Control of Blood Flow to the Extremities
`at Low Ambient Temperature:
`
`S. I. RAPAPORT‘, E. S. FETCHER, H. G. SHAUB, AND J. F.
`HALL. From the Aero Medical Laboratory, Wright-Patterson Air
`Force Base, Dayton, Ohio
`
`118 STUDY was undertaken to explore the extent of autonomic control
`
`of blood flow to the hands and feet. That is, to examine the question—is blood
`flow to the hands and feet at low ambient temperatures still regulated by
`the thermal state of the body as a whole, or is blood flow to the hands and
`feet determined by the known direct constricting effect of cold upon their
`blood vessels? Since the experiments of Sir Thomas Lewis in r931 (I) there has
`been a growing understanding that vasodilatation may be produced in the
`extremities by heating other body areas. An intact sympathetic outflow to
`the extremity has been shown to be necessary for this reaction (I, 2). Pickering
`(3) suggested that the vasodilatation is the response to the circulation of
`warmed blood through the central nervous system, since it does not occur when
`the part heated is small or its circulation occluded. These observations have
`been confirmed repeatedly (4, 5). Recently, Miller has been able to prevent
`freezing of the rabbit’s ear for two hours at — 55°F. by warming the animal’s
`body (6). The experiments reported herein reveal that a similar protection is
`available to the extremities of man. Inversely, Ferris and his co-workers (7) in
`particular have demonstrated that when the body is cooled, heating only the
`hand will not increase its blood flow over that of a non~heated hand.
`
`The experiments were planned to investigate these specific points: a) The
`efiect upon hand and foot temperatures of variation of heat supplied to the
`rest of the body. b) The efiect of warming the body upon the temperature of
`extremities which had become cold. c) The differences in the temperature re-
`sponses between the hands and feet. d) The cficct upon hand temperature of
`a sudden increase in the cold stimulus applied to the hand when the body
`is warm.
`
`METHODS
`
`The main series of experiments was conducted at controlled ambient tem-
`peratures of about 0, — 20 and — 30° F. in a cold room. Four young adult males
`
`served as subjects. They sat quietly throughout the experiments. The duration
`
`Received for publication March 2, 1949 .
`1 Present address: Birmingham Veterans Administration Hospital, Van Nuys, California.
`61
`
`APLl 108
`
`Apple V. Valencell
`IPR2017-00317
`
`APL1108
`Apple v. Valencell
`IPR2017-00317
`
`

`

`62
`
`RAPAPORT, FETCHER, SHAUB AND HALL
`
`Volume:
`
`of the experiments was two hours or longer, unless there was rapid cooling of
`the extremities. The method of circulating air beneath clothing described in
`the preceding paper (8) made it possible to supply the body with as much or as
`little heat as was desired. It also permitted measurement of the rate at which
`heat was being supplied to the body, AH.'/t; and of the rate at which heat
`should be supplied or removed to maintain thermal equilibrium of the man:
`the ‘steady state heat surplus’ or Qo’/t. A comparison of the two gave a quanti-
`tative evaluation of the thermal state of the body, within about IO Cal/hr.
`Methods for the determination of these and other variables are outlined in
`
`the preceding paper and detailed in (9). The hands and feet received no arti-
`ficial heat, being separated from the ventilating circuit by air-tight wristlets
`and anklets. These parts were heated only from their blood supply. Therefore,
`changes in their temperature indicated alterations in their blood flow. The
`thermal stress upon the body and the thermal stress upon the hands and feet
`could be varied independently; the former by variation of the hot air supply,
`and the latter by variation of the ambient temperature and insulation.
`Average hand and average foot temperatures were measured by thermo-
`couples connected in parallel. Those for the hand were located upon the ball
`of the first, third, and fifth fingers, and the palm and dorsum of the hand.
`Those for the foot were placed upon the ball of the great toe, the heel, the
`dorsum of the foot at the base of the first and fifth toes, and the dorsum of the
`foot just below the lateral and medial malleoli. Heavy footgear (insulation
`equivalent to 2.6 clo) and intermediate weight gloves (LO equivalent do)
`were worn. In some experiments one glove was replaced with a rayon insert
`(0.25 clo) and in others, one hand was bated.
`To extend the studies upon the fourth point, above, a. supplementary
`series of experiments was performed in which the bare hand was put into a
`cold box. Each experiment consisted of two periods. In the first, the subject
`lay quietly in the nude at an ambient temperature of 65 to 74° F. for approxi-
`mately 45 minutes, or until toe temperature approached within about 5° F. of
`the ambient temperature. With the body so cooled, one hand was inserted in
`the cold box and average hand and finger tip temperatures recorded. In the
`second period, the body was overheated by the use of an electrically heated
`blanket. When the subject was sweating, and the temperature of the toe of the
`uncovered foot had risen from about room temperature to above 89° F., the
`hand was again placed in the box and its temperature response followed.
`
`RESULTS
`
`Eject upon Hand and Foot Temperatures of Variation of Heat Supplied
`to the Rest of the Body. In 16 experiments over the temperature range from
`o to — 30° F., it was found, without exception, that when the heat supplied
`was equal to or greater than the amount necessary for thermal equilibrium,
`
`

`

`[11414311949
`
`BLOOD FLOW IN THE EXTREMITIES
`
`63
`
`the average temperature of the hands and feet was maintained above minimum
`comfort level (70° F.). But, whenever the heat loss exceeded the heat supply
`by more than about I 5 per cent both the hands and feet became cold, an indi-
`cation of vasoconstriction. These experiments are summarized in table I.
`Experiments listed as A and B were performed consecutively upon the same
`subject. In this table, To is operative temperature. The values for AH,’/t and
`Qa'fl are corrected to a standard surface area, and, for reasons mentioned in
`the previous paper, are for the body excluding the head. It is to be noted that
`the diflerence Qa"/t — AH.,'/t is positive when there is an excess of heat sup-
`plied to the clothing, that is, when the body does not need to conserve heat;
`and negative when there is a net heat loss. The column headed ‘% Difl.’ is
`Qu’/t — AH.’/t
`calculated from ———-— X 100.
`Qa”/t
`The temperatures of the hands and feet in two experiments upon the same
`subject at 0° F. are shown in figure
`10-0.;
`sum. an
`I, which illustrates the main fea-
`m 7-:5 -I.O°F
`exp b-TA +30%:
`tures of the data of table I. In ex-
`
`periment 7-15, there was a net heat
`loss from the body of 72 Cal/hr.
`
`[00
`
`(41% ofQa'/t). Thehandsandfeet ”Em
`
`Fig. r. HAND AND room Tannmmns under
`conditions of thermal equilibrium and of high heat
`1:1,: :2? Eggg‘fafifiégzg M m equwalent
`
`Efi'ect of Warming the Body
`upon Cold Extremities. In four out
`Of
`five eXperimentS: exuemjties
`which had become COld could be
`rewarmed by heating just the body.
`One of the four is illustrated by
`figure 2, the graph of an experiment at 0° F., in which no heat was supplied
`for 45 minutes. Average hand temperature fell to 61° F. (finger tip tempera-
`ture of 53° F.) and average foot temperature from 93 to 86° F. Heating was
`then begun, which reduced the net heat loss rate to I 5 Cal/hr. Average hand
`temperature began to rise almost immediately and reached 90° F. within 55
`minutes. Average foot temperature, however, continued to fall to 75° F. After
`
`cooled rapidly; within 90 minutes
`hand temperature was 60° F. and
`the hands were painfully cold. Foot
`temperature dropped to approxi-
`mately 75° F. In experiment 8-7A,
`the heat supply equalled the heat
`loss. Average hand and foot tem-
`peratures were maintained above
`90° F.
`
`“
`
`‘""
`
`
`
`

`

`64
`
`RAPAPORT, FETCHER, SHAUB AND HALL
`
`Volume:
`
`85 minutes, and concomitant with a reduction in the net heat loss rate to 6
`Cal/hr., the average foot temperature began to rise and was 89° F. when the
`experiment was terminated. In one experiment at -- 30° F. ambient, the hand
`did not rewarm in spite of a heat excess of 39 Cal/hr. supplied to the body.
`Diflerences between Temperature Response of Hands and Feet. When the
`heat supplied to the system exceeded heat loss, both the hands and feet were
`kept within the comfort range, that is above 70° F. In general, however, the
`average temperature of the feet was lower than that of the hands despite the
`greater insulation of the footgear. The difierence varied from about 5° F.
`(exper. 8—7A, fig. 1; expers. 9-9 and 9-10, table I) to 10 or 20° F. (expers. 8-5A,
`
`EXP lO-27
`To-O'F SUBJEJ?
`
`0—0—0 - HAND ind-d -FOOT
`
`c.
`l
`a.
`|
`“wt-o IOV'A'MO-ECALJI-R. loam-e
`
`
`
` A
`
`. Illldfliy
`naulnlmgau
`IIEMIIUIII
`
`
`
`
`
`
`
`
`
`Fig. 2. Enact: or “WARMING the cooled body on hand and foot temperatures.
`
`8-27, and 9-17, table I). When the net heat loss from the system was large,
`both the hands and feet cooled; but the rate of cooling of the hands was greater
`than that of the feet (exper. 7-15, figs. 1, 2). Since, in this circumstance, the
`blood vessels of both the hands and feet are constricted, the slower fall of foot
`temperature is the result of the heavier insulation of the footgear, and the
`smaller surface area per mass of the foot.
`During the latter part of an experiment (8-5) at 0° F. there was a small
`net heat loss which resulted in a fall of average foot temperature but not of
`average hand temperature. In period A (see table I), a slight excess of heat
`was furnished; average hand temperature was maintained at about 90° F.
`and average foot temperature at about 82° F. In periods B and C, the heat
`supply was reduced so that deficits were 17 and 21 Cal/bra, respectively (less
`
`

`

`AugusI1949
`
`BLOOD FLOW IN THE EXTREMITIES
`
`65
`
`than 10% of Qa’fl). Average hand temperature continued above 90° F., but
`average foot temperature fell to 65° F. in about 3% hours.
`When the body was heated after the extremities had been allowed to be-
`come cold, foot temperature continued to drop until the hands had completely
`rewarmed. Figure 2 shows an 8 5-minute lag between the initial rise in hand and
`foot temperatures. Only a very small part of this lag can be attributed to the
`
`TABLE I. SUMMARY OF EXPERIMENTS SHOWING EFFECT OF VARIATION OF HEAT SUPPLIED
`T0 BODY
`
`
`am:
`
`'
`
`L M! '7 our
`('F.)
`(cu/n.)
`°
`
`‘
`
`nmn‘mu newness or HANDS AND rut
`
`7-15
`
`8-7A
`8-78
`
`7-29A
`
`7-29B
`
`8-5A
`
`10-21
`7-31
`8-14
`8- 25
`
`- 1
`
`+3
`+ 2
`
`+1
`
`+ 1
`
`+ 2
`
`+4
`+4
`— 17
`- 19
`
`8-27A
`
`— 20
`
`8-27B
`
`9-9
`
`9-10
`9-1 7
`
`1 1-4
`
`- 21
`
`- 31
`
`—- 31
`—3 1
`
`-31
`
`— 72
`
`—3
`—3o
`
`- 26
`
`~41
`
`+20
`
`+10
`+25
`+42
`+ 28
`
`— 52
`
`+10
`
`+33
`
`+ 19
`+32
`
`+ 13
`
`- 41 Hand temperature fell to 60°F. in 90 min.
`Foot temperature fell to 75°F. in 90 min.
`— 1 Hand and foot temperature kept above 90°F.
`— 15 Hand temperature maintained above 85°F. Gradual
`{all of foot temperature to 75°F. in 2 hrs.
`- 13 Hand temperature fell to 60°F. in 60 min.
`Slow fall of foot temperature to 79°F.
`Electrical heating of hands necessary. Gradual {all of
`foot temperature to 60°F. in 2} hrs.
`+10 Hand temperature kept at 90°F., foot
`above 80°F.
`
`temperature,
`
`— 20
`
`+6 Hand and foot temperature kept above 85°F.
`+1 1 Hand and foot temperature kept at approx. 87°F.
`+ 16 Hand and foot temperature kept at approx. 85°F.
`+ 1 1 Hand temperature kept at about 80°F., foot tempera-
`ture, at about 82°F.
`— 20 Hand temperature fell to 64°F. in 25 min; foot tem-
`perature, to 78°F.
`+5 Hand temperature rose to 90°F., foot temperature kept
`at about 70°F.
`+ I: Hand temperature kept above 90°F., foot
`ture, above 85°F.
`+7 Hand and foot temperature kept between 84—90°F.
`+ 12 Hand temperature kept above 90°l"., foot
`tempera-
`ture, about 70°F.
`+5 Hand and foot temperature kept above 85°F.
`
`tempera-
`
`greater heat capacity of the footgear: about one Calorie is required to rewarm
`the boot.
`
`Eject of a Sudden Increase in Cold Stimulus Applied to the Hand. The
`efiect of a sudden increase in the cold stimulus applied to the hand when the
`body was warm was observed in IO experiments by removing one glove within
`a cold room, and in 9 more by inserting a bare hand into a cold box while the
`body was heated. The former are summarized in table 2. In most of these,
`the assembly received slightly more heat (10 to 38 Cal/hr.) than was calculated
`as being lost. In several, a thin rayon insert was substituted for the glove,
`
`

`

`66
`
`RAPAPORT, FETCHER, SHAUB AND HALL
`
`Volume 2
`
`but in others the hand was bare. There were three experiments (nos. 8—25,
`9-10, and 9-17 first period) in which the temperature of the hand fell rapidly
`requiring termination within 20 minutes. However, in subsequent trials using
`the same subjects, hand temperatures were maintained at or above 70° F.
`In experiments 10-27 and 10-30 hands stayed warm in spite of a heat deficit
`of 8 and 20 Cal/hr.
`Hand temperature fell to about 55° F. when the glove was removed in
`experiments 10-28, and was maintained there for 60 minutes. It was then dis-
`covered that the tube supplying air to the trunk was disconnected. After it
`
`TABLE 2. SMARY OF EXPERIMENTS IN WHICH ONE GLOVE ‘VAS REMOVED IN A COLD BOOK
`
`emu. E
`('F.)
`
`
`msm'norr 9M zmcr upon .wmo: mm remnm
`(cu/n.)
`
`10-21
`
`10-27
`
`10-28
`
`0
`
`0
`
`0
`
`Hand bare
`
`Hand bare
`
`Hand bare
`
`8-25 —2o
`
`Hand bare
`
`8-27 —20
`
`Rayon insert
`
`—30
`9-9
`9-ro —3o
`
`Rayon insert
`Rayon insert
`
`947 —30
`
`Rayon insert
`
`ro-30 —30
`
`Hand bare
`
`1 1-4
`
`— 30
`
`Hand bare
`
`+ro
`
`-8
`
`—
`
`+38
`
`+r0
`
`+33
`+19
`
`+32
`
`—20
`
`+ :3
`
`
`
`Initial fall to 73° F., then rise to 85° F.
`for 50 min.
`Maintained between 70 and 80° F. for
`95 rnin.
`Fell to 55° F. for 60 min. but rose to 78°
`F. when heat to body increased.
`Rapid fall, hand painfully cold after
`min.
`
`Fell to 60° F. in r 5 min., then rose to
`above 70° F. for 30 min.
`Maintained at about 85° F. for 50 min.
`Fell within 10 min. to 40 and 47° F.,
`respectively on two trials, but each
`time returned to above 85° F. when
`glove replaced.
`Fell on first trial to 50° F. within 20 min.
`Maintained between 70 and 80° F. for
`50 min. on second trial.
`Maintained between 77 and 84° F. for
`60 min.
`
`Maintained at about 70° F. for 60 min.
`
`was reconnected, hand temperature rose to 78° F. in 22 minutes. In the re-
`maining experiments, the temperature of the exposed hand was maintained
`above 70° F. for an experimental period of from 45 to 95 minutes. Two experi-
`ments at — 30° F. are illustrated in figure 3. In both instances the temperature
`of the bare hand was maintained above 70° F. for 60 minutes, and the exposure
`probably could have continued.
`Data from the experiments in which the bare hand was placed in a cold
`box are presented in table 3. The temperature of the box air, Ta , was 0° F. in
`the first three experiments, and — 30° F. in the others. Both average hand and
`fingertip temperatures were measured, but only the temperature of the tip
`of the fifth finger, T“ , is given in the table. In that part of the experiment in
`
`

`

`Augm11949
`
`BLOOD FLOW IN THE EXTREMITIES
`
`67
`
`which the hand rapidly became cold, T15 was usually about ro° F. below average
`hand temperature at the end of the exposure. When the body was heated and
`hand temperature maintained at comfort level, T”, was generally about 5° F.
`higher than average hand temperature. However, on occasions, the difference
`was as little as I or 2° F., or as much as 10° F. The time given in the table is
`minutes of exposure. The temperature given at zero minutes was measured just
`before the hand was placed in the box.
`With the box at 0° F. and the body cooled, finger temperatures fell to
`about 40° F., and the hand was painfully cold, within six minutes. With the
`box at — 30° F., the duration of exposure with the body cooled was reduced
`to two to four minutes. (In one experiment in which the body was only slightly
`chilled the duration of exposure was 1’ 3 minutes). In contrast, when the body
`
`To I-30‘F
`
`EXP ”'4— SUBJ. EP
`EXPD‘x‘SUE-l SR.
`06' 7t-AHv1t--20CAL.IFR Oa’lt-AHv’lt-flfi CAL. [Hi
`'—‘—° — HAND
`°-—°—-° — HAND
`
` 20 30 40
`
`
`20o
`l0
`MNUTES
`
`Fig. 3. THE BARE RAND is kept warm at —3o°F. if the body is warm.
`
`was heated in the three experiments at 0° F., finger tip temperatures were sus—
`tained above 70° F. throughout an experimental period of 40 to 60 minutes.
`When the hand was placed in the box at - 30° F. with the body heated, finger
`tip temperatures were maintained above 70° F. for 50 to 60 minutes in five
`experiments. In a. first trial upon S.F., the hand had to be removed from the
`box after 10 minutes. In a second trial, begun a few minutes later, finger tip
`temperatures were maintained at comfort level for fifty minutes. At the end
`of that time, however, the hand again became cold. In an experiment upon
`H.S., skin temperatures were maintained for 30 minutes and then suddenly
`began to fall. In the remaining experiments there was nothing to indicate that
`the exposure could not have been continued. The experiment upon G.H. is
`worthy of comment in that at -— 30° F. finger temperature rose to 98° F. and
`
`

`

`68
`
`RAPAPORT, FETCHER, SHAUB AND HALL
`
`Volume 2
`
`was maintained at that level. As the hand was withdrawn from the box, it
`was noted to be actively sweating. In general, the hand remained comfortable
`in the box at —30° F. whenever finger-tip temperatures were above 70° F.;
`but occasionally a subject complained of coldness of the skin overlying the
`knuckles or along the sides of the hand.
`
`DISCUSSION
`
`These experiments clearly demonstrate that, at least to — 30° F., regulation
`of the blood flow to the hands and feet is primarily determined by the thermal
`state of the body as a whole. Vasoconstriction need not occur provided the body
`does not have to conserve heat. Under conditions comparable to these experi-
`ments, artificial heating of the hands and feet is unnecessary; they will be
`adequately heated by their blood supply. However, the supply of a quantity of
`
`TABLE 3. 50mm! 02‘ COLD BOX EXPERIMENTS PERIOD OF BODY HEATING
`zmsm run: (mm)
`:xrosnur mu (Km)
`
`SUBJECT
`
`Ta. '17-
`
`o l rolaolsolaolsolw
`T’r. 'F.
`
`sum
`
`Ta. °F-
`
`0 lmlaolso wlso|6c
`
`'17
`T];
`
`S.R.
`[1.5.
`1.3.
`5.F-
`S.F.
`
`o
`o
`o
`~30
`—3o
`
`96 82 82‘78 74
`95 87 87 848084
`93 79 73 79 76 75 82
`95 53
`96 77 79 79 81 75
`
`S.R.
`11.5.
`G.H.
`BL
`RS.
`
`—3o — 75 76 72 77 77 78
`—3o
`93 75 72 67
`-3o 96 88 Sr 95 98 98 98
`-3o 94 87 8a 79 8° 74 7s
`
`
`-30 97 84 86 878687
`
`heat which is large but still not equal to that being lost was usually as in—
`efiective in preventing vasoconstriction and subsequent cooling as the failure
`to supply any heat at all. Thus, the hands and feet became cold in those experi-
`ments in which there was a net heat loss of greater than about 15 per cent.
`This observation is confirmed by the example of the electrically heated flying
`suit, in which failure of the power supply to a glove or boot insert will result
`in rapid cooling of the affected extremity despite the considerable amount of
`heat being supplied to the rest of the body. It would appear that cooling of
`the extremities may be used as an indication in many conditions that the
`amount of heat available is insuflicient, that is, that the body is attempting
`to conserve heat.
`
`The experiments in which the extremities were rewarmed demonstrate
`that adequate heating of the body not only can prevent peripheral vasocon-
`striction, but often can reopen constricted vessels in cold extremities. After
`a fall to 55 to 60° F., hand temperature may return to control level in 20 to so
`minutes. No satisfactory explanation can be offered for the failure of the ex-
`
`

`

`August 1949
`
`BLOOD FLOW IN THE EXTREMITIES
`
`69
`
`tremities to rewarrn in one experiment. It emphasizes the need for further
`study. It would also be desirable to know if the extremities could be rewarmed
`by this method after they had been allowed to cool to temperatures just above
`freezing.
`It is a common experience for the feet to feel cold while other body areas
`are comfortable. The data of Roth, Horton, and Sheard (Io) demonstrate that
`the temperature of the toes is the first to drop when the nearly nude body starts
`to cool and the last to rise when it is warmed. The difierences in the tempera-
`ture response between the hands and feet in our experiments are in agreement
`with this observation. In the rewarming experiments, average foot tempera-
`tures continued to fall until hand temperatures had returned to normal.
`That the temperature of the bare hand at — 30° F. was sustained above
`70° F. is striking evidence that the vasoconstrictive effect of severe cold is sub-
`ordinate to the autonomic control of blood flow in the hand. This is not to
`
`say that the cold stimulus is without effect. Hand temperature invariably fell
`5 to 25° F. when the glove was removed or the hand inserted into the cold box.
`The hand did not show the deepening of color and reddening, which is usually
`seen when skin is exposed to cold. The reason for the failure of the hand tem-
`perature to stabilize in three experiments in the cold room and in one cold box
`experiment is not known. In two of these experiments, the temperature of a
`finger on the opposite hand, the one which had remained gloved, also dropped
`sharply (from 88° F. to 65° F. in one experiment and from 90° F. to 58° F. in
`the other). It is our impression that tenseness or anxiety about the experi-
`mental procedure contributed to the vasoconstriction. That emotions of this
`nature may be accompanied by peripheral vasoconstriction is generally recog-
`nized. Of practical importance was the fact that replacement of
`the glove
`brought about a prompt return of hand temperature to comfort level. Increased
`air movement and contact with solids have not been considered; these factors
`would increase the rate of heat removal from the hand.
`
`The experiments in which the glove was removed in the cold room differed
`from the cold box experiments in one important respect. In the former there
`was little or no heat excess supplied to the body; in the latter, there was definite
`overheating and considerable sweating. The fact that hand temperatures were
`sustained in both circumstances indicates that overheating is not essential to
`sustain blood flow through the non-heated extremity at temperatures down
`to -30° F.
`The purport of these results is that the temperature of the extremities can
`be made nearly independent of the ambient temperature and of insulation over
`a wide range; and dependent primarily upon the thermal state of the body as
`a whole. The practical implications are many. For example,most electrically
`
`

`

`7O
`
`RAPAPORT, FETCHER, SHAUB AND HALL
`
`Volume 2
`
`heated clothing supplies large amounts of heat to the hands and feet. Rela-
`tively more of the heat is wasted from these areas than from the trunk and
`limbs because of the lesser insulation of the gloves and boots, and the position
`of the heating elements. Transfer of this heat to the trunk and limbs might
`make such clothing more eflicient, cheaper to manufacture, and more durable.
`The importance of keeping the whole body warm in the prevention of frostbite
`is readily apparent. These results also emphasize the importance of supplying
`heat to the whole body, rather than to the affected part alone, in the relief of
`the vasospasm associated with most peripheral vascular disorders.
`Attempts to induce rapid adaptations or modifications of human physi-
`ology to meet high environmental stresses have been generally unsuccessful.
`The observation that extremity temperature can be made relatively inde-
`pendent of the environmental temperature does offer the possibility of practical
`control of a physiological response. Many problems, theoretical and practical,
`remain to be solved. Among the more important are a) the analysis of the
`mechanisms; b) the extent of individual variation; 6) the relative importance of
`thermal level as compared with the rate and direction of thermal state change;
`and d) the establishment of the lower limits of control.
`
`CONCLUSIONS
`
`The regulation of blood flow to the extremities at low ambient tempera.
`tures is primarily determined by the thermal state of the body as a whole,
`Experiments in which the bare hand was exposed to temperatures of
`o to — 30° F. clearly demonstrate that the vasoconstrictive effect of severe cold
`is subordinate to the autonomic control of blood flow in the extremities, since
`hand skin temperature could be sustained above 70° F.
`Therefore, the temperature of the extremities can be made nearly inde-
`pendent of the ambient temperature and of insulation, over a wide temperature
`range; and dependent primarily upon the thermal state of the rest of the body.
`Under conditions comparable to these experiments, artificial application of
`heat to the extremities is unnecessary for their comfort.
`
`It is our privilege to acknowledge the guidance and encouragement so freely given us by
`Lt. Col. A. P. Gagge and Dr. J. W. Heim; and to own our indebtedness to Capt. R. B. Dorn,
`Miss Patricia Taylor and Lt. E. R. Pullis.
`
`REFERENCES
`
`I. LEWIS, T. AND G. W. PICKERING. Heart 16: 33, 1931.
`2. FREEMAN. N. Am. J. Physiol. 113: 384, 1935.
`3 . PICKERING, G. W. Heart 16: 115, 1932.
`4. LANDIS, E. M. AND J. H. GIBBUN. J. Clin. Investigation 11: 1019, x932
`5. MARTINEZ, C. AND M. B. Vrsscm-m. Am. J. Physiol. 144: 742, 1945
`
`

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`6. MILLER, M. R. Air Univ. School of Aviation Medicine, Randolph Air Force Base, Texas.
`Project 490, Report 1, 1947.
`. leuus, B. G., 111., R. E. Fonsn‘n II, E. L. PILLION AND W. R. CHRISTENSEN. Am. J.
`Physiol. 145: 218, 1945.
`. FETCHER, E. S., S. I. RAPAPORT, J. F. HALL AND H. G. SHAUB. J.Apph'cd Physiol. 2:49,
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`. FETCHER, E. S., S. I. RAPAPORT, AND J. F. HALL. USAF Tech. Rept. 5702, May 1948.
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`Ron-1, G. M., B. T. HORTON, AND C. 81mm. Am. J. Physiol. 128: 782, 1940.
`
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