The influence of skeletal muscle afferents on the pressor response (PR) to isometric exercise in patients with chronic heart failure (CHF) has been reported as greater (Piepoli et al. 1996), no different (Sterns et al. 1991) or smaller (Carrington et al. 2001) when compared with age-matched control subjects. This discrepancy might, in part, be explained by the muscle group chosen for study since muscle fibre type (Carrington et al. 1999) and training status (Fisher & White, 1999) are known to influence the PR in healthy subjects. With ethics committee approval, we examined cardiovascular responses during voluntary isometric plantarflexion (CALF) and voluntary isometric handgrip (HAND) and during subsequent post-exercise circulatory occlusion (PECO). Continuous blood pressure (Finapres, Ohmeda) and heart rate (ECG) responses were recorded in six stable CHF patients, mean (S.D.) age 65.5 (8.3) years (New York Heart Association class IIÐIII) during an 8 min protocol (Fisher & White, 1999). This comprised 2 min rest, 2 min CALF or HAND ischaemic isometric EXERCISE (EX, at 30 % maximum voluntary strength), 2 min PECO and 2 min recovery.
The change in blood pressure at the end of CALF and HAND exercise was not significantly different but HAND PECO produced a significantly greater blood pressure response than CALF PECO (Table 1).
Since the influence of central command and muscle mechanoreflex is absent during PECO, muscle chemoreflex activity must be greater in HAND than CALF. This may be explained by a higher proportion of fast twitch fibres in the forearm than in the calf muscles (though our contractile data indicate a relatively fast calf muscle in these subjects). Alternatively, it may be that the weight-bearing, locomotor role of the calf muscles constitutes a conditioning stimulus in CHF patients, which leads to desensitisation of the muscle chemoreceptors and therefore, a smaller PR (Carrington et al. 1999). We conclude that it would be wrong to make general statements about muscle chemoreflex inputs to cardiovascular control in CHF patients based upon measurements made on only one muscle group and without reference to muscle fibre type and training status.
This work was supported by BHF PG/99148.
All procedures accord with current local guidelines and the Declaration of Helsinki.