An apparatus and associated method may include a light source system that includes a light-emitting component, and a receiver system configured to detect an acoustic wave that corresponds to a photoacoustic response of a blood vessel to light emitted by the light source system. A control system may be configured to determine a wave characteristic from the acoustic wave and to estimate a tensive state classification based on the determined wave characteristic. The tensive state classification may be one of a plurality of tensive state classifications that each include different ranges of diastolic and systolic values.