Paradoxical Potentiation of Exercise Hyperpnea in Congestive Heart Failure Contradicts Sherrington Chemoreflex Model and Supports a Respiratory Optimization Model
Congestive heart failure (CHF) patients suffer decreased exercise tolerance, yet they demonstrate an augmented ventilatory response to exercise such that PaCO2 remains normal (isocapnic) from rest to maximal exercise in the face of increased pulmonary dead space (Fig. 1). On the other hand, the effect of a large external dead space is hypercapnic instead of isocapnic. This discrepancy suggests that external dead space and pulmonary dead space may exert distinct influences on control of breathing. These paradoxical clinical phenomena are at variance with the conventional chemoreflex model (Johnson 2001), but appear to be consistent with the predictions of the optimization model (Poon 2001; Poon, Tin et al. 2007).
Supported by National Institutes of Health grants HL072849. C. Tin is an American Heart Association Predoctoral Fellow.
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