Also, the future update to the Apple Watch's ECG feature could address inconclusive readings for heart rates between 100 and 120 beats per minute.
The Heartline study, open to people aged 65 and older, will research atrial fibrillation and early detection of stroke using Apple's smartwatch.
The Apple Heart and Movement, Women's Health and Hearing Studies are now open for enrollment in the U.S.
The patent describes a method to more accurately determine when someone is asleep, using multiple devices (rather than just one device) as sources of data.
The Cupertino-based company continues to assess the utility of the Apple Watch band as a location for medical sensors.
The studies will be conducted in collaboration with leading medical institutions to examine hearing, women's, mobility and heart health.
The best smartwatch in the world just got better with a slew of new features that will help Apple cement its position at the top of the market.
Tension has been increasing within the team in recent months, according to eight people familiar with the situation.
The early-stage study took place over 12 weeks and included an 82-person healthy control group and 31 individuals with varying stages of cognitive decline.
New capabilities include women cycle tracking, Noise app, Activity Trends and App Store right on the wrist; also, there are new watch faces.