(1) Field of Invention
The present invention relates to health care equipment and more specifically to a sphygmomanometer and method for controlling optimum pressurization and minute exhaustion of air while measuring blood pressure.
(2) Description of the Prior Art
A sphygmomanometer is an apparatus for measuring the blood pressure of a subject. The sphygmomanometer comprises a cuff which is wrapped around the upper arm. The cuff is inflated by a pump which provides sufficient pressure to compress the brachial artery in the upper arm. A pulsation transmitted from the artery to the cuff is processed by an electrical circuit to determine the blood pressure of a patient.
A portable sphygmomanometer is described in Korean Pat. No. 93-24242 filed on Nov. 15, 1993, entitled "A portable sphygmomanometer worked by hand".
A conventional sphygmomanometer is shown in FIG. 1 which includes a key inputting means 11 connected to a microcontroller 13, an air pumping means 15 connected to the output of a the microcontroller 13, a display 14 connected to second output of the microcontroller 13, and a sensor 12, a solenoid valve 16, a cuff 18, and a minute exhaustion valve 17 which are coupled to the air pumping means 15 output through an air duct. The output of the sensor 12 is fed back to the input of the microcontroller 13. The solenoid valve 16 is controlled by a third output of the microcontroller 13.
In operation, a user inputs an operating command with the key inputting means 11 causing the microcontroller 13 to activate the air pumping means 15 to pressurize the air duct. The air pressure is transmitted to the sensor 12, the solenoid valve 16, the cuff 18, and the minute exhaustion valve 17 through the air duct.
During the pressurization process, the microcontroller 13 causes the solenoid valve 16 to remain closed so that the majority of air flow is directed to the cuff 18 wrapped around the upper arm of the subject. During the pressurization process, the sensor 12 begins detecting pressure waves transmitted from the brachial artery and converts them into electrical signals for processing by the microcontroller 13. The pressurization process continues until the processor detects no further pressure waves from the sensor at which point the pressure in the cuff indicated by the sensor is read into memory of the microcontroller 13. This pressure represents the systolic pressure of the subject.
Once the pressurization process is terminated, the depressurization of the air duct occurs by exhausting the air through the minute exhaustion valve 17. Similarly to the pressurization process, the sensor 12 converts the pressure waves from the brachial artery to an electrical signal for processing by the microcontroller 13 until no further pressure waves are detected at which time the pressure in the cuff is read in the memory. This pressure represents the diastolic pressure. The microcontroller 13 outputs data to a display for a visual readout of the systolic and diastolic pressure. Upon displaying the results, the microcontroller causes the air duct to completely depressurized by opening the solenoid valve 16. A graphical representation of the pressure waves during the depressurization process is shown in FIG. 2.
With the recent trend toward improved health care, a demand has arisen for portable sphygmomanometers which can be operated by an individual. A portable sphygmomanometer is described in Korean Pat. No. 93-24242 filed on Nov. 15, 1993, entitled "A portable sphygmomanometer worked by hand." However, to accommodate the commercialization of portable sphygmomanometers, the size and cost of these devices must be reduced.
One obstacle to meeting these commercial objectives is that a conventional sphygmomanometer uses an expensive rolling pump with a large air tank to attenuate pressure fluctuations that would otherwise result in inaccurate blood pressure readings. Moreover, the pump typically generates excessive pressure than that required and therefore results in unnecessary power consumption.
Another obstacle to commercialization of the portable sphygmomanometer is that the minute exhaustion valve is a precision part requiring a complicated manufacturing process to satisfy the standardized exhaustion deviation and thereby contributes to the production costs of the sphygmomanometer. If the exhaustion rate is not within the standardized deviation, according to an arm thickness of the object, the quality and size of the cuff, the pressure fluctuations of the device, the pressurization of the cuff, and heart rate of the patient, the accuracy of the blood pressure measurement will be reduced.