E u r o p e a n J o u r n a l of

Applied Physiology

Eur. J. Appl. Physiol. 42, 141--149 (1979)

and Occupational Physiology 9 Springer-Verlag 1979

Measurement of Forearm Blood Flow by Venous Occlusion Plethysmography: Influence of Hand Blood Flow During Sustained and Intermittent Isometric Exerelse* Carole A. Williams and Alexander R. Lind Department of Physiology, St. Louis University Medical School, 1402 South Grand Blvd., St. Louis, MO 63104, USA

Summary. The requirement for using an arterial occlusion cuff at the wrist when measuring forearm blood flows by plethysmography was tested on a total of 8 subjects at rest and during and after sustained and intermittent isometric exercise. The contribution of the venous effluent from the hand to the forearm flow during exercise was challenged by immersing the arm in water at 20, 34, and 40 ~ C. Occlusion of the circulation to the hand reduced the blood flow through the resting forearm at all water temperatures. There was an inverse relationship between the temperature of the water and the proportion in the reduction of forearm blood flow upon inflation of the wrist-cuff, ranging from 45 to 19% at 20 ~ to 40 ~ C, respectively. However, during sustained isometric exercise at 10% of the subjects maximum voluntary contraction (MVC) there was no reduction in the measured forearm flow when an arterial occlusion cuff was inflated around the wrist. Similarly, there was no alteration in the blood flow measured 2 s after each of a series of intermittent isometric contractions exerted at 20% or 60% MVC for 2 s whether or not circulation to the hand was occluded nor of the post-exercise hyperemia following 1 rain of sustained contraction at 40% MVC. These results indicate that a wrist-cuff is not required for accurate measurement of forearm blood flows during or after isometric exercise. Key words: Forearm blood flow - Venous occlusion plethysmography -- Isometric exercise Grant and Pearson (1938) were the first to point out that if the blood flow to the forearm is to be measured accurately by a plethysmograph, then " . . . the distal circulation required to be arrested . . . immediately below the plethysmograph." Since that time the occlusion of the circulation, particularly to the hand, has become part of the conventional procedure in venous occlusion plethysmography. But Grant and Pearson were careful to point out that in some circumstances there was little * This work was supported by N.I.H. training grant H L O 7050-03, H.E.W. contract 210-770044 and Air Force grant AFOSR-76-3084 B Offprint requests to: Dr. C. A. Williams (address see above)

0301-5548/79/0042/0141/$ 01.80

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difference in the blood flow measured in the forearm whether or not the distal circulation was arrested. Particularly, they showed that when the body was cold, the blood flow through the forearm was similar with and without arrest of the circulation to the hand. When the body was warm, the increase in the volume of the forearm on venous occlusion was markedly higher when the circulation to the hand was intact than when it was occluded, because of the collection in the forearm of a relatively large volume of blood from the hand. Some investigators since then (Kerslake, 1949; Whitney, 1954; Clarke and Hellon, 1957; Quinn, 1965; Mottram, 1965) have explored the possibility of eliminating the wrist-cuff or modifying its time of inflation in relation to the venous collection cuff; those experiments dealt mainly with alterations in the forearm flow during resting conditions. There is ample evidence (e.g., Grant and Pearson, 1938; Cooper et al., 1951; Coles and Cooper, 1957; Humphreys and Lind, 1963) to show that the hyperemia in response to short bouts of either rhythmic or isometric exercise is confined to the active muscles and does not involve the cutaneous vascular bed. An increase in skin blood flow during prolonged rhythmic exercise occurs only on demand of the thermoregulatory systems (Shepherd, 1963). The measurement of forearm blood flow during and after isometric hand-grip contractions is quite feasible (Humphreys and Lind, 1963) but gives rise, particularly following the development of fatigue, to discomfort or to frank pain when the circulation to the hand is occluded. Obviously, the measurement of blood flow through the forearm during and after isometric exercise would be simplified if occlusion of the hand were not necessary. Theoretically, from the evidence cited above, where isometric exercise does not involve an increase in blood flow to the skin and where by far the bulk of the active muscles are in the forearm, with very small muscles in the hand participating in the handgrip contraction, the arrest of blood flow to the hand should make little difference to the amount of blood flowing through the forearm. The experiments reported here were designed to examine the validity of that view.

Methods Eight volunteers acted as subjects for these experiments. Each subject signed a statement of informed consent after the methods and procedures had been explained in detail. Five of them were well-trained and participated in all phases of the investigation.

Training During the first week, the subjects were trained daily. After exerting 3 maximum voluntary contractions (MVCs) on a hand-grip dynamometer(Clarke et al., 1958), they were required to hold to fatigue 5 consecutive contractions at 40% MVC, with a 3-min interval between each contraction. Fatigue was taken to occur when the subject was unable to maintain the required target tension. Subjects continued this protocol every other day in the second and subsequent weeks until the MVCs were within _+ 1% and the durations of the sustained contractions _+ 5%.

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Procedures All experiments were performed with the subjects seated and the test arm in a dependent position with the forearm at an angle of 8 0 - 9 0 ~ at the elbow. The test arm was exposed to the ambient environment ( 2 3 - 2 5 ~ C) or it was immersed in water at 20 ~ 34 ~ or 40 ~ C for 20 min before the measurements began; the upper surface of the forearm was within 0.5 cm of the surface of the water. At the beginning of each experiment, the subject exerted 2 maximal efforts; the higher tension recorded was considered to be the MVC. The blood flow through the forearm was measured by venous occlusion plethysmography with a mercury-in-rubber strain gauge (Whitney, 1953). The gauge was placed on the upper third of the forearm, about 7 - 8 cm from the ulnar process. In all experiments, the venous collection cuff was placed above the elbow and was inflated automatically to a pressure of 5 0 - 5 5 m m Hg for 6 s every 12 s (5 measurements of blood flow. rain 1). A cuff was also set in place around the wrist to be inflated to 2 6 0 - 3 0 0 m m Hg as required.

Blood Flow Through the Resting Forearm The first set of experiments was carried out to test what effect the circulation from the hand had on measurements of resting forearm blood flow over a period of 6 min. As described above, the arm was immersed in water at 20, 34, or 40 ~ C for 20 rain before the measurements of blood flow were initiated. During the first 3 rain of recording, the wrist-cuff was in place around the wrist but not inflated. The recordings of forearm blood flow were continued for another 3 rain after the wrist-cuff had been rapidly inflated to 2 6 0 - 3 0 0 m m Hg. The values of blood flow stated in the text and figures are the average + S.E.M. Levels of significance were determined from Student's t-test at the 95% confidence limit.

Blood Flow in the Forearm During Sustained Isometric Contractions The second series of experiments was designed to study the influence of blood flow from the hand on measurements of forearm blood flow during sustained isometric exercise. Forearm blood flows were recorded at rest for 2 rain and were continued for the next 6 min during sustained contractions at 10% MVC. During the resting period and for the first 3 rain of exercise, the cuff around the wrist was not inflated. After the first 3 rain of contraction at 10% MVC, the wrist-cuff was inflated to a pressure of 2 6 0 - 3 0 0 m m Hg and the recording of forearm blood flows was continued for another 3 min. This type of experiment was carried out after the arm had been immersed for 20 rain in water at 20 ~ 34 ~ and 40 ~ C. In addition, the effect of not using a wrist-cuff on post-exercise hyperemia was determined on 3 subjects. Contractions at 20% MVC were held for 2 min or 40% MVC for 1 rain with the arm in water at 20 ~ or 4 0 ~ blood flows following the exercise were measured until resting levels were attained.

Blood Flow in the Forearm Between Intermittent Isometric Contractions The influence of free or arrested circulation to the hand in response to intermittent isometric exercise was studied in the third set of experiments. Successive contractions at 20% or 60% M V C were exerted for 2 s with 10-s rest intervals between the contractions (Williams and Lind, 1978; Lind and Williams, 1979). Forearm blood flows were measured 2 s after the release of each contraction with the wrist-cuff in place but not inflated. Following a 5-min period of rest, the experiment was repeated and the forearm flows were recorded in the same repetitive manner with the wrist-cuff inflated to 2 6 0 - 3 0 0 m m Hg. These experiments were conducted with the arm exposed to the ambient environment ( 2 3 - 2 5 ~ C) and carried out during the same time each day.

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Results

Blood Flow Through the Forearm at Rest There was a decrease in the blood flow through the resting forearm in all but one of the subjects (see below) when the circulation from the hand was occluded. Figure 1 illustrates the change in blood flow when the arm had been immersed for 20 min in water at 20, 34, and 40 ~ C. The forearm blood flow averaged 2.2 _+ 0.38 ml. min -1 9 100 m1-1 while the arm was immersed in water at 20 ~ C with the circulation to the hand intact (Fig. 1, [i]). When the wrist-cuff was inflated to arrest the circulation to the hand the resting blood flow decreased by 45% to an average of 1.2 _+ 0.19 ml 9 rain -1 9 100 m1-1 (Fig. 1, II). After the forearm had been immersed for 20 min in water at 34 ~ C, the blood flow averaged 5.0 _+ 0.63 ml. min -~ 9 100 ml -~ with a free circulation to the hand (Fig. 1, A) and was 3.1 _+ 0.40 ml. min -~ 9 100 ml -~ (Fig. 1, A) after the circulation to the hand had been arrested. This represents a decrease in the resting blood flow of 38%. To induce a higher skin blood flow, the arm was immersed for 20 rain in water at 40 ~ C. The resting forearm blood flow was 7.7 + 0.56 ml 9 min -~ 9 100 ml -I (Fig. 1, O) when the circulation to the hand was not impeded. Following inflation of the wrist-cuff, the resting flow decreased by 19% to 6.2 _+ 0.39 ml 9 min -1 9 100 ml -~ (Fig. 1, 0). In all those experiments, irrespective of the water temperature, the absolute decrease in resting flow following inflation of the wrist-cuff averaged 1.5 (range 1.0 and 1.9) ml 9 min -1 9 100 m1-1. However, there was an inverse relationship between the proportional decrease in forearm blood flow and the absolute blood flow in the forearm before arrest of the circulation to the hand. Figure 1 shows that the average flows decreased immediately following inflation of the wrist-cuff. In some subjects, there was transient increase or decrease in the blood flow through the forearm upon inflation of the wrist-cuff as has been

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Fig. I. The decrease in resting forearm blood flow in m l . min - I . i00 ml -I measured in 7 subjects before (open symbols)and after (closed symbols)occlusion of the circulation to the hand by inflation of a wrist-cuffto 260-300 nun Hg. Experiments were conducted with the forearm immersed in water at 20~ (v], III); 34~C (A, A); and 40~ C (9 0). Each point represents the average flow _+ S.E.M

Forearm Blood Flow and Venous Occlusion Plethysmography

145

described before (Kerslake, 1949). This response was not found in all the subjects and, when present, was usually complete in 30 s. One of the five trained subjects exhibited no decrease in the resting forearm flows upon inflation of the wrist-cuff regardless of the temperature of the surrounding water. In addition, this subject's blood flows did not increase to the same extent as the other subjects' did in response to local heating. This subject's resting forearm flows averaged 2.1 _+ 0.33 and 2.4 + 0.47 ml 9 min -1 9 100 m1-1 at 20 ~ C with and without a wrist-cuff inflated, respectively, and 2.8 +_ 0.63 and 3.5 + 0.45 m l . rnin -1 9 100 m1-1 at 40~ with and without a wrist-cuff, respectively. Since these results were, in our experience, unique and not readily explainable, these data were not included in the average blood flows described above.

Forearm Blood Flow During Sustained Isometric Exercise Forearm blood flows did not decrease during sustained isometric contractions when the circulation to the hand was arrested. Figure 2 shows the average blood flows in ml. min -1 9 100 m1-1 from the five trained subjects before (open symbols) and after

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Time ( min ) Fig. 2. The forearm blood flow measured on 5 subjects during sustained isometric exercise at 10% MVC before (open symbols) and after (closed symbols) occlusion of the circulation to the band by inflation of a wrist-cuff to 260--300 mrn Hg. One minute of resting flows with a free circulation was measured before the onset of exercise. The forearm was immersed in water at 20 ~ C ([3, II); 34 ~ C (A, A); and 40 ~ C (9 0). Each point represents the average flow + S.E.M

146

c.A. Williams and A. R. Lind

(closed symbols) inflation of the wrist-cuff during contractions held for a total of 6 rain at 10% MVC. There was an approximate doubling of the forearm blood flow above resting levels due to the sustained contraction, irrespective of the water temperature. As shown in Fig. 2, the blood flow increased during the first minute or so of exercise before reaching a steady-state, and remained at that level for the duration of the contraction, before and after occlusion of the circulation to the hand. When the arm was immersed in water at 20 ~ C, blood flow increased from 2.7 to 4.4 ml. min -1 9 100 m1-1 at the end of the first min of exercise with a free circulation and averaged 4.3 + 0.22 ml. min -1. 100 m1-1 for the second and third minute of exercise (Fig. 2, D). Following inflation of the wrist-cuff, blood flow averaged 4.5 + 0.40 ml 9 min -1 9 100 m1-1 (Fig. 2, Ii). The same pattern of response occurred when the water temperature was 34 and 40 ~ C although the absolute values increased with the water temperature. In water at 34 ~ C, forearm flow increased to an average value of 10.3 + 1.17 ml. min -~ 9 100 m1-1 for the second and third minute of the sustained contraction (Fig. 2, z~) and averaged 10.7 + 1.02 ml 9 rain -1 9 100 m1-1 (Fig. 2, A) for the 3 min of contraction after inflation of the wrist-cuff. When the sustained exercise was performed in water at 40 ~ C, blood flow increased to an average of 14.7 + 0.74 ml 9 min -1 9 100 ml-~ during the second and third minute with the circulation to the hand intact (Fig. 2, O) and averaged 15.3 + 0.87 ml 9 m i n - l l 0 0 ml -~ for the 3 rain following the inflation of the wrist-cuff (Fig. 2, Q). It is worth noting that the variance of the blood flow through the forearm increased in each experiment following occlusion of the circulation to the hand. In all experiments, the forearm blood flow after occlusion of the circulation to the hand was not significantly different from the blood flow with a free circulation. The subject whose resting flows did not increase with temperature responded in the same manner to exercise as did the other subjects. That is, blood flows averaged 5.1 + 0.23 and 5.3 + 0.10 ml. rain -~ 9 100 ml -~ during exercise in 20 ~ C water and 11.3 + 0.43 and 10.8 + 0.29 ml. rain -~ 9 100 ml -~ during exercise in 40 ~ C water with and without the wrist-cuff inflated, respectively. The effect of a wrist-cuff on post-exercise hyperemia was determined on three of the subjects. There was no statistical difference between the post-exercise hyperemia following 2 min of exercise at 20% MVC or 1 min at 40% MVC when the arm was immersed in water at 20 or 40~ with a wrist-cuff.

Forearm Blood Flow Following Intermittent Isometric Contractions Figure 3 illustrates the blood flows from one of 4 subjects who performed intermittent isometric exercise with the forearm exposed to an ambient temperature of 2 3 - 2 5 ~ C; the results from the other subjects followed the same pattern although the absolute levels of blood flow varied somewhat from subject to subject. Twenty consecutive contractions were exerted for 2 s every 12 s at a tension of 20% MVC and the blood flows, indicated in Fig. 3, were measured during the 10-s rest interval between each of the contractions. As previously reported (Williams and Lind, 1978; Lind and Williams, 1979), the blood flow reached a steady-state level after only a few contractions. There was no significant difference between the blood flows measured in response to intermittent exercise before (O) and after (O) the circulation to

Forearm Blood Flow and Venous Occlusion Plethysmography

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Fig. 3. The forearm blood flow one subject in ml. rain-~ 9100 ml-~ measured for 2 s after each of a series of intermittent contractions exerted for 2 s in duration at 20% MVC. The number of contractions exerted in succession is indicated on the abscissa. In this series of experiments, the arm was exposed to ambient temperatures. The open circles (9 represent the forearm flow during exercise with a free circulation from the hand and the closed circles (O) represent the flow during exercise following inflation of a wrist-cuff as described before

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the hand was arrested. Before inflation of the wrist-cuff, the blood flows averaged 7.6 + 0.83 ml. min -1 9 100 m1-1 compared to 7.5 + 0.98 ml. min -~ 9 100 -1 after the cuff was inflated. In addition, 2 of the trained subjects performed experiments in which they exerted 2-s contractions at 60% MVC, a tension at which local vessels are occluded (Humphreys and Lind, 1958; Lind and Williams, 1979). With their arms immersed in water at 34 ~ C, the average blood flow following the intermittent contractions was 16.9 + 0.83 ml. min -~ . 100 ml -~ when there was a free circulation to the hand and 17.6 + 0.87 ml. min -1. 100ml -~ when the wrist-cuff was inflated.

Discussion In the resting forearm, our findings confirm those of others (Barcroft and Edholm, 1943; Clarke and Hellon, 1957; Clarke et al., 1958) who have shown that (1) the blood flow increases in the forearm in response to direct heating, and (2) there is a decrease in the blood flow measured in the resting forearm when the circulation from the hand is arrested (Grant and Pearson, 1938; Kerslake, 1949; Whitney, 1954; Quinn, 1965). This proved to be the case in all but one of our subjects, whose forearm blood flow either did not change or increased slightly following inflation of the wrist-cuff; we have no explanation for these aberrant data. Our results also agree with those of Clarke and Hellon (1957) and Clarke (1958) who showed that the reduction in forearm blood flow following occlusion of the circulation to the hand was inversely related to the absolute level of forearm blood flow. Clarke and Hellon explained this on simple hemodynamic principles; as the rate of blood flow through the forearm increases, a proportionately lower volume of blood from the hand can be accepted in the veins of the forearm when the venous collection cuff is inflated. This reasoning was supported by data (Clarke, 1958) which demonstrated that no fall in forearm blood flow occurs following occlusion of the circulation to the hand when the absolute forearm blood flow reaches levels of 15 to 20 ml 9 rain -1 100 m1-1. Furthermore, the reduction of blood flow measured in the forearm following occlusion of the circulation to the hand was small, averaging 1.5 ml 9 min -1 9 100 m1-1 in these experiments, a fact that assumes importance when the arm is exercising.

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It is not thought that myogenic activity contributes to the response of the venous system to changes in rates of flow (Shepherd and Vanhoutte, 1975; Mellander, 1971a; Mellander, 1971b). During both sustained and intermittent isometric exercise there was no decrease in the blood flow through the forearm when the wrist-cuff was inflated. There are three possible explanations for this f'mding. First, we must consider the variation in blood flow measurements during exercise. At 20 ~ C, the standard errors of the mean for measurements of blood flow averaged 0.40 ml 9 min -1 9 100 m1-1 for the last 2 rain of exercise with the wrist-cuff, while at 40 ~ C they averaged 0.87 ml 9 min -1 9 100 m1-1. The average reduction in resting forearm flow following occlusion of the hand was 1.0 ml 9 rain -1 9 100 m1-1 in water at 20 ~ C and 1.5 m l . rain -1 . 100 m1-1 with the arm immersed in water at 40 ~ C. It is probable that the level of variation in the blood flows during exercise would obscure the effect of applying a wrist-cuff to arrest the hand circulation. Secondly, it is possible that the hemodynamic explanation proposed by Clarke and Hellon (1975) with regard to the resting forearm might also be applied to the exercising forearm. The increased blood flow through the forearm due to the exercise, which is directed to the active muscles but not the skin (Humphreys and Lind, 1963), would probably be great enough to reduce the entry of a high proportion of blood flow from the hand. This would certainly be a contributing factor if the venous effluent from the hand were directed to the deep veins of the forearm, but there is no direct evidence to demonstrate this. A hemodynamic explanation for the similarity of exercise flows with and without hand occlusion is supported indirectly by the agreement of the post-exercise volumes with and without hand occlusion. In addition, there were no reported differences in the measurements of calf blood flow during and after rhythmic exercise nor in the calculation of post-exercise hyperemia (Richardson, pers. commun.). Thirdly, it is possible that during sustained hand-grip contractions, there is a reduction in the volume of hand blood that is available to enter the forearm due to mechanical compression of the palmar skin against the poles of the dynamometer. If so, this would diminish or possibly even abolish the influence of occluding the circulation to the hand. However, since the blood flows measured between brief, intermittent contractions were also the same whether or not occlusion was applied at the wrist, this may or may not influence forearm blood flows in these circumstances. The results from this study indicate that inflation of an arterial occlusion cuff around the wrist is unnecessary when measuring forearm blood flows during isometric exercise. This applies whether the exercise is conducted in cold water, where skin flow is minimal, or in warm water, where skin flow is high.

References Bareroft, H., Edholm, O. G.: The effect of temperature on blood flow and deep temperature in the human forearm. J. Physiol. 102, 5-20 (1943) Clarke, R. S. J.: An investigation by new methods of the action of physical and chemical stimuli on human blood vessels. Thesis, Queen's University of Belfast, 1958

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Clarke, R. S. J., Hellon, R. F.: Venous collection in forearm and hand measured by the strain-gauge and volume plethysmographs. Clin. Sci. 16, 103-117 (1957) Clarke, R. S. J., Hellon, R. F., Lind, A. R.: Duration of sustained contractions of the human forearm at different muscle temperatures. J. Physiol. 143, 454-473 (1958) Coles, D. R., Cooper, K. E.: Hyperaemia following arterial occlusion or exercise in the warm and cold human forearm. J. Physiol. 145, 241--250 (1959) Cooper, K. E., Randall, W. C., Hertzman, A. B.: The vascular convection of heat from active muscle to overlying skin. A.F. Teclmical Report No. 6680, Part 7, Wright Air Development Center, Ohio, 1951 Grant, R. T., Pearson, R. S. B.: The blood circulation in the human limb's observations on the differences between the proximal and distal parts and remarks on the regulation of body temperature. Clin. Sci. 3, 119-139 (1938) Humphreys, P. W., Lind, A. R.: The blood flow through active and inactive muscles of the forearm during sustained hand-grip contractions. J. Physiol. 166, 120-135 (1963) Kerslake, D. Mck.: The effect of the application of an arterial occlusion ctfff to the wrist on the blood flow in the human forearm. J. Physiol. 108, 451-457 (1949) Lind, A. R., Williams, C. A.: The control of blood flow through human t'orearm muscles following brief, isometric contractions. J. Physiol. 288, 529-547 (1979) MeUander, S.: Effects of selected vasoactive agents on resistance exchange and capacitance vessels in skeletal muscle. In: Physiology and pharmacology of vascular neuroeffector systems, J. A. Bevan, R. F. Furchgott, R. A. Maxwell, A. P. Somlyo (eds.), p. 333. Basel: Karger 1971a Mellander, S.: Interaction of local and nervous factors in vascular control. Angiology 8, 187-194 (1971b) Mottram, R. F.: Blood flow and muscle contraction in the forearm. J. Physiol. 182, 27-28P (1965) Quinn, R. S.: Wrist cuffs for forearm plethysmography. J. Physiol. 179, 62-63P (1965) Shepherd, J. T.: Physiology of the circulation in human limbs in health and disease. London, Philadelphia: Satmders 1963 Shepherd, J. T., Vanhoutte, P. M.: Veins and their control, pp. 9 9 - I I2. London, Philadelphia: Saunders 1975 Whitney, R. J.: The measurement of volume changes in human limbs. J. Physiol. 121, 1-27 (1953) Whitney, R. J.: Circulatory changes in the forearm and hand of man with repeated exposure to heat. J. Physiol. 125, 1--24 (1954) Williams, C. A., Lind, A. R.: Study of metabolic and myogenic factors in post-contraction vasodilatation. Fed. Proc. 37, 654 (1978) Accepted July 27, 1979

Measurement of forearm blood flow by venous occlusion plethysmography: influence of hand blood flow during sustained and intermittent isometric exercise.

E u r o p e a n J o u r n a l of Applied Physiology Eur. J. Appl. Physiol. 42, 141--149 (1979) and Occupational Physiology 9 Springer-Verlag 1979...
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