Method and apparatus for measuring tissue perfusion

A perfusion monitor for monitoring tissue perfusion in a body including:—

• a probe, arranged to generate a pulsed source of light for irradiation onto a part of a body and a matched sensor, which transduces variations in the reflected light to an electric signal;
• and,
• a signal processor, which receives the electric signal and compares the electrical signal at a first time when the pulsed light source is on with a second time when the pulsed light is off, the first and second times being almost concurrent, the signal processor including
• means for processing the electrical signal to reduce or ameliorate the effect of ambient light in the signal;
• means for generating a pulse curve from the signal
• means for calculating a heart rate (HR) from the pulse curve;
• means for determining a running value A for the area under the pulse curve:
• means for calculating a tissue perfusion index (TPI) from HR×pulse curve area, where
• TPI=A×HR×k
• where:
• A=running value for area under signal curve
• HR=value for Heart Rate
• k=physiological constant for specific tissue.

A method of measuring microcirculatory blood flow in a body comprising the steps of:

• using an emitter of pulsed light to irradiate an area of the body for measurement of microcirculatory changes;
• receiving light reflected from the area at a distance from the area being irradiated by the incident light;
• and
• determining from the reflected light a measure of the changes that correspond with the pulsatile filling and partial emptying of the microcirculation.

A method of calculating the tissue perfusion index for an area or part of a body comprising the steps of:

• using an emitter of pulsed light to irradiate an area of the body part for measurement of microcirculatory changes;
• receiving light reflected from the area at a distance from the area being irradiated by the incident light;
• digitally sampling the signal;
• generating a pulse curve from the signal calculating a heart rate (HR) from the pulse curve;
• determining a running value A for the area under the pulse curve:
• and calculating the Tissue Perfusion Index (TPI) defined by:
• TPI=A×HR×k
• where:
• A=running value for area under signal curve
• HR=value for Heart Rate
• k=physiological constant for specific tissue.