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physiology

Short of breath

São Paulo researchers calculate the capacity of sedentary Brazilians for carrying out physical activity

EDUARDO CESARAnyone who stops breathless and the heart beating so much as if it were about to leap out of the mouth, after walking quickly for five blocks may being showing something more than the simple physical unfitness of someone who leads a sedentary life, like 90 million Brazilians. The difficulty in breathing and the tiredness when doing any exercise, more common from the age of 50 onwards, may indicate that not all is well with the heart or with the lungs, particularly if the person carries out some regular physical activity, and has noted lately that he no longer has the same wind as before. In any of these cases, these symptoms are transmitting a single message from the body: the muscles are not receiving a suitable amount of oxygen for doing exercises.

It has now become easier to identify the cause of the problem. Pulmonary Doctor Luiz Eduardo Nery and José Alberto Neder, of the Federal University of São Paulo (Unifesp), in collaboration with Brian Whipp, from the University of Glasgow, in Scotland, established the parameters that make it possible to calculate the capacity for the Brazilian sedentary adult to carry out physical exercise, as a result of a series of projects financed by FAPESP since 1996. Accordingly, they can manage to estimate the performance expected of the heart, the lungs and the muscles – in other words, the level of physical activity regarded as normal for a person without any health problems.

Walking quickly, something like 2 meters a second, a healthy young adult – aged 30, weighing 70 kilos and 1.70 meters in height – consumes about 1 liter of oxygen a minute. To supply the cells with this volume of oxygen, a gas that is essential for transforming sugar reserves into energy, this man breathes roughly 35 liters of air in this same period of time – equivalent to 40% of the maximum capacity of his lungs. Walking at this speed, the heart also works at a rate of up to 135 beats a minute, almost 70% of its maximum capacity for effort. If this person enjoys good health and is not sedentary, he is capable of walking 2 or 3 kilometers at this pace, without feeling any fatigue nor any difficulty in breathing.

When something is not right, under the same conditions as theprevious example, the muscular part, cardiovascular or pulmonary – which act in an integrated manner – have to work over the limit regarded as normal, which varies as a result of age, body mass, height, sex, and the level of physical activity. If the effort is kept for a prolonged period, from five to ten years, this can jeopardize health and cause, for example, damage to the arteries of the heart – or to the cardiac muscle itself – or lead to a more intense lack of air that limits the capacity for carrying out physical activities.

Until recently, it was complicated to discover in which of these systems the problem lay, without a battery of expensive and complex exams, which make it possible to visualize the cardiac muscle and its arteries or to analyze some aspects of the pulmonary function. Some exams consist if the introduction of a catheter in arteries of the arm, others assess the gases dissolved in the blood. They are needed because the simpler alternatives – the electrocardiogram, the blood test to detect anemia, and a test that measures pulmonary capacity at rest – do not manage to solve one third of the cases in which the origin of the tiredness is unknown and the lack of air does not have an explained origin, since these signs may represent both the excess work of the heart and muscles and of the lungs.

Getting to know the normal capacity to doing exercises is essential for the doctors to discover in an more precise way which part of the organism is not working as it should , by means of a relatively simple examination, the cardiopulmonary exercise test. This test takes about half an hour and provides information on over 40 different parameters related to the cardiovascular, respiratory and muscular systems, and it makes it possible to discover the cause of the disorder in 80% of the cases that escape the more simple examinations. In the other situations, if it does not point out a specific cause, the exercise test works as a compass, indicating to the doctors which of the three systems is not well. It also makes it possible to assess the evolution of the treatment and to indicate the physical exercises most suitable for each person.

Originally presented in a series of ten scientific articles – the most recent will be published this month in the European Respiratory Journal –, the Brazilian parameters for the cardiopulmonary exercise test were compiled by Neder and Nery in their book Fisiologia Clínica do Exercício – Teoria e Prática [Clinical Physiology of Exercise – Theory and Practice], launched at the beginning of the year by Editora Artes Médicas. This profile of the physical capacity of the sedentary Brazilian also gained important backing at the end of last year: it was condensed into one chapter of the most recent consensus of the Brazilian Society for Pneumology and Phthisiology (SBPT), Guidelines for Pulmonary Function Tests, made public in October in the Jornal de Pneumologia [Pneumology Journal]. With the endorsement of the SBPT, the work has come to influence the activity of Brazilian doctors in the area of the clinical physiology of exercise, which studies the responses of the sick organism – or under suspicion of being sick – to physical effort.

It was precisely the lack of a national standard for the capacity of carrying out exercises that made it difficult to apply the cardiopulmonary exercise test for revealing the cause of tiredness and lack of air without any known origin, a complaint made by half the people aged over 70 who look to physician’s surgeries for a clinical assessment, according to Neder. Before the work by the team from Unifesp, the absence of data on the Brazilian population obliged doctors to use as a basis studies carried out in the United States, Canada and Europe. The complication is that the foreign researches were carried out with people with a very different profile from the Brazilian one and with a greater capacity for doing exercise than our population – they generally included shipyard workers, volunteers who carried out physical exercise and even soldiers.

As the most direct and serious consequence, the use of other countries’ standards would frequently induce error in diagnosing a lack of capacity for carrying out exercise, which would amount to some 20%, in the case of younger (between 20 and 40 years old) and taller (over 1.75 meters persons), but it could reach 50% among individuals over 60 years old and less than 1.65 meters in height. “This data”, comments Neder, “indicates that the analysis became more distorted precisely in the population range that is a candidate for the test: sedentary adults with a risk of heart and lung problems, in particular the elderly.”

Overestimated standard
When assessing the parameter that is most representative of the capacity for a person to carry out physical exercise measured by the CRET – the maximum oxygen intake, which indicates at one and the same time the efficiency of the lungs, of the heart and of the muscles in making good use of the oxygen in the air -, the researchers discovered that the American values were 15% higher than the Brazilian ones. A physician who based himself on the foreign standard could conclude that the young man at the beginning of the text – 30 years old, weighing 70 kilos and 1.70 meters in height – could suffer from lung problem should his exercise test indicate a maximum consumption of oxygen of 2.4 liters a minute. This value, normal for a Brazilian with these characteristics, is below what is estimated by the American standard: 3 liters a minute.

Another consequence of the application of foreign values in assessing Brazilians was the possibility of error in judging the concession of allowances for lung diseases caused by the inhalation of dust, the pneumoconioses, by the National Institute of Social Security (INSS The welfare organ of Brazil). In a survey carried out in 1989 with Ericson Bagatin, from the State University of Campinas (Unicamp), and José Roberto Jardim, from Unifesp, Nery had demonstrated the lack of standardization in analyzing the test for diagnosing the commonest form of pneumoconiosis – silicosis, an incurable ailment that causes serious respiratory difficulty -, done at the time by means of detecting nodules in the lungs by chest X-rays, as required by the legislation in force. In the same work, published in the Revista Brasileira de Saúde Ocupacional [Brazilian Magazine of Occupational Health], the researchers were already suggesting that more complete examinations should be adopted, with the cardiopulmonary exercise test. What was lacking, though, was to establish criteria for classification.

It was left to Neder, in his thesis for a doctorate, to develop them, starting from the American standards accepted by the American Medical Association and by the American Thoracic Society. He applied the cardiorespiratory effort test on 75 workers from the ceramics industry who were claiming labor law compensation for showing what was suspected as silicosis. He found that 45% of the workers with a normal capacity for carrying out exercise, and hence considered apt to carry out their activities, would be classified as incapable, on the basis of the standards of the United States, as is attested in the article published in the Brazilian Journal of Medical and Biological Research of May 1998.

Following this finding, Neder proposed alterations to the American standard to adapt them to the Brazilian reality. The adjusted values served as a basis for a 1997 technical standard of the INSS, which governs the concession of allowances for pneumoconioses. But with a proviso: even so, there was the possibility of error in 15% of the assessments. “We saw that, in spite of the changes, this pattern was still a minefield”, Neder comments. It was at that time that the two researchers, unsatisfied with the results, decided to assess what the capacity of the Brazilian adult was for carrying out exercises.

In a wide-ranging study carried out from 1995 to 1998, they applied the cardiopulmonary exercise test to 120 healthy persons of between 20 and 80 years old, a sample that should represent not only the Brazilian population, the majority of which sedentary, but also that of a major part of western countries – the World Health Organization estimates that 75% of adults do not take exercise with the minimum frequency regarded as desirable in the west.

Almost as in a fitness center
The differential of the Brazilian study, recognized by such international organisms as the American Thoracic Society, is that it is the first of this kind to be carried out only with people picked by chance. This fact leads to getting standards of normality closer to those of the population usually submitted to the test. By means of the examination, they assessed some 40 different measurements for each participant, chosen from amongst 8,226 of Unifesp’s staff, and they arrived at 50 mathematical equations that make it possible to put together the profile of the Brazilian’s capacity for effort.

In the laboratory at Unifesp where the tests were done and where Nery’s team carries out between 30 and 50 examinations a month, an environment is to be found that is similar to that of the physical assessment room of a better equipped fitness center. While pedaling stationary bicycle, the person remains connected to at least six different pieces of equipment. A small mask attached to the face has a flexible tube to take away the expired air to a device that measures its flow, a pneumotachometer, and, next, distributed it to two chambers that assess the concentration of oxygen and carbon dioxide of each breath.

A dozen electrodes connected to the patient’s chest inform another piece of equipment, the electrocardiograph, the electrical activity and the rhythm of the heart, while a special clip, attached to the index finger measures the portion of the oxygen of the blood that is bound to hemoglobin, a molecule that gives blood its red color and carries this gas to the cells of the body. The data collected by this set of equipment, called a metabolic cart, is fed to two microprocessors, from which come the estimates of the cardiac, pulmonary and muscular effort made in the course of the exercise.

Introduced into Brazil some 20 years ago, the CRET is thought of having an accessible price – its application, which is now paid by some health plans, costs roughly R$ 400 -, for the quantity of information it provides, and it has been spreading over the country in recent years. It is now done in about 20 medical centers in São Paulo, Rio de Janeiro, Belo Horizonte, Brasilia, Santa Catarina and Rio Grande do Sul, the majority connected with universities.

As recognition of the importance of the Brazilian work, the consensus of the American Thoracic Society, published in January, and one of the main textbooks on the clinical physiology of exercise, Principles of Exercise Testing and Interpretation, now quote the Brazilian parameters. Moreover, three of the six main manufacturers of carros metabólicos, the equipment used to do the CRET, now include the Brazilian equations in the computer program that analyzes the data of the examination.

The Project
Reference Values for Metabolic, Ventilatory and Cardiovascular Variables in Maximum Aerobic Exercise on a Cycle Ergometer (nº 95/09844-7); Modality Regular line of research grants; Coordinator Luiz Eduardo Nery – Unifesp; Investment R$ 12,200.00 and US$ 41,331.00

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