Team Medical has been developing technology to measure in real time the volumetric flow rate of the blood being pumped by the heart. Today, no one can know how well a heart is actually pumping blood for a simple reason: no means exists for measuring the rate that blood flows out of the left ventricle. It is estimated that over 500 people die every day from undetected heart ailments because a fast, accurate, and easy means of measuring cardiac pumping function does not exist. The goal is to measure in real time the rate at which blood flows from the heart using noninvasive means, such as ultrasonic Doppler. Team Medical has filed for patents covering its inventions in this area. Two patent applications have been published. One covers a new means of noninvasively determining the volumetric flow rate of blood. The other covers a novel signal processing technique. Together these applications describe solutions to the two fundamental problems associated with noninvasively measuring in real time the volumetric flow rate of blood. - What is the cross sectional area of the blood vessel? Doppler methods can provide the velocity of flowing blood, but unless the cross sectional area of the blood vessel, such as the ascending aorta, is known the volumetric flow rate cannot be calculated. Previous approaches to estimate the cross-sectional area have attempted to image the blood vessel or bounce signals off the side walls. These methods suffer from many deficiencies, such as needing to get an ultrasonic probe very close to the blood vessel. Team Medical's method is completely new. It recognizes that the rate of change of the blood flow rate itself provides information on the dimensions of the blood vessel and uses this information to determine the dimensions of the blood vessel. This patent application also describes how to avoid problems that can confound using Doppler ultrasound. In particular, the application also describes how to discriminate between the signal that comes from the blood flowing in the vessel from the part of the signal that comes back from all of the other slow moving and stationary tissue structures.
- What is the frequency spectrum of the returned signal when the flow rate is changing and the signal has been quantized by the measurement process? The velocity profile across a blood vessel changes during the cardiac cycle. For major arteries this change is significant and for the aorta the blood flow rate changes quickly enough that the flow rate is never steady state. Consequently, the signals emanating from such sources also change constantly, which means that the spectral content of the signals also changes constantly. Traditional methods of spectral analysis that rely on Fourier and other transform methods cannot handle such nonstationary signals when high resolution is needed. Traditional methods cannot obtain a long enough data stream to provide good frequency resolution. Methods based on analyzing time-series, such as AR and ARMA methods, are poorly suited. For example, the spectra calculated using time series methods strongly depend on the order of the model selected, which cannot be reliably determined. Further compounding the problem is that the data available have been distorted by the measurement process. The continuous signal is converted into numeric values using an analog to digital conversion process that puts measured values into bins, a process that introduces digitization errors. The method described in the patent application calculates continuous spectral density functions using data from nonstationary signals that have digitization errors. Among the features of the method are a novel regularization method that leads to unique solutions (to remove the uncertainty caused by the digitization error) that does not require using external weighting factors, overcoming a deficiency of methods such as Tikhonov regularization.
The technical approaches were developed to overcome problems that are encountered when obtaining data in the real world. For example, any interrogation using an output signal, such an ultrasonic beam, will get signals back from not only the region of interest where blood is flowing, but also from many other tissues. It is impractical to expect a clinically useful device to employ a very narrow beam that only interrogates a tiny hard to locate region deep inside a patient. Therefore, the method for determining channel dimensions has been designed to automatically sort through the returned signal and discriminate between the region that has the blood flow and all of the other regions. A variety of possible implementations exist. In practice, the overall process consists of three steps: (a) send a signal into the tissue and get back a reflected signal, (b) process the reflected signal to get the distribution of velocities of the tissues and determine the area of the channel through which blood is flowing, (c) use the distribution of velocities to calculate the average flow rate of the blood and multiply this value times the area of the channel to obtain the blood's volumetric flow rate. The volumetric flow rate is the much more valuable instantaneous flow rate, not a long term average such as occurs when using cardiac catheters. Plus, it is obtained noninvasively from, for example, an external probe placed on the surface of the skin in the sternal notch rather than using an uncomfortable and inconvenient probe going down the patient’s esophagus. In somewhat more detail, the following steps are used: - Using an interrogating signal, such as ultrasonic Doppler, receive a signal back from the region of interest, such as where the ascending aorta carries blood from the heart.
- Using the signal processing method calculate the signal's spectral density function.
- Calculate the velocity spectrum from the signal's spectral density.
- Calculate the cross sectional area of the channel, such as the ascending aorta, based on changes in the velocity spectrum every, for example, 5/1000 ths of a second.
- Calculate, using the velocity spectrum, the average velocity. Use this value and the cross sectional area to calculate the volumetric flow rate.
- Display the volumetric flow rate directly or use various derived parameters, such as the rate of change in velocity (blood flow acceleration) to evaluate the condition of the patient's heart. These data can be used in other ways, too. For example, the instantaneous volumetric flow rate data can be used in conjunction with an EKG to show heart pumping activity along with the myocardium's electrical activity.
Published United States Patent Application for "Method and system for obtaining dimension related information for a flow channel" - US20030114767.PDF (images of all pages -- this file is 2.7 MB)
- US20030114767 text.PDF (text of description and claims -- this file does not have figures or mathematical expressions. It is much smaller: 0.2 MB)
Published United States Patent Application for "Diagnostic signal processing method and system" - US20040122317.PDF (images of all pages -- this file is 3.4 MB)
- US20040122317 text.PDF (text of description and claims -- this file does not have figures or mathematical expressions. It is much smaller: 0.2 MB)
The technology described differs from all other cardiac output measurements known to Team Medical. For additional information regarding these technologies and opportunities to license them or participate in their development, please contact Warren Heim at Team Medical.
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