Circadian cycles in human subjects during prolonged isolation in constant environment using eight channel telemetry system

Clegg, B. R.

Schaefer, K. E.

English

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U. S. NAVAL SUBWWNE MEDICAL CENTER 
U.S, NAVAL S W I N E  BASE 
GRO'IDN, CONNECTICUT 
MEMORANDUM REPORT NO, 66-4 
MR005 d4-3300-1 a 0 1  
Approved by: 
10 February 1966 
* 
Investigators : 
Bruce R. Clegg 
and 
K m l  E. Schaefer, MOD, 
Physiological Sciences Division 
J. L, Kinsey, CAPT MC USN 
Director, SubMe dResLab 
Approved and Released by: 
C, L, Waite, CAPT MC USN 
Commanding Officer 
INTRODUCTION 
E-!, receEz years telemetry systems have been extensively used i n  
Cardiovascular data were monitored during F-100 aerospace medicine. 
f l i g h t s  (I)p heart r a t e  and respiration response pat terns  during F-105 
f l ighza (2) ,  
radio telemetry system which took in to  account the dema?ads of computer 
an*sis 
Simons and Prather (3) described an improved personalized 
Telemetry of physiological data has been predomimatly used f o r  in- 
termi?z%az+, nmitoririg and data acquisition, This -m also +.he ease in 
Amerian (4) and Russian space fl ights (5). There is a pauci%y of re-  
por+,s ori cmtincous telemetry of multiple physiological f'unctions over 
extezded periods of time, covering several weeks, 
This report  presents experiences obtained w i t h  the uae of 8-channel 
t;eleme%t=y q & i e m ~  i n  cm5in~ous simultaneous mo_n_itorLcg of six physiolog- 
ical Yx.c%Xons (EEG9 EKD, re,s;?iratory rate,  body "uemperatura, &in t em-  
pera%are, BSR) i n  01113 or two subjects d u r a  isolatfon experiments of two 
-50 W e e  -weeks daration, 
R-24, t o  determine the extent of inlxxnal desynchronization in  f r ee  running 
men% i n  a constant environment such ELB those encountered i n  spaceflights 
3z.d -ader=iiter exploration, 
The studies were performed under NASA Contract 
2 L-cEaz"i cycles of p * J r ~ : & ~ @ ~ ~  f iL?Ct iQpa,  lAy&r condi t i (?pa of Cm-f.LQ+. 
Exvir0.nmenta.l Chamber: 
A clfmatized pressuremaI.ti%3e c h m = r  waa used t o  provide a constant 
envircmwnt , 
tic i n s + m n t  controlling a heating-cooling system t o  &;he chamber, and 
m a i n % a i n e d  at  27'C t .lb, 
~ ~ e i e a J J y  activated Ve-rlt-valve. A sensit ive d i f f e ren t i a l  pressure gage, 
Temperature vas regulstec Fy a thermistor-activated pneuma- 
Besametric pressure KGM controlled by a pneu- 
NASA COELIYWA R-24 
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referenced t o  a constant pressure source, provided a set-point signal 
t o  the controlling instrument. 
inches of mercury within a standard deviation of .004 inches, 
chamber WBS continuously vent i la ted w i t h  100 li ters/min provided by a 
lubricant-free air pump. 
by a pneumatically controlled chemical drier. 
30-foot candles during the subjects'  dqy and during the night reduced 
t o  about 3-foot candles. 
1) o n e - w  audio out of the chamber, 2) audio code in to  the chamber, 
and 3) medical-lock writ ten messages. 
The chamber pressure w&s held a t  30.560 
me 
Humidity was kept a t  30 per cent + 5 per cent 
Illumination-k,s set at 
Communication through the chamber was by 
Phvs iological D a t a  Ac au i s i  t ion : 
The following variables were continuously monitored on each sub- 
1) core temperature ( r e c t d ) ,  2)  surface temperature (upper ject:  
mm), 3) b a s a l  skin resiatance (palm), 4) E E G  (occipi ta l ) ,  5) respi-  
ration, and 6) EKG. The subjects wore an FM-FM type telemetry vest  
(Biometrics) . The r a w  data were received at  a cent ra l  locat ion out- 
side the chamber for preliminary reduction and recording. !rhe core 
and surface temperatures and the basal skin resis tances  were d i r ec t  
analogue signals which passed through low pans filters before being 
convertedto d i g i t a l  form and recorded on standard IBM cards once 
every minute. 
cps .) were necessary t o  minimize "aliasing" problems during subse- 
quent spectral  analyses. 
t o  minute-rates and recorded d ig i t a l ly  on cards once a minute, and 
monitored graphically every 15 minutes f o r  a duration of two minutes. 
EEG signals were a lso  graphically monitored every 15 minutes. More- 
over, baseline crossings (indication of prominent EEG frequency) and 
averaged amplitude were d ig i t a l ly  recorded e e r y  minute. 
shows a block diagram of the total. telemetry system which consisted 
of two eight-channel systems (Biometrics). 
units worn by the individual subjects are displayed i n  Figure 2. 
These low pass filters (half power frequency, 6(10)-3 
EKG and respiratory signals were converted 
Figure 1 
The sensor and transmitter 
PROBLEMS ENCOUNTERED 
Electrodesr 
Electrodes we known t o  deter iorate  very rapidly within hours. 
We employed electrodes of the f l u i d  type, which provide a low elec- 
trode impedance. Such electrodes had been successfully used i n  the 
NASA Mercury program ( 6 )  . 
d i s c s  enclosed i n  an inert p l a s t i c  holder w i t h  a layer  of modified 
bentonite electrolyte between the cup and the akin of the subject. 
The advantage of these electrodes were t h a t  they had special  prepwed 
surfaces that did not tend t o  polarize and secondly, the e l ec t ro ly t i c  
They consisted of careful ly  chlorided si lver 
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, 
par t  used was isotonic and l e s s  prone t o  cause skin i r r i t a t ion .  
These electrodes l a s t ed  up t o  six or seven days, depending on the 
application. 
somewhat shorter since the very low potent ia ls  were affected earlier 
by the s low ly  charging resistance of the electrodes. 
r a t ion  prompted us  t o  implant s i lver  wires in subsequent experiments 
and we found t h e m  t o  last 10-12 days. 
or platinum wire method l i e s  i n  the eventual t i s sue  rejection. 
In the case of EXG electrodes, the useful time was 
This deterio- 
The l imitat ion of the silver 
Leads: 
The second problem of the telemetry system consists of fatiguing 
and breaking of electrode w i r e s ,  par t icular ly  of those electrodes 
whose connections are exposed t o  constant movement (EKG, BSR, palm 
electrodes). 
wire, furnishedby Cyanamid, This wire consis ts  of 40 strands of 
extremely f ine  wire, copper wire, suff ic ient  t o  make the gauge a 
standard 22. 
For t h i s  reason, we obtained special  fatigue resistant 
Long t e r m  continuous use of telemetry equipment presents the 
obvious problem of obtaining routine calibrations,  A decision must 
be made whether, at some point, it is  mi%able to interrupt  %he ex- 
periment i n  order t o  caxry out recalibrations. 
Signal Conditioner: 
rr(L, srle t3-$ Gf &,-fa &-L&3-sts &tei-iiines -w-klEt of =-.dog sf@& 
conditioning is  t o  be do3e t o  the telemetry data. 
was desired from the EKG signals and the respiratory signals, 
rate information vas obtained by counting both EKG, BSR complexes 
and the nurnber of inspiration signals during one -minute m d  recording 
this information. 
inent  EEG frequency,, 
the r u b e r  of EEG baseline crossings i n  one minute. 
the E 3 G  signal was obtained by integra+,ion of the signal f o r  one 
minute. Surface temperature, core temperatme and basal skin re- 
s is tance Were recorded e s s e n t i d l y  mmodifled. The s q l i n g  theory 
of da ta  analysis required that freqJencies which were greater than 
half the sampling interval be attenuated. For t h i s  purpose, special  
l o w  pass filters have been used having a t+ constant of three min- 
utes. 
worked out very well. 
R a t e  information 
This  
It was desired t o  obtain an estimate of the prom- 
The most expedient method was simply t o  count 
The average of 
The s ignal  conditioning eqidlpaent was developed loca l ly  m d  
D a t a  Transmission Equipment: 
The output of the signal conditioning equipment was multiplexed 
and converted t o  a d i g i t a l  format for punching with a standard IBM 
-5- 
card punch. The andog d i g i t a l  converter waa furnished by W t o n  In- 
iiiustries, Inc, The casd punch wa6 the weakest l i n k  i n  the data re- 
cording sy~~tern, Reliable card punching represents a major problem 
f o r  continuous long-duration experiments. 
curacy of the cesd punched data, measurements were graphically re- 
corded every f i f teen  minutee fo r  a period of one minute with an Offner 
dynogragh. Und8r our conditions, the une of the punch-card aystcmms 
neccnsery because the exis t ing computer f a c i l i t i e s  had only punch-card 
lnput, Othemrise, it would have been more femible t o  me punched 
paper tape, or magnetic tape. 
In order t o  ver i fy  the ac- 
Corrections of Artifacts i n  Telemetered I>atar 
Several computer programs were developed t o  locate and correct 
many of theae error8, One program corrected mechanical card-punching 
m o r a ,  such ae falsre column regitatration, card order, etc. A necond 
c,orrection program detected errore  i n  telemetry ~ignd, e,g*, loea of 
slgnale or  loss of electrode contact, 
ditiOn6, 1) they had t o  be within a reasonable phyrsiologlcal range, 
and 2) the data could not d i ~ p l v  unphyniologically f a e t  changer. 
Certain typen of errorn aould be Corrected by a linear approximation. 
The corrected data and t h e  Information were plaocd i n  standard binary- 
tape f i l e a h  
'ke data had t o  meet two con- 
Sub jec t n : -
Extended experimants of this type put great demands on the sub- 
jectn, They m e t  be highly motivated, i n t e l l i gen t  and thoroughly ea- 
quainted with the experimantal plan and, furthermore, m a t  be able t o  
make minor repaira t o  telemetry equipment during the experiment, Our 
rubjeatr  conslated of mnrcllcal studentn who par t ic ipated In the NILVY'S 
Roaeesch Clerkahlp P r o g r ~ ,  and ranemah garronnsl. 
'Date, Analyrln for  the Study of Circedian Cyclerr 
The finiahed telemetry data stored on -tic tape m a  f l r a t  
plot ted by tho o q u t e r .  The p l o t r  were then inspected t o  determine 
obviour a r t i f ao ta  i n  the data, Var iour  mute-aorrelation analyrer 
mro performad t o  mako ortirnater of the prominent low-f'requonoiea i n  
tho data. Tho mort auooarrhrl autopoorrelation analyror war b u o d  on 
k 00qpromi.r throe-dqf overlegging M & 1 Y l @ l r  AB pharo information i r  
inhrrontly l o r t  by thir tOOhniQue, a arorr-aorrolation mathod wllr de- 
vrloped t o  determine t h o  p h ~ r  hift o f  t h o  a i rokdim pr r iod io i t ie r ,  
mir WUr done by ororr-oorrelating the data with a rynthotierd 24-hour 
poriodioity of known snrglitudr and phase. Again, t h o  u a l y r r d  duration 
thrre dwr i n  owtrlqpping intormila. 
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In the following, a few examples are given showing acquisition 
and analyses of telemetry data from subjects who were confined f o r  
long periods. 
Figure 3 exhibi ts  the telemetered core temperature data of two 
subjects, 
cated in  the shift of the black bars denoting the sleep period, 
circadian cycles of body temperature s h i f t  correspondingly. 
these conditions, i n  which the subjects retained the i r  normal pattern 
of physical ac t iv i ty  i n  isolation, all of the measured circadian cycles 
of physiological F a c t i o n s  were synclironized with the sleep-wakefdness 
cycle. 
Following isolat ion i n  a constant environment, the sleep- 
The 
yrn-k=F&?=S= qrcle +If+= yegd=pJr +O~J% 1=2 +~~ p e r  Ae-7 UUJ, -0 &A*-- -- -?-A* 
Under 
Figure 4 exhibi ts  the results of a three-day overlapping auto- 
correlation analysis of respiratory r a t e  i n  a subject confined for 
1 2  days i n  a constant environment. It can be seen t h a t  the 24-hour 
component (within tne low frequency band 18-48 hours) of the spectrum 
a i d y s i s  &creases h r l n g  tile f i r s t  days of isolat ion while .the 5-7 
hour frequencies increase. This icdicates t ha t  the stress of isola- 
t i on  produces a marked change i n  the  temporal order of frequencies 
underlying the cycles of physiological functions, 
Figurc 5 gives an example of cross-correlation analysis of body 
temperature from one subject with a synthesized 24-hour periodicity 
of known amplitude and phase, The body temperature did not follow 
the phase s h i f t  of the sleep-wakefulness cycle indicating a desyn- 
chronization of physiological functions. 
i n  contrast  t o  those shown i n  Figure 3, were obtained i n  a subject 
whose physical ac t iv i ty  was greatly reduced during isolat ion in a 
constant environment. It appears that  physical ac t iv i ty  has a coor- 
dinating influence on the cycles of physiological functions. 
These findings, which are 
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B O D Y  TEMPERATURE " C  
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DEGREES PHASE SHIFT (15.. I HOUR 1 
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1. Roman, J.A., Cardiorespiratory Functioning in-Flight, Aerospace 
7 Med., 2:322-337, April 1963. 
2. Helvey, W.M., Albright, G.A. and Axelrod, I., A Review of' Biomedi- 
cal Monitoring Act ivi t ies  and Report on Studies Made on F-125 
Pilots,  Aerospace Med,, 35: 23-27, 1964. -
3. Simons, D.G. and Bather, W., A Personalized Radio Telemetry Sys- 
t e m  f o r  Monitoring Central N e r v o u s  System Arousal i n  Aerospace 
Flight, J. EEE Transactions on Biomedical Engineering, V o l  BME- 
11, 40&L, 1964. - 
4. Catterson, A.D., McCutcheon, E.P., Minners, H.A. and Pollard, R.A., 
Aeromedical Observations, Pg 294-326 i n  R e s u l t s  of the Fourth 
United S ta tes  Manned Orbital Flight, NASA, SP-45, 1963. 
5. Agadzhanyan, N. and Koulinickev, I., Cosmic Biotelemetry, Tekhnika 
Molodezhi, 9:25-26, 1962. English translation: Foreign Technol- 
ogy Divlsiml P62-1908. 
6. Wheelwright, Charles D., Physiological Sensors f o r  Use  i n  Project 
Mercury, NASA, TND-1082. Mmned Spacecraft Center, Houston, 
Texas, 1962. 


Studies of circadian cycles in human subjects during prolonged isolation in a constant environment using 8-channel telemetry systems  Memorandum report no. 66-4

Studies of circadian cycles in human subjects during prolonged isolation in a constant environment using 8-channel telemetry systems Memorandum report no. 66-4

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