What would be exercise limitations for an individual with chronic obstructive lung disease?
What could be central as well as peripheral physiological changes and/or limitations to sustained aerobic activity?
Interesting questions! Please see response below, which is supplemented with two supporting articles.
Question One: What would be exercise limitations for an individual with chronic obstructive lung disease?
Background Treatment Recommendations: A structured, outpatient pulmonary rehabilitation program improves functional capacity in certain patients with COPD. Services may include general exercise training, administration of oxygen and nutritional supplements, intermittent mechanical ventilatory support, continuous positive airway pressure, relaxation techniques, breathing exercises and techniques (such as pursed lip breathing), and methods for mobilizing and removing secretions. For both chronic bronchitis and emphysema, alternative practitioners recommend diet and nutritional supplements, a variety of herbal medicines, hydrotherapy, acupressure and acupuncture, aromatherapy, homeopathy, and yoga.
1. Maximum exercise tolerance is thought to be reduced in patients with severe chronic obstructive pulmonary disease (COPD) because ventilatory demand exceeds capacity (1). Many such patients, however, also develop lactic academia at a low metabolic rate, which contributes to the ventilatory requirement (2). Because respiratory muscles do not seem to be a significant source of lactic acid in such patients (3), it is possible that abnormal O2 transport to, or utilization by, limb skeletal muscle is responsible.
2. Although the submaximal exercise cardiac output is appropriate for the metabolic rate in COPD (4, 5), peak exercise cardiac output is not (4), a finding similar to that in congestive heart failure (8). Whether this is a primary abnormality caused by pulmonary vascular disease and right heart dysfunction (9), or simply a reflection of the patient's terminating exercise because of exhaustion of ventilatory reserve, has not yet been resolved.
3. A growing body of literature also suggests limb skeletal muscle oxidative metabolism is abnormal in some patients with COPD (10). If such a peripheral abnormality is relevant to the depressed oxygen max in COPD, it should be associated with reduced systemic oxygen extraction.
4. Others recently found abnormal extraction in a majority of patients with severe COPD that was correlated with a low lactate threshold (15). As with cardiac output, however, the normal widening of arterial-mixed venous oxygen content during incremental exercise (8, 16) might be truncated by exhaustion of breathing reserve.
5. In conditions complicated by increased turbulent airflow at rest (17), including COPD (18), work of breathing is reduced by breathing a gas less dense than room air such as a helium: oxygen gas mixture (He-O2). During maximum exercise, including aeroic exercise, normal older subjects increase ventilation while breathing He-O2 (19) by similar mechanisms.
6. Oelberg et al (1998) (see attachment) used He-O2 was used as a tool to lift the ventilatory mechanical "ceiling" in severe COPD during incremental exercise. Despite raising the ventilatory ceiling with He-O2, abnormal peak exercise O2, cardiac output, and systemic O2 extraction failed to improve proportionally. These data suggest that abnormalities of O2 transport and utilization may contribute to the depressed ventilation of O2max in severe COPD.
7. Although this study was not aimed at evaluating the effects of He-O2 on pulmonary gas exchange during exercise, the authors found higher peak exercise SaO2 with He-O2, despite no change in PaO2 and with an elevated VD/VT. The increase in SaO2 (and CaO2) with He-O2 must have occurred because of a leftward shift in ...
This solution explains the exercise limitations associated with chronic obstructive lung disease, including the central as well as peripheral physiological changes and/or limitations to sustained aerobic activity. Supplemented with two highly informative articles.