US2826191A - Measurements of blood pressure - Google Patents

Description

March 11, 1958 B. D. BURNS MEASUREMENTS OF BLOOD PRESSURE Filed Dec. 30, 1955 :llllllll W 1v Mun-800mm.

United States Patent MEASUREMENTS OF BLOOD PRESSURE Application December 30, 1955, Serial No. 556,618

2 Claims. (Cl. 128-2.05)

Quebec, Canada, as-

This invention relates to apparatus for the continuous measurement of blood pressure.

It is of considerable advantage to a surgeon to be in possession of a continuous record of the patients blood pressure during an operation, since in this manner a sudden fluctuation of the pressure can more readily and more quickly be detected than by means of a series of individual tests. A number of methods of providing continuous registration of blood pressure has been proposed in the past, but all these methods have suffered from one or other disadvantage. They either involve expensive machinery; are relatively slow to respond to blood pressure variations; or produce discomfort or danger to the patient by selective obstruction of the venous return from the distal parts of a limb. All the prior methods have employed the conventional method of applying an external pressure to the upper arm until the arteries supplying blood to the forearm are compressed, and then gradually releasing the pressure until the flow recommences, a record being taken of the pressure at which this takes place.

In accordance with the present invention, the blood pressure reading is taken not on the patients arm but at an extremity of the body, preferably a finger. It would be conceivable to use another digit, such as a toe, but a finger or thumb is especially convenient in practice. There are available in each finger and each toe arteries which can be employed for the determination of blood pressure.

The accompanying drawings illustrate by way of example one manner in which the invention may be carried into practice. In these drawings:

Figure 1 shows a laid-out view of a finger cuff that wound around the patients finger; and

Figure 2 is a diagrammatic sectioned illustration of such a culf in position and of the mechanical and electrical parts to which this cuff is connected for the purpose of providing a continuous record of blood pressure variations.

Referring firstly to Figure 1, the cult consists of a double thickness of material formed into an elongated member 1 of width somewhat less than the length of an average finger, and of a length sufficient to be wound around the finger approximately three to four times. At one end, the cuff 1 is narrowed down to an end portion 2. Between the two folds of the material in this end portion 2 there is mounted a fiat transducer 3, which may take the form of a Rochelle-salt crystal or a strain gauge, and from which an electric cable 4 extends. In the next and centre part 2a of the cufi 1 there is inserted a tough rubber balloon 5 connected to a tube 6 extending to the exterior of the cuff 1. A seam 7 between the two thicknesses of cloth serves to separate this central portion 2a in which the balloon 5 is situated from the end portion 2. Finally a further seam 8 separates the central portion 2a from an end portion 9 which contains no inserted parts.

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In use, the cufi 1 is wound around a finger 10 as shown in Figure 2. The end portion 2 is first placed so that the transducer 3 lies over the peripheral part of one of the digital arteries and then the cuff 1 is Wound around the finger in the manner of a bandage. The end portion 9, which is of a length approximately equivalent to 1 /2 times the circumference of the remaining cuff when thus wound onto a finger, serves as a cover and provides an inextensible outer casing. It will be secured firmly in place by suitable means such as surgical tape. When air is forced into the balloon 5, as shown in Figure 2, this expands and presses inwardly against the finger to constrict the flow of blood to the middle and distal segments of the digit. When a given pressure is reached the transducer 3 will record no heart beat, whereas when the pressure is somewhat lower, the transducer will detect a heat beat. This issimilar in principle to the normal manner of taking individual blood pressure readings on the upper arm.

The transducer 3 is connected by the cable 4 to an amplifier 11 which may be of any convenient type. The output of this amplifier 11 is fed to a solenoid 12 which controls the movement of an air valve 13 situated in a conduit 14. When the transducer 13 detects, the amplifier 11 will cause the solenoid 12 to open the valve 13.

Air pressure for the balloon 5 is provided from a reservoir 16 supplied by an air compressor 15. This air fiows through a simple preset valve 17 that limits air flow and through a two-position three-way valve 18 and conduit 24 to the tube 6, and hence to the balloon 5. The flow of air between the valves 17 and 18 may either be along a directly connected conduit 19 or through the conduit 14 which contains the valve 13. The path employed will depend upon the setting of the three-way valve 18.

The system also includes a pressure gauge 20 and an air reservoir 22 both connected to the conduit 24 leading directly to the tube 6. An escape valve 25 is provided whereby the conduit 14 may be connected to atmosphere. In addition, there is provided a further pressure gauge 26 recording pressure in the reservoir 16 and a safety valve 27 provided for the relief of pressure in the reservoir. Provision is made for attaching the system to a pressure recorder 21 of conventional type.

Let it be assumed that the three-way valve 13 is in the position shown in Figure 2 and that no air has yet been admitted to the balloon 5. As a result the transducer 3 will detect heart beats and the amplifier 11 will temporarily open the air valve 13. The valve 17 is open so that air will pass from the reservoir 16 through the control valve 13 and the three-way valve 18 to the balloon 5 to increase the pressure therein and constrict the artery in the finger 10.

As soon as the pressure in the balloon 5 reaches a value sufiicient to prevent completely the flow of blood to the tip of the finger 10, the transducer 3 will fail to detect arterial pulsation and the control valve 13 will remain closed. This will prevent the admission of further air to the balloon 5 and the pressure therein will slowly fall by reason of loss of air through the escape valve 25. This will eventually result in pressure in the balloon 5 falling below a figure at which blood flow is prevented, and the transducer 3 will again detect arterial pulsation and further air will be admitted to the balloon 5. The system will thus continue with a pressure in the conduit 24 oscillating slightly about a value equal to the systolic blood pressure. The detection of systolic pressure requires that the net volume of air let into the cufl by the detected pulses be capable of exceeding the preset continuous escape rate through valve 25.

If it is desired to obtain a reading of diastolic blood -a,eae,191

vt.pressure,r.the valve 18 isrotated clockwise through 90 degrees.

The valve 18 will now provide direct connection between the conduits 19 and 24 so that the balloon 5 will be expanded when the control valve 13 is closed. Arterial pulsation is minimal -forcufli pressures lower than diastolic pressure Ascutr" pressure rises just above diastolic pressure the arterial-pulsation -detected by the itransducerincreases steeply The sensitivity of the amplifier 11 is set so that the valve 13 is only opened by pulsation in excess of the minimal value. Provided no pulsation in excess of this critical value is detected valve lowed to escape from -the cufi by the detected pulses be capable of exceeding the preset continuous inflow-rate through-valve 17.

I claim:

1. Apparatus for obtaining a continuous measurement of blood pressure, comprising a digit cutr" including a transducer arranged to lie over an artery within the extremity of the digit whereby to be operated in the presence of a blood pressure fluctuation, and an inflatable balloon for exerting an inward pressure on the digit to restrict the flow of blood to said extremity, an amplifier connected to said transducer to detect and amplify the signal therefrom, a reservoir of air pressure, a control valve, a solenoid for controlling said control valve and connected to the output of said amplifier, means for measuring the air pressure in said balloon, an escape valve, and a two-position valve adapted in one position to connect said air reservoir directly to said balloon and to connect said balloon through said valve to said-escape valve and in a second position to connect said balloon to said air reservoir th rough ,said controlvvalve.

2. A finger cuff for use in apparatus for obtaining a continuous measurement of blood pressure, comprising an elongated envelope of cloth, such envelope being divided transversely of its length into a first portion containing a transducer, a second portion containing an inflatable balloon and a third inextensible portion,,.such envelope being adapted to be wound around a fingerwith the first portion adjacent the finger and the third portion forming an inextensible outer casing.

References Cited in the file of this patent UNITED STATES PATENTS 2,272,836 Gerdien Feb. 10, 1942 2,755,796 Boucke July 24, 1956

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