Surgery – Diagnostic testing
Reexamination Certificate
2000-07-25
2004-03-16
Winakur, Eric F. (Department: 3736)
Surgery
Diagnostic testing
C600S485000, C600S490000, C600S500000, C128S903000, C128S904000
Reexamination Certificate
active
06705990
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to methods and apparatus for monitoring subjects afflicted with various diseases, and specifically to the non-invasive monitoring of physiologic parameters of a subject in the home environment, and communication of this information to a remote location such as a hospital or other medical facility.
2. Description of Related Technology
Congestive heart failure (CHF) is a common, but serious medical condition, which affects hundreds of thousands of people annually. The condition is caused by failure of the heart to function efficiently. In effect, the heart is unable to adequately pump blood throughout the body, which results in a general weakness and lethargy, especially when an individual attempts to exert themselves physically. The greater the severity of the disease, the less capable will be the individual to perform even routine daily activities such as walking, standing, and the like.
Unfortunately, after diagnosis of the condition, which is usually made with a series of tests including cardiac ultrasound, ECG and blood pressure readings, treatment is generally limited to pharmacological therapy including beta-blockers and diuretics to reduce the load on the heart. CHF patients who are otherwise in generally good health are often candidates for heart transplants.
For the majority of patients however, the major challenges are to learn how to alter their lifestyle and live in accordance with the disease limitations. Diet and limited exercise are often prescribed. In addition, a major emphasis is placed on prevention of weight gain, which is often associated with excessive fluid intake or failure to excrete sufficiently, both of which add load to the already failing heart. In many cases, dramatic and rapid changes can occur in an individual, including dyspnea, rapid heart rate and dizziness, if the ejection fraction of the heart falls below certain physiologic limits for a given individual. When this occurs, CHF patients are often emergent cases requiring hospital admission. Subsequently, the typical course of therapy for such patients is increased diuretic therapy to stabilize the situation and them return them to home care.
Medical practitioners generally agree that CHF patients can readily be maintained in their home environment providing that careful monitoring of the key cardiovascular components is routinely performed. Such routine monitoring may be required weekly, daily, or even hourly for certain subjects. Most importantly, the measurement of certain key parameters including weight change, heart rate, and blood pressure would allow for reasonable management of the subject in the home on a day-to-day basis. Changes in peripheral arterial oxygen saturation level, if known, would also be quite useful in the management of the subject. Other parameters relating to the subject's physiology such as basic blood chemistry would also be of use if available. However, under the prior art, no apparatus or techniques exist which provide monitoring of the foregoing physiologic variables of a subject without extensive assistance from a clinician, spouse or other caregiver. Hence, the CHF patient is presently forced to choose between retaining a part- or full-time in-home caregiver, utilizing their spouse extensively (if one exists) as a caregiver, or routinely being transported to a medical facility or visited by a clinician/physician for monitoring. Each of these options has significant drawbacks, ranging from the cost of providing the required care in-home or at the designated medical facility, to the more intangible reduction in quality of life for both the subject and his/her spouse. Clearly, if a CHF (or other) subject could be routinely monitored at home without requiring any significant participation by a caregiver or his/her spouse, then significant benefits in terms of reduced healthcare costs and improved quality of life would be realized.
Another complicating factor in monitoring CHF patients relates to the measurement of blood pressure; routine blood pressure measurements such as those described above can be extraordinarily difficult because of technical limitations associated with current state-of-the-art “cuff” devices, such as those employing the well known auscultation or oscillometry techniques. Specifically, the accuracy of such existing cuff-based blood pressure monitoring devices may be greatly reduced in subjects having low blood pressures and very weak, “thready” (i.e., not steady, or firm) pulses. This reduced accuracy relates in great part to the method by which the cuff devices estimate blood pressure. Furthermore, even if good accuracy is achieved on certain measurements, the clinician or caregiver is left with substantial uncertainty as to which measurements obtained from the subject are accurate or reflective of the actual condition of the subject, and which are not.
Another intrinsic disability of existing blood pressure measurement techniques relates to their non-continuous nature. Specifically, prior art auscultation and oscillometry techniques are geared primarily to “spot” measurement of blood pressure; i.e., at one discrete point in time. As is well known in the medical arts, such spot measurements, even when accurate, may or may not be indicative of the actual physiologic state of the subject. For example, if the blood pressure of the subject is measured during an interval when their blood pressure is artificially increased or depressed, broader trends or patterns in the subject's blood pressure may be masked. As with most any measurement process, observations made on the basis of few data points are generally less reliable and less meaningful than those made on the basis of many data points. In order to obtain a plurality of measurements using the aforementioned prior art techniques, the cuff would need to be inflated and deflated a number of different times, which is very cumbersome and uncomfortable for the subject. Furthermore, repeated inflations of a blood pressure cuff may cause nerve damage to the brachial plexus or damage to the underlying tissues. It is effectively impossible to obtain a truly continuous representation of a subject's blood pressure using these prior art techniques, since there is a practical limit on how rapidly multiple consecutive measurements can be made. Errors due to respiration effects on blood pressure (due largely to the changing volume of the thoracic cavity) may also contribute to the inaccuracy of “spot” blood pressure measurements.
Continuous blood pressure measurements may be made using prior art invasive catheters (commonly known as “A-lines”), however, such devices require the actual surgical implantation of the catheter into the blood vessel of the subject, which is clearly not well suited to long-term daily monitoring of the subject's blood pressure, especially in the home care environment.
In addition to the foregoing, it is often useful to compare values of other physiologic parameters measured concurrently with blood pressure in order to gain a broader perspective on the subject's condition. Prior art blood pressure measurement techniques do not lend themselves well to such simultaneous monitoring, in large part due to the fact that they are “spot” measurements and not continuous in nature. Hence, unless the spot measurement is synchronized to coincide with the other measurements, simultaneous monitoring is not possible. In the context of home healthcare, it is unreasonable to expect a subject (or even a trained caregiver, for that matter) to obtain such synchronized measurements.
Hence, when considered as a whole, the use of cuff-based blood pressure measurement devices on CHF patients (or other subjects with low blood pressure and/or weak, thready pulses) generally produces results which are at best only snapshots of a subject's true blood pressure, and at worst of questionable reliability and poor accuracy. Often, measurements of blood pressure taken by the subject using either automa
Gallant Stuart L.
Markle William H.
Gazdzinski & Associates
McCrosky David J.
Tensys Medical, Inc.
Winakur Eric F.
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