Sensor, apparatus and method for non-invasive measurement of oxygen saturation

Claim 2

Sensor for noninvasive measurement of oxygen saturation by irradiating human tissue with electromagnetic waves and measuring the intensity of the reflected waves comprising: (2.1) carrier means, (2.2) at least one transmitter (15) emitting electromagnetic waves of different wavelengths into the human tissue and mounted on said carrier means, (2.3) at least two receivers (19,23) set up to receive electromagnetic-waves, each of these receivers being sensitive to at least one of said different wavelengths reflected from the human tissue and mounted on said carrier means, characterized in that said at least two receivers (19,23) are mounted on said carrier means in distances selected such that the lengths of the light paths (I₂'+I₁',I₃'+I₄') through the human tissue at both different wavelengths are substantially equal.

Claim 3

Sensor according to claim 1 or 2, characterized in that said carrier means are adapted for application to a specific part of the human body, particularly by means of a certain geometry, and that the distances between transmitter(s) (7,9; 15; 26,26; 33,34; 40,41) and receiver(s) (8; 19,23; 28; 35; 42) are, based on average values of tissue characteristics of said specific human limb, selected such that the light paths (I₁+I₂,I₃+I₄; I₂'+I₁',I₃'+I₄';I₁''+I₂'',I₃''+I₄'';I₅+I₆,I₇+I₈;+I₅'+I₉',I₇'+I₈') at at least two different wavelengths are substantially equal.

Claim 4

Sensor according to claim 3 for measuring oxygen saturation of a fetus prior to and under birth, characterized in that said carrier means is a cap (37) comprising at least two transmitters (40,41), preferably light emitting diodes, emitting electromagnetic waves of different wavelengths, and at least one receiver (42) responsive to said different wavelengths.

Claim 5

Sensor according to claim 4, characterized in that said cap is a suction cup comprising a suction tube (38) connected with a suction source.

Claim 6

Sensor according to claim 3, characterized in that said carrier means (32) is substantially closed in itself in cross-section for application to a finger of an adult person.

Claim 7

Apparatus for noninvasive measurement of oxygen saturation for connection to a sensor according to at least one of claims 3 to 6, characterized by conversion means converting the intensity of the received electromagnetic waves into electrical signals, processing means for the calculation of oxygen saturation from said electrical signals, and plausibility checking means comparing the received signals with predefined limits or predefined signals and generating an alarm or a warning message upon a significant deviation.

Claim 8

Apparatus for noninvasive measurement of oxygen saturation for connection to a sensor, particularly according to at least one of claims 1 to 7, characterized by conversion means converting the intensity of the received electromagnetic waves into electrical signals, comparison means comparing said electrical signals with sets of predefined signals representative of certain places of application at the human body or representative of certain tissue characteristics and selecting the set comprising most common characteristics with said electrical signals, correction means correcting said electrical signals in dependency of the selected set, and processing means for the calculation of oxygen saturation from said corrected electrical signals.

Claim 9

Apparatus according to claim 7 or 8, characterized in that said sets of predefined signals contain attenuation values representative of certain places of application at the human body or of certain human tissue.

Claim 10

Apparatus according to claim 7 or 8, characterized in that said sets of predefined signals contain values of the amplitude of the alternating component representative of certain places of application at the human body or of certain human tissue.

Claim 11

Apparatus according to claim 7 or 8, characterized in that said sets of predefined signals contain signal shapes representative of certain places of application at the human body or of certain human tissue.

Claim 12

Method for calculating oxygen saturation from the intensity of electromagnetic waves of at least two different wavelengths reflected by human tissue, wherein at least the electromagnetic waves incorporating one predefined wavelength pass through human tissue on differing paths, characterized by the following steps: (12.1) converting the intensities of the received electromagnetic waves into electrical signals, (12.2) comparing the electrical signals corresponding to the electromagnetic waves of said predefined wavelength with sets of predefined signals representative of certain places of application at the human body or representative of certain tissue characteristics, (12.3) selecting the set comprising most common characteristics with said electrical signals corresponding to the electromagnetic waves of said predefined wavelength, (12.4) correcting said electrical signals corresponding to the electromagnetic waves of said predefined wavelength in dependency of the selected set, and (12.5) calculating oxygen saturation from said corrected electrical signals.

Claim 13

Sensor according to claim 1, characterized by at least one first transmitter (58) emitting electromagnetic waves of a first wavelength and at least two second transmitters (55,56) emitting electromagnetic waves of a second wavelength, wherein said first and second transmitters (58; 55,56) are mounted on said carrier means (50) in different distances to said at least one receiver (57) such that the length of the light path (62,63) through the human tissue between said first transmitter (58) and said receiver (57) is for tissue (59) with a certain predefined characteristics substantially equal to the length of the light path (60,61) through the human tissue between the first (55) of said second transmitters and said receiver (57), whereas the length of the light path (66,67) through the human tissue between said first transmitter (58) and said receiver (57) is for tissue (68) with another certain predefined characteristics substantially equal to the length of the light path (64,65) through the human tissue between the second (56) of said second transmitters and said receiver (57).

Claim 14

Sensor according to claim 1 3, characterized in that it comprises 2n first transmitters (70a-70d,71a-71d) and 2n second transmitters (72a-72d,73a-73d) arranged symmetrically with respect to the receiver, n being an integer number with n≧1.

Claim 15

Sensor according to claim 2, characterized by at least one first receiver set up to receive electromagnetic waves of a first wavelength and at least two second receivers set up to receive electromagnetic waves of a second wavelength, wherein said first and second receivers are mounted on said carrier means in different distances to said at least one transmitter such that the length of the light path through the human tissue between said transmitter and said first receiver is for tissue with a certain predefined characteristics substantially equal to the length of the light path through the human tissue between said transmitter and the first of said second receivers, whereas the length of the light path through the human tissue between said transmitter and said first receiver is for tissue with another certain predefined characteristics substantially equal to the length of the light path through the human tissue between said transmitter and the second of said second receivers.

Claim 16

Sensor according to at least one of claims 13 to 15, characterized in that said carrier means are adapted for application to a specific part of the human body, particularly by means of a certain geometry.

Claim 17

Sensor according to claim 16 for measuring oxygen saturation of a fetus prior to and under birth, characterized in that said carrier means is a cap comprising at least two first transmitters (81a,81b), preferably light emitting diodes, emitting electromagnetic waves of a certain first wavelength, as well as at least two second transmitters (82a,82b), preferably light emitting diodes, emitting electromagnetic waves of a certain second wavelength, and at least one receiver (83) responsive to said different wavelenghts.

Claim 18

Sensor according to claim 17, characterized in that said cap is a suction cup comprising a suction tube (77) connected with a suction source.

Claim 19

Apparatus for noninvasive measurement of oxygen saturation for connection to a sensor, particularly according to at least one of claims 13 to 18, characterized by conversion means converting the intensity of the received electromagnetic waves into electrical signals, processing means for the calculation of oxygen saturation from said electrical signals, selection input means for selecting the place of application at the human body, and transmitter/receiver selection means responsive to said selection input means and set up to select certain transmitter(s) and/or certain receiver(s) depending on the place of application.

Claim 20

Apparatus according to claim 19, characterized by plausibility checking means comparing the received signals with predefined limits or predefined signals representative of the selected place of application and generating an alarm or a warning message upon a significant deviation.

Claim 21

Apparatus for noninvasive measurement of oxygen saturation for connection to a sensor, particularly according to at least one of claims 13 to 18, characterized by conversion means converting the intensity of the received electromagnetic waves into electrical signals, processing means for the calculation of oxygen saturation from said electrical signals, and application detection means set up to select sequentially certain transmitter(s) and/or certain receiver(s), compare each of the specific electrical signals associated with a certain transmitter and a certain receiver with sets of predefined signals representative of certain places of application at the human body or representative of certain tissue characteristics and select those of said specific electrical signals comprising most common characteristics with a certain of said sets, and selection means set up to select the transmitter(s) and/or receiver(s) associated with said specific electrical signals comprising most common characteristics with a certain of said sets for further measurement.

Claim 22

Method for measuring oxygen saturation from the intensity of electromagnetic waves of at least two different wavelengths reflected by human tissue, wherein at least the electromagnetic waves incorporating one predefined wavelength pass through human tissue on differing paths, characterized by the following steps: (22.1) selecting sequentially certain transmitter(s) and certain receiver(s) so that different paths for said electromagnetic waves are set up, (22.2) converting the intensities of the received electromagnetic waves into electrical signals, (22.3) comparing each of the specific electrical signals associated with a certain transmitter and a certain receiver with sets of predefined signals representative of certain places of application or representative of certain tissue characteristics, (22.4) selecting those of said specific electrical signals which comprise most common characteristics with a certain of said sets, (22.5) selecting the transmitter(s) and/or receiver(s) associated with said specific electrical signals comprising most common characteristics with a certain of said sets, (22.6) performing further measurements only with the transmitter(s) and receiver(s) selected in step (22.5).

Claim 23

Sensor according to any of claims 4, 5, 17 or 18, characterized in that it comprises also electrocardiogram contacts.

Claim 24

Method for calculating oxygen saturation from the intensity of electromagnetic waves of at least two different wavelengths reflected by or transmitted through human tissue, particularly according to at least one of the preceding claims, characterized by the following steps: (24.1) converting the intensities of the received electromagnetic waves into electrical signals, (24.2) performing an autocorrelation (84,84') on at least one specific of said electrical signals, (24.3) detecting the frequency (86,86') of said specific electrical signal from the autocorrelation function, (24.4) performing a cross-correlation (89,89') between said specific electrical signal and a predefined signal of substantially the same frequency, (24.5) detecting the maximum amplitude of said cross-correlation function, (24.6) using said maximum amplitude (90,90') to calculate oxygen saturation.

Claim 25

Method according to claim 24, characterized by (25.3a) entering the place of application of a sensor, and (25.3b) selecting said predefined signal from a set of predefined signals in dependency of the place of application of said sensor.

Claim 26

Method according to claim 24, characterized by (26.3a) comparing said specific electrical signal (93) with sets of pattern signals representative of certain places of application at the human body or representative of certain tissue characteristics, (26.3b) selecting the pattern signal (95) comprising most common characteristics with said specific electrical signal as predefined signal.

Claim 27

Method according to claim 26, characterized in that the comparison between said specific electrical signal and said sets of pattern signals comprises sequential cross-correlations with each pattern signal in said set of pattern signals.

Claim 28

Method according to at least one of claims 24-27, characterized in that a general predefined signal is compressed or expanded (88,93) such that it becomes a predefined signal of the frequency of said specific electrical signal.

Claim 29

Method for measuring the heart rate from the intensity of electromagnetic waves of at least two different wavelengths reflected by human tissue, particularly according to claim 24, characterized by the following steps: (29.1) converting the intensities of the received electromagnetic waves into electrical signals, (29.2) performing an autocorrelation on at least one specific of said electrical signals, (29.3) detecting the heart rate (87) as the frequency of said specific electrical signal (86) from the autocorrelation function.

Claim 30

Apparatus for noninvasive measurement of oxygen saturation from the intensity of electromagnetic waves of at least two different wavelengths reflected by or transmitted through human tissue, characterized by: (30.1) conversion means converting the intensity of the received electromagnetic waves into electrical signals, (30.2) autocorrelation means for performing an autocorrelation on at least a specific one of said electrical signals, (30.3) frequency detection means for detection of the frequency of the autocorrelation function, (30.4) frequency adaptation means to adapt the frequency of a predefined signal to the frequency of the autocorrelation function, (30.5) cross correlation means performing a cross correlation between said specific electrical signal and said predefined signal, (30.6) detection means detecting the maximum amplitude of said cross-correlation function, and (30.7) oxygen saturation calculation means calculating oxygen saturation from said maximum amplitude.

Claim 31

Apparatus according to claim 30, characterized by (31.1) sensor application input means, and (31.2) predefined signal selection means operating in dependency of a sensor application entered via said sensor application input means to select said predefined signal from a set of predefined signals.

Claim 32

Apparatus according to claim 30, characterized by (32.1) pattern signal comparison means comparing said specific electrical signal with sets of pattern signals representative of certain places of application at the human body or representative of certain tissue characteristics, and (32.2) predefined signal selection means selecting the set comprising most common characteristics with said electrical signal as predefined signal.