Bloomberg's Mark Gurman has been reporting on the possible addition of a blood pressure monitor for Apple Watch going back at least to April 2022. Patently Apple began covering blood pressure related patents beginning in 2018 (01, 02, 03, 04, 05, 06, 07 and more) covering different approaches in delivering a solution. Gurman predicted that Apple would introduce this feature in 2024, but that didn't materialize.  

Today the U.S. Patent Office published a patent application of Apple's  relating to an Apple Watch with Blood Pressure monitoring.

Apple notes that it can be difficult to precisely determine conventional blood pressure parameters, such as systolic and diastolic blood pressures, using oscillometry measurement techniques. It may be desirable to more precisely determine events associated with a blood pressure measurement, including the closing and/or opening of a blood vessel during a compression measurement.

Apple's patent covers a blood pressure measurement device that uses a liquid filled sensing chamber to measure blood pressure of a user.

The blood pressure measurement device can include a compression system that is separate from the liquid filled sensing chamber. In these embodiments the sensing chamber can be filled with a fixed amount of liquid and be sealed so that the amount of liquid in the sensing chamber does not vary during a measurement procedure. The compressions system can press the liquid filled sensing chamber against the skin of the user during a blood pressure measurement procedure or blood flow measurement procedure. In some cases, a vibration sensor can be positioned in the liquid filled sensing chamber and measure vibrations transmitted from the user and to the liquid in the sensing chamber. The vibration sensor can be configured to detect vibrations due to blood flow, such as vibration associated with Korotkoff measurements (e.g., opening and closing of a blood vessel). The liquid filled sensing chamber may help transmit vibrations from blood flow (e.g., blood flow sounds) to the vibration sensor, which may allow Korotkoff measurements to be performed by an electronic device.

Additionally or alternatively, the blood pressure measurement devices described herein can be operated to measure vibrations due to blood flow at one or more conditions. For example, the compression system may be inflated until the system determines that a criteria is satisfied (e.g., identifying a maximum sound intensity of blood flow, identifying partial collapse of a blood vessel, etc.). In response to determining that a criteria is satisfied, the blood pressure measurement device may maintain a current inflation condition and measure blood flow sounds over a period of time. The measured blood flow sounds may be used to determine one or more physiological parameters such as heart rate, blood pressure, heart rate variation and so on.

In some cases, the sensing chamber can also include a pressure sensor that is configured to measure pressure of the liquid in the sensing chamber. The liquid filled pressure sensing chamber may be more sensitive to pressure changes in the blood vessel as compared to conventional air filled pressure sensing chambers due to the incompressible nature of liquid. Further, having the vibration sensor and pressure sensor separated from the inflation system may help reduce noise and/or increase accuracy of blood pressure measurements (or other blood flow measurements) as compared to typical blood pressure measurement systems in which a single air inflated cuff is used to both compress a user's arm and measure air pressure in the cuff to estimate blood pressure.

In some embodiments, the blood pressure measurement device is implemented as a pressure sensing stack that includes a liquid filled sensing chamber positioned on an inflatable chamber. A strap can secure the stack against a skin surface of a user such that the sensing chamber is positioned between the inflatable chamber and the user. The inflatable chamber can be inflated to expand towards the user thereby pressing the sensing chamber against the user's skin surface. The sensing chamber can be used to measure vibrations due to blood flow and blood pressure of the user during the inflation and/or deflation of the inflatable chamber. The sensor chamber can include a flexible housing that contains the volume of liquid. In some cases, the stack structure can help decrease the size of the blood pressure measurement device such that it can be integrated into smaller devices while achieving desirable accuracy and reliability.

The blood pressure measurement device can also include a pump that is configured to inflate the inflatable chamber. The pump can be integrated into the pressure sensing stack structure of the pressure sensing device. For example, the inflatable chamber can be positioned on an upper surface of the pump such that when the blood pressure measurement device is worn by the user the stack includes the pump positioned furthest from the user, the inflatable chamber positioned between the pump and the user, and the sensing chamber positioned between the inflatable chamber and the user. The strap can secure the pressure sensing stack to the user such that, as the inflatable chamber is inflated, it expands primarily towards the user.

In some implementations, the blood pressure measurement device includes a support plate that is positioned between the inflatable chamber and the sensing chamber. The support plate can be a rigid or semi-rigid structure that helps distribute the force generated by the inflatable chamber across the sensing chamber and can prevent blood pressure pulse signal loss that may occur between the sensing chamber and the inflatable chamber. In some cases, the inflatable chamber, the support plate, and the sensing chamber can all have similar profiles such that the support plate and/or expansion chamber extend across substantially the entire bottom surface of the sensing chamber.

The blood pressure measurement device can be an independent device that includes a display, dedicated processor, battery, and so on, which can be mounted to or otherwise integrated into the strap. In other cases, the blood pressure measurement device can be integrated to function with a wearable device such as a smartwatch. For example, the pressure sensing stack can be mounted to a smartwatch band and be electrically coupled with the smartwatch. In these cases, the pressure sensing stack could send vibration and/or pressure measurements to the smartwatch and the smartwatch can analyze, display or combine the vibration and pressure data with other data that was collected by the smartwatch, which could include ambient pressure, user movement, other physiological measurements of a user such as electrocardiograms, temperatures, oxygen saturation, and so on. In some cases, the blood pressure measurement device could utilize components of the smartwatch such as a power source, processor, a display or other output devices, communications hardware and so on.

The example of a smartwatch is given as one example of a device that the blood pressure measurement device can be integrated with. However, the blood pressure measurement device can also be configured to detect blood pressure at locations other than the wrist and/or integrated with other devices such as a dedicated display and processing system, a smartphone, other wearable health monitors, portable music players, and the like. For example, the blood pressure measurement device could be mounted to a strap that is configured to wrap around the upper arm, the wrist, and/or other portions of a user to estimate a blood pressure using measurements from one or more of these locations.

In some cases, the blood pressure measurement device can wirelessly communicate with one or more other devices. For example, the pressure sensing device could send blood pressure measurement data to a smartphone, tablet, computer, or other connected devices where it can be viewed, analyzed, stored, or otherwise accessed by the user or other authorized party.

The blood pressure measurement device can be secured to a user in a variety of ways. For example, the blood pressure measurement device can removably couple to a variety of different straps, which can be configured to attach to different body parts of the user. In other cases, the blood pressure measurement device could be integrated into clothing, belts, hats, or other items worn by a user. In some cases, the blood pressure measurement device could be placed on a surface and the user could check their blood pressure by pressing a portion of their body against the device to measure their blood pressure.

Apple's patent FIG. 1A below shows an example blood pressure measurement device being worn by a user; FIG. 1B shows an example cross-sectional view of the example blood pressure measurement device.

Apple's patent FIG. 5A above shows a perspective view of an example blood pressure measurement device; FIG. 5B shows a cross-sectional view of the example blood pressure measurement device shown in FIG. 5A; FIG. 6 shows an example process for operating a blood pressure measurement device; and FIG. 8 shows an example system diagram for a blood pressure measurement device.

Apple's patent published today was invented by Apple's Hardware Engineer Caleb Han, an 11 year veteran.