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 that could be incorporated into an Apple Watch and beyond. Mark Gurman began to report that Apple could possibly add blood pressure monitoring to Apple Watch in 2022. His first prediction of it coming to market in 2024 didn't materialize. Blood pressure and glucose monitoring are likely to be the two biggest health features on Apple's drawing board.

Today the U.S. Patent Office published a granted patent of Apple's that once again relates to Blood Pressure (a.k.a. Hypertension).

In Apple's patent background they note that Current noninvasive blood pressure measurement approaches include ambulatory and home blood pressure measurement strategies. These strategies provide a more complete view of a person's blood pressure characteristics and are often employed in recommended situations. Ambulatory blood pressure measurement is performed while the person performs daily life activities. Currently, ambulatory blood pressure measurements are typically performed every 20 to 30 minutes using brachial oscillometric blood pressure measurement cuffs. Yet ambulatory and home blood pressure measurement approaches fail to provide continuous measurement of blood pressure. In that light, convenient and effective approaches for noninvasive continuous measurement of blood pressure remain of interest.

Blood Pressure Monitoring using Apple Watch+

Apple's granted patent presents non-invasive devices, methods, and systems for determining a pressure of blood within a cardiovascular system of a user, the cardiovascular system including a heart and the user having a wrist covered by skin.

More particularly, Apple's patent discloses a variety of wrist-worn devices having a variety of sensors configured to non-invasively engage the skin on the wrist of the user for sensing a variety of user signals from the cardiovascular system of the user.

Generally, approaches disclosed may passively track blood pressure values without any interaction required on the part of the user, which is of particular benefit during overnight monitoring when the user is asleep or for other periods of extended monitoring.

Passive tracking is particularly ideal as blood pressure values may be obtained consistently, frequently, and/or continuously over a period of time for potentially longer and more accurate and complete data sets as this approach is not dependent on user compliance and eliminates any artifacts (e.g., artificially elevated blood pressure value) associated with the act of taking the actual blood pressure measurement (e.g., white coat syndrome).

Alternatively, approaches may allow for on demand or point measurements of blood pressure values by having a user actively interact with the sensors of the wrist-worn device to initiate the blood pressure measurements.

For example, the user may engage sensors of the wrist-worn device with another part of their body (e.g., arm, fingers, sternum, ear) or the user may need to engage the arm on which the wrist device is worn (e.g., volume or pressure oscillometry).

Approaches disclosed allow for absolute blood pressure values to be determined directly without the requirement for any periodic calibrations (e.g., applanation tonometry as described in greater detail below) or for relative blood pressure values to be tracked so as to provide relative blood pressure indices. The relative blood pressure values may be calibrated with a reference measurement to determine blood pressure values on an absolute scale.

However, relative blood pressure values, even if not calibrated to provide absolute blood pressure values, can be of clinical benefit to the user or the health care professional. For example, providing a blood pressure index can show variations or patterns over time (e.g., trending data) which may be of particular diagnostic or therapeutic value for the user or health care professional. Still further, the present invention provides wrist-worn devices that are portable and compact in design and can be easily and comfortably worn for extended of periods of time. In particular, the wrist-worn devices of the present invention provide accurate and robust blood pressure monitoring and tracking outside the conventional hospital setting, which in turn reduces health care costs and empowers users and their caregivers and/or health care professionals to make more informed decisions.

Methods utilizing hydrostatic pressure changes to determine a mean or absolute blood pressure, and more specifically employing modified volume or pressure oscillometry techniques, are disclosed.

In particular, such methodologies advantageously utilize the pressure changes associated with the natural vertical movement of the user's arm (e.g., actively raising and lowering their fully extended arm) not as a source of error, but instead to non-invasively measure a mean blood pressure.

Methods of the present invention for determining a pressure of blood within a cardiovascular system of a user may comprise receiving a plurality of user signals from the cardiovascular system of the user with a sensor. The sensor non-invasively engages the skin of the user over the wrist of the user, each of the user signals being received by the sensor while the sensor has an associated height relative to the heart of the user. The user moves the wrist between the signals so that the heights of the sensor differ within a range of heights relative to the heart of the user. The different heights are maintained for a sufficient length of time for the device to measure blood pressure at each height. For example, the user may slowly raise their arm from a starting position below the heart to and end position above their head or vice versa, wherein the range of heights relative to the heart of the user may comprises a range from about 1 cm to about 40 cm resulting in a hydrostatic pressure differential in range from just below 1 mmHg to about 31 mmHg. A signal variation amplitude of the plurality of signals associated with the range of heights is identified and a standard pressure of the blood of the user based on the signal variation amplitude and the plurality of signals is determined, the standard pressure having an associated standard blood pressure measurement height relative to the heart.

Apple's patent FIG. 1 below illustrates a propagation path of a blood pressure pulse from ejection from the left ventricle of the heart to a wrist on which a wrist-worn blood pressure measurement device is worn; FIGS. 4-5 are schematic side views of wrist-worn blood-pressure measurement devices; FIG. 6 schematically illustrates electrode locations and related body impedances in an approach for measuring chest-cavity impedance variations.

Apple's patent FIG. 18 above illustrates a cross-section of tissue layers between a wrist skin surface and an underlying artery of a subject; FIG. 19 below illustrates detection of different mean penetration depths of light emitted by a PPG sensor having returning light detectors disposed at different distances from each of two light sources of the PPG sensor.

Apple's patent FIGS. 22-23 above show relative contribution by subsurface layer to returning light detected by the light detectors disposed at different distances for two different light source wavelengths; FIGS. 31A-31C illustrate a method of changing the hydrostatic pressure at the wrist of the user; and FIGS. 33 and 35 illustrate various applanation tonometry devices for measuring pressure pulses at the wrist of the user.

For doctors and super techies, Apple's granted patent 12220213 is an extremely detailed invention worth reviewing. 

A Few of Apple's Inventors 

• Derek Young: Research and Development, Health Technologies
• Richard Kimoto: Senior Research Scientist
• Thomas Sullivan: Lead Sensor System Architect
• Stephen Waydo: Sensing Algorithms and Health Research
• Santiago Quijano: R&D in Health Technologies - Embedded Engineer (HW and FW)
• Erno Klaassen: Former Senior Distinguished Engineer (Sr. Director), Health Technologies (left Apple in Nov. 2024)