EVALUTATING CARDIOVASCULAR HEALTH USING INTRAVASCULAR VOLUME

• US 20150031966A1
• Filed: 07/29/2014
• Published: 01/29/2015
• Est. Priority Date: 07/29/2013
• Status: Active Grant

• Current Assignee: Board of Regents of the University of Michigan (University of Michigan)
• Original Assignee: Board of Regents of the University of Michigan (University of Michigan)
• Inventors: Blum, James M., Ward, Kevin, Tiba, Mohamad Hakam
• Granted Patent: US 10,314,532 B2
• Time in Patent Office: Days
• US Class Current: 600/301
• CPC Class Codes: A61B 5/0075 by spectroscopy, i.e. measuring spectra, e.g. Raman spectroscopy, infrared absorption spectroscopy A61B5/0071 takes precedence
• CPC Class Codes: A61B 5/02 Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
• CPC Class Codes: A61B 5/0205 Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
• CPC Class Codes: A61B 5/0261 using optical means, e.g. infrared light
• CPC Class Codes: A61B 5/0295 using plethysmography, i.e. measuring the variations in the volume of a body part as modified by the circulation of blood therethrough, e.g. impedance plethysmography
• CPC Class Codes: A61B 5/0533 Measuring galvanic skin response
• CPC Class Codes: A61B 5/0535 Impedance plethysmography for measuring blood flow A61B5/0295
• CPC Class Codes: A61B 5/0816 Measuring devices for examining respiratory frequency measuring frequency of electric signals G01R23/00
• CPC Class Codes: A61B 5/1073 Measuring volume, e.g. of limbs
• CPC Class Codes: A61B 5/1075 for measuring dimensions by non-invasive methods, e.g. for determining thickness of tissue layer A61B8/0858 takes precedence
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/4884 inducing physiological or psychological stress, e.g. applications for stress testing
• CPC Class Codes: A61B 5/6822 Neck
• CPC Class Codes: A61B 5/6824 Arm or wrist
• CPC Class Codes: A61B 5/7275 Determining trends in physiological measurement data; Predicting development of a medical condition based on physiological measurements, e.g. determining a risk factor
• CPC Class Codes: A61B 5/7278 Artificial waveform generation or derivation, e.g. synthesising signals from measured signals A61B5/327 takes precedence
• CPC Class Codes: A61B 8/06 Measuring blood flow measuring volume flow in general G01F, e.g. G01F1/66, G01F1/72; measuring speed of fluids in general G01P5/00

Abstract

Non-invasive monitoring of cardiovascular health is performed by monitoring changes in the volume of blood in the venous side of the vascular system. The blood volume changes are determined from measurements of bioimpedance of limbs or neck, in particular changes in bioimpedance in response to blood modulating events performed on the limbs or neck, where bioimpedance is measured and compared before and after such events.

Claims

1. A method for evaluating cardiovascular condition of a patient, the method comprising:

(a) recording a first impedance of a limb or extremity or neck of the patient at a first time in response to receiving a first impedance reading from a plurality of sensors on a limb or extremity or neck;

(b) after the occurrence of an event modulating blood return to the heart via the venous system of the patient, recording a second impedance of the limb or extremity or neck at a second time in response to receiving a second impedance reading from a plurality of sensors on a limb or extremity or neck, wherein the first impedance and the second impedance each correspond to a volume of blood flowing within the limb or extremity or neck; and

(c) determining a change in venous blood volume between the first time and the second time by comparing the first impedance and the second impedance to determine a change in volume of blood.

2. The method of claim 1, wherein (a)-(c) are performed repeatedly over a period of time, the method further comprising:

(d) determining whether the cardiovascular condition of the patient has improved or deteriorated over the period of time.

3. The method of claim 2, wherein determining whether the cardiovascular condition of the patient has improved or deteriorated over the period of time includes monitoring the ventilatory effort of the patient and ventilatory dynamics of the patient.

4. The method of claim 2, wherein determining whether the cardiovascular condition of the patient has improved or deteriorated over the period of time includes:

(1) using a first portion of the recorded impedances to determine a baseline impedance pattern for the patient, and

(2) comparing a second portion of the recorded impedances to the baseline impedance pattern to detect deviations from the baseline impedance pattern.

5. The method of claim 1, wherein placing electrodes on one of a limb or extremity or neck to monitor the impedance of the limb or extremity or neck includes placing two electrodes to inject electrical current and two electrodes to measure impedance.

6. The method of claim 1, wherein the event modulating blood return to the heart includes one or more of spontaneous inspiration, positive pressure mechanical ventilation, raising a limb or extremity or neck of the patient, applying negative or positive pressure to the abdomen or chest, inspiration against a negative impedance valve, or discrete maneuvers performed with mechanical ventilation.

7. The method of claim 6, wherein the discrete maneuvers performed with mechanical ventilation comprise adjusting positive pressure ventilation, negative pressure ventilation, maintaining inspiratory or expiratory pause, or a combination thereof.

8. The method of claim 1, wherein (a) and (b) are performed outside a medical facility.

9. The method of claim 1, wherein the patient is undergoing treatment for one or more of cardiac arrest, edema, burns, trauma, heart failure, sepsis, dehydration, renal failure, or dialysis.

10. The method of claim 1, further comprising:

(d) determining one or more of;

(1) how the patient will hemodynamically respond to one or more of an addition of cardiovascular fluid or removal of cardiovascular fluid,

(2) how the patient will hemodynamically respond to one or more cardiovascular drugs which promote changes in cardiac output, changes in cardiovascular preload, and changes in cardiovascular afterload, or

(3) determining how the patient will respond hemodynamically to changes in mechanical or noninvasive ventilation.

11. The method of claim 1, further comprising:

determining changes in vena cava diameter, central venous pressure, or right atrial venous pressure from the change in venous blood volume.

12. The method of claim 1, further comprising:

determining respiratory rate and effort from the change in venous blood volume.

13. A testing apparatus for evaluating cardiovascular condition of a patient, the testing apparatus comprising:

one or more electrodes;

one or more processors;

a computer-readable memory storing non-transient instructions that when executed by the one or more processors cause the testing apparatus to;

(a) use the one or more electrodes to record a first impedance of a limb or extremity or neck of the patient at a first time in response to receiving a first impedance reading from a plurality of sensors on a limb or extremity or neck;

(b) after the occurrence of an event modulating blood return to the heart via the venous system of the patient, use the one or more electrodes to record a second impedance of the limb or extremity or neck at a second time in response to receiving a second impedance reading from a plurality of sensors on a limb or extremity or neck, wherein the first impedance and the second impedance each correspond to a volume of blood flowing within the limb or extremity or neck; and

(c) determine a change in venous blood volume between the first time and the second time by comparing the first impedance and the second impedance to determine a change in volume of blood.

14. The testing apparatus of claim 13, wherein the non-transient instructions include instructions that when executed by the one or more processors cause the testing apparatus to determine whether the cardiovascular condition of the patient has improved or deteriorated over the period of time.

15. The testing apparatus of method of claim 14, wherein the instructions to determine whether the cardiovascular condition of the patient has improved or deteriorated over the period of time includes instructions to monitor a respiratory rate of the patient and a respiratory effort of the patient.

16. The method of claim 15, wherein the instructions to determine whether the cardiovascular condition of the patient has improved or deteriorated over the period of time includes instructions to:

(1) use a first portion of the recorded impedances to determine a baseline impedance pattern for the patient, and

(2) compare a second portion of the recorded impedances to the baseline impedance pattern to detect deviations from the baseline impedance pattern.

17. The testing apparatus of claim 13, wherein the one or more electrodes include two electrodes to inject electrical current and two electrodes to measure impedance.

18. The testing apparatus of claim 13, wherein the event modulating blood to return to the heart includes one or more of spontaneous inspiration;

positive pressure mechanical ventilation, negative pressure ventilation, or raising a limb or extremity or neck of the patient.

19. The testing apparatus of claim 13, further comprising a photoplethysmograph, a galvanic skin response monitor, a near infrared spectroscopy device, a laser Doppler device with or without speckle tracking, or an ultrasound device with or without speckle tracking.

20. The testing apparatus of claim 13, further comprising impedance cardiography measurement, pulse pressure variation measurement, or stroke volume variation measurement.

21. A closed-loop cardiovascular condition evaluation system comprising:

the testing apparatus of claim 13; and

a processor and a memory, the memory storing instructions that when executed by the processor, cause the processor to evaluate a cardiovascular condition of a subject in response to determining the change in the venous blood volume between the first time and the second time determined by comparing the first impedance and the second impedance, for different treatment cycles.

22. The closed-loop system of claim 21, wherein the different treatment cycles comprising, determining the change in venous blood volume under a first treatment condition and under a second treatment condition.

23. The closed-loop system of claim 22, wherein the first treatment condition is a pre-cardiovascular treatment condition and the second treatment condition is after a cardiovascular treatment has been applied.

24. The closed-loop system of claim 21, wherein the memory stores instructions that when executed by the processor, cause the processor to adjust a cardiovascular treatment in response to the determination in the change of venous blood volume.

25. A method for evaluating the cardiovascular condition of a patient, the method comprising:

(a) determining a first volume of blood of a limb or extremity or neck of the patient at a first time;

(b) after the occurrence of an event causing blood to return to the heart via the venous system of the patient, determining a second volume of blood of the limb or extremity or neck at a second time;

(c) determining a change in venous blood volume between the first time and the second time by comparing the first volume of blood and the second volume of blood; and

(d) determining one or more of,

(1) how the patient will hemodynamically respond to one or more of an addition of cardiovascular fluid or removal of cardiovascular fluid,

(2) how the patient will hemodynamically respond to one or more cardiovascular drugs which promote changes in cardiac output, changes in cardiovascular preload, and changes in cardiovascular afterload,

(3) determining how the patient will response to changes in mechanical or noninvasive ventilation, or

(4) determining respiratory rate and magnitude of respiratory effort.

26. The method of claim 25, wherein the first and second volume of blood in a limb is determined by measuring the diameter of a major vein in the limb or extremity or neck using ultrasonic imagery with our without speckle tracking, or laser Doppler Flowmetry with or without speckle tracking, or near infrared spectroscopy, or photoplethysmography, or galvanic skin response.

27. The method of claim 26, wherein (a)-(c) are performed repeatedly over a period of time, the method further comprising:

(e) determining whether the cardiovascular condition of the patient has improved or deteriorated over the period of time.

28. The method of claim 27, wherein determining whether the cardiovascular condition of the patient has improved or deteriorated over the period of time includes using a learning algorithm to

(1) detect a pattern in the changes of volume of blood over the period of time, and

(2) detect outliers in the changes of volume of blood over the period of time.