Blood Flow Monitoring

Abstract

The present invention relates to a method of utilizing photoplethysmography obtained from a central site and a non-central site to detect a low blood flow or low blood volume condition. Also disclosed are apparatuses and systems designed to acquire and process physiological information based on photoplethysmograpy signal information from dual sites.

Description

CLAIM OF PRIORITY[0001]This application is a continuation of U.S. patent application Ser. No. 11 / 535,295 filed Sep. 26, 2006, which is a continuation of U.S. patent application Ser. No. 10 / 751,308, Filed Jan. 2, 2004, which is a continuation in part of Ser. No. 10 / 749,741 filed Dec. 30, 2003, now U.S. Pat. No. 7,024,235, which is a continuation in part of Ser. No. 10 / 176,310, filed Jun. 20, 2002, now U.S. Pat. No. 6,909,912 and International Application No. PCT / US03 / 19294, filed Jun. 19, 2003, and claims benefits under 35 U.S.C. §§120 for all above-noted applications. These patent applications are hereby incorporated by reference into this application in their entireties.FIELD OF THE INVENTION[0002]The present invention relates to the field of non-invasive measurement of signals indicating arterial blood oxygen saturation by means of pulse oximetry, and of photoplethysmographic signals indicating flow characteristics, and in particular, configurations of a pulse oximeter probe that ...

AI Technical Summary

Benefits of technology

The present invention is a non-invasive vascular perfusion / resistance monitor system that uses two pulse oximeter probes to continuously measure blood oxygen saturation values and blood pressure / pulse values. The system analyzes the signals from the probes and calculates various oxygen saturation and blood pressure values based on the signals from the probes and the light detectors. The system can detect and monitor changes in these values to alert the user and provide information on the vascular perfusion and resistance. The system is designed to be accurate and reliable, and can be used in a variety of medical settings to assess peripheral vascular disease and blood flow.

Problems solved by technology

Diseases, acute injuries, and other conditions can adversely affect blood flow to and in the limbs.

Poor blood flow reduces the amount of oxygen that is carried in the blood stream to cells.

If oxygen levels in the blood become very low at peripheral sites, a variety of problems may occur which include inadequate resuscitation, cell death or necrosis that can lead to non-healing lesions, gangrene and amputation of limbs.

Such patients may have impaired and / or diminished cardiopulmonary capacity.

Hypoxia, low oxygen delivery, or hypoxemia, low oxygen tension in the blood, cause a number of maladies including polycythemia (increased hematocrit) which leads to abnormal clotting.

However, in persons who have impaired cardiocirculatory reserve, increased cardiac output in response to low arterial oxygen level can, under certain circumstances, eventually lead to death.

Chronic hypoxemia can lead to a switch by metabolically active cells to anaerobic metabolism, which, especially in patients with limited cardiopulmonary reserve, can lead to lactic acidosis and eventually death.

Hypoxemia also causes cognitive dysfunction either acutely or chronically which can lead to early dementia and death.

Generally, based on the compensatory mechanisms and effects on body tissues, chronic hypoxemia may affect all organs in the body leading to failure of any or all organs.

Conventional pulse oximetry measurement in certain classes of patients, for instance severely burned patients, can be a significant challenge, yet this monitoring data is vital in operating room and intensive care settings.

However, in one example, patients with severe burns often have only a few sites suitable for the effective placement of the transmitting pulse oximeter sensor.

These patients often have severe circulatory compromise rendering the current peripheral pulse oximeters less effective.

The background absorbance of tissues and venous blood absorbs, scatters and otherwise interferes with the absorbance directly attributable to the arterial blood.

U.S. Pat. No. 6,334,065 does not address the use of two probes for detection, confirmation, or monitoring of perfusion- and resistance-related conditions in the patient.

One major problem with this device is that it does not permit cross-site comparisons of oxygen saturation values between several tissue sites.

U.S. Pat. No. 4,928,691 states that measurement at the preferred central sites provide accurate oxygen saturation and pulse readings for “patients with lowered or inconsistent peripheral perfusion.” Critically, the probes according to U.S. Pat. No. 4,928,691 are highly flexible, leading to a high likelihood that upon typical movement of the patient there would be mal-alignment between the light source(s) and sensor, resulting in skewed, non-usable, or unreliable signals and results.

Also, there is no teaching or suggestion to compare oxygen saturation values between several tissue sites to identify, characterize, or monitor peripheral perfusion conditions in such patients.

However, the '659 patent does not disclose a nasal pulse oximeter probe that does not need to press into the tissue of the nasal septum in order to obtain reliable pulse oximetry data, nor a probe that includes an angle, or bend, to reach a desired highly vascular plexus on the septum.

The application does not teach a method to measure “surface” peripheral or central tissue sites for development of information regarding perfusion status.

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