Systems and methods for processing physiological signals

Claim 4

The system of Claim 1, wherein the filtering means comprises band-reject filter means (40, 46), under the control of the heart rate signal, for suppressing components of the respiration signal having a frequency substantially equal to the patient's heart rate; and low pass filter means (52) for suppressing components of the respiration signal having a frequency equal to or greater than the second harmonic of the p atient's heart rate.

Claim 6

The system of Claim 4, wherein the means for producing the delayed respiration signals comprises a variable delay line (150) coupled to receive the respiration signal, and having a succession of taps, each providing the respiration signal delayed by successively greater time intervals; wherein the longest time interval varies with the heart rate signal such that it is substantially equal to the period between successive heartbeats of the patient; and wherein the summing means is provided with a plurality of summing terminals (152) each coupled with a respective one of the taps, for summing the delayed respiration signals to produce the filtered respiration signal.

Claim 7

The system of Claim 1 wherein the filtering means comprises a low pass filter (82), a high pass filter(84), and means (92) for summing the output signals of the low pass filter (82) and the high pass filter (84) to provide the filtered respiration signal, the low pass filter (82) and the high pass filter (84) being coupled to receive the respiration signal and operative to pass low frequency components and high frequency components, respectively, of the respiration signal, the low pass filter (82) and the high pass filter (84) having operating characteristics under the control of the heart rate signal such that components of the respiration signal at the heart rate are attenuated in the filtered respiration signal.

Claim 8

The system of Claim 6, wherein the gain of the high pass filter (84) is selected at a value lower than the gain of the low pass filter (82) such that components of the respiration signal having frequencies in the range of the harmonic frequencies of the heart rate are suppressed in the filtered respiration signal relative to components of the respiration signal therein having frequencies below the heart rate.

Claim 9

The system of Claim 7, wherein the gain of the high pass filter (84) is approximately one third that of the low pass filter (82).

Claim 10

The system of Claim 1, further comprising threshold crossing detecting means (24) for producing a recurrence signal representative of the recurrence of the patient's respiration in response at least in part to the filtered respiration signal exceeding a threshold level, and means (26, 40, 150, 160, 162, 164) for producing a minimum threshold level from the respiration signal, the threshold crossing detecting means (24) being responsive to the minimum threshold level to maintain the threshold level equal to or in excess of the minimum threshold level.

Claim 11

The system of Claim 9, wherein the means for producing a minimum threshold level comprises means (40, 150, 160, 162, 164) for producing a cardiovascular artifact signal proportional to the cardiovascular artifact in the respiration signal, and envelope detector means (26) responsive to the cardiovascular artifact signal for producing a signal level proportional to the envelope of the cardiovascular artifact signal as the minimum threshold level.

Claim 12

The system of Claim 10, wherein the means for producing a cardiovascular artifact signal comprises bandpass filtering means (40, 150, 160, 162, 164) for suppressing those components of the respiration signal outside a passband including the fundamental frequency of the cardiovascular artifact, and providing the thus filtered respiration signal as the cardiovascular artifact signal.

Claim 15

The method of Claim 12, wherein the step of filtering the respiration signal further comprises suppressing components of the respiration signal having a frequency equal to or greater than the second harmonic of the patient's heart rate.

Claim 16

The method of Claim 12, further comprising the step of determining whether the filtered respiration signal exceeds u threshold level to produce a recurrence signal representative of the recurrence of the patient's respiration, the threshold level being derived at least in part from the unfiltered respiration signal.

Claim 17

The method of Claim 12, wherein the step of filtering the respiration signal comprises producing a plurality of respiration signal values by delaying the respiration signal to produce said plurality of respiration signal values at successive points in time separated by incremental time differences and producing a filtered respiration signal proportional to the sum of the plurality of respiration signal values.

Claim 18

The method of Claim 15, wherein the difference in time between the oldest respiration signal value and the most recent respiration signal value is selected in response to the representative signal as substantially equal to the period between successive heartbeats of the patient.