A critical threshold of exercise capacity in the ventilatory response to exercise in heart failure.

Abstract

During exercise patients with chronic left heart failure ventilate more than normal individuals at the same workload; the ratio of minute ventilation to minute production of carbon dioxide (VE/VCO2) is increased. The relation between increased VE/VCO2, severity of heart failure, and exercise capacity has not been defined. VE/VCO2 was measured in 47 patients with chronic left heart failure (New York Heart Association grades II and III) and in 1009 healthy controls. Exercise capacity was assessed by peak oxygen consumption (VO2max) during progressive exercise. In the controls VO2max ranged from 25 to 93 ml/kg/min; VE/VCO2 was 17-36 and did not correlate with VO2max. In chronic left heart failure the VO2max ranged from 9 to 29 ml/kg/min; VE/VCO2 was 22-42 and correlated strongly with VO2max. End tidal carbon dioxide and respiratory rate at peak exercise were similar in the controls and patients with chronic left heart failure. The increase in VE/VCO2 on exercise in chronic left heart failure indicates increased physiological dead space, presumably caused by a ventilation-perfusion mismatch. In the controls and patients with chronic left heart failure the relation of VE/VCO2 to VO2max was curvilinear with a threshold of VO2max below which VE/VCO2 started to rise above the normal range. This point of inflection may be explained by the existence of a critical level of cardiac function necessary to perfuse adequately all lung zones on exercise.

The role of right and left ventricular function in the ventilatory response to exercise in chronic heart failure.

“…Central to an understanding of the pathophysiology of exercise limitation in patients with chronic heart failure is the need to explain the increase in the VE/VCo2 slope seen in such patients and the association of this increase with the reduction in peak Vo2.8 13 ventilation should occur and how it is sensed by the body. Right ventricular function may be implicated in exercise limitation in patients with chronic heart failure.…”

“…This is in distinction to the control group, who display no such relation, as previously described. 13 …”

Muscle sympathetic nerve activity and ventilation during exercise in subjects with and without chronic heart failure

“…Patients with HF also demonstrate an increased ventilatory response to exercise, ie, a steeper relationship between ventilation (VE) and carbon dioxide output (VCO2), reported as the VE/VCO2 slope (3)(4)(5). VE/VCO2 slope in HF correlates inversely with pVO2 (3,4). Both low pVO2 and increased VE/VCO2 slope identify chronic HF patients with more severe HF symptoms and higher mortality rates (6)(7)(8).…”

“…Their degree of exercise intolerance can be assessed by measuring peak oxygen uptake (pVO2) during incremental exercise testing (2). Patients with HF also demonstrate an increased ventilatory response to exercise, ie, a steeper relationship between ventilation (VE) and carbon dioxide output (VCO2), reported as the VE/VCO2 slope (3)(4)(5). VE/VCO2 slope in HF correlates inversely with pVO2 (3,4).…”

Efeito do treinamento sobre a eficiência ventilatória de indivíduos saudáveis

“…18 e pulmonares e por isso, a mensuração da EV tem sido útil na avaliação e prognóstico desses pacientes 9,11,12 . O valor normal do slope VE-VCO 2 é abaixo de 30 3,7 , sendo que valores acima disso caracterizam uma resposta anormal frequentemente associada à gravidade da IC 7,12 .…”