COMMUNICATIONS
193
Fig. 3.
final assembly is on three etched printed circuit boards in the master station box where the coaxial cables carrying ECG from all the monitors are delivered. The signal is selected from the appropriate patient as an output from the ECG preamplifier and is displayed at the bedside on an oscilloscope, at the physician's telephone, and on the grass recorder and a multichannel display oscilloscope in the Coronary Unit. This system has been used in the Respiratory Care Unit for eight months and has proven its reliability and has had enthusiastic acceptance from the staff.
K
A Transient
Recorder/Digitizer for Biological Applications
R. A. HOFFMAN, J. P. PAINTER, AND D. D. LONG Abstract-A transient recorder with digitized output is described. Four consecutive time regions of an analog voltage signal can be sampled at different rates. A delayed-trigger output is included, which allows the option of triggering the transient subsequent to the starting of the recorder. The timing and control circuit for the recorder is discussed in detail. INTRODUCTION An inexpensive transient recorder has been built to digitize and record time-varying analog voltage signals. The unit has been used to record current signals in voltage clamp experiments on artificial membranes. A feature which might be useful in other measurements for which some general features of the signal are known is the option of sampling four consecutive regions of the transient signal at different rates. Thus, rapidly varying or noisy portions of the signal may be sampled more frequently than less noisy or more slowly varying portions. The recorder input and output are easily adapted to the needs and available equipment of an individual user. For
Manuscript received October 28, 1975. R. A. Hoffman was with the Department of Physics, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061. He is now with the Biophysics and Instrumentation Group, Los Alamos Scientific Laboratory, University of California, Los Alamos, NM 87575. J. P. Painter and D. D. Long are with the Department of Physics, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061.
example, the trigger signal to start a recording can be from any source, and, with the proper interface, the output device can be anything that accepts parallel or serial digital data. Firstin-first-out memories were the easiest to use in our application, but any type of memory could be used. The speed of the A/D converter determines the maximum sampling rate, which in our case was 20 kHz. The control circuit is the only part of the system that cannot be purchased as a nearly complete working unit and will thus be the only part considered in detail. Total cost of the integrated circuits (IC's) and thumbwheel switches for the control circuit was about $175. The SERDEX, clock, 12-bit A/D, 12 X 64 bits of memory, and additional control circuitry cost an additional $400. For our purpose, the recorder functions as well as units costing several thousand dollars and allows easy modification-e.g., substitution of a lower resolution but higher speed A/D converter or addition of memory. RECORDER OPERATION A schematic diagram of the control circuit as well as a block diagram of the other components of our system is shown in Fig. 1. A teletype (TTY) with paper tape punch is the recorder's input and output device and is interfaced to the recorder with an Analog Devices STX1003 SERDEX serial transmitter, which converts parallel data in the memory to serial and transmits it to the TTY. The SERDEX also decodes several special characters received from the TTY into control pulses, and provides the special format required on the paper
tapes. In using the recorder one presets four groups of timing parameters on BCD coded thumbwheel switches. Specifically, in group 1, cl A/D conversions are made, each separated by a time interval of ml X 101-P" seconds. This is followed by C2 - cl conversions separated by m2 X 101-P2 seconds, etc. C4 is the total number of A/D conversions to be performed during the record. Sequencing from one timing group to the next is provided by the 7490 decade counter labeled SEQ in Fig. 1. Outputs A and B from SEQ determine which group's timing parameters are selected by the multiplexers labeled PI, P2, Ml, M2, and Cl -C4 . The overall operation will be illustrated assuming specific settings on the various thumbwheels. The timing diagram for the circuit is shown in Fig. 2. Both it and the following description assume that power has just been applied, that all IC's are in arbitrary states, and that the group parameters are set as follows:
cl = 2, c2 =3, C3 =4, C4 =5,
ml =3, m2 =2, m3 =4,
Pi arbitrary P2 =PI P3 =PI
m4
P4 =PI -1-
=
1,
The sequence of events through the first A/D conversion is follows. A CLEAR signal from the TTY via the SERDEX initializes all the IC's and can be used to reset the circuit at any point in its operation. A RUN signal also from the TTY via the SERDEX sets the RUN flip-flop which allows the 10-MHz clock signal to pass into the chain of decade dividers. The 74151 multiplexer, which is controlled by thumbwheel switches through PI and P2, selects a clock signal of period 10(1-Pl). This clock signal passes to the period multiplier composed of a 7442 BCD-to-decimal decoder and a 74166 shift register. The 7442 decodes m 1 (mI1 = 3) as a 0 (at pin 4) which is loaded into the shift register at a point such that after 3 clock periods (PERIOD) a high-to-low transition occurs at the output of the shift register. This high-to-low transition is interpreted as a clock signal by the rest of the circuit, causing an A/D conversion (which is subsequently stored in memory by a simple circuit not shown) and causing a count to be registered in the 74192 up/down counter. (Capacitor C as
IEEE TRANSACTIONS ON BIOMEDICAL
194
----
TO NOT
--
.
-
.
---
-
--
V
2I
12
74310
1
710 ~~~~~6
10
0E6H
I1
0
.1
MSz
.
2
orlsa. n r=CLOCK 2
67 10
MTz
I
~
~
~
~
~
~
~
~
1±4
CLEAR 2
TTY
CJ4
1977
. - -----
RU
I"aU
RUN
VL
VR
6 710
-iC 3
120
CR1
!-
K5D
c c
S TO P
6
SWITERES~~~~~~~~~~~~~~I ~~
54
3
7
..
2
mm
06
4OJI
EN(GINEERINNG, MARCH
CLEAR
VC0
VC6
14
.
. ro
,
,
SHOW6
.
ED
LAR2Tr
~ ~ ~ EIO
/290
T1 53CL
SECTORSOFLPL
74153
ET
CLEAR
OATA
ROUP
SELEAR
COUNTS
O T
CONVERSION, STORAGE
ANO
TRANSMISSION
Fig. 1. Schematic diagram of the control CirCUit and block diagram of other system components.
II
TTY RUN
RUN FF a I
STOP FF GROUP SELECT A
GROUP SELECT B |
CLEARII CLEAR 2
___
PERIOD OUTPUT OF PERIOD MULT -UP COUNT INPUT
___
DOWN COUNT INPUT UP/DOWN SELECT
__ _
-DETECTOR
I
|
BORROW
AID CONVERT COMMAND _
Fig. 2. Timing diagram showing logic states at various points in the control circuit. Settings of the thumbwheel switches assumed for this particular sequence of operation are given in the text.
removes a glitch that occurs when mi = 1. Its value was made as small as possible, consistent with preventing false triggering.) This sequence of events is repeated, and when the second count is registered in the 74192, the 7485 comparators find the count equal to cl (cl = 2), which is provided as input to the 7485's through multiplexers C1-C4. Detection of equality
causes simultaneous resetting of the decade dividers and advancing of the sequencer SEQ. The timing error produced at this point is 0.1 ,us, since within this time the timing cycle using the group 2 parameters begins. Subsequent operation of the circuit is the same as described above except during the last timing cycle (group 4) for which we have set m4 = 1.
195
COMMUNICATIONS ® INFRARED DIODE ®) PHOTO-TRANSISTOR ( IMEGOHM RESISTOR RED LIGHT DIODE
Thus the period multiplier is disabled, and the PERIOD signal from the 74151 is used directly as the clock signal. When count C4 (C4 = 5) is registered, pin 8 of the sequencer SEQ goes high, triggering the STOP flip-flop, which closes the gate to the 10-MHz input clock and disables the sequencer. The 74192 counters are now in the down-count mode and may be used to sequence the readout of a random-access memory, or, as in our case, simply to indicate when all the data have been read out of memory. The down-count signal is a pulse following the readout of each word of data. When all the data have been read out, the BORROW signal from the 74192 causes the circuit to be reset to its initial state, and the circuit is ready for the recording of another transient. An optional feature of the circuit, which we have utilized is a variable delayed-trigger output. An additional 7485, labeled T. detects when a preset count occurs and causes a trigger signal to be generated. In this way, the signal can be recorded for some predetermined time prior to initiating a transient signal by means of the trigger. For example, as in our experiments, the membrane current resulting from some holding voltage may be recorded for several count periods before using the trigger signal to apply the clamping voltage, thus initiating the variation in membrane current.
A Proposed Miniature Red/Infrared Oximeter Suitable for Mounting on a Catheter Tip SINCLAIR YEE, EUGEN SCHIBLI, AND VEDAVALLI KRISHNAN
®)
(d a)e
--LS
200 MILS
(a)
(b) Fig. 1. Hybrid tip configurations. (a) Invasive tip (proposed). (b) Noninvasive tip.
The oxygen saturation (OS) at specific points within the blood circulatory system is a valuable clinical indicator in the treatment of cardiac and respiratory problems. Also, continuous measurement of the right atrial OS is helpful in locating congenital heart defects in infants. There are mainly two types of oximeters [11 for the OS measurement, namely the transmission oximeter and the reflection oximeter. Reflection oximeters illuminate blood with infrared and red light and measure the backscattered light intensities. The relationship between OS and optical reflection is usually stated as OS = A - B(EilEr) where E, and Er are voltages proportional to the backscattered
infrared and red light intensities, respectively, and A and B are constants that depend upon hematocrit. The existing in vivo reflection oximeters are mostly fiberoptic instruments. The optical fibers are contained in a catheter and transmit the incident and backscattered light between the interior of the body and the outside instrument. Early versions of the fiberoptic oximeter (21 use incandescent light sources and optical filters. More recently, the incandescent lamp and the interference filters have been replaced by two solid-state light-emitting diodes (LED's) [3] that were pulsed alternately. The use of fiberoptics greatly reduces the backscattered signal from the blood, and places an increased demand on the instrument design. The main objective of the present work [4] is to investigate the feasibility for the development of an all solid-state oximeter that eliminates the use of fiberoptics. The long-range goal then is a new instrument, where the light-emitting diodes and the phototransistor are mounted at the tip of the catheter. Wires run through the catheter connecting these solid-state chips to the instrument outside. The whole process of converting the electrical signals into light signals and the backscattered light signals into electrical signals takes place at the catheter tip. This communication describes the development of a hybrid circuit which is suitable for mounting on a catheter tip, and the results of in vitro
Manuscript received September 15, 1975; revised January 16, 1976. This work was supported in part by the National Institutes of Health under Grants GM16436-04 and 16436-08. The authors are with the Microtechnology Laboratory, Center for Bioengineering, and the Department of Electrical Engineering, University of Washington, Seattle, WA 98195.
INSTRUMENT DESIGN The hybrid-circuit tip for the new oximeter [Fig. l(a)] consists of a Litronix, Red-Lit 50 chip (0.017 X 0.007 X 0.007 in) and an infrared (Spectronics, Sec. 450; 0.012 X
Abstract-A miniature red/infrared oximeter has, been developed that is suitable for mounting on a catheter tip and does not use fiberoptics. Two light-emitting diodes (LED's) and a phototransistor are mounted on the catheter tip such that conversion between optical and electrical signals takes place right at the tip. In vitro calibration shows that the infrared-to-red reflectance ratio is essentially linearly dependent on oxygen saturation (OS). The calibration constants depend on hematocrit and on blood flow.
INTRODUCTION
tests.
193
Fig. 3.
final assembly is on three etched printed circuit boards in the master station box where the coaxial cables carrying ECG from all the monitors are delivered. The signal is selected from the appropriate patient as an output from the ECG preamplifier and is displayed at the bedside on an oscilloscope, at the physician's telephone, and on the grass recorder and a multichannel display oscilloscope in the Coronary Unit. This system has been used in the Respiratory Care Unit for eight months and has proven its reliability and has had enthusiastic acceptance from the staff.
K
A Transient
Recorder/Digitizer for Biological Applications
R. A. HOFFMAN, J. P. PAINTER, AND D. D. LONG Abstract-A transient recorder with digitized output is described. Four consecutive time regions of an analog voltage signal can be sampled at different rates. A delayed-trigger output is included, which allows the option of triggering the transient subsequent to the starting of the recorder. The timing and control circuit for the recorder is discussed in detail. INTRODUCTION An inexpensive transient recorder has been built to digitize and record time-varying analog voltage signals. The unit has been used to record current signals in voltage clamp experiments on artificial membranes. A feature which might be useful in other measurements for which some general features of the signal are known is the option of sampling four consecutive regions of the transient signal at different rates. Thus, rapidly varying or noisy portions of the signal may be sampled more frequently than less noisy or more slowly varying portions. The recorder input and output are easily adapted to the needs and available equipment of an individual user. For
Manuscript received October 28, 1975. R. A. Hoffman was with the Department of Physics, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061. He is now with the Biophysics and Instrumentation Group, Los Alamos Scientific Laboratory, University of California, Los Alamos, NM 87575. J. P. Painter and D. D. Long are with the Department of Physics, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061.
example, the trigger signal to start a recording can be from any source, and, with the proper interface, the output device can be anything that accepts parallel or serial digital data. Firstin-first-out memories were the easiest to use in our application, but any type of memory could be used. The speed of the A/D converter determines the maximum sampling rate, which in our case was 20 kHz. The control circuit is the only part of the system that cannot be purchased as a nearly complete working unit and will thus be the only part considered in detail. Total cost of the integrated circuits (IC's) and thumbwheel switches for the control circuit was about $175. The SERDEX, clock, 12-bit A/D, 12 X 64 bits of memory, and additional control circuitry cost an additional $400. For our purpose, the recorder functions as well as units costing several thousand dollars and allows easy modification-e.g., substitution of a lower resolution but higher speed A/D converter or addition of memory. RECORDER OPERATION A schematic diagram of the control circuit as well as a block diagram of the other components of our system is shown in Fig. 1. A teletype (TTY) with paper tape punch is the recorder's input and output device and is interfaced to the recorder with an Analog Devices STX1003 SERDEX serial transmitter, which converts parallel data in the memory to serial and transmits it to the TTY. The SERDEX also decodes several special characters received from the TTY into control pulses, and provides the special format required on the paper
tapes. In using the recorder one presets four groups of timing parameters on BCD coded thumbwheel switches. Specifically, in group 1, cl A/D conversions are made, each separated by a time interval of ml X 101-P" seconds. This is followed by C2 - cl conversions separated by m2 X 101-P2 seconds, etc. C4 is the total number of A/D conversions to be performed during the record. Sequencing from one timing group to the next is provided by the 7490 decade counter labeled SEQ in Fig. 1. Outputs A and B from SEQ determine which group's timing parameters are selected by the multiplexers labeled PI, P2, Ml, M2, and Cl -C4 . The overall operation will be illustrated assuming specific settings on the various thumbwheels. The timing diagram for the circuit is shown in Fig. 2. Both it and the following description assume that power has just been applied, that all IC's are in arbitrary states, and that the group parameters are set as follows:
cl = 2, c2 =3, C3 =4, C4 =5,
ml =3, m2 =2, m3 =4,
Pi arbitrary P2 =PI P3 =PI
m4
P4 =PI -1-
=
1,
The sequence of events through the first A/D conversion is follows. A CLEAR signal from the TTY via the SERDEX initializes all the IC's and can be used to reset the circuit at any point in its operation. A RUN signal also from the TTY via the SERDEX sets the RUN flip-flop which allows the 10-MHz clock signal to pass into the chain of decade dividers. The 74151 multiplexer, which is controlled by thumbwheel switches through PI and P2, selects a clock signal of period 10(1-Pl). This clock signal passes to the period multiplier composed of a 7442 BCD-to-decimal decoder and a 74166 shift register. The 7442 decodes m 1 (mI1 = 3) as a 0 (at pin 4) which is loaded into the shift register at a point such that after 3 clock periods (PERIOD) a high-to-low transition occurs at the output of the shift register. This high-to-low transition is interpreted as a clock signal by the rest of the circuit, causing an A/D conversion (which is subsequently stored in memory by a simple circuit not shown) and causing a count to be registered in the 74192 up/down counter. (Capacitor C as
IEEE TRANSACTIONS ON BIOMEDICAL
194
----
TO NOT
--
.
-
.
---
-
--
V
2I
12
74310
1
710 ~~~~~6
10
0E6H
I1
0
.1
MSz
.
2
orlsa. n r=CLOCK 2
67 10
MTz
I
~
~
~
~
~
~
~
~
1±4
CLEAR 2
TTY
CJ4
1977
. - -----
RU
I"aU
RUN
VL
VR
6 710
-iC 3
120
CR1
!-
K5D
c c
S TO P
6
SWITERES~~~~~~~~~~~~~~I ~~
54
3
7
..
2
mm
06
4OJI
EN(GINEERINNG, MARCH
CLEAR
VC0
VC6
14
.
. ro
,
,
SHOW6
.
ED
LAR2Tr
~ ~ ~ EIO
/290
T1 53CL
SECTORSOFLPL
74153
ET
CLEAR
OATA
ROUP
SELEAR
COUNTS
O T
CONVERSION, STORAGE
ANO
TRANSMISSION
Fig. 1. Schematic diagram of the control CirCUit and block diagram of other system components.
II
TTY RUN
RUN FF a I
STOP FF GROUP SELECT A
GROUP SELECT B |
CLEARII CLEAR 2
___
PERIOD OUTPUT OF PERIOD MULT -UP COUNT INPUT
___
DOWN COUNT INPUT UP/DOWN SELECT
__ _
-DETECTOR
I
|
BORROW
AID CONVERT COMMAND _
Fig. 2. Timing diagram showing logic states at various points in the control circuit. Settings of the thumbwheel switches assumed for this particular sequence of operation are given in the text.
removes a glitch that occurs when mi = 1. Its value was made as small as possible, consistent with preventing false triggering.) This sequence of events is repeated, and when the second count is registered in the 74192, the 7485 comparators find the count equal to cl (cl = 2), which is provided as input to the 7485's through multiplexers C1-C4. Detection of equality
causes simultaneous resetting of the decade dividers and advancing of the sequencer SEQ. The timing error produced at this point is 0.1 ,us, since within this time the timing cycle using the group 2 parameters begins. Subsequent operation of the circuit is the same as described above except during the last timing cycle (group 4) for which we have set m4 = 1.
195
COMMUNICATIONS ® INFRARED DIODE ®) PHOTO-TRANSISTOR ( IMEGOHM RESISTOR RED LIGHT DIODE
Thus the period multiplier is disabled, and the PERIOD signal from the 74151 is used directly as the clock signal. When count C4 (C4 = 5) is registered, pin 8 of the sequencer SEQ goes high, triggering the STOP flip-flop, which closes the gate to the 10-MHz input clock and disables the sequencer. The 74192 counters are now in the down-count mode and may be used to sequence the readout of a random-access memory, or, as in our case, simply to indicate when all the data have been read out of memory. The down-count signal is a pulse following the readout of each word of data. When all the data have been read out, the BORROW signal from the 74192 causes the circuit to be reset to its initial state, and the circuit is ready for the recording of another transient. An optional feature of the circuit, which we have utilized is a variable delayed-trigger output. An additional 7485, labeled T. detects when a preset count occurs and causes a trigger signal to be generated. In this way, the signal can be recorded for some predetermined time prior to initiating a transient signal by means of the trigger. For example, as in our experiments, the membrane current resulting from some holding voltage may be recorded for several count periods before using the trigger signal to apply the clamping voltage, thus initiating the variation in membrane current.
A Proposed Miniature Red/Infrared Oximeter Suitable for Mounting on a Catheter Tip SINCLAIR YEE, EUGEN SCHIBLI, AND VEDAVALLI KRISHNAN
®)
(d a)e
--LS
200 MILS
(a)
(b) Fig. 1. Hybrid tip configurations. (a) Invasive tip (proposed). (b) Noninvasive tip.
The oxygen saturation (OS) at specific points within the blood circulatory system is a valuable clinical indicator in the treatment of cardiac and respiratory problems. Also, continuous measurement of the right atrial OS is helpful in locating congenital heart defects in infants. There are mainly two types of oximeters [11 for the OS measurement, namely the transmission oximeter and the reflection oximeter. Reflection oximeters illuminate blood with infrared and red light and measure the backscattered light intensities. The relationship between OS and optical reflection is usually stated as OS = A - B(EilEr) where E, and Er are voltages proportional to the backscattered
infrared and red light intensities, respectively, and A and B are constants that depend upon hematocrit. The existing in vivo reflection oximeters are mostly fiberoptic instruments. The optical fibers are contained in a catheter and transmit the incident and backscattered light between the interior of the body and the outside instrument. Early versions of the fiberoptic oximeter (21 use incandescent light sources and optical filters. More recently, the incandescent lamp and the interference filters have been replaced by two solid-state light-emitting diodes (LED's) [3] that were pulsed alternately. The use of fiberoptics greatly reduces the backscattered signal from the blood, and places an increased demand on the instrument design. The main objective of the present work [4] is to investigate the feasibility for the development of an all solid-state oximeter that eliminates the use of fiberoptics. The long-range goal then is a new instrument, where the light-emitting diodes and the phototransistor are mounted at the tip of the catheter. Wires run through the catheter connecting these solid-state chips to the instrument outside. The whole process of converting the electrical signals into light signals and the backscattered light signals into electrical signals takes place at the catheter tip. This communication describes the development of a hybrid circuit which is suitable for mounting on a catheter tip, and the results of in vitro
Manuscript received September 15, 1975; revised January 16, 1976. This work was supported in part by the National Institutes of Health under Grants GM16436-04 and 16436-08. The authors are with the Microtechnology Laboratory, Center for Bioengineering, and the Department of Electrical Engineering, University of Washington, Seattle, WA 98195.
INSTRUMENT DESIGN The hybrid-circuit tip for the new oximeter [Fig. l(a)] consists of a Litronix, Red-Lit 50 chip (0.017 X 0.007 X 0.007 in) and an infrared (Spectronics, Sec. 450; 0.012 X
Abstract-A miniature red/infrared oximeter has, been developed that is suitable for mounting on a catheter tip and does not use fiberoptics. Two light-emitting diodes (LED's) and a phototransistor are mounted on the catheter tip such that conversion between optical and electrical signals takes place right at the tip. In vitro calibration shows that the infrared-to-red reflectance ratio is essentially linearly dependent on oxygen saturation (OS). The calibration constants depend on hematocrit and on blood flow.
INTRODUCTION
tests.
