A system to acquire and record physiological and behavioral data remotely from nonhuman primates

IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING. VOL. 38, NO. 12. DECEMBER 1991

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A System to Acquire and Record Physiological and Behavioral Data Remotely from Nonhuman Primates Francis A. Spelman, Member, IEEE, Clifford A . Astley, Eugene V . Golanov, Jerry J. Cupal, Allen R. Henkins, Emilio Fonzo, Thomas G. Susor, Gerald McMorrow, Douglas M. Bowden, and Orville A . Smith Abstract-We describe an integrated system to record physiological and behavioral variables from nonhuman primates in social groups. The system records data simultaneously from two animals in family groups of five. It synchronizes behavioral and physiological data within 16 ms, either on-line or from recordings. Behavioral data are entered by trained observers on-line or from videotape. Recordings of physiological data are produced on-line as stripchart records, tape recordings on the audio channels of video cassettes, and magnetic disk files. The physiological data include two arterial blood flows, arterial blood pressure and heart rate. The data are transmitted from freely behaving animals to a central site via radio telemetry. The infrared link controls the radio transmitter and physiological signal processing electronics, as well as two sources of drugs for each animal. All of the electronics are contained in a small, light backpack that can be worn by either male or female baboons.

I. INTRODUCTION N general, the task of the physiologist is to explain how the body functions. Historically this task has been approached from the “organ” or the “systems” point of view in which the organ or system is isolated from other parts of the body and studied while the animal is under heavy anethesia. The difficulties inherent in deciphering the myriad variables involved in controlling even an isolated organ system in the highly controlled laboratory situation are formidable. The task of explaining how a system actually works in the normal day-to-day existence of a healthy, intact, unanesthetized animal is even more for-

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Manuscript received March 22, 1991; revised August 30, 1991. This work was supported by NIH Grants RR00166, HL16910, and the U . S . / U.S.S.R. Scientific Exchange in the Cardiovascular Area, Program Area Seven, Hypertension (NHLBl). Some of this work was done at the Institute for Experimental Pathology and Therapy, Sukhumi, Georgia, U.S.S.R. F. A . Spelman is with the Regional Primate Research Center and the Center for Bioengineering, University of Washington, Seattle, WA 98195. C. A . Astley, A. R. Henkins, E. Fonzo, T. G . Susor, and D. M . Bowden are with the Regional Primate Research Center, University of Washington, Seattle, WA 98195. E. Golanov is with the Cardiology Institute, Moscow, U.S.S.R. J. J. Cupal is with the Department of Electrical Engineering, University of Wyoming, Laramie, WY 82670. G. McMorrow is with the Diagnostic Ultrasound Corp., Kirkland, WA. 0. A. Smith is with the Regional Primate Research Center and The Department of Physiology and Biophysics, University of Washington, Seattle, WA 98195. IEEE Log Number 9103949.

bidding. Achievement of such a goal necessitates the development of a whole set of techniques that differ from those used in the classic physiology laboratory. These include new surgical techniques, new materials that can be implanted in the body for weeks or months, miniature transducers, and methods for calibrating those transducers in situ, transmitting the data faithfully over long distances, and recording them accurately. Other critical variables not immediately obvious but of equal magnitude in terms of technological advantage include the necessity of measuring and/or recording the behavior of the organism and the relevant environmental variables. A major pioneer in this approach was Rushmer [l], whose research on cardiovascular variables in unanesthetized dogs led to revolutionary thinking about cardiac control. Since 1961, we have been developing techniques for use with primates both in the laboratory and in the field. The methodology presented in this paper extends those techniques to permit recording of multiple cardiovascular variables from more than one animal simultaneously. In these studies the subjects are members of a social group of five animals and their behavioral reactions (both individual and social) must be related to the cardiovascular changes within the timing accuracy of one heart beat. A . Need for the System To record systemic arterial blood pressure and arterial blood flows in several vascular beds of a freely moving primate, one must use a multichannel biotelemetry system [2], [3]. Preferably, the biotelemetry system is a significant part of an integrated hardware and software system that makes possible on-line recording of cardiovascular variables and somatic behavior in several animals, and ensures that the cardiovascular and somatic behaviors are correlated precisely in time [4].

B. Previous Designs Several single- and multichannel biotelemetry systems have been developed to record heart rate [4]-[6], temperature, blood pressure and blood flow [2], [3], [7]-[lo], gastrointestinal pressure [ 111, and other variables [ 121. It was clear to us that while biotelemetry was the sine qua

0018-9294/91$01.00 0 1991 IEEE

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Fig. 1. Block diagram of the data acquisition system. The data flow from right to left, with storage in the computer and observation of the stripchart recordings, videotaped behavior and behavioral codes by an observer. Commands are sent to the equipment in the backpack from left to right.

non of this project, it had to be coordinated with an entire instrumentation system that included remote control of apparatus, video recording, behavioral coding, data collection, and data summary.

C. Specijications for the System Our minimum objectives led to the following specifications: Maximum number of transmittedcage Number of analog channels Assignment of channels Minimum bandwidth per channel Carrier frequency Range Battery life Weight Size Life expectancy of equipment Ambient temperature Humidity Security Recording Synchronization

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11. DESIGN

The specifications listed above led us to early decisions about the design of the system. Since the physiological and behavioral data were to be synchronized precisely, we had to consider a multifaceted recording scheme. The system had to provide an on-line data display to ensure the proper operation of the system, to allow us to troubleshoot problems, and to permit physiological and behavioral investigators to manipulate the animals' environment on the basis of baseline data and observe their cardiovascular reactions immediately. Several technological developments enabled us to incorporate acquisition and analysis of physiological and behavioral data in a single system. 1) Available signal processing circuits, both analog and digital, consume little power and, with surface-mount technology, little space. 2) Computer technology provides sufficient capacity to acquire analog data at the same time that behavioral codes are displayed on an entry screen and entered online. 3) Small, low-power, rapid valves allow infusion of pharmaceutic agents without the need to restrain the subjects. The system is shown in Fig. 1. Each baboon wears a backpack which contains a telemetry transmitter, two Doppler ultrasonic blood flowmeters, a pressure transducer and signal conditioning apparatus, two automatically activated syringes, a command receiver or a timer circuit, a battery pack, and a transmitting antenna (Fig. 2). The baboon carries two flow transducers (Fig. 3) and a catheter-manometer pressure transducer (Fig. 4). The

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Fig. 2. A backpack with the apparatus removed and labeled to show its relative size. The transmitting antenna is built into the top of the backpack. Since only its counterpoise is visible, an antenna spiral has been placed atop the counterpoise for illustrative purposes.

Fig. 3 . Two ultrasonic flow transducers

blood flow transducers are surgically implanted around two arteries, usually those supplying a visceral and a muscular bed. The pressure catheter is surgically implanted into a major artery or directly into the aorta. The transmitted signal is received, demodulated, and distributed to a video cassette recorder (Panasonic PV

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Fig. 4. The pump board and pressure transducers. The spring-driven syringes are clearly visible at the bottom of the photograph: the valves are the white, cylindrical devices just below the pressure transducer.

1545) where it is recorded on one of the two stereo channels. The serially coded signal operates at 4800 baud and can be recorded on the single channel. Behavioral data are recorded with a video camera (Panasonic WV3260).

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Simultaneously, the serial code is delivered to a microprocessor, which decodes it into analog signals. Those analog signals are distributed to a stripchart recorder (Western Graphtex WR3101) and to three channels of a multiplexed analog data acquisition system that is interfaced to an IBM PC/XT. Heart rate is computed in parallel by a heart rate monitor and by the computer (vide infra). Analog data are acquired simultaneously while behavioral codes can be entered into a database within the computer. The data recorded on the videocassette recorder are synchronous within one frame interval (16 ms); the cardiovascular data recorded by the computer are also synchronous within one frame. 111. CARDIOVASCULAR DATAFLOW This section describes the flow of cardiovascular data through the telemetry system. The blood flow, blood pressure, and heart rate signals are traced through the blocks shown in Fig. 1.

A. Blood Flow Signals Blood flow is measured with a 10 MHz, pulsed Doppler ultrasonic flow system. We decided against Rader's [3] phase shift technique because it requires transducers with two crystals. Each transducer in our system is a 2 mm diameter crystal (modified lead metaniobate, Type K83, Keramos) mounted in a silastic housing at an angle of 5 1" with respect to the longitudinal axis of the blood vessel. The silastic housings (Fig. 3) are molded at the University of Washington. The flow module contains a radio frequency (RF) hybrid circuit (Diagnostic Ultrasound) and a nondirectional flow demodulator circuit [8] (Fig. 5). The flow transducer is excited with a 50% duty cycle and a repetition rate of 70 kHz. Each subdivision of the flow module is powered with a separate 5 V regulator; the total current drawn by the module and its regulators is 17 mA at 6.2 V. Two phase-locked flow modules and a pressure module are mounted on a single two-sided surface-mount circuit board, 5 X 7.5 cm. During calibration, an external signal is delivered to the zero-crossing detector and the audio output signal is monitored to ensure proper operation of the radio frequency hybrid circuit and flow transducer. Fig. 6 shows flow signals acquired from renal, mesenteric, and femoral arteries. Since none of the target arteries produces retrograde flow, we use the simpler nondirectional demodulation technique. The flow system has operated stably over a temperature range of 0-35°C during field tests; flow calibrations have deviated no more than 1 % over four weeks during either winter or summer weather in an open compound.

B. Blood Pressure Signals We decided at the outset to use a catheter-manometer pressure system rather than a system based on an implantable transducer. The decision was based on four reasons: 1) implantable transducers have long-term drift and are

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impossible to calibrate in vivo in the field; 2) the opening made in the skin for the wires from the flow transducers can serve either a catheter or wires from a pressure transducer; 3) disposable silicon pressure transducers operate reliably for months; and 4) if an external transducer fails, it is easily replaced. Counter to the arguments in favor of the catheter-manometer stands the requirement to maintain the patency of the catheter for weeks at a time. Fig. 4 shows the transducer (Cobe Instrument Company), the catheter, and its flushing apparatus. The catheter is filled with heparin chloride and is flushed every 24 h, either with a timer or by remote command. The transducer is excited with direct current and its signal is amplified in a straightforward manner. The output of the pressure amplified is passed through an ac amplifier to provide the pulse signal used to drive the heart rate module. Drift tests run on the transducer/amplifier combination have shown that the Cobe transducer drifts least when it is connected directly to an LM308A amplifier (National Semiconductor), Drift was less than 2 torr equivalent at the output for a temperature change from 20 to 40°C in the laboratory. The drift of the pressure system is less than 5 torr equivalent over a temperature range of 0-35 "C in the field. The pressure module consumes less than 13 mW at 6.2 V. C. Telemetry Link

The telemetry system is a fixed-frequency FM transmitter and receiver, modulated by a serial digital data stream [7], [lo]. Both transmitter and receiver modules are available through the Department of Electrical Engineering, University of Wyoming. I ) Telemetry Transmitter: The transmitter is a twoboard module. The first board, a mother board, contains signal processing circuity controlled by a microprocessor [7], [lo]. The microprocessor produces a serial data stream of 4800 baud, multiplexing four data channels and a housekeeping channel. The data channels are low-pass filtered at 34 Hz and sampled 102 times/s; the housekeeping channel is sampled once every 2.5 s. The data channels have an input voltage range of 0-5 VDC and are assigned to two flow signals, a pressure signal and an amplified version of the pulse pressure signal that is used at the receiver to drive the heart rate module (vide infra). The housekeeping channel samples battery voltage. The transmitter module is crystal-controlled at a frequency within the range of 210-220 MHz. It is a daughter board of the digital signal conditioner described above. Both boards are placed between a ground plane and a protective glass-epoxy board held above the component side of the motheddaughter board combination. The transmittedsignal conditioner consumes 75 mW at 5 VDC. 2) Transmitting Antenna: The transmitting antenna, modeled after Fenwick's [I31 design, is a spiral, halfwave loop printed in gold-plated copper on a 0.5 mm circuit board. A copper counterpoise covers a second board,

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SPELMAN et al.: SYSTEM T O ACQUIRE AND RECORD NONHUMAN PRIMATE DATA

whose distance from the antenna board can be varied. The length of the antenna is cut to tune the antenna coarsely. Then the interboard distance is varied from 1.5 mm (2 10 MHz) to 3 mm (220 MHz) to resonate the antenna. A single tuning capacitor (7-40 pf; Johnson 9614), connected from the center of the antenna to the counterpoise, is adjusted to match the antenna to a 50 Q transmission line. The measured standing wave ratio of a properly adjusted antenna is less than 1.2 to 1 over a frequency range of 2 MHz. The antenna and counterpoise fit in the lid of the backpack, in a volume of 7.25 X 7 X 0.5 cm. The radiation pattern of the antenna is symmetric around the center of the loop. It should be similar to that of a toploaded monopole [13], although it is probably modified by the baboon’s body [ 141. (For a compendium of small antenna structures, see [ 151.) 3) Receiving Antennas: The receiving antenna array consists of four loop antennas, with each antenna modeled after the design of Vreeland et al. [16], and scaled to a higher frequency. The design was chosen because of its low profile and easy protection with a small lexan cover to render it immune to manipulation by inquisitive baboons. The loop is built on an aluminum counterpoise of 90 cm2. Each antenna is fitted with an amplifier (Archer 10 dB in-line amplifier, Tandy Corp.). In one location, an iron cage measuring 7 X 4.6 x 2.5 m, two antennas are located 1.5 m above the floor on each long wall and connected via quarter-wave transformers to a second 50 D feed line. The paired antennas are connected via quarter-wave transformers to a common 50 Q line, which is split with two quarter-wave transformers and connected to two receivers. In a second location, the cage is made of ceramic blocks on three sides and steel bars on one, with reinforced concrete ceiling and floor. In that cage, which measures 7 x 3.6 x 2.5 m, a single receiving antenna is placed in the center of the ceiling. The antenna is connected to an amplifier as before and a single 15 m, 50 Q feed line connects the output of the amplifier to the receiver. 4) Telemetry Receiver: Each receiver’s carrier frequency is matched to that of a transmitter. The receiver

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and its digital decoding circuitry are packaged in a 2 inwide module (Vector). The receiver circuitry is mounted on one circuit board and the digital decoding circuitry is mounted on another. The 4800 baud serial bitstream is available at an output pin on the receiver board. The decoding circuitry produces five analog outputs [7], [lo]. The output voltage swings -5 to +5 V for a swing of 0-5 V at the input.

D. Heart Rate Module The heart rate module (Fig. 7) accepts the pulse pressure signal and converts it to a series of pulses coincident with the rising phase of systolic pressure. The pulses are delivered to a digital module in the computer, which converts heart rate internally while it samples the blood flow and pressure signals. The module contains an internal clock and counter to measure the interval between successive pressure pulses. The output word of the 10-bit counter addresses a contents-addressable memory. The 10-bit memory contains data to convert interval to rate, in beats per minute. Those data are latched and input to an eight-bit digital-’to-analog converter which produces a signal proportional to heart rate on the stripchart recorder. The heart rate module has four ranges: 0-200, 50-250, 100-300, and 200-400 beats/min. The output voltage in each case is 0-5 V. Each range can be calibrated independently with an internal calibration circuit. The module is built on a single circuit board in a 2 in Vector module.

E. Recording Systems

1) Computer: The computer is an IBM PC/XT, AT or equivalent clone. We have not tested the software with either a 386- or 486-based computer. The software runs under DOS 2.1 or greater (Microsoft). The software to acquire and display behavioral codes, deliver time markers to the video time mark generator, and acquire and store twelve channels of cardiovascular data was written at the University of Washington. Analog data are input to analog multiplexing and digitizing modules (Lab Master,

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IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. 38, NO. 12, DECEMBER 1991

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Tecmar) in an external cabinet. The data are sampled 100 times/s and stored directly on the computer's internal disk drive. Nine channels are sampled while heart rate is com-

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puted from three animals, time synchronization is maintained, and behavioral data are acquired and displayed on the color monitor.

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2) Data Recorder and Interface Amplijiers: Data are recorded on-line on a stripchart recorder (Western Graphtec WR3101) and on a video cassette recorder (Panasonic PV1545, Fig. 1). The stripchart recorder is used to observe the effects of behavior on cardiovascular parameters in real time; the VCR stores data for subsequent analysis. 3) Video Recorder: The video recorder stores both behavioral and cardiovascular data. The behavioral data are taken from a video camera and the cardiovascular data are taken from the baseband output of the receiver. Since the baseband ouptput of the telemetry is a serial code at 4800 baud, it can be recorded on one of the stereo channels of the VCR, which has a bandwidth of 20-20 000 Hz. When the output of the VCR is conditioned with a simple Schmitt trigger, it is adequate to activate the decoding circuitry of the receiver. Since the VCR has two audio channels, it can record signals from two animals simultaneously. 4) VITC GeneratorlReader: Synchronization of the behavioral and cardiovascular data is critical to the success of the experiments for which this system was designed. Since the data are analyzed automatically, it is necessary to provide the computer with an indication of the time and tape location of the video signal. We record a vertical interlace time code (VITC) on the tape and decode it into time and frame counts during playback. We employ a VITC generator/decoder (Shintron 690) to record the video data simultaneously with a time code accurate to one frame time (16 ms). The time code is visible on the video display during recording and playback. The decoder that is built into the code generator delivers a serial code (RS232) to the computer during playback. Hence, it is possible to locate specific behaviors and then record a behavioral code on the computer while the time of the frame is recorded as well. Data can be recorded before, during, and after a specific behavior and the synchrony between the behavioral and physiological data depends only upon the ability of the observer to identify precisely the onset of the behavior. That identification is done by a team of observers, each of whom observes the video data at real-time speed and at slow speed. When the behavioral code is entered, its time code is acquired from the VCR and filed with the current sample of the cardiovascular data. 5) Interface Amplijers: Simple interface amplifiers

provide a unity gain and adjustable offset to record data either on the stripchart recorder or on the computer. During calibration, the values of offset are measured with a digital voltmeter (Fluke 8060A, John Fluke Mfg. Co.) and recorded so that recordings can be adjusted to the same levels every day. IV. COMMAND AND POWER MODULES The system employs two command and power modules. The first is a simple CMOS timer that cycles every 7 2 h to deliver heparin and anesthetic to the animal and to time the periods of data transmission. The second is an infrared command link that permits arbitrary control of either syringe and of the power to the system’s transmitter. A . Timer The timer is a straightforward implementation of a counter chain which insures that data are transmitted 6 h/day, that heparin is delivered twice during a 72 h cycle, and that the baboon is anesthetized at a convenient time at the end of the cycle. The timer is run from two 3.6 V lithium batteries (Maxell CR2032). Current consumption is less than 40 PA, which guarantees operation for more than two months before a battery change is necessary. The CMOS circuitry, while crystal-controlled, is susceptible to error when it becomes soaked with soapy water and its insulating spacer gets waterlogged. Retiming the circuit in the field (adjusting to changes in time zone or in the schedule of operation) is tedious, and the timing sequence is inflexible. However, the circuit enables us to reduce the number of times that the baboons are trapped and anesthetized, and to reduce the size and weight of the battery pack. The circuit is built on a singlesided circuit board whose dimensions are 6.2 X 5.2 X 1 cm .

B. Command Link The command link (Fig. 8) controls eight signals in the backpack from the location at which data are collected. The link is infrared, operating at a subcarrier frequency of 35.5 kHz. The subcarrier is used to reduce the transmitter and receiver power required by the command link, after the fashion of Takahashi and Pollak [12]. The

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infrared carrier is encoded with a serial code of nine bits. The transmitted code is established and decoded with an encoder/decoder pair designed for the purpose (MC 145026/MC145027, Motorola). The carrier frequency is generated by a 555 timer (Signetics), which drives a VMOS power amplifier (IRFF130, International Rectifier). The power amplifier drives three infrared LED’s (LD271, TRW), each of which produces 16 mW. The LED’s are arranaged to cover the entire volume of the compound. Two photodiodes (SFH205, Siemens) are mounted on the backpack, one at each rostral comer. An LED at the rostral end of the backpack gives visual feedback to the operator when a signal is received and decoded. The receiver is tuned to the carrier frequency by the tuning of the input JFET amplifier and the tone decoder (LMC567, National Semiconductor). Eight signals can be decoded, but only three are implemented for each animal at this time. Two signals control valves and the third controls the power to the telemetry transmitter. The receiver consumes a maximum current of 2 mA at 6.2 V, an average current of 1 mA at 6.2 V. The range of the module is 10 m. C. Battery Power The battery pack for the telemetry unit is made of two lithium cells (AL2AA, Panasonic). The cells deliver 3.6 V at a rating of 1800 mAh. When they are connected in series and deliver 55 mA, the batteries decrease voltage from the open-circuit value to produce 6.2 V. The battery pack delivers the required 55 mA for 32 h, which permits sampled operation over 168 h. Each valve requires 122 mA, which is delivered for a few seconds out of each battery cycle. That energy consumption is negligible.

V. MAINTENANCE SYSTEM A . Fluid Delivery Module Fluid from two syringes can be delivered to the baboon via the blood pressure catheter (Fig. 4). The flow of fluid

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is controlled with two valves (LFAA0501418H, Lee Co.). Each valve operates on 5 VDC but, by using more than 5 V, can control pressure in excess of its 15 psi ratings (personal communication, Lee Applications Engineering). The use of overvoltage and overpressure reduces the rated lifetime of 10 000 000 cycles, an insignificant problem for this application. We have used two syringe designs. We modified plastic 10 cc syringes by removing the finger-lever from the rubber plunger, sealing the end of the syringe with heat and welded polypropylene. In the first design we pressurized the seal with 40 psi. We found that 20% of the syringes leaked, 10% immediately and 10% after five-seven days. In the second design, we replaced the air-powered syringes by spring-powered syringes. The spring-powered syringes have the lever/plunger mechanism modified as before, the end sealed, and a 2.2 cm spring placed behind the rubber plunger. While the second design is slightly larger and heavier, it is now 100% reliable. The volume of fluid delivered via the catheter to the artery is controlled by adjusting the time that the valve is opened to the catheter. When each syringe is calibrated, the times for delivery of a fixed volume are remarkably similar. Calibration of the syringes is done through a catheter system the open end of which is placed in a fluid chamber (another syringe) that is pressurized to 100 torr. In operation, one syringe is filled with 2.0 mL of heparin and the other is filled with 1.5. mL of anesthetic (TelazolTM,A. H. Robins). In the first case, about 1.6 s of power delivers 0.5 mL of heparin during each of three flushes, while in the second, 4 s delivers the entire 1.0 mL of anesthetic in a single bolus. The volumes are relatively large to overcome the 0.5-mL dead space of the catheter. Rapid anesthesia of a 30-kg baboon results from as little as 0.4 mL of TelazoP delivered directly into an artery. The anesthetic remaining in the catheter is delivered to the animal midway through the cycle of battery replacement and calibration of the system.

SPELMAN et al.: SYSTEM TO ACQUIRE AND RECORD NONHUMAN PRIMATE DATA

B. Backpack and Harness The backpack is vacuum-formed of plastic (Kaydex, GE) in two sizes, 14.6 x 12.4 x 14.35 cm for male baboons and 13.2 X 9.8 X 12 cm for female baboons (Fig. 2). The packs are fitted with EnsoliteTMpadding, which is form-fitted to the back of the baboon. The harness (Fig. 2) is made of webbing straps that are wrapped in sheepskin to prevent chafing. Each harness is attached to its pack with titanium fittings for a high strength-to-weight ratio. The pack and harness are custom-fitted to the baboon that wears them. When the fitting is proper, no chafing results. The first fitting is done after surgery, and the straps of the pack are checked at every battery change. The combination weighs 1300-2000 g, depending on pack size. C. Catheters and Cables The catheter is a polyvinylchloride tube about 100 cm long, with an inside diameter of 0.76 mm. It is sheathed in silastic, and only a silastic tip enters the artery in which pressure is measured. The cables of the flow transducers and the catheter leading to the pressure transducer are exteriorized through two puncture sites, 1 cm apart, in the dorsal skin. The puncture sites are maintained infectionfree with the following techniques, which are repeated weekly. The skin around the opening is shaved and washed with surgical scrub (Betadine”, Purdue Frederick Co.). Panalog cream (Solvoy Veterinary, Inc.) is then applied topically to each exit site, and the site is covered with a 1 X 2 cm patch of sterile surgical gauze. An 8 x 8 cm square of Elastikon’” tape (Johnson & Johnson) is centered over the exit sites and pressed firmly to the skin to prevent movement of the catheter and wires through the skin. No infection was observed in the twelve animals in which this technique was used.

D. Calibration and Data Analysis Since data acquisition by radiotelemetry quickly produces tens of megabytes of data, a well-organized approach to data analysis is a necessity. Analytical techniques have been under development for several years. 1) Analog Data: The PC samples the analog data at a rate of 100 samples/s/channel. The data are synchronized with the systolic phase of the blood pressure waveform. A cardiac cycle is defined by the interval between two successive systolic phases. The sampled data are used to compute systolic, diastolic, and mean values of the flow and pressure signals, and those edited variables are accumulated in a file. The file can then be decimated in time, with summary values (median values) of each of the edited data taken for each beat, and later for specific time intervals. The original edited data are held in files, so that beatby-beat analyses can be done if they are needed. Also, the raw data are available from the videotape recordings and can be used to look at the fine structure of the cardiovascular responses. Such instantaneous analysis is particularly interesting for behaviors that are intense but very transient, e.g., climbing, running or threatening.

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2) Behavioral Data: The behavioral data are analyzed with the help of a three-digit coding system devised in this laboratory [ 171. Using this system, we can objectively describe an animal’s behavior, posture, and locomotion while it is either alone or interacting in a complex social setting. The code categorization is specifically oriented toward identifying behaviors that are associated with significant cardiovascular responses. The software used to acquire the code entries captures the VITC from the current video frame when a code is entered, displays real time, and prompts the investigator to enter particular tokens of the code in succession. Identification of each behavior and its onset is crucial to the success of the study. Identification is done by an individual from a group of three observers who then collectively review the videotapes, correct errors, and reach a consensus about questionable behaviors. This two-stage process significantly improves reliability. When necessary, the precise onset of the behavior is determined via frame-by-frame analysis of the recorded videotape in slow motion. The frame time is recorded by the computer, which links the behavior to the cardiovascular data within one heart beat. VI. RESULTS The system has been used in laboratories in Seattle, WA, and Sukhumi, Georgian Socialist Republic, U.S.S.R. to record data from baboons in social groups. In one laboratory, the monkeys live in a compound that is maintained at 23°C. The other laboratory has a compound with indoor and outdoor chambers. The former is used as a sleeping area, while the latter is used for the animals’ daily activity. The outdoor compound, which is equipped with antennas, measures 7 X 4.6 X 2.5 m. Temperatures in that compound ranged from 0 to 35°C during two 6-week observation periods. Sample data recordings are shown in Fig. 6. The entire system provides reliable data recordings in a variety of conditions. However, we have observed two causes of failure: I ) certain positions of animals around the transmitters of the implanted animals cause intermittent dropouts of the radio-frequency signals; 2) at one point, when the CMOS timers were used, the timers failed when the backpack was sprayed accidentally and the timer’s insulating backing was soaked thoroughly. Of the two failure modes observed, the former is of greater concern. Tests with a dummy animal (a container of saline solution) placed under the transmitter produced no dropouts. Furthermore, when an implanted baboon was carried around the compound, no dropouts resulted. However, dropouts were observed when the animals roamed through the cage. The design incorporates on-line acquisition, display and analysis in a system that is portable and has been transported thrice between the U.S. and the U.S.S.R. Flow and pressure signals can be completely processed in the backpack, consuming less than 150 mW at 5 V. Multichannel physiological data can be acquired from several

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animals simultaneously with behavioral data. Computer technology permits the on-line identification of behavioral data and nearly instantaneous correlation with physiological data. Small, low-power components enable the remote delivery of pharmaceutical agents. The system has permitted us to elucidate some fundamental biological problems. Some cardiovascular changes that are observed in restrained animals are also seen in unrestrained animals, while others are not [ 5 ] . Renal blood flow decreases rapidly to zero during startle or emotional stress under both environmental conditions. Systemic arterial blood pressure increases in the restrained baboon during mild exercise, but decreases during rapid locomotion when baboons are not restrained. Other relationships between natural behavior and cardiovascular variables are being observed and analyzed with this system.

VII. DISCUSSION This system meets all but two specifications. Directional blood flowmetry is not yet operational, and occasional dropouts (5-10%) occur in the RF transmission link. Having used the system in a variety of observational conditions, we believe it would benefit from several modifications. The flow module should be made directional, which would permit us to observe coronary blood flow. Frequency should be increased to reduce the size of the transducer. The dropout problem must be eliminated for the radio-frequency link. Dropout results from nulls in the standing wave patterns produced by the transmitter and the cage. Minima in RF signal change with the position of the animals. Since the cage walls are not perfect reflectors, the minima are not true nulls. Hence, dropouts may be reduced by increasing the power of the transmitter or increasing the RF gain of the receiver. Recent experiments in the Seattle compound with a quarter-wave vertical receiving antenna and two 20-dB RF preamplifiers (AC5136, Cougar Components) have reduced dropouts by a factor of 3. Dropout might be avoided by using diversity reception, or the sampling scheme suggested by Pauley [ 181. Additional channels should be provided in the command link. As one reviewer suggested, it is possible to multiplex signals on the audio channel by using a serial multiplexer and a 9600-band modem. However, the cost of the additional apparatus was not considered acceptable for this system at this time. When we record from additional animals in the social group, it will be useful. The telemetry link is available as a custom circuit. All signal processing, timing, and control modules are available as circuit diagrams and circuit-board layouts for construction by other potential users. The video equipment is available commercially. Source code for the software is available to potential users. For details, contact F. A. Spelman at the address given on the title page. ACKNOWLEDGMENT We gratefully acknowledge the efforts of the Bioengineering Division of the Regional Primate Research Cen-

ter. We also thank K. Elias for editorial assistance and M. Domenowske for illustrations.

REFERENCES R. F. Rushmer and 0. A. Smith, Jr., “Cardiac control,” Physiol. Rev., vol. 39, pp. 41-68, 1959. D. L. Franklin, N. W. Watson, K. Pierson, and R. L. Van Citters, “A technique for radio telemetry of blood flow velocity from unrestrained animals,” Amer. J . Med. Electron., vol. 5 , pp. 24-28, 1966. J. D. Meehan, J. P. Henry, and R. D . Rader, “Observation of Arterial Blood Pressure of the Primate,” NASA Contract NSR 05-018087, Final Rep., 1973. M. Reite and J. D. Pauley, “Multi-channel implantable telemetry: Problems, pitfalls and rewards,” in Biotelemetry I I I , T. B. Fryer, H. A. Miller and H. A. Sandler, Eds. New York: Academic, 1976. 0. A. Smith, E. Golanov, C. A. Astley, V. Chalyan, F. A. Spelman, T. Urmancheeva, D. M. Bowden, and M. A. Chesney, “Behavioral stress and the cardiovascular system,” in Neurocardiology, H. Kulbertus and G. Franck, Eds. Mt. Kisco, N.Y.: Futura, 1988. 0. A. Smith, C. A. Astley, M. A. Chesney, D . J. Taylor, and F. A. Spelman, “Personality, stress and cardiovascular disease: human and nonhuman primates,’’ in Neural Mechanisms and Cardiovascular Disease, B. Lown, A. Malliani, and M. Prosdocimi, Eds. Padova: Liviana, 1986. D. L. Reese and J. J . Cupal, “An enhanced multichannel biotelemetry system,” in Proc. 9th Ann. Con$ IEEE/EMBS, 1987, pp. 1505- 1506. H. V. Allen, “Totally implantable bidirectional pulsed Doppler blood flow telemetry: Integrated timer-exciter circuitry and Doppler frequency estimation,” Stanford Electron. Lab. Tech. Rep. 4958-4, 1977. J. W.Knutti, H. V . Allen, and J. D. Meindl, “An integrated circuit approach to totally implantable telemetry systems,” Biotelemet. Parient Monitor., vol. 6, pp. 95-106, 1979. J. J. Cupal and S . F. Faghihi, “A microprocessor controlled multichannel telemetry system,” in Proc. 28th ACEMB, 1985. T. J. Kelly and E. Fromm, “An ingestible gastrointestinal pressure telemeter,’’ in Proc. 9th Ann. Con5 IEEE/EMBS, 1987, pp. 15071508. M. Takahashi and V. Pollak, “Near infra-red telemetry system,” Med. Biol. Eng. C o m p . , vol. 23, pp. 387-392, 1985. R. C . Fenwick. “A new class of electrically small antennas,” IEEE Trans. Antennas Propagot. vol. AP-13, pp. 379-383, 1965. P. A. Neukomm, “Body mounted transmitting antennas: radiation patterns and design of helical dipole antennas,” in Biotelemetry III, T. B. Fryer, H . A. Miller, and H. A. Sandler, Eds. New York: Academic, 1976. K. Fujimoto, A. Henderson, K. Hirasawa, and I. R. James, Small Antennas. London: Academic, 1987. R. W. Vreeland, B. B. Rutkin, and C. L. Yeager, “Tuned loop receiving antennas for indoor telemetry,” in Biotelemetry I I I , T . B. Fryer, H. A. Miller, and H. A. Sandler, Eds. New York: Academic, 1976. C. A. Astley, 0. A. Smith, R. D. Ray, E. V. Golanov, M. A. Chesney, V. G . Chalyan, D. J. Taylor, and D . M. Bowden, “Integrating behavior and cardiovascular responses: the code,” Amer. J . Physiol. : Regular. Integrat. Comp. Physiol., in press. J . D. Pauley and M. Reite, “A command receiver for use with low power implantable biotelemeVy systems,’’ in Biotelemetry I I I , T. B. Fryer, H. A. Miller, and H. A. Sandler, Eds. New York: Academic, 1976.

Francis A. Spelman (S’55-M’60) was born in San Francisco, CA, in 1937. He received the B.S.E.E. degree from Stanford University, Stanford, CA, in 1959, and the M.S.E.E. and Ph.D. degrees from the University of Washington, Seattle, in 1968 and 1975, respectively. He has headed the Bioengineering Division of the Regional Primate Research Center at the University of Washington since 1965. He joined the faculty of the Center for Bioengineering at the University of Washington in 1977, where he is the

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Associate Director. He is a member of the faculties of the Department of Otolaryngology, Head and Neck Surgery and Electrical Engineering. He was a Visiting Researcher at the Department of Bioengineering, Linkoping, Sweden from 1984 to 1985. He is a member of a U.S./U.S.S.R. joint research study of hypertension in baboons. He is investigating the electrical properties of the inner ear, electrical current flow in the inner ear and electrode design for cochlear implants. He also studies local and neural control of peripheral blood flow. He serves on the Editorial Board of the IEEE ON BIOMEDICAL ENGINEERING. TRANSACTIONS Dr. Spelman is a member of Tau Beta Pi, the American Society of Primatologists. the Association of Research in Otolaryngology and the American Association for Research in Otolaryngology - -. and the American Association for the Advancement of Science.

Emilio Fonzo was born in Benevento, Italy, and received a B.S.E.E. degree from Northeastern University, Boston, MA, in 1979. He joined the University of Washington, Seattle, in 1984 after working in industry for five years.

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Clifford A. Astley received the B.S. degree in zoology from Washington State University, Pullman, in 1972 and the M.S. degree in physiology and biophysics from the University of Washington, Seattle, in 1976. Since 1976 he has worked as a research scientist at the Regional Primate Research Center (RPRC) at the University of Washington primarily in the Laboratory of Dr. Orville Smith. Work in the laboratory has been centered around identifying the brain circuitrv resoonsible for controlling the cardiovascular responses associated with emotional behaviors observed in free roaming baboons living in a social setting. He also currently provides computer consulting services for the research and administration divisions and acts as staff surgeon at the RPRC.

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Eugene V. Golanov was born in Stockholm, Sweden, in 1953. He received a degree in general medical sciences, with honors, from the First Moscow Institute of Normal Physiology in Moscow, U.S.S.R. He worked as a Research Scientist at the Institute of Normal Physiology from 1980-1982, and at the All Union Cardiological Research Center, both in Moscow, U.S.S.R. He was appointed Senior Research Scientist at the All Union Cardiological Research Center in 1985. He actively investigates the control of cardiovascular variables by behavior in human and nonhuman primates.

Jerry J. Cupal received the B.S. and M . S . degrees in physics from Michigan Technological University, Houghton, in 1962 and 1967. and the Ph.D. degree in electrical engineering from the University of Wyoming, Laramie, in 1974. He has worked as an engineer for the U . S . Forest Service, Wyoming Highway Department, and the Department of Atmospheric Science at the University of Wyoming. He joined the Department of Electrical Engineering at that university in 1983. His teaching. and research interests include the design of microprocessor controlled instrumentation. Many of the applications of these devices include the use of biotelemetry to acquire information from free roaming animals. both domestic and wild.

Allen R. Henkins received the B.S. degree in mathematics from the University of Washington, - . . Seattle, in I Y I 1 . He began working as a computer programmer in the Department of Physiology and Biophysics at the University Washington in 1966. He has worked extensively i n the area Of analog-to-digita’ time acquisitionand editing Of systems for cardiovascular data.

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Thomas G. Susor was born in Toledo, OH, in 1940. He received the Associate’s degree in mechanical engineering, machine design from the University of Dayton, OH., in 1961. He attended the University of Toledo, Toledo, OH, in 1963 and 1964. During service in the U.S. Navy, he attained the position of MR2 in charge of the Machine Shop facility aboard the USS Enterprise CVAN-65 in 1967. From 1969 to the present he has been with Regional Primate Research Center at the University of Washington as supervising Instrument Maker. Many scientific instrumentation devices and systems as well as animal caging handling and environmental enhancement systems have been designed and built by the Bioengineering Division Machine Shop at the Primate Center.

Gerald McMorrow received the B.S.E.E. degree from the University of Washington, Seattle, in 1974 and the M.S.E.E. degree in 1978. From 1974 to 1976 he worked for Tektronix Ins., 1976 to 1978 for John Fluke Co.. 1978 to 1981 for Opcon Inc. He then founded Diagnostic Ultrasound Corporation and serves as president of the company.

Douglas M. Bowden was born in Durham, NC, in 1937. He received the B A. degree in psychology in 1959 from Harvard College, Cambridge, MA, Certificates in Russian in 1958 and 1961 from Indiana University, Bloomington, and the M D. degree in 1965 from Stanford University School of Medicine, Palo Alto, CA He is Professor of Psychiatry & Behavioral Sciences at the University of Washington and Director of the Washington Regional Primate Research Center, Seattle, WA. Dr. Bowden is a member of the Society for Neurosciences

Orville A. Smith was born

in Nogales, AZ, in 1927 He received the B.A. degree from the University of Anzona, Tucson, in 1949, and the M.A. and Ph.D. degrees from Michigan State University, East Lansing, in 1950 and 1953, respectively. He was a postdoctoral fellow in the Institute for Neurological Sciences (1954-1956) at the University of Pennsylvania and a trainee on the Neurological Training Grant of the Department of Physiology and Biophysics at the University of Washington, Seattle (1956-1958). He was appointed to the faculty of that department In 1958 and became Professor in i967. In 1962 he became Assistant Director of the Regional Primate Research Center and assumed the Directorship in 1971, holding that position until 1988, Dr. Smith was the first President of the American Primatological Society of North America (1977-1980) and President of the Pavlovian Society of North America (1977-1978). He also currently holds memberships in the American Physiological Society, American Association of Anatomists, Neuroscience Society, AAAS, FASEB, and the AAUP.

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