Factors determining symptomsinheart failure: comparison offast andslowexercise tests

SUMMARY Factors determining thesymptomsofbreathlessness andfatigue inpatients with congestive heart failure were investigated bycomparing theresponse toslowandfast exercise. Symptomlimited oxygenconsumption(maximal); minute ventilation, mean pulmonary capillary wedgepressure;andarterial blood gases,pH,andlactate concentrations were measured during treadmill exercise using aslowprotocol in25men (age34-67years) withcongestive heart failure (NewYorkHeart Association class II-III). Tenofthese patients were also exercised according to arapid protocol. Exercise was terminated byfatigue in23/25 patients after theslow testandby breathlessness inall patients after therapid test.Exercise capacity(maximal oxygen consumption andexercise duration) was notrelated toresting orexercise pulmonary capillary wedgepressure or thechange in pulmonary capillary wedgepressureduring exercise, nor was there any difference inpulmonary capillary wedgepressureattheendofexercise within individuals betweenthefast andslowtests.Minuteventilation was greater(51vs 431/min), peakexercise lactate concentration higher (3-7 vs2-2mmol/1), andthechange inpHfromtheresting statewas greater(0-06 vs002)during therapid testthanduring theslowtest.Thesensation ofbreathlessness incongestive heart failure isnotsimply related toraised pulmonary capillary wedge pressure,butmay inpartbeduetostimulation ofperipheral chemoreceptors inresponse to metabolic acidosis. Thecause ofexercise intolerance incongestive heart failure ispoorly understood. Patients treated with diuretics arelimited morebyfatigue thanbybreathlessness. Several studies havesuggested that fatigue isrelated toaninadequate oxygen supply toskeletal muscle,'-3 because during exercise patients with heart failure haveareduced cardiac output, anearly increase inlactate concentration, andaugmented limboxygen extraction.3 Commonexperience suggests thatuntrained normalsubjects performing rapid exercise (for example running) often stopbecause ofbreathlessness, whereas whenthey exercise slowly (for example walking) they stopbecause of fatigue. Inthis study wehaveinvestigated whether theresponse toexercise inpatients withcongestive heart failure issimilar, andifsowhether differences inthemetabolic, haemodynamic, andventilatory re