Cardiopulmonary Exercise Test: Background, Applicability and Interpretation

Abstract

Cardiopulmonary exercise test (CPET) has been gaining importance as a method of functional assessment in Brazil and worldwide. In its most frequent applications, CPET consists in applying a gradually increasing intensity exercise until exhaustion or until the appearance of limiting symptoms and/or signs. The following parameters are measured: ventilation; oxygen consumption (VO2); carbon dioxide production (VCO2); and the other variables of conventional exercise testing. In addition, in specific situations, pulse oximetry and flow-volume loops during and after exertion are measured. The CPET provides joint data analysis that allows complete assessment of the cardiovascular, respiratory, muscular and metabolic systems during exertion, being considered gold standard for cardiorespiratory functional assessment.1-6 The CPET allows defining mechanisms related to low functional capacity that can cause symptoms, such as dyspnea, and correlate them with changes in the cardiovascular, pulmonary and skeletal muscle systems. Furthermore, it can be used to provide the prognostic assessment of patients with heart or lung diseases, and in the preoperative period, in addition to aiding in a more careful exercise prescription to healthy subjects, athletes and patients with heart or lung diseases. Similarly to CPET clinical use, its research also increases, with the publication of several scientific contributions from Brazilian researchers in high-impact journals. Therefore, this study aimed at providing a comprehensive review on the applicability of CPET to different clinical situations, in addition to serving as a practical guide for the interpretation of that test. Resumo O teste cardiopulmonar de exercício (TCPE) vem ganhando importância crescente como método de avaliação funcional tanto no Brasil quanto no Mundo. Nas suas aplicações mais frequentes, o teste consiste em submeter o indivíduo a um exercício de intensidade gradativamente crescente até a exaustão ou o surgimento de sintomas e/ou sinais limitantes. Neste exame se mensura a ventilação (VE), o consumo de oxigênio (VO2), a produção de gás carbônico (VCO2) e as demais variáveis de um teste de exercício convencional. Adicionalmente, podem ser verificadas, em situações específicas, a oximetria de pulso e as alças fluxo-volume antes, durante e após o esforço. A análise integrada dos dados permite a completa avaliação dos sistemas cardiovascular, respiratório, muscular e metabólico no esforço, sendo considerado padrão-ouro na avaliação funcional cardiorrespiratória.1-6 O TCPE permite definir mecanismos relacionados à baixa capacidade funcional, os quais podem ser causadores de sintomas como a dispneia, correlacionando-os com alterações dos sistemas cardiovascular, pulmonar e musculoesquelético. Também pode ser de grande aplicabilidade na avaliação prognóstica em cardiopatas, pneumopatas e em pré-operatório, além de auxiliar na prescrição mais criteriosa do exercício em sujeitos normais, em atletas, em cardiopatas e em pneumopatas. Assim como ocorre com o uso clínico, a pesquisa nesse campo também cresce e várias contribuições científicas de pesquisadores nacionais são publicadas em periódicos de alto fator de impacto. Sendo assim, o objetivo deste documento é fornecer uma revisão ampla da aplicabilidade do TCPE nas diferentes situações clínicas, bem como servir como guia prático na interpretação desse teste propedêutico.

Figure 1

Risk stratification based on CPET results from patients with CHF (Modified from Ribeiro JP, Stein R, Chiappa GR. J Cardiopulm Rehabil. 2006 Mar- Apr;26(2):63-71). CPET: cardiopulmonary exercise test; VO₂ : oxygen consumption; R: respiratory exchange ratio; VE/VCO₂ slope: ratio between pulmonary ventilation and carbon dioxide production; PETCO₂ : extrapolated end-tidal carbon dioxide tension; T_1/2 : time necessary for a post-exertion 50% drop in VO₂ measured; OUES: oxygen uptake efficiency slope; HRR: heart rate recovery.

Figure 2

Cardiopulmonary exercise test in the pre-rehabilitation assessment of a 57-year-old hypertensive, diabetic, overweight male patient with three-vessel coronary disease, who refused to undergo myocardial revascularization surgery eight years earlier. A) evident drop in oxygen pulse. B) early plateau of oxygen consumption. Both changes (A and B) were due to ischemic depression of the ST segment (evident in A), followed by progressive chest pain.

Figure 3

The ΔVO₂ /ΔWR relationship around 10mL.min.Watts suddenly reduces, despite the exercise intensity increase. This loss of linear relationship could indicate the presence of myocardial ischemia by use of CPET performed on a cycle ergometer (modified from reference 52).

Figure 4

Flow-volume curves: A) patient without pulmonary disease; B) patient with chronic obstructive pulmonary disease. Note loop displacement to the left with overlapping. IC: inspiratory capacity; TPC: total pulmonary capacity, TV: tidal volume.