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. 1999 Sep;82(3):357–364. doi: 10.1136/hrt.82.3.357

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

G Armstrong 1, S Carlier 1, K Fukamachi 1, J Thomas 1, T Marwick 1
PMCID: PMC1729165  PMID: 10455090

Abstract

OBJECTIVES—To validate a simplified estimate of peak power (SPP) against true (invasively measured) peak instantaneous power (TPP), to assess the feasibility of measuring SPP during exercise and to correlate this with functional 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 with dilated cardiomyopathy were studied. To assess feasibility and clinical significance in humans, 40 subjects were studied (26 patients; 14 normal controls).
METHODS—In the animal validation study, TPP was derived from ascending aortic pressure and flow probe, and from Doppler measurements of flow. SPP, calculated using the different flow measures, was compared with peak instantaneous power under different loading conditions. For the assessment in humans, SPP was measured at rest and during maximum exercise. Peak aortic flow was measured with transthoracic continuous wave Doppler, and systolic and diastolic blood pressures were derived from brachial sphygmomanometry. The difference between exercise and rest simplified peak power (Δ SPP) was compared with maximum oxygen uptake (V̇O2max), measured from expired gas analysis.
RESULTS—SPP estimates using peak flow measures correlated well with true peak instantaneous power (r = 0.89 to 0.97), despite marked changes in systemic pressure and flow induced by manipulation of loading conditions. In the human study, V̇O2max correlated with Δ SPP (r = 0.78) better than Δ ejection fraction (r = 0.18) and Δ rate-pressure product (r = 0.59).
CONCLUSIONS—The simple product of mean arterial pressure and peak aortic flow (simplified peak power, SPP) correlates with peak instantaneous power over a range of loading conditions in dogs. In humans, it can be estimated during exercise echocardiography, and correlates with maximum oxygen uptake better than ejection fraction or rate-pressure product.


Keywords: stress echocardiography; oxygen consumption; left ventricular function; cardiac power output

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Figure 1  .

Figure 1  

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Haemodynamic alterations in the open chest canine model: screen shots from the custom analysis program showing haemodynamic responses. Flow (thin solid line) is ascending aortic flow from perivascular flow probe. Pressure (thick solid line) is ascending aortic pressure from micromanometer catheter. Power (broken line) is left ventricular power, the instantaneous product of the pressure and flow. (A) Baseline. (B) During partial aortic occlusion; pressure increases, flow falls, but power remains similar to baseline. (C) During vena cava occlusion; pressure, flow, and power all decrease dramatically. See text for further details.

Figure 2  .

Figure 2  

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Differences in peak instantaneous power between normal and cardiomyopathic dogs. True peak instantaneous power per kg body weight for normal and cardiomyopathic dogs during different haemodynamic stages. Error bars represent SEM. VC, vena cava. Cardiomyopathic dogs have lower peak instantaneous power during baseline and aortic occlusion (p < 0.001), but not during vena cava occlusion (p = 0.09).

Figure 3  .

Figure 3  

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Simplified peak power estimates compared with peak instantaneous power in dogs. Simplified peak power (SPP) estimates using peak flow measured with flow probe shows excellent correlation with true peak instantaneous power (A), with minor overestimation of higher levels of power shown on the Bland-Altman plot (B). When echocardiographic estimates of flow are used to estimate simplified peak power there is some increase in scatter but still a good correlation with true peak instantaneous power, using continuous wave (CW) Doppler (C and D) and pulse wave (PW) Doppler (E and F).

Figure 4  .

Figure 4  

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Correlation of cardiac power reserve (ΔSPP) with V̇O2max in 26 patients and 14 control subjects. Non-diagnostic, non-diagnostic exercise test because heart rate response was < 85% of maximum predicted for age. Scar and ischaemia, left ventricular wall motion abnormality by cross sectional echocardiography at rest (scar) or with exercise (ischaemia). Negative and control, exercise echocardiography in patients (negative) and normal volunteers (control) with adequate heart rate response and no wall motion abnormality at rest or on exercise.

Selected References

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