Excerpt from the
Handbook on the Late Effects of Poliomyelitis for Physicians and Survivors©
Ventilators suitable for home use are dependable and simple to operate and to maintain. Most are small enough to be portable and can operate on batteries (DC) as well as house current (AC). They are divided into two main groups: negative and positive pressure. The positive pressure ventilators are further divided into pressure-limited and volume units.
Negative pressure ventilators – The iron lung ventilates by enclosing the person's whole body, except for the head, in a chamber. Negative pressure is created intermittently in the chamber in the space around the body, causing the chest and lungs to expand for inspiration. Iron lungs are very dependable, very efficient, but are quite large, immobile, and limited to AC power. The Porta-Lung™ is a smaller fiberglass version of the iron lung and is somewhat more transportable.
Chest cuirasses, or shells, operate on the same principle as the iron lung. Instead of the whole body being placed in a chamber, only the chest and upper abdomen are covered. The cuirass is then connected by hose to a negative pressure ventilator (such as the NEV-100, Emerson 33-CR, or the old Thompson Maxivent). The cuirass is approximately 60% as efficient as the iron lung, but it cannot overcome a stiff chest wall effectively. Care must be taken to obtain a proper seal between the cuirass and the chest, or there will be a loss of pressure. There are problems of chest shell fit as body weight changes or as spinal curvatures increase. A negative pressure ventilator may also aggravate a tendency to upper airway obstruction, blocking effective ventilation, especially during sleep (Oppenheimer & Baldwin-Myers, 1993).
The rocking bed ventilates by tilting. The bed moves in an arc of about 20 degrees, alternating head down with feet down. With the feet down, the abdominal contents drop, causing inspiration, and move upward with the head down, causing expiration. This unit also requires that the person have no increased airway resistance. Contrary to popular belief, motion sickness is rare since the person is moving in only one plane. Although no longer manufactured, the rocking bed is still used by a few survivors to aid circulation and for daytime naps.
Positive pressure ventilators – Some polio survivors still use the pneumobelt, or exsufflation belt, as a companion to either the iron lung, cuirass, or rocking bed. The system includes an inflatable bladder, placed over the abdomen with a corset holding it in place. The bladder is inflated by positive pressure (30-50cm H20) pumped into it, causing the abdominal contents to displace upward, producing exhalation. When the pressure on the bladder is released, the diaphragm descends by gravity, thus facilitating inhalation. The individual must be sitting upright for inhalation to occur. The pneumobelt is about 50% as efficient as the iron lung and is useful if a polio survivor has compliant lungs. Those with a major degree of chest restriction, or mucus production, probably will not benefit from this system. Pneumobelts are still available on a rental basis, but many polio survivors are switching to other types of assisted ventilation.
Pressure-limited ventilators deliver air until a pre-set amount of pressure has been achieved in the circuit. The primary ventilators in operation from the late '60s until the late '70s, these units, such as the Monaghan, Huxley, and Bantam, are control-cycled with the respiratory rate pre-set. Controlled ventilation generally has worked well on individuals with severe quadriplegia, since these individuals exercise little and usually do not have to change their respiratory rate. These pressure-limited ventilators are no longer being manufactured or serviced; many polio survivors are converting to volume ventilators or to bi-level pressure systems.
In the mid '80s, bi-level pressure support systems became available for noninvasive nasal positive pressure ventilation (NPPV), usually with an interface of a nasal mask or nasal pillows held in place with headgear with adjustable straps. Lightweight (about 10 lbs.), easy to use, and more efficient than other noninvasive techniques to assist ventilation, these systems evolved from CPAP (continuous positive airway pressure) devices for treating sleep apnea and provide expiratory positive airway pressure (EPAP) as well as inspiratory positive airway pressure (IPAP). As of 1999, they are approved as assisted ventilation devices, but are not approved for continuous use over 16 hours per day (life support) or to be connected to a tracheostomy (Make et al., 1998).
Bi-level pressure support systems are approved to assist ventilation for people who can breathe spontaneously at least part of the time. They do not have a built-in battery, but an adapter is usually available for an external battery. Models are available with or with-out timed cycling and backup rate and have limited alarms. Examples include: Respironics Bi-PAP® S/T and Tranquility Bi-Level; Puritan Bennett KnightStar™ 320, 335 from Mallinckrodt; AirSep Remedy™; Sunrise Horizon Bi-Level; and ResMed VPAP II® ST (Resource Directory for Ventilator-Assisted Living). Examples outside the United States include: Breas® PV 101, PV 102, PV 401; Dräger RespiCare; Nippy from Friday Medical; and Taema DP90 (Simonds, 1996).
Portable volume ventilators, used since the late '70s, deliver a pre-set volume of air and adjust the pressure needed to deliver the air, depending on the airway resistance. Volume ventilators can be used to stack breaths to augment effective cough. They have an internal battery that will run the ventilator for about one hour and can be connected to an external rechargeable marine battery to provide portable power for over 12 hours. Equipped with built-in alarms, such as for disconnection or machine failure (low pressure) and for air blockage (high pressure), they are heavier and more expensive in the United States than the bi-level devices, but more powerful. Also, they have more safety features and thus are approved for use up to 24 hours per day for people using tracheostomy positive pressure ventilation (TPPV), as well as for people using NPPV with nasal mask or pillows, or mouthpiece. Examples include: Puritan Bennett LP6 Plus, LP10 from Mallinckrodt; Respironics PLV-100, PLV-102; and Bear 33. Outside the United States, examples include: BiOMS AIROX Home 2; Brompton PAC; Breas® PV 501; Dräger EV 801; Taema Monnal D, Monnal DCC; Saime Eole 2, Eole 3; and Puritan Bennett Companion 2801 from Mallinckrodt (Simonds, 1996).
Ventilators manufactured in the late '90s, such as Pulmonetic Systems' LTV1000™, Impact Instrumentation's UniVent™ Eagle™ 754, and TBird® Legacy from Thermo Respiratory Alternate Care, may prove to be a new generation of positive pressure ventilators for long-term home care: compressorless, turbine-driven, smaller, and lightweight. However, the efficacy of these units has yet to be reported by polio survivors.
When using a positive pressure ventilator noninvasively, a variety of nasal mask interfaces are available in addition to nasal pillows and mouthpiece assemblies. Many people can be ventilated with mouth positive pressure during the day (Bach, 1996). The mouthpiece can be placed on a movable arm to allow it to stay next to the person's mouth for intermittent use – "sip and suck." Persons with no vital capacity can be ventilated during the night with a nasal mask or pillows or a Bennett Seal Mouthpiece Assembly held in the mouth with a headgear assembly or straps. These ventilator users become conditioned to take in sufficient air during their sleep from a cycled ventilator with a fixed rate and a pressure set high enough to compensate for leaks.
The success of NPPV often depends upon an effective cough. There are manual techniques to augment a cough and improve clearance of bronchial secretions, as well as mechanical devices, such as the J.H. Emerson Company's In-Exsufflator to assist cough (see Coughing).
TPPV, invasive positive pressure ventilation via a tracheostomy, may be necessary when noninvasive ventilation is not successful (see Tracheostomy).