Back in August 2021, Patently Apple posted an IP report titled "One of the next Health Features that may be coming to Apple Watch relates to Tracking Hydration Levels of a user." Our report noted that hydration measurements could be used to provide useful information for automated and/or manual tracking of a user's activity and health. A user's hydration level has significant impacts on the health of a user. Dehydration could impair performance and is associated with several deleterious health consequences, including heat strokes. Overdrinking can result in hyponatremia, fatigue, confusion, coma, and even death.

The report further noted that a high level of electrical conductance of the perspiration could indicate a high concentration of electrolytes and a low level of hydration. By further example, a low level of electrical conductance of the perspiration can indicate a low concentration of electrolytes and a high level of hydration. These measurement and calculations could be used to provide feedback and health tracking information to a user, for example, during an activity of the user.

Today the U.S. Patent and Trademark Office officially published a patent application from Apple introduces a new health sensor system. More specifically, the invention covers systems, devices, and methods for calculating a perspiration metric of a user.

Some embodiments are directed to a method for measuring physiological signals using an electronic device comprising a plurality of electrodes. The method includes, during a perspiration measurement session, connecting a first set of electrodes of the plurality of electrodes to capacitive measurement circuitry, performing a set of capacitance measurements using the first set of electrodes, and calculating a perspiration metric using the set of capacitance measurements.

The method further includes, during an electrocardiogram (ECG) measurement, connecting a second set of electrodes of the plurality of electrodes to electrocardiogram measurement circuitry and performing an electrocardiogram measurement to generate an ECG waveform.

In some variations, the perspiration measurement session is initiated while the electronic device is tracking an exercise session. In some of these instances, the perspiration measurement session is initiated automatically in response to the electronic device tracking the exercise session.

Apple Watch could be configured to perform perspiration measurements using one or more perspiration sensors. These measurements are in turn used to calculate an estimated sweat rate of a user and/or additional metrics that utilize a user's estimated sweat rate. Specifically, the estimated sweat rate of a user is a measure of the amount of fluid lost over an interval of time.

In instances where an estimated sweat rate is presented to a user, it may be presented in a number of different ways. In some instances the estimated sweat rate may be presented as a rate of fluid loss (e.g., expressed in fluid ounces per hour, or the like) or as an amount of fluid loss for a specific period of time (e.g., expressed as a volume of fluid).

For example, when Apple Watch is used to track an exercise session (e.g., while a user is engaged in a physical activity such as walking, running, cycling, or the like), the device may calculate and present a first estimated sweat rate over a first interval of time corresponding to the exercise session. This may provide a user with information about the average sweat rate or total fluid loss over the course of the exercise session.

An estimated sweat rate may also be used to calculate one or more additional metrics. In some instances, the estimated sweat rate may be used in calculating a metric indicative of a user's hydration (e.g., a hydration level, a change in hydration of an interval of time, or the like).

In other instances, the estimated sweat rate may be used in calculating an exercise metric, such as workout intensity, calories burned, or the like.

Apple's patent FIGS. 5A-B show rear-facing and side views of Apple Watch that includes a perspiration sensor.

Apple's patent FIG. 3B above illustrates a process flow for performing measurements using the hybrid sensor.

Interestingly Apple once again describes the Apple Watch having an integrated camera. The patent referred to "setting a field of view of a camera and capturing of images," though having no connection to perspiration sensors. 

For full details, review Apple's patent application 20240050013 .