Breathing assistance apparatus

Details Breathing assistance apparatus Breathing assistance apparatus

2002-01-25

2003-11-11

Lo, Weilun (Department: 3761)

Surgery

Respiratory method or device

Means for supplying respiratory gas under positive pressure

C128S204170, C128S204180, C137S383000

Reexamination Certificate

active

06644313

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the use of a pressure regulator in conjunction with a breathing assistance apparatus, particularly though not solely, for regulating the pressure of gases supplied to a patient from a humidified Positive End Expiratory Pressure (PEEP) apparatus.
BACKGROUND ART
At the moment of their first breath, a baby's lungs are collapsed and filled with fluid. The pressures needed to open such lungs, and keep them open, are several times that of a normal breath until the fluid is displaced and the lungs have filled with air. To generate these large pressures, the baby must have strong respiratory muscles, as well as a chemical called surfactant in their alveoli. Surfactant reduces the surface tension of the fluid within the alveoli, preventing the alveolar walls from sticking to each other, like coasters to coffee cups when there is water between them.
Neonates have difficulty in opening their lungs and keeping them open. Reasons for this include:
a) Weak respiratory muscles and low surfactant levels. This means that they cannot generate enough pressure to open the lungs and, should they be resuscitated, tire quickly with the effort of keeping open alveoli lacking in surfactant.
b) Underdeveloped internal tissue structure to support the alveoli.
c) Slower clearance of lung fluid. In very premature neonates, fluid may continue to be secreted in the alveoli even after birth.
d) A soft chest wall, horizontal ribs, and a flatter diaphragm contribute to reduce the inspiratory capacity.
e) The mixing of oxygenated and deoxygenated blood raises blood pressure in the lungs, increasing fluid movement from the blood vessels into the lung tissue. The reduced blood oxygen level starves tissue of oxygen and further weakens respiratory muscles.
f) Weak neck muscles and a lack of neck fat reduce upper airway stability so that collapse on inspiration may occur.
g) Collapsed, damaged alveoli secrete proteins that reduce surfactant function.
To alleviate this it is know to apply positive end expiratory pressure (PEEP) during respiration. In applying PEEP, the neonate's upper airway and lungs are held open during inspiration, while expiration occurs against a pressure that stops alveolar collapse. Lung fluid is pushed back into the circulating blood, alveolar surfactant is conserved, and a larger area of the lung participates in gas exchange with the blood. As blood oxygenation and carbon dioxide removal improves, more oxygen is delivered to growing tissues, while less oxygen and energy is consumed by respiratory muscles.
PEEP therapy is known to cause lung rupture (or pneumothorax) in 0-30% of nasally ventilated neonates with air embolism in the vasculature also known to occur. It was originally thought that air would leak out of the mouth should pressures become to high, and therefore the cause of the ruptures was unclear. Perhaps chin-straps, which are used to stop mouth leak and pressure loss, were used on those neonates who later developed pneumothoraaes. Alternatively, it may be that mouth leak never occurs, even under high pressures, because the neonates are obligatory nose-breathers.
To avoid such side effects it is thought desirable in the art to provide a pressure relief valve as a safety device to prevent the pressure rising above a maximum safe level. Accordingly it is well known in the art to use a spring biased valve which actuates at a level of pressure deemed the maximum permissible to allow the gases to vent eternally. This in turn requires the use of high quality springs which have been individually tested to give a high tolerance spring constant in order to ensure that it actuates at a value substantially that of the maximum safe pressure. Both the manufacture and testing of such a spring necessitates that its cost will be correspondingly high. Accordingly it would be advantageous to provide a pressure relief valve for a breathing assistance system which did not involve the use of such a high tolerance spring.
For example in U.S. Pat. No. 4,515,179 a pressure relief valve including a housing defining an internal valve chamber is described. A valve seat is positioned within the chamber, and a valve pallet is reciprocally mounted within the chamber to engage the seat in a valve closed mode. A spring is mounted with in the housing to bias the valve pallet into engagement with the valve seat. A spring retainer is threaded through an aperture in the housing and extends into the valve chamber. The spring is located with in the retainer. A desired set pressure to be imposed upon the valve pallet is provided by threading the retainer relative to the housing thereby compressing the springs. To lock the retainer relative to the housing an annular lock member is threaded onto the outside of the retainer. Once the desired set pressure is attained, the lock member is threaded on the retainer until it abuts the housing. The lock member includes first and second ends spaced apart to define a gap. A fastener is threaded into the first and second ends across the gap and maybe tightened to narrow the gap and set the lock member onto the retainer. The retain is then locked relative to the housing by a jamming screw threaded through the lock member into engagement with housing. To provide better control of the spring an alternative retainer may be employed. The alternative retained includes a pair of telescoping tubes with the spring positioned with in the tubes. A first tube of the pair extends through end is threaded in a bushing mounted in an aperture in the valve housing. A second tube is connected by a gimbal mounting to the valve pallet. An alternative lock member may be secured to the retain by a radial fastener.
In U.S. Pat. No. 5,664,447 a lockout device is disclosed to prevent tampering with the manually set position of a valve or regulating or other device having a rotatable shaft for adjusting, for example, the flow of fluid through the device, from a position initially set to some other position. The lockout device is usable with a wide range of standard valves and regulators which have a drive stem and includes a drive gear that engages the drive sten and a key locking device mounted in a generally cylindrical handle of the lockout device and being selectively movable from first position in which the handle free-wheels relative to the drive stem of the valve so as to prevent unauthorized moving of the rotational position of the valve stem by any person not having a key to an engaging position in which the handle is locked to the drive stem to permit ordinary rotational movement and setting of the valve stem position.
In U.S. Pat. No. 5,950,623 an adjustable pressure limiting valve having a non-linear biasing means is described. The valve has a movable valve member that can be moved to an open position by a predetermined pressure and a closed position on a valve seat. A rotating control knob is rotated by the use to adjust the bias acting against the movable valve member toward the closed position to, in turn, set the pressure at which the valve opens. A rotating cylindrical drum rotates along with the control knob and has a helical groove formed in its exterior and a pair of fixed pins that ride in the helical groove. When the cylindrical drum is rotated, the fixed pins riding in the helical grove cause the cylindrical drum to move along its longitudinal axis to compress or decompress a spring acting against the movable valve member. The relationship between the rotational movement of the control knob and the longitudinal movement of the cylindrical drum.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a pressure regulator which goes some way to overcoming the above-mentioned disadvantages, or which will at least provide the Healthcare industry with a useful choice.
Accordingly, in a first aspect, the present invention consists in a pressure regulating device for use with a breathing assistance apparatus which conveys gases to a patient requiring breathing assistance, comprising or including:
housing

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