The rate of fall of the hemoglobin level is also important functionally. Those with chronic anemia may demonstrate little decline in ca- pacity even at very low hemoglobin levels, whereas those with acute red cell deficits may decompensate despite more reasonable hemoglobin levels. Anemic states are less well tolerated in the elderly and those with chronic obstructive pulmonary disease or cardio- vascular diseases. Given the variety of clinical factors possibly affecting functional capacity, a fixed criterion of serum hemoglobin level for participation in reha- bilitation therapies is unwarranted. Rather, the best guidance for adjustment of therapeutic activity is ob- tained by checking patient symptomatology, including dyspnea, lightheadedness, and chest pain; pulse and blood pressure; and, occasionally, pulse oximetry. These checks should be made prior to and during activity.