Cold water test

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The cold water test (also known as the Cold Pressor Test , or CPT) is a standardized procedure in which a cardiovascular reaction is induced. This effect is created by immersing individual limbs (hand, foot) in ice-cold water. In pain diagnostics, the test is used to determine the pain threshold and to record the subjective pain quality. In stress research, the cold water test has established itself as a method for inducing moderate stress.

The version of the CPT that has gained importance in research on stress and its origin is the Social Evaluated Cold Pressor Test (SECPT).

history

The test was originally developed in 1932 by Hines and Brown for the experimental induction of cardiovascular stress responses, especially blood pressure. The original version consists in submerging the dominant hand in ice-cold water (0-4 degrees Celsius) up to the wrist for 1-2 minutes. The authors were able to show that the test has a strong blood pressure-increasing effect in 99% of the people tested, which remains constant even after repeated testing. Based on their results, they postulated that vascular hyperreactivity, which manifests itself as an abnormal increase in blood pressure in response to CPT, would prove to be a predictor of later high blood pressure. Studies that have since addressed this question have shown conflicting results.

Hines and Brown primarily viewed cold temperature as a trigger for the rise in blood pressure in response to CPT, regardless of pain perception. Later studies, on the other hand, focused more on pain perception and were able to show a direct relationship between pain perception, temperature and the reactivity of blood pressure. Cold and pain are viewed as two different sensations, which are, however, related in that the pain sensation increases as the temperature increases. These findings opened the way for the CPT to pain research, where it was used to study different clinical and non-clinical populations. Since then it has been used in many studies on pain therapy for the investigation of a wide variety of procedures such as acupuncture and hypnosis or painkillers.

Later, modified versions were developed in which instead of the hand, for example, the foot, the forehead or the entire body is exposed to the cold for a certain period of time.

procedure

At the beginning, the participants are asked to lie on their back or sit quietly for a while. After this rest phase, blood pressure and heart rate are measured with the help of a blood pressure cuff in order to determine normal values. Then one hand of the test person is immersed in the ice water (temperature must be between 0-4 ° C). The test subjects are instructed to keep their hand in the water as long as possible, but to take it out of the water as soon as the cold becomes too painful. During this time, blood pressure and heart rate are determined every 30s and recorded on a data recording sheet. After three minutes at the latest, the test subject's hand is removed from the ice water. Now systolic and diastolic blood pressure are measured and the pulse rate is counted in 30-second intervals until blood pressure and pulse have normalized again.

In addition to recording blood pressure and heart rate, some studies also collected saliva samples from the participants in order to be able to record the hormonal stress reaction through an increase in the concentration of cortisol. To record the cardiovascular stress reaction, an ECG was also used in some studies in order to be able to determine an increase in the pulse.

Main variations of the CPT

SECPT (Socially evaluated cold pressor test). In the SECPT, in addition to the physiological stressor of the CPT (immersing the hand in ice water), a social-evaluative component (observed by the experimenter and recorded on video) is added.

SECPT-G (Socially evaluated cold pressor test for groups). The cold water test under social evaluation (SECPT) can also be carried out in groups (Socially Evaluated Cold Pressor Test For Groups, SECPT-G), so that an even more economical test is possible. The group size varies between the studies. Some studies tested four to six people, others tested at least seven people, and still other studies tested eight participants at once.

CPAW (Cold pressor arm wrap). This is a practical, effective and waterless alternative to traditional CPT. The process uses gel packs that are cooled to a temperature similar to that of the CPT. However, this allows a combined application with imaging methods such as MRT and thus enables further research work.

Physiological response / indicators of stress response

Stress results from a threat to the physiological and / or psychological integrity of a person, which causes an adaptive reaction on a physiological, behavioral, emotional and cognitive level. The decisive factor is not whether there is an objective threat, but whether the stressor is subjectively assessed as threatening. The individual extent of the stress reaction is modeled through the interaction of the individual psychobiological stress reactivity, the subjective threat assessment and the assessment of the available coping resources. Thus, stress is a short-term imbalance between the perceived stress and the available regulatory resources.

The subjective measurement of the stress reaction can take place , for example, using the visual analog scale . This measuring instrument is used for the differentiated recording of, for example, the unpredictability, fear or challenge in the specific stressful situation.

The physiological stress reactions are based on the two most important stress systems of the human body: the hypothalamic-pituitary-adrenal axis (HPA) and the sympathoadrenal system (SAM). These are characterized by various complex feedback mechanisms and interactions and react relatively independently of one another.

Hypothalamus-pituitary-adrenal cortex axis (HPA): The standard measurement of the cortisol content in saliva (significant increase> 2 nmol / l), since salivary cortisol is the most prominent marker of the HPA. With regard to the activation of the HPA axis, an unclear picture emerges: several authors can show little or no increase in the cortisol concentration in connection with the CPT. The CPT is less suitable for provoking the HPA than the SAM.

Sympathoadrenal system (SAM). The parameters recorded in the cold water test are blood pressure and heart rate (50-100 beats per minute at rest), and more rarely the pulse rate as the difference between systolic and diastolic blood pressure (normally 40 mm Hg). The secretory alpha-amylase (sAA) serves as an additional indicator for the activity of the autonomic nervous system . Studies on the CPT, however, were able to determine an increase in sAA; the current state of science requires further research for the SECPT. Another indicator is an increase in skin conductivity .

Hines and Brown assumed that the vasoconstriction ( vasoconstriction ) is triggered by a neurogenic reflex arc in response to the ice water. Recent studies have shown that exposure to cold water activates afferent nerves of pain and temperature perception, which in turn stimulate efferent neurons in the central nervous system. Furthermore, the reaction to the CPT shows an increase in the concentration of norepinephrine , which as a neurohormone is significantly involved in the control of the cardiovascular reaction to stress . With regard to dopamine , the study situation is still unclear.

Correlations

The current state of research indicates a variety of factors that correlate with different responses to the CPT. For this purpose, among other things, the factors: age, gender, ethnicity and fitness and health level can be listed.

One study showed that the response of femoral blood flow to hypoxia did not differ between the sexes; the increase in femoral blood flow is attenuated in older women compared to younger women. This could indicate that younger women show paradoxical vasodilation on CPT.

Significant correlations can also be found in measurements of increased tenderness to pressure in parts of the body (neck, dorsal wrist), gender (female), higher waist-to-hip ratio and poor mental health. In addition, there are significant correlates of increased levels of sensitivity to cold pain with gender (female), poor mental health and nicotine consumption.

The cold pain tolerance is lower among students of African descent compared to students of European descent (for both genders), and the pressure pain tolerance is lower among female students than among male students (for both ethnicities).

Fitness level could be another important factor. One study showed that after the end of the test, both heart rate and cardiac contractility decreased in subjects with a low fitness level, but not in those with a high fitness level. These findings suggest that the state of exercise affects the sympathetic neural response of the heart to exposure to cold. It was found that this is inversely related to increases in systolic and diastolic blood pressure and muscle-sympathetic nerve activity (MSNA) during CPT in women, but not in men. The pattern of responses in fitter women is consistent with decreased central sympathetic outflow, which among other things leads to decreased stroke volume . In fitter men and women, the blood pressure rose (stress was triggered) only when doing a task in the form of mental arithmetic. Further correlations between the fitness level and the stress reaction could not yet be directly demonstrated.

The current state of research disagrees with regard to the relationship between CPT and blood pressure hyperreactivity .

One study suggests that women, older age, and elevated baseline blood pressure levels are associated with an increased blood pressure response to CPT. In addition, physical inactivity, obesity and alcohol consumption can also be linked to hyperreactivity in blood pressure to stress.

While another study found no blood pressure hyperreactivity to the CPT.

Comparison of the CPT with SECPT and TSST

If one compares the CPT with SECPT, it could be shown that the cortisol response to the SECPT is significantly stronger than to the original CPT. The maximum in the cortisol level is increased by 45% when using the SECPT, compared to the original CPT. In addition, it was shown that the responder rate, i.e. the number of participants who react to the procedure with significant stress and show increased cortisol values, is significantly higher with the SECPT compared to the CPT.

In a modified version, the SECPT is carried out with warm instead of cold water. It could be shown that this version of the SECPT did lead to increased blood pressure and increased subjective stress ratings in the test subjects, but did not trigger an increased reaction of the HPA axis. Studies show that the response to the HPA axis triggered by the SECPT is not solely due to the socio-evaluative component of the test. This weakened version of the SECPT cannot therefore be used as an equivalent stress method in practice.

If one compares the original version of the CPT with the Trier Social Stress Test (TSST), another stress test widely used in research, it becomes clear that there are differences in the respective stress reaction to the procedure. Overall, the TSST triggered higher concentrations of ACTH and cortisol in the subjects than the CPT. The time course of these stress parameters up to the return to the starting position also differed for the procedures. It can be stated that the TSST with a social stressor triggers a stronger reaction on the HPA axis than the CPT with an exclusively physical stressor. Looking at the subjective perception of stress as a reaction to the procedure, it could be shown that both procedures produce high stress ratings and that these develop back to a normal starting level over the recorded time course. However, this development was somewhat slower after using the TSST than after using the CPT. The authors were also able to provide indications that the TSST is associated with an expected subjective deterioration in mood even before the start of the procedure (baseline measurement) compared to the CPT. In contrast to the CPT, this deterioration in the mood of the test subjects appears to persist for up to an hour after the TSST has ended.

Criticism / Limitations

Findings on quality criteria or limitations of the procedure:

Even very small differences in the selected water temperature of the CPT can lead to considerable differences in the effect on the pain perception and tolerance of test subjects. The lack of standardization and control of the water temperature in the application of the CPT can have negative effects on the comparability and reliability of the procedure.

The type of instruction can have an influence on the outcome parameters of the CPT. In their study, the authors compared the two common paradigms of the CPT: the instruction to the test subjects to hold the hand in cold water as long as possible ( tolerance paradigm ) and the instruction to hold the hand in it for a fixed period of time (e.g. for three Minutes; fixed latency paradigm ). The results suggest that the subjectively reported pain in the fixed latency paradigm is lower than in the tolerance paradigm . Accordingly, the subjects in the tolerance paradigm show overall longer latency times when they simultaneously applied cognitive strategies. These findings indicate that the two paradigms of the CPT should not be viewed as equivalent and interchangeable in practice, but rather represent a disruptive influence on the reliability and comparability of the procedure.

The menstrual cycle of female participants can also be mentioned as a possible confounding variable. It could be shown that female participants endured significantly more pain on the 20th to the 25th day of their cycle than was the case on the second to the fourth day of their cycle.

Another disadvantage of the CPT / SECPT could be that some people, such as people with skin diseases , syncope (medicine) and Raynaud's syndrome are excluded from participation.

In addition, repeated testing of the SECPT can lead to a habituation of the heart rate.

Furthermore, performing a CPT is not compatible with imaging methods such as MRI . For example, spilled water can pose a threat to the delicate and expensive MRI scanner. In addition, the water would interfere with the MRI signal due to the high proton density. The waterless variant of the CPT, the CPAW, which can be combined with the MRT, is, however, very complex both in preparation and in implementation.

Future research

The aim of the current research efforts is to demonstrate and describe new effects of stress and cortisol on cognitive and / or affective processes. Currently, non- genomically mediated, rapid effects of cortisol receive special attention .

Subjective stress assessments, HPA and SAM activation suggest that CPAW is an effective stressor. Accordingly, future research should focus on a careful comparison of the amount of HPA and SAM activation with that of traditional CPT, as well as other physiological indices (e.g. heart rate and blood pressure).

Research to date encourages consideration of cardiorespiratory fitness as a modifying covariate when using CPT as a predictor of future hypertension in women. Furthermore, previous studies show significant, gender-specific differences in stress responses. In the Trier social stress test (TSST), for example, men usually show higher reactions on the HPA axis than women. Previous research by the SECPT has mainly focused on young men, so future studies with female subjects should be verified . Future research should also investigate whether the SECPT leads to altered reactions at earlier times of the day. In addition, other physiological stress markers (e.g. heart rate variability and inflammation markers) should be included in future studies.

Since fight or flight reactions can be activated differently as part of the human behavioral repertoire under stress, research into the underlying mechanisms is essential. The research results can also be used to develop more specific diagnostic and treatment approaches for patients with social anxiety disorders .

swell

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