Tissue fluid pressures - Muscle Physiology

Journal of Orthopaedic Research
7902-909 Raven Press, Ltd., New York
0 1989 Orthopaedic Research Society
Kappa Delta Award Paper
Tissue Fluid Pressures: From Basic Research Tools to
Clinical Applications
Alan R. Hargens, Wayne H. Akeson, Scott J. Mubarak, Charles A. Owen,
David H. Gershuni, Steven R. Garfin, Richard L. Lieber, Larry A. Danzig,
Michael J. Botte, and Richard H. Gelberman
Division of Orthopaedics and Rehabilitation, University of California and V.A. Medical Center,
San Diego, California, U.S.A.
Summary: The two basic research tools developed to measure tissue fluid
pressure (wick catheter) and osmotic pressure (colloid osmometer) have un-
dergone extensive validation and refinement over the past 20 years. Using
these techniques, basic science investigations were undertaken of edema in
Amazon reptiles, pressure-volume relations in animals and plants, adaptive
physiology of Antarctic penguins and fishes, edema in spawning salmon, tissue
fluid balance in humans under normal conditions and during simulated weight-
lessness, and orthostatic adaptation in a mammal with high and variable blood
pressures-the giraffe. Following and sometimes paralleling this basic research
have been several clinical applications related to use of our colloid osmometer
and wick technique. Applications of the osmometer have included insights into
(a) reduced osmotic pressure of sickle-cell hemoglobin with deoxygenation and
(b) reduced swelling pressure of human nucleus pulposus with hydration or
certain enzymes. Clinical uses of the wick technique have included (a) im-
provement of diagnosis and treatment of acute and chronic compartment syn-
dromes, (b) elucidation of tissue pressure thresholds for neuromuscular dys-
function, and (c) development of a better tourniquet design for orthopaedics.
This article demonstrates that basic research tools open up areas of basic,
applied, and clinical research. Key Words: Tissue fluid pressures-Clinical
applications-Osmometer-Compartment syndrome-Tourniquet .
Twenty years ago, techniques were developed for
basic science studies of interstitial fluid pressure
and colloid osmotic pressure during the 1967 R/V
ALPHA HELIX Expedition to the Amazon River
(21,43). The wick catheter technique was used to
examine pressure-volume relationships in animal
tissues, and a simple colloid osmometer was em-
ployed to assess blood samples from Amazon ani-
mals. These techniques were refined during subse-
quent expeditions from Scripps Institution of
Address correspondence and reprint requests to Dr. A. R.
Hargens, Life Science Division (239-17), NASA-Ames Research
Center, Moffett Field, CA 94035, U.S.A.
902
Oceanography [University of California, San Diego
(UCSD), CA, U.S.A.] to investigate physiological
adaptations of Antarctic penguins (22), polar fishes
(7), and Pacific salmon (18). Later studies using the
same techniques focused upon normal transcapil-
lary fluid balance in humans (13,36), fluid shifts re-
lated to simulated weightlessness in preparation for
a Space Shuttle project (23), and orthostatic adap-
tations in the giraffe (15).
In 1973, a clinical wick catheter was developed
for monitoring intracompartmental pressures in pa-
tients with possible acute and chronic compartment
syndromes. Our initial experiments on animals,
ourselves (“normal” subjects), and patients proved

successful as did subsequent research that contin-
ued our wick catheter investigations of (a) compart-
ment syndromes, (b) pressure thresholds for nerve
dysfunction, and (c) tourniquet design in orthopae-
dics. Parallel studies using new and improved os-
mometers have examined (a) osmotic dehydration
of sickle cells during deoxygenation (12) and (b)
swelling pressures of normal and enzyme-treated
nucleus pulposus. The primary theme of this review
article is that simple, basic research tools, such as
the wick catheter and colloid osmometer, have
opened up many areas of basic, applied, and clinical
research.
BASIC RESEARCH METHODS FOR
MEASURING FLUID PRESSURES IN TISSUE
AND BLOOD
Wick Catheter
The methods used in this paper were developed
at the Scripps Institution of Oceanography, UCSD
during 1966-1971. Previous needles and catheters
used for measuring interstitial fluid pressure re-
quired saline infusion in order to maintain patency
of the probe (9). This requirement precluded mea-
surements of negative fluid pressure in tissue, a
concept that Guyton (6) pioneered in the early
1960s. Although Guyton’s capsule provided dy-
namic measurements of tissue fluid pressure, it was
relatively large and required implantation 6 weeks
prior to any determinations (1).
The wick catheter was developed to provide im-
mediate, equilibrium measurements of tissue fluid
pressure without saline infusion (Fig. 1). Micro-
scopic channels of free fluid between the wick fi-
bers maintained catheter patency and offered a rel-
atively large pickup area for sensing changes in tis-
sue pressure. The wick technique (43) was first used
during the R/V ALPHA HELIX Expedition to the
FIG. 1. Close-up view of wick catheter tip showing micro-
scopic wick fibers that provide contact with tissue fluids and
maintain catheter patency without saline infusion. (From
Adair et al., ref. 1, with permission.)
TISSUE FLUID PRESSURES 903
SKIN
FASCIA
MUSCLE
-4.5 cm-HqO
MEASURED PRESSURE = -5.5 -4.5 = -10 cm H20
FIG. 2. Principles of measuring tissue fluid pressure in mus-
cle using the wick technique. Wick (w) is held within tubing
by thread (t). Glass capillary (g.c.) is adjusted vertically until
read-out meniscus (m) is stationary, indicating equilibrium is
reached. In this case, intramuscular fluid pressure equals
hydrostatic height (-5.5 cm H,O) plus capillarity (-4.5 cm
H,O) to give -10 cm H,O. (Modified from Hargens et al., ref.
11, with permission.)
Amazon River in 1967. A simple catheter system
made from Teflon tubing, a cotton wick, glass tube,
and custom manometer were designed especially
for field-type research. The system was thoroughly
tested to insure that it accurately measured hydro-
static fluid pressures only, especially under condi-
tions of negative fluid pressures where needle tech-
niques were found inoperative. The wick technique
was also tested in model systems of dehydration (8),
e.g., in monitoring development of negative pres-
sure in starch suspensions during water evapora-
tion. These initial studies were extended to mea-
surement of fluid pressure in subcutaneous, perito-
neal, and muscle tissues (Fig. 2).
The basic principles for measuring tissue fluid
pressure in animals were applied and refined for
intracompartmental studies in humans (1 1,33). For
example, intramuscular fluid pressures in the fore-
arm could be measured instantaneously using the
glass capillary technique or continuously using a
pressure transducer (17). Revisions of the original
technique included use of braided suture for wick
material, smaller catheter tubing and improved
techniques to minimize trauma during insertion,
heparinized saline to prevent coagulation, and ster-
ilization of all system components to minimize risks
of infection. Over time, a “wick kit” was developed
that included a pressure transducer, minirecorder,
wick catheters, and all other items necessary for
sterile measurements of intracompartmental pres-
sure. Later, a “slit catheter” was developed and
J Orthop Res, Vol. 7, No. 6, 1989
t

904 A. R. HARGENS ET AL.
tested. This catheter was based upon the wick prin-
ciple and offered higher frequency of response for
exercise studies (32,40). During 1975-1984, patients
were evaluated for suspected acute compartment
syndromes within the San Diego and Orange
County areas using these methods (over 150 cases
in these patients were positive). More than 2,000
studies of intramuscular pressure were undertaken
in patients and volunteers at UCSD over the past 10
years, and only one infection occurred using our
technique.
Colloid Osmometer
Colloid osmometers have been available for over
100 years, but recent improvements in membrane
and pressure-sensing technology make their use
more general and reliable. Colloid osmometry is im-
portant for studying (a) the capacity of blood to
absorb tissue fluid, specifically edema fluid, (b) the
colloid osmotic pressure of interstitial fluid that
counteracts the colloid osmotic pressure of blood,
and (c) the ability of a tissue matrix (e.g., nucleus
pulposus of the intervertebral disc) to swell. The
importance of these phenomena in tissue fluid ho-
meostasis and other orthopaedic considerations will
become evident below.
Our first colloid osmometer was developed for
field physiology research where electric power was
not always available (Fig. 3). Principles for measur-
ing osmotic pressures were similar to those outlined
- I cm
SPACER
VENT
MEMBRANE
RUBBER SUPPORT
UlU‘UXXXXm
MANOMETER
FIG. 3. Colloid osmometer uses a stretch mounting for its
membrane. (A) Exploded cross-section showing assembly.
(B) Osmometer for measuring colloid osmotic pressure. (C)
Submerged osrnometer. (From Hargens and Scholander, ref.
21, with permission.)
J Orthop Res, Vol. 7, NO, 6, 1989
previously for the wick catheter technique. Basi-
cally, our new technique employed a stretch mount-
ing of the membrane in order to measure weak os-
motic pressures accurately to within 1% (21).
All techniques for measuring negative tissue fluid
or osmotic pressures use the “push” or “pull”
technique to release trapped fluid. Scholander and
colleagues (42) employed the push technique to ver-
ify experimentally Dixon’s transpiration model (3)
for the ascent of fresh water sap in all vascular
plants. Briefly, Scholander and co-workers (42)
placed a cut branch in a pressure bomb and com-
pressed the plant tissue until the water meniscus
returned to its initial position at the cut surface.
Recently, we employed a similar technique to mea-
sure the enormous swelling pressure of tissues with
high glycosaminoglycan content (e.g., nucleus pul-
posus). Previous osmometric techniques were un-
reliable because of cavitation (gas bubble forma-
tion) on the side of the membrane opposite the
swelling tissue.
Our new compression-type osmometer (Fig. 4)
consists of a sample chamber over a rigid Millipore
filter (0.5-pm pore diameter). Samples of nucleus
pulposus are compressed over the membrane by ni-
trogen gas to prevent swelling of the tissue. Equi-
librium swelling pressure is reached within 10-30
min and measured by a Heise precision gauge. Pres-
sure gradients across the membrane are detected
using a low volume displacement, pressure trans-
ducer, and nullified by the pressurized gas.
To examine the accuracy of our new osmometer,
five 20-mg samples of pooled dog or pooled pig nu-
cleus pulposus from lumbar intervertebral discs
were placed in the osmometer and the maximum
swelling pressures were measured (5). Samples of
dog and pig nucleus pulposus were also evaluated
with the equilibrium dialysis technique (26) using
2,000 M.W. cutoff dialysis tubing and 8,000 M.W.
polyethylene glycol (PEG) solutions ranging in con-
centration from 0.05 to 0.80 mg of PEG/ml of H,O.
Mean equilibrium swelling pressures of dog and
pig nucleus pulposus measured by direct osmome-
try were 2.3 f 0.3 and 0.5 k 0.002 atm, respec-
tively, agreeing well with the calculated values ob-
tained by the dialysis technique (1.9 and 0.4 atm,
respectively). Therefore, this osmometer provides a
simple, rapid, and direct measurement of swelling
pressure. It can be used to investigate enzymatic
and hydration effects on the nucleus pulposus
swelling pressure in relatively small samples. The

FIG. 4. New compression-type
osmometer for measuring
swelling pressure of nucleus
pulposus. Left: Plexiglas os-
mometer mounted on stand
with nitrogen gas inlet at top.
The osmometer is connected
to a nitrogen gas source, pre-
cision pressure gauge, and
pressure transducer. Trans-
membrane pressure gradients
are continuously measured by
a strip-chart recorder. Right:
Cross-section of osmometer
with sealing of membrane by
the crimp rings (CR) on the
screw-down Plexiglas plate.
The nucleus pulposus is
placed in the sample well (SW)
on top of the membrane (M).
Pressure gradients across the
membrane are transmitted by
the fluid column (S) and mon-
itored by the pressure trans-
ducer (PT) fitted tightly to the
bottom of the osmometer by
an 0 ring (OR). (From Glover
et al., ref. 5.)
high swelling pressures of disc samples cannot be
measured using standard osmometers because of
cavitation problems beneath the membrane. This
osmometer provides equilibrium measurements
within 10-30 min as compared to 24-48 h for the
indirect, equilibrium-dialysis technique.
ACUTE CHRONIC COMPARTMENT
SYNDROMES
Definitions
A compartment syndrome is a condition charac-
terized by high muscle pressure, myoneural pain,
paresthesis, paresis, pink skin color, and presence
of distal pulse (the six p’s of a compartment syn-
drome) (Fig. 5). The syndrome is induced by high
tissue pressure within a confined region of skeletal
muscle, causing sufficient ischemia to compromise
myoneural structures (27). Elevated pressure is pro-
duced by internal swelling or external compression
of muscle and may occur in almost any region of the
body. Muscle compartments of the leg are involved
most frequently, but compartment syndromes are
reported in thigh, buttock, shoulder, arm, and hand
muscles as well (31,37). Typically, muscles in-
volved in this ischemic process are enclosed within
relatively impermeable, noncompliant osseofascial
boundaries that preclude spontaneous dissipation of
tamponade within the involved compartment.
TISSUE FLUID PRESSURES 905
Therefore, surgical decompression by fasciotomy is
required to renew adequate blood flow through
ischemic tissues. If intracompartmental pressure re-
mains elevated for a sufficiently long period of time
without fasciotomy , necrosis of intracompartmental
tissues will occur. The well-known clinical entity of
Volkmann’s contracture may thus result if prompt
diagnosis and treatment of the jeopardized limb are
not undertaken (31).
Pulse
Paresthes,a@
Parnls t
- Pink color
Pam wth stretch
FIG. 5. Comparison of normal leg (left) and leg with compartment
syndrome (right). When tissue fluid pressure within one
or more muscle compartments rises above the capillary
blood pressure (30-40 mm Hg), ischemia occurs and blood
flow IS confined solely to large vessels and collateral circulations
(From Mubarak and Hargens, ref. 31, with permission.)
J Orthop Res, Vol. 7, No. 6, 1989

906 A. R. HARGENS ET AL.
Acute Compartment Syndrome
Compartment syndromes are commonly divided
into two forms, acute and chronic, based on etiol-
ogy and reversibility. An acute compartment syn-
drome develops when intramuscular pressure ex-
ceeds capillary blood pressure for a prolonged
period of time. In this setting, immediate decom-
pression is necessary to prevent myoneural necro-
sis and Volkmann’s contracture. Acute compart-
ment syndromes are produced by trauma, arterial
injury, arterial reconstruction, extreme exertion, or
prolonged limb compression.
Chronic Compartment Syndrome
A second form of syndrome is defined as a
chronic (exertional) compartment syndrome, also
termed recurrent compartment syndrome by some
authors. This condition occurs when exercise in-
creases intramuscular pressure sufficiently to cause
ischemia, pain, and, on some occasions, decreased
sensibility or dysfunction (39). Commonly, these
symptoms disappear when the activity is stopped
and reappear during the next exercise activity.
However, if muscular activity is maintained despite
pain, neurologic deficit, and persistent tamponade,
a chronic compartment syndrome can precipitate an
acute compartment syndrome, which then requires
immediate fasciotomy .
Measurement of Intracompartmental Pressure
Because high intracompartmental pressure is the
underlying pathogenic factor common to all acute
compartment syndromes, its measurement is often
required, especially in patients who are uncooper-
ative (children), unresponsive, or comatose. Sev-
eral clinical techniques for monitoring intracom-
partmental pressure are available today. However,
some techniques are preferred over others in terms
of accuracy, safety, and cost.
Advantages of the wick technique include a rela-
tively large area for sensing tissue fluid pressure,
avoidance of saline infusion (equilibrium measure-
ments are thus obtained), and continuous monitor-
ing of pressure. Disadvantages include possible co-
agulation around the catheter tip, especially if the
wick fibers are packed too tightly in the catheter tip,
and relatively slow response to pressure changes
during exercise studies. Overall, the wick technique
J Orthop Res, Vol. 7, No. 6, 1989
is simple, accurate to +1 mm Hg, and reliable for
diagnosis of compartmental tamponade.
The slit catheter technique (40) represents an at-
tempt to improve the wick catheter by a more open
catheter tip. This design allows a higher frequency
response to intracompartmental pressure changes
and thus is preferred for studies of chronic compart-
ment syndrome as discussed below. The slit cathe-
ter is less prone to coagulation, but air bubbles form
more easily around the tip, which may reduce re-
sponse time and invalidate a measurement. Overall,
however, the wick and slit catheters are equally ac-
curate and reliable for diagnosis of acute compart-
ment syndromes.
Thresholds of Pressure and Time
for Fasciotomy
Based on several clinical studies (3 1,33,35) and
animal experiments (10,19,20), decompressive fas-
ciotomy is recommended for normotensive patients
with positive clinical findings and intracompartmen-
tal pressures >30 mm Hg when duration of in-
creased pressure is unknown or thought to be 2 8 h
after the initial trauma event. Undoubtedly, there
exists a broad spectrum of tolerance to compart-
mental tamponade and ischemia among patients.
However, considering the disastrous results of an
unrelieved acute compartment syndrome, we rec-
ommend that any compartment with stable or rising
pressures >30 mm Hg be decompressed if clinical
indications are positive. When clinical signs of a
compartment syndrome are difficult to obtain (e.g.,
uncooperative or unconscious patient), fasciotomy
should be performed on any compartment with
pressure >30 mm Hg. Recent animal and clinical
experiments indicate that, in some instances, the
previously indicated thresholds for fasciotomy
should be revised. Under conditions of low blood
pressure, the fasciotomy pressure and time thresh-
olds fall to 20 mm Hg and 6 h, respectively (47).
Using a reliable technique for assessing long-term
muscle function in dogs (16), a significant decrease
in contractile properties occurs 2 days after main-
taining intracompartmental pressure at 40 mm Hg
for 8 h. In the subsequent period of 7-28 days, iso-
metric twitch torque and isometric tetanic torque
return to their normal, precompartment syndrome
values (30). Muscle fiber types in dogs, however,
may be more resistant to ischemia than human mus-
cle. Our studies of pressure thresholds for nerve
dysfunction in normal human subjects provide im-

portant insights into pressure and time thresholds
for fasciotomy and emphasize the important role of
systemic blood pressure.
Finally, recent studies using hyperbaric oxygen
(HBO) to treat impending compartment syndromes
in dogs indicate that muscle necrosis and edema
formation are significantly reduced following imme-
diate (45) and 2-h delayed (46) treatments with HBO
(p < 0.05). Clinically, however, HBO treatments
are still experimental and their availability does not
alter our recommended fasciotomy thresholds.
Treatment
The principles of treating compartment syn-
dromes and specific surgical procedures for the
arm, hand, and leg are presented in detail elsewhere
(3 1). We recommend the curvilinear volar incision
(4) for arm compartments and a double-incision fas-
ciotomy technique (34) to decompress the anterior,
lateral, posterior, and deep posterior compartments
of the leg. Besides its usefulness in diagnosing acute
and chronic compartment syndromes, intracom-
partmental pressure measurement is valuable in fol-
lowing the adequacy of treatment of compartment
syndromes. During fasciotomy, the decrease in in-
tracompartmental pressure is measured at the prox-
imal and distal limits of the compartment to monitor
the effectiveness of surgery. Moreover, intraopera-
tive recording of pressure enables us to close skin
incisions without again inducing tamponade. Der-
motomy (skin incision) decreases pressure in a mi-
nor way, whereas fasciotomy lowers intracompart-
mental pressure to a level within normal range.
Epimysiotomy also has little effect on pressure.
With early fasciotomy, muscle color usually goes
from gray to pink. In summary, intraoperative mea-
surements of muscle pressures have allowed us to
optimize fasciotomy procedures, avoid fibulec-
tomy, and minimize the extent of skin incisions.
DEVELOPMENT OF BETTER
TOURNIQUET DESIGN
More Effective Compression of Deep Tissues Using
Wider Tourniquet Cuffs
Occlusion of blood flow by a pneumatic tourni-
quet is used routinely for orthopaedic surgery on
the upper and lower limbs to provide a bloodless
operating field. The common acceptance of the
tourniquet as a surgical tool, however, should not
suggest that its use is without risk. Complications
are more common than may be appreciated, and
TISSUE FLUID PRESSURES 907
some of the morbidity of tourniquet use is often
unrecognized (25). Reported complications are
muscle damage observed histologically, function-
ally, and biochemically and vascular problems such
as deep vein thrombosis, arterial thrombosis, false
aneurysm, fractured vessel walls, and postischemic
edema (for review, see ref. 14).
The time period during which it is safe to apply a
tourniquet on a limb is important in surgical prac-
tice (24,41). Similarly, the orthopaedist should
know the minimum pressure necessary to occlude
blood flow in a limb so as not to cause complica-
tions due to excessive compression. However,
these minimum pressures for adequate hemostasis
are not well defined. For a standard 8-cm wide tour-
niquet, recommended cuff pressures for the arm
and leg range between 250-300 and 300-400 mm
Hg, respectively. Most previous studies of tourni-
quet injury have focused upon the effects of isch-
emia in tissues distal to the applied cuff. Impor-
tantly, however, recent studies of the effects of
tissue pressures on muscles, nerves, and blood ves-
sels directly beneath the tourniquet cuff suggest
that these underlying tissues are more seriously
jeopardized (14,28,38,44).
Distributions of tissue fluid pressure were exam-
ined beneath a standard pneumatic tourniquet in six
upper extremities and six lower extremities of fresh
human cadavera, disarticulated at the shoulder and
hip, respectively, leaving muscle compartments in-
tact. An 8-cm wide tourniquet cuff was applied at
midhumerus or midfemur position. Tissue fluid
pressure was always maximal in subcutaneous tis-
sue at midcuff. Transmission of cuff pressures to
deeper tissues was significantly less in the 40-52-cm
girth thighs than in the 22-33-cm girth arms. At the
four tissue depths studied, tissue fluid pressures fell
steeply in a longitudinal direction near the cuff edge
to levels near 0 at a point 1-2 cm outside each cuff
edge (14). In another study (2), longitudinal and ra-
dial tissue fluid pressure distributions were deter-
mined beneath and adjacent to wide (12 and 19 cm)
pneumatic tourniquet cuffs placed on intact human
cadaveric arms and legs. Tissue fluid pressures ex-
hibited relatively broad maxima at midcuff and in
most cases showed no difference at the various
depths studied. Therefore, wide cuffs transmit a
greater percentage of the applied tourniquet pres-
sure to deeper tissues than 8-cm cuffs, which are
conventionally used for extremity surgery. Our re-
sults suggest that wider cuffs are required on thighs
than on arms to provide a bloodless field during
I Orrhop Res, Val. 7, NO. 6, 1989

908 A. R. HARGENS ET AL.
surgery. Also, because they allow lower inflation
pressures, wider cuffs may avoid underlying tissue
injury associated with high cuff pressures.
Relationship Between Pneumatic Tourniquet Width
and the Inflation Pressure Required to Eliminate
Blood Flow
In another series of tourniquet experiments (29),
we investigated the pressure required to eliminate
blood flow (measured by a Doppler flowmeter) to
the upper extremity using three different tourniquet
widths in 10 normal volunteers. The clinical utility
of a wide cuff (15.5 cm) was then assessed in a va-
riety of unselected upper and lower extremity pro-
cedures, employing a reduced tourniquet inflation
pressure.
A significant negative correlation was found be-
tween cuff width and the pressure required to elim-
inate arterial flow. The widest cuff eliminated blood
flow at the lowest inflation pressure in all subjects.
Specifically, the mean pressure that eliminated flow
was significantly lower for the 15.5-cm wide cuff
(104 mm Hg) than for the standard 8.0-cm wide cuff
(123 mm Hg) and the narrow 4.5-cm wide cuff
(150 mm Hg). Arterial occlusion pressure was also
significantly correlated with arm circumference.
A wide (15.5 cm) cuff was used in 23 unselected
upper and lower extremity surgeries while the pa-
tients’ blood pressures were recorded every 15 min.
In most cases, initial inflation pressures were 150
and 200 mm Hg for upper and lower extremity sur-
geries, respectively. The surgeon then judged
whether or not the bloodless field was adequate,
and cuff pressure was increased if necessary. Clin-
ical evaluation of the wide (15.5 cm) tourniquet was
performed in 16 upper extremity and seven lower
extremity cases. For upper extremity cases, ade-
quate hemostasis was obtained in 69% of cases with
pressures between 100 and 150 mm Hg and 100% of
cases with maximum inflation pressures of 180 mm
Hg using the wide cuff. For lower extremity proce-
dures, 100% of patients had adequate operative he-
mostasis with inflation pressures of 200 mm Hg.
Two patients requiring bilateral lower extremity
tendon transfers had a wide tourniquet on one leg
and a standard 8.0-cm tourniquet on the contralat-
era1 leg. Initial inflation pressure for both cuffs was
200 mm Hg, but inadequate hemostasis with the
narrow cuff required inflation to 300 mm Hg. The
wide cuff required no adjustments in inflation pres-
sure.
J Orthop Res. Vol. 7, No. 6, 1989
Current recommendations for pressurization of
pneumatic tourniquets used in surgery range from
250-300 mm Hg for the upper extremity and 300-
400 mm Hg for the lower extremity. Our data sug-
gest that significantly lower pressures produce a
bloodless field for orthopaedic surgery if wider
tourniquets are used. Lower inflation pressures
may reduce the incidence neuropraxiae and postop-
erative muscle injury.
Acknowledgment: As evidenced by the numerous co-
authors on articles and books referenced in this review,
our research and clinical progress was only made possible
by a team effort of many colleagues, fellows, residents,
students, and staff at UCSD and V.A. Medical Center,
San Diego. Their contributions and those of co-workers
from other cooperating institutions combined with con-
tinued research support from the Veterans Administra-
tion, several institutes of the NIH, NASA, the NSF, and
the National Geographic Society are gratefully acknowl-
edged. We thank the following individuals who contrib-
uted to various portions of this research: UCSD faculty,
visitors, and staff P. F. Scholander, Lawrence P. Ga-
retto, Karen L. Evans, Mary R. Gonsalves, Peggy Gor-
ball, C. M. Tipton, John B. Cologne, Barbara Sverdrup,
Sanford S. Zweifach, Vivian Drake, Goran N. Lundborg,
Bjorn L. Rydevik, H. T. Hammel, Michael B. Strauss,
Albert G. Crenshaw, Robert M. Szabo, Sunny Schacher,
Kurt Smolen, M. Jean Robison, Linda Kitabayashi,
Tracy Tangen, Sharon Gott, and Janeen McCracken;
UCSD residents and fellows: Ladd Rutherford, Donald
A. Schmidt, Robert K. Smith, Robert N. Gould, Yu Fon
Lee, Jan Fronek, Wayne Mortensen, Charles E.
Rhoades, Michael J. Skyhar, Jan Friden, Michael G.
Glover, Michael R. Moore, Thomas R. Ferro, and Rob A.
Pedowitz. This research was supported by the Veterans
Administration and by grants from USPHSNIH (AM-
18824, GM-24901, AM-25501, AM-26344, and HL-32703),
NASA (NAS9-16039), NSF (DCB 84-09253), National
Geographic Society (3072-85), and by a Research Career
Development Award to A.R.H. (AM-00602). This study
won the Elizabeth Winston Lanier Kappa Delta Award
from the American Academy of Orthopaedic Surgeons
and the Orthopaedic Research Society, San Francisco,
CA .
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