| Method of controlling blood pressure cuff deflation -> Monitor Keywords |
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Method of controlling blood pressure cuff deflationRelated Patent Categories: Surgery, Diagnostic Testing, Cardiovascular, Measuring Pressure In Heart Or Blood Vessel, Force Applied Against Skin To Close Blood VesselMethod of controlling blood pressure cuff deflation description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070123784, Method of controlling blood pressure cuff deflation. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] The present invention generally relates to a method of controlling the operation of an automatic, non-invasive blood pressure (NIBP) monitor. More specifically, the present invention relates to a method of controlling the operation of a NIBP monitor to utilize both a linear deflation technique and step deflation technique to determine blood pressure. [0002] Automated blood pressure monitors employ an inflatable cuff to exert controlled counter-pressure on the vasculature of a patient. One large class of such monitors, exemplified by that described in U.S. Pat. Nos. 4,349,034 and 4,360,029, both to Maynard Ramsey, III and commonly assigned herewith and incorporated by reference, employs the oscillometric methodology. [0003] In accordance with the Ramsey patents, an inflatable cuff is suitably located on the limb of a patient and is pumped up to a predetermined pressure above the systolic pressure. The cuff pressure is then reduced in predetermined decrements, and at each level, pressure fluctuations are monitored. The resultant arterial pulse signals typically consist of a DC voltage with a small superimposed variational component caused by arterial blood pressure pulsations (referred to herein as "oscillation complexes" or just simply "oscillations"). The oscillation amplitudes measured from the cuff can range from a fraction of a mmHg to as much as 8 mmHg. [0004] After suitable filtering to reject the DC component and to provide amplification by a scale factor, peak oscillation amplitudes measured above a given base-line are stored. As the cuff pressure decrementing continues, the peak amplitudes will normally increase from a lower level to a relative maximum, and thereafter will decrease. These amplitudes form an oscillometric envelope for the patient. The lowest cuff pressure at which the oscillations have a maximum value has been found to be representative of the mean arterial pressure (MAP) of the patient. Systolic and diastolic pressures can be derived either as predetermined fractions of the oscillation size at MAP, or by more sophisticated methods of direct processing of the oscillation complexes. [0005] The step deflation technique as set forth in the Ramsey patents is the commercial standard of operation. A large percentage of clinically acceptable automated blood pressure monitors utilize the step deflation rationale. When in use, the blood pressure cuff is placed on the patient and the operator usually sets a time interval, typically from 1 to 90 minutes, at which blood pressure measurements are to be made. The noninvasive blood pressure (NIBP) monitor automatically starts a blood pressure determination at the end of the set time interval. [0006] Generally, conventional NIBP monitors of the type described in the afore-mentioned patents use oscillation pulse amplitude matching at each pressure level as one of the ways to discriminate good oscillations from artifacts. In particular, pairs of oscillation pulses are compared at each pressure level to determine if they are similar in amplitude and similar in other attributes, such as shape, area under the oscillation curve, slope, and the like. If the oscillation pulses compare within predetermined limits, the average pulse amplitude and cuff pressure are stored and the pressure cuff is deflated to the next pressure level for another oscillation measurement. However, if the oscillation pulses do not compare favorably, the attributes of the earlier oscillation are typically ignored and the attributes of the latter oscillation are stored. The monitor does not deflate; instead, the monitor waits for another oscillation to compare with the one that was stored. This process continues until two successive oscillation pulses match or a time limit is exceeded. [0007] Although the step deflation technique described above can eliminate or reduce the effect artifacts have in the blood pressure determination, the step deflation technique typically requires the detection of two oscillation pulses during each pressure step. Sometimes under artifact free circumstances an attempt can be made to obtain only one pulse at each step; however, there are still time inefficiencies even in this case. Even when the detected oscillation pulses are very clean and artifact free, the step deflation technique has an inherent delay in order to control the pressure level of each step. Therefore, the amount of time required to make a blood pressure determination will be extended by the time that the technique uses at each pressure step to control the pressure. [0008] An alternate method of obtaining a blood pressure measurement is to operate the NIBP monitor using a continuous deflation from an initial inflation pressure to a final pressure. Typically, the recommended continuous deflation pattern is linear. During the linear deflation, the cuff pressure is decreased at a specific rate (mmHg/second) and the oscillation pulse amplitudes are measured for the cuff pressure as the pressure is continuously decreased. Since, in the case when the oscillometric signal is not corrupted by artifact, the NIBP system does not need to maintain pressure at a defined step to obtain high quality pulses, an NIBP system utilizing the linear deflation technique can often obtain a blood pressure measurement more quickly than a system utilizing the step deflation technique. However, note that other factors, like pulse pressure and heart rate, do influence the time it takes to complete a blood pressure determination for either the linear or step deflate patterns. [0009] However, since the pressure of the blood pressure cuff is deflated continuously, if any one of the oscillation pulses is inaccurate due to an artifact introduced by the patient or some other external variable, the linear deflation technique does not include a mechanism to compare recorded oscillation pulse amplitudes, as is possible when utilizing the step deflation technique. Therefore, it can be understood that operating an NIBP monitor utilizing either a step deflation technique or a linear deflation technique has relative drawbacks in certain types of situations. Selectively operating an NIBP monitor utilizing both the step deflation technique and the linear deflation technique would be an improvement over the state of the art. SUMMARY OF THE INVENTION [0010] The following describes a method for measuring and displaying the blood pressure of a patient utilizing a non-invasive blood pressure (NIBP) monitor that includes an inflatable and deflatable blood pressure cuff and pressure transducer. The method obtains a series of oscillation pulses from the pressure transducer of the NIBP monitor, which are utilized to develop an oscillometric envelope and estimate the patient's blood pressure. [0011] Initially, the blood pressure cuff of the NIBP monitor is inflated to an inflation pressure above the systolic pressure for the patient. Once the pressure cuff is inflated to the initial inflation pressure, the central processor of the NIBP monitor begins to deflate the pressure cuff utilizing a continuous deflation technique. As noted previously, one possible way to continuously deflate the cuff is to use a linear pattern. The linear deflate can be accomplished with and by controlling a proportional deflate valve. However, other continuous patterns could be used just as effectively. For example, rather than maintaining a linear pattern the deflate valve could simply be opened and air allowed to escape without further control. [0012] As the pressure cuff is linearly deflated, the NIBP monitor obtains a series of oscillation pulses from the pressure transducer. Each of the oscillation pulses from the pressure transducer is compared to a predicted pulse estimate. The predicted pulse estimates can be calculated utilizing various estimation techniques, such as a simple prediction of the size of the next pulse to be observed based trends in previous pulses, a period measurement between the pulses based upon the period between previous pulses or a predicted estimate of the pulse size based upon the pulse size at the same cuff pressure from a previous blood pressure measurement cycle. Various methods and algorithms are contemplated for specifying a predicted pulse estimate that can be utilized by the central processor for comparison to a measured oscillation at some particular cuff pressure. [0013] If the central processor determines that the obtained oscillation pulse varies from the predicted pulse estimate by more than a given tolerance or percentage, the central processor interrupts the linear deflation technique and holds the pressure cuff at the current cuff pressure. [0014] While the pressure cuff is held at the current pressure, the central processor obtains additional oscillation pulses that are compared to the predicted pulse estimate and to each other. If the additional oscillation pulses do not closely correspond to each other and to the predicted pulse estimate, the central processor holds the cuff pressure constant until at least two oscillation pulses closely correspond to each other. Values for the accepted oscillation pulses are then stored and utilized when calculating a blood pressure estimate from an oscillometric envelope. [0015] Once acceptable oscillation pulses have been found, the central processor deflates the pressure cuff in a series of distinct pressure steps or it reverts to the continuous deflation technique depending on the quality of match with the predicted pulse estimate. If the central processor determines that the step deflation technique shall be used, the central processor waits for closely corresponding oscillation pulses before transitioning to the next pressure level or reverting to the continuous deflation technique. Thus, the central processor transitions from the continuous deflation technique to a pressure step deflation technique when the obtained oscillation pulses do not correspond to predicted pulse estimates. [0016] If the central processor determines that the obtained oscillation pulses during the step deflation technique closely correspond to the predicted pulse estimate, the central processor can again transition to the continuous deflation technique and again compare the obtained oscillation pulses to predicted pulse estimates. [0017] In this manner, the NIBP monitor is operated using the linear deflation technique unless the linear deflation technique is obtaining oscillation pulses that do not correspond to predicted pulse estimates. Only when the obtained oscillation pulses do not closely correspond to the predicted pulse estimates will the NIBP monitor be operated utilizing a step deflation technique, which is more effective in reducing error due to artifacts encountered during the blood pressure determination. BRIEF DESCRIPTION OF THE DRAWINGS [0018] The drawings illustrate the best mode presently contemplated of carrying out the invention. In the drawings: [0019] FIG. 1 is a high level diagram of a non-invasive blood pressure (NIBP) monitoring system; [0020] FIG. 2 illustrates oscillometric data including step deflate and oscillation pulse amplitudes derived using the NIBP monitoring system of FIG. 1; [0021] FIG. 3 illustrates oscillometric data including a linear deflate curve and oscillation pulse amplitudes derived using the NIBP monitoring system of FIG. 1; and Continue reading about Method of controlling blood pressure cuff deflation... Full patent description for Method of controlling blood pressure cuff deflation Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Method of controlling blood pressure cuff deflation patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. 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