Blood pulse detection method using autocorrelation

A method performed by a medical monitor in order to determine a period of a physiological function of a patient, wherein the method comprises steps of:

• operating a probe to produce an electrical signal which represents the physiological function;
• periodically sampling the electrical signal at a given sampling rate to acquire a plurality of signal samples X(i), where i is an integer that designates a particular signal sample;
• storing the plurality of signal samples in a memory;
• applying serial autocorrelation to the plurality of signal samples to produce a sequence of summation values S(n), where n is a positive integer which designates a particular summation value and an order of the summation values in the sequence;
• storing the sequence of summation values in the memory;
• locating a peak summation value S(max), where max is a positive integer;
• determining a count of summation values in the sequence of summation values from an initial summation value to the peak summation value S(max);
• deriving the period from the count of summation values and the given sampling rate;
• locating a first summation value S(period1) where period1 is an integer less than max;
• and
• locating a second summation value S(period2) where period2 is an integer greater than max.

A method performed by a medical monitor in order to determine a period of a physiological function of a patient, wherein the method comprises steps of:

• operating a probe to produce an electrical signal which represents the physiological function;
• periodically sampling the electrical signal at a given sampling rate to acquire a plurality of signal samples X (i), where i is an integer that designates a particular signal sample;
• storing the plurality of signal samples in a memory;
• applying serial autocorrelation to the plurality of signal samples to produce a sequence of summation values S(n), where n is a positive integer which designates a particular summation value and an order of the summation values in the sequence;
• storing the sequence of summation values in the memory;
• locating a peak summation value S(max), where max is a positive integer;
• when the peak summation value S(max) can not be located within a predefined amount of summation values, then increasing a time scaling factor f.sub.T by two, shrinking the sequence of summation values by one-half, and disregarding every other previously acquired signal sample in subsequent production of summation values;
• determining a count of summation values in the sequence of summation values from an initial summation value to the peak summation value S(max);
• and
• deriving the period from the count of summation values and the given sampling rate.

A method performed by a medical monitor in order to determine a period of a physiological function of a patient, wherein the method comprises steps of:

• operating a probe to produce an electrical signal which represents the physiological function;
• periodically sampling the electrical signal at a given sampling rate to acquire a plurality of signal samples X(i), where i is an integer that designates a particular signal sample;
• storing the plurality of signal samples in a memory;
• applying serial autocorrelation to the plurality of signal samples to produce a sequence of summation values S(n), where n is a positive integer which designates a particular summation value and an order of the summation values in the sequence;
• storing the sequence of summation values in the memory;
• locating a peak summation value S(max), where max is a positive integer;
• when a signal sample exceeds a predetermined magnitude, doubling an amplitude scaling factor f.sub.A, dividing each previously acquired signal sample by two, dividing each of the sequence of summation values produced previously by four, and dividing each signal sample acquired thereafter by the amplitude scaling factor f.sub.A ;
• determining a count of summation values in the sequence of summation values from an initial summation value to the peak summation value S(max);
• deriving the period from the count of summation values and the given sampling rate.

A medical apparatus for monitoring a physiological function of a patient, wherein the medical apparatus comprises:

• a probe for sensing the physiological function and producing an electrical signal indicative thereof;
• a converter connected to said probe to sample the electrical signal at a given sampling rate and produce a plurality of signal samples X(i), where i is an integer that designates a particular signal sample;
• a first memory which receives and stores the plurality of signal samples produced by said converter;
• a mechanism that applies serial autocorrelation to the plurality of signal samples to produce a sequence of summation values S(n), where n is a positive integer which designates a particular summation value and an order of the summation values in the sequence;
• a second memory which stores the sequence of summation values produced by said mechanism;
• a means for locating a peak summation value S(max) produced by said mechanism, where max is a positive integer;
• a means for determining a count of summation values in the sequence from an initial summation value in the sequence to the peak summation value S(max);
• a means for deriving a period of the physiological function from the count of summation values and the given sampling rate;
• means for increasing a time scaling factor f.sub.T by two;
• means for disregarding every other signal sample stored in the first memory;
• and
• means for shrinking the sequence of summation values stored in the second memory by one-half.

A medical apparatus for monitoring a physiological function of a patient, wherein the medical apparatus comprises:

• a probe for sensing the physiological function and producing an electrical signal indicative thereof;
• a converter connected to said probe to sample the electrical signal at a given sampling rate and produce a plurality of signal samples X(i), where i is an integer that designates a particular signal sample;
• a first memory which receives and stores the plurality of signal samples produced by said converter;
• a mechanism that applies serial autocorrelation to the plurality of signal samples to produce a sequence of summation values S(n), where n is a positive integer which designates a particular summation value and an order of the summation values in the sequence;
• a second memory which stores the sequence of summation values produced by said mechanism;
• a means for locating a peak summation value S(max) produced by said mechanism, where max is a positive integer;
• a means for determining a count of summation values in the sequence from an initial summation value in the sequence to the peak summation value S(max);
• a means for deriving a period of the physiological function from the count of summation values and the given sampling rate;
• means for doubling an amplitude scaling factor f.sub.A ;
• means for dividing each signal sample stored in said first memory by two;
• means for dividing each summation value stored in said second memory by four;
• and
• means for dividing each signal sample from the converter by the amplitude scaling factor f.sub.A.