BLOOD FLOW PRESSURE MEASUREMENT TECHNIQUE EMPLOYING INJECTED BUBBLED AND ULTRASONIC FREQUENCY SCANNING

• US 3,640,271 A
• Filed: 06/30/1969
• Issued: 02/08/1972
• Est. Priority Date: 06/30/1969
• Status: Expired due to Term

• Current Assignee: John W. Horton
• Original Assignee: John W. Horton
• Inventors: Horton, John W.
• Primary Examiner(s): Kamm, William E.
• Application Number:
  US04/837,737
• Time in Patent Office: 953 Days
• Field of Search: 128/2.5A,2.5D,2.5F,2.5M,2.5N,2.5Q,2.5R,2.5V,24A 73/194,388
• US Class Current: 600/438
• CPC Class Codes: A61B 8/04 Measuring blood pressure
• 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 8/481 involving the use of contrast agent, e.g. microbubbles introduced into the bloodstream analysis of echo signal exploiting properties of a contrast enhancer in devices for short-range imaging with acoustic waves G01S7/52039

Abstract

A nonsurgical technique of measuring blood characteristics of pressure and flow by injecting minute gas bubbles into the bloodstream. The bubbles are subjected to a beam of ultrasonic radiation and flow is determined by detecting the resultant scattering which is indicative of the time taken for the bubble to pass between two points, while blood pressure is determined by varying the frequency of the ultrasonic beam to determine the resonant frequency of the bubbles which is proportional to pressure.

Claims

1. The method of determining blood pressure in a bloodstream comprising:

injecting a blood compatible solution containing gaseous bubbles into said bloodstream, said solution being filtered to inject only one said bubble at a time into the bloodstream;

detecting the resonant frequency of a bubble at a known pressure immediately prior to entering the bloodstream;

detecting the resonant frequency of said bubble after entering the bloodstream; and

determining the pressure of said bloodstream by determining the difference between said first detected resonant frequency and said second detected resonant frequency adjusted for temperature variations, and slight changes in mass if such occurs, and relating said frequencies to said known pressure in accordance with a definition of the relationships of the resonant frequency of bubbles of said gas to pressure gradients.

2. A method of determining blood characteristics such as pressure and rate of flow in a bloodstream under the surface of the body, comprising the steps of:

injecting a blood-compatible solution containing gaseous bubbles in the range of 0.001 to 0.01 centimeters in diameter into said bloodstream, subjecting a bubble to a scan of ultrasonic radiation having a frequency range including a frequency equal to the resonant frequency of said bubble to produce a scattered wave from said bubble which is at its maximum at the resonant frequency of said bubble, detecting the occurrence of the maximum of said scattered wave, correlating said maximum with said frequency scan to determine the resonant frequency of said bubble, and determining the pressure of said blood based on the resonant frequency of said bubble.

3. The method of claim 2, wherein said pressure based on the resonant frequency of said bubble is determined from the following relationship:

where fo is the resonant frequency of said bubble, gamma is the ratio of specific heat at constant pressure to specific heat at constant volume, Rm is the gas constant per gram, m is the mass of gas per volume, T is the blood temperature, and Rho is the density of the blood.

4. The method of claim 2, wherein a determination of blood flow based on the detection of said scattered wave is obtained by a Doppler shift technique in accordance with the following expression:

V c( Delta f/f)cos theta where c is the velocity of sound, Delta f is the Doppler frequency shift, f is the frequency of the ultrasonic radiation, and theta is the angle of the ultrasonic radiation relative to the bloodstream.

5. The method of claim 2, wherein the source of said ultrasonic radiation and detector of said scattered wave are a single transducer operating in a duplex mode of alternate transmission and reception.

6. The method of claim 2, wherein said ultrasonic radiation is applied at two points along said bloodstream to provide an indication of the arrival of said bubble at said two points and the velocity of said bubble determined from the distance between said two points and the time taken by said bubble passing therebetween.

7. The method of claim 5, wherein said bubble is subjected to said ultrasonic radiation through a space between said source of ultrasonic radiation and said body surface which is filled with an impedance matching liquid having a wave impedance substantially equal to that of said body.