Metabolically exaggerated cardiac reactions to acute psychological stress revisited.

The reactivity hypothesis postulates that large magnitude cardiovascular reactions to psychological stress contribute to the development of pathology. A key but little tested assumption is that such reactions are metabolically exaggerated. Cardiac activity, using Doppler echocardiography, and oxygen consumption, using mass spectrometry, were measured at rest and during and after a mental stress task and during graded submaximal cycling exercise. Cardiac activity and oxygen consumption showed the expected orderly association during exercise. However, during stress, large increases in cardiac activity were observed in the context of modest rises in energy expenditure; observed cardiac activity during stress substantially exceeded that predicted on the basis of contemporary levels of oxygen consumption. Thus, psychological stress can provoke increases in cardiac activity difficult to account for in terms of the metabolic demands of the stress task.