Recomendações sobre o uso dos testes de exercício na prática clínica

Resumo: A elaboração deste documento pelo grupo de trabalho da European Respiratory Society tem como objectivo apresentar as recomendações sobre o uso clínico dos testes de exercício em doentes com patologia cardiorrespiratória, dando particular ênfase à avaliação funcional, à avaliação do prognóstico e à avaliação das intervenções terapêuticas.A intolerância ao esforço físico é um dos sintomas mais frequentes, condicionando a perda de qualidade de vida do doente com patologia cardiorrespiratória crónica. Pode definir-se âintolerância ao exercícioâ numa perspectiva clínica à incapacidade que o doente apresenta para realizar tarefas que os indivíduos saudáveis considerariam toleráveis.A intolerância ao exercício, considerada em termos do pico de consumo de oxigénio atingido no esforço máximo (VâO2pico) não pode ser prevista por parâmetros avaliados em repouso, como o volume expiratório máximo no primeiro segundo (FEV1), a transferência alvéolo-capilar do monóxido de carbono (DLCO), a fracção de ejecção do ventrículo esquerdo ou o índice de massa corporal (IMC). A avaliação em exercício impõe alguns desafios técnicos: a aplicação de protocolos específicos de incremento de carga de forma precisa e reprodutível, com o recurso habitual a ergómetros, tais como a bicicleta ergométrica e o tapete rolante.A prova de exercício cardiorrespiratória (CPET) é considerada o gold standard na avaliação das causas de intolerância ao exercício em doentes com doença cardíaca e pulmonar e é baseado no princípio de que a falência do sistema ocorre tipicamente quando o sistema (seja ele músculo-energético, cardiovascular ou pulmonar) se encontra sob stress. A CPET compreende a imposição de um exercício com cargas crescentes (ou seja, incremental) limitado por sintomas, enquanto se monitorizam as variáveis cardiopulmonares (exemplo: consumo de oxigénio (VâO2), produção de dióxido de carbono (VâCO2), ventilação minuto (VâE), frequência cardíaca (fC)), a percepção de sintomas (exemplo: a dispneia e o desconforto nos membros inferiores) e, quando necessárias, as avaliações da dessaturação arterial do oxigénio relacionada com o esforço, da hiperinsuflação dinâmica e da força muscular dos membros. Os sistemas são forçados até ao seu limite tolerável, de forma controlada, o que permite detectar respostas que identificam padrões de alteração e que podem ser relacionadas com padrões de referência previamente estudados e publicados pelas sociedades respiratórias europeia e americanas1-3.Neste documento, é descrito o papel da CPET como auxiliar no diagnóstico e na avaliação funcional e prognóstica. A CPET pode: â Fornecer uma medição objectiva da capacidade para o exercício; â Identificar os mecanismos que limitam a tolerância ao exercício; â Estabelecer índices de prognóstico; â Monitorizar a progressão da doença e a resposta às intervenções terapêuticas. â Auxiliar no diagnóstico, em situações de broncoconstrição induzida pelo exercício e de dessaturação arterial do oxigénio. Na identificação das causas de intolerância ao exercício, a CPET pode detectar: â Alterações na entrega de oxigénio (desde a sua entrada nas vias aéreas, passando pelo sistema de transporte cardiocirculatório, até à entrega às mitocôndrias das fibras musculares); â Limitação ventilatória no exercício; â Alteração do controlo ventilatório; â Alteração das trocas gasosas pulmonares; â Percepção excessiva de sintomas (exemplos: dispneia, precordialgia, fadiga muscular periférica); â Disfunção metabólica muscular; â Descondicionamento; â Fraco esforço dispendido. Com um bom esforço realizado, se o valor do pico do consumo de oxigénio atingido foi normal e o motivo para parar a prova foi dispneia ou fadiga muscular, então pode considerar-se que o indivíduo estudado tem uma normal tolerância ao exercício. Este cenário irá excluir doença pulmonar (DPOC, doença intersticial pulmonar, doença vascular pulmonar) ou cardíaca (insuficiência cardíaca congestiva) significativas como causa de intolerância.A prova de exercício cardiopulmonar pode auxiliar no diagnóstico diferencial entre limitação no esforço de origem pulmonar ou cardiocirculatória. Pode fornecer um perfil de respostas que caracterizam determinadas doenças; exemplo: na DPOC são frequentes a limitação ventilatória, a hiperinsuflação dinâmica, a dessaturação arterial com o exercício, a dispneia, a disfunção dos músculos periféricos; na doença intersticial pulmonar são frequentes a dispneia, a restrição ventilatória mecânica e as alterações graves das trocas gasosas. Outros padrões de respostas podem ser encontrados na broncoconstrição induzida pelo exercício, na doença vascular pulmonar, na insuficiência cardíaca e em cardiopatias congénitas. A avaliação cardiorrespiratória no exercício fornece ainda indicadores prognósticos em várias doenças. Descrevem-se neste documento vários trabalhos que estudaram os parâmetros indicadores de prognóstico em doenças como a DPOC, a doença intersticial pulmonar, a hipertensão pulmonar primária, a fibrose quística e a insuficiência cardíaca.Este documento demonstra ainda a utilidade dos testes de exercício na definição das respostas às intervenções terapêuticas, em avaliações seriadas.O grupo de trabalho envolvido neste documento considerou importante apresentar as indicações baseadas na evidência para a realização dos testes de exercício na prática clínica. A evidência actual é clara quanto à utilidade da prova de exercício cardiopulmonar, das provas de marcha e das provas de carga constante na avaliação do grau de intolerância ao exercício, do prognóstico e dos efeitos das intervenções terapêuticas em doentes adultos com doença pulmonar crónica (DPOC, doença intersticial pulmonar, hipertensão pulmonar primária), em crianças e adultos com fibrose quística, em crianças e adultos com broncospasmo induzido pelo exercício, em adultos com insuficiência cardíaca congestiva e em crianças e adolescentes com cardiopatias congénitas.Na elaboração deste documento, os autores pretenderam fornecer as respostas às perguntas que se colocam com frequência na prática clínica: â Quando se deve pedir uma avaliação da intolerância ao esforço? â Qual o teste mais adequado? â Quais as variáveis a seleccionar na avaliação do prognóstico de determinada doença ou na avaliação do efeito de uma intervenção terapêutica particular? O documento contém ainda um suplemento que pode ser obtido on-line e que descreve as bases fisiológicas subjacentes aos parâmetros avaliados nas provas de exercício cardiopulmonar

Strategic positioning:an integrated decision process for manufacturers

Purpose – This paper describes research that has sought to create a formal and rational process that guides manufacturers through the strategic positioning decision. Design/methodology/approach – The methodology is based on a series of case studies to develop and test the decision process. Findings – A decision process that leads the practitioner through an analytical process to decide which manufacturing activities they should carryout themselves. Practical implications – Strategic positioning is concerned with choosing those production related activities that an organisations should carry out internally, and those that should be external and under the ownership and control of suppliers, partners, distributors and customers. Originality/value – This concept extends traditional decision paradigms, such as those associated with “make versus buy” and “outsourcing”, by looking at the interactions between manufacturing operations and the wider supply chain networks associated with the organisation

Noninvasive estimation of the lactate threshold in a subject with dissociated ventilatory and pulmonary gas exchange indices : a case report

This case report describes the responses to incremental work-rate exercise in a healthy subject (with normal pulmonary function), for whom the pulmonary gas exchange (V-slope) and ventilatory-related indexes (ie, ventilatory equivalents and end-tidal partial pressures for O2 and CO 2) uncharacteristically do not occur at the same metabolic rate. Based on the results of additional constant-work-rate exercise tests, we propose that in the (occasional) event of such a dissociation between the V-slope and ventilatory-related responses normally associated with the lactate threshold (\u3b8L), then the V-slope index should take priority as the \u3b8L estimator

Is breath-hold time an objective index of exertional dyspnoea in humans?

Since dyspnoeic sensation (δ) increases progressively with work rate (WR) and the duration of a volitional breath-hold (t BH) shortens, we wished to explore whether t BH might correlate sufficiently closely with δ to provide a quantitative and descriptor-free index of respiratory sensation during dynamic exercise. Nine healthy males exercised on a cycle ergometer at a series of constant WRs, above and below the lactate threshold. Ventilatory and gas exchange variables were measured breath-by-breath. At each WR, breath-holds to the limit of tolerance were taken; δ was recorded (visual-analog scale) immediately prior to and throughout each breath-hold. During breath-holds, δ increased with time as a "break-away" monoexponential characteristic, reaching the maximum (100%) at the break-point. Despite end-tidal partial pressure of carbon dioxide at the break-point being higher and end-tidal partial pressure of oxygen being lower with increasing WR, the relationship between WR and t BH declined curvilinearly (i.e. with large falls in t BH occurring in the low WR range, but far smaller reductions at higher WRs). The t BH/minute ventilation relationship had a similar form. The relationship between pre-breath-hold δ and t BH was also complex: the large reductions in t BH in the low WR range were associated with only modest increases in pre-BH δ while, at higher WRs, the progressively smaller decrements in t BH were associated with progressively larger increases in δ. We therefore conclude that breath-hold duration is unlikely to provide a useful correlate of exertional dyspnoea during dynamic exercise. Furthermore, the relative prolongation of t BH at high WRs (accounting for the more-extreme levels of end-tidal gas tensions) may reflect the attention-diverting influence of the exercise per se

Exertional oxygen uptake kinetics: a stamen of stamina?

The fundamental pulmonary O2 uptake (o2) response to moderate, constant-load exercise can be characterized as (do2/dt)(τ) + Δo2 (t) = Δo2SS where Δo2SS is the steady-state response, and τ is the time constant, with the o2 kinetics reflecting intramuscular O2 uptake (o2) kinetics, to within 10%. The role of phosphocreatine (FCr) turnover in o2 control can be explored using 31P-MR spectroscopy, simultaneously with o2. Although τo2 and τPCr vary widely among subjects (approx. 20–65 s), they are not significantly different from each other, either at the on- or off-transient. A caveat to interpreting the ‘well-fit’ exponential is that numerous units of similar Δo2SS but with a wide τ distribution can also yield a o2 response with an apparent single τ. This τ is, significantly, inversely correlated with lactate threshold and o2max (but is poorly predictive; a frail stamen, therefore), consistent with τ not characterizing a compartment with uniform kinetics. At higher intensities, the fundamental kinetics become supplemented with a slowly-developing phase, setting o2 on a trajectory towards maximum o2. This slow component is also demonstrable in Δ[PCr]: the decreased efficiency thereby reflecting a predominantly high phosphate-cost of force production rather than a high O2-cost of phosphate production. We also propose that the O2-deficit for the slow-component is more likely to reflect shifting Δo2SS rather than a single one with a single τ

ERS School Course Basic principles of clinical exercise testing - Clinical exercise testing

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Negative accumulated oxygen deficit during heavy and very heavy intensity cycle ergometry in humans

The concept of the accumulated O2 deficit (AOD) assumes that the O2 deficit increases monotonically with increasing work rate (WR), to plateau at the maximum AOD, and is based on linear extrapolation of the relationship between measured steady-state oxygen uptake (V̇O2) and WR for moderate exercise. However, for high WRs, the measured V̇O2 increases above that expected from such linear extrapolation, reflecting the superimposition of a "slow component" on the fundamental V̇O2 mono-exponential kinetics. We were therefore interested in determining the effect of the V̇O2 slow component on the computed AOD. Ten subjects [31 (12) years] performed square-wave cycle ergometry of moderate (40%, 60%, 80% and 90% θˆL ), heavy (40%Δ), very heavy (80%Δ) and severe (110% V̇O2 peak) intensities for 10–15 min, where θˆL is the estimated lactate threshold and Δ is the WR difference between θˆL and V̇O2 peak. V̇O2 was determined breath-by-breath. Projected "steady-state" V̇O2 values were determined from sub- θˆL tests. The measured V̇O2 exceeded the projected value after ~3 min for both heavy and very heavy intensity exercise. This led to the AOD actually becoming negative. Thus, for heavy exercise, while the AOD was positive [0.63 (0.41) l] at 5 min, it was negative by 10 min [−0.61 (1.05) l], and more so by 15 min [−1.70 (1.64) l]. For the very heavy WRs, the AOD was [0.42 (0.67) l] by 5 min and reached −2.68 (2.09) l at exhaustion. For severe exercise, however, the AOD at exhaustion was positive in each case: +1.69 (0.39) l. We therefore conclude that the assumptions underlying the computation of the AOD are invalid for heavy and very heavy cycle ergometry (at least). Physiological inferences, such as the "anaerobic work capacity", are therefore prone to misinterpretation

The effect of resistive breathing on leg muscle oxygenation using near-infrared spectroscopy during exercise in men

The effect of added respiratory work on leg muscle oxygenation during constant-load cycle ergometry was examined in six healthy adults. Exercise was initiated from a baseline of 20 W and increased to a power output corresponding to 90 % of the estimated lactate threshold (moderate exercise) and to a power output yielding a tolerance limit of 11.8 min (± 1.4, S.D.) (heavy exercise). Ventilation and pulmonary gas exchange were measured breath-by-breath. Profiles of leg muscle oxygenation were determined throughout the protocol using near-infrared (NIR) spectroscopy (Hamamatsu NIRO 500) with optodes aligned midway along the vastus lateralis of the dominant leg. Four conditions were tested: (i) control (Con) where the subjects breathed spontaneously throughout, (ii) controlled breathing (Con Br) where breathing frequency and tidal volume were matched to the Con profile, (iii) increased work of breathing (Resist Br) in which a resistance of 7 cmH2O l-1 s-1 was inserted into the mouthpiece assembly, and (iv) partial leg blood flow occlusion (Leg Occl), where muscle perfusion was reduced by inflating a pressure cuff (~90 mmHg) around the upper right thigh. During Resist Br and Leg Occl, subjects controlled their breathing pattern to reproduce the ventilatory profile of Con. An ~3 min period with respiratory resistance or pressure cuff was introduced ~4 min after exercise onset. NIR spectroscopy data for reduced haemoglobin-myoglobin ([Delta][Hb]) were extracted from the continuous display at specific times prior to, during and after removal of the resistance or pressure cuff. While the [Delta][Hb] increased during moderate- and heavy-intensity exercise, there was no additional increase in [Delta][Hb] with Resist Br. In contrast, [Delta][Hb] increased further with Leg Occl, reflecting increased muscle O2 extraction during the period of reduced muscle blood flow. In conclusion, increasing the work of breathing did not increase leg muscle deoxygenation during heavy exercise. Assuming that leg muscle O2 consumption did not decrease, this implies that leg blood flow was not reduced consequent to a redistribution of flow away from the working leg muscle

Noninvasive monitoring of tissue oxygenation and redox status in humans

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