ANESTHETIC DEPTH DETECTOR

Abstract: From a fluctuation of pulse periods of a subject continuously measured by a pulse period measuring device, a first pulse period fluctuation signal HFC RR which corresponds to a first pulse period fluctuation component produced in substantial synchronism with a respiration of the subject and a second pulse period fluctuation signal LFC RR which corresponds to a second pulse period fluctuation component having a predetermined frequency lower than a frequency of the first pulse period fluctuation component are extracted by a pulse period fluctuation signal extracting means. Then, based on a ratio (HFC RR /LFC RR ) of the first pulse period fluctuation signal HFC RR to the second pulse period fluctuation signal LFC RR , an anesthetic depth of the subject is calculated by an anesthetic depth calculating means. Thus, the present apparatus can objectively or quantitatively calculate the anesthetic depth of the subject. Additionally, the apparatus can accurately measure the anesthetic depth of the subject without needing operator's skill or the like.

Description: The present invention relates to an anesthetic depth measuring apparatus for measuring an anesthetic depth of a living subject. When a patient is anesthetized for a surgery or the like, it is required to maintain a suitable anesthetic depth so as to protect the patient from stress or pain due to the surgery. Conventionally, for example, an anesthetic depth has been subjectively or empirically recognized by monitoring a change of a blood pressure, a heart rate or a respiration rate of the patient, resulting from a stimulation of the surgery, or observing a reflex of eyelashes, a dimension of a pupil, a hue of a limb or a body temperature of the patient. EP-A-0232234 discloses an anesthetic depth measurement device according to the pramble of claim 1 measuring the blood pressure and the pulse period at the same time and using a change rate evaluation method. WO 92/06632 discloses an anesthetic depth monitoring device measuring respiration frequency and pulse period at the same time. However, since the anesthetic depth recognition based on the change of the blood pressure, the heart rate or the respiration rate, or based on the reflex of the eyelashes, the dimension of the pupil, the hue of the limb or the body temperature is performed depending on a subjective judgement of anesthetists or the like, the anesthetists are required to have a long-time experience and a skill. In addition, it is not easy to objectively or accurately recognize the anesthetic depth. It is therefore an object of the present invention to provide an anesthetic depth measuring apparatus for objectively measuring an anesthetic depth of a living subject. The inventors of the present invention have continued their study in the background of the above described situation, and they have found that a magnitude of a pulse period fluctuation component produced in synchronism with a respiration of a subject, a magnitude of a blood pressure fluctuation component having a frequency lower than a frequency of the respiration of the subject or a rate of change of the pulse period to the blood pressure of the subject has a close relation to an activity level of subject's parasympathetic nerve or sympathetic nerve, whereby an anesthetic depth of the subject can be objectively measured on the basis of the magnitude of the above mentioned fluctuation component, when the subject is anesthetized. Moreover, the present inventors have found that the influences of the anesthesia on a peripheral body temperature and a deep body temperature are different from each other, and a difference between the peripheral body temperature and the deep body temperature has a close relation to an activity level of a nerve of the subject, whereby an anesthetic depth of the subject can be objectively measured on the basis of the difference. The present invention has been developed based on those findings. The above object may be achieved according to the invention by an anesthetic depth measuring apparatus for measuring an anesthetic depth of a living subject, comprising a pulse period measuring device which continuously measures a period of a pulse of the subject; and pulse period fluctuation signal extracting means for extracting, by frequency analysis of fluctuation of the pulse periods continuously measured by said pulse period measuring device, a first pulse period fluctuation signal which corresponds to a magnitude of a first pulse period fluctuation component having a frequency in a first predetermined frequency range including a frequency of respiration of the subject and the anesthetic depth measuring apparatus being characterized by further comprising: the pulse period fluctuation signal extracting means for further extracting a second pulse period fluctuation signal which corresponds to a magnitude of a second pulse period fluctuation component having a frequency in a second predetermined frequency range including a frequency of one third to one fourth of the frequency of respiration of the subject; and first anesthetic depth calculating means for calculating a first anesthetic depth of the subject based on a ratio of said first pulse period fluctuation signal to said second pulse period fluctuation signal. In the above mentioned apparatus, from a fluctuation of the pulse periods continuously measured by the pulse period measuring device, the first pulse period fluctuation signal which corresponds to the first pulse period fluctuation component produced in substantial synchronism with the respiration of the subject and the second pulse period fluctuation signal which corresponds to the second pulse period fluctuation component having a predetermined frequency lower than a frequency of the first pulse period fluctuation component are extracted by the pulse period fluctuation signal extracting means. Then, based on a ratio of the first pulse period fluctuation signal to the second pulse period fluctuation signal, the anesthetic depth of the subject is calculated by the anesthetic depth calculating means. Thus, the present apparatus can objectively or quantitatively calculate the anesthetic depth of the subject. Additionally, the apparatus can accurately measure the anesthetic depth without needing operator's skill or the like. The above object may be achieved according to a further embodiment of the invention by the anesthetic depth measuring apparatus for measuring an anesthetic depth of a living subject, mentioned above, comprising a blood pressure measuring device which continuously measures a blood pressure value of the subject; blood pressure fluctuation signal extracting means for extracting, by frequency analysis of fluctuation of the blood pressure values continuously measured by said blood pressure measuring device, a blood pressure fluctuation signal which corresponds to a magnitude of a blood pressure fluctuation component having a frequency in a predetermined frequency range including a frequency of one third to one fourth of the frequency of respiration of the subject; second anesthetic depth calculating means for calculating a second anesthetic depth of the subject based on a magnitude of said blood pressure fluctuation signal; and anesthetic depth determining means for determining a third anesthetic depth of the subject based on the first anesthetic depth calculated by said first anesthetic depth calculating means and the second anesthetic depth calculated by the second anesthetic depth calculating means, so that the determined third anesthetic depth is displayed on a display device. In the above mentioned apparatus, the pulse period of the subject is continuously measured by the pulse period measuring device, the blood pressure value of the subject is continuously measured by the blood pressure measuring device, and a rate of change of one of the blood pressure values and the pulse periods to the other of the blood pressure values and the pulse periods is calculated by the change rate calculating means. Then, based on the rate of change, the anesthetic depth of the subject is determined by the anesthetic depth determining means. Thus, the present apparatus can objectively or quantitatively determine the anesthetic depth of the subject. Additionally, the apparatus can accurately measure the anesthetic depth without needing operator's skill or the like. Further embodiments of the present invention are disclosed in the following description and claimed in the further subclaims. Fig. 1 is a diagrammatic view for illustrating the construction of an anesthetic depth measuring apparatus embodying the present invention. Fig. 2 is a block diagram for explaining various functions of a control device of the apparatus of Fig. 1. Fig. 3 is a view for illustrating a fluctuation of pulse periods T RR measured by the apparatus of Fig. 1. Fig. 4 is a view for illustrating a first pulse period fluctuation signal HFC RR , a second pulse period fluctuation signal LFC RR and a pulse period direct current component DC RR which are extracted from the fluctuation of the pulse periods T RR measured by the apparatus of Fig. 1. Fig. 5 is a graph showing a relationship used by the apparatus of Fig. 1 for calculating an anesthetic depth D RR . Fig. 6 is a graph showing a relationship used by the apparatus of Fig. 1 for calculating an anesthetic depth D SYS . Fig. 7 is a flow chart representing the operation of the control device of the apparatus of Fig. 1. There will be described in detail an embodiment of the present invention, referring to the drawings. Fig. 1 is a diagrammatic view for illustrating the construction of an anesthetic depth measuring apparatus embodying the present invention. In the figure, an electrocardiographic waveform detecting device 10 includes a plurality of electrodes 12 which are put on a living subject. The device 10 continuously supplies a well-known electrocardiographic waveform signal successively produced in synchronism with a heartbeat of the subject who is generally anesthetized by an inhalation anesthetic, such as isoflurane, to a CPU 18 of a control device 16 via an A/D converter 14. A blood pressure measuring device 20 includes a pressure pulse wave detecting probe 22 adapted to be pressed, with a band (not shown), to an artery of the subject, such as a carotid artery, a radial artery or a pedal dorsal artery. The device 20 continuously measures a blood pressure value of the generally anesthetized subject based on each one pulse of the detected pulse wave and supplies a blood pressure signal representative of the blood pressure value to the CPU 18 of the control device 16 via an A/D converter 24. This blood pressure measuring device 20 is constructed similarly to the blood pressure monitoring apparatus disclosed in U.S. Patent No. 4,423,738 or laid-open publication No. 5-253196 of unexamined Japanese Patent Application. The control device 16 is provided by a so-called microcomputer including the CPU 18, a ROM 26 and a RAM 28. The CPU 18 processes input signals, that is, the electrocardiographic waveform signal and the blood pressure signal, according to control programs pre-stored in the ROM 26 by utilizing a temporary-storage function of the RAM 28, and controls a display device 30 so as to display an anesthetic depth D of the subject. Fig. 2 is a block diagram for explaining various functions of the control device 16. In the figure, a pulse period measuring means 50 measures a pulse period from a heartbeat synchronous wave, such as an electrocardiographic waveform, a pulse wave produced from an artery, or the like, produced in synchronism with a heartbeat of the subject. Preferably, by calculating a time interval between each pair of successive two pulses of the electrocardiographic waveform, for example, R-waves of the successive two pulses, the pulse period measuring means 50 continuously measures a pulse period T RR of the anesthetized subject. The thus measured pulse periods T RR have a fluctuation as shown in Fig. 3, for example. A pulse period fluctuation signal extracting means 52 extracts, from the fluctuation of the pulse periods T RR continuously measured by the pulse period measuring means 50, a first pulse period fluctuation signal HFC RR which corresponds to a first pulse period fluctuation component produced in substantial synchronism with a respiration of the subject and a second pulse period fluctuation signal LFC RR which corresponds to a second pulse period fluctuation component having a predetermined frequency lower than a frequency of the first pulse period fluctuation component. The pulse period fluctuation signal extracting means 52 performs a frequency analysis of the fluctuation of the pulse periods T RR , with a fast Fourier transformation (FFT) method, an autoregression (AR) method, or the like. Then, the pulse period fluctuation signal extracting means 52 outputs, as the first and second pulse period fluctuation signals HFC RR , LFC RR , a magnitude (power) of a signal component having a frequency in the neighborhood of the frequency of the respiration of the subject and a magnitude (power) of a signal component having a frequency in the neighborhood of one third to one fourth of the frequency of the respiration of the subject, respectively. Specifically, the pulse period fluctuation signal extracting means 52 outputs, as the first and second pulse period fluctuation signals HFC RR , LFC RR , a magnitude of a signal component having a peak frequency in a predetermined frequency range including a frequency (e.g., 0.25 Hz) of the respiration of the subject and a magnitude of a signal component having a peak frequency in a predetermined frequency range including a frequency (e.g., 0.07 Hz) of about one third to one fourth of the frequency of the respiration of the subject, respectively. Fig. 4 respectively illustrates respective magnitudes of the first and second pulse period fluctuation signals HFC RR , LFC RR and a 0 Hz frequency component (direct current component) signal DC RR which are extracted from the fluctuation of the pulse periods T RR . A first anesthetic depth calculating means 54 included in an anesthetic depth determining means 62 calculates a first anesthetic depth D RR of the subject based on a ratio (LFC RR /HFC RR ) of the first pulse period fluctuation signal HFC RR to the second pulse period fluctuation signal LFC RR which are extracted by the pulse period fluctuation signal extracting means 52. The first anesthetic depth calculating means 54 calculates the first anesthetic depth D RR based on the actual ratio (LFC RR /HFC RR ) according to a pre-stored relationship shown in Fig. 5, for example. It is speculated that, in the action of a cardiac vagus nerve that is an efferent nerve originating from a circulatory center, a respiratory fluctuation occurs due to the interference of a respiratory center with the circulatory center at the level of a brain stem and a respiratory fluctuation of afferent signals produced from cardio-pulmonary receptors. Therefore, a fluctuation appearing in a frequency of ignition of a sino-auricular node can be regarded as a magnitude (power) of a signal component having a peak frequency in a frequency range including a frequency (e.g., 0.25 Hz) of the respiration of the subject, that is, the first pulse period fluctuation signal HFC RR . Moreover, the respiratory fluctuation occurs to the action of a sympathetic nerve which controls the sino-auricular node. However, since the pulse rate control under the sympathetic nerve has a characteristic as a low frequency range filter, the sympathetic nerve can transmit only pulse rate fluctuations having extremely low frequencies, e.g., frequencies not higher than 0.15 Hz, and HFC RR having an ordinary respiration frequency is exclusively mediated by the vagus nerve. Thus, the amplitude of HFC RR , that is, magnitude of HFC RR is in proportion to the activity of the cardiac vagus nerve and may be used as a useful and quantitative index of the cardiac vagus nerve activity. Meanwhile, it is speculated that the second pulse period fluctuation signal LFC RR corresponding to a fluctuation component having a frequency of about one third to one fourth of a frequency of the first pulse period fluctuation signal HFC RR is caused by a pulse rate fluctuation which occurs via a baroreceptor reflex mechanism. Afferent and efferent nerves of the reflex are an aortic sinus nerve, and cardiac parasympathetic and sympathetic nerves, respectively. Since the signal LFC RR is in proportion to a product of the amplitude of the blood pressure and the sensitivity of the baroreceptors, the sympathetic nerve activity cannot be evaluated, if the baroreceptor reflex sensitivity is not constant. Thus, the ratio (LFC RR /HFC RR ) closely corresponds to the nerve activity, because of being freed from an influence of an individual difference. The relationship shown in Fig. 5 is experimentally obtained in advance, based on the above described facts. A blood pressure measuring means 56 which is provided by, for example, the blood pressure measuring device 20, continuously measures a blood pressure value of the subject. A blood pressure fluctuation signal extracting means 58 extracts, from a fluctuation of the blood pressure values, for example, systolic blood pressure values P SYS , continuously measured by the blood pressure measuring means 56, a blood pressure fluctuation signal LFC SYS which corresponds to a blood pressure fluctuation component having a predetermined frequency lower than the frequency of the respiration of the subject. The blood pressure fluctuation signal extracting means 58 performs a frequency analysis of the fluctuation of the blood pressure values P SYS , with a fast Fourier transformation (FFT) method, an autoregression (AR) method, or the like, and outputs, as the blood pressure fluctuation signal LFC SYS , a magnitude (power) of a signal component having a peak frequency in a frequency range including a frequency (e.g., 0.07 Hz) of about one third to one fourth of the frequency of the respiration of the subject. A second anesthetic depth calculating means 60 included in the anesthetic depth determining means 62 calculates a second anesthetic depth D SYS of the subject based on a magnitude of the blood pressure fluctuation signal LFC SYS according to a pre-stored relationship as shown in Fig. 6, for example. Since it is speculated that the blood pressure fluctuation signal LFC SYS representative of the fluctuation of blood pressure values results from a delay of a sympathetic vasomotor regulation system, an amplitude (magnitude) of the signal LFC SYS may be used as a quantitative index of a vasomotor sympathetic nerve activity. A relationship shown in Fig. 6 is experimentally obtained in advance, based on the above described facts. The anesthetic depth determining means 62 determines a third anesthetic depth D based on the first anesthetic depth D RR calculated by the first anesthetic depth calculating means 54 and the second anesthetic depth D SYS calculated by the second anesthetic depth calculating means 60. For example, if the first and second anesthetic depths D RR , D SYS are extremely different from each other, the anesthetic depth determining means 62 judges, based on respective time-wise changes of the two anesthetic depths, which one of the two anesthetic depths D RR and D SYS is abnormal, and determines, as the third anesthetic depth D, the other of the anesthetic depths D RR and D SYS , or calculates respective weighing factors based on the respective time-wise changes of the two anesthetic depths and determines, as the third anesthetic depth D, an average value of the respective weighed values of the anesthetic depths D RR and D SYS . Meanwhile, if the first and second anesthetic depths D RR , D SYS are not so different from each other, the anesthetic depth determining means 62 determines, as the third anesthetic depth D, one of the two anesthetic depths D RR , D SYS , or an average value of the two anesthetic depths D RR and D SYS . Fig. 7 is a flow chart representing the operation of the control device 16, which shows a routine carried out in synchronism with a pulse or an input of a blood pressure value. In Fig. 7, at Step SA1 corresponding to the pulse period measuring means 50, a pulse period T RR is calculated as a time interval between respective R-waves of successive two pulses of the electrocardiographic waveform input from the electrocardiographic waveform detecting device 10. Step SA1 is followed by Step SA2, corresponding to the pulse period fluctuation signal extracting means 52, to perform a frequency analysis of a fluctuation of the pulse periods T RR with a fast Fourier transformation (FFT) method, an autoregression (AR) method, or the like, and extract, as first and second pulse period fluctuation signals HFC RR , LFC RR , a magnitude (power) of a signal component having a peak frequency in a frequency range including a frequency (e.g., 0.25 Hz) of a respiration of the subject and a magnitude (power) of a signal component having a peak frequency in a frequency range including a frequency (e.g., 0.07 Hz) of about one third to one fourth of the frequency of the respiration of the subject, respectively. Step SA2 is followed by Step SA3, corresponding to the first anesthetic calculating means 54, to calculate a first anesthetic depth D RR of the subject based on a ratio (LFC RR /HFC RR ) of the first pulse period fluctuation signal HFC RR to the second pulse period fluctuation signal LFC RR according to the pre-stored relationship shown in Fig. 5, for example. Next, the control of the CPU 18 goes to Step SA4. At Step SA4, a blood pressure value P SYS input from the blood pressure measuring device 20 is read in. Step SA4 is followed by Step SA5, corresponding to the blood pressure fluctuation signal extracting means 58, to perform a frequency analysis of a fluctuation of the blood pressure values P SYS , with a fast Fourier transformation (FFT) method, an autoregression (AR) method, or the like, and extract, as the blood pressure fluctuation signal LFC SYS , a magnitude (power) of a signal component having a peak frequency in a frequency range including a frequency (e.g., 0.07 Hz) of about one third to one fourth of the frequency of the respiration of the subject. Step SA5 is followed by Step SA6, corresponding to the second anesthetic depth calculating means 60, to calculate a second anesthetic depth D SYS of the subject based on the blood pressure fluctuation signal LFC SYS extracted at Step SA5 according to the pre-stored relationship shown in Fig. 6, for example. Subsequently, the control of the CPU 18 goes to Step SA7, corresponding to the anesthetic depth determining means 62, to determine a third anesthetic depth D having a higher reliability, based on the first anesthetic depth D RR calculated on the basis of the fluctuation of pulse periods and the second anesthetic depth D SYS calculated on the basis of the fluctuation of blood pressure values. For example, if the first and second anesthetic depths D RR , D SYS are extremely different from each other, one of the first and second anesthetic depths D RR , D SYS is judged as an abnormal value, based on respective time-wise changes of the two anesthetic depths, and the other of the first and second anesthetic depths D RR , D SYS is determined as the third anesthetic depth D. If the first and second anesthetic depths D RR , D SYS are not so different from each other, an average value of the first and second anesthetic depths D RR , D SYS is determined as the third anesthetic depth D. Step SA7 is followed by Step SA8 to quantitatively display, on the display device 30, the anesthetic depth D determined at Step SA7, in digits, a trend graph, or the like. For instance, the anesthetic depth D is expressed with numerals by dividing the axis of abscissas of Fig. 5 or 6 into predetermined units. In the above described embodiment, from the fluctuation of the pulse periods continuously measured at Step SA1 corresponding to the pulse period measuring means 50, the first pulse period fluctuation signal HFC RR which corresponds to the first pulse period fluctuation component produced in substantial synchronism with the respiration of the subject and the second pulse period fluctuation signal LFC RR which corresponds to the second pulse period fluctuation component having the predetermined frequency lower than the frequency of the first pulse period fluctuation component are extracted at Step SA2 corresponding to the pulse period fluctuation signal extracting means 52. Then, the first anesthetic depth D RR of the subject is calculated at Step SA3 corresponding to the first anesthetic depth calculating means 54, based on the ratio (LFC RR /HFC RR ) of the first pulse period fluctuation signal HFC RR to the second pulse period fluctuation signal LFC RR . Thus, the present apparatus can objectively or quantitatively calculate the first anesthetic depth D RR of the subject and accurately obtain the anesthetic depth D RR without needing operator's skill or the like. In the present embodiment, the blood pressure values P SYS of the subject are continuously measured by the blood pressure measuring means 56. From the fluctuation of the continuously measured blood pressure values P SYS , the blood pressure fluctuation signal LFC SYS which corresponds to the blood pressure fluctuation component having the predetermined frequency lower than the frequency of the respiration of the subject is extracted at Step SA5 corresponding to the blood pressure fluctuation signal extracting means 58. Then, the second anesthetic depth D SYS of the subject is calculated at Step SA6 corresponding to the second anesthetic depth calculating means 60, based on the magnitude of the blood pressure fluctuation signal LFC SYS . Thus, the present apparatus can objectively or quantitatively calculate the second anesthetic depth D SYS of the subject and accurately obtain the anesthetic depth D SYS without needing operator's skill or the like. In the present embodiment, based on the first anesthetic depth D RR calculated on the basis of the fluctuation of pulse periods T RR and the second anesthetic depth D SYS on the basis of the fluctuation of blood pressure values P SYS , the third anesthetic depth D having a higher reliability is determined at Step SA7 corresponding to the anesthetic depth determining means 62, whereby the anesthetic depth D quantitatively displayed on the display device 30 enjoys the higher reliability. While the present invention has been described in its preferred embodiments by reference to the drawings, it is to be understood that the invention may otherwise be embodied. In the embodiment shown in Fig. 2, both the means 50, 52, 54 for calculating the first anesthetic depth D RR from the fluctuation of the pulse periods T RR , and the means 56, 58, 60 for calculating the second anesthetic depth D SYS from the fluctuation of the blood pressure values P SYS are employed. However, even if one of the two means for calculating the first and second anesthetic depths D RR , D SYS is omitted, the apparatus can have the function of measuring an anesthetic depth. Moreover, in the embodiment of Fig. 2, the pulse . period T RR of the subject is continuously measured by calculating a period of an electrocardiographic waveform (ECG) detected by the electrocardiographic waveform detecting device 10, for example, calculating a time interval between respective R-waves of each pair of successive two pulses of the electrocardiographic waveform. However, it is possible to employ a means for pulse-synchronously calculating a period of a pulse wave detected by a well-known cuff or pressure pulse wave sensor from an artery of a living subject, or a means for pulse-synchronously calculating a period of a volume pulse wave detected by a photoelectric pulse wave sensor. In short, any kind of means for continuously measuring a pulse period of the subject may be provided. For example, when a pulse period is measured on the basis of the pressure pulse wave detected by the pressure pulse wave detecting probe 22 of the blood pressure measuring device 20, the electrocardiographic detecting device 10 is not needed. In the embodiment shown in Fig. 2, as the pulse period T RR , the blood pressure value P SYS , or the anesthetic depth D RR or D SYS , a moving average of values pulse-synchronously obtained within a predetermined period may be used. Further, the pulse period T RR or the blood pressure value P SYS may be obtained based on every second or third pulse. In the embodiment shown in Fig. 2, the pulse period fluctuation signal extracting means 52 or the blood pressure fluctuation signal extracting means 58 may be provided by a digital filter for discriminating a micro-oscillation signal having a low frequency. In the embodiment shown in Fig. 2, for the anesthetic depth D SYS calculation, the fluctuation of the systolic blood pressure values P SYS measured by the blood pressure measuring means 56 are used. However, a fluctuation of mean blood pressure values P MEAN or diastolic blood pressure values P DIA measured by the blood pressure measuring means 56 may be used. In the embodiment shown in Fig. 2, the first and second pulse period fluctuation signals HFC RR , LFC RR are obtained from the pulse periods T RR continuously measured by the pulse period measuring means 50. However, since the pulse period T RR (sec.) corresponds to a pulse rate PR (= 60/T RR ), one to one, a means for measuring a pulse rate PR may be employed in place of the pulse period measuring means 50, and, from a fluctuation of the pulse rates PR, a first pulse rate fluctuation signal corresponding to a respiratory fluctuation and a second pulse rate fluctuation signal corresponding to one third to one fourth of the respiratory fluctuation may obtained. In the embodiment shown in Fig. 2, the first anesthetic depth D RR of the subject is calculated on the basis of the ratio (LFC RR /HFC RR ) of the second pulse period fluctuation signal LFC RR to the first pulse period fluctuation signal HFC RR and the second anesthetic depth D SYS is calculated on the basis of the magnitude of the blood pressure fluctuation signal LFC SYS . However, the ratio (LFC RR /HFC RR ) or the blood pressure fluctuation signal LFC SYS may be corrected or modified based on other parameters. In any case, the first anesthetic depth D RR of the subject is calculated on the basis of the ratio (LFC RR /EFC RR ) of the second pulse period fluctuation signal LFC RR to the first pulse period fluctuation signal HFC RR and the second anesthetic depth D SYS is calculated on the basis of the magnitude of the blood pressure fluctuation signal LFC SYS . It is to be understood that the present invention may be embodied with other changes and modifications that may occur to those skilled in the art without departing from the scope of the invention. It is understood from the above description that since the anesthetic depth measuring apparatuses according to the present invention can quantitatively and objeetively measure an anesthetic depth of a patient, they are suitable for use in an operating room, an intensive care unit, or the like where the patient is generally anesthetized.

Claims: An anesthetic depth measuring apparatus for measuring an anesthetic depth of a living subject, comprising: a pulse period measuring device (50, SA1) which continuously measures a period of a pulse of the subject; and pulse period fluctuation signal extracting means (52, SA2) for extracting, by frequency analysis of fluctuation of the pulse periods continuously measured by said pulse period measuring device, a first pulse period fluctuation signal which corresponds to a magnitude of a first pulse period fluctuation component having a frequency in a first predetermined frequency range including a frequency of respiration of the subject, the anesthetic depth measuring apparatus being characterized by further comprising: the pulse period fluctuation signal extracting means for further extracting a second pulse period fluctuation signal which corresponds to a magnitude of a second pulse period fluctuation component having a frequency in a second predetermined frequency range including a frequency of one third to one fourth of the frequency of respiration of the subject; and first anesthetic depth calculating means (54, SA3) for calculating a first anesthetic depth of the subject based on a ratio of said first pulse period fluctuation signal to said second pulse period fluctuation signal. An anesthetic depth measuring apparatus according to claim 1, further comprising: a blood pressure measuring device (20, 56) which continuously measures a blood pressure value of the subject; blood pressure fluctuation signal extracting means (58, SA5) for extracting, by frequency analysis of fluctuation of the blood pressure values continuously measured by said blood pressure measuring device, a blood pressure fluctuation signal which corresponds to a magnitude of a blood pressure fluctuation component having a frequency in a predetermined frequency range including a frequency of one third to one fourth of the frequency of respiration of the subject; second anesthetic depth calculating means (60, SA6) for calculating a second anesthetic depth of the subject based on a magnitude of said blood pressure fluctuation signal; and anesthetic depth determining means (62, SA7) for determining a third anesthetic depth of the subject based on the first anesthetic depth calculated by said first anesthetic depth calculating means and the second anesthetic depth calculated by said second anesthetic depth calculating means, so that the determined third anesthetic depth is displayed on a display device (30). An anesthetic depth measuring apparatus according to claim 1, wherein said pulse period measuring device comprises an electrocardiographic waveform detecting device (10) which includes a plurality of electrodes (12) which are put on the subject and detects an electrocardiographic waveform of the subject, and wherein said pulse period measuring device calculates, as a period of a pulse, a time interval between each pair of successive two pulses of the electrocardiographic waveform detected by the electrocardigraphic waveform detecting device. An anesthetic depth measuring apparatus according to claim 1, wherein said pulse period measuring device comprises a pressure pulse wave sensor, and wherein said pulse period measuring device pulse-synchronously calculates a period of a pulse wave detected by the pressure pulse wave sensor. An anesthetic depth measuring apparatus according to claim 1, wherein said pulse period measuring device comprises a cuff, and wherein said pulse period measuring device pulse-synchronously calculates a period of a pulse wave detected by the cuff. An anesthetic depth measuring apparatus according to claim 1, wherein said pulse period measuring device comprises a photoelectric pulse wave sensor, and wherein said pulse period measuring device pulse-synchronously calculates a period of a volume pulse wave detected by the photoelectric pulse wave sensor. An anesthetic depth measuring apparatus according to claim 2, wherein said blood pressure measuring device (20, 56) comprises a pressure pulse wave detecting probe (22) adapted to be pressed against an artery of the subject, and wherein said blood pressure measuring device continuously measures a blood pressure value of the subject based on each one pulse of the detected pressure pulse wave. An anesthetic depth measuring apparatus according to claim 1, wherein said first anesthetic depth calculating means comprises a memory in which a predetermined relationship between anesthetic depth and signal magnitude ratio of first pulse period fluctuation signal to second pulse period fluctuation signal is stored, and wherein said first anesthetic depth calculating means calculates a first anesthetic depth, based on an actual signal magnitude ratio of the first pulse period fluctuation signal to the second pulse period fluctuation signal, according to the predetermined relationship. An anesthetic depth measuring apparatus according to claim 2, wherein said second anesthetic depth calculating means (62, SA7) comprises a memory in which a predetermined relationship between anesthetic depth and blood pressure fluctuation signal magnitude is stored, and wherein said second anesthetic depth calculating means calculates a second anesthetic depth, based on an actual magnitude of the blood pressure fluctuation signal, according to the predetermined relationship.

Inventors: NOMURA TAKASHI, TSUDA HIDEICHI, NOMURA, TAKASHI, TSUDA, HIDEICHI
Applicants: COLIN CORP, COLIN CORPORATION
Application year: 1996
Main classification: A61B5
IPC codes: A61B5