DTIC ADA559061: Thermal Face Protection Delays Finger Cooling and Improves Thermal Comfort during Cold Air Exposure

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2011 Journal Article-Eur Journal of Applied Physiology
4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER
Thermal face protection delays Fnger cooling and improves thermal comfort
during cold air exposure
5b. GRANT NUMBER
5c. PROGRAM ELEMENT NUMBER
6. AUTHOR(S) 5d. PROJECT NUMBER
C. O’Brien, J.W. Castellani, M. Sawka
5e. TASK NUMBER
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7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION
REPORT NUMBER
Thermal and Mountain Medicine Division
M10-47
U.S. Army Research Institute of Environmental Medicine
Natick, MA 01760-5007
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13. SUPPLEMENTARY NOTES
14. ABSTRACT
When people dress for cold weather, the face often remains exposed. Facial cooling can decrease finger blood flow, reducing finger
temperature (Tf). This study examined whether thermal face protection limits Wnger cooling and thereby improves thermal comfort
and manual dexterity during prolonged cold exposure. Tf was measured in ten volunteers dressed in cold-weather clothing as they
stood for 60 min facing the wind (¡15°C, 3 m s¡1), once while wearing a balaclava and goggles (BAL), and once with the balaclava
pulled down and without goggles (CON). Subjects removed mitts, wearing only thin gloves to perform Purdue Pegboard (PP) tests
at 15 and 50 min, and Minnesota Rate of Manipulation (MRM) tests at 30 and 55 min. Subjects rated their thermal sensation and
comfort just before the dexterity tests. Tf decreased (p < 0.05 for time £ trial interaction) by 15 min of cold exposure during CON
(33.6 § 1.4–28.7 § 2.0°C), but not during BAL (33.2 § 1.4–30.6 § 3.2°C); and after 30 min Tf remained warmer during BAL (23.3 §
5.9°C) than CON (19.2 § 3.5); however, by 50 min, Tf was no difference between trials (14.1 § 2.7°C). Performance on PP fell (p <
0.05) by 25% after 50 min in both trials; MRM performance was not altered by cold on either trial. Subjects felt colder (p < 0.05)
15. SUBJECT TERMS
and more uncomfortable (p < 0.05) during CON, compared to BAL. Thermal face protection was effective for maintaining warmer
TRfe falnedx tvhaesromcoaln cstormicftioornt ,d Hureiantg l ocsosl,d T ehxepromsualr es;e hnosawtieovner, local cooling of the hands during manual dexterity tests reduced this
physiological advantage, and performance was not improved.
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a. REPORT b. ABSTRACT c. THIS PAGE ABSTRACT OF Catherine O'Brien
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Thermal face protection delays finger
cooling and improves thermal comfort
during cold air exposure
Catherine O’Brien, John W. Castellani &
Michael N. Sawka
European Journal of Applied
Physiology

ISSN 1439-6319
Volume 111
Number 12

Eur J Appl Physiol (2011) 111:3097-3105
DOI 10.1007/s00421-011-1931-2
1 23
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Author's personal copy
Eur J Appl Physiol (2011) 111:3097–3105
DOI 10.1007/s00421-011-1931-2
ORIGINAL ARTICLE
W
Thermal face protection delays nger cooling and improves
thermal comfort during cold air exposure
Catherine O’Brien · John W. Castellani ·
Michael N. Sawka
Received: 27 January 2011 / Accepted: 16 March 2011 / Published online: 3 April 2011
© Springer-Verlag (outside the USA) 2011
Abstract When people dress for cold weather, the face warmer during BAL (23.3§5.9°C) than CON (19.2§3.5);
often remains exposed. Facial cooling can decrease Wnger however, by 50min, T was no diVerent between trials
f
blood Xow, reducing Wnger temperature (T). This study (14.1§2.7°C). Performance on PP fell (p<0.05) by 25%
f
examined whether thermal face protection limits Wnger after 50min in both trials; MRM performance was not
cooling and thereby improves thermal comfort and manual altered by cold on either trial. Subjects felt colder (p<0.05)
dexterity during prolonged cold exposure. T was measured and more uncomfortable (p<0.05) during CON, compared
f
in ten volunteers dressed in cold-weather clothing as they to BAL. Thermal face protection was eVective for main-
stood for 60min facing the wind (¡15°C, 3ms¡1), once taining warmer T and thermal comfort during cold expo-
f
while wearing a balaclava and goggles (BAL), and once sure; however, local cooling of the hands during manual
with the balaclava pulled down and without goggles dexterity tests reduced this physiological advantage, and
(CON). Subjects removed mitts, wearing only thin gloves performance was not improved.
to perform Purdue Pegboard (PP) tests at 15 and 50min,
and Minnesota Rate of Manipulation (MRM) tests at 30 and Keywords ReXex vasoconstriction · Heat loss · Thermal
55min. Subjects rated their thermal sensation and comfort sensation
just before the dexterity tests. T decreased (p<0.05 for
f
time£trial interaction) by 15min of cold exposure during
CON (33.6§1.4–28.7§2.0°C), but not during BAL Introduction
(33.2§1.4–30.6§3.2°C); and after 30min T remained
f
While most people wear a hat during cold exposure, the
face often remains exposed. Thermal face protection may
Communicated by George Havenith. be neglected for practical reasons, such as diYculty accom-
modating a balaclava under a helmet, or for personal rea-
The opinions or assertions contained herein are the private views of the
author(s)and are not to be construed as oYcial or as reXecting the sons, such as not liking the appearance. Thermal face
views of the Army or the Department of Defense. Human subjects protection may also be overlooked because face skin tem-
participated in these studies after giving their free and informed
perature remains warmer during cold exposure than most
voluntary consent. The investigators have adhered to the policies for
other regions of the body (Boutcher etal. 1995; Webb
protection of human subjects as prescribed in Army Regulation 70–25,
and the research was conducted in adherence with the provisions of 32 1992), and, while the face is sensitive to small changes in
CFR Part 219. Any citations of commercial organizations and trade temperature (Stevens and Choo 1998), cooling the face
names in this report do not constitute an oYcial Department of the
results in less thermal discomfort compared to the same
Army endorsement of approval of the products or services of these
degree of cooling in other regions of the body (Nakamura
organizations.
etal. 2008). However, the higher facial skin temperature
C. O’Brien (&) · J. W. Castellani · M. N. Sawka allows greater heat loss (Froese and Burton 1957), and
Thermal and Mountain Medicine Division, facial cooling induces a reXex vasoconstriction that reduces
U.S. Army Research Institute of Environmental Medicine,
blood Xow to the Wngers and toes (Brown etal. 2003; Heath
Natick, MA 01760-5007, USA
e-mail: [email protected] and Downey 1990). Extremity cooling during cold-weather
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3098 Eur J Appl Physiol (2011) 111:3097–3105
activity is an important concern in military, occupational temperature during whole-body cold exposure over a pro-
and sports medicine communities for physical comfort longed period. This could be important for thermal comfort,
(Adams and Smith 1962; Heus etal. 1995), manual dexter- manual dexterity, and risk of cold injury for people work-
ity (Enander 1987), and prevention of cold injury (Castel- ing in cold environments. Therefore, this study examined
lani etal. 2006). Interventions that blunt or delay the initial Wnger temperature during cold air exposure in subjects
vasoconstrictor response in the extremities may be eVective dressed in cold-weather clothing and their face was covered
in maintaining warmer Wnger temperatures during cold by a balaclava and goggles, and compared those responses
exposure and deserve more attention. Whether extremity to a condition where the face remained bare. We hypothe-
cooling can be limited by wearing thermal face protection sized that reXex vasoconstriction from facial cooling when
during prolonged whole-body cold exposure is unknown. the face was bare, in combination with greater heat loss
Cold exposure of the face stimulates the trigeminal from the exposed face, would reduce Wnger temperatures to
nerve, which activates a sympathetic pathway that induces a greater extent than when thermal face protection was
vasoconstriction, as well as a parasympathetic pathway that worn. We also examined whether thermal face protection
induces bradycardia (Brick 1966; Heath and Downey 1990; improved perception of thermal comfort, and whether the
Heistad etal. 1968; Hilz etal. 1999). Several studies have diVerence in Wnger temperature between conditions would
examined the impact of brief (up to 60s) application of be large enough to aVect manual dexterity.
cold (0°C) compresses to the forehead and found reductions
in Wnger and toe blood Xow as high as 50–70% in subjects
resting in a normal room temperature (Brown etal. 2003; Methods
Heath and Downey 1990; Hilz etal. 1999). In the only
study with a longer cold exposure, Jennings etal. (1993) Ten healthy males participated in this study, which was
found a small (»0.6°C), but persistent decrease in Wnger approved by the appropriate scientiWc and human use
skin temperature after 20min of circulating cold water review boards of the U.S. Army Research Institute of Envi-
(10°C) through tubing on the cheeks of recumbent subjects ronmental Medicine and U.S. Army Medical Research and
during REM sleep. On blowing cold air (4°C, 18ms¡1) on Materiel Command. Each person volunteered after being
the face of subjects for 4min, LeBlanc and Mercier (1992) informed of the purpose, experimental procedures, and
found a 25% increase in circulating norepinephrine, indi- known risks of the study. Investigators adhered to Army
cating sympathetic activation, although they did not report Regulation 70–25 and U.S. Army Medical Research and
the Wnger temperature. The results of these studies suggest Materiel Command Regulation 70–25 on the use of volun-
that protecting the face from cold could delay or blunt teers in research. Participants were medically screened to
reXex vasoconstriction in the extremities, and thereby also exclude prior cold injury and any condition or medication
delay or blunt the Wnger cooling that occurs during cold that could interfere with body temperature regulation. The
exposure. participants were 22§3years old, 177.6§6.9cm in
Over a prolonged cold exposure, heat loss from a bare height, had a body mass of 82.4§17.9kg, body surface
face can also contribute to extremity cooling. Rapaport area of 2.0§0.2m2 (DuBois and DuBois 1916) and body
etal. (1949) reported that hands and feet will cool when fat, estimated from skinfold measurements (Durnin and
whole-body heat loss exceeds heat production by 15%. Wormersly 1974), of 18.6§3.6%.
Such a diVerence can easily occur with a bare face at low Experiments were conducted at the same time of day,
temperatures, because although the surface area of the face and subjects were familiarized with each experimental pro-
is small (»0.04m2), there is minimal vasoconstriction in cedure. Each volunteer completed two cold air exposure tri-
this region, resulting in a high rate of heat loss. Froese and als, once while wearing a balaclava (0.8clo on the face)
Burton (1957) provide an example of whole-body cold and goggles to protect the face from direct cooling (BAL),
exposure (¡4°C, 2.2ms¡1 wind) where about half of the and on another occasion with the balaclava pulled down oV
resting heat production would be lost from a bare head if the face and no goggles to expose the face to cold wind
the rest of the body was well insulated (5clo). They (Froese (CON). The balaclava had a nylon mesh that covered the
and Burton 1957) estimated that the addition of relatively mouth. Volunteers were otherwise dressed in U.S. Army
little insulation (2.4clo) on the head would restore heat bal- Extended Cold-Weather Clothing System (ECWCS, GEN
ance, although a higher amount (3.5clo) would be required 3) Polartec Power Dry grid Xeece and loft parka and trou-
if the face remained exposed to cold. If thermal face protec- sers for a total measured insulation value of 3.6clo. They
tion can restore heat balance, extremity cooling would also dressed in a 21°C room, donning parka, handwear, bala-
likely be limited. clava, and goggles just before entering the cold chamber
To our knowledge, no one has investigated the eVect of to avoid overheating. Handwear consisted of insulated
thermal face protection, compared to a bare face, on Wnger mitts worn over thin polyester gloves. Mitts were removed
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Eur J Appl Physiol (2011) 111:3097–3105 3099
during dexterity tasks, which were performed wearing only sites: cheek, hand, Wnger, foot, arm, chest, back, and calf.
the thin gloves. The two trials were counterbalanced and The core temperature (T ) was measured with either a rectal
c
spaced about a week apart. The temperature (¡15°C) and thermistor (5 subjects) inserted 10cm past the anal sphinc-
wind speed (3ms¡1) in the environmental chamber were ter, or an esophageal thermistor (5 subjects) inserted to a
equivalent to a wind chill temperature of ¡20°C (National depth of one-quarter of the subject’s height, then adjusted
Weather Service Windchill Chart). These conditions were 1–2cm in either direction to locate the highest local tem-
selected to provide marked cooling to the face during CON perature (both thermistors: Measurement Specialties, Inc.,
with little risk of frostbite, such that the face protection dur- Hampton, VA). Subjects who were unable to place the
ing BAL might have the best conditions for reducing heat esophageal thermistor used the rectal thermistor; the same
loss and minimizing extremity vasoconstriction. thermistor was used for both trials. Core and skin tempera-
Volunteers entered the cold chamber and stood facing ture data and heat Xux were recorded every 10s. Mean
the wind for 60min. The wind was uniform across the front weighted skin temperature (T ) and heat Xux were calcu-
sk
of their body, with the exception of a 30-cm high board at lated using a modiWed Hardy and Du Bois (1938) formula:
about waist level, which was attached to a table for the dex- 0.02£cheek+0.4£chest+0.14£arm+0.05£hand+
terity tests and protected the pieces from moving due to the 0.19£thigh+0.13£calf+0.07£foot. This formula was
wind. The timeline for cold exposure is shown on Fig.1. used because it included regions that experienced greater
After 15min, volunteers removed their mitts to perform a cooling (hand, foot, face). Cheek temperature was used
Purdue Pegboard (PP) task that requires Wne dexterity. The instead of forehead temperature used in the original for-
Wrst part of the test involved placing as many pegs into mula, and the weighting was reduced (from 0.07 to 0.02) to
holes as possible for 30s with the right hand, left hand, and represent the smaller surface are of the face (»0.04m2)
both hands. The second part of the test involved assembling compared to the whole head. Since the temperature on the
a peg, washer, spacer, and another washer in each hole as head was not measured, weighting for the chest was
many times as possible for 1min. Data analysis for PP used increased (from 0.35 to 0.40), as this site would have the
the combined score of the average of peg placements (right least stimulus for vasoconstriction and the head also had lit-
hand, left hand, both hands) plus the score for assembly tle vasoconstrictor response to cold (Froese and Burton
(counting each piece). They then put their mitts back on 1957). Mean body temperature (T ) was calculated as
b
until 30min, at which time they removed the mitts to per- 0.67£T +0.33£T . A polar watch (Polar Electro Oy,
c sk
form a Minnesota Rate of Manipulation (MRM) task that Finland) was used to measure heart rate, which was
requires gross hand dexterity. Data analysis for MRM used recorded every 5min.
the combined score of the average of four times for placing Data were analyzed using a two-factor (trial£time)
blocks plus the time for turning blocks. They put their mitts repeated measures ANOVA. For continuously measured
back on once more until 50min, at which time they com- variables, Wve time points (initial, 15, 30, 50, and 60min)
pleted the PP task immediately followed by the MRM task. were analyzed for cheek, core, foot, and mean skin temper-
Before the cold trials were conducted, volunteers had prac- atures and for heart rate. For Wnger and hand temperatures,
ticed both dexterity tests in temperate conditions while seven time points were analyzed, including the lowest val-
wearing the thin gloves Wve to six times until performance ues achieved during each of the dexterity tests, which
showed no further improvement over two sequential ses- occurred between 15 and 20; between 30 and 35, and
sions. Volunteers were asked to rate their thermal sensation between 50 and 60min. Tukey’s Honestly SigniWcant
(TS) on a scale from 0.0 (unbearably cold) to 8.0 (unbear- DiVerence test was applied when signiWcant main eVects
ably hot) (Young etal. 1987) and thermal comfort (TC) on were found. Statistical signiWcance was set at p<0.05.
a scale from 1 (comfortable) to 4 (very uncomfortable) Sample size estimation (Statistica, StatSoft, Inc.) based on
(Gagge etal. 1967) just before performing the dexterity an expected 2.3°C standard deviation in Wnger temperature
tasks. after 60min (Gonzalez etal. 1998) and a 2.5°C Wnger tem-
Heat Xux transducers with integrated thermistors (Con- perature diVerence at which signiWcant diVerences in
cept Engineering, Old Saybrook, CT) were attached at eight Purdue Pegboard scores have been observed with cooling
Fig.1 Timeline of cold
exposure and dexterity tasks
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3100 Eur J Appl Physiol (2011) 111:3097–3105
(Flouris etal. 2006) with power of 80% suggests that nine Core Temperature
subjects would be required to detect a signiWcant diVerence 38.0 Balaclava
between BAL and CON. Data are expressed as mean§ Control
standard deviation.
37.5
C
°
e,
Results ur
at 37.0 § § §
er §
p
Figure2 shows T and T during cold exposure for both tri- m
c sk e
als. Initial T was similar between trials (both 37.0§ T 36.5
c
0.3°C) and did not change during BAL, but fell (p=0.001
for time£trial interaction) during CON to 36.8§0.4°C
36.0
after 60min. Esophageal temperature responds more
quickly to changes in body temperature than rectal temper- Mean Skin Temperature
ature (O’Brien etal. 1998), and in the Wve subjects using
34
the esophageal thermometer the fall in core temperature
was signiWcant at 30min, whereas for the Wve subjects 33
using the rectal thermometer the change was signiWcant at C 32
60min. Initial Tsk was similar between trials, but decreased e, ° 31 §
faster (p=0.001 for time£trial interaction) during CON ur §
at 30
(33.0§0.5°C initially to 27.7§0.6°C at 60min) than er §
BAL (33.1§0.5–28.3§0.7°C). Note that the calculation mp 29
e
for Tsk included hand temperature, and at 60min the mitts T 28 §
were oV as subjects performed dexterity tests. Initial T was
b 27
similar between trials, but decreased faster (p<0.001 for
time£trial interaction) with cold exposure during CON 26
(35.7§0.3°C initially to 33.8§0.3°C at 60min) than
Mean Weighted Heat Flux
BAL (35.7§0.2°C initially and 34.2§0.2°C at 60min). 120
Heart rate (81§9bmin¡1) did not diVer between trials or
110
over time.
Cheek temperature, shown in Fig.3, was higher through- 2 100 §
out cold exposure during BAL, compared to CON, and -m 90
W
decreased over time on both trials (p<0.001 for x, 80
time£trial interaction). Finger, hand and foot tempera- Flu
tures are shown in Fig.4. There was a signiWcant time£ at 70
e
trial interaction (p=0.012) for Wnger temperature. After H 60
15min of cold air exposure, Wnger temperature was lower
50
during CON, compared to the initial value, whereas Wnger
temperature did not decrease during BAL. Thereafter, 40
0 15 30 50 60
Wnger temperature decreased on both trials and each time Time, min
point was signiWcantly diVerent from the next. Finger tem-
Fig.2 Core and mean skin temperatures and mean weighted heat Xux
perature was higher during BAL than CON at the time of
during cold exposure are presented for each trial. Values are
the Wrst dexterity test (PP) and at 30min. Finger tempera- mean§SD. §SigniWcant diVerence between trials
tures did not diVer between trials at subsequent time points.
There was a signiWcant time£trial interaction (p<0.001)
for hand temperature. During BAL, hand temperature was to perform dexterity tests, and Wnger temperature was addi-
not signiWcantly diVerent after 15min, but thereafter each tionally inXuenced by direct contact with cold metal and
time point was signiWcantly diVerent from the next. During wood pieces of the dexterity tests. Foot temperature
CON, hand temperature decreased initially and was signiW- decreased (p<0.001) similarly in both trials and was lower
cantly diVerent from each time point to the next. Hand tem- from each time point to the next.
perature was signiWcantly higher during BAL than CON Cheek heat Xux, shown in Fig.3, did not change over
from the time of the second dexterity test (MRM). Hand time during BAL (148.7§63.8Wm¡2 initially and
temperatures were inXuenced by periodic removal of mitts 215.2§40.0Wm¡2 during cold exposure), but decreased
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Eur J Appl Physiol (2011) 111:3097–3105 3101
Cheek Skin Temperature Finger Skin Temperature
35 40
Balaclava
Control 35 Balaclava
30 § Control
C C 30
mperature, ° 122505 § § § * §§ mperature, ° 2205 § §
Skin Te 10 Skin Te 1105
5
5
*
0
0
Cheek Heat Flux
Hand and Foot Skin Temperatures
800 Balaclava
35
Control
600 30
2 C
-m °
W e,
Flux, 400 § § § § § eratur 25 §
Heat Temp 20 §
200 n
ki
S
15 §
0
Initial 15 30 50 60
10
Fig.3 Cheek temperature and heat Xux during cold exposure are pre- Initial 15 min PP 30 min MRM 50 mi n PP-MRM
sented for each trial. Values are mean§SD. §SigniWcant diVerence
Fig.4 Finger, hand (circles), and foot (squares) temperatures during
between trials cold exposure are presented for each trial. PP lowest Wnger tempera-
ture during the Wrst (15min) Purdue Pegboard test, which lasted
(p<0.001 for time£trial interaction) during CON and 4–5min; MRM lowest Wnger temperature during the Wrst (30min)
Minnesota Rate of Manipulation test at 30min, which lasted 7–8min;
was higher at all time points (654.9§96.5–478.3§
PP-MRM lowest Wnger temperature during both tasks (at 50min),
167.8Wm¡2 during cold exposure), compared to BAL. which lasted 12–15min. Foot temperatures are presented at 0, 15, 30,
Mean weighted heat Xux, shown in Fig.2, was higher over- and 60min. Dashed lines are drawn at the Wnger skin temperature asso-
all during CON (p=0.032 for trial main eVect) than BAL, ciated with discomfort (20°C), impaired manual dexterity (15°C), and
and increased (p<0.001 for time main eVect) during cold loss of tactile sensitivity (8°C). Values are mean§SD. §SigniWcant
diVerence between trials
exposure after the initial value (CON 67.3§9.2Wm¡2 to
an average of 102.0§9.3Wm¡2 during cold exposure;
BAL 63.2§14.9–98.5§5.8Wm¡2). It should be noted without the insulation of the mitts, and the temperature of
that the gradient for heat Xux is only directly from skin tem- the mitts was lower when they were put back on after the
perature to ambient air temperature for the face during dexterity tests, having lost heat that was previously con-
CON; in all other regions, the presence of clothing reduces tained by the insulation.
the gradient somewhat. Initial heat Xux values are therefore Table1 shows dexterity, TS, and TC during cold expo-
relatively low, as the temperature inside the clothing has sure for each trial. Finger dexterity was degraded by 50min
been warmed by body heat before entering the chamber; of cold exposure, with lower (p<0.05) scores on the PP
however, during cold exposure some of this heat escapes task after 50min (15§3units), compared to both baseline
through the clothing and the air temperature near the skin is (the Wnal practice with gloves at normal room temperature)
reduced, thereby increasing the gradient for heat Xux. In the (20§3units) and the performance after 15min of cold
hands and Wngers, this temperature was further reduced exposure (18§3units), but there were no diVerences
each time the mitts were removed to perform dexterity between trials. There was no statistically signiWcant diVer-
tests. At those times, heat Xux increased dramatically ence in performance on the MRM task due to cold exposure
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3102 Eur J Appl Physiol (2011) 111:3097–3105
Table1 Purdue Pegboard and Minnesota Rate of Manipulation dex- ReXex vasoconstriction has been shown to occur rapidly
terity tests, and thermal sensation and thermal comfort ratings during with facial cooling (Brown etal. 2003; Heath and Downey
cold exposure are presented for each trial 1990; Heistad etal. 1968; Jennings etal. 1993) and was
Trial Baseline 15min 30min 50min likely an important early mechanism for Wnger cooling dur-
ing CON, where cheek temperature fell abruptly upon cold
Purdue Pegboard (pieces) exposure and Wnger temperature fell by 4.9°C in the Wrst
CON 20§3* 18§3* – 14§2
15min. Thermal face protection during BAL attenuated
BAL 20§3* 18§3* – 15§3 this reXex vasoconstriction, resulting in a slower initial rate
Minnesota Rate of Manipulation (s) of Wnger cooling on that trial. ReXex vasoconstriction also
CON 100§11 – 109§5 112§18 occurs with whole-body cooling, beginning as mean skin
BAL 100§11 – 108§12 113§22 temperature falls from thermoneutral. The greater initial
Thermal sensation (4=comfortable) fall in both mean skin and core temperatures during CON
CON – 3.0§1.2* 2.4§1.1* 1.9§0.9 likely also contributed to more rapid Wnger cooling on that
BAL§ – 3.4§1.1* 2.8§1.1* 2.4§1.2 trial. Finally, local cooling was a factor during both trials as
Thermal comfort (1=comfortable) mitts were periodically removed to perform dexterity tests.
CON – 2.0§0.5* 2.4§0.3* 2.7§0.7 ReXex vasoconstriction primarily regulates blood Xow to
BAL§ – 1.6§0.5* 1.8§0.6* 2.0§0.5 cutaneous blood vessels and to arteriovenous anastomoses,
which are important in the regulation of blood Xow in the
“Baseline” is the score from the last practice session at a normal room
temperature while wearing gloves. Values are mean§SD Wngers (Hales and Iriki 1977; Roberts etal. 2002). Local
*SigniWcant diVerence from 50min; §signiWcant diVerence between cooling may modulate the contractile response in the capil-
trials laries through adrenergic mechanisms, including altering
the response of vascular smooth muscle to norepinephrine
(100§11s during baseline; 108§13s at 30min cold (NE), altering release, reuptake or breakdown of NE, alter-
exposure; 113§20s at »55min cold exposure), nor was ing the aYnity of (cid:2)2-adrenoceptors for NE, or inducing
there any diVerence between trials. TS decreased with cold translocation of receptors to cell membranes; through non-
exposure (15 vs. 30 and 30 vs. 50min; p<0.001) and was adrenergic mechanisms, such as inhibition of the nitric
lower (p=0.012) during CON, indicating that subjects felt oxide system; and through a direct eVect of cold on blood
colder during CON, compared to BAL. TC increased with vessels (Alvarez etal. 2006; Chotani etal. 2000; Flavahan
time (15 vs. 50min, p=0.003) and was higher (p=0.002) etal. 1985; Jeyaraj etal. 2001; Shepherd etal. 1983;
during CON, indicating that subjects felt more uncomfort- Wenger etal. 1985). While reXex and local cooling vaso-
able during CON, compared to BAL. constrictor responses are not entirely additive, each can
contribute to the overall degree of vasoconstriction, and the
magnitude of each eVect is related to the degree of cooling
Discussion in that region (Alvarez etal. 2006). The addition of local
cooling may explain the lack of diVerence in Wnger temper-
This study was the Wrst to examine the potential beneWt of atures between trials at the end of the 60-min exposure,
thermal face protection on Wnger temperature, thermal com- even though Wnger temperature was higher for the Wrst half
fort, and manual dexterity during prolonged cold air expo- of the cold exposure during BAL.
sure. We hypothesized that limiting the degree of facial The higher Wnger temperature during BAL was not asso-
cooling during cold air exposure by wearing a balaclava ciated with improved manual dexterity, compared to CON.
and goggles would reduce the stimulus for extremity vaso- Manual performance degrades if cooling is suYcient to
constriction, resulting in higher Wnger temperatures, com- reduce not only skin surface temperature, but also underly-
pared to a bare face. The results support this hypothesis. ing tissue temperatures; therefore, a longer duration of
During BAL, Wnger temperatures remained higher during cooling has a greater eVect on reducing performance (Clark
the Wrst 30min and hand temperatures remained higher and Cohen 1960). Reduced strength as muscle temperature
thereafter, compared to CON. In addition, the mean skin falls below »28°C (Bergh and Ekblom 1979), decreased
temperature remained warmer, core temperature was main- joint mobility as synovial Xuid viscosity increases below
tained, and subjects reported better thermal comfort and »27°C (Hunter etal. 1952), slower nerve conduction
thermal sensation during BAL, compared to CON. While velocity at nerve temperatures below »20°C (de Jong etal.
manual dexterity was not improved by face protection, this 1966), and reduced tactile sensation at skin temperature
may have been confounded by the local cooling that below »8°C (Provins and Morton 1960) can all contribute
occurred when mitts were removed to perform the dexterity to reductions in performance. Finger dexterity degrades
tasks. sharply below a Wnger temperature of 15°C, most likely due
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Eur J Appl Physiol (2011) 111:3097–3105 3103
to reductions in nerve conduction velocity and joint mobil- subjects, Heath and Downey (1990) reported reductions in
ity (Enander 1987; Heus etal. 1995). In the present experi- both toe and Wnger blood Xow upon application of a cold
ment, Wnger temperature was well above this level for the compress to the forehead, but the reduction in toe blood
Wrst PP test, and no performance degradation occurred on Xow was »20% less than that in the Wnger. This suggests
either trial. At the time of the second PP test, the Wnger tem- that the foot may be less responsive to reXex vasoconstric-
perature was well below 15°C on both trials, and perfor- tion than the hand. Bader and Macht (1948) found that
mance was similarly degraded on both. when seated subjects were in a cool (15°C) room, warming
Hand temperature was above 20°C when subjects began the face (to 42–44°C) increased hand skin temperature and
the last dexterity tests (PP, followed by MRM). By the end blood Xow, but toe temperatures were only minimally
of the MRM test, the hand temperature remained above aVected, suggesting that the toe may also be less responsive
15°C during BAL (16.0§3.1°C), but had fallen below that to reXex warming. However, when they repeated the exper-
threshold during CON (13.8§2.2°C); however, there was iment at a room temperature of 23.5°C, both hand and toe
no degradation in MRM performance on either trial, and no temperatures increased upon warming the face (Bader and
diVerence between trials. Since this temperature was only Macht 1948). Thus, the cold environment appeared to blunt
reached at the end of the MRM test, the duration of cooling the increase in blood Xow due to reXex warming in the feet,
may not have been long enough to impair performance dur- but not in the hands. Likewise, in our subjects, either
ing CON. In addition, the sensor was placed on the dorsal whole-body or local cooling may have a stronger inXuence
hand, not over a hand muscle; therefore, hand muscle tem- on the feet, making those vessels less responsive to reXex
perature may not have fallen below the level at which per- changes. Foot temperature initially fell faster than hand
formance degradation would occur. Hand dexterity on the temperature, which could reXect greater sensitivity to cold
MRM tests is more likely to be inXuenced by reduced mus- of the blood vessels in the feet and/or inXuence of conduc-
cle temperature, since it does not require the same Wne tive heat loss to the Xoor due to insuYcient boot insulation.
motor control as the PP test. Besides the eVects of reXex and local cooling, facial
The periodic removal of mitts to perform dexterity tasks, cooling during CON also likely increased the metabolic
in combination with the conductive cooling of the Wngers as rate (Stroud 1991). Stroud (1991) found an increase in rest-
they handled the pegs and blocks, likely allowed the direct ing metabolic rate of »11.6W when cold (¡20°C) air was
eVect of local cooling to ultimately eliminate the advantage blown on the face of seated subjects. A similar increase in
of the balaclava for blunting the fall in Wnger temperature heat production in the present study would likely have pre-
that was evident after 30min, whereas hand temperature vented the fall in core temperature during CON; therefore,
was higher during BAL for the remainder of the cold expo- metabolic rate either did not increase to that extent, and/or
sure. While Wnger temperature decreased during both trials, other avenues of heat loss were important during CON.
it was initially at a slower rate during BAL (0.17°Cmin¡1), One important source is respiratory convective and evapo-
compared to CON (0.33°Cmin¡1). If subjects had not rative heat losses, which can be 11% (Brebbia etal. 1957)
experienced additional local cooling when they removed to 25% (Cain etal. 1990) of resting metabolic rate at ambi-
their mitts to perform dexterity tasks, such rates of cooling ent temperatures of ¡20°C. Respiratory heat losses can be
may have persisted, resulting in warmer Wnger temperatures limited by simply covering the mouth and nose with a scarf,
during BAL throughout cold exposure. surgical mask, or screen (Cain etal. 1990; Rosen and
While wearing face protection during cold exposure Rosen 1995), such as the nylon mesh that covered the
resulted in higher hand and Wnger temperatures, foot tem- mouth during BAL. Thus, while metabolic rate may have
perature did not diVer between trials. Several factors could been higher during CON, respiratory heat loss was also
contribute to this, including the dependent position of the likely higher on that trial, whereas it was likely somewhat
feet in standing subjects, lower sensitivity to reXex control conserved during BAL. Clearly, any increase in heat pro-
of blood Xow compared to the hand, and conductive heat duction during CON was not suYcient to oVset the higher
loss to the Xoor. Dependent position of a limb results in heat loss from the exposed face. Total mean weighted heat
increased local pressure, vasoconstriction, and lower skin Xux was 7.6W higher during CON than BAL, whereas for
temperature (Hassan and Tooke 1988a; Youmans etal. the face alone heat Xux was 10.5W higher during CON.
1935). These changes are primarily due to the venoarterio- This indicates that heat Xux over the rest of the body was
lar reXex, a myogenic response that may be mediated by actually lower during CON, yet core temperature still fell
local nonadrenergic neurogenic mechanisms (Crandall slightly (0.2°C) during the trial. Unfortunately, no measure-
etal. 2002; Hassan and Tooke 1988b). While a dependent ments of metabolic rate or respiratory heat losses were
position could explain why foot temperature was lower made in the present investigation.
than that of the hand, it was not clear why foot temperature To distinguish the eVects of reXex vasoconstriction from
was not aVected by thermal face protection. In supine a negative heat balance and from direct eVects of local
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