Preparation of the Femoral Loop.-Under ether anaesthesia and with. limb, but in my experience these were not satisfactory, and inflation of a

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1 A METHOD OF DETERMINING THE ARTERIAL BLOOD PRESSURE OF CONSCIOUS DOGS. By W. J. O'CONNOR. From the Department of Physiology, Medical School, University of Leeds. (Received for publication 2nd February 1955) THE arterial blood pressure of conscious dogs has been determined usually by one of two methods, both of which are described by Verney and Vogt [1938]. In one method the systolic pressure is determined indirectly as the pressure necessary to obliterate the palpable pulse by inflating a cuff applied to the common carotid artery previously enclosed in a loop of skin [van Leersum, 1911]. In the other method the mean pressure is recorded directly by a manometer connected to a cannula inserted under local anaesthesia into a superficial branch of the femoral artery or the artery itself. Neither of these methods could be used to record the blood pressure during occlusion of both carotid arteries, with frequent repetition on the same dog. An indirect method has therefore been developed using the femoral instead of the carotid artery. Janeway [1908], Kolls [1920] and Allen [1923] have described methods in which compression cuffs were applied to the fore or hind limb, but in my experience these were not satisfactory, and inflation of a cuff on a limb disturbed the animals. In the method to be described a cuff similar to that used by Verney and Vogt [1938] was applied to the femoral artery enclosed in a skin loop, so avoiding compressing the whole limb. Systolic and diastolic pressures were determined by an oscillometer similar to that of Patterson [1928]. A summary of the method has been published previously [O'Connor, 1953]. To illustrate its use, the blood pressures and pulse rates of three trained dogs at rest are given, and the effects of occlusion of both carotid arteries and of emotion are described. METHOD Preparation of the Femoral Loop.-Under ether anaesthesia and with aseptic precautions, the femoral artery from the inguinal ligament to the origin of the saphenous artery was freed and enclosed in a skin loop [van Leersum, 1911]. Usually some small muscular branches had to be ligated, but no large vessels arose from this length of artery. Fine silk 225

2 226 O'Connor was used for the sutures, dressings were held in place by a spica bandage including both hind legs, and Procaine Penicillin G was injected on each of the first 14 days after operation. Healing was uncomplicated, and loops cm. long were obtained after each of 5 operations. Three of these loops have been used for blood-pressure determinations without complication for as long as 18 months. In two, both on the same dog, abscesses formed in the leg under the loop 2-3 months after operation; these were slow to heal and the loops became useless. Compression Cuffs were constructed in imitation of those of Verney and Vogt [1938]. The window of loose thin rubber through which the pressure was transmitted to the loop was 1-0-2'5 cm. wide, varying with the length of femoral loop available. Cuffs of varying size within this range gave the same readings when tested on the same dog. B t FIG. 1.-The arrangement of the oscillometer. For description and lettering see text. The Oscillometer.-The modification of the apparatus, from that of Patterson [1928], is shown in fig. 1. The cuff (A) was connected to a mercury manometer (B) writing on the kymograph drum, and to a tambour (C), the movements of which were magnified by a double lever and also recorded on the drum. The membrane, 2 cm. in diameter, was of thin, slack rubber dam. The tambour was enclosed by a bottle of about capacity, which was connected through the tap (D) either to a hand-pump (E) and release tube (F) or to a slow air leak (G). To obtain a uniform fall of pressure in the bottle the slow leak (G), consisting of a length of fine tubing, was connected to a vacuum pump. The tube (H), which could be closed by Spencer-Wells forceps, provided a free connexion between the cuff-manometer system and the bottle. In

3 Blood Pressure of Conscious Dogs 227 Aiddition, there was a petratent smiall opening throtigh the membrane (C); in practice this was ptovided by not removing the wrinkles which form when the thin rubber dam was being tied in position. The arrangement of the air-tight fulcrum (J) where the lever passd through the bung of the bottle Was simpler than that of Patterson [1928]. A Perspex cup 1-7 em. in diameter was fitted through the bung to leave its flat bottom plate flush with the inside of the bung. Through the bottom of the cup was a hole, 2 mm. in diameter. A disc of rubber about 1 mm. thick was sealed to the inside of the bung, and carried a hole 1 mm. in diameter corresponding in position to the hole in the floor of the cup. Finally, a sheet of rubbet damn was sealed over the hole, and the lever, a large needle, thrust through the rubber dam. This provided a satisfactory airtight fulerum. Procedure.-When the blood pressure was being recorded, the animal lay quietly on a warm table. One end of the cuff was slipped under the femoral loop and the two sides held together by a screw clamp, so that the cuff lay loosely around the artery. For each observation the pressure throughout the apparatus and cuff was taised above the systolic pressure by the hand-pump (E), the separating clamp (H) being open. The clamp was then closed, the tap (D) turned to allow a slow escape of air via (G), and the kymograph started. As the pressure in the bottle fell, air passed through the leak in the membrane (C) so that the pressure fell equally on its two sides. The falling pressure in the cuff was recorded by the mercury manometer (B) as in the examples shown in fig. 2. Sudden oscillations imparted to the cuff by the pulsating artery were recorded by the tambour and levers and, as in fig. 2, followed a definite sequence of changes as the pressure in the cuff fell from above systolic to below diastolic ptessure. There were sometimes small oscillations with the pressure in the cuff above systolic pressure, due to the impact of the pressure pulse on the upper edge of the cuff; but as the pressure fell below the systolic pressure the oscillationos suddenly increased in size and continued to increase as the pressure fell further. Tho point on the oscillometer record at which the pulsations suddenly and progressively increased was marked 5, as in fig. 2, and the ptessure in the cuff at that time was read from the manometer record to give the systolic pressure. The oscillations continued to inictease in size until the pressute in the cuft fell belowv the diastolic pressute, when they decreased again. The point where the oscillations began to decrease again was marked (D in fig. 2), and the pressure at that time was read from the manometer record as the diastolic pressure. Thus, in the examples of fig. 2A, B, C the blood pressures were recorded as 155/70, 210/115 and 170/70 mm. Hg.

4 w U A B C )1()(o)IprIure. IFIom above dvonwxarcls FIG Fl(Oss", 21 kg. rltlore- d(termilnations of (ll-tribl od the tracinlgs sbo: pr(e S ill tle I off S ()(lg: H- osillomtoter roc( ltode in 1-sec. i'ntervals. In A. bloodl pressure Nvas orio. Hg, pulse roett ;(0per to. inim B). duiring oelusilon of both caroti(l arteries, 210, 11 5, 75 aolnil(n. after release of tle (carotiml arteries, , 63. 1'or further (leseription see text.

5 Blood Pressure of Conscious Dogs 229 THE ACCURACY OF THE METHOD Comparison with Auscultation.-In one instance, where the femoral loop was long enough to allow the application of a stethoscope below the cuff, the Korotkov sounds could be heard and used to determine the blood pressure. In a series of experiments the usual oscillometer record was taken, but, in addition, a signal was used to mark on the drum the moment of recognition of systolic and diastolic pressures by auscultation as the pressure in the cuff fell, giving simultaneous readings by the two methods. There was good agreement: in 25 such comparisons the difference in either systolic or diastolic pressure was only once greater than 10 mm. Hg; in the average the systolic pressure by auscultation was 2 mm. Hg and the diastolic pressure 1 mm. Hg below the values determined by the oscillometer. Obviously either method could be used; oscillometry has been preferred, as it can be used even if the loop is not long enough to accommodate both cuff and stethoscope, and also it is more satisfactory to determine the pressures from the permanent kymograph records rather than by immediate subjective decision. Comparison with an Optical Manometer (with the collaboration of Dr. R. J. Linden).-Two acute experiments were performed on dogs anaesthetized with morphine, Dial (Ciba) and pentobarbitone; with this anaesthetic the heart rate remained low as in the conscious animal [Coleridge and Linden, 1955]. The right femoral artery was enclosed in a loop of skin as in the aseptic operations and the oscillometer cuff immediately applied. A T-cannula was inserted into the left femoral artery and the lateral pressure recorded by an optical manometer with a natural frequency of 500 c/s and adequate sensitivity [Coleridge and Linden, 1954]. Manometric records of the intravascular blood pressure were made while the usual record was obtained from the oscillometer, and various procedures-occlusion of the carotid arteries, overventilation, section of the vagi, haemorrhage-provided a range of blood pressure from 210/130 to 60/40 mm. Hg and of pulse rate from 60 to 170 per min., at which comparison of the two methods was made. Critical comparison was possible, for example, during the period of apncea following overventilation, when the normal variation of blood pressure with respiration was abolished (fig. 3). The optical records showed practically no variation of systolic or diastolic pressure between individual beats, so that steady figures were available with which to compare the values of systolic and diastolic pressure derived by the indirect method. In this instance the indirect readings were 7 and 9 mm. Hg higher than the direct values. The two experiments provided 14 comparisons similar to that of fig. 3, and in these the systolic blood pressure determined by the indirect method varied from 10 above to 6 mm- Hg below the manometric reading, the diastolic from 12 above to 5 mm. Hg below. In the average, the indirect determination of

6 230 O'Connor systolic blood pressure was 2-5 (standard deviation 4 8) and of diastolic pressure 4 (standard deviation 4 6) mm. Hg above the direct value. These differences are of doubtful statistical significance, and so no correction has been applied to the values obtained by the indirect method. A B I I I I I Mm. Hg C 0 I A I I a ' a t sss' bo z:: : 140 IDO 60 FIG. 3.-Experiment on ansesthetized dog. A is an oscillometer record from the right femoral artery, similar to fig. 2. B and C are optical manometer records from the left femoral artery at the times when systolic and diastolic pressures were determined in A. Systolic pressure: By oscillometer By manometer Diastolic pressure: By oscillometer By manometer Heart rate 140 mm. Hg mm. Hg ^ 104 mm. Hg mm. Hg 88 per min. On other occasions in the two acute experiments the optical records were like those of fig. 4, where there was large variation in systolic and diastolic blood pressure between individual heart beats in each respiratory cycle. Then there was no satisfactory figure for the intravascular blood pressure with which to compare the indirect determination, which was itself made uncertain by the varying size of the individual beats in the oscillometer record. In 15 comparisons of this type the estimations of systolic and diastolic pressure by the oscillometer fell

7 Blood Pressure of Conscious Dogs within and close to the upper end of the range of values determined from the optical records. In assessing the reliability of determinations on conscious dogs by the oscillometer method, it must be remembered that the measurements A 231 B Mm. Hg 170 C so FIG. 4.-As in fig. 3. Systolic pressure: By oscillometer mm. Hg By manometer mm. Hg Diastolic pressure: By oscillometer.. 93 mm. Hg By manometer mm. Hg Heart rate per min. are made under conditions similar to those of fig. 4 rather than fig. 3. The oscillometer records from a resting conscious dog in fig. 2A and C were typical in that there was obvious sinus arrhythmia with considerable variation in the size of individual beats. Manometric records from the carotid artery of conscious dogs by Gregg, Eckstein and Fineberg [1937] showed variations of 10 mm. Hg in the systolic and diastolic pressure of individual pulses. Clearly in the presence of sinus arrhythmia a determination by this, or any other, indirect method can only

8 232 O'Connor be an approximation to within about 10 mm. Hg of an average value for systolic or diastolic blood pressure; the acute experiments showed satisfactorily that the oscillometer method is without large systematic error. RESULTS The Blood Pressure of the Resting Conscious Dog.-Fig. 5 shows typical experiments. The animal was catheterized, given 300 ml. of 0 9 per cent sodium chloride by stomach tube and placed on its side HEART~~~~ I2 I I B I-.I I ;- '. 220 A I B HEART A RATE I ; l BLOODI PRESSURE 80 mm. Hg * *1 k..s*..-* TIME (min.) FIG. 5.-Effect of occlusion of both carotid arteries. A, "Tyke", 12 5 kg. B, "Skewbald", 15 kg. Both carotid arteries were occluded during the period of the black rectangles. Abscisss, time in min. Ordinates, from above down; heart rate, per min.; systolic and diastolic blood pressure, mm. Hg. Average value in periods of min. is shown by the broken lines. on a warmed table. The animals were thoroughly accustomed to these procedures and lay quietly on the table with only light restraint. Every 2-4 min. oscillometer records were obtained from the femoral artery, and the values for blood pressure and heart rate derived from the records were plotted as in fig. 5. In each phase of the experiments of fig. 5 individual readings of systolic and diastolic blood pressure vary from each other within a range of about 20 mm. Hg. The previous section shows that experimental error would cause such a scatter even if the actual blood pressure remained constant. The blood pressure was thus sufficiently stable to use the average of individual observations to indicate the blood pressure in each period of an experiment, and these values are given by the dotted lines in fig. 5.

9 Blood Pressure of Conscious Dogs During the period before occlusion of the carotid arteries in fig. 5 the animals were quite quiet and, except on two occasions, the heart rate was less than 90 beats per min. There was always definite arrhythmia, which is suggested by Wiggers [1938] as a criterion of the basal state. Table I summarizes the figures for the blood pressures and pulse rates under these resting conditions on 39 occasions with 3 dogs. These TABLE I.-ARTERIAL BLOOD PRESSURE AND PULSE RATE OF RESTING CONSCIOUS DOGS 233 The highest and lowest values are given, with the average in brackets. Mean blood pressure is calculated as the diastolic pressure plus one-third of the pulse pressure. " Floss" "Tyke" "Skewbald" Number of experiments Systolic pressure, mm. Hg (148) (140) (134) Diastolic pressure, mm. Hg (76) (62) (57) Mean blood pressure, min. Hg (100) (88) (83) Pulse rate per min (77) (75) (82) figures are rather lower than the blood pressures of conscious dogs previously reported: e.g. in the experiments of Verney and Vogt [1938] the mean blood pressure recorded by a mercury manometer connected to a cannula in the saphenous or femoral artery varied from 100 to 160 mm. Hg. Gregg, Eckstein and Fineberg [1937] measured the blood pressure in the carotid artery by means of an optical manometer and give the value of 124/85 (mean 98) mm. Hg as the resting blood pressure of normal conscious dogs. Effect of Occlusion of the Carotid Arteries.-Fig. 5 shows the effect of occlusion of both carotid arteries, enclosed in van Leersum loops, in 2 experiments which are typical of 18 which have been carried out with 3 dogs. In the 18 experiments the systolic blood pressure rose by mm. Hg (average 53) and the diastolic pressure by (average 36). The increase in systolic pressure was always larger than the increase in diastolic pressure. One minute after occlusion of the carotids the blood pressure had reached its highest level, and returned to the resting level within one minute of the release of the occlusion. The raised blood pressure persisted without diminution when the carotid arteries were kept occluded for minutes, so that there was no adaptation in the reflex within that period. The increase in heart rate shown in fig. 5A is typical of 2 of the 3 dogs, and was usually beats and never more than 22 beats per min. In the third animal (fig. 5B) the increase was usually about 35 beats per min., and sometimes as much as 55 beats per min. Again the full increase and decrease of the heart rate was attained within one minute of occlusion or release of the carotid arteries, and there was no sign of adaptation during occlusions lasting min. Occlusion of one carotid artery produced changes in blood pressure

10 234 O'Connor and heart rate about one-third as large as those produced by occlhsion of both vessels. Verney and Vogt [1938] and Verney [1947] have reported experiments in which the rise of mean arterial pressure on occlusion of the carotid arteries was measured by cannulation of the femoral artery or its saphenous branch in conscious dogs. They found rises in blood pressure equal to or rather larger than those reported above, although most of their experiments were after destruction of part of the sympathetic nervous system. Spontaneous Changes in Blood Pressure and Heart Rate.-In general the blood pressure and heart rate increased by only 10 mm. Hg, or beats per min. when the attention of the animal was attracted by noises HEART RATE /min BLOOD PRESSURE tnm. Hg I I I I I ~~~~ I I I I I * I I I I I TIME (min.) FIG. 6.-Effect of emotion in "Tyke", 12*5 kg. Plotting as in fig. 5. From 0 30 onwards the animal was restless, as described in the text. of traffic in the streets or of movement within the building, and these increases quickly subsided. In contrast 1 of the 3 animals sometimes became restless after 1-1 hour on the table. About 5 min. after restlessness was apparent, the blood pressure and heart rate increased as in the example of fig. 6, where the pressure increased from 136/73 to 200/126 mm. Hg and the heart rate from 71 to 106 per min.; and it is of interest to

11 Blood Pressure of Conscious Dogs observe that the increased heart rate and blood pressure produced by the emotion can persist for as long as 1 hour without great fluctuations. That the blood pressure and heart rate of the conscious dog are steady is therefore not proof that a basal state has been attained. 235 DIscussIoN The experiments presented here are intended to illustrate the possibilities and limitations of the method. In practice observations could be obtained every two minutes without disturbance to the dog; any single estimate was probably within 10 mm. Hg of the true value but, by repetition, a satisfactory average could be obtained for the blood pressure in any period within an experiment. The method failed when the blood pressure or the pulse pressure was changing. For example, sometimes during a record there was a deep sighing respiration, and this was accompanied by several rapid heart beats, followed by a slowed rate for about 15 seconds; accompanying the changes in rate there were changes in the size of the oscillometer beats which completely obscured the sequence normally due to falling cuff pressure. Usually about one record in ten had to be rejected for this reason. SUMMARY 1. A method is described in which the systolic and diastolic blood pressure of the conscious dog have been determined by means of an oscillometer connected to an occluding cuff applied to the femoral artery, previously enclosed in a skin loop. 2. The accuracy of the method has been confirmed by comparison with the values recorded by an optical manometer. 3. The effects on blood pressure and heart rate of occlusion of the carotid arteries and of emotion have been recorded. ACKNOWLEDGMENTS In addition to the collaboration of Dr. Linden, I am grateful to Dr. J. C. G. Coleridge for his help in the acute experiments, to Dr. W. J. Allen and other members of the Department who have assisted at the operations, and to Mr. K. A. Pearce for his patient technical assistance. Part of the expenses were met by the Government Grants Committee of the Royal Society. VOL. XL, NO

12 236 O'Connor REFERENCES ALLEN, F. M. (1923). "Auscultatory estimation of the blood pressure of dogs", J. metab. Res. 4, COLERIDGE, J. C. G. and LINDEN, R. J. (1954). "The measurement of effective atrial pressure", J. Physiol. 126, COLERIDGE, J. C. G. and LINDEN, R. J. (1955). "The effect of intravenous infusions upon the heart rate of the anesthetized dog", J. Physiol. 128, GREGG, D. E., ECKSTEIN, R. W. and FINEBERG, M. H. (1937). "Pressure pulses and blood pressure values in unanaesthetized dogs", Amer. J. Physiol. 118, JANEWAY, T. C. (1908). "A modification of the Riva-Rocci method of determining blood pressure for use on the dog", Proc. Soc. exp. Biol. N.Y. 6, KOLLS, A. C. (1920). "An indirect method for the determination of blood pressure in the unanaesthetized dog", J. Pharmacol. 15, LEERSUM, E. C. VAN (1911). "Eine Methode zur Erleichterung der Blutdruckmessung bei Tieren", Pflug. Arch. ges. Physiol. 142, O'CONNOR, W. J. (1953). "The indirect determination of systolic and diastolic blood pressures in conscious dogs", J. Physiol. 122, 68 P. PATTERSON, W. D. (1928). "Circulatory and respiratory changes in response to muscular exercise in man", J. Physiol. 66, VERNEY, E. B. (1947). "The antidiuretic hormone and the factors which determine its release", Proc. Roy. Soc., B, 135, VERNEY, E. B. and VOGT, M. (1938). "An experimental investigation into hypertension of renal origin, with some observations on 'convulsive ureemia"', Quart. J. exp. Physiol. 28, WIGGERS, C. J. (1938). "The dynamics of hypertension", Amer. Heart J. 16,