A blow out preventer for operating between a spear of a tubular gripping tool and a tubular gripped by the tool includes: an expandable seal carried on the spear and expandable to seal between the spear and the tubular’s inner wall, the expandable seal being operable as a back up to a primary seal operable between the spear and the tubular’s inner wall. While the cuff pressure is increased, combinations of the plurality of pairs of the light emitting elements and the light receiving elements are switched, and volume pulse waves are obtained from each of the combinations. The Rfdet signal is a signal having H level when a laser spot falls in a data-recorded area on an optical disk, and having L level when in a non-recorded area. Then, for each detected arrhythmia, a determination is made based on the data, whether there was a myocardial ischemic episode detected within a specified temporal proximity of the arrhythmia.