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Air stacking


Air Stacking

\ˈer ˈsta-kiŋ\

Air stacking is used to expand the lungs beyond the deepest possible breath that one can take (the vital capacity or VC). If the VC is limited to half of normal, then the other half of the lungs remain closed (termed "atelectasis"). When the air sacs that make up the lung close, the lungs stiffen and it becomes more difficult for the breathing muscles to ventilate them. In addition, decreased breathing capacity (VC) restricts the ability to inhale deep volumes of air that are necessary for an effective cough. To maintain VC and lung compliance, air stacking is routinely used to expand the lungs the deepest possible volume. To air stack, air volumes can be consecutively delivered from a manual resuscitator (Ambu bag) or volume-preset ventilator:

-The glottis (throat) holds the first volume of air.

-The person's glottis holds a second volume of air to add to the first volume (stack).

The maximum volume of air that the glottis can hold by air stacking is the "maximum insufflation capacity" or MIC. Air stacking allows for deeper insufflations for coughing, extended/louder talking, and more time for swallowing food. Air stacking is crucial to improve cough flows, promote lung and chest wall growth, and to maintain the elasticity and integrity of the lungs to optimize lung health. It is active lung volume recruitment (LVR).

Note: Setting ventilators to volume-preset rather than pressure-preset (as in bi-level PAP or CPAP) permits air stacking.


Arterial Blood Gas (ABG)

\är-ˈtir-ē-əl ˈbləd ˈgas\

An arterial blood gas test measures the acidity (pH) and the levels of oxygen (PaO2) and carbon dioxide (PaCO2) in the blood.


Assisted Coughing

\ə-ˈsis-təd ˈkȯ-fiŋ\

Assisted coughing combines air stacking and an abdominal thrust applied at the initiation of glottis opening (cough) to increase cough peak flows.


Bi-level Positive Airway Pressure (Bi-level PAP, "BiPAP")

\ˈbī-ˈle-vəl ˈpä-zə-tiv ˈer-wā ˈpre-shər\

Bi-level PAP is a continuous flow of air delivered at higher pressure when inhaling and at lower pressures when exhaling. It can be delivered via nasal or oronasal interface. The pressure when inhaling (termed inspiratory PAP or IPAP) assists breathing, but the positive pressure when exhaling (termed expiratory PAP or EPAP) hinders exhalation. Bi-level PAP can be used for ventilatory support and to rest inspiratory muscles during sleep, but the difference between the IPAP and EPAP must be 18 cm H2O or more ("high-span bi-level PAP"). The IPAP must be increased by the amount of the EPAP for the same level of inspiratory assistance as without EPAP, so bi-level PAP can be less comfortable, less effective, and because it is pressure-preset, it gushes high level air flows to compensate for air leakage during sleep, awakening users. Bi-level PAP, rather than full noninvasive ventilatory support and mechanical insufflation-exsufflation, continues to be commonly prescribed for people with neuromuscular disease as well as for patients post-extubation, but often patients are suboptimally placed on inadequate low-span bi-level PAP and fail extubation as a result. Use of NVS and MIE is preferable.


Chest Physiotherapy (CPT or Chest Physical Therapy)

\ˈchest ˌfi-zē-ō-ˈther-ə-pē\

Manual chest tapping ("percussion") and mechanical methods to vibrate the chest (e.g. intermittent percussive ventilation, oscillation devices, and vibration vests) may be helpful for people with diseases of the lungs and airways to help carry debris from the peripheral lung to the central airways so that it can be coughed out. However, chest physiotherapy is not apparently helpful for people with healthy airways, and it has neither been shown by evidence-based medicine to be beneficial nor does it have the capacity to be used prophylactically to prevent serious respiratory infections. Chest physiotherapy is not a substitute for effective coughing to clear the central airways.


Capnograph (End-Tidal Carbon Dioxide Meter)


A device that painlessly measures end-tidal CO2 (CO2 concentration of exhaled air).


Continuous Positive Airway Pressure (Continuous PAP, CPAP)

\kən-ˈtin-yə-wəs ˈpä-zə-tiv ˈer-wā ˈpre-shər\

Continuous positive airway pressure is used to help keep the airways open to prevent obstructive sleep apneas. CPAP can be likened to breathing with the head out of the window of a car going 60 mph. It is a constant stream of air that acts like a pneumatic splint to keep the airways open but does not assist weak respiratory muscles. It is useless for people with neuromuscular disease whose principal problem is inspiratory muscle weakness as opposed to obstructive apneas and hypopneas.


Cough Peak Flow (CPF)

\ˈkȯf ˌpēk-ˈflō\

Unassisted cough peak flows are obtained by spontaneously coughing into a cough peak flow meter. Assisted cough peak flows are obtained after air stacking and then applying a manual abdominal thrust while coughing into a cough peak flow meter.


End-tidal Carbon Dioxide (EtCO2)

\ˈend-ˈtī-dəl ˈkär-bən dī-ˈäk-ˌsīd\

The end-tidal carbon dioxide is the partial pressure or maximal concentration of carbon dioxide at the end of an exhaled breath. Measuring EtCO2 with capnography can be a noninvasive method of estimating PaCO2, since PaCO2 is approximately 1 to 6 mm Hg higher than EtCO2.




The act of removing an endotracheal tube from the trachea after intubation for respiratory failure. Conventionally, extubation is only done when a person is strong enough to breathe on his/her own (termed “weanable” from ventilator use). However, "unweanable" intubated patients can be extubated to continuous noninvasive ventilatory support (CNVS) and mechanical insufflation-exsufflation (MIE) thereby avoiding tracheotomy.


Glossopharyngeal Breathing (GPB, "Frog Breathing")

\ˌgläs-ō-fə-ˈrin-j(ē-)əl ˈbrē-thiŋ\

Glossopharyngeal breathing permits people with weak inspiratory muscles and reduced vital capacity or breathing tolerance to more fully inflate the lungs without using a manual resuscitator or ventilator to air stack. GPB involves the glottis holding a large tidal volume of air in the lungs while concurrently gulping additional boluses of air to increase lung volumes that can approach and sometimes exceed the maximum insufflation capacity attained by air stacking. Up to 70% of CNVS users can also use glossopharyngeal breathing for free time from ventilatory support, in many cases, up to all day.




The presence of excessive amounts of carbon dioxide (CO2) in the blood, typically caused by inadequate ventilation.




The brain sends signals to the inspiratory muscles to breathe more shallow than normal to avoid fatigue but in doing so blood CO2 levels rise and the ventilatory drive to breathe is diminished.


Inspiratory Capacity

\in-ˈspī-rə-ˌtōr-ē kə-ˈpas-ət-ē\

The total amount of air that can be drawn into the lungs by a maximal inspiration.




Ventilation interfaces can be invasive (e.g. tracheostomy and endotracheal tubes) or noninvasive (e.g. oral, nasal, and oronasal interfaces). Non-vented interfaces or interfaces with holes covered must be used with active ventilator circuits whereas vented interface or interfaces with holes open are used for bi-level PAP and CPAP. The ventilation interface is connected to the ventilator tubing to deliver air to the patients.


Intermittent Positive Pressure Ventilation (IPPV)

\ˌint-ər-ˈmit-ənt  ˈpä-zə-tiv ˈpre-shər ˌvent-əl-ˈā-shən\

Intermittent positive pressure ventilation is provided via portable ventilators to augment breaths. Unlike bi-level PAP, IPPV permits the person to exhale unencumbered, that is, without the need to overcome expiratory positive airway pressure (EPAP) or positive end-expiratory pressure (PEEP).




The passage of an “endotracheal tube” through the nose or mouth into the trachea to deliver invasive mechanical ventilation and to suction the airways.


Life Support Device

\ˈlīf sə-ˈport ˈlīf\

The problem of physicians failing to understand how to avoid invasive tracheostomy ventilation is compounded by a misunderstanding of what is needed in a “life support device” for people with breathing muscle weakness. The US Food and Drug Administration (FDA) and other regulatory bodies recognize life support ventilators/respirators as only those devices used by people who have a continuous need for them and hence must have the ability to operate 24 hours/day without malfunctioning and have internal batteries, disconnect sensors, and alarms. While it is true that comatose and other people incapable of directing their own care cannot use CNVS, there are many self-directed people who have lived for decades receiving CNVS via simple mouthpieces connected to tubing from blowers or simple ventilators with no alarms and have not suffered as a result. Indeed, for many, the ventilator can fail and they can support themselves by GPB.


Lung Volume Recruitment (LVR)

\ˈləŋ ˈväl-yəm ri-ˈkrüt-mənt\

There are both active and passive ways to inflate the lungs to approach the normal maximal lung volumes of people who have no respiratory muscle weakness. Passive LVR involves using MIE at high insufflation pressures, a manual resuscitator with the exhalation valve blocked, or a pressure preset ventilator set a pressures over 40 cm H2O to expand the lungs fully. Active LVR is air stacking. Infants and small children need passive lung volume recruitment to mobilize the lungs and chest walls or simply need sleep NVS.


Manually Assisted Coughing (MAC)

\ˈman-yə-wə-lē ə-ˈsis-ted ˈkȯ-fiŋ\

Manually assisted coughing is the combination of air stacking for people with vital capacities less than 1500 mL, followed by manually applying an abdominal thrust timed to glottis opening to increase cough flows.


Maximum Insufflation Capacity (MIC)

\ˈmak-s(ə-)məm ˌin(t)-sə-ˈflā-shən kə-ˈpas-ət-ē\

The maximum volume of air that the glottis can hold after air stacking. Maximum insufflation capacity (MIC) is commonly performed by using an ambu bag to deliver a maximum volume of air above a patient’s vital capacity. Then, the volume is measured with a spirometer. Routine MIC measurements are important to assess lung compliance. Improved lung compliance results in better air delivery via portable ventilator and reduced leakage from oral and nasal interfaces. It also improves CoughAssist efficacy. To improve MIC, patients should air stack 3 times a day (10-15 cycles per session).


Mechanical Insufflation-Exsufflation (MIE)

\mi-ˈka-ni-kəl ˌin(t)-sə-ˈflā-shən ˌeks-sə-ˈflā-shən\


Assisted Coughing
Ventilator Circuit
Portable Ventilator
Peak Flow Meter
Plateau VC


Mechanical insufflation-exsufflation devices (e.g. CoughAssist[TM], Philips-Respironics Inc. or VitalCough[TM], ResMed Inc.) alternate positive and negative pressure to the airways to simulate a strong cough and greatly increase cough peak flows to clear airway secretions, so that the lungs can function normally.

MIE is used at positive pressures of 50 to 60 cm H2O to the airways during inspiration to fill the lungs. To full apparent expansion of the chest, this usually takes about 2 seconds at these pressures for older children and adults. Then, the insufflation is switched to a negative pressure of -50 to -60 cm H2O until the chest appears to be completely emptied to create effective cough flows. Once the duration for full chest expansion and emptying are determined. The automatic mode can be used for cooperative patients.

For infants and small children, the same pressures of 50 to 60 cm H2O are used, but the insufflations and exsufflations must be timed to the infant’s breathing since smaller children cannot cooperate with the device or the CoughTrack[TM] can be used on the cough assist so the infant can trigger the MIE. Since smaller children breathe so quickly, full chest expansion and emptying is difficult to achieve and MIE is less effective.

For patients who are intubated or those with tracheostomy tubes, pressures of 60 to 70 cm H2O must be used because the narrow diameter of the invasive tubes decreases flows and pressures. In this situation, it is sometimes beneficial to use exsufflation-timed abdominal thrusts to increase MIE peak exsufflation flows (MIE-EF).


Muscles of Respiration

\ˈmə-səl əv ˌres-pə-ˈrā-shən\

There are three respiratory muscle groups:

-The inspiratory muscles,

-The expiratory muscles (predominantly abdominal and chest wall) for coughing, and

-The bulbar-innervated muscles, especially the glottis, which protect the airways. The glottis also holds deep volumes of air for coughing.

The inspiratory and expiratory muscles can be fully supported as they are for patients with no vital capacity (no ability to breathe on their own) who have used continuous noninvasive ventilatory support for over 60 years without resort to tracheostomy. However, there are currently no effective noninvasive measures to assist bulbar-innervated muscle dysfunction.


Noninvasive Interface (“Mask”)

\ˌnän-in-ˈvā-siv, ˈint-ər-ˌfās\

Noninvasive interfaces are interfaces between the ventilator circuit and the user’s nose (nasal), mouth (oral), or mouth and nose (oronasal). These include 15-mm angled mouthpieces for daytime use, over 100 available nasal interfaces for daytime and/or nighttime use, and oronasal interfaces for those for whom nasal interfaces are inadequate for sleep due to air leakage.


Noninvasive Ventilation (NIV)

\ˌnän-in-ˈvā-siv ˌvent-əl-ˈā-shən\

Conventionally, the term noninvasive ventilation refers to bi-level PAP and CPAP. Bi-level PAP and CPAP are inadequate to fully rest or support the inspiratory muscles. Also, NIV can include the use of body ventilators which are also suboptimal for this patient population.


Noninvasive Ventilatory Support (NVS)

\ˌnän-in-ˈvā-siv ˈvent-əl-ə-ˌtōr-ē sə-ˈport\

See Critical Concepts. The term NVS has grown in popularity in modern literature to distinguish full noninvasive ventilatory support from bi-level PAP and CPAP, which invariable become inadequate with time.




Shortness of breath when lying flat on one's back (supine). Orthopnea can be caused by heart failure or diaphragm weakness and can be the presenting sign of many neuromuscular disorders as well as obesity hypoventilation syndrome.


Oximeter (Pulse Oximeter)


A device used for continuously measuring the oxygen saturation (O2 sat) of circulating blood. The sensor is placed on a thin part of a person's skin, usually on a finger, toe, or ear lobe. When a person with (low) cough peak flows <300 L/min has an upper respiratory tract infection or is in respiratory distress, O2 sat should be continuously monitored and be maintained above 94% without oxygen administration.


Oximetry Feedback Protocol

\äk-ˈsi-mə-trī ˈfēd-ˌbak ˈprō-tə-ˌkȯl\

See Critical Concepts.


Peak Flow Meter

\ˈpēk ˈflō ˈmē-tər\

A device that measures the maximum rate of air flow out of the mouth during forced expiration and can also be used to measure unassisted and assisted cough flows.


Plateau Vital Capacity (Plateau VC)

\pla-ˈtō əv ˈvī-təl kə-ˈpa-sə-tē\

Normally, the vital capacity plateaus around age 19 and then decreases by 1% (males) to 1.2% (females) per year. For people with neuromuscular disease, the vital capacity can plateau sooner (e.g. in Duchenne muscular dystrophy, the plateau occurs at the mean age of 13 years and in spinal muscular atrophy type 1, the plateau often occurs before age 4) and then decreases by more than 1% per year. Loss of lung volume and compliance can accelerate after plateau of vital capacity, so lung volume recruitment becomes necessary.




A record of physiological variables during sleep used to diagnose “sleep disordered breathing” which is a combination of central and obstructive apneas and hypopneas.

-Central apneas occur when the brain does not trigger one to breathe.

-Obstructive apneas occur when the throat obstructs breathing.

-Hypopneas are minimal breaths also caused by “central” and “obstructive” events.

For people with severe respiratory muscle weakness, polysomnograms attribute to the brain and the throat what the diaphragm and other respiratory muscles cannot do, that is, ventilate the lungs. Polysomnography is used to “titrate away” apneas and hypopneas by increasing bi-level positive airway pressures, pressures that augment inspiration but hamper expiration, during sleep. Patients who are sent for polysomnograms typically use bi-level PAP during sleep until they develop acute respiratory failure, get intubated, then either die or are told that they need tracheostomy tubes to survive. We have found that a better strategy is to provide full ventilator setting noninvasive ventilatory support (NVS) to rest inspiratory muscles during sleep. This normalizes daytime CO2 levels, relieves symptoms of hypoventilation, and with further generalized muscle weakening, is extended into daytime hours and eventually to continuous NVS, often without the user requiring hospitalizations or developing acute respiratory failure. NVS is provided without expiratory positive airway pressure (“EPAP” or “PEEP”), that is, a flow of air into the lungs during exhalation that is uncomfortable and hinders exhalation.

Physicians often use the term noninvasive ventilation (NIV) synonymously with CPAP and bi-level PAP. While bi-level PAP can assist inspiratory muscles, it is typically prescribed at ineffective low-span pressures, where the EPAP is uncomfortable and unnecessary. Furthermore, bi-level PAP cannot be used for air stacking which is critical to keep the lungs healthy. CPAP and bi-level PAP are treatments for “sleep disordered breathing” which is the combination of central and obstructive apneas and hypopneas that people can develop during sleep. Since polysomnograms only consider central and obstructive explanations for symptoms of underventilation and do not consider muscle weakness as the cause of the problem, physicians almost invariably mistakenly prescribe CPAP or bi-level PAP for people who need NVS. To avoid confusion of full noninvasive ventilatory support with CPAP and bi-level PAP, more and more physicians are using the terminology NVS rather than NIV.


Portable Ventilator

\ˈpȯr-tə-bəl ˈven-tə-ˌlā-tər\

Portable ventilators deliver air to support inspiration. Most portable ventilators can be set (preset) to deliver specific volumes of air. Volumes are typically preset at 700 to 1500 mL with backup rates of 10 to 14 breaths per minute for both daytime and nightime ventilation for older children and adults. For infants and small children, pressures are preset at about 18 to 20 cm H2O for infants and small children with backup rates dependent on age. Volume-preset is preferred for people who can air stack because air stacking is impossible with pressure-preset. Pressure-preset is preferred if volume-preset causes too much stomach distension during sleep, and it is preferred for small children who cannot air stack.


Positive End-Expiratory Pressure (PEEP)

\ˈpäz-ət-iv ˈend-ik-ˈspī-rə-ˌtȯr-ē ˈpre-shər\

This is ventilator delivered air during expiration that prevents full exhalation, so that an increased amount of air remains in the lungs following expiration. It is warranted for people using tracheostomy mechanical ventilation but virtually never for NVS users.


Partial pressure of carbon dioxide in arterial blood (PaCO2)

\ˈpär-shəl ˈpre-shər əv ˈkär-bən dī-ˈäk-ˌsīd ˈin är-ˈtir-ē-əl ˈbləd\

The partial pressure of carbon dioxide in the blood can be measured with an arterial blood gas. Normal range is 35 to 45 mm Hg. The partial pressure of carbon dioxide can also be measured with end-tidal capnography, which gives end-tidal carbon dioxide (see above).


Partial pressure of oxygen in arterial blood (PaO2)

\ˈpär-shəl ˈpre-shər əv ˈäk-si-jən ˈin är-ˈtir-ē-əl ˈbləd\

The partial pressure of oxygen in the blood can be measured with an arterial blood gas. Normal range is 80 to 100 mm Hg.


Pulmonary Function Testing (PFT)

\ˈpu̇l-mə-ˌner-ē,ˈfəŋ(k)-shən ˈtest\

This is a complete evaluation of lung volumes and flows with and without bronchodilator response, lung diffusion, plethysmography, provocative tests such as methacholine challenges for asthma and exercise challenges, and gas exchange tests by painful arterial blood gas analyses. Pulmonary function testing is unnecessary and almost useless for people with breathing and coughing muscle weakness who need vital capacity, maximum insufflation capacity, cough peak flows, capnography, and oximetry instead.




A device for measuring the air volumes leaving the lungs. Spirometry is used to evaluate vital capacity in sitting and supine positions with bracing on and off and for maximum insufflation capacity and glossopharyngeal breathing volumes.




The hole in the neck created by the tracheotomy procedure. It permits invasive tracheostomy mechanical ventilation (TMV) and airway suctioning.




A surgical procedure in which an cut is made through the skin and an airway tube is passed through the neck and into the windpipe (trachea). The airway tube is passed through the “strap” muscles in the neck. As a result, tracheotomy may cause difficulty swallowing, speaking, and protecting the airway.


Vital Capacity (VC)

\ˈvī-təl kə-ˈpa-sə-tē\

The maximum amount of air that can be exhaled into a spirometer after a full inspiration.




Able to become free of or less dependent on ventilator use.


Ventilator Circuit

\ˈven-tə-ˌlā-tər ˈsər-kət\

Ventilator circuits deliver air from the ventilator to the patient interface. They can be active or passive:

An active circuit has an exhalation valve so that if the ventilator user exhales through the tubing, the exhaled air along with its CO2 enters the atmosphere via the valve. When active circuits are used, the noninvasive patient interface must be non-vented, so any holes in the interface or air leakage must be blocked or covered.

A passive circuit has no exhalation valve. This interface is usually vented, so exhaled CO2 escapes via the holes. Passive circuits with vented interfaces are used for bi-level PAP and CPAP.








ABG – Arterial blood gas


ALS – Amyotrophic lateral sclerosis


BIM –Bulbar-innervated muscle


CO2 – Carbon dioxide


CNVS – Continuous noninvasive ventilatory support


CPAP – Continuous positive airway pressure


CPF – Cough peak flow


CPT – Chest physiotherapy or chest physical therapy


CNVS – Continuous noninvasive ventilatory support


CTMV – Continuous tracheostomy mechanical ventilation


DMD – Duchenne muscular dystrophy


EPAP – Expiratory positive airway pressure


EtCO2 – End-tidal carbon dioxide


GPB – Glossopharyngeal breathing or frog breathing.


IC – Inspiratory capacity


ICU – Intensive care unit (Critical care unit, CCU)


IPAP – Inspiratory positive airway pressure


IPPV – Intermittent positive pressure ventilation


LVR – Lung volume recruitment


MAC –Manually assisted coughing


MIC – Maximum insufflation capacity


MIE – Mechanical insufflation-exsufflation


MIE-CPF – Cough peak flow created by using mechanical insufflation-exsufflation


MIE-EF – Mechanical insufflation-exsufflation peak exsufflation flows


NIV – Noninvasive ventilation


NMD – Neuromuscular disease


NVS – Noninvasive ventilatory support


O2 – Oxygen


O2 sat – Oxygen saturation or oxyhemoglobin saturation (Normal > 95%)


PaCO2 – Partial pressure of carbon dioxide in arterial blood


PAP – Positive airway pressure


PaO2 – Partial pressure of oxygen in arterial blood


PEEP – Positive end-expiratory pressure


PFT – Pulmonary function testing


SMA - Spinal muscular atrophy


TMV - Tracheostomy mechanical ventilation


URI - Upper respiratory tract infection


VC – Vital capacity

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