Splenic contraction during breath-hold diving in the Korean ama

Abstract

Major increases of hemoglobin concentration and hematocrit, possibly secondary to splenic contraction, have been noted during diving in the Weddell seal. We sought to learn whether this component of the diving response could be present in professional human breath-hold divers. Splenic size was measured ultrasonically before and after repetitive breath-hold dives to approximately 6-m depth in ten Korean ama (diving women) and in three Japanese male divers who did not routinely practice breath-hold diving. Venous hemoglobin concentration and hematocrit were measured in nine of the ama and all Japanese divers. In the ama, splenic length and width were reduced after diving (P = 0.0007 and 0.0005, respectively) and calculated splenic volume decreased 19.5 +/- 8.7% (mean +/- SD, P = 0.0002). Hemoglobin concentration and hematocrit increased 9.5 +/- 5.9% (P = 0.0009) and 10.5 +/- 4% (P = 0.0001), respectively. In Japanese male divers, splenic size and hematocrit were unaffected by repetitive breath-hold diving and hemoglobin concentration increased only slightly over baseline (3.0 +/- 0.6%, P = 0.0198). Splenic contraction and increased hematocrit occur during breath-hold diving in the Korean ama.

Full text

Splenic contraction during breath-hold diving
in the Korean ama
WILLIAM E. HURFORD, SUK KI HONG, YANG SAENG PARK, DO WHAN AHN,
KEIZO SHIRAKI, MOTOHIKO MOHRI, AND WARREN M. ZAPOL
Department of Anesthesia, Massachusetts General Hospital and Harvard Medical School, Boston,
Massachusetts
02114;
Department of Physiology, School of Medicine and Biomedical Sciences, State
University of New York at Buffalo, Buffalo, New York
14214;
Department of Physiology, Diving Science
Institute, Kosin Medical College, Pusan, Korea; Department of Physiology, School of Medicine, University
of Occupational and Environmental Health, Kitakyushu; and Underwater Physiology Division,
Japan Marine Science and Technology Center, Yokosuka, Japan
HURFORD, WILLIAM E., SUK KI HONG, YANG SAENG PARK,
Do WHAN AHN, KEIZO SHIRAKI, MOTOHIKO MOHRI, AND
WARREN M. ZAPOL.
Splenic contraction during
breath-hold
diving in the Korean ama. J. Appl. Physiol. 69(3): 932-936,
1990.-Major increases of hemoglobin concentration and hem-
atocrit, possibly secondary to splenic contraction, have been
noted during diving in the Weddell seal. We sought to learn
whether this component of the diving response could be present
in professional human breath-hold divers. Splenic size was
measured ultrasonically before and after repetitive breath-hold
dives to -6-m depth in ten Korean ama (diving women) and in
three Japanese male divers who did not routinely practice
breath-hold diving. Venous hemoglobin concentration and
hematocrit were measured in nine of the ama and all Japanese
divers. In t.he ama, splenic length and width were reduced after
diving (P = 0.0007 and 0.0005, respectively) and calculated
splenic volume decreased 19.5 t 8.7% (mean t SD, P = 0.0002).
Hemoglobin concentration and hematocrit increased 9.5 k 5.9%
fP = 0.0009) and 10.5 t 4% (P = O.OOOl), respectively. In
Japanese male divers, splenic size and hematocrit were unaf-
fected by repetitive breath-hold diving and hemoglobin concen-
tration increased only slightly over baseline (3.0 t 0.6%, P =
0.0198). Splenic contraction and increased hematocrit occur
during breath-hold diving in the Korean ama.
blood hematocrit; exercise; ultrasonography
KOREAN AMA
(sea women) are professional breath-hold
divers who dive in the Sea of Japan and Yellow Sea to
depths of 5-20 m for periods of 30-90 s while harvesting
abalone, sea urchins, and octopuses. Surfacing for brief
rest periods, they dive repeatedly for up to 4 h/day,
spending 2530% of their time underwater. Their unique
and skillful diving ability has attracted the attention of
physiologists who for over 25 years have intensively
studied their diving habits and physiological adaptations
to their aquatic workplace
(11-17).
A central question in
this
research is whether human adaptations to habitual
breath-hold diving parallel those of other diving mam-
mals
(12). Whereas bradycardia during diving has been
well described in the Korean ama and human volunteers
(3, 16), the presence of other components of the diving
response in humans is unclear.
One additional component of the diving response was
recently reported by Qvist and co-workers
(21),
who
consistently measured a 60% increase of arterial hemo-
globin concentration within the first 12 min of a dive in
Weddell seals. These pinniped divers are capable of dives
of up to
1
h to depths of X100 m. Qvist et al. speculated
that the increased hematocrit may be an integral part of
the diving response and could be due to splenic contrac-
tion during diving.
No one has reported whether the spleen of human
habitual breath-hold divers contracts during diving ac-
tivities. Some researchers using sonographic or radio-
nuclear techniques have observed that the human spleen
contracts during epinephrine injection or maximal exer-
cise (8,22). Accordingly, we hypothesized that the human
spleen may contract and hematocrit may increase during
breath-hold diving in the ama, paralleling the increase
measured in the Weddell seal. Because the seal’s hema-
tocrit takes lo-12 min to increase to a stable level (21)
and because human dives are much shorter, we hypoth-
esized that the human spleen may contract only after
sympathetic stimulation by a series of long breath-hold
dives. We tested our hypothesis during a field study of
Korean ama diving activities by measuring splenic size
with a portable real-time ultrasonic scanner before and
after 3-h shifts of repetitive breath-hold diving. Venous
blood samples for hemoglobin concentration and hema-
tocrit were obtained immediately before and after the
diving shift. To examine whether the effects we found
were simply associated with water immersion or casual
breath-hold diving, we obtained additional measure-
ments from Japanese male divers who did not routinely
practice breath-hold diving.
METHODS
Subject characteristics. Ten Korean ama (38-60 yr old)
who were experienced divers and members of the local
diving union were studied during routine 3-h shifts of
repetitive breath-hold diving conducted while harvesting
abalone, shellfish, octopuses, sea urchins, and seaweed
in Suyongman Bay, Pusan, Korea, during August 1989.
Seawater temperature at this time averaged 25°C. Phys-
932
0161-7567/90 $1.50 Copyright 0 1990 the American Physiological Society

SPLENIC CONTRACTION IN THE AMA
933
ical characteristics recorded included age, height, weight
before and (in 3 subjects) after diving, length of the
diving shift, and number and length of dives. Their
biophysical characteristics are listed in Table
1.
The ama
had an average of
34
t 7 (SD) yr (range
23-44
yr) of
breath-hold diving experience. All the ama dived year-
round and wore complete wet suits, face masks, and fins.
None of the ama had smoked cigarettes, and all were in
good general health. All ama were continuously moni-
tored for heart rate, depth, and dive time by a self-
contained backpack computer monitor. Each diver was
instructed to follow her normal pattern of diving. The
length of a diving shift was considered to be the time
elapsed between the time the diver entered and left the
water (total time diving plus time spent on the surface).
When not diving underwater, the ama rested on a small
surface float or swam for short distances to new fishing
locations. They did not leave the water during their
diving shift.
Three divers who did not routinely practice breath-
hold diving were also studied. These subjects were young
healthy Japanese males who agreed to attempt to repro-
duce the diving pattern of the ama for
1
h. These studies
were conducted in Sagami Bay, Miura Peninsula, Japan,
in August
1989
(average seawater temperature 25’C).
These three subjects were SCUBA and deep-sea satura-
tion divers but did not professionally practice breath-
hold diving. All wore full wet suits, face mask, fins, and
snorkel. Dive time was monitored by observers on the
surface, and the depth of the dives was reported by the
divers. All studies were approved by the appropriate
review committees of the Kosin Medical College, Pusan,
Korea, the Massachusetts General Hospital, Boston,
Massachusetts, the State University of New York at
Buffalo, and the Japan Marine Science and Technology
Center, Yokosuka, Japan. All procedures were explained
in detail, and informed consent was obtained from the
subjects by Korean or Japanese members of the research
team.
Sonography. Splenic size was measured with a real-
time 3.5MHz sector transducer and a portable battery-
operated ultrasound scanner (ScanMate, Damon, Need-
ham Heights, MA). Multiple tomographic parasagittal
intercostal images were acquired with the subject lying
in the right lateral decubitus position before diving and
again immediately on return to the beach after the diving
shift. Imaging was completed within
lo-20
min of the
subject’s last dive. Real-time images from the scanner
screen were recorded on PolaPan CT135 film (Polaroid,
Cambridge, MA) with an Olympus OM-3 camera (expo-
sure 0.25 s at f/3.5) equipped with a motor drive. Splenic
TABLE 1.
Biophysical characteristics
of
ama
Korean Ama Untrained Japanese
(n = 10)
Divers
(n = 3)
Age, Yr 51t7 24tl
Height, cm 154.7k5.8 172tll
Weight, kg 55*6 67tl
Years diving 34t7 8tl
Length of diving shift,* min 174t46 7328
Values are means t SD. * Surface + diving time.
size was quantified by projecting the photographic images
and comparing the dimensions of the greatest longitudi-
nal (length) and transverse (width) axes to corresponding
centimeter marker dots presented along the outer mar-
gins of the sector scan. Repetitive measurements were
consistent to within 0.25 cm. Splenic cross-sectional area
was calculated according to the formula area = 0.8
(length
x
width), and volume was estimated as volume
= (7.53
X
area) - 77.56 by the method of Koga
(18).
Hemoglobin and hematocrit. After venipuncture of an
antecubital vein immediately before and after the diving
shifts, blood was collected into preheparinized syringes.
Phlebotomy was accomplished in Cl0 s with the aid of a
loosely fitting venous tourniquet while the subjects were
in the sitting position with their arms at their sides.
Hemoglobin was determined by the cyanmethemoglobin
method (Sigma kit 525A and a Bausch and Lomb Spec-
tronic 21 spectrophotometer), and hematocrit was the
average of quintuplicate samples after microcentrifuga-
tion (Adams MHCT II). Additional measurements ob-
tained in Japanese divers included erythrocyte count,
plasma sodium, osmolarity, and total protein concentra-
tion.
Statistics. All results are expressed as means t SD.
Splenic size, hemoglobin concentration, and hematocrit
before and after diving were assessed by a paired Stu-
dent’s
t
test. Differences between ama and Japanese
divers were assessed by an unpaired
t
test
(10).
P <
0.05
was considered significant.
RESULTS
Diving characteristics. The ten ama repeatedly dived
to depths of -5-7 m. A diving shift lasted 174 t 46 min
and included -115 dives. Of the time spent in the water,
26.7% (52 +- 6 min) was spent diving underwater; the
remainder was spent resting on a surface float or swim-
ming to new fishing locations. The average longest dive
for each ama was to a depth of 6.0 t 1.3 m and lasted 40
t 10 s. The three Japanese male divers attempted to
mimic the diving pattern of the ama but could only work
for 73 t 8 min and made correspondingly fewer dives.
To observers timing the dives on the surface, the duration
of their dives appeared equivalent to that of the ama.
The three ama who were weighed lost 1.0 t 0.7 kg body
wt during their diving shift, whereas the three Japanese
divers lost 0.6 t 0.3 kg.
Splenic size. Splenic contraction occurred during div-
ing in nine of ten Korean ama (Table 2). Representative
sonograms are shown in Fig. 1. In the three Japanese
divers, no significant change of splenic size occurred after
breath-hold diving. Splenic size was normal in all sub-
jects studied, and there was no difference between the
size of the spleen in the ama and the Japanese male
divers before diving. In the ama, however, both splenic
length and width were reduced after diving (P =
0.0007
and 0.0005, respectively). Cross-sectional area and esti-
mated splenic volume were reduced 13.9 t 6.4% (P =
0.0002) and 19.5 t 8.7% (P = 0.0002), respectively. The
length, width, cross-sectional area, and estimated volume
of the spleen were unaffected by breath-hold diving in
the Japanese male divers.

934
SPLENIC CONTRACTION IN THE AMA
TABLE
2. Splenic dimensions before and after diving
Before After
P*
Ama (n = 10)
Length, cm 9.1kO.9 8&0.6 0.0007
Width, cm 5.2-t-0.6 4.8kO.7 0.0005
Cross-sectional area, cm2 37.756.6 32.3k5.5 0.0002
Volume, cm3 206.2t49.0 1656242.3 0.0002
Untrained Japanese divers (n = 3)
Length, cm 8.9fl.l 9.0f1.2 0.4226
Width, cm 5.6kO.4 5.5kO.5 0.4226
Cross-sectional area, cm* 40.0t6.1 39.7k7.6 0.7418
Volume, cm” 223.3548.0 222.Ok57.6 0.8399
Values are means -t SD. * Before vs. after.
Hemoglobin and hematocrit.
Hemoglobin concentra-
tion and hematocrit were increased after diving in all
ama (Table 3). Baseline hemoglobin and hematocrit were
both moderately reduced below normal Occidental levels
but were within the range of Korean ama and controls
reported previously
(17).
After diving, the hemoglobin
concentration of ama increased 9.5 f 5.9% (P = 0.0009)
and the hematocrit increased 10.5 ?I 4% (P = 0.0001).
The hemoglobin-to-hematocrit ratio was unchanged
after diving.
Hemoglobin concentration and hematocrit were higher
in the Japanese male divers. The hemoglobin concentra-
tion increased slightly (3.0 + 0.6%,
P
= 0.0198), but
hematocrit was unchanged after diving. The hemoglobin-
to-hematocrit ratio was unchanged after diving. Hemo-
globin and hematocrit changed less in Japanese divers
than in the ama
(P
= 0.02 and 0.0035, respectively). The
correlation coefficient
(r
value) for the linear correlation
between the change of hematocrit and the percent change
of splenic volume was 0.49 for all subjects studied.
Plasma sodium, osmolarity, and total protein concentra-
tions, measured in the Japanese male divers, were normal
and unaffected by diving.
DISCUSSION
The most important finding of our study is that the
spleen contracted and hematocrit increased during re-
petitive breath-hold diving in the Korean ama. These
effects did not occur in Japanese male divers who did
not routinely practice breath-hold diving. This suggests
that splenic contraction and increased hematocrit occur
as a response to breath-hold diving activities in the
Korean ama. They did not occur during shorter periods
of breath-hold diving in subjects who do not habitually
participate in breath-hold diving activities.
We used a portable real-time two-dimensional ultra-
sound unit to image the spleen immediately before and
after the end of a diving shift. The estimated splenic
FIG.
1. Representative parasagittal inter-
costal sonograms of left upper quadrant show-
ing spleen (S), left kidney (K), and diaphragm
(D) before (A-C) and after (D-F) a diving shift
in a Korean ama. Before diving, spleen meas-
ured 10.5 cm long and 4.75 cm wide (cross-
sectional area 39.9 cm*, estimated volume 233
cm”). After diving, spleen measured 9 cm long
and 4.25 cm wide (cross-sectional area 30.6 cm’,
estimated volume 153 cm’).

SPLENIC CONTRACTION IN THE AMA
935
TABLE
3. Hemoglobin and hematocrit
before and after diving
Before After
Ama (n = 9)
Hemoglobin, g/d1 11.8t1.0 12.9kO.8
Hematocrit, % 35.OA2.3 38.6t2.1
Untrained Japanese divers (n = 3)
Hemoglobin, g/d1 15.421.3 15.8t1.3
Hematocrit, % 48.5t3.2 49.0t2.3
Values are means -+ SD. * Before vs. after.
P*
0.0009
0.0001
0.0198
0.4647
volume of our subjects was within the range of normal
determined by computed tomographic studies of normal
Korean adults performed by Oh and co-workers
(19).
They reported that splenic volume averaged
160 t 62
(SD) cm3 in females and 173 t 59 cm3 in males. Splenic
length and width in transverse section in their study
averaged 9.3 2 1.4 and 3.7 t 0.7 cm, respectively. The
difference in values for splenic width between the study
of Oh et al. and this study is probably due to differences
in the dimensions of images derived by using only trans-
verse sections of the splenic hilum in their computed
tomographic study. We evaluated multiple parasagittal
imaging angles to determine the greatest cross-sectional
dimension in our ultrasound study.
Splenic contraction has been well described in experi-
mental animal studies. In animals, such as racehorses,
dogs, and sheep, splenic contraction is believed to be an
integral component of the response to exercise and is
associated with a large increase of hematocrit. In these
animals, the exercise-induced increase of hematocrit is
greatly reduced by splenectomy
(1, 20, 23).
The role of
splenic contraction during diving is less clear. The ex-
tremely large size of the spleen, relative to body weight,
in certain diving mammals suggests that splenic function
may be particularly important to their diving response
(21).
Qvist and co-workers
(21)
noted large increases in
hematocrit during diving in the Weddell seal, suggesting
that an infusion of erythrocytes into the central circu-
lation was perhaps secondary to splenic contraction;
however, they did not assess splenic size
(21).
In humans,
splenic contraction has been reported to occur in re-
sponse to extreme exercise or after the subcutaneous
injection of epinephrine (8,
22).
Any important role for
splenic contraction in the human is controversial.
Splenic contraction may be another manifestation of the
increased sympathetic tone and peripheral vasoconstric-
tion reported during face immersion and breath holding
(2)
ihe increased hematocrit during repetitive breath-
hold diving may have an important role. Increases of
hematocrit during diving in the Weddell seal may aid in
the uptake of oxygen and unloading of carbon dioxide
during the short surface time between dives. If splenic
contraction occurs at depth, the injection of erythrocytes,
previously sequestered at ambient pressure, into the cen-
tral circulation could also serve to dilute nitrogen com-
pressed into the arterial blood during descent (21). In
humans, this reservoir function would be minimal. How-
ever, the increased hemoglobin concentration could in-
crease the ability to take up oxygen at the surface be-
tween dives. The increased hematocrit could also in-
crease peripheral oxygen delivery during diving.
Decreased plasma volume secondary to dehydration
and water immersion was probably a major contributor
to the increased hemoglobin concentration and hemato-
crit that we measured in the ama. Hemoglobin and
hematocrit have been reported to remain unchanged or
to decrease, presumably secondary to an increase of
central plasma volume, during head-out immersion stud-
ies of human subjects in thermoneutral water (7, 9).
Immersion in cold water (<25”C), on the other hand, has
been reported to decrease plasma volume due in part to
increased urine flow (4, 5, 24). Although the subjects we
studied wore full wet suits while working in 25°C water,
their extremity temperature was probably below the level
observed in subjects immersed in thermoneutral water.
It is therefore possible that a temperature-induced re-
duction in plasma volume occurred. With the assumption
that the increased hemoglobin concentration and hema-
tocrit were due entirely to decreased plasma volume,
plasma volume, as calculated by the formulas suggested
by Dill and Costill (6), would have decreased during the
diving shift by -13.7% in the Korean ama and 3.5% in
the Japanese divers.
Splenic contraction may have contributed to the in-
creased hemoglobin concentration and hematocrit. After
diving, the spleen was -40 cm3 smaller than before
diving. Erythrocytes, previously sequestered in the
spleen, may have been released into the central circula-
tion during splenic contraction. This effect could con-
found measurements of plasma and erythrocyte volume
changes that are derived from measurements of hemo-
globin concentration and hematocrit and assume that
the number of erythrocytes within the central circulation
is constant (6).
The different responses observed in the ama and the
Japanese male divers are intriguing. The ama were fe-
male, older, habituated to breath-hold diving, and had a
longer diving shift, perhaps greater reductions of plasma
volume, and a lower baseline hemoglobin concentration
and hematocrit. It is impossible to determine from our
data whether any of these variables was responsible for
the differences. Differences of sympathetic tone, work
load, level of hypoxia, age, sex, or hemoglobin concentra-
tion may account for the different findings. Both groups,
however, were exposed to water immersion and repetitive
breath-hold diving to depths ranging from
4
to 7 m,
suggesting that the changes we observed in the ama were
not simply due to water immersion or brief periods of
breath-hold diving.
The splenic response of trained Japanese male breath-
hold divers may differ from the untrained divers we
studied. We had the opportunity to study a single Japa-
nese male breath-hold diver (53 yr old with 15 yr of
breath-hold diving experience) in Matsuwa, Japan. After
he repeatedly dove for 201 min to depths of 5-10 m, the
cross-sectional area of his spleen decreased from 34.6 to
30.4 cm2 and his estimated splenic volume decreased
17%, from 183 to 151 cm3. This diver refused blood
sampling but had a hemoglobin concentration of 15.0 g/

936
SPLENIC CONTRACTION IN THE AMA
dl and a hematocrit of
45%
during prior medical exami-
nations. Although only a single observation, this finding
suggests that splenic contraction during breath-hold div-
ing may not be related to sex or hemoglobin concentra-
tion and hematocrit but, more likely, is triggered by the
greater duration and activity of professional breath-hold
diving.
In summary, repetitive breath-hold diving in the Ko-
rean ama was associated with a 20% decrease of splenic
volume and a
10%
increase of hemoglobin concentration
and hematocrit. These changes were not observed in
Japanese male divers who did not normally practice
breath-hold diving. This suggests that splenic contrac-
tion and increased hematocrit occur during breath-hold
diving in the ama but are not simply associated with
water immersion or casual breath-hold diving.
The authors gratefully acknowledge the excellent cooperation of the
Korean ama and Japanese divers involved in this study. The authors
also acknowledge the expert technical assistance of Kevin Stanek and
John Henderson and the assistance and discussions of Dr. K. Falke
(University of Berlin), Dr. Y. D. Cho and J. S. Kim (Kosin Medical
College), and Dr. N. Naraki and H. Takeuchi [Japan Marine Science
and Technology Center (JAMSTEC)]. They also thank the staffs of
the Institute of Marine Sciences, Pusan, Korea, and JAMSTEC, Yo-
kosuka, Japan. The ultrasound equipment was modified for field use
by Dr. E. Schaner (Fairfax Hospital, Fairfax, VA) and provided by Dr.
(J. Bengston (National Marine Mammal Laboratory, Seattle, WA).
This study was supported by grants from the Kosin Medical College,
.JAMSTEC, and the Massachusetts Humane Society.
Address for reprint requests: W. E. Hurford, Dept. of Anesthesia,
Massachusetts General Hospital, Boston, MA 02114.
Received 18 December 1989; accepted in final form 2 May 1990.
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