Rate adaptive cardiac rhythm management device control algorithm using trans-thoracic ventilation
First Claim
1. A rate-adaptive cardiac rhythm management device including:
- (a) means for sensing trans-thoracic impedance variations in a patient due to respiratory and cardiac activity;
(b) variable rate pulse generator means for stimulating said patient'"'"'s heart;
(c) means for deriving from said sensed impedance variations a control signal proportional to the patient'"'"'s minute ventilation, said pulse generator being connected to receive said control signal for varying the rate at which the stimulation occurs between a lower rate limit and an upper rate limit, with said means for deriving said control signal having(i) analog-to-digital converter means coupled to receive an analog signal corresponding to said trans-thoracic impedance variations due to respiratory and cardiac activity for converting same to a serial digital signal train,(ii) a digital filter having an input connected to receive said digital signal train and an output, said filter operating to attenuate components to said signal train due to cardiac activity over a range of heart rates and respiratory rates while passing components in said signal train due to respiratory activity,(iii) peak detecting means coupled to said output of said digital filter for locating the maximum and minimum values of said components in said signal train due to respiratory activity,(iv) tidal volume determining means responsive to said peak detecting means for determining the patient'"'"'s instantaneous tidal volume and average tidal volume over a predetermined number of breathing cycles,(v) ventilatory index determining means responsive to said tidal volume determining means for summing said average tidal volumes over a predetermined time interval, yielding said ventilatory index,(vi) means for establishing a baseline value by computing the exponential average of said ventilatory index over a time interval that is long compared to said predetermined time interval,(vii) means for computing a ventilatory ratio as the quotient of said ventilatory index and said baseline value, and(viii) means for adding a pacing rate increment to said lower rate limit, said increment being the product of said ventilatory ratio and a predetermined constant.
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Accused Products
Abstract
A rate adaptive cardiac rhythm management device in which the pacing rate is adjusted in accordance with changes in the patient'"'"'s minute ventilation. An adaptive four-pole elliptic digital filter, preferably implemented in software, functions to attenuate any signal components due to cardiac activity and motion from the minute ventilation signal over the range of breathing frequencies encountered in going from a sedentary state to active exercise. The pacemaker incorporates a microprocessor-based controller that is programmed to compute from peak-to-peak excursions of the sensed parameter the instantaneous tidal volume. Likewise, it computes, using a zero-crossing technique, the breathing interval. Knowing the breathing interval and the instantaneous tidal volume, it is possible to compute minute ventilation over a predetermined time interval and it is that factor that is employed in developing the ultimate control signal used to vary the stimulating rate between a lower rate limit and an upper rate limit.
434 Citations
9 Claims
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1. A rate-adaptive cardiac rhythm management device including:
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(a) means for sensing trans-thoracic impedance variations in a patient due to respiratory and cardiac activity; (b) variable rate pulse generator means for stimulating said patient'"'"'s heart; (c) means for deriving from said sensed impedance variations a control signal proportional to the patient'"'"'s minute ventilation, said pulse generator being connected to receive said control signal for varying the rate at which the stimulation occurs between a lower rate limit and an upper rate limit, with said means for deriving said control signal having (i) analog-to-digital converter means coupled to receive an analog signal corresponding to said trans-thoracic impedance variations due to respiratory and cardiac activity for converting same to a serial digital signal train, (ii) a digital filter having an input connected to receive said digital signal train and an output, said filter operating to attenuate components to said signal train due to cardiac activity over a range of heart rates and respiratory rates while passing components in said signal train due to respiratory activity, (iii) peak detecting means coupled to said output of said digital filter for locating the maximum and minimum values of said components in said signal train due to respiratory activity, (iv) tidal volume determining means responsive to said peak detecting means for determining the patient'"'"'s instantaneous tidal volume and average tidal volume over a predetermined number of breathing cycles, (v) ventilatory index determining means responsive to said tidal volume determining means for summing said average tidal volumes over a predetermined time interval, yielding said ventilatory index, (vi) means for establishing a baseline value by computing the exponential average of said ventilatory index over a time interval that is long compared to said predetermined time interval, (vii) means for computing a ventilatory ratio as the quotient of said ventilatory index and said baseline value, and (viii) means for adding a pacing rate increment to said lower rate limit, said increment being the product of said ventilatory ratio and a predetermined constant. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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Specification