Purpose: To compare cardiopulmonary exercise test (CPET) parameters, including VO2, VCO2, respiratory exchange ratio (RER), respiratory rate (RR), heart rate (HR), oxygen saturation (SpO2), and blood pressure (BP), between COPD smokers and healthy smokers, and to assess their relationship with 6-minute walking distance (6MWD) and spirometric values. Methodology: The study employed an evaluative approach to compare CPET parameters between COPD smokers and healthy smokers. Ethical approval was obtained, and the sample included 50 participants from each group. Data collection involved spirometry, 6-minute walking tests, and CPET using a treadmill under the modified Bruce Protocol. Parameters such as VO2, VCO2, RER, heart rate, and oxygen saturation were measured pre- and post-exercise. Pulmonary function was assessed using spirometry, and the results were analyzed using statistical tests, including Chi-square, with significance determined at p < 0.05. Result: This evaluative study, conducted over 15 months, enrolled 100 participants equally divided between chronic obstructive pulmonary disease (COPD) smokers and healthy smokers, revealing a male predominance (96%). Key findings included significant differences in cardiopulmonary exercise testing (CPET) parameters: COPD smokers had a mean VO2 of 429.20 ± 158.88 ml/min compared to 1569.88 ± 356.74 ml/min in healthy smokers (P < 0.001). Correlation analysis demonstrated a strong relationship between FEV1 (%) and FEV1/FVC (%) (R = 0.906, P < 0.001), while lower oxygen saturation was associated with decreased exercise performance (R ranging from -0.719 to -0.805). Post-CPET assessments showed significantly higher respiratory rates (28.24 ± 1.64 vs. 25.52 ± 3.03, P < 0.01) and heart rates (158.96 ± 7.81 vs. 169.28 ± 7.06, P < 0.01) in COPD smokers, alongside elevated O2 desaturation (9.92 ± 2.23 vs. 1.28 ± 1.05, P < 0.01). Notably, the 6-Minute Walk Distance (6MWD) was significantly lower in COPD smokers with higher smoking indices, with a mean 6MWD of 308.75 ± 49.53 meters for those with a smoking index of 151-250 (P = 0.04), illustrating the adverse effects of smoking exposure on physical performance. Conclusion: Overall, these results highlight the utility of Cardiopulmonary Exercise Testing (CPET) in identifying the underlying causes of exercise limitation and assessing the maximal exercise capacity in COPD patients. In situations where CPET is unavailable, the 6MWD serves as a practical alternative exercise test that closely correlates with CPET parameters, making it a valuable tool for evaluating the functional status of COPD patients.
Cardiopulmonary exercise testing (CPET) is an essential diagnostic tool used to evaluate the integrated responses of the cardiovascular, pulmonary, and muscular systems during exercise. This non-invasive test provides comprehensive insights into a patient’s functional capacity and the mechanisms underlying exercise intolerance. Unlike traditional assessments that often focus on isolated parameters, CPET captures the dynamic interactions between multiple physiological systems, making it invaluable for both diagnostic and prognostic purposes in various clinical settings. By measuring parameters such as oxygen uptake (VO2), carbon dioxide production (VCO2), ventilation (VE), and heart rate response, CPET can effectively differentiate between cardiac, pulmonary, and other causes of exercise limitation (1,2). The 6-minute walk test (6MWT) is often used alongside CPET to assess functional exercise capacity, especially in populations such as those with chronic obstructive pulmonary disease (COPD), where walking endurance reflects overall health status (3).
COPD is a prevalent respiratory condition characterized by persistent airflow limitation and is a leading cause of morbidity and mortality worldwide. The Global Initiative for Chronic Obstructive Lung Disease (GOLD) estimates that over 250 million people globally are affected by COPD, and it is projected to become the third leading cause of death by 2030(4). Patients with COPD often experience exercise intolerance, significantly impacting their quality of life. By employing CPET and the 6MWT, clinicians can gain valuable insights into the degree of exercise limitation and the underlying pathophysiological mechanisms in this patient population. The identification of exercise-induced abnormalities in oxygen delivery and utilization helps guide therapeutic decisions and tailor rehabilitation programs (5,6).
One of the key advantages of CPET is its ability to identify patients at risk for adverse outcomes in cardiovascular and respiratory diseases. For instance, a reduced VO2 max during exercise is associated with increased morbidity and mortality in patients with heart failure, COPD, and other chronic conditions (7). Furthermore, CPET can be instrumental in risk stratification, allowing clinicians to tailor interventions based on individual patient needs. In COPD patients, improvements in exercise capacity measured through CPET can indicate successful responses to pulmonary rehabilitation programs (8), reinforcing the importance of these tests in managing chronic diseases.
In addition to its diagnostic utility, CPET plays a pivotal role in evaluating the efficacy of therapeutic interventions. For instance, in patients undergoing pulmonary rehabilitation, improvements in exercise capacity measured through CPET can indicate successful responses to therapy(9). Likewise, CPET can assess the effectiveness of pharmacological treatments and surgical interventions, providing objective measures that complement clinical judgment. This dynamic assessment not only enhances patient care but also fosters research into new treatment modalities and their impact on functional outcomes (10).
Moreover, CPET can be utilized to investigate the mechanisms underlying specific exercise limitations. By analyzing the ventilatory and gas exchange responses during incremental exercise, clinicians can discern whether limitations stem from cardiovascular dysfunction, respiratory impairment, or musculoskeletal issues (11). This nuanced understanding is particularly beneficial in complex patients where multiple factors may contribute to exercise intolerance. For instance, identifying the predominant limiting factor allows for targeted interventions that address the root cause of the problem, ultimately improving patient outcomes (12).
CPET is a powerful tool in contemporary clinical practice, providing critical information on exercise capacity, prognostic stratification, and the effectiveness of interventions. Its ability to evaluate multiple physiological systems during exercise makes it a gold standard for assessing exercise intolerance across diverse patient populations. As our understanding of the intricacies of CPET continues to grow, so does its potential for enhancing patient care and outcomes in those with cardiovascular and pulmonary conditions. Continued research and integration of CPET into routine clinical practice will likely yield further benefits for both patients and healthcare providers alike. Purpose of this study is To compare cardiopulmonary exercise test (CPET) parameters, including VO2, VCO2, respiratory exchange ratio (RER), respiratory rate (RR), heart rate (HR), oxygen saturation (SpO2), and blood pressure (BP), between COPD patients and healthy smokers, and to assess their relationship with 6-minute walking distance (6MWD) and spirometric values.
Study Design and Setting
This prospective observational study was conducted over a 15-month period, from August 1, 2017, to October 30, 2018, at the Department of Respiratory Medicine at JLN Medical College, Ajmer, Rajasthan. Ethical approval for the study was obtained from the institutional ethical committee prior to the commencement of data collection.
Participants
A total of 100 participants were enrolled, consisting of 50 smokers diagnosed with chronic obstructive pulmonary disease (COPD) and 50 healthy smokers.
Inclusion-Criteria
Participants were selected based on the following criteria:
Exclusion-Criteria
Participants were excluded based on the following criteria:
Evaluation Process
A comprehensive evaluation was conducted for all participants, which included a detailed medical history focusing on smoking habits and pre-existing medical conditions, along with clinical examinations concentrating on general health and specific assessments related to respiratory function. Baseline parameters were recorded prior to exercise testing, including subjective dyspnea assessment using the Modified Medical Research Council (MMRC) scale. Measurements of pulse rate, respiratory rate, oxygen saturation (SpO2), and blood pressure (BP) were also taken. The smoking index for each participant was calculated. Spirometry was used to classify participants into either COPD smokers or healthy smokers, with the severity of COPD further categorized. A six-minute walk test (6MWT) was conducted prior to the exercise test in both groups. An ECG and two-dimensional ECHO were performed on all participants to exclude any underlying cardiac pathology.
Cardiopulmonary Exercise Testing (CPET)
Cardiopulmonary exercise testing (CPET) was conducted on a treadmill using the modified Bruce protocol. After a warm-up period of 30 minutes, the treadmill's inclination increased every three minutes. The following parameters were continuously monitored during the test: oxygen consumption (VO2), carbon dioxide production (VCO2), respiratory exchange ratio (RER), respiratory rate, heart rate, and oxygen saturation (SpO2). Blood pressure was also recorded. Participants terminated the test either when they could no longer continue or when their Respiratory Exchange Ratio (RER) reached 1 or above. Post-test measurements of blood pressure, respiratory rate, heart rate, and SpO2 were recorded. The collected data were subsequently analyzed to compare the parameters between the two groups.
Pulmonary Function Measures
Pulmonary function was assessed before and after exercise using a HELIOS-402 spirometer. The following parameters were measured: Forced Vital Capacity (FVC), which is the maximum volume of air that can be exhaled after a maximum inspiration; Forced Expiratory Volume in One Second (FEV1), which is the volume of air exhaled in the first second of a forced expiration and is indicative of airway obstruction severity; the FEV1/FVC ratio, expressed as a percentage, which differentiates obstructive from restrictive pulmonary dysfunctions; and Peak Expiratory Flow Rate (PEFR), which is the maximum airflow rate during forced expiration and is useful for monitoring bronchoconstriction.
Six-Minute Walk Test (6MWT)
The six-minute walk distance (6MWD) was measured for all participants, serving as an indicator of exercise capacity and providing insight into the impact of interventions on exercise performance.
Data Collection and Analysis
Data collected from the study were entered into Microsoft Excel and organized into a master chart for analysis. The data were tabulated and evaluated according to the study's objectives using appropriate statistical software. Chi-square tests were applied to determine significance, with p-values interpreted as follows: p > 0.05 (not significant), p < 0.05 (significant), p < 0.01 (very significant), and p < 0.001 (highly significant). The results were compared with findings from previous studies, focusing on exercise limitations, particularly when the respiratory quotient was observed to be lower than 1.0.
In this study, a total of 100 participants were enrolled, equally divided between chronic obstructive pulmonary disease (COPD) smokers (n=50) and healthy smokers (n=50). This balanced design allows for a comprehensive comparison between individuals with COPD and those without, providing insights into the disease's impact on respiratory and overall health. The selection of healthy smokers as a control group is particularly relevant, as it helps to elucidate the specific effects of COPD while controlling for the influence of smoking.
Basic Demographic Table
Characteristic |
COPD Smokers |
Healthy Smokers |
Total |
P-value |
Gender |
|
|
|
|
Female |
2 (4.0%) |
2 (4.0%) |
4 (4.0%) |
- |
Male |
48 (96.0%) |
48 (96.0%) |
96 (96.0%) |
|
Age (years) |
|
|
|
|
46-55 |
10 (20.0%) |
16 (32.0%) |
26 (26.0%) |
0.34 |
56-65 |
28 (56.0%) |
23 (46.0%) |
51 (51.0%) |
|
>65 |
12 (24.0%) |
11 (22.0%) |
23 (23.0%) |
|
Mean Age (years) |
61.08±5.88 |
59.88±6.62 |
- |
|
The study population had a male preponderance, with 96% males in both groups. The mean age was comparable between COPD smokers and healthy smokers. The majority of participants from both groups were in the 56-65 years age range (56% in COPD smokers and 46% in healthy smokers). The mean ages were 61.08 ± 5.88 for COPD smokers and 59.88 ± 6.62 for healthy smokers, showing both groups are comparable in terms of age distribution.
Comparison of Cardiopulmonary Exercise Testing (CPET) Parameters
Table 2: Comparison of CPET Parameters Between COPD and Healthy Smokers
Parameter |
COPD Smokers (Mean ± SD) |
Healthy Smokers (Mean ± SD) |
P-value |
VO2 (ml/min) |
429.20 ± 158.88 |
1569.88 ± 356.74 |
<0.001 |
VO2 (ml/kg/min) |
5.89 ± 3.04 |
22.50 ± 4.86 |
<0.001 |
VCO2 (ml/min) |
439.92 ± 157.64 |
1610.28 ± 346.79 |
<0.001 |
RER (VCO2/VO2) |
1.02 ± 0.02 |
1.01 ± 0.03 |
0.01 |
In examining cardiopulmonary exercise testing (CPET) parameters, significant differences emerged between COPD smokers and healthy smokers. The mean VO2 (ml/minute) for COPD smokers was 429.20 ± 158.88, whereas healthy smokers exhibited a substantially higher mean of 1569.88 ± 356.74 (P < 0.001). This disparity was echoed in the VO2 (ml/kg/min) values, where COPD smokers recorded a mean of 5.89 ± 3.04 compared to 22.50 ± 4.86 in healthy smokers (P < 0.001). The VCO2 (ml/min) values similarly demonstrated this trend, with COPD smokers at 439.92 ± 157.64 and healthy smokers at 1610.28 ± 346.79 (P < 0.001). While the respiratory exchange ratio (RER) showed no significant difference between groups (P = 0.01), the data indicates that COPD smokers display severely compromised respiratory function compared to their healthy counterparts.Correlation Analysis of Pulmonary and Cardiorespiratory Parameters
Table 3: Spearman’s Correlation Coefficients
Variable |
FEV1/FVC (%) |
FEV1 (%) |
6MWD (m) |
Time on CPET (minutes) |
VCO2 (ml/min) |
RER (VCO2/VO2) |
FEV1 (%) |
0.906 |
|
|
|
|
|
6MWD (m) |
0.734 |
0.755 |
|
|
|
|
Time on CPET (min) |
0.741 |
0.799 |
0.814 |
|
|
|
VCO2 (ml/min) |
0.757 |
0.805 |
0.800 |
0.895 |
|
|
RER (VCO2/VO2) |
-0.164 |
-0.271 |
-0.308 |
-0.189 |
-0.179 |
|
% O2 Desaturation |
-0.760 |
-0.775 |
-0.719 |
-0.805 |
-0.786 |
0.285 |
The Spearman’s correlation coefficients revealed strong positive correlations between various pulmonary and cardiorespiratory parameters, particularly with FEV1 (%), 6-Minute Walk Distance (6MWD), and time on CPET. For instance, the correlation coefficient (R) for FEV1 (%) with FEV1/FVC (%) was 0.906 (P < 0.001), indicating a robust relationship. Additionally, the 6MWD demonstrated a significant correlation with other measures, such as VCO2 (R = 0.800, P < 0.001) and time on CPET (R = 0.814, P < 0.001). Conversely, percentage O2 desaturation was negatively correlated with the majority of parameters (R ranging from -0.719 to -0.805), illustrating that lower oxygen saturation correlates with decreased performance in exercise testing. Overall, the data signifies that impaired pulmonary function and increased oxygen desaturation are interrelated, which is particularly relevant in the context of COPD.
Comparison of Cardiorespiratory Parameters Between COPD and Healthy Smokers
Table 4: Comparison of Cardio-Respiratory Parameters Between COPD and Healthy Smokers
Parameter |
COPD Smokers (Mean ± SD) |
Healthy Smokers (Mean ± SD) |
P-value |
Respiratory Rate (Pre-test) |
16.64 ± 3.01 |
15.24 ± 0.87 |
0.11 |
Respiratory Rate (Post-test) |
28.24 ± 1.64 |
25.52 ± 3.03 |
<0.01 |
% O2 Desaturation |
9.92 ± 2.23 |
1.28 ± 1.05 |
<0.01 |
Heart Rate (Pre-test) |
81.84 ± 10.30 |
82.64 ± 5.01 |
0.39 |
Heart Rate (Post-test) |
158.96 ± 7.81 |
169.28 ± 7.06 |
<0.01 |
When comparing cardiorespiratory parameters between the two groups, significant differences were noted post-CPET. While pre-test respiratory rates and heart rates showed no statistically significant differences (P = 0.11 and P = 0.39, respectively), post-test measurements revealed a marked increase in both rates for COPD smokers. The post-test respiratory rate averaged 28.24 ± 1.64 for COPD smokers compared to 25.52 ± 3.03 for healthy smokers (P < 0.01). Likewise, the heart rate post-test for COPD smokers was 158.96 ± 7.81, significantly higher than the healthy smokers’ 169.28 ± 7.06 (P < 0.01). Moreover, the percentage of O2 desaturation was significantly greater in COPD smokers at 9.92 ± 2.23 compared to just 1.28 ± 1.05 in healthy smokers (P < 0.01). These findings emphasize the elevated cardiorespiratory stress experienced by COPD smokers during physical exertion, further underscoring the disease's detrimental impact on exercise tolerance.
Association of 6MWD with Smoking Index in COPD Smokers
Table 5: Association of 6MWD with Smoking Index in COPD Smokers
Smoking Index |
6MWD (Mean ± SD) |
Time on CPET (min, Mean ± SD) |
P-value |
151-250 |
308.75 ± 49.53 |
4.17 ± 0.75 |
0.04 |
251-350 |
278.89 ± 32.33 |
4.09 ± 0.93 |
0.01 |
>350 |
270.71 ± 58.06 |
3.06 ± 1.05 |
- |
The association between the 6-Minute Walk Distance (6MWD) and the smoking index in COPD smokers demonstrated statistically significant results. The mean 6MWD for individuals with a smoking index of 151-250 was 308.75 ± 49.53 meters, while those with a smoking index of 251-350 and >350 exhibited lower distances at 278.89 ± 32.33 meters and 270.71 ± 58.06 meters, respectively (P = 0.04). Similarly, time spent on CPET was significantly affected by the smoking index, with participants in the 151-250 category averaging 4.17 ± 0.75 minutes compared to 4.09 ± 0.93 and 3.06 ± 1.05 minutes for the other two categories (P = 0.01). These results suggest that higher smoking indices correlate with decreased functional capacity, reinforcing the notion that the extent of smoking exposure directly influences physical performance outcomes in COPD smokers.
The present study highlights the demographic characteristics of the participants, revealing a mean age of 61.08 ± 5.88 years among the 100 individuals, with a range of 49 to 72 years. This aligns with Sobonya's (1994) observation that severe COPD is infrequently diagnosed in individuals younger than 40, with the majority seeking medical attention between the ages of 55 and 65 (11). Comparative data from various international studies show similar age trends, indicating a global pattern in the age of COPD diagnosis. For instance, Wong (2005) (12) reported a mean age of 74 years in a Hong Kong cohort, whereas Singh et al. (2003) documented a mean age of 59 years in an Indian population (13). Such demographic patterns underline the importance of early detection and management strategies targeted at the older population, particularly those who are smokers. Gender distribution in the study revealed a significant bias towards male participants, with only four females reporting smoking behavior. The reluctance among women to disclose smoking habits may be attributed to sociocultural stigmas prevalent in Rajasthan, where female smoking is often frowned upon. This observation underscores a critical gap in understanding the prevalence of COPD among women, particularly given the hormonal influences discussed in the literature. Previous studies indicate that women may experience a higher susceptibility to COPD following menopause, potentially due to hormonal changes affecting airway function. The predominance of male subjects in this study necessitates caution in generalizing findings to female populations and highlights the need for targeted outreach and education to encourage female participation in COPD research.
The results of the CPET demonstrated significant differences between COPD smokers and healthy smokers, particularly in terms of VO2 max and VCO2 levels. The mean VO2 max for COPD smokers was recorded at 429.20 ± 158.88 ml/min, significantly lower than the healthy smokers’ mean of 22.50 ± 4.86 ml/kg/min. This stark contrast emphasizes the impact of COPD on aerobic capacity and overall cardiovascular fitness. In comparison to previous findings, such as those by Ganju et al.,(14) who reported a mean VO2 max of 17.1 ± 5.23 ml/kg/min in COPD patients, our findings align with existing literature confirming the severe limitations in exercise capacity experienced by individuals with COPD.
The respiratory equivalent ratio (RER) findings indicated no significant difference between the two groups, with RER values of 1.01 ± 0.03 in healthy smokers and 1.02 ± 0.02 in COPD smokers. This stability in RER suggests that while overall exercise capacity is impaired in COPD smokers, the efficiency of gas exchange remains relatively constant. These results support the notion that COPD primarily affects the volume and intensity of exercise rather than the mechanics of respiration during exercise. This is crucial for clinicians to consider when developing rehabilitation strategies for COPD patients, as it may indicate that respiratory training could be beneficial even in the presence of significant disease.
Significant increases in heart rate and respiratory rate were observed post-exercise in both groups. For COPD smokers, the heart rate increased from 81.84 ± 10.30 bpm to 158.96 ± 7.81 bpm, while in healthy smokers, it increased from 82.64 ± 5.01 bpm to 169.28 ± 7.06 bpm. This doubling of heart rate illustrates the cardiovascular strain experienced during CPET, common to both groups but accentuated in COPD smokers due to underlying respiratory limitations. The increase in respiratory rate from 16.64 ± 3.01 to 28.24 ± 1.64 in COPD smokers further highlights the body's compensatory mechanisms in response to oxygen demand. These findings align with previous research, indicating that COPD patients often demonstrate exaggerated cardiovascular responses to exercise, necessitating tailored cardiac rehabilitation programs.(15)
Correlational analysis demonstrated significant positive relationships between various CPET parameters, with strong correlations found between FEV1 and FEV1/FVC (R=0.906) and between 6MWD and FEV1 (R=0.755). Such correlations indicate that pulmonary function, as measured by spirometry, is intimately connected to exercise capacity, further validating the use of CPET as an assessment tool in managing COPD. The findings are consistent with previous studies by Agrawal et al.(16) and Chen et al., (17)confirming the positive relationship between 6MWD and spirometry parameters. Additionally, negative correlations between percentage desaturation and lung function measures reinforce the need for comprehensive evaluations of lung function in predicting exercise capacity and desaturation risk during physical activities.
The relationship between smoking index and pulmonary function test (PFT) parameters revealed no significant correlation in either group, suggesting that the established PFT values in COPD smokers were already compromised due to the disease. This aligns with findings from Nawafleh et al. (18)and Bano et al.,(19) which illustrate that smoking impacts PFT values; however, in established COPD cases, smoking does not seem to further exacerbate the decline in lung function parameters. This raises important considerations for managing COPD patients, as interventions may need to focus on disease progression rather than solely on smoking cessation.
The results indicated a decrease in both 6MWD and CPET time as the smoking index increased, suggesting that higher smoking exposure correlates with reduced functional exercise capacity. This aligns with previous studies, indicating a direct impact of smoking on exercise performance. The findings highlight the importance of functional assessments, such as the 6MWT, in the management of COPD and underscore the need for personalized rehabilitation strategies that consider the individual smoking history and its impact on functional capacity.
The primary aim of this study was to investigate the differences in pulmonary function, exercise capacity, and associated demographic factors between individuals with chronic obstructive pulmonary disease (COPD) who smoke and healthy smokers. The findings reveal a significant disparity in exercise performance, with COPD smokers demonstrating substantially lower values in key cardiopulmonary parameters such as VO2 and VCO2 compared to their healthy counterparts, underscoring the severe functional limitations imposed by COPD. Additionally, the analysis highlights a predominantly male demographic among study subjects, suggesting a potential area for targeted public health interventions focused on smoking cessation. The correlation between 6-Minute Walk Distance (6MWD) and smoking index further emphasizes the negative impact of cumulative smoking exposure on exercise capacity, affirming the necessity for proactive strategies to mitigate smoking-related health consequences. Overall, this study not only delineates the functional impairments associated with COPD but also emphasizes the critical need for early detection, tailored rehabilitation, and smoking cessation programs to improve patient outcomes and enhance the quality of life for individuals suffering from this chronic condition.
Conflicts of interest: Nil