(E.M.I.), age years. In the main series of experiments, twenty-four in all,

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1 63 J. Physiol. (I95I) II3, THE PROPORTION OF THE TOTAL HAND BLOOD FLOW PASSING THROUGH THE DIGITS A. D. M. GREENFIELD, J. T. SHEPHERD AND R. F. WHELAN From the Department of Physiology, The Queen's University of Belfast (Received 26 June 1950) The blood flow through a finger varies over a much greater range than does that through the hand, and may reach a considerably higher level in terms of flow per 100 ml. of tissue per min. (Freeman, 1935; Wilkins, Doupe & Newman, 1938; Burton, 1939). We have been unable to find, however, direct observations on the proportion of the total hand blood flow passing through the digits at various levels of vasodilatation or on the range and variability of the blood flow through the remainder of the hand. Such information was needed in the planning of other experiments. We therefore carried out experiments to determine these proportions and ranges. METHODS Observations were made on seven healthy subjects, six men and one woman (E.M.I.), age years. In the main series of experiments, twenty-four in all, each subject was examined on at least three occasions under different environmental conditions which included: (a) lightly clad in a room at ' C. (cool environment); (b) normally clad in a room at 20-29' C. (comfortably warm environment); (c) wrapped in blankets in a room at C. and with both feet and calves in a stirred water-bath at 430 C. (Gibbon & Landis, 1932) (hot environment). In general, these conditions caused respectively, constriction of the hand vessels, moderate dilatation, and dilatation in response to indirect heating. In most of the subjects the hand blood flow could have been still further reduced by greater cooling, but the flows would then have been too small for reliable estimation. Subjects were comfortably seated, with arms and hands outstretched in front of them on an inclined plane, and about 10 cm. above the sternal angle. The hands were inserted into loosely fitting rubber gloves invaginated into plethysmographs of the type described by Barcroft & Edholm (1945), filled with

2 64 A. D. M. GREENFIELD, J. T. SHEPHERD AND R. F. WHELAN water at 32 C. and coupled to matched float recorders. The rate of blood flow was observed by inflating cuffs on both wrists simultaneously to 70 mm. Hg according to the principles of Brodie & Russell (1905) and Hewlett & Zwaluwenburg (1909). After an initial observation period, which provided evidence of the degree of symmetry of the circulation through the two hands, the left hand was removed from its plethysmograph, a tight rubber band applied to the base of each digit, the hand re-inserted, and observations resumed. This operation usually occupied 4-5 min. After further blood flow records had been obtained the right hand was, in some experiments, similarly treated and observations were again resumed. Finally, wrist cuffs were inflated to 200 mm. Hg, and the system calibrated by adding measured volumes of water to, and withdrawing them from, the plethysmographs. The volumes of the digits and hands were measured by displacement of water. Preliminary calibration procedures The ability of the rubber bands to arrest the digital circulation. An index finger was immersed to the proximal interphalangeal joint in a calorimeter (Greenfield & Shepherd, 1950b) containing 1 1. of water at C. The change in temperature each minute was noted. Observations were made until a reasonably steady state was attained, the temperature changes being to +116 milli 0 C. per min. The finger was then momentarily removed, and a rubber band applied at the base. On re-insertion into the calorimeter, the temperature change declined to a steady value of -5 milli 0 C. per min. An arm cuff was then inflated to 230 mm. Hg. The temperature change each minute was unaltered. After 5 min. the cuff was released, and the temperature change each minute was again unaltered, being still -5 milli C. On then releasing the rubber band, the temperature changes in the following minutes were: + 59, + 198, and milli C. There was therefore no evidence that inflation of a cuff on the upper arm to 230 mm. Hg was more effective in arresting the circulation to the finger than was the rubber band applied to the base of the finger. Observations were also made on an index finger with a plethysmograph (Greenfield & Shepherd, 1950a) connected to a soap-bubble volume recorder (Greenfield, 1948). When the rubber band was applied at the base, the pulsations disappeared. Inflation of a pneumatic cuff over the rubber band to a wide range of pressures failed to produce any changes in finger volume which could be interpreted as showing that blood was passing under the band. The same rubber bands were used throughout the experiments. As it was thought possible that they might have weakened they were re-tested at the conclusion of the series of experiments. Further, to be sure that they were effective not only on the index finger but on all fingers, and also at the height of

3 DIGITAL AND HAND BLOOD FLOWS 65 vasodilatation in response to indirect heating, we carried out the following experiment. The subject was wrapped in blankets and had his feet in a stirred water-bath at 430 C. for 20 min. before starting observations. The four fingers of the left hand were immersed in a calorimeter containing 4 1. of water at C. (Greenfield & Scarborough, 1949). After an initial period of observation in which the temperature change each minute was + 32 to + 36 milli C. a band was applied to the base of each finger and the temperature change settled at + 2 milli C. per min. Inflation of an arm cuff to 220 mm. Hg reduced the temperature change to + 1 milli 0 C. per min., but there was a further drop to 0 milli 0 C. per min. when the arm cuff was released, the finger bands being still in position. There was therefore no evidence in any experiment of any blood flow through the fingers with the bands in position. The rubber bands were 0 9 mm. thick, 3*O mm. broad and 108 mm. in total length when not stretched. In all the experiments described, each band encircled the base of the digit three times. When it encircled the digits twice only the circulation was not completely arrested. The constricting force was therefore not greatly in excess of that required and the bands were not painful. The influence of the constricting bands round the digits on the bloodflow through the remainder of the hand. Barnes & Trueta (1942) found that a tight wire tourniquet applied to the root of the hindlimb and left in place for 41 hr. produced a severe arterial spasm in the hindlegs of rabbits which persisted for as much as 72 hr. The spasm often involved the collateral arteries and even the main artery of the opposite limb. Had our rubber bands at the root of the fingers caused a similar condition in the palmar arteries the method would have been useless for our purpose. We have no direct evidence to offer, but the following observations are relevant: (1) The bands we used were not excessively tight. When made to encircle the digit twice instead of three times, they failed to arrest the circulation completely. (2) On removal of the bands, the fingers quickly became flushed, showing that no serious degree of spasm persisted. By spasm we mean a persistent active arterial constriction, which may involve a considerable length of artery. (3) In experiments of the type shown in Fig. 2, following the application of bands at different times to the digits of the two sides, the blood flows were either equal or else at a constant ratio similar to that through the hands before the bands were applied. This shows that if there was any spasm it must have been immediate in onset, and then constant in degree. (4) It was thought that if one rubber band at the base of each digit caused some spasm, two bands might increase the spasm. This point was tested as follows. One rubber band was applied to each digit of both hands. The blood PH. CXIII. 5

4 66 A. D. M. GREENFIELD, J. T. SHEPHERD AND R. F. WHELAN flows through the bodies of the hands were then observed plethysmographically and expressed as ml./100 ml./min. The averages of ten readings were Left 8-0 Right 8-9 Left=900/ right. A second band was now applied to each digit on the left side, and the averages of ten readings were Left 6*7 Right 7-8 Left= 860% right. In a second experiment on a different subject the corresponding readings before the extra bands were applied were Left 7-6 Right 8&3 Left=920/ right. and afterwards Left 5-2 Right 5-8 Left= 89% right. The extra bands evidently made little difference to the ratio of the blood flows on the two sides. (5) A comparison was made between the heat elimination from the body of the hand and thumb before and after application of the rubber bands to the fingers. The main uncertainty in interpreting the results of these experiments is the relationship between heat elimination and blood flow in the different parts of the hand. The heat elimination from the fingers on both sides was first measured (period 1), and in two subjects was found to agree within 1 %. The whole hand was now immersed on one side, and after conditions had become stable, the heat elimination from the whole hand was compared with that from the fingers on the opposite side (period 2). The hand was removed, rubber bands applied to the bases of all the fingers, and heat elimination from the body of the hand and thumb compared with that from the fingers on the opposite side (period 3). The results are shown in Table 1. TABLE 1. Comparison of the heat elimination, in calories per 10 min., from the right fingers, whole hand, and whole hand with finger circulation occluded. The heat elimination from the fingers of the left hand is used as a control throughout. Subject Period Left Right L.G. 1 Fingers, 396 Fingers, Fingers, 420 Whole hand, Fingers, 312 Whole hand, fingers occluded, 387 R.F.W. 1 Fingers, 840 Fingers, Fingers, 915 Whole hand, Fingers, 704 Whole hand, fingers occluded, 620 Considering the results on L.G.: With the circulation free, heat elimination from the whole hand less the fingers = cal. = 560 cal. With the circulation arrested, heat elimination from the whole hand less the fingers= 387 cal.

5 DIGITAL AND HAND BLOOD FLOWS 67 Between the second and third periods the heat elimination from the left fingers had dropped from 420 to 312 cal. On the assumption that heat elimination changes symmetrically, the heat elimination from the whole hand less fingers would have dropped to 560 x 312/420 cal., that is to 427 cal. On this basis, with the rubber bands in position the heat elimination from the whole hand less the fingers was 387/427, or 91 %, of that when the circulation was free. In the second experiment, the proportion was 93-5 %. Although no critical experiment has been devised the weight of this indirect evidence makes it very unlikely that the bands we used caused spasm of the vessels proximal to the constriction and of sufficient extent to interfere with our method. RESULTS The results of a typical experiment will first be described (Fig. 1). The subject had been in the room at 270 C. for more than an hour. He was wrapped in blankets and had his feet in a stirred water-bath at 430 C. for 10 min. before observations started. 120 A.D.M.G. * Left o Right 3: 80 / OXE C(rp t Time (min.) Fig. 1. A.D.M.G. during indirect heating. Blood flow in ml./min. through the right and left hands. At the vertical broken line the circulation was arrested through all the digits of the left hand. Volumes: left hand 411 ml., left digits 95 ml., right hand 438 ml. In the initial period (0-10 min.) the hands were observed under as nearly as possible identical conditions. The blood flow on the right was, however, consistently higher than that on the left, but the fluctuations in flow were symmetrical. The averages of the flows for the whole hands in ml./min. (not ml./ 100 ml. of hand per min.) were right 88-7, left A band was then applied to the base of each digit (including the thumb) of the left hand. The flows in the whole hands on the two sides were now at very different levels, but the fluctuations were still symmetrical. The averages of the flows in this period were right 84.2, left No method is available for observing the digital and whole hand flows simultaneously in the same hand. It was therefore necessary to arrive at 5-2

6 68 A. D. M. GREENFIELD, J. T. SHEPHERD AND R. F. WHELAN a figure for the expected blood flow in the left hand in the second half of the experiment, had the digital flow not been arrested. Owing to the variability of the blood flow through the hand, it could not be assumed that the flow in the left hand would have remained at the same level as in the first part of the experiment, but it is reasonable to assume that the flow through the two sides would have continued at a constant ratio. In the initial period the flow in the left hand was 73.0/88.7 of that in the right. This gives for the second half of the experiment: 73 0 Expected blood flow through left hand = 887 x 84-2 ml./min. = 69-5 ml./min. (or 16*9 ml./100 ml. of tissue per min.). Measured blood flow through left hand less digits = 29-1 ml./min. (or 9-2 ml./ 100 ml. of tissue per min.). Bloodflowthroughdigits = 40*4ml./min. (or42.5 ml./100ml. of tissue permin.). Proportion of total hand flow passing through the digits = 58%. H.S.N. o Left 712 o Right 0~~~~~~~~~~ Time (mtn.) Fig. 2. H.S.N. while comfortably warm. Blood flow in ml./min. through the right and left hands. At the first vertical broken line the circulation was arrested through all the digits of the left hand. At the second vertical broken line the circulation was also arrested through all the digits of the right hand. Volumes: left hand 488 ml., left digits 112 ml., right hand 488 ml. Note that this subject when comfortably warm had a higher blood flow through the hand than had A.D.M.G. when indirectly heated. In most of the experiments the discrepancy between the two hands was less than on this occasion, but in the experiments on moderately warm subjects, of which Fig. 2 is an example, the symmetrical fluctuations in blood flow were greater. The average discrepancies between the blood flows through the two hands with the subjects cool, warm and indirectly heated were, in ml./100 ml./ min., 0 3 (128% 6 1), 144 (13.7%) and 2s2 (11 %) respectively. There was no apparent regularity in the predominance of one hand over the other; taking all the results from twenty-four experiments okensen subjects into account there was only a 3%eh difference between the blood flow through the right and left hands in terms of ml./100 ml. of tissue per min.

7 DIGITAL AND HAND BLOOD FLOWS 69 In those experiments which were concluded by observing both hands with the digital circulation arrested, the blood flows through the remainder of the hands were either identical or in about the same proportion as the flows through the whole hands in the initial period (Fig. 2). The percentage of the total hand blood flow passing through the digits under different environmental conditions. The results of twenty-four experiments of the type illustrated in Figs. 1 and 2 are summarized in Fig. 3. The percentage of the total hand blood flow passing through the digits has been plotted against the hand blood flow expressed as a percentage of the individual maximum Cool Comfortably warm Hot LC 0 l..< 0. 4' x ( *0 60 ~~V D x Total hand flow as percentage of individual maximum Fig. 3. The percentage of the total hand blood flow which passes through the digits (ordinate) under cool, comfortably warm and hot conditions. In each case the total hand blood flow in ml./100 ml./min. is expressed as a percentage of that observed in the same subject in response to indirect heating (abscissa). In the hot condition, total hand flow is for all subjects 100%, in the comfortably warm condition between 7 and 96 %, and in the cool condition between 3 and 15% of the individual maximum. V J.J.F. * A.D.M.G. 3 E.M.I. C1 J.I. * H.S.N. O J.T.S. x R.F.W. obtained by indirect heating. While there is a large individual variation, it is clear that, in general, the percentage of the total flow which passes through the digits is greater when the subject is comfortably warm than either when he is lightly clad under cooler environmental conditions or when he is indirectly heated in a hot environment. With the subject comfortably warm 46-82% (average 69%) of the total flow passed through the digits. When cooler the percentage varied from 19 to 64% (average 438 %), and when indirectly heated from 27 to 58% (average 44-5 %). In one case (H.S.N.) the percentage passing through the digits remained relatively constant (between 46 and 48%) under the three conditions. In another case (R.F.W.) the hand blood flow under comfortably warm conditions

8 70 A. D. M. GREENFIELD, J. T. SHEPHERD AND R. F. WHELAN was nearly equal to that obtained in a hot room with indirect heating on another occasion, but the proportions of the total blood flow passing through the digits were 76 and 46% respectively. Fig. 4 shows for each individual subject the maximum and minimum blood flows observed under our conditions and expressed in ml./100 ml./min. passing through the body of the hand (black), the whole hand (hatched), and digits (clear). The blood flow through the digits showed the greatest range of variability, and that through the body of the hand the least. The mean values for S60 E * Body of hand _ Whole hand Digits ill A.D.M.G. J.T.S. R.F.W. J.l. J.J.F. H.S.N. E.M.I. Fig. 4. The maximum and minimum blood flows, observed in response to indirect heating and general body cooling respectively, through the body of the hand, whole hand and digits of seven normal subjects. The top of each rectangle represents the maximum, and the bottom the minimum value for the individual. The maximum or minimum refers to the average level during an experiment of the type shown in Figs. 1 and 2, and not to a single observation. Blood flows are expressed in ml./100 ml. of tissue per min. The minimum values are not the lowest obtainable, but the lowest that could be accurately observed. minimum and maximum blood flows respectively in the seven subjects were: body of the hand *8, whole hand *0, digits *0 ml./100 ml./min. It must be emphasized that the minimum flows mentioned were the lowest which allowed the application of the method with reasonable accuracy, but that still lower flows could have been obtained by further cooling. DISCUSSION The assumptions made in interpreting our measurements were that: (1) The blood flows through the two hands would, in any one experiment, have remained at a constant ratio, usually close to unity, had the digital circulation not been occluded on one side. This assumption is supported by the steady ratio generally maintained in the initial period of observation (Figs. 1 and 2).

9 DIGITAL AND HAND BLOOD FLOWS 71 (2) The application of constricting bands to the bases of the digits did not alter the blood flow through the remainder of the hand. It might have done so in two ways: (a) By increasing the perfusion pressure available for the rest of the hand. Kerslake's experiments (1949) on the forearm blood flow show that after the first minute the apparent forearm blood flow is the same whether the wrist cuff is inflated to 70 or 200 mm. Hg. This indicates that obstructing the arteries at the wrist does not alter the forearm blood flow. It therefore seems likely that obstructing the digital arteries will not alter the flow through the remainder of the hand. (b) By causing spasm in the proximal arteries. None of the experiments we have performed to investigate this point is by itself decisive, but the weight of evidence already presented makes it very unlikely that spasm, if it occurs at all, interferes seriously with our findings. If these assumptions are granted, the main point of interest is the much larger percentage of the total hand blood flow passing through the digits when the subject is comfortably warm than when either cool or indirectly heated. As the subject is progressively warmed, the digital vessels dilate at a lower level of warming than do those in the remainder of the hand. These differences may be largely due to the distribution of arterio-venous anastomoses and proportions of skin and muscle in the digits and remainder of the hand. The behaviour ofthe resting blood flow through the body ofthe hand resembles more closely that of the digits than that of the forearm. The spontaneous fluctuations in the blood flow through the digits (Burton, 1939) and whole hand (Freeman, 1935) are seen also in the body of the hand. As in the digits, these fluctuations are symmetrical on the two sides. SUMMARY 1. A method is described for estimating the percentage of the total hand blood flow passing through the digits, and the uncertainties are discussed. 2. Twenty-four observations were made on seven subjects. 3. When a subject is comfortably warm a greater percentage (average 69 %) of the total hand flow passes through the digits than when he is cool (average 43-8 %) or indirectly heated (average 44-5 %). 4. The digital vessels appear to dilate at a lower level of general body heating than do those of the body of the hand. 5. The body of the hand shows the irregular fluctuations in blood flow which occur synchronously in all the extremities. We wish to thank the students who acted as subjects in these experiments.

10 72 A. D. M. GREENFIELD, J. T. SHEPHERD AND R. F. WHELAN REFERENCES Barcroft, H. & Edholm, 0. G. (1945). J. Physiol. 104, 161. Barnes, J. M. & Trueta, J. (1942). Brit. J. Surg. 30, 74. Brodie, T. G. & Rusell, A. E. (1905). J. Phy8iol. 32, 47P. Burton, A. C. (1939). Amer. J. Phyeiol. 127, 437. Freeman, N. H. (1935). Amer. J. Phy8iol. 113, 384. Gibbon, J. E. & Landis, E. M. (1932). J. clin. Inve8t. 11, Greenfield, A. D. M. (1948). J. Phy8iol. 107, 17P. Greenfield, A. D. M. & Scarborough, H. (1949). Clin. Sci. 8, 211. Greenfield, A. D. M. & Shepherd, J. T. (1950a). J. Phy8iol. 111, 40 P. Greenfield, A. D. M. & Shepherd, J. T. (1950b). Clin. Sci. 9, 323. Hewlett, A. W. & van Zwaluwenburg, J. G. (1909). Heart, 1, 87. Kerslake, D. McK. (1949). J. Physiol. 108, 451. Wilkins, R. W., Doupe, J. & Newman, H. W. (1938). Clin. Sci. 3, 403.