Validation of an automated bilateral feet cold pressor test.

The Cold Pressor Test (CPT) is often used in psychobiological research. However, the classical CPT version (unilateral hand immersion into ice-water) involves some disadvantages: hands may be needed for further applications, attentional drift towards the affected sensory hemi-field and/or physiological activation of the contralateral hemisphere may produce a laterality bias. Furthermore, instruction-induced motor activity may bias physiologic reactivity. To avoid these problems, a fully automated bilateral feet CPT was developed and tested for validity and feasibility. The test procedure is based on computerized control of water influx and efflux. This allows for maximal standardization and precise timing. Furthermore, water is kept in permanent flow to prohibit formation of stable temperature layers in skin proximity. Laterality bias, instructions effects and motor responses (e.g. lifting feet out of a water basin) are avoided. In a counterbalanced within-subject design, 28 healthy male students were exposed to the CPT and to a warm water control (CNT) condition twice, one week apart. Cardiovascular parameters, salivary cortisol and subjective ratings (stress, arousal and pain) were assessed before, during, and after interventions. The CPT profoundly affected physiology as well as subjective ratings. Expectation effects (immediately before testing) were small. Furthermore, post-CPT (presumably compensatory/counter-regulatory) effects on heart rate and stroke volume were found. In conclusion, the automated bilateral feet CPT is a valid and feasible stress test modification. Hemodynamic, subjective and endocrine stress responses are substantial, suggesting that this test version represents an advanced and suitable tool in human stress research.