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A radiotelemetry system for chronic measurement of blood pressure and heart rate in the unrestrained rat validation of the method
JPM Vol. 28, No. 2 September 199299-105
A Radiotelemetry System for Chronic Measurement of Blood Pressure and Heart Rate in the Unrestrained Rat Validation of the Method Chantal Department
of Pharmacology,
Guiol,
Clara Ledoussal,
and Jean-Marc
Bristol-Myers Squibb Pharmaceutical
Surge
Research
Institute, Lognes,
France
Chronic measurements of systemic arterial blood pressure and heart rate via a chronically implanted telemetric transmitter in unrestrained rats, was validated in a three-phase study. In the first part, week-to-week variability of systolic, diastolic, and mean arterial pressures, and heart rate was found to be minima1 over the course of nine weeks. In the second part, the reproducibility of cardiovascular response to three successive administration of sotalol, an antihypertensive agent, was studied. In the last part, cardiovascular parameters determined by telemetry were compared to those obtained by direct arterial catheterization and showed a good linear correlation between those two methods.
Key words: Radiotelemetry;
Long-term monitoring:
Cardiovascular
system; Unrestrained
rats
Introduction Very few studies using noninvasive methods have been developed to determine blood pressure in the conscious rat (Hassler et al., 1979). The most commonly used method for long-term studies on the cardiovascular system in this species remains the chronic catheterization of a systemic artery. Telemetry systems for chronic implantation have progressed over the last 25 years from simple devices allowing the measurement of one physiological parameter (Mackay, 1970) to more complex systems capable of simultaneously monitoring several cardiovascular variables in large animals (Fryer et al., 1969; Rubenson et al., 1984). As a consequence of continued advances in miniaturization techniques, telemetry units small enough in size to be implanted inside the body cavity are now available (Murray et al., 1978). However, little work has been published on the cardiovascular system in small animals using telemetry (Brockway et al., 1989; Greene et al., 1991).
Address reprint requests to Dr. C. Guiol, Department of Pharmacology, Bristol-Myers Squibb Pharmaceutical Research Institute, rue de la Maison Rouge, 77185, Lognes, France. Received
February
1992; accepted
June
1992.
Journal of Pharmacological and Toxicological Methods 28, 99-105 (1992) 0 1992 Elsevier Science Publishing Co., Inc., 655 Avenue of the Americas, New York, NY 10010
Therefore, this paper describes the telemetry method that has been developed in our laboratory for measuring blood pressure and heart rate in the unrestrained rat. In the first phase of this study, physiological values were determined, and the variability of these data was assessed. In the second phase, sotalol, an antihypertensive agent, was studied for its effects on blood pressure and heart rate to prove the effectiveness of the method and the reproducibility of the data obtained. In the last phase, blood pressure and heart rate determined by telemetry method were compared to those obtained by direct arterial catheterization.
Methods Electronics The telemetry and data acquisition system purchased from Data Sciences Inc. (St Paul, MN) consists of four parts: 1) the implantable transmitter, which measures the pressure. This device contains a highly stable, ion-implant, semiconductor, strain-gauge sensor and battery-powered electronics to process the information from the pressure sensor and to telemeter it from within the animal. Arterial pressure is referred to the sensor via a 0.7-mm diameter, fluid-filled catheter (Figure 1); 2) the receiver which detects the signal from
1056-8719/92/$5.00
100
JPM Vol.28,No. 2 September 1992:9%105
Highly stable
Figure 1. Schematic of telemetry transmitter. Noncompressable
Battery Thin-walled antithrombogenic
tip with yd film applied
the implantable transmitter and converts it to a form readible by computer; 3) the pressure reference module, which measures atmospheric pressure to allow for the telemetered absolute pressure to be converted to a gauge pressure; and 4) the data acquisition software DATAQUEST III,which accepts data from the reference module and the receivers, filters corrupt samples from the incoming data stream, converts the telemetered pressure to millimeters of mercury, subtracts atmospheric pressure from the telemetered pressure, and stores the data for retrieval, plotting, and analysis. Dataquest 111 runs on the IBM PC/XT. Animals During the quarantine period lasting 5 days or more, Sprague-Dawley male rats (270-370 g) were housed up to five per polycarbonate cage containing sawdust bedding at a temperature of 21” t 2°C and a humidity of 50% ? 14% in a controlled room with a 7.00 AM to 7.00 PM light cycle. Rats were provided with pellets UAR no. AOACR and fresh drinking water ad libitum. After surgery, rats identified with an indelible ink mark on the coat were randomly allocated to the study groups and individually housed. To validate the telemetric system, we administered rats sotalol at the dose of 500 mg/kg p.o. This compound, obtained from Bristol-Myers Squibb, Montpellier France, was freshly prepared in sterile water for injection (Meram Laboratories). Methods of Implantation Telemetry transmitter. At 1 week before the beginning of the series of experiments, the rats were anesthetized with sodium pentobarbitol(50 mg/kg i.p.). The transmitter body was implanted under aseptic conditions into the peritoneal cavity with the sensing catheter placed in the descending aorta below the renal arteries, pointing up stream. Just before the implantation, the values from calibration of the transmitter (depend-
ing on the transmitter and indicated on the sterile package) were entered into the Dataquest System, which was configurated to monitor cardiovascular parameters. We prepared the animal by shaving its abdomen. An incision was made (about 4-5 cm long on the midline), and the descending aorta was exposed below the renal arteries. Sterile cotton swabs were used to remove the fascia on the vessel, and gauze pads or retractors held back the intestines from the sides of the artery. A vascular clamp was made by putting two surgical threads on the proximal and distal part of the artery. The sterile pack containing the transmitter was opened, and the protective cover from the catheter tip was removed. Then an incision was made in the vessel, and the catheter was inserted; the area surrounding the entry point was dried with a cotton swab, and a patch of hemostatic sponge was placed under the vessel. Next, a drop of cardiovascular glue (cyanoacrylate glue, Histoacryl, Braun Laboratories) was applied to the dry entry point. The transmitter was sutured to the abdominal musculature with 00 absorbable suture by passing the suture through the 1) muscle, 2) tab located along the length of the transmitter body, and 3) muscle on the other side of the suture. The skin was closed with wound clips. During the postsurgical period the animals were administered bristopen 50 mg/kg S.C. immediately after surgery and daily for 3 days and were monitored for general health and satisfactory arterial pressure pulse and heart rate. Femoral artery catheterization. At 24 hr before the day of the experiment, the rats were anesthetized with chloral hydrate (300 mg/kg i.p.) and surgically prepared for recording blood pressure and heart rate. The femoral artery was cannulated with an indwelling polyvinyl tube, which exited externally at the nape of the neck. The catheter filled with heparinized saline was secured, checked for patency, and plugged distally. During the recovery period, the rats were monitored for general health and satisfactory arterial pressure pulse
GUIOL ET AL. A RADIOTELEMETRY
101 SYSTEM FOR CHRONIC MEASUREMENT
OF BLOOD PRESSURE AND HEART RATE
and heart rate. Direct measurements of arterial blood pressure were performed via the cannulated femoral artery in conscious rats restrained in small individual boxes. Diastolic (DAP) and systolic (SAP) arterial pressures were recorded using a Statham P23 ID transducer connected to a two-channel Gould Recorder. Mean arterial pressure (MAP) was obtained by using the formula: DAP + $ (SAP-DAP). Heart rate (HR) was monitored with a cardiotachometer triggered by the peak of pressure waveform. Cardiovascular (CV) parameters were recorded over a 1-min period on chart paper. Numerical data values were calculated manually every 10 set during the 1-min period from the chart paper tracing and averaged.
Experimental
Design
Phase 1. Week-to-week variability of cardiovascular parameters was simultaneously determined in five rats implanted with the telemetry transmitter. Diastolic, systolic, and mean arterial pressures were monitored once a week for 9 weeks, at the same time of day (11 .OOhr). For each animal, blood pressure and heart rate were averaged over 1 min by the software. Phase 2. The reproducibility of three successive hypotensive responses to sotalol were evaluated in five other telemetry-implanted rats. The three trials (deter-
1
I
1
1
2
3
minations), separated by 2 weeks each, were made prior to oral administration of sotalol at the dose of 500 mg/kg and at 0.5, 1, 1.5, and 2 hr postdosing to determine the time point corresponding to the maximal cardiovascular effect. At each time point, MAP and HR were averaged over 1 min by the data acquisition system. Phase 3. MAP and HR values determined by the telemetry method in the five previously tested rats were compared to those obtained by direct arterial catheterization performed in five rats. Whatever the method used, cardiovascular values were determined prior to oral administration of sotalol at 500 mg/kg and at time (t), that is, 0.5, 1, 1.5, and 2 hr postdosing. At each time point, the MAP and HR averaged data, obtained during a I-min period by the two methods, were compared.
Statistical Methods All data are presented as mean ? SEM. Data were analyzed by paired Student’s t test. Data were considered significantly different at p < 0.05.
Results As shown in Figures 2 and 3, no consistent variability of DAP, SAP, MAP, and HR was detected over the
I
-
4 SAP
&dw, TIME .-.... QAp
I
I
I I
I
6
7
8
9
4
e*-, MAP
Figure 2. Week-to-week variability of diastolic, systolic, and mean arterial pressures over the course of 9 weeks in telemetryimplanted rats. Each point represents the mean -t SEM of five rats.
102
JPM Vol. 28, No. 2 September 1992:99-105
500
400
o-
L
1
2
1
1
8
9
I
4
3
5
6
7
TIME (W.&s)
Figure 3. Week-to-week
variability
of heart rate in the same telemetry-implanted
rats. Each point represents
the mean 2
SEM of five rats.
l-
1
El I
CONTROL
E2 0
E3 SOTALOL
Figure 4. Effects of three successive oral administrations (E), separated by 2 weeks each, of sotalol at 500 mg/kg or mean arterial pressure. Each column represents the mean MAP r SEM of five telemetry-implanted rats at 90 min postdose (time corresponding to the maximal hypotension).
GUIOL ET AL. A RADIOTELEMETRY
SYSTEM FOR CHRONIC MEASUREMENT
OF BLOOD PRESSURE AND HEART RATE
103
100 a 1
3 50
0
m
A
TIME (hr) AFTER P.0 SOTALOL 0 TELEMETRIC SYSTEM FEMORAL CATHETER
110
Y’
- 7.2330
+ 1,1262x
R-2 = 0.973
c
80
V 80
B
I
I
90
100
TELEMETRY - MAP (mmHg
1
Figure 5. (a) Comparison of telemetry and invasive (femoral artery catheterization) methods measuring MAP in rats treated with sotalol at 500 mg/kg p.o. Each column represents the mean MAP ? SEM of five rats. (b) Relationship between MAP values obtained by invasive and telemetry methods under the experimental conditions described in (a).
JPM Vol. 28, No. 2 September 1992:99-105
104
500
400
h .E E . 5
r
300
E 200
-
-
100
0
+
0.5
0
-
-+ 1
TIME (hr) AFTER P.0 SOTALOL FEMORAL CATHETER 0 TELEMETRIC
-
1 ,s SYSTEM
360 y = 139.97
+ 0.71887x
0
R-2 = 0,993
350
‘/
Figure 6. (a) Comparison of telemetry and invasive (femoral artery catheterization) methods measuring HR in rats treated with sotalol at 500 mg/kg p.o. Each column represents the mean HR * SEM of five rats. (b) Relationship between HR values obtained by invasive and telemetry methods under the experimental conditions described in (a).
320
6
TELEMETRY
- HR ( b/min
1
of 9 weeks. Mean DAP ranged from 77.4 ? 2.8 mmHg with a maximal variation of - 8.7%; mean SAP ranged from 112.8 & 4.9 to 103.0 & 2.3 mmHg with a maximal variation of - 8.7%; mean MAP ranged from 87.8 ? 2.3 to 97.6 + 4.3 mmHg with a maximal variation of - 10%; and mean HR ranged from 320 + 20 to 290 + 27 beats per minute (bpm) with a maximal course
variation of - 9.4%. The effects of successive administrations of sotalol on MAP determined in five other rats implanted with the telemetry transmitter are presented in Figure 4. No statistically significant difference in the hypotensive responses to sotalol was noted between the three trials separated by 2 weeks. At t = 90 min after administration corresponding to the maximal car-
GUIOL ET AL. A RADIOTELEMETRY
105 SYSTEM FOR CHRONIC MEASUREMENT
OF BLOOD PRESSURE AND HEART RATE
diovascular effect, the fall in blood pressure induced by this compound was - 22.4%, - 20.3%, and - 19.2% compared to the respective basal values. In the last series of experiments, MAP and HR responses to sota101determined by telemetry and arterial catheterization methods were compared. No statistically significant difference in the MAP responses to sotalol was noted between the two methods [Figure 5(a)]. The MAP variation between the two techniques ranged from - 2.1% to 6.9% according to the time point considered. Figure 5(b) displays values of MAP from both measurement methods. A high correlation existed between the two series of data (correlation coefficient r = 0.973, p = O.OOSl), and the slope of regression was almost equal to 1 (1.1262). Variations in HR responses between the two techniques (Figure 6(a)] were more important than those observed in the MAP responses. However these variations, ranging from - 21.6% to - 16.5%, were not statistically significant. Furthermore, a very high correlation [Figure 6(b)] was obtained between the two series of measurements (correlation coefficient r = 0.993, p = 0.0006), and the regression slope was not very different from 1 (0.71887).
mean arterial pressure and heart rate measured by telemetry were compared to those determined by femoral artery catheterization. Our results indicated that the telemetric method gave the same blood pressure readings as the invasive method. Similar results have been obtained in rats by Brockway et al. (1989) and in dogs by Armentano et al. (1989). As indicated by the correlation coefficient, there was a strong linear correlation between telemetric and invasive heart rate measurements. However, heart rate parameters were overestimated by the catheterization method. One explanation for this discrepancy could be that the telemetered data were undertaken in relaxed conditions as these rats were freely moving, whereas the catheter-implanted animals were restrained in small cages. This technique provides an accurate and reliable means of determining cardiovascular parameters in long-term studies and yielded chronic measurements that were repeatable and free of stress-induced artifacts.
Discussion
Brockway BP, Mills PA, Miller JT, Azar SA (1989) A new radiotelemetry system for continuous chronic measurement and recording of blood pressure, heart rate and activity in the rat. Abstract no. 1000, Conference on SHR and related studies, Iowa City, USA.
The telemetry system described herein has permitted chronic measurements of systemic arterial blood pressure and heart rate via a chronically implanted transmitter in unrestrained rats. In the first phase of this study, the week-to-week variability of systolic, diastolic, and mean arterial pressures, and heart rate was found to be minimal over the course of 9 weeks. These results suggest that ability of this system to provide accurate information for long-term cardiovascular studies in this species. Unfortunately, chronic cardiovascular experiments using the telemetry system in small animals are poorly documented. Only Brockway et al. (1989) have shown that no consistent change in systemic arterial pressure and heart rate were observed within a 1lo-day period after telemetric implantation in rats. Indeed, most of the work has been done with dogs, baboons (Van Citters and Franklin, 1966), chimpanzees (Sandler and Stone, 1972), and other wild animals (Van Citters et al., 1966). In the second part of the study, the ability of the telemetry technique to detect potential and repetitive effects of a drug upon the cardiovascular system during long-term studies was demonstrated as shown by the reproducibility of cardiovascular responses to three successive administrations of sotalol. In the last part,
References Armentano R, Cabrera-Fischer E, Breitbart G, Pichel R, Levenson J, Chau NP (1990) Telemetry of aortic pressure in unrestrained animals: Validation of the method over a wide range of blood pressure. Medical Prog Technol 16: 125-129.
Fryer TB, Sandler H, Freund W, McCutgeon P, Carlson EL (1975) A multichannel implantable telemetry system for flow, pressure and ECG measurements. .I Appl Physiol39:318-326. Greene SA, Keegan RD, Gallgher LV, Alexander JE, Harrari J (1991) Cardiovascular effects of halothane anesthesia after diazepam and ketamine administration in beavers during spontaneous or controlled ventilation. Am J Vet 52:665-668. Hassler CR, Lutz GA, Linebaugh R, Cummings K (1979) Identification and evaluation of noninvasive blood pressure measuring techniques. Toxicol Appl Pharmacol47: 193-201. MacKay X (1970) Sensing and Transmitting from
Animals
and Man in Biomedical
Biological Telemetry.
Information
New-York:
Wiley J and Sons, pp. 1l-17. Murray RH, Marko A, Kissen AT, McGuire DW (1968) A new miniatrurized multichannel personal radiotelemetry system. J Appl Physiol24:588-597.
Rubenson D, Griffin JC, Ford A, et al. (1984) Telemetry of electrophysiological variables from conscious dogs. Am Heart J 107: 90-96.
Sandler H, Stone HL (1972) Use of implantable telemetry system for study of cardiovascular phenomena. Circ Res 3O:S85-SlOO. Van Citters L, Franklin DL (1966) Telemetry of blood pressure in free ranging animals via an intravascular gauge. J Appl Physiol 21:1633-1636.
Van Citters L, Kempers WS, Franklin DL (1988). Blood pressure responses of wild giraffes studied with radiotelemetry. Science 152:384-386.
A Radiotelemetry System for Chronic Measurement of Blood Pressure and Heart Rate in the Unrestrained Rat Validation of the Method Chantal Department
of Pharmacology,
Guiol,
Clara Ledoussal,
and Jean-Marc
Bristol-Myers Squibb Pharmaceutical
Surge
Research
Institute, Lognes,
France
Chronic measurements of systemic arterial blood pressure and heart rate via a chronically implanted telemetric transmitter in unrestrained rats, was validated in a three-phase study. In the first part, week-to-week variability of systolic, diastolic, and mean arterial pressures, and heart rate was found to be minima1 over the course of nine weeks. In the second part, the reproducibility of cardiovascular response to three successive administration of sotalol, an antihypertensive agent, was studied. In the last part, cardiovascular parameters determined by telemetry were compared to those obtained by direct arterial catheterization and showed a good linear correlation between those two methods.
Key words: Radiotelemetry;
Long-term monitoring:
Cardiovascular
system; Unrestrained
rats
Introduction Very few studies using noninvasive methods have been developed to determine blood pressure in the conscious rat (Hassler et al., 1979). The most commonly used method for long-term studies on the cardiovascular system in this species remains the chronic catheterization of a systemic artery. Telemetry systems for chronic implantation have progressed over the last 25 years from simple devices allowing the measurement of one physiological parameter (Mackay, 1970) to more complex systems capable of simultaneously monitoring several cardiovascular variables in large animals (Fryer et al., 1969; Rubenson et al., 1984). As a consequence of continued advances in miniaturization techniques, telemetry units small enough in size to be implanted inside the body cavity are now available (Murray et al., 1978). However, little work has been published on the cardiovascular system in small animals using telemetry (Brockway et al., 1989; Greene et al., 1991).
Address reprint requests to Dr. C. Guiol, Department of Pharmacology, Bristol-Myers Squibb Pharmaceutical Research Institute, rue de la Maison Rouge, 77185, Lognes, France. Received
February
1992; accepted
June
1992.
Journal of Pharmacological and Toxicological Methods 28, 99-105 (1992) 0 1992 Elsevier Science Publishing Co., Inc., 655 Avenue of the Americas, New York, NY 10010
Therefore, this paper describes the telemetry method that has been developed in our laboratory for measuring blood pressure and heart rate in the unrestrained rat. In the first phase of this study, physiological values were determined, and the variability of these data was assessed. In the second phase, sotalol, an antihypertensive agent, was studied for its effects on blood pressure and heart rate to prove the effectiveness of the method and the reproducibility of the data obtained. In the last phase, blood pressure and heart rate determined by telemetry method were compared to those obtained by direct arterial catheterization.
Methods Electronics The telemetry and data acquisition system purchased from Data Sciences Inc. (St Paul, MN) consists of four parts: 1) the implantable transmitter, which measures the pressure. This device contains a highly stable, ion-implant, semiconductor, strain-gauge sensor and battery-powered electronics to process the information from the pressure sensor and to telemeter it from within the animal. Arterial pressure is referred to the sensor via a 0.7-mm diameter, fluid-filled catheter (Figure 1); 2) the receiver which detects the signal from
1056-8719/92/$5.00
100
JPM Vol.28,No. 2 September 1992:9%105
Highly stable
Figure 1. Schematic of telemetry transmitter. Noncompressable
Battery Thin-walled antithrombogenic
tip with yd film applied
the implantable transmitter and converts it to a form readible by computer; 3) the pressure reference module, which measures atmospheric pressure to allow for the telemetered absolute pressure to be converted to a gauge pressure; and 4) the data acquisition software DATAQUEST III,which accepts data from the reference module and the receivers, filters corrupt samples from the incoming data stream, converts the telemetered pressure to millimeters of mercury, subtracts atmospheric pressure from the telemetered pressure, and stores the data for retrieval, plotting, and analysis. Dataquest 111 runs on the IBM PC/XT. Animals During the quarantine period lasting 5 days or more, Sprague-Dawley male rats (270-370 g) were housed up to five per polycarbonate cage containing sawdust bedding at a temperature of 21” t 2°C and a humidity of 50% ? 14% in a controlled room with a 7.00 AM to 7.00 PM light cycle. Rats were provided with pellets UAR no. AOACR and fresh drinking water ad libitum. After surgery, rats identified with an indelible ink mark on the coat were randomly allocated to the study groups and individually housed. To validate the telemetric system, we administered rats sotalol at the dose of 500 mg/kg p.o. This compound, obtained from Bristol-Myers Squibb, Montpellier France, was freshly prepared in sterile water for injection (Meram Laboratories). Methods of Implantation Telemetry transmitter. At 1 week before the beginning of the series of experiments, the rats were anesthetized with sodium pentobarbitol(50 mg/kg i.p.). The transmitter body was implanted under aseptic conditions into the peritoneal cavity with the sensing catheter placed in the descending aorta below the renal arteries, pointing up stream. Just before the implantation, the values from calibration of the transmitter (depend-
ing on the transmitter and indicated on the sterile package) were entered into the Dataquest System, which was configurated to monitor cardiovascular parameters. We prepared the animal by shaving its abdomen. An incision was made (about 4-5 cm long on the midline), and the descending aorta was exposed below the renal arteries. Sterile cotton swabs were used to remove the fascia on the vessel, and gauze pads or retractors held back the intestines from the sides of the artery. A vascular clamp was made by putting two surgical threads on the proximal and distal part of the artery. The sterile pack containing the transmitter was opened, and the protective cover from the catheter tip was removed. Then an incision was made in the vessel, and the catheter was inserted; the area surrounding the entry point was dried with a cotton swab, and a patch of hemostatic sponge was placed under the vessel. Next, a drop of cardiovascular glue (cyanoacrylate glue, Histoacryl, Braun Laboratories) was applied to the dry entry point. The transmitter was sutured to the abdominal musculature with 00 absorbable suture by passing the suture through the 1) muscle, 2) tab located along the length of the transmitter body, and 3) muscle on the other side of the suture. The skin was closed with wound clips. During the postsurgical period the animals were administered bristopen 50 mg/kg S.C. immediately after surgery and daily for 3 days and were monitored for general health and satisfactory arterial pressure pulse and heart rate. Femoral artery catheterization. At 24 hr before the day of the experiment, the rats were anesthetized with chloral hydrate (300 mg/kg i.p.) and surgically prepared for recording blood pressure and heart rate. The femoral artery was cannulated with an indwelling polyvinyl tube, which exited externally at the nape of the neck. The catheter filled with heparinized saline was secured, checked for patency, and plugged distally. During the recovery period, the rats were monitored for general health and satisfactory arterial pressure pulse
GUIOL ET AL. A RADIOTELEMETRY
101 SYSTEM FOR CHRONIC MEASUREMENT
OF BLOOD PRESSURE AND HEART RATE
and heart rate. Direct measurements of arterial blood pressure were performed via the cannulated femoral artery in conscious rats restrained in small individual boxes. Diastolic (DAP) and systolic (SAP) arterial pressures were recorded using a Statham P23 ID transducer connected to a two-channel Gould Recorder. Mean arterial pressure (MAP) was obtained by using the formula: DAP + $ (SAP-DAP). Heart rate (HR) was monitored with a cardiotachometer triggered by the peak of pressure waveform. Cardiovascular (CV) parameters were recorded over a 1-min period on chart paper. Numerical data values were calculated manually every 10 set during the 1-min period from the chart paper tracing and averaged.
Experimental
Design
Phase 1. Week-to-week variability of cardiovascular parameters was simultaneously determined in five rats implanted with the telemetry transmitter. Diastolic, systolic, and mean arterial pressures were monitored once a week for 9 weeks, at the same time of day (11 .OOhr). For each animal, blood pressure and heart rate were averaged over 1 min by the software. Phase 2. The reproducibility of three successive hypotensive responses to sotalol were evaluated in five other telemetry-implanted rats. The three trials (deter-
1
I
1
1
2
3
minations), separated by 2 weeks each, were made prior to oral administration of sotalol at the dose of 500 mg/kg and at 0.5, 1, 1.5, and 2 hr postdosing to determine the time point corresponding to the maximal cardiovascular effect. At each time point, MAP and HR were averaged over 1 min by the data acquisition system. Phase 3. MAP and HR values determined by the telemetry method in the five previously tested rats were compared to those obtained by direct arterial catheterization performed in five rats. Whatever the method used, cardiovascular values were determined prior to oral administration of sotalol at 500 mg/kg and at time (t), that is, 0.5, 1, 1.5, and 2 hr postdosing. At each time point, the MAP and HR averaged data, obtained during a I-min period by the two methods, were compared.
Statistical Methods All data are presented as mean ? SEM. Data were analyzed by paired Student’s t test. Data were considered significantly different at p < 0.05.
Results As shown in Figures 2 and 3, no consistent variability of DAP, SAP, MAP, and HR was detected over the
I
-
4 SAP
&dw, TIME .-.... QAp
I
I
I I
I
6
7
8
9
4
e*-, MAP
Figure 2. Week-to-week variability of diastolic, systolic, and mean arterial pressures over the course of 9 weeks in telemetryimplanted rats. Each point represents the mean -t SEM of five rats.
102
JPM Vol. 28, No. 2 September 1992:99-105
500
400
o-
L
1
2
1
1
8
9
I
4
3
5
6
7
TIME (W.&s)
Figure 3. Week-to-week
variability
of heart rate in the same telemetry-implanted
rats. Each point represents
the mean 2
SEM of five rats.
l-
1
El I
CONTROL
E2 0
E3 SOTALOL
Figure 4. Effects of three successive oral administrations (E), separated by 2 weeks each, of sotalol at 500 mg/kg or mean arterial pressure. Each column represents the mean MAP r SEM of five telemetry-implanted rats at 90 min postdose (time corresponding to the maximal hypotension).
GUIOL ET AL. A RADIOTELEMETRY
SYSTEM FOR CHRONIC MEASUREMENT
OF BLOOD PRESSURE AND HEART RATE
103
100 a 1
3 50
0
m
A
TIME (hr) AFTER P.0 SOTALOL 0 TELEMETRIC SYSTEM FEMORAL CATHETER
110
Y’
- 7.2330
+ 1,1262x
R-2 = 0.973
c
80
V 80
B
I
I
90
100
TELEMETRY - MAP (mmHg
1
Figure 5. (a) Comparison of telemetry and invasive (femoral artery catheterization) methods measuring MAP in rats treated with sotalol at 500 mg/kg p.o. Each column represents the mean MAP ? SEM of five rats. (b) Relationship between MAP values obtained by invasive and telemetry methods under the experimental conditions described in (a).
JPM Vol. 28, No. 2 September 1992:99-105
104
500
400
h .E E . 5
r
300
E 200
-
-
100
0
+
0.5
0
-
-+ 1
TIME (hr) AFTER P.0 SOTALOL FEMORAL CATHETER 0 TELEMETRIC
-
1 ,s SYSTEM
360 y = 139.97
+ 0.71887x
0
R-2 = 0,993
350
‘/
Figure 6. (a) Comparison of telemetry and invasive (femoral artery catheterization) methods measuring HR in rats treated with sotalol at 500 mg/kg p.o. Each column represents the mean HR * SEM of five rats. (b) Relationship between HR values obtained by invasive and telemetry methods under the experimental conditions described in (a).
320
6
TELEMETRY
- HR ( b/min
1
of 9 weeks. Mean DAP ranged from 77.4 ? 2.8 mmHg with a maximal variation of - 8.7%; mean SAP ranged from 112.8 & 4.9 to 103.0 & 2.3 mmHg with a maximal variation of - 8.7%; mean MAP ranged from 87.8 ? 2.3 to 97.6 + 4.3 mmHg with a maximal variation of - 10%; and mean HR ranged from 320 + 20 to 290 + 27 beats per minute (bpm) with a maximal course
variation of - 9.4%. The effects of successive administrations of sotalol on MAP determined in five other rats implanted with the telemetry transmitter are presented in Figure 4. No statistically significant difference in the hypotensive responses to sotalol was noted between the three trials separated by 2 weeks. At t = 90 min after administration corresponding to the maximal car-
GUIOL ET AL. A RADIOTELEMETRY
105 SYSTEM FOR CHRONIC MEASUREMENT
OF BLOOD PRESSURE AND HEART RATE
diovascular effect, the fall in blood pressure induced by this compound was - 22.4%, - 20.3%, and - 19.2% compared to the respective basal values. In the last series of experiments, MAP and HR responses to sota101determined by telemetry and arterial catheterization methods were compared. No statistically significant difference in the MAP responses to sotalol was noted between the two methods [Figure 5(a)]. The MAP variation between the two techniques ranged from - 2.1% to 6.9% according to the time point considered. Figure 5(b) displays values of MAP from both measurement methods. A high correlation existed between the two series of data (correlation coefficient r = 0.973, p = O.OOSl), and the slope of regression was almost equal to 1 (1.1262). Variations in HR responses between the two techniques (Figure 6(a)] were more important than those observed in the MAP responses. However these variations, ranging from - 21.6% to - 16.5%, were not statistically significant. Furthermore, a very high correlation [Figure 6(b)] was obtained between the two series of measurements (correlation coefficient r = 0.993, p = 0.0006), and the regression slope was not very different from 1 (0.71887).
mean arterial pressure and heart rate measured by telemetry were compared to those determined by femoral artery catheterization. Our results indicated that the telemetric method gave the same blood pressure readings as the invasive method. Similar results have been obtained in rats by Brockway et al. (1989) and in dogs by Armentano et al. (1989). As indicated by the correlation coefficient, there was a strong linear correlation between telemetric and invasive heart rate measurements. However, heart rate parameters were overestimated by the catheterization method. One explanation for this discrepancy could be that the telemetered data were undertaken in relaxed conditions as these rats were freely moving, whereas the catheter-implanted animals were restrained in small cages. This technique provides an accurate and reliable means of determining cardiovascular parameters in long-term studies and yielded chronic measurements that were repeatable and free of stress-induced artifacts.
Discussion
Brockway BP, Mills PA, Miller JT, Azar SA (1989) A new radiotelemetry system for continuous chronic measurement and recording of blood pressure, heart rate and activity in the rat. Abstract no. 1000, Conference on SHR and related studies, Iowa City, USA.
The telemetry system described herein has permitted chronic measurements of systemic arterial blood pressure and heart rate via a chronically implanted transmitter in unrestrained rats. In the first phase of this study, the week-to-week variability of systolic, diastolic, and mean arterial pressures, and heart rate was found to be minimal over the course of 9 weeks. These results suggest that ability of this system to provide accurate information for long-term cardiovascular studies in this species. Unfortunately, chronic cardiovascular experiments using the telemetry system in small animals are poorly documented. Only Brockway et al. (1989) have shown that no consistent change in systemic arterial pressure and heart rate were observed within a 1lo-day period after telemetric implantation in rats. Indeed, most of the work has been done with dogs, baboons (Van Citters and Franklin, 1966), chimpanzees (Sandler and Stone, 1972), and other wild animals (Van Citters et al., 1966). In the second part of the study, the ability of the telemetry technique to detect potential and repetitive effects of a drug upon the cardiovascular system during long-term studies was demonstrated as shown by the reproducibility of cardiovascular responses to three successive administrations of sotalol. In the last part,
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