Providing temporal information of a subject

A method providing temporal information on a subject, the method comprising:

• receiving a ballistocardiographic signal of a subject;
• processing the ballistocardiographic signal to obtain at least a beat-to-beat time (TB2B) signal and a stroke volume (SV) signal;
• producing a filtered TB2B signal by filtering the TB2B signal to remove erroneous values not caused by heart beats, wherein said filtering the TB2B signal comprises:
• calculating an average TB2B signal strength over a first time period;
• defining an allowed variation range for the TB2B signal strength;
• and
• removing any peaks from the TB2B signal that do not fit within the allowed variation range for producing the filtered TB2B signal;
• producing a filtered SV signal by filtering the SV signal to remove erroneous SV values not caused by heart beats;
• calculating a true HR signal from the filtered TB2B signal, wherein the true HR signal is substantially free from errors caused by erroneous peaks not caused by heart beats;
• calculating a true SV signal and a stroke volume variability (SVV) signal from the filtered SV signal;
• filtering the true HR signal to detect abnormal heart beats and filtering at least one of the true SV signal and the SVV signal for detecting changes in variation of the stroke volume and using such changes in variation of the stroke volume as additional parameters facilitating separation of abnormal heart beats from normal heart beats;
• and
• if abnormal heart beats are detected, further identifying type of arrhythmia related to the detected abnormal heart beats;
• and
• outputting temporal information on occurrence and type of the identified arrhythmia and temporal information on the detected changes in variation of stroke volume,
• wherein the method further comprises:
• in connection to filtering the TB2B signal and filtering the SV signal, obtaining information on occurrence of at least one of the erroneous TB2B signal peaks and erroneous SV signal values;
• obtaining a signal strength (SS) signal by calculating an average root mean square of the strength of the received ballistogardiographic signal;
• using the SS signal for discriminating whether the received signal represents actual detected BCG signal, background noise, or movement of the subject, wherein a SS signal within a predefined signal strength interval is deemed to represent actual BCG measurement result, a SS signal weaker than the predefined signal strength interval is deemed to represent noise, and a SS signal stronger than the predefined signal strength interval is deemed to represent movement of the subject;
• and
• outputting temporal indication of movement of the subject on basis of the information on occurrence of at least one of the erroneous TB2B signal peaks and the erroneous SV signal values.

A system providing temporal information on a subject, the system comprising:

• an accelerometer configured to obtain a ballistocardiographic signal of a subject;
• processing means configured to process the ballistocardiographic signal to obtain at least a TB2B (beat-to-beat time) signal, an RR (respiration rate) signal and an SV (stroke volume) signal, wherein the processing means comprises:
• a first filter configured to produce a filtered TB2B signal by filtering the TB2B signal to remove erroneous TB2B signal peaks not caused by heart beats, wherein the first filter is configured:
• to calculate an average TB2B signal strength over a first time period;
• to define an allowed variation range for the TB2B signal strength;
• and
• to remove any peaks from the TB2B signal that do not fit within the allowed variation range for producing the filtered TB2B signal;
• a second filter configured to produce a filtered SV signal by filtering the SV signal to remove erroneous SV signal peaks not caused by heart beats;
• calculation means configured to calculate a true HR signal from the filtered TB2B signal, wherein the true HR signal is substantially free from errors caused by erroneous peaks not caused by heart beats;
• calculation means configured to calculate a true SV signal and a stroke volume variability, SVV, signal from the filtered SV signal;
• a third filter configured to filter the true HR signal to detect abnormal heart beats;
• wherein the processing means is configured to filter the true SV signal and the SVV signal for detecting changes in variation of the stroke volume and using such changes in variation of the stoke volume as additional parameters facilitating separation of abnormal heart beats from normal heart beats, and if abnormal heartbeats are detected, the processing means is further configured to identify type of arrhythmia related to the abnormal heart beats and to output temporal information on occurrence and type of the identified arrhythmia and temporal information on the detected variations of stroke volume,
• wherein the processing means is further configured:
• to obtain information on occurrence of at least one of the erroneous TB2B signal peaks and erroneous SV signal values in connection to filtering the TB2B signal and filtering the SV signal;
• to obtain a signal strength (SS) signal by calculating an average root mean square of the strength of the received ballistogardiographic signal;
• and
• to use the SS signal for discriminating whether the received signal represents actual detected BCG signal, background noise, or movement of the subject, wherein a SS signal within a predefined signal strength interval is deemed to represent actual BCG measurement result, a SS signal weaker than the predefined signal strength interval is deemed to represent noise, and a SS signal stronger than the predefined signal strength interval is deemed to represent movement of the subject, and in that
• the output unit is further configured to provide a temporal indication of movement of the subject on basis of the information on occurrence of at least one of the erroneous TB2B signal peaks and the erroneous SV signal values.

A computer program product embodied on a non-transitory computer-readable medium, said computer program comprising instructions configured perform a method of providing temporal information on a subject, which, when executed by a computing device or system, cause the computing system or device to perform the steps of:

• receiving a ballistocardiographic signal of a subject;
• processing the ballistocardiographic signal to obtain at least a beat-to-beat time (TB2B) signal and a stroke volume (SV) signal;
• producing a filtered TB2B signal by filtering the TB2B signal to remove erroneous values not caused by heart beats, wherein said filtering the TB2B signal comprises:
• calculating an average TB2B signal strength over a first time period;
• defining an allowed variation range for the TB2B signal strength;
• and
• removing any peaks from the TB2B signal that do not fit within the allowed variation range for producing the filtered TB2B signal;
• producing a filtered SV signal by filtering the SV signal to remove erroneous SV values not caused by heart beats;
• calculating a true HR signal from the filtered TB2B signal, wherein the true HR signal is substantially free from errors caused by erroneous peaks not caused by heart beats;
• calculating a true SV signal and a stroke volume variability (SVV) signal from the filtered SV signal;
• filtering the true HR signal to detect abnormal heart beats and filtering at least one of the true SV signal and the SVV signal for detecting changes in variation of the stroke volume and using such changes in variation of the stroke volume as additional parameters facilitating separation of abnormal heart beats from them from normal heart beats;
• and
• if abnormal heart beats are detected, further identifying type of arrhythmia related to the detected abnormal heart beats, and
• outputting temporal information on occurrence and type of the identified arrhythmia and temporal information on the detected changes in variation of stroke volume,
• wherein the steps further comprise:
• in connection to filtering the TB2B signal and filtering the SV signal, obtaining information on occurrence of at least one of the erroneous TB2B signal peaks and erroneous SV signal values;
• obtaining a signal strength (SS) signal by calculating an average root mean square of the strength of the received ballistogardiographic signal;
• using the SS signal for discriminating whether the received signal represents actual detected BCG signal, background noise, or movement of the subject, wherein a SS signal within a predefined signal strength interval is deemed to represent actual BCG measurement result, a SS signal weaker than the predefined signal strength interval is deemed to represent noise, and a SS signal stronger than the predefined signal strength interval is deemed to represent movement of the subject;
• and
• outputting temporal indication of movement of the subject on basis of the information on occurrence of at least one of the erroneous TB2B signal peaks and the erroneous SV signal values.