PATIENT CHARACTERISTICS: Age: 16 and over Performance status: Not specified Life expectancy: Greater than 10 days Hematopoietic: Hemoglobin at least 8.5 g/dL Hepatic: AST/ALT no greater than 2 times upper limit of normal (ULN) No liver disease Renal: Creatinine no greater than 2 times ULN No kidney disease Cardiovascular: No acute congestive heart failure Greater than 3 months since prior myocardial infarction No coronary artery disease where cardiac stimulation might prove harmful (i.e., no unstable angina) No uncontrolled hypertension Pulmonary: See Disease Characteristics Other: Folstein Mini-Mental Status Exam score of at least 24 Able (i.e., sufficiently fluent) and willing to complete quality of life questionnaire and other assessments in either English or French No history of clinically significant allergy or intolerance to theophylline, aminophylline, or other methylxanthines No active peptic ulcer disease No uncontrolled hyperthyroidism