Surgery – Diagnostic testing – Cardiovascular
Utility Patent
1999-03-24
2001-01-02
Nasser, Robert L. (Department: 3736)
Surgery
Diagnostic testing
Cardiovascular
C600S493000, C600S494000
Utility Patent
active
06168567
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a sphygmomanometer; that is, a device for measuring blood pressure using the standard Korotkoff arm cuff. More particularly, the present invention concerns a blood pressure meter for use by a physician or trained operator which incorporates electronics to overcome the disadvantages of a conventional mechanical device.
Blood pressure measurement is a standard part of any medical examination; in fact, it is the most common reason for visiting a doctor. The basic process involves two components: one is the measurement of the pressure of a cuff encircling the arm; the other is the estimation of the blood pressure based on the detection of sounds or oscillations as the cuff is gradually deflated. The standard technique, against which all others are compared, uses a mercury sphygmomanometer and a stethoscope, with a trained operator listening for Korotkoff sounds. In this case, the cuff pressure is measured by the mercury column, and the operator estimates the blood pressure from this column by the appearance and disappearance of the Korotkoff sounds.
While this technique is accepted as the “gold standard” of blood pressure measurement, it is subject to avoidable errors such as operator bias (the tendency of the operator to over or under estimate the blood pressure as the mercury column falls), excessively rapid deflation of the cuff, and digit preference (the excessive use of five's or zero's for the terminal digits).
A variant of the mercury sphygmomanometer is the aneroid device, in which the mercury column is replaced by a pressure gauge with a dial. The accuracy of these devices is questionable, however, because it is not possible to calibrate the gauge and the dial is relatively difficult to read as compared to a linear mercury column. Furthermore, the accuracy of the pressure gauge may change over time.
An increasing number of electronic devices is available in which the cuff pressure is detected by an electronic transducer and the blood pressure is derived, either from the oscillations of pressure within the cuff (the oscillometric method) or from electronic detection of the Korotkoff sounds (the auscultatory method). In both cases, the blood pressure is estimated using some electronic algorithm rather than by direct observation. The accuracy of such electronic devices varies greatly, even though they are calibrated against a mercury sphygmomanometer. The cause of the inaccuracies is not the measurement of the cuff pressure, but the algorithm used to estimate blood pressure.
It is desirable, therefore, to retain the involvement of the trained operator in blood pressure measurement. One such “hybrid” electronic blood pressure measuring device is disclosed in the U.S. Pat. No. 5,201,320. This device incorporates an electronic transducer for measuring the cuff pressure in addition to the conventional mercury pressure column. The primary use of the mercury column is the calibration of the pressure transducer and the electronic control and display circuitry. The device regulates the release of air from the cuff using an electronically controlled solenoid outlet valve. The operator presses a button when he/she hears the systolic and diastolic pressures, and the pressure values are displayed on two LED displays. This system has the advantage of utilizing the expertise of the operator in identifying the Korotkoff sounds while eliminating some of the operator bias or error in identifying the systolic and diastolic pressures. This system has the disadvantage of lacking accurate control of the cuff deflation so that the rate of deflation is not a constant. This impairs the accuracy of the correction for reaction time of the operator.
The U.S. Pat. No. 5,464,017 discloses a blood pressure meter which eliminates entirely the mercury column for measuring pressure. As in the case of the '320 patent referred to above, this device uses an electronic transducer and displays the cuff pressure with an array of LED's. In particular, the device includes a first LED display for indicating whether the blood pressure values are increasing or decreasing and second and third LED displays for displaying the systolic and diastolic blood pressure values, respectively. A physician/operator closes a switch on hearing the Korotkoff sounds which denote systolic and diastolic pressures. This signal is transmitted via an infrared or high frequency signal to a receiver, amplified and then supplied as an interrupt signal to a microprocessor to latch the blood pressure values.
This device has the advantage of eliminating the use of mercury in measuring pressure. Mercury is highly toxic and has, in fact, been banned in several European countries on environmental grounds. However, the transmitter/receiver arrangement for signaling the Korotkoff sounds is unnecessarily complicated and expensive and the LED display does not convey to the operator, in an easy-to-read way, the same pressure information as a mercury column.
SUMMARY OF THE INVENTION
It is a principal object of the present invention to provide a “hybrid” sphygmomanometer which combines the advantages of the mercury sphygmomanometer and an electronic device.
A more particular object of the present invention is to provide a blood pressure measurement device which relies on a trained operator to detect Korotkoff sounds.
It is a further particular object of the present invention to provide a blood pressure measurement device which is easy to use.
It is a further particular object of the present invention to provide a blood pressure measurement device which is inexpensive and accurate and which does not require calibration.
It is a further particular object of the present invention to provide a blood pressure measurement device having an improved system for control of cuff deflation.
It is a further particular object of the present invention to provide a blood pressure measurement device which has one or more electronic outputs for electronically downloading blood pressure measurements to a computer.
These objects, as well as other objects which will become apparent from the discussion that follows, are achieved, according to the present invention, by providing a sphygmomanometer which comprises:
(a) an arm cuff with an inflatable air bladder;
(b) a pumping device for inflating the air bladder;
(c) a manually and/or electrically actuated air outlet valve for deflating the air bladder;
(d) an air pressure transducer operative to receive the pressure in the air bladder and to produce an electrical signal representing this pressure;
(e) a manually operated switch for generating systolic and diastolic interrupt signals;
(f) a first electronic display for displaying the measured instantaneous pressure in the air bladder in the form of a bar graph;
(g) a second electronic display for displaying systolic and diastolic pressures; and
(h) an electrical circuit, connected to the pressure transducer and to the switch, for controlling said first and second display.
According to one preferred feature of the present invention, the first display, for displaying the instantaneous pressure in the air bladder, is a simulated mercury column; i.e., a bar graph formed of an LED or LCD display or a display screen, such as a CRT or flat panel display.
The two displays are preferably implemented with either LCDs or LEDs. Advantageously, a linear, LED display may be used to implement the simulated mercury column.
According to another preferred feature of the present invention, the electrical circuit provides digital signals, representing the systolic and diastolic pressures, for use by a computer for storage and processing. These signals may be transmitted directly via a serial or parallel port, radio frequency transmission, or via a modem which converts the signals into tones for transmission over a conventional telephone line.
The pumping device for inflating the air bladder may be a conventional squeeze bulb, as is used in conventional mercury sphygmomanometers, or an electrically operated pump.
The e
Holland John
Pickering Thomas G.
Pickering William
Weiss Stephen Nicholas
Accusphyg, LLC
Milde Hoffberg & Macklin, LLP
Nasser Robert L.
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