| 摘要 |
<p>The appts. is worn on the wrist like a watch, to continuously indicate the cardiac frequency, and contains an adjustable audible alarm. An ultrasonic transceiver measures the Doppler frequency of a continuous or pulsed ultrasonic wave reflected by the blood flowing in an artery or a vein inside the wrist. The appts. includes, between the ultrasonic source and the skin, a medium which adapts the source to the skin impedance. The audible alarm sounds when the cardiac frequency is higher than a threshold which is adjusted by the user. The appts. can also be combined with an electronic watch. The waves are produced by a piezoelectric transducer with a metallised surface and a dia. of between 2 and 3mm.</p> |
