Obesity is a worldwide public health problem, and more than 50% of adults in the United States are overweight or obese.Obesity is associated with numerous medical diseases, including diabetes mellitus, hypertension, cardiovascular disease, stroke, dyslipidemia, osteoarthritis, cancer, obstructive sleep apnea, and gall bladder disease. (83) Moreover, obesity is associated with an increased risk of thromboembolic disease, aspiration, and complications of mechanical ventilation or anesthesia.(84)
Obesity is associated with several abnormalities of respiratory function. Obesity is characterized by altered respiratory system mechanics, resulting in decreased lung volumes. This is related to decreased chest wall compliance from an elastic load on the chest and abdomen as well as decreased lung compliance resulting from the closure of dependent airways. Because of these abnormalities, a greater negative pleural pressure is needed to initiate airflow. Obese patients may also have reduced respiratory muscle strength. Respiratory system resistance is increased as a result of smaller airway caliber associated with decreased lung volumes. The resistance in the larger airways is typically normal. Some people with obesity may be hypoxemic, resulting from ventilation–perfusion mismatching, especially in the poorly expanded lung bases. Most obese patients, however, remain normocapnic.
Sleep-disordered breathing, including obstructive sleep apnea (OSA) and alveolar hypoventilation, is extremely common among obese people and can contribute to the development of pulmonary hypertension and cor pulmonale. Morbidly obese patients are at increased risk for developing overt respiratory failure. Obesity hypoventilation syndrome (OHS), which is usually seen in more severe obesity, is characterized (in addition to hypoxemia) by daytime hypercapnia, an impaired central respiratory drive, and nocturnal hypoventilation. Such people often develop pulmonary hypertension, cor pulmonale, and respiratory failure.
Obesity is a major cause of dyspnea, exercise intolerance, functional limitation, disability, and impaired quality of life. (85-89)The following physiological conditions impair exercise tolerance: (84,90-92)
- Pulmonary function and gas exchange derangements
- Increased metabolic rate relative to lean body mass
- High metabolic (oxygen) cost to perform modest exercise
- Exaggerated cardiorespiratory response to exercise
- Circulatory impairment (claudication, microvascular disease, or both)
- Cardiac impairment (as a result of myocardial ischemia; pulmonary or systemic hypertension; and a hypervolemic, hyperdynamic state)
- Reduced respiratory muscle strength
- Mechanical inefficiency
- Musculoskeletal disturbances
Regular exercise is recommended by the American College of Sports Medicine and the U.S. Centers for Disease Control and Prevention (93, 94) as a crucial component of weight loss intervention programs. Exercise training, particularly in conjunction with calorie restriction, can lead to decreased body weight and fat, increased fat-free mass, improved strength and endurance, and improved aerobic fitness. However, traditional weight loss programs are generally not configured to meet the needs of morbidly obese people or obese patients with gas exchange impairments or respiratory failure. Comprehensive pulmonary rehabilitation is better suited to meet these complex needs, utilizing its components of exercise training (including recommendations for long-term adherence), collaborative self-management education, nutrition counseling, and psychological support for anxiety and depression while closely monitoring the patient’s respiratory status. Pulmonary rehabilitation can lead to lower body weight and improved functional status and health status in obese patients. (95-99)
Goals of pulmonary rehabilitation for obese people with respiratory impairment include the following:
- Increased exercise tolerance
- Weight loss
- Increased self-efficacy
- Decreased disability and return to ADLs, hobbies, and work
- Acclimatization to or optimization of use of CPAP or BiPAP
- Optimal utilization of assistive equipment (related to mobility, self-care, and hygiene), home care services, and outpatient resources
When feasible, cardiopulmonary exercise testing, pulmonary function testing, and assessment of gas exchange should be performed on obese people to identify factors contributing to functional limitation before the initiation of pulmonary rehabilitation. If cardiopulmonary exercise testing is not available, consideration should be given to pharmacological stress testing to exclude unrecognized myocardial ischemia as a factor contributing to dyspnea. Consultation with a cardiologist, a physiatrist, or both may be necessary to assist in formulating the exercise prescription for some people. Oxygen saturation, pulse, and blood pressure should be monitored closely during exercise training. Educational sessions should focus on dietary counseling and the health benefits of weight loss, the rationale for and benefits of CPAP and BiPAP, anxiety management, coping strategies, and available community resources.
Additional special considerations apply to the rehabilitation of people with morbid obesity and people with severe obesity with concomitant lower-extremity musculoskeletal disturbances. In general, such rehabilitation requires special equipment that can accommodate people of extreme weight. Morbidly obese people may not be able to use standard exercise equipment such as cycle ergometers and treadmills. Staff members must be familiar with the weight limits of the equipment in their programs. Walking, low-impact aerobics, and water-based activities are suitable forms of aerobic exercise for these patients. Recumbent bicycles, bariatric walkers, quad canes, commodes, wheelchairs, lifts, scales, and beds specially designed for obese people are commercially available. Extra staff may be needed to assist the morbidly obese patient with ambulation, transfers, stair climbing, and bed mobility.Extra-wide chairs that can accommodate extra weight should be available. Special considerations for pulmonary rehabilitation for patients with obesity-related respiratory impairment are shown in figure 7.6.