Cardiopulmonary exercise testing can be used for early detection of respiratory disorders in the obese

Cardiopulmonary exercise testing (CPET), also known as ergospirometry, can be used for early detection of respiratory disorders in overweight and obese individuals. This is the main finding of a study by Brazilian researchers who set out to assess the influence of obesity on the physiological responses obtained in CPET.

CPET combines a conventional ergometric test with analysis of expelled air to obtain measurements of pulmonary oxygen uptake (VO₂), carbon dioxide production (VCO₂), respiratory rate, and pulmonary ventilation. It determines the level of aerobic conditioning and is indicated for initial assessment in physical exercise programs, both in clinical practice and for amateur or high-performance athletes.

The study showed that the main ventilatory responses were unaltered in obese volunteers. For example, the ratio of minute ventilation (VE, the volume of air exhaled in one minute) to VCO₂, averaged 25.4 for the obese group and 25.6 for the non-obese control group. The ratio corresponds to the quantity of ventilation used to eliminate a given amount of carbon dioxide during the test and is considered an indicator of respiratory efficiency.

The finding that obesity did not influence this variable means abnormal values can be useful for early detection of respiratory disorders and can point to potential problems before symptoms appear, regardless of obesity.

However, as expected, obesity impaired performance in almost all of the many maximal and submaximal variables analyzed in the study. The most influenced were the cardiovascular, metabolic, and gas exchange variables. 

An article reporting the study is published in PLOS ONE. Most of the authors are researchers in the Department of Human Movement Sciences at the Federal University of São Paulo (UNIFESP) in Santos. The study was supported by FAPESP. Three physicians affiliated with the Angiocorpore Institute of Cardiovascular Medicine in Santos also participated.

“CPET is insufficiently used for obese patients. It can bring to light many potential issues and has substantial diagnostic and pre-diagnostic potential, which isn’t adequately explored. Our study shows that if ventilatory efficiency is altered, the reason is highly likely to be an incipient respiratory disorder, rather than a consequence of obesity,” said Victor Zuniga Dourado, head of UNIFESP’s Epidemiology and Human Movement Laboratory (EPIMOV) and principal investigator for the study. 

The test does not diagnose a specific disorder or disease, Dourado explained, but can be used for early detection of exercise intolerance and to help identify its causes, so that the patient can be referred to a specialist for a more precise diagnosis.

“There are respiratory alterations that can take a long time to be detected at rest. Exercise is an excellent challenge to identify them early on. Our findings are highly applicable in practice to identify exercise limitation, regardless of overweight or obesity,” he said. 

The study was part of the master’s research of Bárbara de Barros Gonze, first author of the article. According to Gonze, one of its innovations was the assessment of maximal and submaximal physiological responses during CPET. These vary depending on each person’s physical fitness. “Submaximal data don’t require maximum effort and can therefore be useful to diagnose incipient exercise tolerance limitations, especially in people who aren’t very fit or have a chronic disease. In the study, we showed that measuring and interpreting submaximal responses to the test can be encouraged in routine clinical practice,” she said.

“To our knowledge, this is the first study to investigate the influence of obesity, according to severity and adjusted for the main cardiovascular risk factors, on the dynamic physiological responses obtained in the CPET in a robust sample,” the authors write.

Methods

The group conducted a cross-sectional study involving retrospective analysis of 1,594 adult CPETs (755 obese) carried out between 2013 and 2018. The test results were extracted from the database of Angiocorpore Institute’s endocrinology outpatient clinic and from UNIFESP’s Epidemiological Study of Human Movement (EPIMOV), whose primary purpose is to investigate the association between low levels of physical activity and fitness and the development of chronic conditions, especially cardiovascular, respiratory and musculoskeletal diseases.

Obesity is a chronic disease characterized by an excessive amount of body fat. The criterion most often used to diagnose it in adults is body mass index (BMI), which equals weight in kilograms divided by the square of height in meters. A BMI of 25-29.9 kg/m² is considered overweight by the World Health Organization (WHO), while 30 kg/m² or more is considered obese.

Obesity is one of the world’s leading health problems and more than doubled in the period 2012-19 in Brazil, where growing numbers of children and young adults are obese. The proportion of the adult population considered obese rose from 12.2% to 26.8% in the period. The proportion considered overweight or obese rose from 43.3% to 61.7%, according to the 2019 National Health Survey (Pesquisa Nacional de Saúde). 

A high BMI is a major risk factor for cardiovascular disease, musculoskeletal disorders and cancer, as well as severe COVID-19.

The criteria for inclusion in the study were absence of previously diagnosed heart, lung or locomotor diseases, and being capable of performing physical effort. The researchers performed a series of multivariate covariance analyses to evaluate the effect of obesity on CPET variables, comparing data for non-obese subjects (normal weight and overweight) with data for obese subjects.

The test was performed on a motorized treadmill in accordance with an individualized ramp protocol. The same variables were considered for automatic increases in speed and grade, starting at 3kmph and 0% respectively. The treadmill software estimated maximum VO₂ based on age, sex, body mass, height, and physical activity level. 

Adult resting VO₂ averages 3.5 mL/kg/min, often called metabolic equivalent of task (MET).  Maximum VO₂ averages 35-40 mL/kg/min for untrained healthy men and 27-30 mL/kg/min for women, while elite athletes can reach 70 ml/kg/min. 

In the study, maximum VO₂ averaged 39.6 mL/kg/min for normal-weight volunteers, and 33.8 and 19.2 mL/kg/min for overweight and obese participants respectively.

Before the test, subjects remained at rest for three minutes while baseline measurements were made. The test then proceeded to exhaustion within 8-12 minutes of exercise (or interruption due to symptoms), followed by three minutes of recovery.

Cardiovascular, metabolic, and gas exchange variables were the most influenced by obesity. Other maximal and submaximal responses were altered only in morbidly obese subjects.  

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