The management of chronic respiratory disease has advanced significantly over the past few years. In particular, pulmonary rehabilitation has gradually been accepted as the gold standard of care for patients with chronic obstructive pulmonary disease (COPD). According to the National Institute of Health (NIH) Workshop on Pulmonary Rehabilitation Research, the goal of pulmonary rehabilitation is directed at achieving and maintaining the individual's maximum level of functioning in the community. In order to improve the functional status of patients, it is imperative that the exercise-training component of any pulmonary rehabilitation programme is emphasised and the importance of this is supported by scientific evidence.

Singapore started its first pulmonary rehabilitation programme in 1998. This was a hospital-based and multi-disciplinary programme with emphasis on the exercise training component. Exercise training was supervised and the training intensity was individualised and graded, with a target exercise intensity of 80% of the peak work-rate as determined during baseline cardiopulmonary exercise testing (CPET). In addition to evaluating baseline exercise capacity and for exercise workload prescription, CPET was also found to be very useful in determining the factors contributing to exercise limitation in each patient as well as the requirement of supplemental oxygen during exercise. Figure 1 shows some of our patients undergoing exercise training during the pulmonary rehabilitation programme. Figure 2 shows a patient undergoing evaluation by CPET.

The optimal intensity of exercise training is undefined in the literature. Yet it is important to decide on the intensity of exercise training as patients may not tolerate training continuously at too high a workload and too low an intensity of exercise training may not achieve the desired outcomes for patients (no pain, no gain). The prescription of an optimal training intensity is much harder in patients with COPD patients than normal individuals as the majority of them have ventilatory limitation of exercise and/or significant oxygen desaturation reducing the ability to train at desirable workloads. Casaburi et al showed that the physiologic outcomes attained in patients with COPD after exercise training is significantly greater after training at higher intensity (at workloads > 80% peak workrate at baseline). It is questionable whether the majority of patients with COPD can train at such high intensity workloads. We decided to prescribe an intensity of exercise training starting at a workrate slightly higher than that attained at anaerobic threshold, if this was detected non-invasively during CPET, or at an empirical 80% of baseline peak workrate if the anaerobic threshold was not attained or detectable. An early study of 34 patients with predominantly moderate-to-severe COPD reported clinically and statistically significant improvement in their functional capacity as determined by the mean six-minute walk distance after completion of a 6-week outpatient pulmonary rehabilitation programme and in their health status (see Figures 3 and 4). Although training intensity was individualised and aimed at achieving physiological responses in these patients, it is noteworthy that not all patients were able to train at the desired workloads because of the severity of their ventilatory limitation. Future considerations include using assisted non-invasive ventilatory support during exercise training sessions for such patients.

We also found that the baseline aerobic exercise capacity of the COPD patients in our population to be decidedly lower than their counterparts in Western countries. This may be due to differing anthropometric factors e.g. height and weight that can affect exercise capacity. However, among healthy subjects in our population, we found that previously established predictive equations for maximal exercise performance during CPET based on non-Chinese populations cannot be applied to Chinese subjects in our population as the maximal exercise capacity of our healthy subjects are consistently lower than subjects from Western populations. We theorize that this is due to the lower level of habitual activity of the subjects in our population. A worrying point about this is that, if healthy subjects in our population have a lower overall exercise capacity, the baseline exercise performance of our patients with chronic lung disease like COPD is likely to be correspondingly reduced. Hence exercise reconditioning during pulmonary rehabilitation for our patients may be more challenging than it is for other populations with more physically active people.

Based on the initial success of pulmonary rehabilitation for COPD patients, subsequent efforts were made to initiate and combine home care with pulmonary rehabilitation, as both interventions are thought to promote patients' self-help techniques and coping mechanisms. This will hopefully reduce the frequency of healthcare resource utilisation, especially Emergency Department attendance and hospitalization, which are currently imposing a major burden on the major hospitals in the country. Initial results of 111 COPD patients enrolled into a combined programme of nurse-administered home care and pulmonary rehabilitation are very encouraging with greater than 50% reduction in hospitalization rates for COPD, including early readmission shortly after hospital discharge. Figures 5 and 6 show our Home Nurse visiting and assessing patients in their homes.

Besides COPD, pulmonary rehabilitation has also been offered to patients with other chronic respiratory diseases in Singapore. An analysis of 17 patients with chronic respiratory disease other than COPD (mostly post-tuberculosis bronchiectasis) who completed pulmonary rehabilitation showed approximately similar magnitude of improvement in functional capacity and health status to our patients with COPD.

References

ACCP/AACVPR Pulmonary Rehabilitation Guidelines Panel. Pulmonary Rehabilitation: Joint ACCP/AACVPR Evidence-Based Guidelines. Chest 1997; 112:1363-96.

KC Ong, YY Ong. Cardiopulmonary Exercise Testing in Patients with Chronic Obstructive Pulmonary Disease. Ann Acad Med Singapore 2000; 29:648-52.

Casaburi R, Patessio A, Joli F, Zanabouri S, Donner C, Wasserman K. Training in patients with obstructive lung disease: reductions in exercise lactic acidosis and ventilation as a result of exercise. Am Rev Respir Dis 1991; 143:9-18.

KC Ong, WP Wong, AR Jailani, S Sew, YY Ong. Effects of a Pulmonary Rehabilitation Programme on Physiologic and Psychosocial Outcomes in Patients with Chronic Respiratory Disorders. Ann Acad Med Singapore 2001; 30:15-21.

KC Ong, CM Loo, YY Ong, SP Chan, A Earnest, SM Saw. Predictive values for cardiopulmonary exercise testing in sedentary Chinese adults. Respirology 2002; 7:225-31.

Ong Kian Chung, MD

Dr. Ong Kian Chung obtained his medical degree at the National University of Singapore and his MRCP (UK) Part 2 Examination in Glasgow. He was a Clinical Research Fellow at the Pulmonary & Critical Care Division and Sleep Disorders Clinic at Stanford University Medical Center, USA. In 1999, he became officially a member of the Respiratory Physician, Roll of Specialist in Singapore. He is also a Fellow of the Royal College of Physicians in Edinburgh. He currently holds a number of very important positions in Tan Tock Seng Hospital which includes acting as the head of the Respiratory Function Laboratory, Non Invasive Ventilation Unit, Pulmonary Rehabilitation Program, Health Service Development Project and COPD Clinical Pathway Development Team. He is a clinical teacher, Faculty of Medicine at the National University of Singapore. He is also reviewer of the Journal of Respirology, Singapore Medical Journal and at present the editor of Medical Digest.