Surgery – Truss – Pad
Patent
1996-04-19
1998-03-03
Bahr, Jennifer
Surgery
Truss
Pad
128687, A61B 502
Patent
active
057224145
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to systems for measuring arterial blood pressure. In particular, the invention relates to a sensor assembly for measuring arterial blood pressure in a relatively continuous and non-invasive manner.
Blood pressure has been typically measured by one of four basic methods: invasive, oscillometric, auscultatory and tonometric. The invasive method, otherwise known as an medal line (A-Line), involves insertion of a needle into the artery. A transducer connected by a fluid column is used to determine exact arterial pressure. With proper instrumentation, systolic, mean and diastolic pressure may be determined. This method is difficult to set up, is expensive and involves medical risks. Set up of the invasive or A-line method poses problems. Resonance often occurs and causes significant errors. Also, if a blood clot forms on the end of the catheter, or the end of the catheter is located against the arterial wall, a large error may result. To eliminate or reduce these errors, the set up must be adjusted frequently. A skilled medical practitioner is required to insert the needle into the artery. This contributes to the expense of this method. Medical complications are also possible, such as infection or nerve damage.
The other methods of measuring blood pressure are non-invasive. The oscillometric method measures the amplitude of pressure oscillations in an inflated cuff. The cuff is placed against a cooperating artery of the patient and thereafter pressurized to different levels. Mean pressure is determined by sweeping the cuff pressure and determining the mean cuff pressure at the instant the peak amplitude occurs. Systolic and diastolic pressure is determined by cuff pressure when the pressure oscillation is at some predetermined ratio of peak amplitude.
The auscultatory method also involves inflation of a cuff placed around a cooperating artery of the patient. Upon inflation of the cuff, the cuff is permitted to deflate. Systolic pressure is indicated when Korotkoff sounds begin to occur as the cuff is deflated. Diastolic pressure is indicated when the Korotkoff sounds become muffled or disappear. The auscultatory method can only be used to determine systolic and diastolic pressures.
Because both the oscillometric and the auscultatory methods require inflation of a cuff, performing frequent measurements is difficult. The frequency of measurement is limited by the time required to comfortably inflate the cuff and the time required to deflate the cuff as measurements are made. Because the cuff is inflated around a relatively large area surrounding the artery, inflation and deflation of the cuff is uncomfortable to the patient. As a result, the oscillometric and the auscultatory methods are not suitable for long periods of repetitive use.
Both the oscillometric and auscultatory methods lack accuracy and consistency for determining systolic and diastolic pressure values. The oscillometric method applies an arbitrary ratio to determine systolic and diastolic pressure Values. Similarly, the auscultatory method requires a judgment to be made as to when the Korotkoff sounds start and when they stop. This detection is made when the Korotkoff sound is at its very lowest. As a result, the auscultatory method is subject to inaccuracies due to low signal-to-noise ratio.
The fourth method used to determine arterial blood pressure has been tonometry. The tonometric method typically involves a transducer including an array of pressure sensitive elements positioned over a superficial artery. Hold down forces are applied to the transducer so as to flatten the wall of the underlying artery without occluding the artery. The pressure sensitive elements in the array typically have at least one dimension smaller than the lumen of the underlying artery in which blood pressure is measured. The transducer is positioned such that at least one of the individual pressure sensitive elements is over at least a portion of the underlying artery. The output from one of the pressure sensit
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Archibald G. Kent
Curran Timothy G.
Danielson Orland H.
Poliac Marius O.
Thede Roger C.
Bahr Jennifer
Medwave, Inc.
Yarnell Bryan K.
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