Journal of Nursing Education

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The Quieting Response (QR): A Modality for Reduction of Psychophysiologic Stress in Nursing Students

Doris Heaman, DSN, RN

Abstract

ABSTRACT

The purpose of this study was to investigate the effects of a 5- week stress management program for 40 junior baccalaureate nursing students. A quasi-experimental pretest-posttest control group design was used. The stress management group included training sessions using cognitive modification techniques and Stroebel's Quieting Response (QR) augmented with biofeedback techniques for self-relaxation.

A significant reduction of state anxiety (P<.001) was reported on the State-Trait Anxiety Inventory (STAI) by the experimental groups, while the state anxiety of the control groups remained relatively unchanged. There were no significant changes in trait anxiety scores. Urinary potassium excretion was measured as an index of the adrenal stress response. Findings revealed no statistically significant correlation between potassium excretion and scores on the STAI.

These results support the benefits of integrating a stress management program into curricula for nursing students.

Abstract

ABSTRACT

The purpose of this study was to investigate the effects of a 5- week stress management program for 40 junior baccalaureate nursing students. A quasi-experimental pretest-posttest control group design was used. The stress management group included training sessions using cognitive modification techniques and Stroebel's Quieting Response (QR) augmented with biofeedback techniques for self-relaxation.

A significant reduction of state anxiety (P<.001) was reported on the State-Trait Anxiety Inventory (STAI) by the experimental groups, while the state anxiety of the control groups remained relatively unchanged. There were no significant changes in trait anxiety scores. Urinary potassium excretion was measured as an index of the adrenal stress response. Findings revealed no statistically significant correlation between potassium excretion and scores on the STAI.

These results support the benefits of integrating a stress management program into curricula for nursing students.

Introduction

Undergraduate nursing students frequently experience high levels of anxiety, especially during clinical courses. A multitude of situational and developmental stressors impinge on learning as well as physiological health (Beck & Srivastara, 1991; Speck, 1990). Assimilation of the current knowledge explosion is a major stressor. Furthermore, students are often perceived as nurses in terms of accountability and responsibility, rather than learners, when they are in the clinical setting (Infante, 1985). Additionally, many times students find that the reality of being a nurse is unlike their lay perception of the role (Pagana, 1988; Simpson, 1979). Not only can the educational journey be a stressful experience which produces anxiety, but students enter a profession high in potential stressors such as increased acuity of clients, rapid technological advances, and the HIV/AIDS epidemic. (Biggers, Zimmerman, & Alport, 1988; Lees & Ellis, 1990; Parkes, 1985).

Stress is a part of life and is experienced by everyone. However, when stress reaches a high level, the student may start to react with aggressive, submissive, and maladaptive behaviors. These behaviors are damaging to the student and present problems for student and nurse educator (Bell, 1991; Blainey, 1980; Charlesworth, Murphy, & Beutler, 1981; McKay, 1978; Strauss & Hutton, 1983).

While the stressors of nursing students' education have been documented, little attention has been devoted to integration of coping skills into baccalaureate nursing programs (Johansson, 1991; Manderino, Ganong, & Darnell, 1988; Russler, 1991). Academic settings tend to focus on curricula, and faculty may be less responsive to the stressors students experience. Assisting students to cope with anxiety is an important component of the faculty role (Blainey, 1980; Russler, 1991; Strauss & Hutton, 1983). Likewise, in order to develop effective stress management programs, there is a need for experimental investigations which examine systematic approaches for students to learn adaptive stress reduction techniques (Russler).

The purpose of this study was to determine the effects of a 5-week stress management program on junior nursing students' level of anxiety using Stroebel's (1983) Quieting Response (QR). Stress management training sessions were augmented with biofeedback to teach self-relaxation.

Stress and Anxiety

Stress is a familiar concept that has been researched from psychophysiological perspectives, but there is little consensus as to its meaning. Robinson (1990) emphasized that "the stress response is, in fact, a prolonged psychophysiologic reaction* (p. 935), and "anxiety is the psychophysiologic signal that the stress response has been initiated" (p. 942). Lazarus (1966) referred to stress as a descriptive term for the phenomena that produce anxiety and psychological disorder. The transactional model further describes stress and coping as process oriented and based on the individual's cognitive appraisal of a situation (Folkmann & Lazarus, 1985; Lazarus).

Anxiety is characterized by "subjective feelings of tension, apprehension, nervousness, and worry, and by activation or arousal of the autonomic nervous system" (Spielberger, Gorsuch, Lushene, Vagg, & Jacobs, 1983, p. 1). The feeling of uneasiness may be conceptualized as a response to a real or imagined threat stimulus (stressor), and used as an index of psychological stress (Guzetta & Forsythe, 1979).

Physiological indicators of stress are well documented in the literature. Selye (1976), the pioneer of stress theory, described stress as a response syndrome that is manifested physiologically by a specific syndrome which includes non-specific responses within the body. As part of the stress response, adrenocorticotropic hormone (ACTH) from the anterior pituitary stimulates the adrenal cortex to produce mineralcorticoids (primarily aldosterone) and glucocorticoids. Aldosterone enhances the tubular reabsorption of sodium and chloride and the subsequent loss of potassium and hydrogen in the urine (Clochesy, Breu, Cardin, Rudy, & Whittaker, 1993; Guzzetta & Forsythe, 1979; Hopping, 1980).

Review of Literature

In a quasi-experimental design, Speck (1990) noted that first semester baccalaureate nursing students performing their first injections reported statistically significant lower anxiety levels on the State-Trait Anxiety Inventory (Spielberger, Gorsuch, Lushene, Vagg, & Jacobs, 1983) after using guided imagery to reduce anxiety levels. McDonald, Collins, and Walker (1983) reported a significant drop in attrition for nursing students who participated in a program focusing on emotional, behavioral, and cognitive coping. Upon analysis of qualitative data, Russler (1991) found that 90% of beginning baccalaureate students participating in multidimensional stress management training reported the program was effective.

Pride (1968) used urinary potassium excretion as an adrenal stress index when studying anxiety in hospitalized medical patients. The EPAT Anxiety Scale (1963) was used as a verbal measure of situational anxiety. Findings revealed a decrease in urinary potassium in those patients receiving nursing interventions directed toward alleviating stress.

Quieting Response (QR) Training

A review of the literature reflected studies which investigated relaxation techniques (Benson, Beary, & Carol, 1974; Farr, Keene, Samson, & Michael, 1984; Pender, 1985; Summers, Hoffman, Neff, Hanson, & Pierce, 1990). However, none was found that investigated the effects of the Quieting Response (QR), a simple automatic 6-second technique for stress reduction. The Quieting Response (QR), developed by Stroebel (1983), is a selfregulation skill to maintain an alert mind in a relaxed body.

The quickness and automaticity of the QR are advantageous for the real world. The QR is different from many self-regulation techniques for stress management in two ways. The QR permits the alert mind to shift gears from "passing* to "coasting" without dropping out in order to deal with the stressor at hand. Additionally, after the initial learning and practice, QR becomes automatic whenever the body begins to perceive stimuli as stressful. Thus, it can be used in a clinical situation without time out from ongoing activities. Automaticity may be attained in approximately 6 months with practice. The QR also offers a way of providing a natural mechanism for preventing stress-related disease (Stroebel, 1983).

Biofeedback- Aided Relaxation

Biofeedback enables individuals to become active participants in altering physiological responses. The physiological information is translated into various forms such as tone, meter signal, digital display, and light change intensity which is fed back to the individual. With practice, the trainee can begin to influence the direction and degree of change (Cromwell, Weibell, & Pfeiffer, 1980; Sutterly, 1979).

A frequently used biofeedback instrument is the electromyograph (EMG). Other forms of instrumentation for providing feedback include thermistors for skin temperature changes and sensors for measuring galvanic skin resistance (GSR). Biofeedback-augmented relaxation was used by Kamholtz (1982) and Fehring (1983) for stress reduction in college students.

Research Questions

The research questions posed for this study were:

1. Will junior nursing students who participate in a 6-week stress management program report less anxiety than students in a control group?

2. Is there an association between reported anxiety and urinary potassium excretion?

Methodology

The sample consisted of 40 female junior nursing students in a baccalaureate program who were randomly assigned to two experimental and two control groups. Students were in their first year of clinical courses. Participation was totally voluntary.

The age range of subjects was 20 to 50 years (x = 28.9, S.D. = 8.23). The ages of subjects in Experimental Groups I and II ranged from 22 to 50 years (x = 34.3, S.D. = 10.4) and from 21 to 42 years (x = 25.8, S.D. = 6.9) respectively. The ages of subjects in the control groups ranged from 20 to 44 years (x = 25.8, S.D. = 7.6) and 20 to 37 years (x = 26.4, S.D. = 6.0) respectively.

An experimental group-control group, pretest-posttest design was used. There were 10 subjects each in Experimental Group I and Control Group I. There were 11 subjects in Experimental Group II and 9 subjects in Control Group II. A total of five students withdrew from the program because of scheduling problems relating to work and family needs. An initial screening question regarding the presence of any primary endocrine or health disorder was included with the explanation of the program to the potential subjects.

Experimental treatment. The stress management sessions consisted of five 90-minute training sessions conducted once weekly over a 5-week period at the College of Nursing. Because of class and clinical constraints, Experimental Group I met weekly after their hospital clinical experience, and Experimental Group II met weekly after lecture. Student participation was on their own time. The format for sessions consisted of (1) didactic information which addressed stress and coping from physiological, psychological, and cognitive perspectives; (2) students sharing their QR diaries (monitoring logs); (3) use of Quieting Response Audio Cassettes (Stroebel, 1978) for relaxation training; and (4) augmentation of practice training with electromyography, skin temperature sensors, and galvanic skin resistance monitors to provide for active subject involvement.

The training cassettes started with breathing, which is a basic element of the QR, and proceeded to the use of the QR in daily life. The QR Diary was adapted from Stroebel's diary scan as a learning log to assist students in identifying and heightening their awareness of situations causing stress and their response to the situation. Students were provided with individual tapes for home practice between sessions, and a learning curve was used to represent acquisition of quieting skills. Both the QR tapes and biofeedback equipment were available in the Learning Resources Center for practice.

Spielberger, Gor such, Lushene, Vagg, and Jacobs' (1983) State-Trait Anxiety Inventory (STAI) was used to measure anxiety in pretesting and posttesting. The STAI consists of two 20-item self-report scales. Subjects rated themselves on a four-point scale for each item. Form Y-I is designed to measure the current level of tension and apprehension (state), and Form Y-2 is designed to measure anxiety proneness (trait). Reliability and validity have been well documented with the STAI. The overall median alpha reliability coefficient for the State-Anxiety and Trait-Anxiety are .92 and .90 respectively (Spielberger, Gorsuch, Lushene, Vagg, & Jacobs).

Control treatment. The control groups did not participate in any of the stress management activities. Pretesting and posttesting were done on the same days as the experimental group, but in a different location in the building.

The measure of weekly urinary potassium excretion was also used as an indicator related to stressors. Serial mine specimens for potassium were collected in the early morning prior to breakfast and were measured by flame photometry.

Results

Posttreatment state anxiety scores of subjects in the stress management program were significantly lower than scores of the control group. Data were analyzed by means of SPSS MANCOVA. The pre-trait and pre-state anxiety scores were analyzed to determine if significant differences between the two experimental groups did exist before treatment. Likewise, significant differences between the two control groups on prescores were tested. Because there were no statistically significant differences for either group on either of the anxiety prescores, the two experimental groups were combined and the two control groups were combined for posttreatment analysis.

Results of the evaluation of assumptions of normality, homogeneity of variance-covariance, matrices, linearity, multi-collinearity, and homogeneity of regression were satisfactorily met. The set of covariates (pretreatment trait and pretreatment state anxiety) were judged to be significantly related to the set of dependent variables (posttreatment trait and posttreatment state anxiety) to warrant covariance analysis.

Analysis of data revealed a significant difference in anxiety associated with treatment after adjustment for individual differences at beginning of treatment (Pillar's F [2, 351 = 8.13, <.0001). Pillai's criterion, a conservative test of significance, was selected to evaluate the multivariate significance. According to Olsen (1979), Pillai is reported to be more robust than Wilk's Lambda, Hotelling's Trace, or Roy's get criterion. Additionally, Tabachnick and Fidell (1989) have suggested using Pillai's criterion when there are small and/or unequal numbers in the cells or when the research design is not ideal.

Because there was a significant overall treatment difference on the set of dependent variables of posttreatment trait and posttreatment state scores after adjustment, the question was "Did both variables contribute to that difference?"' Data from the univariate analysis can be found in Table 1 and Table 2.

Epsilon squared, a measure of relative treatment magnitude and an index of the efficacy of the experimental treatment, was calculated to be .29. This value indicates that 29% of the total variability in state anxiety of nursing students can be accounted for by the experimental treatment of stress management. According to Cohen (1977), who is cited in Keppel (1982), this value represents more than a moderate association between stress management training and state anxiety.

Because the correlation between state and trait anxiety was in excess of .30, stepdown analysis was deemed appropriate for further investigation. Additionally, stepdown analysis is a means of controlling in a precise way against Type I error. Theoretically, state anxiety (situation anxiety) is not possible without the personality dimension of trait anxiety (anxiety proneness). Traits are dispositional tendencies acquired in childhood that are latent until a situation activates them (Atkinson, 1964). Therefore, trait anxiety was entered first in the stepdown analysis and served as a covariate in adjusting for the effects of state anxiety.

Table

TABLE 1Univariate Analysis of Covariance for PostTreatment Trait Anxiety

TABLE 1

Univariate Analysis of Covariance for PostTreatment Trait Anxiety

Table

TABLE 2Univariate Analyses of Covariance for PostTreatment State Anxiety

TABLE 2

Univariate Analyses of Covariance for PostTreatment State Anxiety

Data for the comparison of the univariate and stepdown analysis are reported in Table 3. As noted, only posttreatment state anxiety contributed to the difference between the two treatment groups.

Subjects who participated in the stress management program had significantly lower posttreatment state anxiety scores than the subjects in the control groups (see Table 4). The difference in the adjusted means of the experimental and control groups trait scores was 2.71, whereas the difference in the adjusted means of the experimental and control groups state scores was 10.53. It was noted that Experimental Group I reported a greater decrease in state anxiety than Experimental Group II. Scores of Control Group I reflected no change in state anxiety, while Control Group II reflected a very slight decrease in state anxiety.

Interestingly, trait anxiety scores (x = 36.40) of Experimental Group I were slightly lower (x = 34.90) following treatment. Likewise, trait anxiety scores (x = 42.63) of Experimental Group II were slightly lower (x = 39.36) following treatment. However, there was essentially no difference in trait anxiety scores of Control Group I U =39.30, (x=39.10) and Control Group II (x= 42.77, ? = 42.33) when measured at the same times as the experimental groups (see Table 5).

The question was raised whether there was a relationship between urinary potassium excretion, a physiological index for stress, and scores on the STAI. Pearson correlation coefficients did not reflect significant relationships between potassium excretion and STAI scores in control or experimental groups. Therefore, in this study urinary potassium excretion, a dependent variable, was not related to anxiety scores.

Discussion

The findings of this study suggest that participation in a systematic stress management program had a significant effect on the reported state anxiety of junior baccalaureate nursing students. A lack of significant change in trait anxiety was not unexpected from a theoretical perspective because trait anxiety is a relatively stable individual difference in anxiety proneness.

There was a greater reduction in anxiety scores in Experimental Group I which met after their clinical experience than in Experimental Group II which met after lecture. Clinical site stressors and fatigue would conceivably be more responsive to relaxation training than a lecture period experience (except on examination days). Also, the additional life experiences of Group I (mean age of 34.3) over Group II (mean age of 25.8) would provide adroitness and maturity in managing stressors.

In a 6-month follow-up of the groups, students reported they were using the QR to reduce their anxiety during classroom testing and in the clinical setting. Several students also reported they were successful in using the QR with patients who were anxious. A student who worked in the Emergency Room of a large hospital related that she had frequently used the QR to reduce her anxiety and that of individuals in crisis situations. One student related with a sense of humor that she had prayed for her safety and the ability to use the QR when she was in a severe thunderstorm with tornado warnings as she was driving home from the university. Students were encouraged to continue using their logs in self-assessment.

Additionally, practice of the QR was recommended in order to retain automaticity in responding to stressors. Students from the experimental groups strongly recommended that stress management sessions be integrated into the curriculum beginning at the sophomore level in order to increase students' coping skills. Approximately a year after completing the stress management sessions, a new graduate called to comment on the usefulness of the QR during her NCLEX examination. An additional benefit that other faculty in the college observed, as a result of the study, was the interest in stress management techniques that was generated among students. A number of students who participated in the study developed proposals based on concepts of stress, anxiety, and coping in their research course.

Table

TABLE 3Univariate and Stepdown Analyses

TABLE 3

Univariate and Stepdown Analyses

Table

TABLE 4Pre-, Post- and Adjusted Means for Anxiety Scores

TABLE 4

Pre-, Post- and Adjusted Means for Anxiety Scores

Table

TABLE 5Pre-, Post-, State and Trait Mean Scores and Standard Deviations for Individual Groups

TABLE 5

Pre-, Post-, State and Trait Mean Scores and Standard Deviations for Individual Groups

Limitations and Future Research

The results of the study are subject to the limitation of a small sample size from one setting. In order to provide adequate time for group process, the number in the groups was limited. Increasing the sample size would provide for more diversity in age, sex, ethnicity, and other program levels of students. It should be noted that no control was made for individual dietary regimens. Also, urine potassium specimens were not collected over a 24-hour period to allow for variations due to circadian rhythms and eating habits.

Data collected by subjects in their diary logs were discussed in the group sessions but were not subjected to statistical analysis. Study of this information may also reflect individual patterns of response to stressful situations. A longitudinal study would assist in evaluating the effects of stress management on clinical and academic performance of nursing students as they progress through a nursing program.

There is a great need to identify coping patterns and increase students' behavioral competence in personal stress management. Results of this study offer evidence for incorporating stress management skills into nursing curricula. Stress management would be beneficial as a component of entry-level clinical courses or taught as an elective course for interested students. Student interest in stress management was demonstrated by students volunteering to participate in the sessions on their own time.

It is not always possible to alter the stress associated with nursing education and practice. However, it is both possible and propitious to teach individuals the skills needed to cope more effectively with stressors in nursing programs and ultimately in professional practice.

References

  • Atkinson, J. W. (1964). An introduction to motivation. Princeton, NJ: Van Nostrana.
  • Beck, D.L., & Srivastara, R. (1991). Perceived level and source of stress in baccalaureate nursing students. Journal of Nursing Education, 30(3), 127-133.
  • Bell, M.L. (1991). Learning a complex nursing skill: Student anxiety and the effect of preclinical skill evaluation. Journal of Nursing Education, 30(5), 222-226.
  • Benson, H., Beary, J.F., & Carol, M.P. (1974). The relaxation response. Psychiatry, 37, 37-45.
  • Biggers, T., Zimmerman, R.S., & Alport, G. (1988). Nursing, nursing education, and anxiety. Journal of Nursing Education, 27(9), 411-417.
  • Blainey, CG. (1980). Anxiety in the medical-surgical clinical student. Journal of Nursing Education, 19, 33-36.
  • Charlesworth, E.A., Murphy, S., & Beutler, L.E. (1981). Stress management skill for nursing students. Journal of Clinical Psychology, 37, 284-290.
  • Clochesy, J.M., Breu, C, Cardin, S., Rudy, E.B., & Whittaker, A.A. (1993). Critical care nursing. Philadelphia: W.B. Saunders.
  • Cohen, J. (1977). Statistical power analysis for the behavioral sciences. (2nd ed.) New York: Academic Press.
  • Cromwell, L., Weibell, E., & Pfeiffer, E.A (1980). Biomedical instrumentation and measurements. Englewood Cliffs, NJ: Prentice-Hall.
  • Farr, L., Keene, A., Samson, D., & Michael, A. (1984). Alterations in circadian excretion of urinary variables and physiological indicators of stress following surgery. Nursing Research, 33, 140-146.
  • Fehring, R. J. (1983). Effects of biofeedback-aided relaxation on the psychological stress symptoms of college students. Nursing Research, 32, 362-366.
  • Folkman, S., & Lazarus, R.S. (1985). If it changes, it must be a process: Study of emotion and coping during a college examination. Journal of Personality and Social Psychology, 48, 150-170.
  • Guzetta, C, & Forsythe, G. (1979). Nursing diagnostic pilot study: Psychophysiologic stress. Advances in Nursing Science, 2(1), 27-44.
  • Handbook for the JPAT Anxiety Scale Questionnaire. (1963). Champaign, IL: Institute for Personality and Ability Testing.
  • Hopping, B. (1980). Physiological response to stress: A nursing concern. Nursing Forum, 19, 259-269.
  • Infante, M.S. (1985). The clinical laboratory in nursing education. (2nd ed.) New York: John Wiley & Sons.
  • Johansson, N. (1991). Effectiveness of a stress management program in reducing anxiety and depression in nursing students. Journal of American College Health, 40(3), 125-129.
  • Kamholtz, JD. (1982). The effects of a stress reduction workshop on undergraduate college level students possessing type A behavior pattern. Health Education, 23(6), 42-44.
  • Keppel, G. (1982). Design and analysis: A researchers handbook. (2nd ed.) Englewood Cliffs, NJ: Prentice-Hall.
  • Lazarus, R.S. (1966). Psychological stress and the coping process. New York: McGraw-Hill.
  • Lees, S., & Ellis, N. (1990). The design of a stress management program for nursing personnel. Journal of Advanced Nursing, 15, 946-961.
  • Manderino, M.A., Ganong, L.H., & Darnell, KF. (1988). Survey of stress management content in baccalaureate nursing curricula. Journal of Nursing Education, 27(7), 321-325.
  • McDonald, J.M., Collins, R.F., & Walker, A.R. (1983). Success: A program to reduce student nurse attrition. Nurse Educator, 8(4), 17-20.
  • McKay, S.R. (1978). A review of stress in nursing education programs. Nursing Forum, 177, 377-393.
  • Olsen, CL. (1976). On choosing a test statistic in multivariate statistics. Psychological Bulletin, 83, 579-586.
  • Pagana, K.D. (1988). Stresses and threats reported by baccalaureate students in relation to an initial clinical experience. Journal of Nursing Education, 27(9), 418-424.
  • Parkes, K.R. (1985). Stressful episodes reported by first-year student nurses: A descriptive account. Social Science and Medicine, 20, 945-953.
  • Pender, N.J. (1985). Effects of progressive muscle relaxation training on anxiety and health locus of control among hypertensive adults. Research in Nursing and Health, 8, 67-72.
  • Pride, L.F. (1968). An adrenal stress index as a criterion measure for nursing. Nursing Research, 17, 292-303.
  • Robinson, L. (1990). Stress and anxiety. The Nursing Clinics of North America, 25, 935-943.
  • Russler, M.F. (1991). Multidimensional stress management in nursing education. Journal of Nursing Education, 30(8), 341-346.
  • Selye, H. (1976). The stress of life. New York: McGraw-Hill.
  • Simpson, LH. (1979). From student to nurse. Cambridge, MA: Cambridge University Press.
  • Speck, B.J. (1990). The effect of guided imagery upon first semester nursing students performing their first injections. Journal of Nursing Education, 29(8), 346-350.
  • Spielberger, CD., Gorsuch, R.L., Lushene, R.E., Vagg, RR., & Jacobs, G.A. (1983). Manual for the State Trait Anxiety Inventory (Form Y). Palo Alto, CA: Consulting Psychologists Press.
  • Strauss, S.S., & Hutton, E.B. (1983). A framework for conceptualizing learning. Journal of Nursing Education, 22, 367-371.
  • Stroebel, CF. (Preparer). (1978). Quieting Response Training (Cassettes, Copyright 1978). New York: BMA.
  • Stroebel, CF. (1983). QR: The quieting reflex. New York: Berkley.
  • Summers, S., Hoffman, M.A., Neff, E.J., Hanson, S., & Pierce, K (1990). Journal of Nursing Education, 29(2), 66-70.
  • Sutterly, D. (1979). Stress and health: A survey of self-regulation modalities. Topics In Clinical Nursing, 1(1), 1-31.
  • Tabachnick, B., & Fidell, L. (1989). Using multivariate statistics. New York: Harper & Row.

TABLE 1

Univariate Analysis of Covariance for PostTreatment Trait Anxiety

TABLE 2

Univariate Analyses of Covariance for PostTreatment State Anxiety

TABLE 3

Univariate and Stepdown Analyses

TABLE 4

Pre-, Post- and Adjusted Means for Anxiety Scores

TABLE 5

Pre-, Post-, State and Trait Mean Scores and Standard Deviations for Individual Groups

10.3928/0148-4834-19950101-04

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