Methods and apparatus for noninvasively estimating a blood pressure are provided. A target interval is determined from a diastolic signal such that the target interval includes an S2 component. The S2 component is extracted from the diastolic signal using the target interval and is analyzed in the target interval to obtain a number of oscillations in the S2 component. A predetermined relationship between the number of oscillations in the S2 component and blood pressure is used to generate a blood pressure estimate.
