Yonago Acta medica 2002;45:43–47

Stress Tolerance in Subjects with Myocardial Infarction
Kimiko Hiramatsu, Junko Nagasawa, Yuka Hirai, Sumiko Iyama, RumikoNagami, Keiko Kurashiki, Miyoko Matsuo and Tadasu Ikeda
Department of Adult and Geriatric Nursing, School of Health Science, Tottori University,
Yonago 683-8503 Japan
In our course of surveys to study the relationship between stress and myocardial
infarction (MI), we have investigated whether stress tolerance may play a significant
role when MI develops. To elucidate the possible role of stress tolerance, we examined
96 patients with MI (68 men and 28 women, age 40–90 years) with a stress tolerance
check list in which stress tolerance was quantified as total points for 20 self-evaluateditems, each scored between 1 and 4 points. Their scores were compared with control
values obtained from persons not suffering from MI, and further analyzed by dividingthem into 3 groups according to their grade of stress tolerance; that is, low (39 or less inscore), moderate (40–49) and high (50–80). The mean stress tolerance score (± SD) was
significantly lower in the 96 MI patients (49.5 ± 8.90 points) than in the controls (60.8 ±7.3 points). The stress tolerance grade was low in 13 of the 96 (13.5%), moderate in 34(35.5%) and high in 49 (51.0%). In MI patients, lowly or moderately stress-tolerant
persons were significantly higher in percentage (49.0%) than in the controls (6.3%).
These results clearly indicate that low stress tolerance is a risk factor in the developmentof MI.
Key words: myocardial infarction; stress tolerance; stress tolerance check list

them from falling into stressful conditions(Murakami, 1992); that is, people with highstress tolerance can withstand stress even when
they undergo a severe case of it. This suggeststhat stress tolerance may play a significant rolein the development of MI. To our knowledge,
stress tolerance in persons suffering from M I
has not been reported yet. In this article, we investigated what role stress tolerance plays when
MI develops.

Stress is known to be a risk factor in the development of myocardial infarction (MI). When
stress is present in the human body, it activates
reactions of the autonomic nervous system andendocrine system: catecholamine secretion increases, and blood pressure elevation andimmunosuppression follow, which result in facilitation of the aggregation and coagulation
system of thrombocytes. If this facilitation continues for a longer period, it may cause arteriosclerosis, which could end up with the onset ofMI (Nagata et al., 1992).
Some workers reported a high correlation
between MI and stress generated in daily living(Rahe et al., 1976), while another reported norelevance (Romo et al., 1974). Generally considering, the level of severeness in stress a person feels originates from individual personality
characteristics. If their ability for stress tolerance is sufficiently high, this helps to prevent

Subjects and Methods
Subjects
Subjects were selected from in- and outpatientsdiagnosed with MI whose symptoms were stabilized by medical treatment at Tottori University Hospital between April 1992 and March

Abbreviations: MI, myocardial infarction; STCL, stress tolerance check list

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K. Hiramatsu et al.

Table 1. Stress tolerance check list

12
3
4
5
678
910
1112
13
14
15
16
17
18
1920

Making a calm judgment
BrightApt to express feelings
JoyfulSensitive to others’ moods
Positive
EnviousFond of exercising
Critical of others
Evaluating others’ merits
Flexible
Apt to reply to letters soon
Easygoing
Apt to make sure of things
Thoughtful of others
Able to thank others
Having many friends
Discordant within the family
Overloaded with work
Enjoying a hobby

SeldomSometimes

Often

Always

1
1
1
14
14
14
1
1
111
1
1
144
12
2
2232323
2
22
2
2222
3
32

3
3
332323233333333
223444414
141444444441
1
4Devised by K. Katsura (Murakami, 1992).

seldom, 3 for sometimes, 2 for often and 1 foralways. A full score was 80 points: stresstolerance was graded into 3 levels of low when
the score was between 39 points or less, moderate when it was between 40 and 49 points, andhigh when it was between 50 and 80 points.

2002. They consisted of 68 men (78%) and 28
women (22%), aged 40 to 90 years. Written
informed consent was obtained from all patients, who clearly understood the object of thestudy. The period from the onset of MI to thepresent study ranged between 1 month and 10years (mean, 3 years and 9 months).
The data reported from 272 persons who
had no MI were used as controls (Settsu et al.,1990).

Statistical analysis
Data were expressed as mean ± SD. The analysis of variance was used for statistical analysis
to test differences between groups. P values of< 0.05 were considered statistically significant.

Methods
To quantify stress tolerance as a score, we used
the stress tolerance check list (STCL) devisedby K. Katsura (Settsu et al., 1990; Murakami,1992), which was used for the 272 abovementioned persons. The list consisted of 20
questions for the self-evaluation of personality
characters as point(s), each between 1 and 4: 1
point for seldom, 2 points for sometimes, 3
points for often and 4 points for always (Table1). The evaluation points were reversed foritems number 5, 7, 9,18 and 19; that is, 4 forResults
Patients characteristics
Table 2 shows sex- and age-classified distributions of the 96 MI patients graded by stress tolerance as low, moderate and high according tothe obtained score: of the 96, 13 (13.5%) wereof low grade, 34 (35.5%) were of moderate
44

Stress tolerance in myocardial infarction

Table 2. Patients’ characteristics
Age(year)

Low*
Male Female

40–49
50–59
60–69
70–79
80–90
Total

00
151
7000
42
6Total0( 0 )0( 0 )
1 ( 1.0)
9 ( 9.4)
3 ( 3.1)
13 (13.5)

NS

Stress tolerance grade
Moderate*
Male Female Total

High*
Male Female Total

24865253
1010103360
016292 ( 2.1)
4 ( 4.2)
9 ( 9.4)
12 (12.5)
7 ( 7.3)
34 (35.5)

NS02353133 ( 3.1)
12 (12.5)
13 (13.5)
15 (15.6)
6 ( 6.3)
49 (51.0)

NS( ), percentage out of the whole 96 patients.
* Stress tolerance score (mean ± SD): low, 36.5 ± 3.4; moderate, 45.5 ± 2.4; high, 55.7 ± 4.6.
NS, not significant.
Differences among the 5 age-classified subgroups were not significant in each group; low-, moderate- or
high-grade.

Sex-classified differences were further examined: comparison between male patients(50.1 ± 7.5 points) and male controls (60.6 ± 7.9points) showed a significant difference (P <0.01). The difference between female patients(48.1 ± 8.9 points) and female controls (61.3 ±7.9 points) was also significant (P < 0.01).

grade and 49 (51.0%) were of high grade. Statistical differences in age and sex were not significant.
Stress tolerance score in MI patientsand controls
Table 3 compares stress tolerance scores between our patients and normal controls. The
mean stress tolerance score (± SD) was 60.8 ±7.3 points out of the whole controls group and49.5 ± 7.9 points out of the whole patients group.
The difference between the paired groups compared showed a significantly lower level forpatients (P < 0.01).

Comparison of stress tolerance grade
Table 4 compares grades of stress tolerance between sex-classified patient and control groups.
Stress tolerance was graded high in 93.8% of
male controls and 52.9% of male patients, andsimilarly high in 93.6% of female controls but
only in 44.8% of female patients.

Table 3. Sex-classified comparison of stress tolerance scores between MI patients andnormal controls
Stress tolerance score
WomenMenControl subjects
MI patients

60.8 ± 7.3 [272]49.5 ± 8.0 [ 96]

Total

60.6 ± 7.9 [191]*50.1 ± 7.5 [ 68]Mean ± SD. [ ], number of subjects.
MI, myocardial infarction.
* P < 0.01.
Data of control subjects were cited from Settsu et al. (1990).

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61.3 ± 7.9 [81]*48.1 ± 8.9 [28]*K. Hiramatsu et al.

Table 4. Sex-classified distribution of MI patients and control subjects analyzed by stress
tolerance grade

Low(%)
Men
Control subjects [191]MI patients
[ 68]
Women
Control subjects [ 81]MI patients[ 28]

Sress tolerance grade
Moderate(%)

High(%)

0.5 [1]
10.3 [7]*5.7 [11]36.8 [25]*93.8 [179]52.9 [ 36]*

1.3 [1]
21.4 [6]*5.1 [ 4]32.1 [ 9]*93.6 [ 76]46.5 [ 13]*[ ], number of subjects.
MI, myocardial infarction.
* P < 0.01.
Data of control subjects were cited from Settsu et al. (1990).

Stress tolerance was moderate in 5.7% of
male controls and 39.7% of male patients, andin 5.1% of female controls and 34.5% of female
patients.
Low tolerance was observed in 0.5% ofmale controls and 7.4% of male patients, and in
1.3% of female controls and 20.7% of female
patients.
In all grades of stress tolerance, the paired
groups compared showed significant differences (P < 0.01).

et al. (1974) observed no correlation between
MI and stress; however, his conclusion might
have been different if he had counted stress tolerance as one of the analytical measures.
When we investigate stress as a factor relevant to the onset of MI, it is quite significant inthrowing light on a person’s individual ability
to tolerate stress . To date, few papers have reported stress tolerance in persons with MI. It isobvious, however, if stress tolerance in a person
is sufficiently high, the body may not identify
stress so that catecholamine secretion is not increased when stressful events are experienced.
The present study has explored the theory thatstress is less tolerated in patients with MI thanin normal persons: low stress tolerance must
contribute to the occurrence of MI.
We used Katsura’s STCL for this study, as itis the only reported tool to evaluate stress tolerance. We are now preparing a new checklist
which may be more valid in assessig stress
tolerance for further studies. On the other hand,the data we used as controls for comparison
were collected by Settsu et al. (1990) as normal
values on stress tolerance, which is the only
study relevant to the present one. Of theirsubjects, 80% were in their 50’s and 60’s, both
men and women together, and younger than ourpatients. Their study lacked any age-classifed
analysis of stress tolerance: so, we did not compare in the present study stress tolerance gradesby age between our patients and their subjects.

Discussion
Stress is known to act as a trigger for the onsetof MI (Friedman and Rosenman, 1993;
Sekiguchi, 1993). However, stress-induced
symptoms do not appear if stress tolerance ishigh enough to withstand high levels of stress.
That is, people with high stress tolerance have
low or little probability to suffer an attack ofMI.
The possible role of stress tolerance in thedevelopment of MI has not been elucidated yet.
In the present study, we observed that stress
tolerance in MI patients was lower than incontrols. Among all the patients, those withlow and moderate grades of stress tolerance occupied significantly higher percentages thancontrols. As this result clearly indicates, stress
tolerance is low in persons who have MI. Romo46

Stress tolerance in myocardial infarction

Knofp Inc., 1974.
2 Kimura K. [Internal disease and type A]. Gendai
No Esupuri (L’esprit d’aujourd’hui) 1995;(337):
43–53 (in Japanese).
3 Murakami M. [Stress test.] Nurse +1 1992;2
Suppl 13:36–49 (in Japanese).
4 Murakami M, Matsuno T, Nakamura N, Kasai T,
Arai Y, Kamoshita I, et al. Investigation on
stress-induced condition of healthy people: diagnosis and management of stress-related symptoms. Shinshin Iryo 1989;1:72–82 (in Japanese).
5 Nagata K. [Physiology and pathology of stress.]
Nurse +1 1992;2 Suppl 13:14–19 (in Japanese).
6 Rahe RH, Arajarvi H, Arajarvi S, Punsar S,Karvonen MJ. Recent life changes and coronary
heart disease in east versus west Finland. J Psychosom Res 1976;20:431–437.
7 Romo M, Siltanene P, Theorell T, Rahe RH.
Work behavior, time urgency and life dissatisfactions in subjects with myocardial infarction:a cross-cultural study. J Psychosom Res 1974;
18:1–8.
8 Sekiguchi M. [Beginning of type A studies inJapan]. In: Momoo H, Hayano J, Hosaka T,
Kimura K, eds. Taipu A Kodo Patan [Type Abehavior patterns]. Tokyo: Seiwa Shoten; 1993.
Chapter 3. p. 18-21 (in Japanese).
9 Settsu M, Murakami M, Katsura K. Life styleand stress of healthy people. Shinshin Iryo 1990;
12:89-96 (in Japanese).

In the analysis of age-classified groups of ourpatients, stress tolerance lowered as age advanced but with no significant differences.
Comparison between sex-classified subgroups
showed no significant difference either.
In further studies, we will develop an agematched design for statistical analysis, andcompare stress tolerance grades between MI patients and controls by collecting data of normal
persons. As we were deeply inspired here, thepossibility of contracting MI becomes higher
when stress tolerance is lowered rather than at
the onset of stress itself. It is difficult to avoid
various causes of stress arising from daily living. People can have the ability to deal with theseby heightening their ability to tolerate stress.
Stress management should be consideredalso from the viewpoint of stress tolerance. We
would like to apply the present observations
into a life guidance plan or patient education,
especially for people with coronary risk factors
such as hypertension, diabetes mellitus andhyperlipidemia.

References
1 Friedman M, Rosenman RH. Taipu A: Seikaku
To Shinzobyo. Tokyo: Sogensha; 1993. p. 126–
133 (in Japanese). Sinzato R, translator. Type A
behavior and your heart. New York: Alfred A.

Received March 25, 2002; accepted May 7, 2002
Corresponding author: Dr. Kimiko Hiramatsu

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