The present invention deals with a mechanically constructed portable device commonly known in the pulmonary field as the peak expiratory flow meter, and, more specifically, with a device that is compact, portable and can fit into a very small purse or pocket.
In the management of pulmonary diseases, and particularly in the management of asthma, it is very common to monitor the patients' peak expiratory flow rate by means of peak flow meters. Most pulmonary patients are supposed to monitor their peak expiratory flow several times a day, record it, and present the data to their physicians on a regular basis. Furthermore, patients may experience a shortness of breath caused by a certain activity or a change in medication. In order to avoid a false alarm and panic, the value of peak expiratory flow is used as one of the first and reliable indicators of lung performance. In both regular and emergency monitoring the patient has to have a peak flow meter readily available: in a purse or a pocket. Often the patient wants a socially acceptable device that doesn't obviously suggest a medical instrument, as well as a device that doesn't require multiple actions in for example, preparation for use or to record the reading.
In accordance with the National Heart, Lung and Blood Institute guidelines mechanical peak flow meters have to be accurate over a full range to .+-.10%, the reproducibility being .+-.5% and interdevice variability being .+-.5%. When we add ease of viewing, size, manufacturing cost, ease of cleansing, and ease of recording a rather complex set of problems arises, some of them contradictory. Neither today's market nor patent art have a single mechanical peak flow meter which satisfies all of these requirements. This invention is the first one that addresses and fulfills all of them.
Although many mechanical peak flow meters are labeled as "portable" and "friendly" to use, they do not in fact satisfactorily meet these requirements. There is a need for a beeper-size device with approximate dimensions of 27/8".times.21/4".times.5/8". The device described in U.S. Pat. No. 5,224,487 which claims to be the smallest and is marketed as such, has the dimensions of 63/8".times.2".times.7/8". Its volume is almost three times the volume of the device according to this invention; when it is unfolded and ready to use, its volume is even greater. It also contains one loose piece.