1995-02-09
1997-06-03
Cohen, Lee S.
Surgery
Truss
Pad
A61B 508
Patent
active
056344716
DESCRIPTION:
BRIEF SUMMARY
This invention concerns flowmeters and, more particularly, such meters for measuring peak expiratory flow, commonly denoted as PEF.
BACKGROUND OF THE INVENTION
PEF meters are now seen to be of clinical value in the diagnosis and management of asthma and they are widely prescribed for this purpose in a portable form suited to domiciliary usage. This last form typically involves a piston-and-cylinder assembly through which the piston is movable against a spring bias by the action of a forced expiration, with the piston position affording a measure of the expiratory flow. A well known meter of this form is described in UK Patent Specification No. 1,463,814.
In any event, notwithstanding the value and usage of PEF meters, work leading to development of the present invention indicates that they have shortcomings and are open to improvement. More specifically their operation is effort-dependent. As a consequence of this, successive measures taken over a period of time by the same subject are not necessarily usefully comparable, and comparability between measures taken from different patients is probably less reliable.
SUMMARY OF THE INVENTION
An object of the present invention is to improve this situation and, to this end, it is proposed that a PEF meter be provided with means normally effective to inhibit expiratory flow through the meter, such means being operable in response to attainment of a predetermined expiratory pressure to allow the expiratory flow.
In a preferred form the flow inhibiting means of the invention comprises a valve mechanism which normally closes the expiratory flow path through the meter, the mechanism being operable to open the path.
The flow inhibiting means is preferably of a fast acting form when operated, in the sense that its operation takes a short time relative to the duration of a forced expiration and does not take significantly longer than attainment of peak flow during such expiration.
Preferably the flow inhibiting means is adapted to operate in a time significantly shorter than that taken for attainment of peak flow during forced expiration.
For these last purposes, the flow inhibiting means suitably comprises a shutter or flap valve mechanism operable to open in response to an electrical signal from a pressure detector. Such a mechanism will provide a fast-acting flow inhibiting means of minimal resistance when open.
In an alternative arrangement, the flow inhibiting means comprises a mechanism of a mechanical or magnetic form operable to open in direct response to the relevant pressure.
The meter will of course comprise some means for measuring the expiratory flow after the operation of the flow inhibiting means. This flow measuring means preferably provides an electrical signal representation of the measured flow, and for this purpose, a flow transducer of hot wire anemometer form is appropriate.
Given the signal output from such a transducer, it is a simple matter to display and/or record the flow through the expiration, or just the peak value attained during expiration.
The predetermined expiratory pressure is preferably a pressure value preset for the meter. This value may or may not be adjusted from one measure to the next or from one subject to the next.
The invention also envisages a pressure threshold whose value is not preset for the meter, but decided automatically during use. To this end the meter is provided with computing means to decide the value of the predetermined pressure in response to the electrical signal.
In this way the pressure threshold at which the flow inhibiting means operates is predetermined in the sense that, although its value is not preset, the manner in which it is determined is prescribed.
In a preferred form, a release pressure value for the flow inhibiting means is preset, and the computing means is programmed to open the flow inhibiting means at a pressure level lower than this release pressure value if such a pressure level is maintained for a predetermined length of time.
In another aspect of the invention, a method of measuri
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Fairfax Andrew J.
Hitchings David J.
British Technology Group Limited
Cohen Lee S.
Winakur Eric F.
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