A simple measurement — the cardiorespiratory optimal point (COP) — could predict how long someone will live or the severity of their heart failure, according to clinicians who champion the assessment. The COP is easier to obtain than cardiorespiratory measures that require people to exercise to their limit, advocates say; rather than running full speed, someone can walk or lightly jog on a treadmill, with a COP value obtained easily.
But other clinicians argue that maximal exercise tests have many prognostic benefits, and that physicians should do everything in their power to push patients to exercise as hard as possible. In particular, the VO2 max test captures the maximum amount of oxygen someone uses when exercising at their capacity and is the gold standard for measuring cardiovascular endurance.
The COP is a measure of the minimum number of liters of air during breathing required to move one liter of oxygen through the bloodstream. The lower the COP the better, because this means that someone is working less strenuously than someone else to transport the same amount of oxygen, denoting a more efficient interaction between their heart and lungs.
The COP for a fit person might be 15, about 20-25 for a healthy person, and 35 for someone with heart failure, according to Claudio Gil Araújo, MD, PhD, director of research and education at CLINIMEX, an exercise medicine clinic in Rio de Janeiro, Brazil.
"Max VO2 is very important, that's indisputable. But when do you use max VO2 in your daily life? Never," Araújo said. But almost anyone can generate a COP.
Emerging Uses for the COP
"I can put someone on the treadmill or bike, and after 3 or 4 minutes I have the COP. It's like a walking pace," Araújo said. Yet the values are obtained with roughly half the effort as VO2 max. Other clinicians argue exercising to the limits of endurance offers unique clinical insights.
"We should do everything in our power to exercise our patients to maximum. How long a patient is able to go is really important," said Anu Lala, MD, a cardiologist who specializes in heart failure treatment at Mount Sinai Hospital in New York City. A full-capacity exercise test gives useful insights into someone's heart rate, heart rate recovery, blood pressure, and ECG response to vigorous exercise, Lala added, all of which are important clues to someone's overall health.
In 2012 Araújo co-authored a study that first defined the COP, which is calculated by measuring expired gasses people produce while gently exercising, perhaps to the point where they begin to perspire, and then dividing their breathing capacity by their oxygen uptake every minute. The lowest value obtained during any exercise session is the COP.
Various studies show that higher COP values are associated with more severe heart lesions in patients with congenital heart disease; higher levels of mortality in seemingly healthy male adults; and with worse prognoses in patients with heart failure. These studies all appeared within the last 7 months.
The mortality study, which Araújo co-authored, compared COP in more than 3000 US men and women who completed an exercise test from 1973-2018 and were tracked for an average of 23 years. Although COP was introduced as an assessment in 2012, calculating the value from tests prior to that date was possible because those tests had captured the relevant breathing rate and oxygen uptake. In males aged 18-85 years, a worse COP was significantly associated with an increased risk for earlier death. This finding did not hold for females, however; Araújo noted that more research is needed to understand the discrepancy in COP's predictive power by sex.
In the heart failure study, everyone enrolled had heart failure and completed a COP test. People with the worse COPs also had the worst symptoms of heart failure, but completing an exercise rehabilitation program improved COP values when researchers measured them again. Araújo was also part of this study, based in the Netherlands.
"I think the COP could become a novel parameter in clinical care," for most people, said Thijs Eijsvogels, PhD, an exercise physiologist at Radboud University in Nijmegen and the senior author of the heart failure study. That said, Eijsvogels said elite athletes will always be more interested in measuring VO2 max.
Lala agreed that tests such as the COP have some value. Her own work has shown that measuring the efficiency of someone's breathing patterns for exhaling carbon dioxide, which can also be done without making people exercise full strength, has prognostic value for patients with advanced heart failure. Even so, she said she would like to see maximal effort tests used as much as possible.
"I worry about saying we're going to settle for a parameter that can be achieved at 50% of peak VO2 and then we don't exercise our patients," Lala said.
Araújo said he plans to continue to measure VO2 max but he believes COP has utility — even for elite athletes. One of his patients is a frequent ironman competitor who competes well despite having a solid but not amazing VO2 max level. But her COP is quite low, Araújo said, which to him suggests an especially efficient interaction between her respiratory and cardiovascular systems.
"We have a new player in the game," Araújo said.
The sources in this study report no relevant financial relationships.
Marcus A. Banks, MA, is a journalist based in New York City who covers health news with a focus on new cancer research. His work appears in Medscape, Cancer Today, The Scientist, Gastroenterology & Endoscopy News, Slate, TCTMD, and Spectrum.