Biologic Theory
In general, studies have evaluated the links between anxiety and the following: catecholamines; neuro- endocrine measures; neurotransmitters such as serotonin, and cholecystokinin; and autonomic reactivity. Neuroimaging studies have also been performed.
Studies evaluating catecholamine levels have shown that these levels in clients with anxiety appear to be similar to those of normal control clients. Neuroendocrine studies have been inconclusive.
Neurotransmitter studies have revealed that serotonin plays a role in causing anxiety. Specifically, excessive serotonin activity in critical brain areas such as the raphe nucleus, hypothalamus, thalamus, basal ganglia, and limbic system may relate to anxiety. Agents such as buspirone and benzodiazepines inhibit serotonin transmission, which leads to the relief of anxiety symptoms.
Neuroimaging research focuses on normal anatomy and neurochemistry, and behavioral, pharmacologic, and cognitive challenge theories to understand the biologic basis of anxiety. Research focuses on identifying potential predictors of treatment response. For example, positron emission tomography studies have shown increased metabolic activity and blood flow in the frontal lobes, basal ganglia, and the cingulum of clients with the diagnosis of OCD.
Laboratory studies have shown that a panic attack is characterized by a sudden increment in tidal volume rather than in respiratory frequency. In these studies, a computerized, calibrated body suit (Respitrace) was used to allow 24-hour recordings. Results have shown that clients who have spontaneous panic attacks experience a tripling of respiratory tidal volume.
Studies also have attempted to study the correlation between anxiety and heart disease. Kawachi, Sparrow, Vokonas, and Weiss (1994) examined the relationship between anxiety symptoms and the risk of coronary heart disease. This study concluded that there is a strong association between symptoms of anxiety and the presence of coronary artery disease.