Threshold caloric test on normal subjects - responses to hot and cold caloric stimulatio

Mc Leod, M. E.

Meek, J. C.

English

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THRESHOLD CALORIC TEST: IN NORMAL SUBJECTS 
Michael E. McLeod and Joseph C .  Meek 
JOINT REPORT 
GPO PRICE $ 
CSFTl FRICE(S! $ 
ff 653 July 65 
UNITED STATES NAVAL SCHOOL OF AVIATION MEDICINE 
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
https://ntrs.nasa.gov/search.jsp?R=19650026824 2020-03-16T22:05:58+00:00Z
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Research Report 
A THRESHOLD CALORIC TEST: RESULTS IN NORMAL SUBJECTS* 
Michael E. McLeod and Joseph C. Meek 
Bureau of  Medicine and Surgery 
Project MR005.13-6001 
Subtask 1 Report No. 72 
NASA Order No. R-47 
Approved by Released by 
Captain Ashton Graybiel, MC USN Captain Clifford P. Phoebus, MC USN 
Director of Research Commanding Officer 
9 July 1962 
*This research was conducted under the sponsorship of the Off ice of Life Science 
Programs, National Aeronautics and Space Administration. 
U. S. NAVAL SCHOOL OF AVIATION MEDICINE 
U. S. NAVAL AVIATION MEDICAL CENTER . 
PENSACOLA, FLORIDA 
SUMMARY PAGE 
THE PROBLEM 
A threshold caloric test procedure i s  described and the results of  the test i n  104 
subjects are presented. 
FINDINGS 
In a young male population, the threshold responses to hot and cold caloric 
stimulation w i l l  be found within 1.5OC either side of body temperature. Threshold 
values greater than 1.5OC from body temperature may indicate an abnormal laby- 
rinth. Evidence i s  shown which suggests that repeated threshold caloric irrigations 
produce l i t t le or no habituation. 
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INTRODUCTION 
The caloric test i s  one of  the most frequently used methods o f  evaluating the 
function o f  the semicircular canals. The use of thermal stimulation enables the 
investigator to assess individual labyrinthine function, determine directional pre- 
ponderance, and to study the effects o f  drugs, infection, and other extra-labyrinthine 
factors. Many improvements have been made in the caloric test procedure, including 
control o f  mental alertness (l), accurate head positioning to insure that the hori- 
zontal canal is  vertical, elimination o f  ocular fixation (1,8), and the use of  electro- 
use (3,5) have limitations. Habituation to repeated caloric stimulation has been 
demonstrated in animal (4) and man (7), and small decreases in vestibular function 
may be masked when strong caloric stimulation i s  used to el ic i t  a nystagmic response. 
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I nystagmography . Despite these improvements, many of  the caloric tests currently i n  
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Kobrak (6) was the first to use the minimal stimulation technique, the test 
developing out o f  the need for a more sensitive method to evaluate neurological 
patients and those with MeniQre's disease. Kobrak was concerned primarily with 
avoiding giddiness which was freqently produced when ice water was used during 
the caloric irrigation. He felt this sensation influenced the response obtained. 
Since that time, improved methods for more accurate temperature regulation and 
awareness o f  other variables have provided means for improving a threshold caloric 
test. 
The purpose of this report is  to describe a threshold caloric test devised in this 
laboratory and to show results which have been obtained in  normal subjects using this 
technique. 
PROCEDURE 
SUBJECTS 
The subjects i n  this study were divided into two groups. Group A consisted of  
fourteen normal males between the ages of  18 and 37, and the screening procedure 
used in selecting subjects for Group A was a negative history for ear disease. Group 
B was made up of  ninety enlisted personnel, predominantly between ages 17 and 25, 
who had passed the minimum medical requirements for military service. A past 
history of  ear disease did not prevent a subject from inclusion in Group B. 
APPARATUS 
The apparatus consisted o f  a constant temperature regulator, a thermistor, and 
a telethermometer to maintain the water temperature bath constant. The thermistor 
was used in the t ip  of  the irrigating nozzle to detect water temperature as i t  left the 
end of the irrigating tube, and the telethermometer recorded the thermistor 
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temperature to the nearest 0.2OC. The nozzle t ip  was 1 mm in diameter and 
delivered a water volume of 100 cc during the forty seconds of  irrigation. 
Horizontal nystagmus was recorded in Group A only, using a Sanborn poly- 
graph recorder, by means of  the corneo-retinal potential technique and the 
nystagmus was observed through Frenzef lens during the recording procedure. 
METHOD 
Each subject was positioned in an E N T  chair so that a line drawn from the 
outer canthus o f  the eye to the tragus of the ear would be vertical. This placed 
the horizontal canals approximately in the vertical plane. When electronystag- 
mography was used (Group A )  20-degree eye movement calibrations were obtained 
prior to caloric irrigation. Frenzel lens were placed over the subject's eyes in both 
Groups A and B to decrease ocular fixation and allow visual observation. The 
stimulus was 100 cc of  water delivered against the ear drum in a period of forty 
seconds. Ten seconds prior to the cessation of stimulation, the subject was given 
a mathematical problem to maintain mental alertness, and the room was darkened. 
The Frenzel lens remained illuminated. The eyes were also observed for a nystag- 
mic response for a period of forty-five to sixty seconds after cessation of  irrigation. 
Visual observation and the findings on electronystagmography in Group A were 
recorded independently. A positive response was defined as a minimum of three 
nystagmic beats in succession in the appropriate direction. The subject was 
instructed to look straight forward, i .e. , toward the ceiling, even though the lens 
and darkened room prevented vision. 
In Group A, the init ial  temperature used in irrigation was 36.4OC and 38.OoC 
for the cold and hot thresholds, respectively. The temperature was adjusted down 
or up 0.4OC until a response was obtained and the threshold was determined to the 
nearest 0.2OC. Cold threshold determinations were made first. 
Group B received only cold threshold calorics, and 36.4OC was used as the 
arbitrary upper limit in order to shorten the procedure. This figure was selected 
because the results in earlier tests had indicated few responses above the 36.4OC to 
36.6OC range. Visual observation alone was used in determining the threshold in 
Group B. 
RESULTS AND DISCUSSION 
The values obtained by visual observation and electronystagmography for the 
cold and hot threshold caloric test in Group A were recorded separately and are 
presented in Table 1. Frequency distribution o f  these threshold values for the cold 
and hot caloric test as determined by visual observation alone are shown in Figures 1 
and 2, respectively. There was general agreement between the threshold values 
determined by visual observation and electronystagmography , but visual observation 
in general was more sensitive in detecting a minimal response. The difference 
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between the visual threshold and recorded threshold never exceeded 0.4OC in 
35.8OC and body temperature in the cold threshold determination; and 96 per cent 
were between 35.4OC and body temperature. Figure 2 shows that 93 per cent of 
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Group A. In Figure 1 ,  89 per cent of  the canalicular responses were between - 
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the hot threshold values as determined by visual observation were between 37.4' and 
38.4OC. 
The findings in Group B are demonstrated i n  Figure 3 in a frequency distribu- 
tion. Although Group A was more carefully screened by medical history than 
Group 8, the findings were about the same for the two groups in regard to frequency 
distribution of threshold responses. The generally higher values in the fourteen 
subjects in Group A may be explained by the selection procedure used in these 
subiects; i .e. , a past history of  ear disease excluded subjects from Group A but not 
from Group B. The similar findings in Group A and B support the use of  36.4OC as 
a reasonable arbitrary starting point in Group B. 
In this study, with the head properly positioned and the subject mentally alert, 
95 per cent of  a l l  subjects had threshold values between 35.4OC and body temperature. 
On a statistical basis, it i s  reasonable to believe that values outside this range may be 
indicative o f  an abnormal labyrinth, Using the threshold technique, preliminary 
testing in a few patients with Meni6re's disease and positional vertigo with values 
below 35.8OC in the suspected abnormal ear lends support to this contention. 
Ninety-three per cent of Group A had hot threshold determinations between 
37.4 and 38.4OC. Experience with the hot threshold caloric test i s  limited, and 
more work i s  needed to define the normal range as well as explore its use with the 
cold threshold caloric test in determining directional preponderance. 
An indication that this test procedure avoids some variability due to habitua- 
tion was obtained from four subjects who were exposed to constant rotation on the 
Pensacola Slow Rotation Room (2). Daily cold water threshold determinations during 
the ten-day experiment revealed no tendency toward habituation to the caloric 
procedure, the threshold values showing l i t t le or no change from day to day. 
The threshold caloric test as discussed in this report can be modified, i f  
necessary, to meet the requirements of  the investigator. The clinician, lacking 
the equipment required for electronystagrnography, can use this test to evaluate 
the canal function by direct visual observation and to follow progressive vestibular 
pathology without adaptation to repeated caloric irrigation. This test has been used 
by the authors i n  studying the effect o f  streptomycin on squirrel monkeys and in 
following the course o f  recovery from damage induced by streptomycin. Electro- 
nystagmography can be used in order to provide permanent records. However, normal 
values established with electronystagrnography w i l l  differ from those determined by 
visual inspection, particularly i f  the Frenzel lens are eliminated and no light i s  
present, or the subject's eyes are closed. 
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The results of the threshold caloric test in this experiment reveal that the 
threshold values for a population of  young males fall within a narrow raqge, and a 
value outside this range suggests the presence of  a labyrinth abnormality. The 
findings indicate l i t t l e  or no adaptation to repeated threshold caloric irrigations 
o f  the type used in the present study. 
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RE FE R E N  CES 
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1. Collins, W. E., Guedry, F. E . ,  and Posner, J. B., Control of caloric nystagmus 
by manipulating arousal and visual fixation distance. Ann.OtoI. , etc. , 
St. Louis, 71:187-202, 1962. 
-- -
- 
2. 
3. 
4. 
5. 
6. 
7. 
8. 
Bergstedt, M., -- et al., In preparation. 
Fitzgerald, G. , and Hallpike, C. S. , Studies i n  human vestibular function. 
I. Observations on the directional preponderance ("nystagmusbereitschaft") 
of  caloric nystagmus resulting from cerebral lesions. -- Brain, 65: 115-137, 1942. 
Henriksson, H . J. , Femandez, C., and Kohut, R. I .  , The caloric test in the 
cat. Acta otolaryng., Stockh., 53:21-32, 1961. - -- I 
Jongkees, L. B. W., Which i s  the preferable method of  performing the caloric 
test? Arch. otolaryng . , - 49594-608, 1949. -
Kobrak, F., Zur Frage einer exakten Messbarkeit der Sensibilittit des 
Vestibularappurates . Arch. Ohr. -Nas. u. Keh IkHei Ik. , - 105: 132- 134, 1920. - - - -  
Lidvall, H. F. , Specific and nonspecific traits o f  habituation in nystagmus 
responses to caloric stimuli. Acta otolaryng ., -- Stockh ., - 55:315-325, 1962. -
Mahoney, J. C., Harlan, W. L., and Bickford, R. G., Visual and other 
factors influencing caloric nystagmus in  normal subjects. Arch. otolaryng . , 
- 66:46-53, 1957. 
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A threshold caloric test- results in normal subjects

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