2 sensors are available: accelerometer (G) and minute ventilation (MV).
- accelerometer: the activity sensor detects physical movement and increases the rate according to the level of activity
- minute ventilation: this sensor measures the change in respiration rate and lung volume via transthoracic impedance
- dual-sensors function (Twin-Trace): rate -adaptive pacing based on both minute ventilation and acceleration
- dual-sensors function: G sensor is used at the onset of exercise for a fast response
- dual-sensors function: MV data is used during exercise because of its correlation with VO2
- dual-sensors function: G sensor used for deceleration at the end of exercise
- the two sensors cross-check each other
Antero-posterior acceleration is measured with an accelerometer that works by capacitance variations (plate “vertical” in capacitor).
The G transfer function assigns to the Basic rate and to the Max rate, respectively a rest acceleration and an acceleration corresponding to maximum exercise in daily life.
- between these two points, the device assigns a linear relation (RR auto) or the slope is fixed by the physician (RR fixed)
- the G sensor target rate is determined by a linear relation with metabolic power; it is limited by the basic rate and the maximum rate
Calibration establishes a relation between sensor output and sensor rate.
- the G sensor calibration associates a G- rate with every value of G sensor output
- the G transfer function assigns to the basic rate and to the maximum rate, respectively a rest acceleration and an acceleration that corresponds to maximum exercise in daily life between these two points, respectively called the low and high points, the pacemaker assigns a linear relation
The slope can be automatically adapted by the device based on the Max rate and Max exercise detected by the sensor.
- in a daily basis, the device will check what is the Max exercise of the patient
MV can be measured by measuring the changes in electrical impedance across the chest cavity to calculate changes in lung volume over time.
Minute ventilation (MV) is the volume of air introduced into the lungs per unit of time. MV has 2 components:
- Tidal volume: the volume of air introduced into the lungs in a single respiration cycle
- respiration rate: the number of respiration cycles per minute
Transthoracic impedance is a good indicator of the level of exercise: when the patient exercises, the transthoracic impedance increases (because the volume of air in the lungs increases). This sensor is able to respond to emotional stress (respiratory rate increases when there is an emotion).
- The range of impedances that the pacemaker can measure extends from 0.3 to 6 ohms.
- The pacemaker measures the period and amplitude of the respiration signal on each respiration cycle.
- Every respiration cycle, the algorithm calculates VE = amplitude/period.
- Every respiration cycle, the pacemaker calculates the MV interval as a function of the minute ventilation, which corresponds to the respiration amplitude divided by the respiration period (VE = A / P).
- Every 8 respiration cycles, the system calculates the average of the last 8 respiration cycles (VE8) for Twin-Trace status management.
- Every 4 cardiac cycles, the pacemaker calculates the MV intervals.
- For Rate Response application, MV is averaged on 8, 32 or 128 cycles.
Twin Trace (MV + G)
This permits combining the g sensor’s rapid response and its sensitivity at the beginning and the end of exercise with the MV sensor’s physiological response.The basic principle for two-sensor rate response is to use the g sensor to indicate the beginning and end of exercise. It only uses the MV sensor output to set the rate during confirmed exercise phases. The two sensors also cross-check each other which means that rate response will only continue if both sensors simultaneously detect activity.
When Twin Trace is programmed, with fixed slope
- the programmed fixed slope will be applied to MV only
- the slope for the G sensor is fixed to Medium
Rate response is available in the following modes:
- SafeR, DDD, DDT, DDI, VDD, VVI, VVT, AAI, AAT
COMBINATION of the best indicators :
- Minute Ventilation: response to exercise reliable and proportional to metabolic demand
- Acceleration: rate change is fast at the onset and termination of exercise
- CROSS CHECKING of both sensors:
- RR continues as long as both sensors detect exercise.