Food in chronic heart failure: improvement in central haemodynamics but deleterious effects on exercise tolerance

Food has been known to have significant central haemodynamic effects for over half a century; it causes an increase in cardiac output and a fall in systemic vascular resistance. These changes are potentially desirable in patients with chronic heart failure but how they relate to exercise tolerance is unknown. This study was designed to examine the haemodynamic effects of food with changes in exercise capability in a group of patients with chronic heart failure. Fifteen patients with chronic heart failure and 10 normal control subjects were studied. They underwent treadmill exercise testing whilst fasting and after a standardized meal. Measurements were made of symptom-limited exercise tolerance, cardiac output, limb blood flow and respiratory gases. Superior mesenteric artery blood flow was measured fasting andpostprandially only. Despite an increase in cardiac output, at rest and during exercise, which was not, however, as great as that in the control subjects, the symptom-limited exercise tolerance of the patients fell by 37s postprandially (P < 0·05). Superior mesenteric artery blood flow increased postprandially by a mean of 133 ml .min−1 (P<0·05) in the patients and 424 ml. min−1 (P<0·01) in the control subjects. Calf blood flow increased in both groups during exercise, but there was no change in limb blood flow when comparisons were made between the fasting and postprandial states. The normal postprandial increase in oxygen consumption did not occur in the patients although their minute ventilation was higher than the control subjects (P<0·01). There was a fall in resting diastolic blood pressure in the patients (P<0·05) but no change in the control subjects. This study emphasises the need to investigate the regional distribution of cardiac output in heart failure. Despite improved central haemodynamics postprandially the exercise tolerance of the patients fell, probably because the increased cardiac output was delivered to the gut and not the skeletal muscle of the limbs.