Apple has applied for several patents relating to future Blood pressure taking device designs since 2018 as covered in these reports 01, 02, 03, 04 and 05. The latter patent application, filed in October, resembles Apple’s latest patent filing for a blood pressure measuring device published last Thursday by the US Patent & Trademark Office titled "Integrated Flexible Sensor for Blood Pressure Measurements."

The application generally relates to devices, methods and systems for measuring a physiological parameter of a user. More particularly, it relates to flexible sensors that can be integrated with a blood pressure cuff and used to estimate a blood pressure of a user. One advanced model illustrates that use of multiple flexible sensors.

In Apple's patent background they note that a user may monitor one or more of his or her physiological parameters by attaching a monitoring device, such as a blood pressure monitor, to one of his or her limbs. The blood pressure monitor may include an inextensible cuff that secures an inflatable bladder against a limb of the user. The inflatable bladder can be expanded and the inextensible cuff may cause the bladder to compress the limb, thereby compressing one or more blood vessels in the limb and restricting and/or stopping blood flow through the vessels. The various pressures in the inflatable bladder that restrict and/or stop blood flow through the vessels in the limb may be measured and used to determine one or more physiological parameters of a user such as a blood pressure of the user.

Techniques for determining blood pressure metrics, such as mean pressure, diastolic pressure and/or systolic pressure, include monitoring oscillatory pressure changes within the cuff due to changes in blood flow through a user's limb. In isolation, such oscillatory measurement may not be as accurate as desirable in determining some metrics such as systolic pressure and/or diastolic pressure. This is what Apple's latest patent addresses.

Apple's invention is directed to a blood pressure measurement device having a cuff that wraps around a limb of a user and includes a bladder and a flexible blood flow sensor. The blood flow sensor can be used to detect sounds that correspond to changes in blood flow due to compression of the bladder around the limb.

For example, the blood flow sensor can detect Korotkoff sounds that occur as a bladder compresses a user's limb to restrict and/or stop blood flow through vessels in the patient's limb. Signals from the blood flow sensor can be filtered to isolate sounds that occur due to changes in blood flow from other physical phenomena detected by the blood flow sensor such as signal components due to pressure fluctuations within the bladder.

In some cases, the blood pressure measurement device can include a pressure sensor that is used to detect the air pressure within the bladder. The detected air pressure can be correlated to the Korotkoff sounds detected by the blood flow sensor to determine a blood pressure of a user.

For example, a first Korotkoff sound that corresponds to partial collapse of the vessel can be used to determine a diastolic pressure, and a second Korotkoff sound that occurs just before the stoppage of blood flow through the vessel can be used to determine a systolic pressure of the user.

In some embodiments the blood flow sensor includes a flexible piezoelectric strip that is integrated with the cuff such that the blood flow sensor wraps around the limb of the user. Accordingly, the blood flow sensor can detect changes in blood flow through one or more vessels in the limb without requiring the blood flow sensor to be oriented in a specific relation to the limb.

The flexible piezoelectric strip can conform to the limb of the user which can help couple the blood flow sensor to the limb and minimize gaps or other separations between the blood flow sensor and the limb.

In some embodiments, having a flexible sensor integrated with the cuff, such as a flexible piezoelectric sensor, can allow the cuff and sensor to adapt to limbs of different sizes and shapes as well as changes in the shape or size of a limb such as due to movement.

For example, a flexible blood flow sensor may be more likely to remain coupled to a limb (e.g., lie flat against an arm) as compared to more rigid sensor. Such coupling between the flexible blood flow sensor and a limb can increase the signal quality such as by reducing noise due to air gaps, movement, etc.; increasing the signal strength detected by the sensor; and so on.

The flexible blood pressure sensor can facilitate easy positioning of the cuff on a user by allowing the sensor to conform to a limb of the user in multiple orientations while maintaining close coupling of the sensor to the limb.

Additionally, or alternatively, the blood flow sensor can be positioned downstream of the direction of blood flow through the limb with respect to the bladder. As the bladder is expanded to compress the limb, the piezoelectric sensor can detect downstream changes in blood flow due to compression of one or more blood vessels in the limb. In other embodiments, the blood flow sensor can be located upstream of the bladder, between the bladder and the limb, on a separate band or cuff from the bladder, or in any other suitable configuration.

The blood pressure measurement device can also include a pump for inflating the bladder. The bladder can be coupled with the cuff such that when it is inflated by the pump, the bladder expands inward to compress a limb of the user. In some cases, the pump can operate at frequencies that are above those detected by the blood flow sensor.

For example, the pump can be an ultrasonic pump, and the blood flow sensor can detect frequencies due to changes in blood flow and that are below those produced by the ultrasonic pump. In this regard, noise produced by the pump and detected by the blood flow sensor may be reduced or separated from signal frequencies that are related to auditory changes in blood flow. In some cases, the flexible blood pressure sensor can react to changes in pressure in the bladder by conforming to the arm.

In other embodiments, the blood pressure measurement device can include a pressure sensor for measuring a pressure within the bladder. The pressure sensor can output a pressure signal that indicates the pressure within the bladder. The blood pressure measurement device can include a processor that receives the blood flow sensor signal and the pressure sensor signal, and uses these signals to determine blood pressure metrics for a user.

For example, the blood flow signal can be filtered and processed to identify the occurrence of Korotkoff sounds due to compression of the limb. A first Korotkoff sound, that occurs when the bladder compresses the limb enough to begin to collapse the blood vessel and cause changes in the blood flow (e.g., inducing turbulent flow) can be identified using the blood flow signal and correlated to a first detected pressure in the bladder. This first pressure can be used to determine the diastolic blood pressure of a user.

A second Korotkoff sound that occurs when the bladder compresses the limb enough to stop blood flow through the blood vessel can be identified using the blood flow signal and correlated to a second detected pressure in the bladder. This second pressure can be used to determine a systolic pressure of a user.

Apple’s patent FIG. 1 below illustrates an example of a blood pressure measurement device as worn by a user.

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Apple's patent FIG. 2 below illustrates another view of a blood pressure measurement device; FIG. 3 shows an example measurement output from a blood pressure measurement device.

Apple's patent FIGS. 4A-4D below illustrate examples of a blood pressure measurement device that include a single flexible sensor used to perform blood pressure measurements; In patent FIG. 5 below, we're able to see that Apple envisions possibly including multiple flexible sensors to perform more accurate blood pressure measurements.

In some cases, the flexible sensor can be a piezoelectric sensor that is operative to detect sounds or changes in sounds that are associated with different blood flow patterns or events. For example, the flexible sensor can be a differential piezoelectric sensor that includes electrodes attached to opposite sides of a piezoelectric material and operated to differentially sense sounds produced by the flow or change in flow of blood through a vessel.

A differential sensor can be operated to provide high-fidelity sensing of mechanical vibrations (such as those due to blood flow or changes in blood flow) while reducing noise by producing out-of-phase signals corresponding to mechanical vibrations that can constructively interfere and amplify the mechanical vibrations.

The piezoelectric material can include polyvinylidene difluoride (PVDF), such as a PVDF film, PVDF-copolymer, a PVDF/poly-L-lactide (PLLA) blend, or other material that generates an electric response in response to mechanic stress. The differential sensor can also include a differential amplifier that is connected to the first and second electrodes that are attached to opposite sides of the piezoelectric material.

The differential amplifier can provide an amplified differential output (e.g., an amplification of a pair of signals obtained from the piezoelectric material) that includes biological vibrations sensed by the piezoelectric material. The signals from each of the electrodes in the differential output can be subtracted to produce amplified signals corresponding to mechanical vibrations, such as vibrations due to blood flow. In some cases, the sensor can include a flexible piezoelectric sensor, such as a flexible differential piezoelectric sensor. For example, the flexible sensor may be a formed in a film or strip that can bend with the cuff 202 around the limb of the user.

In other cases, the sensor can include rigid piezoelectric sensors, microelectromechanical (MEMs) based pressure sensors, MEMs microphone sensors, MEMs accelerometers, electret microphones, mini-voice coils, fabric based sensors, and the like, or a combination thereof.

Review Apple's patent application number 20220015652 that provides greater detail on each of the blood pressure device design presented in this report.