Sleep screening system with time based modulated data

A portable sleep monitoring system for recording on tape, transcribing and charting a plurality of physiologic data channels recorded relative to a known constant, user-transparent time base. Selected ECG, air flow, impedance and pulse oximetry sensor inputs are recorded under microprocessor control relative to a crystal controlled 40 Hz signal modulated with the physiologic data from one of the sensors. Upon reading the physiologic data from tape and/or charting, the collected data is displayed with the time base, normalized to the known crystal controlled timing signal. In the heart rate mode, QRS occurences are displayed on the heart rate trace line as singular hash marks. The presence of motion at the pulse O2 sensor is indicated by multiplexing high frequency hash markings onto the O2 saturation trace line. Calibration levels relating to four different O2 saturation percent vales are periodically written to tape for reference during tape reading.

BACKGROUND OF THE INVENTION 
The present invention relates to a cardio-respiratory recording system and, 
in particular, to a portable, multi-channel polygraph system for recording 
and replaying ECG, respiratory effort, respiratory airflow, and oxygen 
saturation levels in order to document abnormal sleep respiration 
patterns, most notably apnea. 
Traditionally, polysomnography studies have been conducted using either 
two-channel pneumocardiograms (i.e. ECG and respiratory impedance data) or 
multi-channel recordings of sixteen to twenty channels. Although performed 
more conveniently, two-channel recordings are limited in the amount of 
information they can provide for meaningful diagnosis. Sixteen to twenty 
channel studies, in contrast, are limited to sleep laboratories with 
corresponding higher study costs associated with the capital equipment, 
personnel and plant. A trade-off must thus normally be made by the 
clinician or diagnostician between limited data, which can produce 
misdiagnosis or missed significant respiratory events, and almost 
unlimited data with its greater attendant costs. 
Of the systems of which Applicant is aware, sensor data is collected from 
two to twenty channels relative to a separate time channel, or through 
calibration of mechanical components of a system which may vary in speed 
and could effect timing and rate calculations. Data is typically collected 
and displayed one channel per track without multi-plexing or overlaying 
physiologically distinguishable data on a single track during replay. For 
example, heart rate data is either displayed as a singular trace heart 
rate line at relatively slow chart rates or as individual QRS waveforms at 
a fast chart rate. Both are not shown together on a single track. 
Applicant is also not aware of any system particularly displaying heart 
rate data with a hash or "tic" mark relative to the trend or trace line to 
indicate the time occurrence of each QRS complex. 
Similarly and relative to O2 saturation and motion artifact, applicant is 
unaware of any system which distinguishes motion from true O2 
desaturations. Additionally existing systems do not provide periodic 
calibration levels as reference points. Such multiplexed data, not only 
maximizes the data display, but also provides meaningful information to 
the clinician to permit on going confirmation of the oximetry sensor 
calibration which may change over the course of a study session. 
A need therefore exists for an economical data collection system of fewer 
than 12 to 20 channels in a portable construction whereby a subject's 
sleep patterns may be monitored at home or in a clinical setting and which 
data may be used in evaluating and pre-screening suspected sleep or other 
cardio-pulmonary disorders. Advantages are thereby attainable to the 
clinician and third-party payors. In the case of infants and out-patient 
care, apnea monitoring programs may also be more economically conducted on 
a longterm basis. 
SUMMARY OF THE INVENTION 
It is accordingly a primary object of the present invention to provide a 
portable, low cost, multi-channel cardio-respiratory recorder for home and 
clinical use for recording and replaying monitored events. 
It is a further object of the invention to provide a multi-channel system 
for recording ECG, respiratory effort (i.e. impedance, strain gage, etc.), 
respiratory airflow (i.e. nasal/oral thermistry, expired CO2, pressure 
etc.) pulse/oximetry and other physiologic data (i.e. sophageal PH), 
relative to a normalized user-transparent time base. 
It is a further object of the invention to modulate a 40Hz, crystal 
oscillator time base signal on one of the channels whereby mechanical 
speed variations between recorder, scanner and chart paper devices can be 
negated. 
It is a yet further object of the invention to multiplex physiologically 
distinguishable data onto single charter tracks. 
It is a still further object of the invention to provide a system wherein 
during a heart rate mode, individual QRS events are notated with a hash 
mark. 
It is a yet further object of the invention to provide a system wherein 
detected pulse/motion data is multiplexed onto sensed oximetry data and 
whereby confirmation of oximetry calibration can also be obtained. 
Various of the above objects, advantages and distinctions of the invention 
are particularly achieved in a presently preferred system comprising a 
portable, multi-channel, magnetic tape recorder including input circuitry 
selectively compatible with a wide variety of physiologic sensors, 
including ECG, pulse oximetry, thermistry and impedance respiration 
sensors. The recorder also includes associated microprocessor control 
circuitry for preparing a four-track data tape, having a time reference 
produced from a user-transparent normalized time base signal modulated 
with one of the sensor's data tracks. 
Separate charter and tape player apparatus each include means for 
de-modulating the time base data from one of the physiologic channels and 
displaying the physiologic data in a hardcopy format in proper time 
synchronization. Selectable means coupled to the pulse oximetry data 
permit the multiplexing of the pulse plethysmographic waveform data onto 
the O2 saturation data prior to charting. Associated QRS detect circuitry, 
during a heart rate trend mode, and under microprocessor control, causes a 
hash mark to be printed onto the ECG trend line timed with the occurrence 
of each QRS complex. The microprocessor also compares collected ECG and 
pulse plethysmographic data to display motion when they are not 
equivalent. 
Still other objects, advantages and distinctions of the invention, along 
with its detailed construction, will become more apparent hereinafter upon 
reference to the following description thereof with respect to the 
appended drawings. Before referring thereto, it is to be appreciated the 
following description is made by way of a presently preferred embodiment 
only, which should not be interpreted in limitation of the spirit and 
scope of the invention claimed hereinafter. To the extent modifications or 
improvements have been considered, they are described as appropriate.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIGS. 1a, 1b and 1c, functional block diagrams are shown of 
the circuitry included in the individual multi-channel recorder 2, charter 
4 and tape scanner 6 devices of the present system. Each device 2, 4 and 6 
is constructed as a stand-alone assembly within its own chassis. In normal 
use, the multi-channel recorder 2 of FIG. 1a is coupled to a plurality of 
sensor inputs from leads secured to the patient under study. A magnetic 
tape of suitable length is mounted in an associated tape drive 14 to 
record the collected data over the study period. Simultaneously, the 
charter 4 might be coupled to the tape drive inputs to chart the data 
directly via thermal printing onto a 43/4 inch Z-fold strip chart. 
Alternatively, the tape may later be replayed on the scanner 6 with the 
data of each channel then being charted. 
Mounted on the console of the recorder 2 is a switch panel (reference 
channel selection/signal set up switches 31 at FIG. 1c) which provides for 
a plurality of selectable settings relative to the subject being 
monitored. That is, an infant/adult switch selects circuitry for 
accommodating higher ECG rates commonly associated with infants versus 
adults along with other signal filtering. 
A calibration switch induces associated circuitry during the first six 
minutes of a study to produce predefined reference signals from a read 
only memory (ROM) which are charted on the selected charter tracks and 
relative to which equipment offset and gain may be ascertained and 
adjusted to properly print each channel's data relative to the strip 
chart. ECG is calibrated at 0.5mv, 120 BPM; impedance at 0.5 ohm, 30 BPM; 
strain gauge at 30 BPM and thermistor at 30 BPM; and O2 saturation is 
calibrated at 0%, 50%, 75% and 100% with calibration occurring over a 
three-second period at each level. Once every six minutes thereafter, the 
four calibration levels are rewritten. If a de-saturation event occurs 
(i.e. the detected level is less than 88% O2 saturation) during the time 
the calibration sequence is being written, the sequence is abbreviated to 
only 0.5 seconds per level so that a significant event is not missed. 
An impedance switch permits a normal pneumogram or a low gain waveform 
setting. Other sensor input switches define the selection of a strain 
gauge or nasal thermistor, whether alarms are annunciated or not, and 
establish the gain level. If an oximetry sensor is used, a code may be set 
relative to specific manufacturer's sensor, along with whether O2 or O2 
plus pulse data is monitored. Lastly, channel selector switches for tape 
channels 2 to 4 selectively define the various input sensors coupled 
thereto. Channel 1 however is always relegated to ECG data. 
Once the proper switch parameters are established and the sensors are 
appropriately coupled to the recorder 2, the analog sensor input data is 
coupled by way of the channel selector and signal conditioning circuitry 
12 to the appropriate data channels 1 to 4 at the tape drive 14. There the 
data is recorded in conventional fashion. The selector/conditioning 
circuitry 12 thus essentially multiplexes or couples the monitored data to 
a desired and calibrated channel. 
Referring also to FIG. 2 and appreciating that a variety of factors may 
affect data collection and replay, such as time varying tape speeds, tape 
stretch, etc., the recorder 2 produces a user transparent, 40Hz time base 
signal via a crystal oscillator 18, which normally is included with the 
CPU 10. By dividing down the clock output via appropriately configured 
counters, a periodic 25 msec time base signal is obtained which is 
modulated with the impedance respiration data at the selector/conditioning 
circuitry 12 before the modulated signal is coupled to the user defined 
tape channel. Because the time base signal occurs at a distinguishable 
frequency from the normally occurring impedance respiration signal, the 
time base signal does not deleteriously affect the data signal and is 
relatively easily de-modulated by the scanner 6 during later replay 
In a similar fashion and appreciating that a subject's pulse rate occurs at 
a frequency distinguishable from the O2 saturation trend line, the O2 
saturation data can be hardwire OR'ed at the selector/conditioning 
circuitry 12 with the pulse input waveform data and selectively displayed 
on a single channel, as opposed to separate channels (reference FIGS. 5d, 
5e). By combining distinguishable data on single tracks, other tracks are 
freed up other input data, such as from a nasal/oral thermistor. 
Alternatively and depending upon the selected switch settings, the pulse 
input data may be separately displayed from the O2 saturation data 
(reference FIGS. 5b, 5c). 
If the collected data is to be simultaneously charted, a charter 4 may also 
be coupled to the output bus 16 via read switch 19. Upon enabling the read 
switch 19 and connecting the charter 4 to a parallel coupled jack at the 
recorder's chasis, the data is also coupled via bus 17 to the charter's 
inputs. Simultaneously, the CPU 10 couples encoded switch data and 
detected ECG and respiration events to the charter 4 via bus 20, the 
reasons for which will become more apparent from the discussion of the 
recorder 6 of FIG. 1c. 
The CPU 10 additionally monitors pulse detection signals relative to ECG 
detect signals to derive motion control signals which are coupled to the 
charter and tape. The motion control signals are particularly determined 
via a motion detection algorithm which equates the ECG and pulse detect 
signals to one another. A clinician may again selectively choose to enable 
this feature or not at his/her preference. A more detailed discussion 
follows with respect to FIG. 4. 
Turning attention to FIG. 1c, a block diagram is shown of the tape scanner 
circuitry 6 and upon which the tapes recorded via the recorder 2 are 
replayed. The charter 4 of FIG. 1b includes a goodly portion of the same 
circuitry as in the scanner 6, except for the tape control and the 
circuitry in the monitor 8 and CPU 10 for demodulating the 40Hz time base 
signal and producing the tic marks and motion indicators. Accordingly and 
for convenience, the following description is only directed to the 
circuitry of the scanner 6 which includes the combination circuitry. 
The scanner 6 particularly includes QRS detect circuitry 22 and 
de-modulation circuitry 24. The QRS detect circuitry 22 monitors the 
recorded ECG data relative to a predetermined reference threshold to 
produce ECG detect signals which are coupled to the scanner's CPU 26. The 
demodulation circuitry 24, in turn, de-modulates the impedance respiration 
data from the proper one of channels 2 through 4 to separate out the 40Hz 
time base signal, which also is coupled to the CPU 26 via the analog to 
digital converter 25. 
Otherwise, control of tape replay is separately performed by a CPU 28 which 
controls the operation of the tape player 30 relative to the selected 
inputs at the tape controls 32. As mentioned, during scanning, a variety 
of selectable functions may also be enabled via the CPU 26, over and above 
mere tape replay, upon appropriately setting the channel and setup 
switches 31 provided at the scanner 6. This switch data is encoded and 
stored in a buffer 33. 
In particular and relative to the QRS detector 22, the gain at which the 
detector 22 operates may be set to avoid sensing excessive false ECG 
signals or missing faint ECG signals, although the detector 22 is normally 
operated in an auto position. An infant/adult switch is provided, along 
with an O2 saturation scale select of either 0 to 100% or 50% to 100%. A 
keyboard input is also provided to permit a programmable search function 
relative to tape position and whereby the scanner 6 may be advanced to a 
desired point and time at which replay and charting may be begun. Power, 
tape location, search location and active channel indicators are 
additionally provided. 
Otherwise and relative to the charting of the replayed data via printer 34, 
a chart/pause switch enables/disables the printing of the replayed data. 
The printer speed (i.e. 0.5, 1, 2, 5 and 10 mm/sec) may be selected such 
that the real time recorded study data may be compressed, yet still be 
intelligible at a resolution which displays in a meaningful fashion the 
recorded data. When a desired event is located, however, the chart speed 
may be increased to display the event in an expanded fashion (i.e. 12.5, 
25 or 50 mm/sec). The normal chart speed however is 1mm/sec which equates 
with the scanning of a 12 hour tape in approximately 30 minutes. 
Also provided are offset and gain control switches for each of the four 
input channels whereby the printed data may be vertically centered 
relative to grid tracks provided on the chart paper. FIG. 5b shows an 
example during a "Calibration" portion of the stored calibration signal 
used to set offset and gain for the pulse/oximetry channel. 
In passing, it is to be noted that the printer 34 prints the four separate 
grid tracks which appear as a checkerboard pattern having intermediate 
rows and columns indicated by dotting at the same time as the data on 
blank chart paper at appropriate grey tones relative to the other outputs 
of channel data ,.and ,scale and sensor identification alpha-numerics. For 
drawing clarity, only a portion 13 of the grid track pattern is shown in 
FIG. 5b. A similar pattern otherwise normally appears with all the 
waveforms. A time reference indicated with short vertical has marks is 
also printed along the bottom chart edge, using the detected time base 
signal, in 10 second increments with one minute numeric notations being 
indicated at emboldened arrows, reference FIG. 5c. Scaling values 
cyclically appear in a vertical column superimposed over the data and grid 
tracks. 
Returning attention to the CPU 26 and with additional attention to the flow 
diagram of FIG. 2, upon receipt of the 40Hz time base time signal from the 
CPU's crystal oscillator and the ECG input, the CPU 26 controls a pair of 
counters (not shown) to count between each input event. Each count of the 
time base signal counter is reflective of the period of time between each 
successively detected QRS complex and each of the known 40Hz time base 
(TBC) signal, although may be off by a clock cycle, but which at the 
selected clock rate is not significant. That is, the absolute value of the 
difference between the starting and ending counts between events for each 
counter are compared every 400 counts to produce an ECG beat per minute 
(BPM) value from the following equation 1 which reflects the ECG beat per 
minute (BPM) trend rate. 
##EQU1## 
Where t.sub.ECG =period of ECG interval Thus, the ECG rate in beats per 
minute can be simplified to a ratio of the two counts which are readily 
computed in the CPU 26. This data is then plotted at the thermal printer's 
34 sampling rate to produce an essentially continuous trace or trend line 
of the heart rate. 
Similarly, the analog data on each of the other channels 2 to 4 are 
sampled, converted to digital data and valued in magnitude relative to the 
operator established gain and offset and displayed on the appropriate 
track portions of the chart paper. 
With attention next directed to FIG. 3, a flow chart is shown of the 
operations enabled by micro-coding stored in ROM which relative to the ECG 
detect signals of detector 22 and heart rate trace line, when the scanner 
is in a trend display mode, causes individual hash or "tic" marks to be 
printed on the trace line which are indicative of each detected QRS 
complex. That is, with the selection of a trend mode of scanner 6 
operation, the CPU 26 monitors each ECG detect signal relative to a 
predetermined threshold magnitude and causes the printer 34 to print a 1mm 
vertical hash line below the then current computed rate value. Instead 
therefore of a continuous line, a series of hash marks are produced on the 
line which may be manually counted for any selected time period and 
extrapolated onto other data tracks to confirm the displayed rate. 
For example, the diagnostician by counting the tic marks and pulse events 
for a particular study between the A--A extrapolation points of the ECG, 
pulse and/or finger O2+pulse waveforms of FIGS. 5a and 5c can compare the 
pulse and ECG data to confirm,,.correspondence or not. In passing, it is 
to be appreciated the waveforms of FIGS. 5a-5d are not from the same study 
and are shown only as representative indicators of the point being made. 
Another extrapolation of the ECG date and CARDIO TICKS onto the impedance 
respiration waveform from the same study and as shown in FIGS. 6a and 6b 
between extrapolation points B--B confirms the presence of a cardiac 
artifact. That is, the chest wall movement which occurs from breathing as 
in FIG. 6b may include movement or noise coincident with the beating of 
the heart which improperly appears as respiration. 
Still another extrapolation of the hash marks or CARDIO TICKS from another 
study onto related SaO2 data, as shown in of FIGS. 7a and 7b between 
extrapolation marks C--C, confirms a motion artifact or not relative to 
the displayed O2 saturation data. 
Appreciating that the clinician may select the automatic motion detection 
feature of the invention, attention is directed to FIG. 4 which shows a 
flow diagram of the manner in which motion is displayed on the O2 
saturation data. A motion artifact is particularly displayed as a 10 Hz 
signal which is superposed over the O2 data by the CPU 26, upon comparing 
the ECG detect and pulse detect signals for equivalence (reference FIG. 
5b). The pulse detect signals may either be separated out of the pulse 
oximetry data, or may be independently monitored. If a determined count 
value between detected ECG events and pulse detect events are not 
determined to be equivalent, CPU 26 calls a sub-routine which sums a 10Hz 
motion artifact on the pulse oximetry data. Otherwise, if near equivalence 
is found, no motion artifact is added. 
From FIG. 4 and the following definitions, 
PR.sub.A : active pulse average (PR.sub.1 +PR.sub.IT) 
PR: PR.sub.1 +PR.sub.2 
HR.sub.1 : HRI.sub.1 +HRI.sub.2 
HR.sub.2 : HRI.sub.2 +HRI.sub.3 
the CPU 26 essentially performs a number of comparisons of the periods 
between pairs of successive pulse detects (PR.sub.N) relative to 
successive pairs of ECG (HRI.sub.N) detects and relative to pre-defined 
tolerances established for various ECG rate ranges. If the average pulse 
rate falls within the established equivalence window for at least one of 
two comparisons performed over three events, no motion is shown. In the 
alternative, if a pulse is not detected but the ECG rate falls within the 
equivalence window of the prior average pulse rate, then again no motion 
is shown. 
If motion is detected and before indicating the motion, CPU 26 also 
confirms that the motion has existed for at least a predetermined number 
of cycles. It does this by setting a counter to the predetermined number 
of cycles for which the motion must exist. As each subsequent motion event 
is confirmed, the counter is appropriately decremented or incremented. 
With the last confirmation of a motion detect, the motion artifact 
printing subroutine is initiated. 
In passing and for the presently preferred embodiment, if motion is not 
indicated for at least three successive cycles, the motion detect flag is 
cleared. If too the scanner is still within its six minute calibration 
cycle, the CPU 26 disables the motion detect feature. 
Otherwise, in a manual circumstance and with reference to FIGS. 5a and 5e, 
the clinician may extrapolate between the Cardio Ticks on the heart rate 
data track and the pulse data on a degrading O2 saturation data track to 
confirm correspondence directly on the chart. If correspondence between 
each tick mark and each pulse mark is not found, the O2 data is suspect 
and can be interpreted as subject motion, in contrast to a change in O2 
saturation. Calibration drift in the oximetry equipment may be similarly 
detected and which condition is not otherwise readily detectable. 
While the present invention has been described with respect to its 
presently preferred embodiment, it is to be appreciated still other 
modifications may be made thereto without departing from the spirit and 
scope of the following claims. It is accordingly contemplated that the 
following claims should be interpreted to include all those equivalent 
embodiments within the spirit and scope thereof.