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A JOWER BODY NEGATIVE PRESSURE BOX FOR +Gz | / 1} ai Febsnmageas 79
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FAA Civil Aeromedical Institute
P.0. Box 25082 TI. Contract or Grant Ne,

Oklahoma City, Oklahoma 73125

13. Type of Report ond Period Covered

12, Sponsoring Agency Nome ond Address
Office of Aviation Medicine
Federal Aviation Administration

800 Independence Avenue, S.W. 1
Washington, D.C. 20591

15. Supplementery Notes

This research was performed under Task AM-A-77-PHY-99.

ee,

6. Abstrect
ithe cost of purchasing and operating a human centrifuge is substantial. Lower body
negative pressure (LBNP) is considered an acceptable experimental substitute for
the +Gz stress of the centrifuge. Since civil aviation pilots are usually
subjected to +Gz stress in an upright seated position, an upright seated version
of the supine LBNP box was developed. In this version, a negative pressure of
-40 mm Hg is considered the equivalent of a +2 Gz stress. This box has successfully
withstood a test pressure of -120 mm Hg. Pedal ergometry within the box is easily
accomplished. The box was anthropometrically engineered to accommodate a human
height range of 160-195 cm. Locating the box within an altitude chamber allows
the application cf LBNP at any level of chamber altitude. The total cost of
fabrication is approximately $500. }

«
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1. Key Words V8. Diswibution Srerewent .
Lower Body Negative Pressure Document is available to the public
LBNP Box through the National Technical Information
4+Gz Simulation

Service, Springfield, Virginia 22161
4+G6z Tolerance

Civil Aviation Pilots

19, Security Closeil. (of thra report) BO. Security Classil. (of this poge) ‘21. No. of Peges | 22. Price
Unclassified Unclassified : 7

Form DOT F 1700.7 «6-72) Repredection of completed page outhorized

VL “2307 m..

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seals are similar to those reported previously by others for use with the
supine LBNP box (6). The hatch-cover port is angled upward at 43° from the
horizontal plane. This anthropometrically determined angle was the minimum
allowable value for frontal waist-sealing without compromising thoracic
ventilatory excursions, and for pedal ergometry without the knees bumping
into the hatch cover. This angle and the adjustment ranges of seating height
and pedal length were anthropometrically determined to accommodate a subject
height range of 160-195 cm.

~A 0-75-horsepover_vasuum cleaner (Figure 1) is ordinarily used as the
source of negativé pressure. When our LBNP box is used at substantial
chamber altitudes, the negative pressure source is the vacuum-accumulator
tank of the altitude chamber. | The level of negative pressure inside the

box is regulated by an adjustable orifice located in the upper-left sidewall,
and the pressure magnitude is continuously indicated by a mercury-calibrated
differential pressure gauge connected to the inside of the box (Figure 1).

The pedal ergometer (Figures 1 and 2) (Pedalmate, Warren E. Collins,
Inc., Braintree, MA) is mounted on an adjustable locking slide track to
accommodate interindividual variability in leg lengths. The adjustment for
leg lcngth is made via the plexiglass access door. The ergometer console
for controlling load and revolutions per minute is located on the top of the
LBNP box (Figure 2).

Operation.

For our experimental purposes, the LBNP box is located inside one of
our altitude chambers. Thus, it can be used at ground level or at any
desired chamber altitude. Initially, the subject is seated in the box fer
determination of the maximum seat height which still includes the iliac
crest within the box, and the optimum pedal distance for comfortable ergo-
metry. The subject then exits the box and is fitted with all the sensors
to be used during the experiment. The sheet-rubber waist seals are tied
circumferentially in place, and the subject is reseated in the box. The
hatch cover is positioned and bolted in place. The three contoured slats
are adjusted to the individual's waist size, and the rubber waist seals are
superimposed upon them. The generation of negative pressure within the
box causes the waist seals to be pulled toward the waist/slats junction and
thereby produces a seal of sufficient degree to maintain the desired level
of LBNP. .

In terms of blood volume and heart rate displacements (4,5), a negative
pressure of -50 mm Hg in the supine LBNP box is considered to be equivalent
to a +2 Gz stress. Based on our measurements of heart rate, a -50-mm-Hg
pressure in the supine LBNP box is equivalent to -40 mm Hg in the upright
seated LBNP box. At a chamber altitude of 3,810 m MSL, we have standardized



dundant reinforcement. The
don four 10.2-cm casters for easy mobility, Although this box
is routinely used at a Negative pressure of ~40 mm Hg, it has withstooa a
test pressure of -120 om Hg.

| FIGURE 1. Side viuw of the upright seated LBNP box.

The back Support is angled at 125° from the horizontal Plane. The
8e€at~cushion ae te is 50.8 om wide, 59.7 om long, and its front edge

is angled upward from the horizontal plane. These seat and back angles
were determined ant! ‘Opometrically for maximizing seated comfort and for
minimizing "kinking" of the femoral artery durin§ pedal ergometry. The seat



(
‘

|

A LOWER BODY NEGATIVE PRESSURE BOX FOR +Gz SIMULATION
IN THE UPRIGHT SEATED POSITION

Introduction.

je The necessity to assess the effects of zero-G space flight on the +Gz
tolerances of astronauts led to the development of the lower body negative
pressure (LBNP) box,({5)s¥ In terms of construction cost, size, and opera-
tional complexity/ this simple means of simulating a +Gz stress by shifting
blood volume to the lower half of the body is much more advantageous than
the use of a human centrifuge. As reviewed recently (3), the supine

[ version of the LBNP box has been used in several types of experimental

(

studies.

A

Although supine application of LBNP retains many useful experimental
purposes, the upright seated position of the civil aviation pilot in flight
has led to the development of an LBNP box which applies the same simulated
+Gz stress in the upright seated positica. Because our previously standard-
ized pedal ergometry was also applied in the upright seated position (1),
it was logical to combine both equipment setups into one by installing a
pedal ergometer within our LBNP box. This allowed the ergometry and +Gz
testing to be run sequentially without dislocation of the subjects from one
equipment setup to another. With this unified setup, if desirci, the option
of simultaneous application of ergometry and +Gz testing is also afforded.
Since our LBNP box was easily accommodated within our altitude chambers,
the ergometry or LBNP testing could be applied at ground level or at
altitude. | This device was tested successfully and has since been adopted
as a si lard method in our aeromedical research for testing +Gz and ergo-
metric tolerances at simulated chamber altitudes up to 3,810 m MSL (2).
For those who may desire to construct and use this version of the LBNP box,
this paper provides a physical description of the device and its salient
operational characteristics.

Physical Description.

Figures 1 and 2 present side and.internal views of our LBNP box. Figure

3 depicts the hatch cover and its adjustable waist~surrounding iris system.
“fhe internal dimensions of the box are: maximum height = 98.5 cm, maximum
height at rear of seat = 53.3 cm, width = 59.7 cm, floor length = 154.9 cm,
length at 53.3~cm-height level = 179.1 cm, and length of top = 54.6 cm.

The plexiglass access door is 53.3 cm wide, 58.4 cm long, and 1.3 cm thick.
The empty internal volume of thia box is » :proximately 0.81 m. This is

approximately twice the empty volume of thc supine LBNP box (5). The back
and floor consist of 2.5-cm-thick plywood, and the sides, front, top, hatch
cover, and seat-cushion support consist of 1.9-cm-thick plywood. Internal



4

The hatch cover (Figure 3) is 69.9 cm wide, and 66.7 cm long with a
waist-front opening of 40.6 cm wide, and 26.7 cm long. The padded semicir-
cular waist-back opening (Figure 3) is 40.6 cm wide and 10.8 cm deep. The
three adjustable waist-contoured slats (Figure 3) and the sheet-rubber waist

1
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FIGURE 3. External view of the hatch cover and its three
adjustable waist-contoured slats.,



UNCLASSIFIED

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\ References

| >
Lategoia, M. T.: Assessment of Cardiovascular Function After Exposure
to the Aviation Stress Protocol~Simulation, in Three Reports Relevant
to Stress in Aviation Personnel. FAA Office of Aviation Medicine Report.
No. AM-78-5, 1978.

Lategola, M. T., A. W. Davis, Jr., P. J. Lyne, and M. J. Burr: CGardio-
respiratory Assessment of Decongestant-Antihistamine Effects on Altitude,
+Gz, and Fatigue Tolerances. FAA Office of Aviation Medicine Report No.
AM-78-20, 1978.

Montgomery, L. D., P. J. Kirk, P. A. Payne, R. L. Gerber, S. D. Newton,
and B. A. Williams: Cardiovascular Responses of Men and Women to Lower
Body Negative Pressure, AVIAT. SPACE ENVIRON. MED., 48:138-145, 1977.

Musgrave, F. S., F. W. Zechman, and R. C. Mains: Changes in Total Leg

Volume Dyring Lower Body Negative Pressure, AEROSP. MED., 40:602-606,
1969.

Stevens, P. M., and L. E. Lamb: Effects of Lower Body Negative Pressure
on the Cardiovascular System, AM. J. CARDIOL., 16:506-515, 1965.

Wolthuis, R. A., G. W. Hoffler, and J. T. Baker: Improved Waist Seal
Design for Use With Lower Body Negative Pressure (LBNP) Devices,
AEROSP. MED., 42:461-462, 1971.

0.3, GOVERNMENT PRRETNG OFFICE: 1978 0 - 190-036

pan tenn = ee nc nn ee OE a cn Haan

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our LBNP test at -40 mm Hg for a duration of 2 min. Variables urually assessed
during this LBNP test are: single-lead electrocardiogram, heart rate, aus-
cultative blood pressure, earoximetric arterial oxyhemoglobin saturation,
temporal artery blood flow velocity (Doppler), tidal volume, and respiratory
frequency (2). When experimentally desirable, psychomotor tests of the

manual speed and coordination types are quite easily applied to the subject
while seated in the LBNP box.

Exclusive of the pedal ergometer and the vacuum cleaner, our LBNP box
can be fabricated for a combined labor and materials cost of approximately
$500. This inexpensive device should provide access to seated +Gz studies
by any investigator who cannot afford the cost of acquiring or operating a
human centrifuge.



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and back cushions consist of 10.2-cm-thick foam rubber with polyvinyl covers.
The seat board is supported at each of its four corners by a notched metal
stanchion. The four stanchions are notched at 2.5-cm intervals to accommo-
date individuals of different heights.

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FIGURE Z. Internal view of the upright seated,LBNP box.

3





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