The four-dimensional stress test: Psychological, sympathetic-adrenal-medullary, parasympathetic and hypothalamic-pituitary-adrenal responses following inhalation of 35% CO(2).

摘要

BACKGROUND: Hypercapnia is a threat to homeostasis and results in neuroendocrine, autonomic and anxiogenic responses. The inhalation of carbon dioxide (CO(2)) may, therefore, provide a good paradigm for exploring the pathways by which stress can lead to increased susceptibility to ill-health through physiological and psychological stress reactivity. The current study was designed, therefore, to assess the psychological and physiological responses to the inhalation of CO(2). METHODS: Healthy participants (N=24) inhaled a single vital capacity breath of a mixture of CO(2) (35%) and oxygen (65%). Blood pressure and heart rate were recorded for 5min before and after the test and blood and saliva samples were taken immediately before and 2, 10, 20 and 30min post-inhalation for the measurement of noradrenaline, salivary and serum cortisol and salivary alpha amylase. In addition, psychosomatic symptoms were recorded immediately before and after the test. The same protocol was repeated 4-6 weeks later at the same time of day. RESULTS: A single inhalation of CO(2) increased blood pressure, noradrenaline, salivary alpha amylase and psychosomatic symptoms, but decreased heart rate at both testing sessions. Analyses of salivary cortisol data revealed that 70% of the sample could be reliably classified as either responders (i.e. demonstrated a post-CO(2) cortisol increase) or non-responders (i.e. responded with a decrease or no change in cortisol following CO(2)) at both test sessions. Responders also perceived the test to be more aversive than non-responders. CONCLUSIONS: Inhalation of 35% CO(2) reliably stimulated the key mechanisms involved in the human stress response. The inter-individual differences in the reactivity of the hypothalamic-pituitary-adrenal axis were also related to differences in the perception of the test.