Methods of and apparatus for measuring physiological parameters

Apparatus for measuring physiological parameters in a blood vessel of a subject, the apparatus comprising:

• a means for attachment of the apparatus on a part of the subject's body;
• at least one acoustic sensor positionable on the part of the subject's body and configured to receive an acoustic signal from the blood vessel, the at least one acoustic sensor comprising:
• a first microphone positioned to measure an acoustic signal from the blood vessel,
• a second microphone positioned to measure ambient background noise, and
• a processor for receiving signals from the first microphone and the second microphone, the processor being configured to generate a noise-reduced acoustic signal by subtracting the background noise measured by the second microphone from the acoustic signal measured by the first microphone;
• an optical sensor comprising a light source, and comprising a photosensor configured to measure one or more properties of the light source through absorption, refraction, or reflection of the light source from the blood vessel;
• and
• a motion sensor for determining whether the apparatus is being worn by a subject;
• wherein the apparatus is configured to activate the optical sensor only when the motion sensor determines motion representative of the apparatus being worn by the subject;
• and
• wherein the apparatus is configured to activate the first microphone and the second microphone only when the optical sensor determines light absorption, refraction, or reflection representative of the apparatus being located in close proximity to the blood vessel.