Method and apparatus for noninvasively determining hematocrit

A system for noninvasive determination of hematocrit of blood of a patient, the system comprising:

• signal generation circuitry to produce alternating signals at various frequencies and out-of-phase signals with respect to the alternating signals;
• processing, sensing, and application circuitry to provide current signals through the blood in response to the alternating signals, and that senses the current signals being applied and produces current indicating signals in response thereto, and that senses voltage signals over a section of the blood and produces voltage indicating signals in response thereto;
• processing and demodulation circuitry to receive and mix the current indicating signals and the alternating and out-of-phase signals to produce inphase and out-of-phase current representing signals and to receive the voltage indicating signals and mix the voltage indicating signals and the inphase and out-of-phase voltage representing signals to produce inphase and out-of-phase voltage representing signals;
• and
• evaluation circuitry to receive and process the inphase and out-of-phase current representing signals and inphase and out-of-phase voltage representing signals to determine the hematocrit.

A system for noninvasive determination of hematocrit of blood in a body portion of a patient, the system comprising:

• signal generation means for producing alternating and quadrature signals at various frequencies;
• processing, sensing, and application means for providing first signals through the body portion in response to the alternating signals, and sensing the first signals being applied and producing first indicating signals in response thereto, and sensing second signals over a section of the body portion and producing second indicating signals in response thereto;
• processing and demodulation means for receiving and mixing the first indicating signals and the alternating and quadrature signals to produce inphase and quadrature first representing signals, and receiving the second indicating signals and mixing the second indicating signals and the alternating and quadrature signals to produce inphase and quadrature second representing signals;
• and
• evaluation means for receiving and processing the inphase and quadrature first representing signals and inphase and quadrature second representing signals to determine the hematocrit.

A method for noninvasive determination of hematocrit of blood in a body portion of a patient, the method comprising:

• injecting alternating current signals having various frequencies into the body portion at different blood volumes, the injected alternating current signals being responsive to generated alternating signals having the various frequencies;
• providing current indicating signals representative of the current signals injected into the body portion;
• measuring voltage signals across a section of the body portion through which the current signals pass;
• providing voltage indicating signals representative of the measured voltage signals;
• mixing the current indicating signals with the generated alternating signals and with quadrature signals to produce inphase and quadrature current representative signals;
• mixing the voltage indicating signals with the generated alternating signals and with the quadrature signals to produce inphase and quadrature voltage representative signals;
• and
• determining the hematocrit by considering parameters of the inphase and quadrature current representative signals and the inphase and quadrature voltage representative signals.

A system for developing a group of data with which a hematocrit of blood of a particular patient may be determined, the system comprising:

• signal generation circuitry that produces alternating and quadrature signals at various frequencies;
• processing, sensing, application circuitry that provides current signals through a body portion of numerous patients in response to the alternating signals, and that senses the current signals being applied and produces current indicating signals in response thereto, and that senses voltage signals over a section of the body portion and produces voltage indicating signals in response thereto;
• and
• processing and demodulation circuitry that receives and mixes the current indicating signals and the alternating and quadrature signals to produce inphase and quadrature current representing signals, and receives and mixes the voltage indicating signals and the alternating and quadrature signals to produce inphase and quadrature voltage representing signals;
• and
• evaluation circuitry that receives and processes the inphase and quadrature current representing signals and inphase and quadrature voltage representing signals and compares parameters of the inphase and quadrature current representing signals and inphase and quadrature voltage representing signals with various pre-gathered data to produce the group of data.

An apparatus for noninvasive determination of the relative volume percent of erythrocytes, also termed the hematocrit, of blood having an impedance, comprising:

• means for producing a constant current at a first low and at least one second high carrier wave frequencies, said first low frequency being below a frequency zone within which said erythrocytes significantly affect the magnitude of the impedance of said blood, and said at least one second high frequency being within said frequency zone;
• means for stimulating a patient body portion including at least one pulsatile vascular compartment containing said blood with said first low and said at least one second high carrier wave frequencies;
• means for sensing voltage signals at each of said first low and said at least one second high carrier wave frequencies across said stimulated patient body portion;
• means for amplifying said sensed voltage signals;
• means for demodulating said amplified, sensed voltage signals to produce at least two complex waveforms respectively proportional to the magnitude of impedance of said blood at said first low and said at least one second high carrier wave frequencies;
• and
• means for processing said at least two complex waveforms to determine said hematocrit of said blood.

A method for noninvasive determination of the relative volume percent of erythrocytes, also termed the hematocrit, of blood having an impedance, comprising:

• producing a constant current at a first low and at least one second high carrier wave frequencies, said first low frequency being below a frequency zone within which said erythrocytes significantly affect the magnitude of the impedance of said blood, and said at least one second high frequency being within said frequency zone;
• stimulating a patient body portion including at least one pulsatile vascular compartment containing said blood with said first low and said at least one second high carrier wave frequencies;
• sensing voltage signals at each of said first low and said at least one second high carrier wave frequencies across said stimulated patient body portion;
• amplifying said sensed voltage signals;
• demodulating said amplified, sensed voltage signals to produce at least two complex waveforms respectively proportional to the magnitude of impedance of said blood at said first low and said at least one second high carrier wave frequencies;
• and
• processing said at least two complex waveforms to determine said hematocrit of said blood.

An apparatus for determining blood pressure in a pulsatile vascular compartment of a patient body portion containing blood, comprising:

• means for producing a constant current at a carrier wave frequency;
• means for stimulating said patient body portion including said pulsatile vascular compartment containing said blood with said constant current;
• means for sensing a voltage signal at said carrier wave frequency across said stimulated patient body portion;
• means for amplifying said sensed voltage signal;
• means for demodulating said amplified, sensed voltage signal to produce a plethysmographic waveform signal;
• means for sensing the existence, magnitude and shape of said plethysmographic waveform signal;
• means for selectively occluding said pulsatile vascular compartment to completely occlude said pulsatile vascular compartment and suppress said plethysmographic waveform signal, to subsequently reduce said complete occlusion by a degree sufficient to induce the appearance of said plethysmographic waveform signal, to further reduce said occlusion by a degree sufficient to maximize the intensity of said plethysmographic waveform signal, and to still further reduce said occlusion until said plethysmographic waveform undergoes no further change.