产品功能起搏疗法课件.ppt

* Acceleration detection circuit The acceleration detection circuit converts physical motion into an electrical signal proportional to the level of movement. A count is generated each time the activity sensor signal exceeds a user-programmable (positive) activity threshold level and subsequently returns to below the negative threshold level (see for a more detailed description of the threshold: Programming the sensor – Activity Threshold). * Acceleration detection circuit Activity sensor signal frequency band The activity sensor signal frequency band is from 1Hz to 10Hz. The accelerometer sensing element mechanically dampens frequencies above 45 Hz, which makes the sensor system less sensitive to false positive responses. * Algorithm The rate response algorithm converts the activity counts generated by the acceleration detection circuit into an appropriate sensor-indicated heart rate. This is done in a four step procedure. 1) Sum four beats Activity Counts are accumulated in the activity counter over four heart beats to smooth abrupt changes in activity counts in the first step of the algorithm. This procedure is illustrated in the lower part of the figure. Hence, the interval between successive heart beats decreases with increasing heart rate. At higher heart rates, relatively more counts per unit time are necessary to evoke a similar change in pacing rate compared to lower heart rates. This feedback mechanism causes a better proportionality during the upper rate approach i.e. prevents a too aggressive upper rate approach. 2) Smoothing Abrupt changes in activity counts are further suppressed by a running average software routine in the second step of the algorithm. 3) Count to Interval Transform The smoothed activity counts signal is transformed into a heart rate in the third step of the algorithm. The smoothed number of activity counts is compared to a reference number of activity counts at the current pacing rate. A change in the number of activity counts in