Fig. 18.—Rogers' "Tycos" dial sphygmomanometer.
An instrument devised by Dr. Rogers (the "Tycos") has met with considerable popularity. (Fig. 18.) This is not an instrument which operates with a spring and lever. The instrument is composed essentially of two metal discs carefully ground and attached at their circumferences to the metal casing below the dial. There is an air chamber between these discs through the center of which air is forced by the syringe bulb. When air is forced into the space between these two discs, they are forced apart to a very slight extent, with the highest pressures only 2-3 mm. of bulging occurs. From data gathered after extensive use for five years these discs were not found to have sprung. A lever attached to a cog which in turn is attached to the dial needle magnifies to an enormous extent the slightest expansion of the discs. Every dial is handmade and every division is actually determined by using a U. S. government mercury manometer of standard type. No two dials therefore are alike in the spacing of the divisions of the scale but every one is calibrated as an individual instrument. There is no doubt in the author's mind that for the general practitioner the instrument has some advantages over the mercury instruments. It reveals the slightest irregularity in force of the heart beat. The oscillation of the dial needle is more accurately followed by the eye than is that of the column of mercury. The needle passes directly over the divisions of the scale, while with usual mercury instruments the scale is an appreciable distance (sometimes .5 cm.) from the column of mercury at the side. (Fig. 19.) The diastolic pressure is more easily read on the "Tycos." It is where the maximum oscillation of the needle occurs as the pressure is slowly released from the cuff. Although it does not appear that this instrument, if properly made and standardized, could become inaccurate, nevertheless it is advisable to check it every few months against a known accurate mercury manometer instrument.
Fig. 19.—Detail of the dial in the "Tycos" instrument.
Fig. 20.—Faught dial instrument.