The stimulus causing the increased f has yet to be identified. The VT/f slope was the same in patients with chronic heart failure and controls, so change in respiratory pattern cannot explain the increase in VE/VCO2 slope. CONCLUSIONS-The relation between anatomical dead space ventilation and VE/VCO2 slope is expected: as f increases, so do VE/VCO2 slope and anatomical dead space ventilation. There were weak relations within the heart failure group alone between VT/f slope and peak VO2 and VE/VCO2 slope. At peak exercise anatomical dead space ventilation was the same in both groups, but was lower expressed as a percentage of total VE in the control group (9.8 (3.3) v 13.5 (4.0) P < 0.001). Anatomical dead space ventilation was lower in the controls at submaximal work load (4.17 (1.56) v 5.58 (1.93) l/min P < 0.001). The intercept of the relation was greater for the control group (1.31 (1.28) v 0.59 (0.83) P < 0.001). The VT/f slope was the same (0.04 (0.04)) in both groups. At peak exercise there was no difference in f, but VT was higher in the controls (2.66 (0.97) v 1.90 (0.61) 1 P < 0.001). Anatomical dead space was estimated from a standard formula and anatomical dead space ventilation calculated. Peak oxygen consumption (VO2), VE/VCO2 slope, and the slope of the relation between f and VT were derived. METHODS-The ventilatory responses in 88 patients with chronic heart failure and 43 age matched controls during maximal incremental treadmill exercise were analysed. Patients have an altered respiratory pattern with an increased respiratory rate (f) at a given tidal volume (VT), which may result in increased anatomical dead space ventilation. BACKGROUND-Patients with chronic heart failure have an excessive ventilatory response to exercise, characterised by an increase in the slope of the relation between ventilation and carbon dioxide production (VE/VCO2 slope).
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