Patent ID: 7621877

Claim:
A probe for application to a selected area of a subject's skin covering a body part, which selected area serves as a measurement site for measuring changes in the pulsatile arterial blood volume thereat, comprising: a base for application to the selected area of the subject's skin at said measurement site; a pressure applicator carried by said base for applying a static pressure to the subject's skin at said measurement site when said base is applied thereto; and a sensor carried by said pressure applicator for sensing changes in the pulsatile arterial blood volume at said measurement site when the base is applied thereto; said pressure applicator being designed to apply to said measurement site, when the base is applied thereto, a static pressure of a sufficient magnitude to partially unload the wall tension of, but not to occlude, the arteries at said measurement site; said pressure applicator being configured to substantially prevent venous distention and blood pooling at said measurement site by applying sufficient external counter pressure to effectively collapse the underlying veins and limit the local venous blood flow to the arterial throughput while permitting free venous drainage with respect to said measurement site through tissues surrounding said measurement site; said probe being configured to be applied to a relatively restricted area of the subject's skin, to apply said static pressure to said relatively restricted area , which area does not completely encircle the body part at said measurement site, said pressure applicator occupying a relatively small fraction of the surface perimeter of the respective body part at said measurement site, to thereby permit free venous drainage from said measurement site via a wide region of unrestricted passageways surrounding the measurement site; wherein said pressure applicator comprises a fluid chamber with at least one elastic wall constructed to utilize Laplace's law and including a self-contained fluid for applying said static pressure to said measurement site such that the level of pressure applied by said probe is substantially unaffected by the mechanical characteristics of the underlying tissues.