fig1 is a general block diagram illustrating the system of the present invention . a patient 10 to be monitored is coupled to an ambulatory eeg monitoring system comprising a transducer assembly 12 and a solid state recording and control apparatus 14 , hereinafter referred to as recorder 14 . although it may become possible to provide a single piece of equipment providing the transducer and recorder functions , due to present limitations of technology transducer assembly 12 and recorder 14 are desirably provided as separate pieces of equipment interconnected by a communication channel 2 . electrical signals relating to brainwave and other physiological data are stored in recorder 14 . transducer assembly 12 includes patient monitoring electrodes for producing electrical signals representing physiological conditions of the patient , including eeg signals or brainwaves . such electrodes are coupled to the patient to be monitored at predetermined locations , or in a &# 34 ; montage &# 34 ;, in accordance with the monitoring procedure desired to be performed . desirably , electrodes are provided to perform monitoring of at least about 16 channels of eeg data ; other physiological parameters may also desirably be simultaneously monitored , such as ekg parameters . an input 22 to transducer assembly 12 may be provided , to enable signals generated by a calibrator 18 to be applied to the system for calibration and checking purposes . desirably , the electrodes are cup - shaped silver - silver chloride electrodes , which are glued at appropriate locations to the scalp of the patient 10 being monitored to provide the input 20 to the transducer assembly . to minimize stray signals and movement artifacts in the measurement of the very small eeg signals , transducer assembly 12 is desirably located immediately adjacent to the patient &# 39 ; s head . however , with presently available technology it is impossible to include the recorder function in a structure which is mountable on a patient &# 39 ; s head . therefore a separate recorder 14 is provided , having an input 26 coupled to the output 24 of the transducer assembly by communication channel 2 . thus , transducer 12 produces signals at its output 24 which are suitable for transmission from the head - mounted transducer assembly 12 to a recorder 14 which may be carried elsewhere on the body of the patient while ambulatory . applicants prefer a recorder 14 which is adapted to be worn at the waist . recorder 14 includes a solid state memory sufficient to hold waveform data for desirably about 16 channels of eeg data for intermittent recording over a period of several hours to several days . such a memory is unaffected by patient movement , unlike tape recorders . recorder 14 includes an input / output port ( i / o port ) 28 , to enable communication with an auxiliary computer 16 via a communication channel 4 and an i / o port 30 associated with the auxiliary computer . as will be described more fully below , auxiliary computer 16 may be portable but is generally not adapted to be worn by the patient during ambulatory monitoring . several different functions may be performed by auxiliary computer 16 , and these functions may be implemented by different computers . the recorder 14 may be coupled to a first auxiliary computer during set up of the apparatus to download patient data and operating instructions ; a second auxiliary computer in the home environment to augment data storage capabilities and to provide for automatic event detection ; and a third auxiliary computer after monitoring is complete , to transfer the recorded information for processing , analysis , permanent storage , and generation of printed outputs . fig2 shows a more detailed block diagram including the transducer assembly 12 . transducer 12 includes amplifier 34 ; desirably , one amplifier is provided for each channel of physiological data to be obtained . amplifier inputs 40 are coupled to appropriate sensing or reference electrodes 32 coupled to the patient . in order to facilitate the transmission of amplifier output signals to the recorder , the amplifier outputs 44 are coupled to the input of multiplexer 36 , whereby the output signals at multiplexer output 46 may be transmitted over a common communication channel . fig3 is a block diagram of the preferred recording apparatus of the present invention . recorder 14 operates under control of microprocessor 50 , which includes a central processing unit 54 , program memory 56 such as eeprom , and analog - to - digital (&# 34 ; a / d &# 34 ;) converter 52 . multiplexed eeg signals from transducer 12 are received at i / o port 26 . such signals are buffered by amplifier 88 and coupled by mux line 72 to the input 58 of a / d converter 52 . such analog input signals are digitized by a / d converter 52 and stored in static ram 61 under control of cpu 54 . ram 61 desirably has at least about 1 megabyte of memory capacity , and preferably at least 4 megabytes of memory capacity . a push - button 84 is coupled to microprocessor 50 by lines 86 , and actuation of the push - button 84 causes storage of data in static ram 61 . such stored data includes data occurring both prior to and after actuation of the push - button . accordingly , the patient or another person can initiate data storage when the patient is experiencing a &# 34 ; funny spell &# 34 ; or other symptom . operating power for recorder 14 is provided by battery 68 , which is coupled to a regulator circuit 70 to generate + 5 v , gnd , and - 5 v supply potentials 78 , 80 , and 82 , respectively . in addition to powering the recorder 14 , these potentials are also coupled via port 26 to the transducer assembly 12 . communication channel 2 also couples clk line 74 and sync line 76 to the microprocessor 50 and the transducer assembly 12 , to control transfer of information . microprocessor 50 drives an alphanumeric display 62 , such as an lcd display , which may be used to indicate the number of events which have been recorded , battery condition , patient information , set up parameters , and the like . a crystal 66 is incorporated into a clock circuit to provide a time base for microprocessor 50 . microprocessor 50 also provides an output port 28 for interchanging information with auxiliary computers . fig4 shows a schematic diagram of the preferred recorder 14 . a microprocessor 50 , type mc68hc11f1 , provide a cpu 54 , and a / d converter 52 , and eeprom 56 . static ram 61 comprises 32 ic &# 39 ; s , each of which is a type hm628128 128 k × 8 static ram . as space is a substantial concern in portable , patient - worn equipment , applicant &# 39 ; s have developed a novel means for interconnecting these ic &# 39 ; s . rather than mounting them in a planar fashion to a circuit board , applicants have instead stacked the ic &# 39 ; s vertically . almost all corresponding pins of the ic &# 39 ; s are to be connected together in the memory circuit ; the pins overlap one another when stacked vertically , and can be soldered together . corresponding pins which are not to be connected together on all ic &# 39 ; s , such as chip select pins , may be bent outwardly and appropriately connected by wires soldered to the pins . applicants have found it desirably to configure the memory in two such stacks of 16 ic &# 39 ; s each . other aspects of the operation of the operation of the circuit of fig4 will no doubt be apparent to a person of ordinary skill in the art upon inspection of this detailed schematic , and will not be further discussed here . fig5 is a block diagram of a portable auxiliary computer system which is desirably used with the previously described apparatus . this portable computer would generally be carried home by the patient , and used at certain times in conjunction with the recorder to perform several functions . first , the transportable auxiliary computer provides an increased data storage capability , such as on disk . this permits longer term monitoring , recording of more frequent events and / or recording more data in connection with each event . second , the auxiliary computer includes signal processing software which , for practical reasons , has not been included in recorder 14 . more specifically , the transportable auxiliary computer includes seizure and spike detection software . this permits data capture and storage upon the occurrence of predetermined types of eeg signals which may indicate a seizure or other event , regardless of whether the patient is able to actuate the push - button . for instance , the patient may interconnect the recorder 14 to the portable auxiliary computer 16 before going to sleep and the system will record waveform data for events occurring during the patient &# 39 ; s sleep . also , the patient can interconnect the recorder 14 to the auxiliary 16 while the patient is at home and awake but inactive . this permits recording of events which might be missed by the patient , and recording of event during which the patient is unable to actuate the push - button . suitable seizure and spike detection software is commercially available . it is expected that as larger static memories become available , all necessary memory might be included in recorder 14 . at such time , it might be desirable also to transfer the seizure and spike detection software and other control and communication software from portable auxiliary computer 16 in the recorder 14 . in the portable auxiliary computer of fig5 multiplexed eeg waveform data from recorder 14 is coupled via port 28 to phase locked loop 100 . the phase locked output signal is coupled to a / d converter 102 , where it is digitized , and the digitized output signal is coupled to fifo buffer 104 . data output from fifo buffer 104 is input to a processor 106 , where it is analyzed in accordance with a seizure and spike detection algorithm to determine whether a seizure or spike event has taken place . processor 106 is coupled via a scsi bus to disk controller 118 for controlling storage of data on hard disk 116 . in response to detection of an event , pre - event and post - event waveform data is stored on hard disk 116 . a real time clock 110 for generation of time signals , and indicators 108 , are coupled to processor 106 . an rs - 232 port 120 and a scsi port 122 are also provided by processor 106 , for communication with other devices such as a host computer as described later . operating power for the portable computer is supplied by power supply 114 , which may be powered from the ac mains since portable auxiliary computer 16 is not intended to be worn by the patient . fig6 is a software block diagram of the operating software of the recorder 14 . a first portion of the software is stored in eeprom , and a second portion of the software is a downloadable module which is stored in ram prior to monitoring a patient . this module is downloaded from another auxiliary computer 16 , which is referred to as a &# 34 ; host &# 34 ; computer . such a host computer would generally be maintained at the place where monitoring electrodes are fitted to the patient . such a host computer is provided to configure the portable auxiliary computer and the recorder for performing a particular monitoring procedure on a particular patient . the same or a similar host computer may be used to receive data after completion of monitoring , for analysis and generation of appropriate outputs . the firmwire module stored in eeprom 56 establishes communication with the host computer ; controls timing of the multiplexer ; configures the inputs and outputs ; and loads and runs the downloadable module . the downloadable module performs several functions in connection with operation of the system . it maintains a real time clock , derived from the microprocessor clock after initialization by the host computer . it maintains a delay buffer , used to temporarily store signals representing pre - event data . such data will be stored as monitoring results if the push - button is actuated . it controls storage of waveform data , in response to a switch actuation or at periodic intervals . the downloadable module puts time of day data on the sync line , for communication to the portable auxiliary computer . it also monitors battery voltage , provides a watchdog timer , and performs error recovery in the event of a system error . a patient parameter block is also downloaded . this block also includes data identifying the patient being monitored and the technician setting up the monitoring procedure ; time of day ; number of events saved ; the electrode montage used ; and the length of time before and after an event during which data will be stored . in addition to storing waveform date occurring before and after a switch actuation , in a particularly preferred embodiment , the system also periodically stores waveform data for a short period of time . for instance , the system may store about 20 seconds of waveform data every 10 minutes . this enables later verification that the system likely was properly functional throughout the duration of the monitoring procedure . fig7 shows a software block diagram illustrating the preferred operating software for the portable auxiliary computer . blocks of waveform - related data are read into a fifo buffer in blocks 130 , 132 , and 134 . this data is placed in a circular ram buffer , time stamped , and set up in epochs in blocks 136 and 138 . the seizure and spike detection software of block 140 is then called and operates on the data in the buffer . this software determines whether a strong or weak seizure event or spike event has occurred , and whether the push - button has been actuated or the time for sampling has arrived . if such events have occurred , waveform data is stored on hard disk in steps 144 , 146 , and 148 . the amount of data stored may be made variable in accordance with nature of the event which has occurred ; for instance , less pre - event and post - event data may need to be stored in connection with a spike event than a seizure event . in step 146 , a file name for the data to be stored is established in accordance with the type of event giving rise to the data . rules of precedence are applied to determine how much data should be stored if events are overlapping . for instance , if a push - button event occurs during a sample interval , push - button actuation would be given precedence and data would be stored in accordance with the pre - event and post - event parameters established for push - button events , e . g . 2 minutes before and after push - button actuation . after determination of the amount of data to be saved , block 146 determines where the data that should be saved , and if data is being saved in response to push - button actuation , the time of actuation is marked on a particular channel ( channel 8 ). data is then saved to hard disk in step 148 , and a log file entry is created in step 150 in connection with the event . detection of a seizure or a spike event may also cause illumination of an indicator in step 142 to indicate this fact . fig8 is a flow diagram of preferred method for performing patient monitoring using the apparatus of the present invention . in step 160 , a physician refers a patient for eeg services . in step 162 , the patient is set up in a lab or the physician &# 39 ; s office . in this step , electrodes and a transducer assembly are coupled to the patient , the transducer assembly is connected to the recorder , and the recorder , portable auxiliary computer , and host computer are interconnected . the downloadable module is loaded into the ram in recorder 14 establishing operating and patient parameter information . proper setup may be checked by applying a calibrating signal to the transducer , and the eeg waveforms may be viewed on a monitor coupled to the host computer for verification of proper setup . eeg waveform data may be stored and printed to provide reference or baseline data . setup step 162 would also include any necessary communication with the patient regarding the monitoring procedure to be performed . in step 164 , the patient goes home with the patient - worn and transportable monitoring equipment previously described , and monitoring as described takes place for an extended period on the order of a day . in step 166 , the patient returns to the lab or physician office and data store in the recorder or portable auxiliary computer is downloaded to a workstation auxiliary computer . the downloaded data is transmitted to an electroencephalographer in step 168 , either as data or in the form of printout of eeg traces . the waveform data is reviewed by the electroencephalographer in step 170 and pertinent eeg waveform samples as well as a narrative report are sent to the referring physician . by storage of waveform data in digital form , eeg information can be transmitted , processed , and printed by digital means , which provides for extremely high quality traces . in particular , graphic output may be provided by a laser printer . fig9 shows a printout of the sort generated by the system of the present invention . in the preferred embodiment , the system prints information stored in the patient parameter block , such as montage and patient identifying information , as well as eeg traces . fig1 perspective illustration showing a preferred structure for the amplifier 34 and multiplexer 36 of the present invention . these components are housed within a housing 180 having a concave surface 182 having a curvature adapted to conform to the head of the patient being monitored . thus , the curvature of surface 182 is desirably in the range of about 2 inches to about 5 inches . connectors 184 are provided for connection of an electrode set 32 to the amplifiers . by placing the housing 180 on the top of the patient &# 39 ; s head , the lengths of conductors connected to the electrodes may be minimized , which reduces the stray signal pick up of the system . after placement of the electrodes and the housing on the patient &# 39 ; s head , they may be secured to the patient &# 39 ; s head such as by wrapping it with a cloth . this minimizes stray signals caused by movement by electrodes or conductors during monitoring . further artifact reduction is desirably provided by an emg filter , preferably a digital filter . applicants have applied a known emg filter algorithm to uploaded data in the host computer , but such a digital filter might also be included in the recorder or in the portable auxiliary computer . less preferably , an analog emg filter may be provided in one of these locations . while particular embodiments of the invention have been shown and described , variations will no doubt occur to those skilled in the art without departing from the spirit or scope of the present invention .
an ambulatory electroencephalography system includes a self - powered recording apparatus adapted to be worn by a patient . the recording apparatus includes an a / d converter and a digital memory capable of storing digital data representing analog waveform signals derived from a large number of electrodes secured to the patient . recording of digital waveform data is governed by a controller , which upon the occurrence of a neurologically significant event causes the storage of waveform data over an interval immediately preceding the event and immediately following the event .