Naval Submarine Medical Research Laboratory

NSMRL REPORT 1200 22 MAY 1996

Decompression Sickness

Resulting From Long Shallow Air Dives

C. L. Shake

P. K. Weathersby

D. Wray

and

E.C.Parker

1

Released by

R. G. Walter, CAPT, DC, USN

Commanding Officer

Naval Submarine Medical Research Laboratory

DTIC QUALITY INSPECTED 1

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Decompression Sickness Resulting From Long Shallow Air Dives

C. L. Shake

P. K. Weathersby

D. Wray

E. C. Parker

Naval Submarine Medical Research Laboratory

NSMRL Report 1200

Naval Medical Research and Development Command

Research Work Unit 63713N M0099.01A-5201

Approved and Released by

R. G. Walter, CAPT, DC, USN

Commanding Officer

Approved for public release; distribution unlimited
Summary Page

The Problem

The objective of this research was to provide human decompression data, including the occurrence and timing of resulting DCS cases, in a range of depths and bottom times which are inadequately represented in the Primary Air and Nitrogen-Oxygen (N2-O2) data set (Weathersbv

et al. 1992).

The Findings

The occurrence of decompression sickness (DCS) was examined in 57 man-dives to depths

between 8.5 and 12.2 msw (28 and 40 fsw) for six hours on air. During exposure, divers exercised using a bicycle ergometer at a moderate workload (100 watts) on a 50% work/50% rest cycle. After six hours bottom time, divers were immediately brought to the surface. Three DCS

cases and two marginal DCS cases resulted from decompression from the deepest depths of 11.6

and 12.2 msw (38 and 40 fsw).

Application

The data from these and other dives were added to a master data base for diving at the Naval

Medical Research Institute. This addition has allowed for further development of the probabilistic decompression model by providing the first available data in an important depth and bottom time range. The model's predictions of DCS risk for dives in this range are improved by the

presence of these profiles in the calibration data set.

Administrative Information

This research was conducted under Naval Medical Research Work Unit 63713NM0099.01A5201, Submarine related decompression problems. The views expressed in this report are those

of the authors and do not reflect the official policy or position of the Navy, Department of Defense, or the U.S. Government. This report was approved for publication on 22 May 1996 and

has been designated as NSMRL Report 1200.

n
Abstract

The objective of this research was to provide human decompression data, including the occurrence and timing of resulting DCS cases, in a range of depths and bottom times which are inadequately represented in the Primary Air and N2-O2 data set.

The occurrence of DCS was examined in 57 man-dives to depths between 8.5 and 12.2 msw

(28 and 40 fsw) for six hours on air. During exposure, divers exercised using a bicycle ergometer at a moderate workload (100 watts) on a 50% work/50% rest cycle. After six hours bottom

time, divers were immediately brought to the surface. Three DCS cases and two marginal DCS

cases resulted from the deepest depths of 11.6 and 12.2 msw (38 and 40 fsw). The data from

these and other dives were added to a master data base for diving at the Naval Medical Research

Institute.

111
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IV
DECOMPRESSION SICKNESS

RESULTING FROM LONG SHALLOW AIR DIVES

Decompression table development historically has been approached through simple

table calculation, limited testing on very few

profiles, and reiteration of table calculation.

More recently, probabilistic modeling and

maximum likelihood analysis (Weathersby,

et al., 1984; Weathersby, 1989; Weathersby,

et al., 1992) have been used. From these,

improved assessment of decompression sickness (DCS) risk for proposed yet untested

decompression schedules is possible.

Data from the past few years has been

collected from a wide variety of dives. These

data have been put into a master data base for

decompression modelling (Weathersby, et

al., 1992). With these data available for

calibration, probabilistic models have been

developed for bounce dives in the range of 3

to 64 meters sea water (msw) (10 to 210 feet

sea water (fsw)) which include up to two

hours of decompression stops (Weathersby, et

al., 1992). Diving profiles which are not well

represented in the data base have poorer predictive ability with the model. Long, nonsaturated no decompression (no-D) dives

(6-12 hours) at fairly shallow depths are an

example of such dive profiles. The recent

summary of the data base shows only 91 air

dives conducted at 18.6 msw (61 fsw) in this

bottom time category (Weathersby, et al.,

1992).

One of the earlier probabilistic models

(Hayes et al., 1986) predicted a 1.0% incidence of DCS risk following no-D dives to

5.8 msw (19 fsw), 5.0% DCS risk for dives to

8.5 msw (27.9 fsw), and 10% DCS risk for

dives to 11.0 msw (36 fsw). Another model

generated at the Naval Experimental Diving

Unit (NEDU) (Thalmann, 1986), predicted

that a diver could stay at 9.1 msw (29.9 fsw)

for six hours, and then surface safely at the

end of the dive.

The objective of this research was to provide data in a depth/bottom time range not yet

represented in the data base. This was to be

accomplished by: a) prediction of initial

limits with existing models, b) performance of

a test dive series using a sequential experimental design, and c) combination oftest dives with

other data for a robust prediction oflimits.

Methods, Materials and Design

All dives were conducted dry in the

"Genesis" hyperbaric chamber at the Naval

Submarine Medical Research Laboratory

(NSMRL) in Groton, Connecticut. Simulated

depth was maintained within ± 0.15 msw

(+0.5 fsw). Temperature and humidity were

adjusted for subject comfort. Oxygen was

continuously maintained at 20.94% (air)

±0.05%. Carbon dioxide was maintained at

or below 0.5% surface equivalent.

All subjects were qualified military divers

(active duty and reserve). Three to four subjects were used in each exposure. Divers

refrained from all pressure exposure for at

least three days before the experiment. Alcohol consumption and the taking of any drugs

(including aspirin) were prohibited within 24

hours prior to the dive. Divers also abstained

from any exercise the morning of the dive.

Subjects were allowed to repeat an experiment,

but not at the same depth. Any diver who

suffered from DCS was not allowed to reenter the experiment until two weeks after

completion of therapy. Divers were advised to

neither dive nor fly for 36 hours after surfacing.
Six hours (including compression time of

1 to 7 minutes) were spent breathing air at

simulated depths from 8.5 to 12.2 msw (28 to

40 fsw). During the exposure, subjects exercised on a bicycle ergometer at a paced rate of

67 revolution per minute (rpm) and a workload of 100 watts on a 30 minutes work/30

minutes rest cycle for a total of four exercise

periods (two hours work total). After the six

hour bottom time, an immediate ascent to the

surface was made at a rate of 7.6 to 18.3 msw

(25 to 60 fsw) per minute (average rate of 17

msw (55.8 fsw) per minute), except for 6 exposures at 8.5 msw (28 fsw) which reached

the surface in 3 minutes.

Decompression Monitoring

A qualified Diving Medical Officer (DMO)

made a diagnosis in accordance with conventional diagnostic categories (NAVSEA, 1987).

Evaluation of subjects was based both on

spontaneous reporting of symptoms and postdive medical examinations. All divers were

examined immediately after surfacing, about

two hours after surfacing, and again 24 hours

after surfacing. All divers were strongly

encouraged to report any unusual feelings,

regardless of whether or not they appeared to

be dive related. When a diagnosis of DCS

was made, appropriate treatment was immediately initiated (NAVSEA, 1987). Treatment

table extension was performed as required.

Sequential Design

The experimental series started with dives

to a depth of 8.5 msw (28 fsw) for six hours.

If no DCS occurred in at least ten man-dives,

then the depth was increased by 1.2 msw

(4 fsw), and ten additional man-dives were

conducted. If two cases of DCS occurred in

any number of man-dives at a given condition, then the depth was decreased by 0.6

msw (2 fsw). The test protocol was sequentially repeated following the same decision

rules.

Results

A total of 57 man-dives were conducted

with 50 different divers (49 males and 1

female, mean age = 26.7 years). Five divers

performed a total of two dives and one diver

performed a total of three dives. None of the

repeat divers suffered DCS. Table 1 outlines

the incidence of DCS and marginal DCS for

these dives. Marginal cases are considered

minor decompression-related problems that

are not diagnosed as DCS but represent unusual feelings or fleeting pains that occur

following a dive (Table 1).

Table 1.

Incidence ofDCS andMarginalDCS casesfollowing

shallow 6 hr air dives

Depth Cases Cases

msw/fsw N DCS Marginals

8.5/28

9.8/32

11.0/36

11.6/38

12.2/40

10

11

11

10

15

0

0

0

1

2

0

0

0

1

1
Three treated cases and two marginal cases

of DCS resulted from the entire series. These

decompression problems occurred following

dives to the two deepest depths, 11.6 and 12.2

msw (38 and 40 fsw). Following treatment,

divers with DCS had complete resolution of

DCS symptoms, with no residuals.

The first case of DCS occurred in a 29 year

old male following a 11.6 msw (38 fsw) exposure. Approximately 2 hours after surfacing,

the subject developed severe throbbing left

retro-orbital pain. He had a history of cluster

headaches, usually precipitated by alcohol and

fatigue, and this headache was not different

than those previously experienced. The headache resolved within 3 hours and the subject

slept comfortably. At 65 hours post-dive, the

diver noted the sudden onset of left hip pain,

made much worse with weight bearing. The

pain was described as "deep-seated" and

"within the hip joint." There was not a history

of recent trauma or previous hip pain. The

pain progressed over a 1 to 2 hour period to

the point where the subject was unable to bear

weight on the left leg (10 out of 10 in severity). There were no other complaints. Examination of the left hip revealed no erythema or

swelling. Slight tenderness was elicited with

palpation of the greater trochanter. Range of

motion of the affected hip was limited, especially abduction and extension. Strength was

decreased secondary to pain. Sensation in the

left leg was intact. Deep tendon reflexes in

the lower extremities were 3+ and equal bilaterally. The subject was unable to bear weight

on the left leg. The remainder of the neurological and general physical examination were

normal. An x-ray of the left hip was normal.

Although the symptoms occurred very late

post-dive, there was no other clear explanation for the severe pain and loss of function.

The subject was compressed to 18.3 msw (60

fsw) on oxygen and had a 50% reduction in

pain (now 5/10) after the first 20 minute oxygen

breathing period. Symptoms continued to decrease in severity and were essentially resolved

after a total of 5 oxygen breathing periods at

18.3 msw (60 fsw). The U.S. Navy extended

Treatment Table 6 (TT6) was completed without complication and on surfacing, the subject

had only mild residual left hip soreness. Posttreatment examination was normal. The soreness slowly resolved over the next 3 to 5 days.

The second case of DCS occurred following a dive to 12.2 msw (40 fsw). The subject,

a 30 year old male, reported right shoulder

pain approximately 1 hour 5 minutes after

surfacing. The pain was described as poorly

localized with an intensity of 2 out of 10

which increased to 3/10 during the first few

minutes of the DMO examination, then gradually decreased. Two hours and 20 min. after

surfacing, the subject was treated on a TT6.

Following the second 20 minute 02 breathing

period (with 5 min air breathing between 02

periods) at 18.3 msw (60 fsw), the patient reported prior fleeting left shoulder pain that he

stated occurred during pressurization but resolved quickly at approximately 7.6 msw (25

fsw) on descent. The patient also reported

being free of symptoms after this time. The

standard TT6 was completed with no residual

problems after treatment.

The third case of DCS encountered occurred

after a 12.2 msw (40 fsw) dive. At 2 hours

and 10 minutes post dive a 32 year old male

complained of mild left posterior knee stiffness. He stated it began approximately 10

minutes after surfacing but that the discomfort

had not progressed. The diver also complained

of minor neck "stiffness." Examination of the

left knee, left leg, and neck were normal. At

about 3.5 hours after surfacing, the diver

noted a dull pain in his left hand between the

fourth and fifth metacarpal. He also described

dull pain in both the left triceps and left trapezius muscles. The neck discomfort persisted

and intermittently radiated to his left arm. A

variety of additional symptoms noted included
transient left ankle and left foot pain, brief

periods oflight-headedness, and short episodes

of a "cold, clammy feeling all over." These

additional symptoms resolved prior to treatment. At 5 hours post-dive, the subject

complained only of pain in the left hand, left

triceps and left trapezius muscles. The severity

was graded 2/10. The neck stiffness persisted. Neurological examination, including

motor, sensory, and cerebellar testing, was

normal. A diagnosis of neurological DCS

was made, and the subject was compressed to

18.3 msw (60 fsw) on 100% oxygen. He

noted complete resolution of all muscular pain

and neck stiffness 10 minutes into the first

oxygen breathing period. Left hand stiffness

was relieved 20 minutes into the first oxygen

period. A TT6 was completed without complication. Examinations immediately after treatment and on the following day were normal.

The first marginal DCS case occurred 10

hours after surfacing from a dive to 11.6 msw

(38 fsw). The case involved a male diver (age

= 33 years) who had fleeting minor pain in his

right wrist and left elbow which was not sustained nor well defined. All symptoms were

gone by 16 hrs post-dive without treatment.

The second marginal DCS case occurred

18 hours and 40 minutes after surfacing from

a dive to 12.2 msw (40 fsw). This case also

involved a male diver (age = 30 years) who

had transient and intermittent pain in his left

knee. About 45 minutes after surfacing all

symptoms were gone and no treatment was

necessary.

Discussion

No cases of DCS resulted from dives to

depths of 8.5, 9.8, and 11.0 msw (28,32, and

36 fsw). The incidence of DCS was 10.0%

for dives to 11.6 msw (38 fsw) and 13.3% for

dives to 12.2 msw (40 fsw). These results

however, are of limited use because of the

small number of replicate exposures at each

depth. Decompression testing having a substantial degree of confidence is not practical

since the number of replicate exposures

needed for a single dive profile is very large.

For example, to be 95% confident that the

Table 2.

Predictions ofDCS incidence for 6 hour dives

Model Predictions (Parker, et al. 1992)

Avg% (95% Confidence Limits)

msw/fsw DCS Lower Upper

8.5/28 4.04 2.44 5.62

9.8/32 5.26 3.91 7.57

11.0/36 7.52 5.42 9.58

11.6/38 8.50 6.25 10.70

12.2/40 9.42 7.04 11.76
underlying incidence of DCS risk is less than

10%, one would need to conduct 54 mandives per profile and encounter only one case

of DCS. Conducting a large number of mandives is theoretically possible, but it is also

economically unfeasible. A more practical

alternative is to use a large collection of exposures from a variety of dives performed at

various laboratories to allow quantitative

extrapolation into other risk conditions

(Weathersby, et al., 1984).

One such probabilistic model reported in

1992 (Parker, et al.,) was used to predict DCS

risk for the shallow 6 hour dives of this study

(Table 2). This model predicted 4.0,5.3, 7.5,

8.5, and 9.4% DCS for dives to 8.5, 9.8,11.0,

11.6, and 12.2 msw (28,32,36,38, and 40

fsw), respectively.

The addition of new data to the master data

base should improve predictions for untested

long shallow bounce dive scenarios. As this

database grows with the addition of data from

similar dives, no-D limit predictions for nonsaturation bounce dives will become more accurate. As DCS risk predictions improve,

planned management of those risks becomes

more quantitative.

References

Hayes, J. R., Hart, B. L, Weathersby, P. K.,

Survanshi, S. S., Homer, L. D., & Flynn,

E. T. (1986). Statistically based decompression tables IV. Extension to air and

N2-O2 decompression (NMRI Report 86-

51). Bethesda, MD: Naval Medical Research Institute.

Kelleher, P. C, Thalmann, E. E., Survanshi,

S. S., & Weathersby, P.K. (1992). Verification trial of a Probabilistic decompression model. Undersea Biomedical

Research, 19, Supplement, 78-79.

NAVSEA. (1987). U.S. Navy Diving Manual Vol.1. (NAVSEA0094-LP-001-

9020). Washington: Navy Department.

Parker, E. C, Survanshi, S. S., Weathersby, P.

K., and Thalmann, E. D. (1992). Statistically based decompression tables. VIII.

Linear-exponential kinetics (NMRI

Report 92-73) Bethesda, MD: Naval

Medical Research Institute.

Thalmann, E. D. (1986). AU-N2-O2 Decompression computer algorithm development

(Report 8-85). Bethesda, MD: Naval

Medical Research Institute.

Weathersby, P. K. (1989). Uncertainty in decompression safety. In H. R. Shreiner, &

R. W. Hamilton (Eds.). 37th UHMS

Workshop. Validation of Decompression

Tables (UHMS Publication 74(VAL) 1-1-

88) (pp 125-129). Bethesda, MD: UHMS.

Weathersby, P. K., Homer, L. D., & Flynn, E.

T. (1984). On the likelihood of decompression sickness. Journal of Applied Physiology: Respiratory, Environmental and

Exercise Physiology, 57, 815-825.

Weathersby, P. K., Survanshi, S. S., Nishi,

R.Y., and Thalmann, E.D. (1992). Statistically based decompression tables VII. Selection and treatment of primary air and

N202 data (Joint Report: NSMRL Report

1182; NMRI Report 92-85). Groton, CT:

Naval Submarine Medical Research Laboratory.

Weathersby, P. K., Survanshi, S. S., Homer,

L.D., and Parker, E.C. (1993). Predicting

the time of occurrence of decompression

sickness. Journal ofAppliedPhysiology,

72,1541-1548.

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(U) Decompression sickness resulting from long shallow dives

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C. L. Shake. P. K. Weathersbv. D. Wrav. and E. C. Parker

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1996 May 22

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Decompression; shallow; air; dive

19. ABSTRACT (Continue on reverse if necessary and identify by block number)

The objective of this research was to provide human decompression data, including the occurrence and

timing of resulting DCS cases, in a range of depths and bottom times which are inadequately represented in

the Primary Air and N2-O2 data set.

The occurrence of DCS was examined in 57 man-dives to depths between 8.5 and 12.2 msw (28 and 40

fsw) for six hours on air. During exposure, divers exercised using a bicycle ergometer at a moderate

workload (100 watts) on a 50% work/50% rest cycle. After six hours bottom time, divers were

immediately brought to the surface. Three DCS cases and two marginal DCS cases resulted from the

deepest depths of 11.6 and 12.2 msw (38 and 40 fsw). The data from these and other dives were added to a

master data base for diving at the Naval Medical Research Institute.

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Susan D. Monty, Editor

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