Apparatus and Method for Monitoring Tissue Vitality Parameters

Abstract

Apparatus for determining the oxygenation state of at least one tissue element, comprising: a) illumination means for illuminating said tissue element with an illuminating radiation at a predetermined wavelength via at least one illumination location with respect to said tissue element, said illuminating radiation being at a wavelength within the NADH excitation spectrum or the Fp excitation spectrum; b) radiation receiving means and detection means for measuring the intensity of the corresponding NADH fluorescence or Fp fluorescence emitted by the tissue element at at least two predetermined wavelengths within the range of wavelengths comprised within the corresponding fluorescence emission spectrum.

Description

RELATED APPLICATIONS [0001] The present application is a divisional application of U.S. application Ser. No. 10 / 381,383, filed on Mar. 25, 2003, which is a U.S. national application of PCT Application No. PCT / IL01 / 00906, filed on Sep. 25, 2001.FIELD OF THE INVENTION [0002] The present invention relates to apparatuses and methods for enabling simultaneous, pseudo-simultaneous, or individual monitoring of a plurality of tissue vitality parameters, particularly in-vivo, with respect to an identical tissue layer element or volume. In particular, such parameters include blood flow rate, NADH concentration, blood volume, blood oxygenation state and flavoprotein concentration. BACKGROUND [0003] Mammalian tissues are dependent upon the continuous supply of oxygen and glucose needed for the energy production. This energy is used for various types of work, including the maintaining of ionic balance and biosynthesis of various cellular components. The ratio or balance, between oxygen supply an...

AI Technical Summary

Benefits of technology

"The present invention relates to an apparatus for selectively monitoring blood flow rate and tissue viability parameters in a tissue element. The apparatus includes illumination means for illuminating the tissue element with first and second wavelengths of light, and first and second radiation receiving means for receiving first and second radiation, respectively, from the tissue element. The first and second radiation receiving means are displaced from the illumination location. The apparatus can selectively detect the blood flow rate and tissue viability parameters using the first and second radiation, respectively. The first and second wavelengths are typically chosen to lie at a suitable isosbestic point of the NADH. The apparatus can provide improved monitoring of tissue health and function."

Problems solved by technology

In most pathological states, the limiting factor for this process is O2 availability.

The concentration of the reduced form of the molecule (NADH) rises when the rate of ATP production is low, and is unable to meet the demand in the tissue or cells.

Fp concentration drops when the rate of ATP production is reduced, and is unable to meet the demand in the tissue or cells.

An increase in the level of NADH with respect to NAD and the resulting increase in fluorescence intensity indicate that insufficient Oxygen is being supplied to the tissue.

These devices are relatively complicated and susceptible to interference from ambient light, as well as various electronic and optic drifts.

For the monitoring of different parameters to have maximum utility however, the information regarding all parameters is required to originate from substantially the same layer of tissue, and preferably the same volume of tissue, otherwise misleading results can be obtained.

These devices suffer from a major drawback however.

The complex biochemical mechanisms that determine tissue viability are such that short time deviations between measurement at short distances between points of measurement can provide inaccurate or even misleading information.

Another drawback encountered in NADH measurements is the Haemodynamic Artifact.

This refers to an artifact in which NADH fluorescence measurements in-vivo are underestimated or overestimated due to the haemoglobin present in blood circulation, which absorbs radiation at the same wavelengths as NADH, and therefore interferes with the ability of the light to reach the NADH molecules.

However, U.S. Pat. No. 4,449,535 has at least two major drawbacks; firstly, and as acknowledged therein, using a single optical fiber to illuminate the organ, as well as to receive emissions therefrom causes interference between the outgoing and incoming signals, and certain solutions with different degrees of effectiveness are proposed.

This results in measurements that are incompatible one with the other, the blood volume measurement relating to a greater depth of tissue than the NADH measurement.

Therefore, the device disclosed by this reference does not enable adequate compensation of NADH to be effected using the simultaneous, though inappropriate, blood volume measurement.

Further, there is no indication of how to measure other parameters such as blood flow rate or blood oxygenation level using the claimed apparatus.

Although U.S. Pat. No. 5,916,171 and U.S. Pat. No. 5,685,313 represent an improvement over the prior art, they nevertheless have some drawbacks: (i)The oxidation level of the blood will introduce artifacts, affecting both the Mitochrondrial Redox State measurement (NADH fluorescence) and the microcirculatory blood volume (MBV) since these patents do not specify how to compensate for the oxygenation state of the blood in the tissue, i.e., the relative quantities of oxygenated blood to deoxygenated blood in the tissue.

Using a relatively high intensity UV laser illumination source as proposed raises safety issues, especially for long-term monitoring.

Such lasers at these wavelengths are also not standard components and are indeed quite difficult to come by, which might lead to supply problems.

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