System and method for measuring of lung vascular injury by ultrasonic velocity and blood impedance

• US 5,935,066 A
• Filed: 02/27/1998
• Issued: 08/10/1999
• Est. Priority Date: 02/27/1997
• Status: Expired due to Term

• Current Assignee: Vanderbilt University
• Original Assignee: Vanderbilt University
• Inventors: Harris, Thomas R.
• Primary Examiner(s): Jaworski, Francis J.
• Application Number:
  US09/032,713
• Time in Patent Office: 529 Days
• Field of Search: 600/438, 600/371, 600/506, 600/547
• US Class Current: 600/436
• CPC Class Codes: A61B 5/0275 using tracers, e.g. dye dilution
• 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 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
• CPC Class Codes: A61B 8/12 in body cavities or body tracts, e.g. by using catheters catheters per se A61M25/00

Abstract

The present invention is a method for assessing capillary permeability to determine vascular lung injury without requiring the injection of radioactive material or requiring the sampling of blood. The method includes measuring impedance and ultrasonic velocity of blood flow through a lung. A hypertonic bolus is injected into the blood flow, and measurements of the blood flow are taken to determine the ultrasonic velocity and the electrical impedance of the blood. These measurements are used to calculate the capillary transport quantity, which is the product of the reflection coefficient for movement of fluid across the capillary barrier and the filtration coefficient. The measured value of the capillary transport quantity can then be compared to a conventional capillary transport quantity for healthy lungs, and one can determine injury by a significant decrease in the measured capillary transport quantity as compared to the standard measurements.

Furthermore, a comparison of the osmotic transient graphs of the plotted indicator curves can serve to acknowledge lung vascular injury. Lung injury can be determined from the measured data when the point of osmotic equilibrium (where the indicator curve crosses the baseline) is significantly delayed as compared to the point of osmotic equilibrium plotted for a healthy lung.

Claims

1. A method of measuring microvascular injury to a lung in a patient comprising the steps of:

a) positioning a sound velocity sensor and an impedance measurement sensor whereby a sound velocity and an impedance in blood flowing through the patient'"'"'s lung at a predetermined location in the patient'"'"'s vascular system can be simultaneously measured;

b) introducing a quantity of an osmotic indicator material into blood entering the lung so that a portion of the indicator material passes with the blood through a bed of capillaries in the lung before leaving the lung;

c) simultaneously obtaining at least one sound velocity measurement and one impedance measurement of the blood as it passes the sound velocity and impedance sensors with the indicator material in the blood;

d) deriving at least one post-injection capillary transport factor from the sound velocity and impedance measurements, the post-injection capillary transport factor including the product of at least one capillary reflection coefficient and at least one capillary filtration coefficient corresponding to the capillaries in the lung; and

e) comparing the post-injection capillary transport factor to a pre-injection capillary transport factor corresponding to capillaries in a non-injured lung.

2. The method of claim 1 wherein the osmotic indicator material comprises a hypertonic fluid.

3. The method of claim 2 wherein the hypertonic fluid comprises hypertonic saline.

4. The method of claim 3 wherein multiple sound velocity and impedance measurements are obtained during a period of time after the hypertonic saline is introduced into the blood to provide an observed sound velocity curve and an observed impedance curve, and wherein the step of comparing the post-injection capillary transport factor to the pre-injection capillary transport factor includes comparing the observed sound velocity curve to a predicted sound velocity curve.

5. A method of measuring injury to the blood capillaries in the lungs of a patient comprising the steps of:

a. coupling a sound velocity sensor and a blood impedance sensor to a portion of the patient'"'"'s vascular system downstream of the lung;

b. injecting a pre-determined volume of saline into the vascular system upstream of the lung;

c. taking a series of post-injection sound velocity and blood impedance measurements over a period of time corresponding to passage of blood combined with at least some of the saline through the lung and proximate the sound velocity and blood impedance sensors; and

d. comparing the post-injection sound velocity and blood impedance measurements to pre-determined sound velocity and blood impedance measurements corresponding to a non-injured lung.

6. The method of claim 5 wherein the sound velocity sensor and the blood impedance sensor are mounted together to a catheter tip that is attachable to a catheter and wherein the step of coupling the sound velocity and blood impedance sensors to the vascular system includes introducing the catheter into the vascular system so that the blood will pass the catheter tip.