Estimation of cardiac reserve by peak power: validation and initial application of a simplified index

Objectives-To validate a simplified estimate of peak power (SPP) against tr ue (invasively measured) peak instantaneous power (TPP), to assess the feas ibility of measuring SPP during exercise and to correlate this with functio nal capacity. Design-Development of a simplified method of measurement and observational study. Setting-Tertiary referral centre for cardiothoracic disease. Subjects-For validation of SPP with TPP, seven normal dogs and four dogs wi th dilated cardiomyopathy were studied. To assess feasibility and clinical significance in humans, 40 subjects were studied (26 patients; 14 normal co ntrols). Methods-In the animal validation study, TPP was derived from ascending aort ic pressure and flow probe, and from Doppler measurements of flow. SPP, cal culated using the different flow measures, was compared with peak instantan eous power under different loading conditions. For the assessment in humans , SPP was measured at rest and during maximum exercise. Peak aortic flow wa s measured with transthoracic continuous wave Doppler, and systolic and dia stolic blood pressures were derived from brachial sphygmomanometry. The dif ference between exercise and rest simplified peak power (Delta SPP) was com pared with maximum oxygen uptake ((V) over dot O(2)max), measured from expi red gas analysis. Results-SPP estimates using peak flow measures correlated well with true pe ak instantaneous power (r = 0.89 to 0.97), despite marked changes in system ic pressure and flow induced by manipulation of loading conditions. In the human study, (V) over dot O(2)max correlated with Delta SPP (r = 0.78) bett er than Delta ejection fraction (r = 0.18) and Delta rate-pressure product (r = 0.59). Conclusions-The simple product or mean arterial pressure and peak aortic fl ow (simplified peak power, SPP) correlates with peak instantaneous power ov er a range of loading conditions in dogs. In humans, it can be estimated du ring exercise echocardiography, and correlates with maximum oxygen uptake b etter than ejection fraction or rate-pressure product.