Calibration of a doppler velocimeter for stroke volume determination
First Claim
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1. A method of monitoring the stroke volume (SV) of a subject'"'"'s heart at different time periods, comprising the steps of:
- determining a reference stroke volume (SVREF) of the subject'"'"'s heart by a first method different from Doppler velocimetry in a first time period;
simultaneously determining a reference systolic velocity integral (SVICAL) by Doppler velocimetry;
calculating a constant kCAL, wherein
kCAL=SVREF/SVICAL;
determining a systolic velocity integral (SVI) at later time periods by Doppler velocimetry; and
determining the stroke volume (SV) at said later periods by setting SV=kCAL·
SVL.
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Abstract
Doppler Velocimetry is a widely used method for estimating stroke volume (SV). The accuracy and reliability of its measurement however, is dependant on
- a) the correct assessment of the aortic valve cross-sectional area (CSA), and
- b) the maximal systolic velocity integral (SVI).
The invention avoids the conventional assessment of aortic valve CSA by using a calibration method: a reference stroke volume SVREF is determined by a method different from Doppler velocimetry, e.g. by thoracic electrical bioimpedance (TEB), or thoracic electrical bioadmittance, measured via surface thorax electrodes (transthoracic approach) or via electrodes located directly on an esophageal catheter/probe (esophageal approach). In the latter case, if esophageal Doppler velocimetry is used, the same catheter can be used for the placement of the electrodes and for an ultrasound transducer. In the case of esophageal Doppler velocimetry, an additional benefit of the invention is that the Doppler catheter/probe does not need to be aimed precisely at the site of maximum flow amplitude, as long as a stable catheter/probe location is maintained within the esophagus.
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Citations
19 Claims
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1. A method of monitoring the stroke volume (SV) of a subject'"'"'s heart at different time periods, comprising the steps of:
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determining a reference stroke volume (SVREF) of the subject'"'"'s heart by a first method different from Doppler velocimetry in a first time period; simultaneously determining a reference systolic velocity integral (SVICAL) by Doppler velocimetry; calculating a constant kCAL, wherein
kCAL=SVREF/SVICAL;determining a systolic velocity integral (SVI) at later time periods by Doppler velocimetry; and determining the stroke volume (SV) at said later periods by setting SV=kCAL·
SVL. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A system for monitoring the stroke volume (SV) of a subject'"'"'s heart at different times, comprising:
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a reference device for determining a reference stroke volume (SVREF) by using a first method different from Doppler velocimetry; a Doppler velocimeter for determining reference systolic velocity integral (SVIREF) and systolic velocity integral (SVI) at different times; and a device for calculating, said calculating device being adapted to obtain the reference stroke volume (SVREF) from said reference device and the systolic velocity integral from said velocimeter.
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11. A system for monitoring the stroke volume (SV) of a subject'"'"'s heart at different times, comprising:
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a reference device for determining a reference stroke volume (SVREF) by using a first method different from Doppler velocimetry; a Doppler velocimeter for determining reference systolic velocity integral (SVIREF) and systolic velocity integral (SVI) at different times; a device for calculating; and a controller for switching between; a) a calibration mode in which said reference device and said Doppler velocimeter are activated, and b) a measurement mode in which only said Doppler velocimeter is activated.
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12. An apparatus for monitoring the stroke volume (SV) of a subject'"'"'s heart at different times, comprising:
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a thoracic impedance measuring unit, including; an alternating current (AC) source connected to two ports for attaching electrodes, and a voltmeter connected to two ports for attaching electrodes; a Doppler velocimeter unit including a controller for controlling an ultrasound emitter and a signal receiving device for obtaining signals from an ultrasound receiver; and a processing unit connected to said thoracic impedance measuring unit and said Doppler velocimeter unit, said processing unit being adapted to obtain a reference stroke volume (SVREF) from said thoracic impedance measuring unit and a systolic velocity integral from said velocimeter. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19)
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Specification