Dyspnea is understudied. There is a great need for research on the pathophysiology of dyspnea in cancer patients. Potential mechanisms for dyspnea include respiratory muscle weakness due to anorexia and cachexia, chemoreceptor stimulation, and efferent activity from the respiratory center by direct ascending stimulation.
Despite the various treatments that are used, few clinical trials of their effectiveness for relieving dyspnea in cancer patients have been carried out (LeGrand and Walsh, 1999). Opioids are often used for patients with dyspnea, but there have been too few well-controlled clinical trials to determine the ideal drug, route, or regimen. Corticosteroids are also commonly used, but even less is known about the effectiveness of these drugs in relieving dyspnea. Benzodiazepines or nebulized opioids have not proven effective for the treatment of dyspnea in clinical trials. Transfusion therapy has been used to relieve dyspnea in patients with anemia, but the effectiveness of this treatment is unclear. Bronchodilators are used to improve breathing in many patients with lung cancer and chronic obstructive pulmonary disease (COPD), and may also be helpful for patients without COPD who have dyspnea.
Major questions for basic research include the following:
standardization of measurement and assessment of dyspnea,
possible animal model for dyspnea,
relationship of dyspnea to the anemia of chronic illness,
role of respiratory muscle metabolism/function in dyspnea, and
establishing a link between cachexia, tumor necrosis factor, muscle fatigue or weakness, and dyspnea.
Clinical trials should focus on the following:
descriptive studies of prevalence, severity, and current treatment;
trials examining effectiveness of opioids by different routes;
trials of other agents (corticosteroids); and
trials of methylxanthine drugs, which may have a role in treating dyspnea by stimulating respiratory muscles.
Searching the CRISP database of current federal funding using the terms cancer and dyspnea produced four hits. Only one relates to basic or