A Samsung patent that was recently discovered points to blood pressure tracking being possible on the 'Gear X' which could be an upcoming smartwatch from the company. That said it is worth noting that the diagrams in the patent filing show a square-shaped watch that looks very much like the old Gear Live and the original Galaxy Gear, Samsung's one and only Android Wear smartwatch and its very first smartwatch that launched with Tizen, so the the pictures used in the patent filing are not likely to be the actual design for a new watch.
As to the blood pressure sensor Samsung's patent describes using polarized and depolarized light to read the blood pressure through a user's skin, and then allow the watch to display that data on the screen of the watch like shown in the image above. Something to consider is that it is possible that the Gear X is not meant to be a smartwatch in the same way that the recently launched Gear Sport is, and may be more of a health-related wearable meant mostly for this purpose of capturing the user's blood pressure so it could be monitored more easily.
That said, other diagrams in the patent filing show the watch as having a number pad dialer for what would presumably be making phone calls, and that it would have NFC and possibly MST technology built-in so it could be used for making mobile payments. These factors point to this being more of a full-fledged smartwatch but there's not much detail that can be gathered from the filing other than these few pieces of information as the majority of the writing is all in Korean. There's no mention of when Samsung might release a smartwatch with a blood pressure sensor, and since the Gear Sport launched just within the last six months, it isn't likely Samsung will have a new watch available anytime soon, which could mean a device with a BP sensor is further out, assuming that Samsung is even developing such a device in the first place and not just sitting on these designs for the time being.