Eur J Appl Physiol (2007) 102:73–78

DOI 10.1007/s00421-007-0566-9

ORIGINAL ARTICLE

Cold-induced vasodilatation in the foot is not homogenous or trainable over repeated cold exposure

Luke F. Reynolds · Igor B. Mekjavic · Stephen S. Cheung

Accepted: 3 September 2007 / Published online: 22 September 2007© Springer-Verlag 2007

Abstract Cold-induced vasodilatation (CIVD) is pro-posed to be a protective response to preserve tissue integ-rity in the extremities during cold exposure, but littleresearch exists on either the trainability or the spatial pat-tern of CIVD response in the foot. We investigated the ther-mal response across the foot with repeated cold exposure.Ten healthy subjects immersed their left foot to the ankle in8°C water for 30 min 5 days/week for 3 weeks. Skin tem-perature was recorded on the medial side of the nail bed ofthe 5 toes and the dorsum of the foot. The presence ofCIVD, deWned as an increase of 1°C at any time duringcooling, was rare with our protocol. While a CIVDresponse was observed at least once in 8 of the 10 subjects,only 122 instances of CIVD were observed out of a total of900 possible observations (10 subjects £ 6 sites £ 15trials). Furthermore, thermal habituation was not evi-dent, with toe temperatures at the end of each immersion(8–11°C) remaining near water temperature throughout the15 sessions. Even within the two subjects exhibiting the mostincidence of CIVD, high variability existed in the occur-

rence, magnitude, and/or onset times. Synchronicity wasoften observed where more than one toe exhibited CIVD,though the magnitude varied greatly (range 1–9°C). Weconclude that, under realistic conditions of whole-footimmersion in cold water, CIVD is not a common or train-able response.

Keywords CIVD · Cold water immersion · Adaptation

Introduction

Shortly upon exposure to cold environments, skin tempera-ture of the extremities can rapidly increase and decrease ina cyclic fashion. This cold-induced vasodilatation (CIVD)phenomenon was Wrst reported by Lewis (1930) in theWngers, and has been presumed to perform a cryoprotectivefunction to maintain tissue integrity and minimize the riskof cold injuries. Since this initial report, the vast majority ofCIVD research has been performed on the hands (Daanen2003), though CIVD has also been observed in the face(Brajkovic and Ducharme 2006), forearm (Ducharme et al.1991), and feet (GreenWeld et al. 1951). Few researchershave studied the response of the foot or toes to acute orrepeated cold exposures, despite it being the dominant sitefor actual cold injuries. For example, Daanen and van derStruijs (2005) reported 41, 14, and 2 cases of cold injuriesto the feet, hands, and head, respectively, in a group of sol-diers operating in Arctic terrain. In contrast, 29 studieswere found on PubMed (December 10, 2006) using thesearch terms “Hand and CIVD” while only 2 studies werefound with the search terms “Foot and CIVD.”

An intensiWed CIVD response has been reported in pop-ulations regularly exposed to cold during work (Leblanc1962; Leblanc et al. 1960; Nelms and Soper 1962) or

L. F. Reynolds · S. S. CheungEnvironmental Ergonomics Laboratory, School of Health and Human Performance, Dalhousie University, 6230 South St., Halifax, NS B3H-3J5, Canada

I. B. MekjavicDepartment of Automation, Biocybernetics and Robotics, Jozef Stefan Institute, Jamova 39, Ljubljana 1000, Slovenia

S. S. Cheung (&)Department of Physical Education and Kinesiology, Brock University, 500 Glenridge Ave., St Catharines, ON L2S-3A1, Canadae-mail: stephen.cheung@brocku.ca

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everyday living (Miller and Irving 1962) compared to con-trol populations, leading to a presumption that CIVD is atrainable response. Leblanc (1960) found that a group ofGaspé Wsherman who were acclimatized to cold waterimmersion had an increased CIVD response compared to anon-acclimatized group, while Krog et al. (1960) observedan earlier CIVD onset time in Lapps and North NorwegianWsherman. Longitudinal acclimatization studies presentequivocal results, with an improved CIVD response andperipheral blood Xow in tropical inhabitants after sevenweeks of exposure to the arctic environment (Purkayasthaet al. 1992), but also an increased vasoconstrictive tone fol-lowing two weeks of cold exposure in Canadian soldiers(Livingstone 1976). In laboratory studies, four dailyimmersions of the index Wnger in ice water for a monthelicited faster onset of CIVD and a decrease in pain in theindex Wnger compared to non-trained digits (Adams andSmith 1962), suggesting adaptations via local mechanisms.However, Geurts et al. (2005) found lower mean and mini-mum Wnger temperatures and also delayed onset time overthree weeks of daily 30 min hand immersion in 8°C water,suggesting that the risk for cold injuries actually increaseswith repeated cold exposures.

Therefore, the primary objective of the present studywas to investigate the trainability of CIVD in the foot in acontrolled laboratory setting by tracking the foot’s thermalresponses over 15 days of repeated local immersion in cold(8°C) water. A secondary objective was to test the spatialand temporal homogeneity of the CIVD response across thedigits of the foot. Our null hypotheses were that: (1) CIVDwould be similar in frequency, magnitude, onset tempera-ture, and onset time over the acclimation period, and (2)CIVD prevalence, magnitude, and onset time and tempera-ture would occur in a homogenous pattern across the digitsand dorsum of the toe.

Methods

Subjects

This study was conducted following the Canadian Tri-Council Policy for the ethical treatment of human partici-pants as part of the Helsinki Declaration II and approvalwas obtained from the appropriate institutional researchethics board at Dalhousie University. Prior to data collec-tion, each subject was given a clear description of what wasrequired for participation and then asked to carefully readand sign the consent form. Five healthy adult males, aged22–26, and Wve healthy females, aged 19–24, volunteeredto participate in the experiment. All subjects were non-smokers, were not on any medications, did not suVer fromRaynaud’s Syndrome, and were right foot dominant. Data

collection occurred during September and October to avoidacclimatization to either sustained ambient heat or coldexposure.

Experimental design

The acclimation protocol consisted of subjects resting in aseated posture and immersing their left foot to the ankle in astirred 8°C water bath for 30 min 5 days/week for 3 weeks.Tests were performed in a laboratory maintained at »22°Cand »40% relative humidity. For each subject, all testswere performed at the same time of the day, and 250 mL offruit juice was provided upon arrival. Tympanic tempera-ture was measured using an infrared thermometer (Thermo-scan IRT 3020, Braun, Kronberg, Germany) upon thecompletion of instrumentation.

Breathable surgical tape (Tegaderm, 3 M Health Care, StPaul, USA) was used to lightly tape thermistors (MA-100,Thermometrics, Edison, NJ) to the medial aspect of the nailbed of all Wve toes and the dorsum of the foot. A data log-ger (Smartreader 8 Plus, ACR, Vancouver, Canada) wasused to collect temperature values every 8 s.

Upon instrumentation and baseline recording, initialvasodilatation and a consistent starting foot temperaturewas achieved by placing the left foot up to the medial mal-leolus into 35°C water for 5 min. The foot was then trans-ferred to 8°C water for 30 min, followed by a Wnal 5 minrecovery period in ambient air temperature. During the pro-tocol, the foot was enclosed in a loose-Wtting thin plasticbag to minimise the risk of water loosening the thermistors.Non-immersed extremities were maintained in a normalresting position with minimal movement throughout theprotocol.

Data analysis

For each measurement site, minimum skin temperature(Tmin) was deWned as the lowest skin temperature observedover the 30 min and mean skin temperature (Tmean) was cal-culated from 5–30 min of foot immersion in 8°C water. Noclear consensus is present on the threshold rise in tempera-ture required to ascertain a CIVD incidence, so we chose todeWne CIVD relatively liberally as an increase in digit/siteskin temperature >1°C. We further categorized CIVD aseither “weak” (between a 1.0 and 2.0°C increase) or“strong” (>2.0°C). Onset time and onset skin temperaturefor each CIVD were determined at the initiation of skintemperature rise, and the amplitude was determined fromthe skin temperature at onset to the peak temperature of therise. To examine the time course of adaptation, the acclima-tion period was separated into four days (days 1, 5, 10, and15) and repeated measures ANOVA was performed onSPSS (14.0.1, SPSS, Chicago, IL, USA) software at an

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alpha level of 0.05. All results are presented as mean (SD)unless otherwise noted.

Results

Baseline tympanic temperature did not change betweendays 1, 5, 10, or 15 in either the females alone or in theentire group, ranging from 36.2–36.3°C. For all subjects(i.e., regardless of presence or absence of CIVD), tempera-ture responses followed a general exponential decay pat-tern. Minimum skin temperature at each of the sixmeasured sites were similar at days 1, 5, 10, and 15 (Fig. 1),with minimum digit temperatures at the toes all remaining<11.5°C. Similarly, mean toe temperature also were similarat days 1, 5, 10, and 15, remaining <13.5°C for all toes.Dorsum minimum and mean temperatures were slightlyhigher than the values of the digits during the middle phaseof the acclimation period, but mean temperature remained<15°C.

Over the course of the 15 cold exposure sessions for all10 subjects, 122 instances of CIVD were observed at the 6

measured sites out of 900 total possible CIVD opportuni-ties. Eight of ten subjects exhibited at least one CIVDresponse during the 15 days of exposure although themajority of responses came from 2 individuals. The preva-lence of CIVD tended to decrease over the course ofrepeated exposures, with 43% of the 122 total instances ofCIVD occurring on days 1–5, 32% on days 6–10, and 25%during the last 5 days (Table 1). Although the frequency ofCIVD decreased over the course of repeated cold expo-sures, this was not compensated by systemic changes inoverall thermal responses at the foot such as mean and min-imum temperatures (Fig. 1).

The characteristics of the CIVD response with our proto-col are presented in Tables 2, 3 and 4. Although the magni-tude of CIVD responses varied from 1 to 10°C, 86% of theresponses were between 1 and 4°C, with 25% of the totalCIVDs being weak (<2°C) responses (Table 2). Overall, themean magnitude of all observed CIVD was 3.1 (1.8)°C. NodiVerences in magnitude were observed over the three Wve-day periods, with magnitudes of 3.2 (1.7), 3.2 (2.0), and 2.7(1.6)°C, respectively. The majority of CIVD responses wereinitiated at skin temperatures between 8 and 13°C butranged widely from 7 to 28°C, with 19 CIVD responsesoccurring at onset temperatures above 15°C (Table 3).Onset temperature was 12.4 (4.4)°C for all CIVDs, withsimilar responses over the three 5-day periods at tempera-tures of 11.5 (2.6), 13.4 (5.4), and 12.7 (5.2)°C, respectively.CIVD onset was approximately evenly spread throughout

Fig. 1 Minimum (a) and mean (b) skin temperature values for the 5digits and the dorsum of the left foot at days 1, 5, 10, and 15 of accli-mation

Table 1 Prevalence of cold-induced vasodilatation (CIVD) responsesover 15 trials in all digits of the foot (digit 1 = big toe) and the dorsum

Subject numbers (1–10) are used to represent a single CIVD responseon a respective day. For example, during Trial 1, Subject 7 exhibited aCIVD for digit #1 and #2

Multiple numbers represent two or more CIVD at that measurementsite. In total, there were 122 CIVD responses out of 900 measurements

Trial Digit #1 Digit #2 Digit #3 Digit #4 Digit #5 Dorsum

1 7, 10 7,10 9, 10, 10

2 5, 7 5, 5, 7 5, 5, 7 5, 5 5, 5

3 7, 10 5, 7, 10 7, 10 5, 7 5, 7

4 7, 10 5, 7, 10 5, 7, 10 5, 7, 9 5

5 7, 7 5, 7 5, 7 5 5

6 7, 10 7 7 6 6

7 5, 7, 7 4, 5, 6, 7, 7 4, 5, 6, 6 4, 5 4, 5

8 7, 7 7, 7

9 7 7 7 5

10 1, 6, 7 1, 6 6 4, 6 4, 5, 6 4

11 10 5 5, 6 4, 5

12 7 7 5 5 7

13 10 5 4

14 5, 6 2, 10

15 1 1, 7 1, 6, 10 1, 4, 5, 6 4, 10

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the 30-min immersion (Table 4), occurring at 13:36 (5:22)min. However, while onset times were similar between theWrst 5-day period [14:04 (4:46) min] and the Wnal Wve-dayperiod [15:10 (5:19) min] it occurred signiWcantly earlierduring the middle 5-day period [12:01 (5:48) min].

Discussion

The objectives of this experiment were to investigate thehomogeneity (similar patterns in onset time, onset tempera-

ture, or magnitude across the digits during one exposure)and trainability (systematic changes in frequency, onsettime, onset temperature, or magnitude over repeated expo-sures) of the CIVD response in the foot under carefullycontrolled conditions. We hypothesized that our subjects’CIVD responses, characterized by onset time and magni-tude, would not become faster and stronger followingrepeated exposure to a strong cold stimulus. In support ofthis, following 15 days of cold exposure, no observablechange in the nature of CIVD response within or betweensubjects was detected, with the overall responses character-

Table 2 Histogram of magnitude of each cold-induced vasodilatation (CIVD) response

Subject number (1–10) is used to signify a CIVD response with respective magnitude

The majority of CIVD responses were characterized by increases of <4°C

Magnitude (°C) Incidence Total

1 2, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5, 5, 6, 6, 6, 6, 6, 7, 7, 7, 7, 7, 7, 7, 9, 9, 10, 10, 10 31

2 1, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 6, 6, 6, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 10, 10, 10, 10, 10, 10,10

40

3 1, 1, 1, 1, 4, 4, 5, 5, 5, 5, 5, 5, 6, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 10, 10, 10, 10, 10 28

4 1, 5, 5, 6, 7, 7 6

5 5, 5, 5, 5, 5, 7 6

6 5, 5, 7, 7, 7, 10 6

7 5, 7 2

8 5 1

9 6, 6 2

Table 3 Histogram of onset temperature of each cold-induced vasodilatation (CIVD) response

Onset temperatures(°C)

Incidence Total

7 7 1

8 1, 1, 1, 1, 1, 7, 7, 7, 7, 7, 7, 7, 7, 10, 10 15

9 5, 5, 5, 5, 5, 5, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 10, 10, 10, 10, 10 23

10 1, 2, 5, 5, 5, 5, 5, 6, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 9, 10 20

11 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 6, 7, 7, 7, 7, 7, 10, 10, 10, 10 23

12 4, 5, 5, 5, 5, 5, 5, 5, 6, 7, 9, 10 12

13 5,5,6 3

14 4, 5, 6, 10, 10 5

15 5 1

16 4, 6, 10 3

17 6, 6 2

18 6 1

19 0

20 4, 4 2

21 4, 6, 6 3

22 6 1

23 4, 4 2

24 4, 4, 4 3

25 0

26 4 1

27 0

28 4 1

Subject numbers (1–10) are used to indicate a response at respec-tive onset temperatures

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ized by great variability both within and between subjects.Furthermore, the frequency of CIVD response actuallytended to decrease over the acclimation period. While thisstudy did not test CIVD responses in the Wngers, our Wnd-ings support the spatial heterogeneity of thermal responsesin the Wngers previously reported during a single exposure(Chen et al. 1996; Cheung and Mekjavic 2007), and high-lights the need for multiple temperature sites to gain a com-prehensive view of the thermal status of the extremities.

No consistent pattern of progressive improvement inperipheral thermal response was observed, suggesting thatsigniWcant adaptation of the toes cannot be reliablyachieved by repeated local cold exposure. The current pro-tocol only evoked 122 CIVD responses out of 900 possibleevents (6 sites £ 10 subjects £ 15 days, Table 1), andthroughout the 15 trials the response did not increase in fre-quency or magnitude. Historically, the majority of studiesdemonstrating local cold adaptation have compared indi-viduals living in cold environments with control popula-tions, providing little information about the time course ofadaptation. Purkayastha et al. (1992) demonstrated that nat-ural acclimatization, via transporting a group of tropicalinhabitants to an Arctic environment, brought about localcold responses in the hand to levels similar to individualsliving in cold climates for brief (<1 year) periods but lowerthan that of Arctic natives. This suggests that limited localadaptation is indeed possible, but may require consistent,natural exposure to cold environments over a longer periodof time than feasible in most lab-based acclimation proto-cols.

Beyond the lack of acclimation, the pattern of thermalresponse in the foot to cold immersion was highly heteroge-neous, both spatially and temporally. Similar to a studytesting the reproducibility of the CIVD response in a singleWnger (O’Brien 2005), we either eliminated or kept con-stant conditions known to aVect the variability of CIVDresponses and measured temperatures at the nail bed ofeach toe to minimize variability compared to the digit pad.All subjects were non-smokers, had no health issues, were

not on any medications, and did not suVer from Raynaud’sSyndrome. To control nutrition and posture, subjects werealso provided with 250 mL of fruit juice upon arrival at thelab and assumed a seated neutral posture in an oYce chairfor the remainder of the experiment. Furthermore, weachieved a stable thermal baseline prior to cold immersionby pre-immersing the foot for 5 min in 35°C water. Despitethese controls, the response was erratic day-to-day bothwithin and between subjects. The large variability in theresponse is similar to results of Chen et al. (1996), whereCIVD was not present in all Wngers and the onset time var-ied when the Wngers were in contact with cold material.More recently, Cheung and Mekjavic (2007) reported thatthe CIVD response in the hand is highly heterogeneous spa-tially, with only 2 of their 10 subjects experiencing a syn-chronicity of responses across every digit of the hand andmagnitudes ranging from 1.4 to 7.5°C.

The degree of thermal stress may inXuence CIVDresponse. An appropriate protocol to test the trainability ofCIVD must balance the need for suYcient stimulus withsubject tolerance and practicality. It has been reported that acold stimulus decreasing skin temperature below 15–18°Cis strong enough to elicit a CIVD response (Lewis 1930).Prior pilot work has established that hand immersion in<8°C water with non-acclimatized subjects brings the riskof hypotension and fainting, while hand immersion in 8°Ccan produce consistent CIVD responses at the index Wngerin most subjects with no dropout due to either pain intoler-ance or hypotension (Geurts et al. 2005). Core temperatureand external environmental temperatures may inXuenceCIVD response, but minimal Xuctuations in baseline tym-panic temperatures were observed. While acknowledgingpotential methodological concerns with infrared tympanictemperature, it is likely that similar thermal status wasmaintained throughout the testing period. The experimentwas performed during September and October in easternCanada, with mean ambient (16.2 and 10.9°C, respectively)and mean minimum (11.0 and 6.7°C, respectively) temper-atures at levels unlikely to elicit signiWcant heat or cold

Table 4 Histogram of the onset time following cold water immersion of each cold-induced vasodilatation (CIVD) response

Onset time (min)

Incidence Total

0–3 4, 4 2

4–6 4, 4, 4, 4, 4, 4, 4, 4, 4, 6, 7, 7, 7, 7, 7, 7, 10 17

7–9 4, 5, 5, 5, 5, 6, 7, 7, 7, 9, 10, 10, 10 13

10–12 5, 5, 5, 5, 5, 5, 5, 5, 5, 6, 6, 6, 6, 6, 7, 7, 7, 7, 7, 7, 10 ,10, 10, 10 24

13–15 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 6, 7, 7, 7, 7, 7, 7, 7, 9 22

16–18 1, 1, 4, 5, 5, 5, 5, 6, 6, 7, 7, 7, 7, 7, 7 15

19–21 1, 1, 1, 2, 5, 5, 6, 6, 7, 7, 7, 7, 7, 10, 10, 10, 10, 10, 10 19

22–24 1, 5, 5, 5, 7, 7, 7, 7, 10, 10 10

Subject number (1–10) is used to signify CIVD response with respective onset time

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acclimatization. To ensure a stable core temperature, alltests were performed at the same time of day for each sub-ject to remove potential eVects of circadian rhythm, andsubjects avoided exercise prior to testing. Females weretested randomly over the course of their menstrual cycles,but no diVerences in baseline tympanic temperatures wereevident in the females alone.

The lack of consistency in CIVD response across stud-ies could be due to methodological diVerences such as thefoot versus the hand or Wnger, total foot immersion versussingle digit immersion, or the strength of the stimulus. Itcan be argued that the cold stimulus was possibly insuY-cient to produce long-term, systemic changes in the ther-mal response of the foot. However, the local exposureprotocol we chose was identical to one previouslyemployed in our laboratory that elicited signiWcant thermalresponses in the hand (Cheung and Mekjavic 2007; Geurtset al. 2005) though not in the foot (Cheung and Mekjavic2007). Furthermore, whole-hand immersion over threeweeks in 8°C water resulted in consistent CIVD responsesand a signiWcant decrease in both mean and minimum tem-perature in the index Wnger, with most of the changesoccurring within Wve days (Geurts et al. 2005). Certainly itis diYcult to compare our short-term exposure protocol, orindeed any lab-based acclimation protocol, with the sus-tained natural acclimatization (e.g., longer or whole-bodyexposures, circulatory or hormonal responses from coretemperature changes) to cold achieved by previouslyexamined population groups such as Gaspé Wshermen(Leblanc 1962), Inuit (Irving et al. 1960), and northernScandanavians (Krog et al. 1960). However, the upperlimit for mean digit temperature in our protocol was 11.5(2.0)°C, well below the 15°C threshold for CIVD sug-gested by Lewis (1930), so it is unlikely that the low inci-dences of CIVD would be due to an insuYciently strongthermal stimulus. Additionally, we observed multipleinstances of CIVD even at toe temperatures much higherthan 15°C, such that CIVD does not appear to require athreshold skin temperature.

In summary, CIVD in the foot does not seem to be ahomogenous or trainable response in a laboratory acclima-tion setting, with no progression of CIVD prevalence orchange in characteristics over 15 days of whole foot immer-sion for 30 min in 8°C water. Overall, our data supportsprevious proposals (Chen et al. 1996; Cheung and Mekja-vic 2007) that modelling extremity responses to cold expo-sure requires a more comprehensive reporting of thermalresponses throughout the extremity.

Acknowledgments The authors wish to express their gratitude to thesubjects for their participation. This research was funded by a Discov-ery Grant (S.S. Cheung and G.G. Sleivert) from the Natural Sciencesand Engineering Research Council (NSERC) of Canada.

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