Exercise training in pulmonary rehabilitation should encompass both upper- and lower-extremity endurance training, strength training, and possibly respiratory muscle training. Duration, frequency, mode, and intensity of exercise should be included in the patient’s individualized exercise prescription, based on disease severity, degree of conditioning, functional evaluation, and initial exercise test data. Various guidelines for exercise training have been suggested. (3-4) Aerobic endurance training may be performed at high or low intensity. (44-45)
High-intensity training of 60 to 80% of peak work rate must be undertaken to gain maximal physiological improvements in aerobic fitness such as increased .V O2max, delayed anaerobic threshold, decreased HR for a given work rate, increased oxidative enzyme capacity, and capillarization of muscle. (39,44-45,62,67) These physiological changes result in a lower ventilatory requirement for a given exercise task as well as a more efficient pattern of breathing, with reduced dead space ventilation due to increased tidal volume and decreased respiratory rate. High-intensity training is associated with substantial gains in exercise endurance. (44)
Not all patients can tolerate sustained high-intensity exercise at the outset of training. However, those patients working at their maximal tolerated exercise level will achieve gains over time. (62) Interval training, alternating periods of high and low intensity (or rest), is an effective training option for persons who cannot sustain extended continuous periods of higher-intensity exercise. (63-65)
Traditional physiological changes associated with aerobic fitness from high-intensity training are not required to improve exercise tolerance and function in many patients with chronic lung disease. This is important because the unpleasant dyspnea and leg fatigue associated with high-intensity exercise may interfere with its incorporation into patients’ daily lives. Moreover, it has not been proven conclusively that high-intensity exercise, with achievement of physiological gains in aerobic fitness, leads to greater improvement in day-to-day functional activity. Lower-intensity aerobic exercise training leads to significant improvements in exercise endurance, even in the absence of measured gains in aerobic fitness. (9,66) Lower-intensity
training may be more readily incorporated into the patients’ daily activities, although this has not been demonstrated in clinical trials.
Transcutaneous neuromuscular electrical stimulation can improve lower-extremity muscle strength and exercise endurance even in the absence of traditional cardiovascular exercise training. (68-70) Although no large trials are available, this may be an option for patients with very severe diseases who are unable to participate in a conventional exercise training program.
Frequency and Duration of Exercise
In general, the frequency and duration of the supervised exercise component during a pulmonary rehabilitation program may vary from three to five times per week (2-3,35-37,39,41,44), 20 to 90 minutes per session (3,40-41,43), and extend over a period of 4 to 12 weeks (2,4,11-12,42-43). If program constraints will not allow for supervised exercise at least 3 days per week, one or more unsupervised sessions per week, in the home, with specific guidelines and instruction, may be an alternative option. However, it remains to be determined if this approach is as effective. (3,37) If the patient is very debilitated, the duration of the initial exercise sessions can be shorter with more frequent rest breaks; however, the ultimate goal is to achieve fewer or no rest breaks and at least 30 minutes of endurance exercise within the first few weeks of rehabilitation. An example of achieving 30 minutes of endurance exercise with a very debilitated patient is given in figure 4.8.
Modes of Exercise
Many different modes of exercise training have been used successfully with pulmonary patients, including walking (e.g., treadmill; track; supported walking via walker or wheelchair), cycling, stationary bicycling, arm ergometry, arm lifting exercises with or without weights, step exercise, rowing, water exercises, swimming, modified aerobic dance, and seated aerobics. Warm-up and cool-down periods must be included in each exercise session. Warm-up exercise allows for gradual increases in heart rate, blood pressure, ventilation, and blood flow to the exercising muscles. A cool-down reduces the risk of arrhythmias, orthostatic hypotension, syncopal episodes, and bronchospasm. (43,71)
Intensity of Exercise
Because exercise training is in many ways a tool to help patients learn to cope with the frightening and disabling sensation of breathlessness that often limits their exercise capacity, almost any type of exercise that the patient enjoys or is willing to do can be helpful. When developing the exercise prescription, the rehabilitation team must incorporate the patient’s activity goals into the training plan. For example, if the patient wants to be able to walk the dog for 30 minutes each day at a relatively slow but steady pace without rest stops, the intensity of training should be designed to accomplish that goal.
As previously noted, both high- and low-intensity exercise training may be used to improve patient exercise tolerance. Principles of basic exercise training suggest that the intensity of exercise should be related to time, workload, and physiological responses. The rehabilitation team may choose to have the patient work up to a selected level on the perceived exertion scale. Similarly, the team may instruct the patient to work up to a certain point on the dyspnea scale or to a predetermined MET level. A target heart rate is not always used during exercise training in the pulmonary population. However, it is always prudent to be aware of the patient’s heart rate at rest and with exercise, keeping in mind the age-predicted maximum heart rate; the upper limits achieved on the exercise test; and other factors that influence heart rate, such as medications and deconditioning.
In exercising patients with chronic lung disease, it is important to evaluate and monitor oxyhemoglobin saturation to determine the need for supplemental oxygen. In particular, the arterial oxygen levels of patients with chronic lung disease change with exercise in an unpredictable fashion and cannot be reliably predicted by any measurement made at rest. (72) In general, oxyhemoglobin saturation should be maintained at a level greater than 88% during exercise. (73-74) Cutaneous oximetry only estimates true arterial oxygen saturation within about ± 3 to 5% accuracy.
Supplemental oxygen therapy should be available in the rehabilitation setting for those patients with hypoxemia during exercise. Interestingly, supplemental oxygen allows for higher levels of exercise training in COPD patients who do not have significant desaturation. (3,75-76) The mechanisms underlying this benefit are not clear but might involve decreased dyspnea from decreased carotid body stimulation, allowing for a slower respiratory rate and longer expiratory time, thereby decreasing dynamic hyperinflation. Reduced pulmonary vascular resistance may also be important.
Previously unrecognized exercise-induced oxygen desaturation should be reported to the patient’s physician so that consideration can be given to initiate a home oxygen prescription. Pulse delivery of oxygen via electronic demand device may not provide adequate oxygen saturation for some patients during activity. Instead, continuous flow delivery of oxygen may be required, particularly in the patient with fibrotic lung disease. Patients should ultimately be tested during the maximal intensity level exercise they may undertake when at home, using the type of portable oxygen system they will use outside the program. The adequacy of the patient’s oxygen system, and recommendations, should be reported to the patient’s physician.
It is important to optimize bronchodilator and other pharmacological therapy before and during an exercise program. This includes assuring not only that maintenance bronchodilators are taken but also that short-acting bronchodilators are taken, when indicated, before initiating exercise. (3) Optimization of respiratory status allows for exercise training at higher intensities in patients with dyspnea limitation. Bronchodilators should also be part of any emergency cart in the exercise area.