Noninvasive motion and respiration monitoring system
A non-invasive motion and respiration monitor receives impulses from a subject's movement, heartbeat, and respiration. The raw signal is biased and digitized, and a signal processor applies a Fast Fourier Transform to the signal. The transformed signal is filtered to isolate the component representing heart rate from the component representing respiration. An Inverse Fast Fourier Transform is then applied to the component signals, which are sent to a processor. The processor is programmed to detect irregularities in the respiration and heart rate. If severe irregularities or complete cessation is detected in either signal, a mechanical stimulator is actuated to try to stimulate the subject, and an alarm is sounded to alert a caregiver such as a parent or nurse.
1. A method of non-invasively monitoring heart rate and respiration of an infant for mitigating the risk of sleep apnea comprising the steps of:
receiving a time-domain composite signal from a single impulse-sensitive sensor array comprising impulse-sensitive transducers connected in series so as to reduce dependence of the receiving on the positional placement of the transducers with respect to the body of the infant, the time-domain composite signal comprising a respiration rate component and a heart rate component;
applying a Fast Fourier Transform function to the time-domain composite signal to convert the time-domain composite signal to a frequency-domain composite signal;
filtering the frequency-domain composite signal through a first bandpass filter with a pass band between 0.4 and 0.98 hertz to provide a frequency-domain respiration rate signal and
filtering the frequency-domain composite signal through a second bandpass filter with a pass band between 0.98 and 2.54 hertz to provide a frequency-domain heart rate signal;
applying an inverse Fast Fourier Transform function to the frequency-domain respiration rate signal and heart rate signal to provide a time-domain respiration rate signal and time-domain heart rate signal; and
providing an alert if either the time-domain heart rate signal or the time-domain respiration rate signal is interrupted for a time span between two and twenty seconds.
2. The method of claim 1 further comprising the step of providing a shrill alarm to the infant upon receiving the alert.
3. The method of claim 1 further comprising the step of automatically gently agitating the infant upon receiving the alert.
4. A non-invasive monitoring system comprising:
a sensor array comprising impulse-sensitive transducers connected in series so as to reduce dependence of a sensing function on the positional placement of the transducers with respect to the body of an infant, the sensor array configured to be disposed adjacent to an infant mattress and to carry out the sensing function by providing a time-domain composite output waveform responsive to the infant's respiration and heart beat;
an infant agitator;
a signal processor configured to:
receive the time-domain composite output waveform;
apply a Fast Fourier Transform to the time-domain composite output waveform to provide a frequency-domain composite waveform;
filter the frequency-domain composite waveform through a first bandpass filter having a pass band between 0.4 and 0.98 hertz to provide a frequency-domain respiration signal, and filter the frequency-domain composite waveform through a second bandpass filter having a pass band between 0.98 and 2.54 hertz to provide a frequency-domain heart rate signal;
apply an inverse Fast Fourier Transform to the frequency-domain respiration signal to provide a time-domain respiration signal, and apply an inverse Fast Fourier Transform to the frequency-domain heart rate signal to provide a time-domain heart rate signal;
upon failing to detect either a time-domain respiration signal or a time-domain heart rate signal for a time period between two and twenty seconds, enter an alert state and activate the infant agitator.
5. The system of claim 4 wherein the sensor array comprises piezoelectric sensors.
6. The system of claim 4 wherein the output of the sensor array is biased to a desired output level by means of a voltage divider.
7. The system of claim 4 wherein:
the sensor array provides the time-domain output waveform to the signal processor by means of an analog-to-digital converter; and
the signal processor is a field-programmable gate array configured to receive a digital input signal.
8. The system of claim 4 wherein the infant agitator is a physical agitator configured to gently agitate the mattress to awake the infant.
9. The system of claim 4 wherein the infant agitator is a shrill alarm configured to sit near the mattress.
10. The system of claim 4 further comprising a wireless link to a parental unit, the parental unit configured to:
receive a signal form the alert state; and
provide a parental notification alarm.