Wrist worn accelerometer for pulse transit time (PTT) measurements of blood pressure

A method 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, the method comprising:

• detecting, with an accelerometer of a wrist-worn device non-invasively engaging an anterior surface of the wrist of the user, a first signal indicative of when blood is ejected from the left ventricle of the user's heart;
• detecting, with a PPG or a pulse pressure sensor of the wrist-worn device non-invasively engaging the skin on the wrist of the user, a second signal indicative of when a blood pressure pulse corresponding to the blood ejection arrives at the wrist;
• storing acceleration data corresponding an output of the accelerometer for a recording time period;
• using the second signal to select a candidate time period within the recording time period to select the acceleration data to evaluate to identify when the blood election from the user's left ventricle occurred corresponding to the blood pressure pulse;
• calculating a pulse transit time (PTT) for the blood pressure pulse from the ejection of the blood from the left ventricle to arrival of the blood pressure pulse at the wrist;
• and
• generating one or more relative blood pressure values for the user based on the PTT.