Method of blood constituent monitoring using improved disposable extracorporeal conduit

• US 6,746,415 B1
• Filed: 05/25/2000
• Issued: 06/08/2004
• Est. Priority Date: 10/23/1996
• Status: Expired due to Term

• Current Assignee: Fresenius Medical Care Holdings Incorporated (Fresenius Medical Care AG)
• Original Assignee: HEMA Metrics Incorporated
• Inventors: Miller, David R., Steuer, Robert R.
• Primary Examiner(s): Sykes, Angela D.
• Assistant Examiner(s): Deak, Leslie R.
• Application Number:
  US09/577,944
• Time in Patent Office: 1,475 Days
• Field of Search: 210/103, 210/97, 210/645-646, 738/611.8, 604/4.01, 604/5.01
• US Class Current: 604/4.01
• CPC Class Codes: A61M 1/3609 Physical characteristics of the blood, e.g. haematocrit, urea
• CPC Class Codes: A61M 1/3624 Level detectors; Level control
• CPC Class Codes: A61M 1/367 Circuit parts not covered by the preceding subgroups of group A61M1/3621

Abstract

A cuvette having a pedestal for transmitting light through a relatively thin layer of blood. While the pedestal enables the use of a small path length it also permits the use of a high volume and/or high flow rate conduit. The pedestal further enables methods of determining various blood parameters in which the path length, d, is fixed; i.e., there are little or no pulsatile variations. Hence, the flow-through cuvette accommodates a large range of blood flow rates without any reduction in accuracy of the hematocrit measurement. The pedestal, because of its elliptical shape, does not damage or hemolyze the individual red blood cells as they pass through. A quantitative method for determining changes in blood volume in view of the path length is provided along with a method for measuring a patient'"'"'s cardiac output and oxygen consumption rate. Cardiac output is obtained by injecting a saline arterial bolus and a saline venous bolus into a patient and measuring the change in hematocrit caused by each bolus. The oxygen consumption rate is then determined using the cardiac output and measuring the degree of oxygen saturation.

Finally, an improved cuvette and corresponding method of measuring microemboli is provided. The cuvette contains multiple mini-lenses that focus narrow beams of light through the blood. These narrow beams of light are individually monitored by detectors.

Claims

1. A noninvasive method of measuring cardiac output in a dialysis system having arterial and venous tubing lines using a first extracorporeal cuvette located at an input to a dialyzer in said dialysis system and a second extracorporeal cuvette located at an output of said dialyzer, each extracorporeal cuvette having an inlet, an outlet, and a conduit in fluid communication therebetween, said conduit having first and second opposed walls allowing electromagnetic radiation therethrough with inner surfaces thereof having a first predetermined separation therebetween, outer surfaces and said inner surfaces of said first and second opposed walls being planar, said inner surface of said first wall including a pedestal emanating outwardly toward the inner surface of said second wall, said pedestal having a planar end surface defining a second predetermined separation from said second wall, said first predetermined separation being greater than said second predetermined separation so that a shorter radiation path length is created across said second predetermined separation, said method comprising the steps of:

injecting a first saline bolus into the arterial tubing;

injecting a second saline bolus into the venous tubing;

determining the blood flow rate through at least one of said extracorporeal cuvettes in the dialysis system;

selecting the first saline bolus as a reference bolus and the second saline bolus as a measuring bolus;

determining a first ratio of the measuring bolus to the reference bolus;

determining the change of hematocrit over time for the reference bolus by comparing an output of said first extracorporeal cuvette with an output of said second extracorporeal cuvette;

determining the change of hematocrit over time for the measuring bolus by comparing an output of said first extracorporeal cuvette with an output of said second extracorporeal cuvette;

determining a second ratio of the reference bolus over time to the measuring bolus over time; and

calculating the product of the first ratio, the second ratio and the blood flow rate.

2. A method for detecting blood emboli using an extracorporeal cuvette having an inlet, an outlet, and a conduit in fluid communication therebetween, said conduit having first and second opposed walls with inner surfaces thereof having a first predetermined separation therebetween, said method comprising the steps of:

allowing blood to flow from said inlet to said outlet through said conduit;

emitting, with an emitter on an outer surface of said first wall, radiation through said first wall into the blood flow in said conduit;

receiving, with a sensor on an outer surface of said second wall, radiation passing through the blood flow in said conduit;

defining, with a plurality of lenses arranged along the surface of said second wall, a region of illumination to focus the radiation from the emitter and received by said sensor; and

detecting, by said sensor, a change in radiation when a blood embolus passes through said region of illumination, said change in radiation indicating a number and size of blood emboli.

3. The method as set forth in claim 2, wherein said emitter is a photoemitter and said plurality of lenses act to strobe and focus a plurality of LED light sources in said photoemitter independently such that only a narrow section of the conduit is optically viewed for any given wavelength of said LED light sources.

4. A method for monitoring blood constituents using an extracorporeal cuvette having an inlet, an outlet, and a conduit in fluid communication therebetween, said conduit having first and second opposed walls allowing electromagnetic radiation therethrough with inner surfaces thereof having a first predetermined separation therebetween, outer surfaces and said inner surfaces of said first and second opposed walls being planar, said inner surface of said first wall including a pedestal emanating outwardly toward the inner surface of said second wall, said pedestal having a planar end surface defining a second predetermined separation from said second wall, said first predetermined separation being greater than said second predetermined separation, said method comprising the steps of:

allowing blood to flow from said inlet to said outlet through said conduit;

emitting, with an emitter on an outer surface of said first wall, radiation through said first wall into the blood flow in said conduit, a path length of said radiation corresponding to said second predetermined separation between the planar end surface of said pedestal and said inner surface of said second wall; and

receiving, with a sensor on an outer surface of said second wall, radiation passing through the blood flow in said conduit across the radiation path length, the first wall, the second wall and the pedestal.