual assisted cough), huff, speak or sing, as desired.

Additional features include:

• tracheostomy connector, provided the tracheostomy has a deflated cuff or is cuffless to permit glottal control, but these must be used with extreme caution due to the risk of volutrauma/barotrauma
• use of a mouthpiece with nose clip is highly preferred to a non-vented mask, so that the user can control detachment from the LVR bag as necessary
• some users may be able to self-administer the technique—for example, by positioning the bag between the elbow and trunk and squeezing it like a bagpipe; this offers additional safety, given the user is able to control insufflation within their comfort range; however, they must also be able to disconnect from the device for each exhalation.

Some LVR instruction videos can be found here and here.

Using resistance principles similar to conventional muscle training, one simple method involves placing an appropriate weight on the abdomen in supine, creating resistance to abdominal rise—as the diaphragm descends during inspiration. Most commonly, IMT is typically delivered through an electronic threshold device via a mouthpiece, which can be set to incrementally increase the effort required for inspiration as inspiratory muscle strength improves.

Training can be performed in various positions, including supine or upright sitting—wearing an abdominal binder to optimise diaphragm positioning. Palpation of both abdominal rise and chest wall movement can be used with verbal coaching, to maximise effort.

Training recommendations suggest completing IMT sessions up to twice daily, five days per week, for 6–8 weeks or longer. Resistance should be progressively increased, with intensity potentially guided by the Borg RPE scale.

Similar to conventional exercise programs, strength gains are maintained only while the exercise program continues.

An IMT program can be found here.

Some IMT instruction videos can be found here.