Chronic Obstructive Pulmonary Disease (COPD) is a common disease “characterized by persistence of air flow limitation that is progressive and associated with an enhanced chronic inflammatory response in the airways and lungs to noxious particles or gases” (Pauwels, Buist, Calverley, Jenkins, &Hurd, 2001). COPD is the fourth killer disease globally, and it is projected that the disease will be the third cause of mortality by the year 2020 (Adams et al., 2007; US Department of Health and Human Services, 2003). It is categorized under chronic illnesses with most of the patients being aged people. COPD limits the daily activities of aged patients over time. Research indicates that exercise improves muscle endurance and strength in patients with COPD that lead to improvements in daily life activities of the patients (Nici et al., 2006). Additionally, Lacasse et al. (1996) indicates that pulmonary rehabilitation programs are designed to prescribe functional and maximal exercises that improve health related issues in patients with COPD.
The six-minute walk test (6MWT) and incremental shuttle walk test (ISWT) have been used in a number of studies to measure the functional capacity outcome in patients (Lacasse et al., 1996; Dourado et al., 2009). However, there has not been a maximal capacity outcome from the 6MW and ISW tests. In Australia, a 6MWT is used to prescribe exercise plans to patients with COPD. Moreover, 6MWT is used as a baseline for outcome measures (Lung Foundation Australia, 2012). A cross sectional study by Pitta et al (2005) based on 6MWT shows the relationship between physiological variables and physical activities in daily life in patients with COPD that makes it suitable for outcome measure. During the study, 50 patients with stable COPD were included and theirs results analyzed against 25 healthy elderly individuals. Pitta and colleagues found that 6MWT had a positive correlation with walking time and movement intensity during daily life walk in COPD patients (0.28< r < 0.76, p < 0.05, and r = 0.38, p = 0.006 respectively). Similarly, in a randomized controlled trail, Leung, Alison, McKeough and Peters (2010) reported a better improvement in functional capacity in COPD patients. Endurance shuttle walk test (ESWT) showed 68% improvement in walking time in cases of training walk conducted in groups compared to the cycle training group. These findings proved paced walking tests reflect functional exercise level for daily physical activities in a better way than maximal exercise capacity test (MECT). Consequently, the use of 6MWT, ISWT, ESWT as an assessment test only reflects the improvement in the functional exercise capacity.
COPD patients experience muscle weakness that limit exercise/activity performance in daily life. According to Vonbank et al. (2011), stronger muscles enhance high work capacity and low COPD symptom. As a result, a MECT is suitable to assess the patient’s potential workload and capacity. A prospective randomized study, by Vonbank et al (2011), compared three training modalities, and used the MECT as the baseline and outcome measures. Strength training (ST) consisted of eight different exercises with 8-15 recurrences until the occurrence of severe fatigue among the subjects. Endurance training (ET) was conducted two times per week with every session consuming 20 minutes at 60% of peak oxygen uptake (VO¬2 peak). In addition, Combination Training (CT) (Strength Training and Agility Training) was performed twice weekly for a 12-week training duration. This research showed that a substantial improvement in maximal exercise ability (P < 0.05) and muscle power (P < 0.001) was seen in both training classes, where the VO2 peak was substantially increased and was only visible in the ET and CT groups (P < 0.05). In all three categories subjected to the analysis, improvements in health quality questionnaires and dyspnea index scores indicated a substantial rise in (Vonbank et al., 2011). To measure workload performance, VO2 peak, and other important physiological parameters prior to and after the completion of the programme, the full exercise capacity test was used. These results were identical to the research performed by Ortega et al (2002), with the exception of peak oxygen uptake and maximal workout ability, which in the stamina category only showed a substantial increase. Remarkably, considering the benefits of field walking tests such as ease of performance and usage of cheap instruments, detailed physiological parameters were not obtained from field walking tests such as 6MWT, ISWT, or ESWT (Nici et al., 2006).
The exercise capacity is obtained from a MECT, which is expressed in terms of metabolic equivalents (MET) used to measure exercise tolerance (Myers et al., 2002). Some COPD patients may have cardiac issues that limit exercise performance and tolerance. During exercise of COPD patients, the heart may develop complications because of chronic lung disease (Puente-maestu et al., 2000; Santos et al., 2002). The exercise capacity raised a concern to Myers et al., (2002) that it can be used individually as a predictor of death risks. Subsequently, Myers et al., (2002) conducted a study involving 6213 men that were referred to exercise testing for medical reasons. Results indicated that 59.2% have had cardiovascular disease with 40.7% defined as normal subjects. All participants did a cardiopulmonary exercise testing (MECT) on a treadmill to measure their maximal capacity. A follow up period for the study was approximately 6.2±3.7 years with a mortality rate of 2.6%. The age was adjusted continuous variable that was used for the analysis. The study revealed that peak exercise capacity was the best predictor of increased risk of death in both normal and cardiovascular groups with hazard ratio for death (95% CI), respectively, 0.84 (0.79-0.89) and 0.91 (0.88- 0.94). In a healthy person, smoking was the second predictor of mortality risk. On the other hand, the history of congestive heart failure was the second predictor in cardiovascular disease patients. Consequently, the peak exercise capacity plays a major role in predicting the risk of death. Myers et al. (2002) indicates that low capacity exercise facilitate lower survival rate (P<0.001).
The exercise capacity can be drawn from the maximal exercise capacity test that uses an incremental treadmill and/ cycle ergometer where workload is added every minute until participant is fatigued or dyspneic in a test that should last between 10 -14 minutes (Gloeckl et al., 2013). Unlike field walking tests, MECT gives a comprehensive insight into the patient’s physiological parameters, including VO2peak, peak heart rate, and peak work rate and capacity (Gloeckl et al,. 2013; Trooster et al., 2010; Nici et al., 2006). A review paper by Ferrazza et al (2009) summarized the benefits of MECT that it can be used to differentiate between diagnoses and limit the range of suspected diseases. Additionally, it can distinguish between pulmonary and cardiac issues during the test by looking at the pattern of cardiopulmonary and gas exchange. Additionally, Ferrazza and colleagues pointed out the importance of MECT in evaluating disease progression and response to prescribed exercise by looking at pre and post exercise variables.
The initial assessment on exercise limitation and the formulation of exercise plan can apply cardiopulmonary exercise testing in a rather helpful manner. Additionally, it provides significant basis for the outcome assessment. Mechanisms of exercise intolerance that are enhanced by physiological measurements play a key role in COPD patients. Remarkably, the cardiopulmonary exercise testing help in the regulation of constant work rate indicated by the maximal symptom limitation. However, this approach is restricted to specialized centers due to its complexity and cost.