Sensing respiration parameters based on an impedance signal

A method comprising:

• evaluating, by processing circuitry of a medical device, at least one of a heart rate, a patient posture, a patient activity level, an electrocardiogram (ECG), a presence or an absence of one or more arrhythmias, or data from an acoustic sensor to determine at least one of the presence of one or more arrhythmias, a change in the heart rate, a change in the patient posture, a change in the patient activity level, or detection of sound in the data from the acoustic sensor;
• triggering performance of, based on the at least one of the presence of the one or more arrhythmias, the change in the heart rate, the change in the patient posture, the change in the patient activity level, or the detection of sound in the data from the acoustic sensor and by sensing circuitry of a medical device subcutaneously inserted into a patient and via a plurality of electrodes of the medical device, an impedance measurement to collect a set of impedance values over a period of time, wherein the set of impedance values is indicative of a respiration pattern of a patient, and wherein at least one of the plurality of electrodes is disposed on a proximal portion of a housing of the medical device and at least another one of the plurality of electrodes is disposed on a distal portion of the housing;
• identifying, by the processing circuitry of the medical device, a set of positive zero crossings based on the set of impedance values;
• determining, by the processing circuitry and based on the set of positive zero crossings, a first set of respiration intervals, wherein each respiration interval of the first set of respiration intervals corresponds to a respective full respiratory cycle within the respiration pattern and wherein each respiration interval of the first set of respiration intervals comprises an amount of time separating each pair of consecutive positive zero crossings of the set of positive zero crossings;
• identifying, by the processing circuitry, a set of negative zero crossings based on the set of impedance values;
• determining, by the processing circuitry and based on the set of negative zero crossings, a second set of respiration intervals, wherein each respiration interval of the second set of respiration intervals corresponds to a respective full respiratory cycle within the respiration pattern and wherein each respiration interval of the second set of respiration intervals comprises an amount of time separating each pair of consecutive negative zero crossings of the set of negative zero crossing;
• determining, by the processing circuitry and for the impedance measurement, a value of a respiration metric using both the set of negative zero crossings and the set of positive zero crossings, wherein determining the value of the respiration metric comprises determining a median respiration interval of a third set of respiration intervals including the first set of respiration intervals and the second set of respiration intervals, and calculating, based on the median respiration interval, a respiration rate corresponding to the impedance measurement;
• determining a median duration of the third set of respiration intervals;
• determining a respiration interval duration window;
• determining a number of respiration intervals of the third set of respiration intervals which define a duration outside of the respiration interval duration window;
• determining that the number of respiration intervals satisfies a threshold number of respiration intervals;
• and
• determining to use the impedance measurement for the determination of the value of the respiration metric based on the determination that the number of respiration intervals satisfies the threshold number of respiration intervals.

Non-transitory computer-readable media storing instructions for causing processing circuitry of a medical device to:

• evaluate at least one of a heart rate, a patient posture, a patient activity level, an electrocardiogram (ECG), a presence or an absence of one or more arrhythmias, or data from an acoustic sensor to determine at least one of the presence of one or more arrhythmias, a change in the heart rate, a change in the patient posture, a change in the patient activity level, or detection of sound in the data from the acoustic sensor;
• triggering sensing circuitry to obtain, based on the at least one of the presence of the one or more arrhythmias, the change in the heart rate, the change in the patient posture, the change in the patient activity level, or the detection of sound in the data from the acoustic sensor, an impedance measurement to collect a set of impedance values over a period of time;
• identify a set of positive zero crossings based on a set of impedance values;
• determine, based on the set of positive zero crossings, a first set of respiration intervals, wherein each respiration interval of the first set of respiration intervals corresponds to a respective full respiratory cycle within a respiration pattern of a patient and wherein each respiration interval of the first set of respiration intervals comprises an amount of time separating each pair of consecutive positive zero crossings of the set of positive zero crossings;
• identify a set of negative zero crossings based on the set of impedance values;
• determine, based on the set of negative zero crossings, a second set of respiration intervals, wherein each respiration interval of the second set of respiration intervals corresponds to a respective full respiratory cycle within the respiration pattern and wherein each respiration interval of the second set of respiration intervals comprises an amount of time separating each pair of consecutive negative zero crossings of the set of negative zero crossings;
• determine, for an impedance measurement, a value of a respiration metric using both the set of negative zero crossings and the set of positive zero crossings, wherein to determine the value of the respiration metric, the instructions are configured cause the processing circuitry to determine a median respiration interval of a third set of respiration intervals including the first set of respiration intervals and the second set of respiration intervals, and calculate, based on the median respiration interval, a respiration rate corresponding to the impedance measurement;
• determine a median duration of the third set of respiration intervals;
• determine a respiration interval duration window;
• determine a number of respiration intervals of the third set of respiration intervals which define a duration outside of the respiration interval duration window;
• determine that the number of respiration intervals satisfies a threshold number of respiration intervals;
• and
• determine to use the impedance measurement for the determination of the value of the respiration metric based on the determination that the number of respiration intervals satisfies the threshold number of respiration intervals, and
• wherein the medical device comprises a plurality of electrodes and a housing, at least one of the plurality of electrodes being disposed on a proximal portion of the housing and at least another one of the plurality of electrodes being disposed on a distal portion of the housing, and the sensing circuitry configured to perform, using the plurality of electrodes, the impedance measurement to collect the set of impedance values over a period of time, wherein the set of impedance values is indicative of the respiration pattern of the patient.