Acceleration stress in monkeys, and breathing rate, electrocardiographic, and skin temperature measurements during centrifugatio

Knepton, J. C., Jr.

English

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NAMI-997 
i 
CENTRIFUGATION OF THE 
WHITE-FRONTED CAPUCHIN MONKEY, Cebus albifrons (Humboldt) 
James C. Knepton, Jr. 
JOINT REPORT 
NAVAL AEROSPACE MEDICAL INSTITUTE 
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
December 1966 
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Distribution of this document i s  unlimited. 
CENTRIFUGATION OF THE 
WHITE-FRONTED CAPUCHIN MONKEY, Cebus -albifrons (HumboIdt)* 
James C. Knepton, Jr. 
Bureau of Medicine and Surgery 
MR005.04-0032.3 
NASA Request R-10-009-027 
Approved by 
Ashton Graybiel, M.D. 
Director of Research 
Released by 
Captain H. C. Hunley, MC USN 
Commanding Officer 
30 December 1966 
*This research was conducted under the sponsorship of the Office of Space Science 
and Applications, Bioscience Programs, Environmental Biology, National Aeronautics 
and Space Administration. 
NAVAL AEROSPACE MEDICAL INSTITUTE 
NAVAL AEROSPACE MEDICAL CENTER 
PENSACOLA, FLORIDA 
SUMMARY PAGE 
THE PROBLEM 
In planning for biological experiments aboard space vehicles it i s  necessary that 
the orbiting specimens be able to tolerate certain maximum acceleration levels. Non- 
human primate specimens wi l l  be required for these experiments, and the screening for 
l ikely candidates i s  being carried out. A promising monkey i s  Cebus albifrons 
(Humboldt), the whi te-fronted capuchin, which has not h e r e t o f a e e n  exposed to 
higher than normal levels of acceleration insofar as we are aware. Three 
unanesthetized, restrained capuchins were placed on a centrifuge and exposed to five 
headward-directed acceleration levels extending up to 10 g . Their electrocardiograms 
were recorded before, during, and after each test; skin temperatures were taken before 
and after the exposures; and breathing rates were measured from the ECG. 
FIND1 NGS 
The electrocardiograms of three C. albifrons (one male, two female) accelerated 
on a centrifuge show that at the beginnin-is marked tachycardia. Bradycardia 
appears within 6-7 minutes at 7.5 g and by 1 Q  minutes at 10.3 g. A squeal usually 
accompanies the onset of bradycardia . There were no significant skin temperature 
changes. The breathing rates before and after centrifuging were from 40-50 breaths 
per minute with an increase to 75-80 breaths per minute during exposure. Upon 
returning to 0 g the normal heart rate soon appears. 
The ECG findings indicate that the autonomic nervous system i s  a prime contributor 
to the bradycardia which results from insufferable acceleration. Cebus i s  a good animal 
in which to study this cardiac phenomenon. 
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Our results indicate that Cebus albifrons i s  satisfactory for use i n  space-located -
I aboratori es . 
ACKNOW LE DGM E NTS 
Dr. D. E. Beischer has given encouragement and guidance to this pilot 
experiment using a centrifuge for small animals for which I am very appreciative. 
Mr. J .  M. Cloud, Engineering Technician, under whose supervision the centrifuge 
was constructed, cooperated in every phase of the project and it i s  for this that I 
extend to him my gratefulness. I wish to thank Dr. Fred Guedry and Mr. Carroll Hixson 
for their generosity in giving time and thought to discussions about acceleratory forces. 
Experiments reported herein were conducted according to the principles enunciated 
in "Guide for Laboratory Animal Facilities and Care" prepared by the Committee on the 
Guide for Laboratory Animal Resources, National Academy of Sciences, National 
Research Counci I .  
.. 
I I  
INTRODUCTION 
The National Aeronautics and Space Administration i s  planning to use nonhuman 
primates in space experiments for which a type of monkey that may be chosen i s  the 
white-fronted capuchin, Cebus albifrons (Humboldt). Any living material that i s  sent 
into space w i l l  have to w-ndmesses imposed upon i t  during the ascent phase 
of the spaceward flight. One of the stresses i s  that of acceleration greater than 1 g. 
Before entering into any details of planning for the use of Cebus -in space laboratories, 
i t s  response to increased acceleration should be studied. 
As a result of subjecting three C. albifrons to varying headward-directed 
accelerations (+4) up to approximaiely 10 g, i t was found that at the onset of 
centrifugation there was a marked tachycardia and with an increase of acceleration 
there was a diminishing amount of time before bradycardia occurred. In most cases 
the onset of bradycardia was accompanied with a squeal emitted by the monkey. Skin 
temperature and breathing rate did not change significantly. 
ANIMAL CENTRIFUGE 
In early 1965 a small, motor-driven, animal centrifuge with an arm diameter of 
approximately 6 feet was constructed in this laboratory. One end of the rotating arm 
holds a monkey chair and the other, a counterweight. Angular velocity can be varied 
by mechanically setting a rotating rubber tire at various distances from the center of a 
metal wheel that i s  geared to the a x i s  of the revolving arm, A hand brake provides 
rapid deceleration. Calibration of the device in rpm i s  accomplished by comparing 
the voltage output of a tachometer with the number of counts per minute registered by 
a photocell-activated counter (see Figure 1). The maximum velocity of the centrifuge 
i s  100 rpm,and twenty-three seconds are required to reach this speed; deceleration time 
to rest from this speed i s  the same. 
METHOD 
Three C. albifrons (A01, female, 1561 grams; A03, female, 1691 grams; and 
A46, male,-1476 grams) were used in the experiments. The animals had been kept in 
the colony at Pensacola for some time prior to the experiments under the full-time 
supervision of a certified veterinarian. At no time before or during the experiments 
were the animals given anesthesia or any other drugs. Prior to centrifugation the 
animal was placed in a fitted chair and restrained by fasteners of Velcro (American 
I Velcro, Inc.) (Figure 1). 
For recording the electrocardiogram small disk-shaped silver electrodes, 0.9 cm 
i in diameter, were taped to the left and right side of the chest on the anterior axillary 
paste was placed between the electrode and shaved chest. A Cardiette (Sanbom 
line at the level of the fifth intercostal space. Plastic foam soaked with electrode 
Company), located near the centrifuge and connected by shielded wires through a slip- 
ring assembly of the centrifuge (see Figure 1) to the electrodes, recorded the tracings 
obtained immediately before, as well as during and after exposure to centrifugation. 
I 
1 
2 
Ambient and skin temperatures were measured with a Yellow Springs Instrument 
Company recorder just before and after each centrifugation . The skin temperature 
electrode was taped to the medial side of the animal's left thigh. 
An experimental schedule was established that took into consideration the 
desirability of exposing a l l  three subjects during a single working day to the same 
acceleration level, with the increase in level being on a day-to-day basis. That is, 
each monkey was exposed to a single acceleration level each day which was greater 
than the level of the previous day. In this way the physiological endpoint was 
established and at the same time each individual's sensitivity was determined. 
- 
Five different resultant linear acceleration levels ( I A I = 1.6, 2.8, 5.3, 7.6, 
and 10.3 g) were used. These were calculated using the formula 
where w = angular velocity in radians per second; R = center of centrifuge to 
Xiphisternum (approximately 3.032 feet). The monkey seat i s  pivoted so that the axis 
of the seat's rotation during centrifuging i s  perpendicular to his skeletal axis and 
xiphisternum with the head always moving towards the center of centrifugation. At 
each acceleration level, the seat was ti l ted so that the resultant acceleration at 
radius R of the monkey seat was in aligrment with the I (head-foot) axis of the subiect. 
The motion parameter of the centrifuge and the magnitude of the headward-directed 
linear acceleration stimulus, +4, are listed in  Table 1. 
Table I 
Headward-Di rected Resultant Linear Acceleration (Az), Centrifuge Velocity (RPM), 
Time (T i )  to Accelerate Centrifuge to Constant Velocity, 
and Time (T2) to Decelerate Centrifuge to Rest, 
RPM 
F i  nt Remainder of 
A, Minute Exposure T i  (sec.) T2 (sec.) 
+ 1.69 35 35 (Prompt I y) (Prompt I y) 
+ 2.8g 49 
+ 5.39 67 
+ 7.6g 78 
+ 10.39 83 
50 2 2 
71 4 4 
85 8 8 
1 00 23 23 
3 
Evaluation of the electrocardiogram (ECG) was made for heart rate and breathing 
rate. Heart rate was determined for each three-second portion of the ECG with a 
Viso-Cardiette Record Inserter (Sanborn Company), and breathing rate was estimated 
from the number of cycles of R-wave amplitude changes for each three-second 
recording. 
RESULTS 
The progressive diminution of the time for bradycardia to occur as a function of 
the magnitude of the resultant linear acceleration stimulus i s  shown in Figure 2. This 
graph demonstrates that al l  three monkeys found 4 = +7.5 g to be an intolerable level 
of acceleration for more than six to seven minutes and were physiologically normal for 
only a l itt le over a minute at the A, = +10 g level. Table II gives the numerical heart 
rate data which portray what was actually observed in  the laboratory. At the 
beginning of centrifugation there was a change from the normal heart rate to 
tachycardia. At the lower accelerations tachycardia persisted for a short time, while 
at the higher ones this condition remained until there was a drastic drop in the heart 
rate. Figure 3 i s  typical of the type of graph obtained when a Cebusl heart rate i s  
plotted as a function of centrifuging time at 100 rpm (Az = + 1 0 . 3 .  At the lower 
acceleration levels and depending upon the individual monkey, the bradycardia did not 
appear (see Figure 2 and Table 11). With exception of one instance (A46 at 10.3 g), 
the animals let out an unusually loud squeal at the onset of bradycardia. The data i n  
column E of Table I t  show that the Cebus recovered quickly from bradycardia after 
centrifugation ceased. 
Skin temperatures recorded before and after each centrifuge run did not vary 
significantly (average skin temperature = 38.3OC). Ambient temperature did not vary 
over 3OC during a day's series of exposures and ranged during the entire experiment 
from 23.0' to 29.8OC. 
Breathing rates could not be determined from ECG's during the episodes of 
bradycardia, but at the other periods of the experiment they were measured. When 
the centrifuge was at rest, respiratory rate was 40 to 50 per minute but with 
tachycardia this increased to 75-80 breaths per minute. After centrifugation, 
restoration of the normal breathing rate was almost immediate. 
DISCUSS I ON 
Several other investigators (1 -3) have observed the same heart rate pattern of 
centrifugation as was evident in this experiment. First, with an onset of centrifugation 
there was a tachycardia which at low levels of acceleration may give way to the normal 
heart rate, But i f  the acceleration level was too great for tolerance, the tachycardia 
was replaced by bradycardia. Upon restoration of the animal to normal ambient 
conditions his heart rate soon returned to i t s  normal value. Mehelas and Pinc (3) have 
observed this sequence of events in squirrel monkeys (Saimiri sciureus (Linnaeus)) 
exposed to high accelerative forces (50 to 430 9). 
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Britton - -  et a1 .(1) exposed rhesus monkeys (Macaca mulatta -- (Zimrnerman)) to (+A,) 
accelerations and found that acceleration of theheart rate showed a proportionality to 
the intensity and time of application of the stimulus. They also reported that, under 
prolonged exposure (5-10 minutes, 3-4 g), bradycardia set in, but recovery was rapid 
on stopping the centrifuge. 
Kotovskaya and his co-workers (2), using M. mulatta and baboons (Papio (Mbller)), 
exposed their subjects to "chest-back" (A,) acZlerations to determine theurat ion of 
tolerance of "12 accelerations" (units). They found that, as rotation speed increased, 
cardiac and respiratory rates intensified; the tolerance for 12 units was for 1 to 4* 
minutes. The l imits of tolerance were marked by such things as prolonged respiratory 
arrest or standsti II , pronounced bradycardia, or disorders of automatism, and 
exci tab i I i t  y . 
The findings of those investigators coupled with our results seem to substantiate the 
electrocardiogram as an indicator of tolerance to acceleration. The tachycardia of 
acceleration i s  possibly a stress reaction involving cardiac pressor reflexes, emotions, 
sympathetic impulses, and hormones. Bradycardia, indicating that the acceleration i s  
intolerable, probably shows altered sympathetic input to the myocardium which results 
in parasympathetic takeover of the heart's regulation and a consequent decrease of 
heart rate. Respiratory distress may also be involved. Taylor, Rhein, and Beers (4) 
have shown that bradycardia i s  abolished in humans injected with atropine sulphate 
before exposure to backward-facing impact at 15 g. They stated that this evidence 
supports their hypothesis that bradycardia i s  due to a vagal reflex from an undetermined 
sensor system. Further experimentation could show the same situation in Cebus. The 
unknown sensors might be i n  the aorta and carotid sinus, which are influenced by 
carotid artery blood volume and pressure, or in the right atrium. Findings of 
Kotovskaya et - al. appear to implicate a neuralhormonal interaction that brings about 
bradycardia. n e y  found large amounts of epinephrine and very l i t t le norepinephrine 
in hearts of monkeys excised thirty minutes after rotation. The adrenals showed very 
l i t t le epinephrine. The mechanism of bradycardia i s  one that could be readily studied 
in  Cebus on a centrifuge. 
-
-
At no time during centrifugation other than at the onset of bradycardia did the 
Cebus squeal . This occurred i n  every case except one (Table 11). Kotovskaya et al. 
(2)scribed their monkeys as screaming when accelerations increased, but they used 
rhesus and baboons instead of Cebus. It would be interesting to pursue research to 
find i f  there i s  a relationship between the bradycardia and squealing Cebus accelerated 
to the point of intolerance. 
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8 
REFERENCES 
1. Britton, S. W., Pertzoff, V. A., French, C. R., and Kline, R. F, Circulatory 
and cerebral changes and protective aids during exposure to acceleratory forces. 
Amer. J. Physiol., - 150:7-26, 1947. - -  . 
2. Kotovskaya, A. R., Vasilyev, P. V., Lapin, B. A,, Simpura, S. F., 
Grishina, I .  S., and Kulinsky, V. I ., Effect of prolonged lateral accelerations 
on monkeys. In: Parin, V. V. (Ed.), Aviation and Space -Medicine. 
NASA TT F-228. Washington, D. C .: Nationaleronautics and Space 
Administration, 1964. Pp. 254-257. 
3. Mehelas, J. N., and Pinc, 8. W., The response of squirrel monkeys to high 
accelerative forces. NASA CR-236. Washington, D. C.: National 
Aeronautics and Space Administration, 1965. 
4. Taylor, E. R., Rhein, L. W., and Beers, G. R., Effect of atropine upon the 
relative bradycardia associated with impact. ARL-TDR-62-13. Holloman Air 
Force Base, New Mexico: 6571st Aeromedical Research Laboratory, 1962. 
(AD 282 884) 
9 
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Naval Aerospace Medical Institute Unclassified 
Pensacola, Florida 32512 2b. G R O U P  
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I 
R E P O R T  T I T L E  
CENTRIFUGATION OF THE WHITE-FRONTED CAPUCHIN MONKEY, Cebus albifrons 
(H umbo I dt) 
D E S C R I P T I V E  N O T E S  ( T y p e  of report and inclusive dates)  
N/A 
A U T H O R I S I  ( F i r a t  name. middle ini t ia l ,  I a a t  name) 
James C. Knepton, Jr. 
R E P O R T D A T E  
30 December 1966 
P. C O N T H A C T  OR G R A N T  N O  
NASA Request R-10-009-027 
b. P R O J E C T  NO BuMed MR005.04-0032 
c. 
d. 
0 .  D I S T R I B U T I O N  S T A T E M E N T  
7a. T O T A L  N O .  O F  P A G E S  7b. N O .  O F  R E F S  
9 4 
3a. O R l G l N A T O R * S  R E P O R T  N U M B E R I S )  
NAMl-997 
3b. O T H E R  R E P O R T  N O ( S I  (Any other numbers that may be assigned 
this report) 
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1 -  S U P P L E M E N T A R Y  N O T E S  12 .  S P O N S O R I N G  M I L I T A R Y  A C T I V I T Y  
I 
3 .  A B S T R A C T  
In preparation for biological experiments aboard orbiting laboratories three Cebus albifrons, 
white-fronted capuchin monkey, were exposed to five headward-directed (+A,) =ant linear 
acceleration stimuli aboard a centrifuge and their ECG’s, skin temperatures, and breathing rates 
recorded. Marked tachycardia was noted at the start of the centrifugation, followed by 
bradycardia within 6 to 7 minutes at 7.5 g and within 1 Q  minutes at 10.3 g. Concomitant with 
the onset of bradycardia, a loud squeal was usually heard. There were no significent temperature 
changes, and breathing rates did not vary from normal. Normal heart rate was restored upon 
cessation of centrifugation. It appears that the Cebus -can withstand the acceleration of space 
travel and therefore wi l l  be a good experimental animal in that environment. 
FORM 3D 1 N O V 6 5 1 4 7 3  ( P A G E  ’ )  Unclassified 
Unclassified 
Security Classification 
Electrocardiography- 
Acceleration effects 
Laboratory animals 
I L I N K  A I L I  - 
W T  
- N K  D 
K E Y  W O R D S  
4. 
R O L E  W T  R O L E  
L I N K  C -
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Centrifugation of the white-fronted Capuchin monkey, Cebus albifrons /Humboldt/

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