Passive and active ventricular elastances of the left ventricle

BACKGROUND: Description of the heart as a pump has been dominated by models based on elastance and compliance. Here, we are presenting a somewhat new concept of time-varying passive and active elastance. The mathematical basis of time-varying elastance of the ventricle is presented. We have defined elastance in terms of the relationship between ventricular pressure and volume, as: dP = EdV + VdE, where E includes passive (E(p)) and active (E(a)) elastance. By incorporating this concept in left ventricular (LV) models to simulate filling and systolic phases, we have obtained the time-varying expression for E(a )and the LV-volume dependent expression for E(p). METHODS AND RESULTS: Using the patient's catheterization-ventriculogram data, the values of passive and active elastance are computed. E(a )is expressed as: [Image: see text]; E(p)is represented as: [Image: see text]. E(a )is deemed to represent a measure of LV contractility. Hence, Peak dP/dt and ejection fraction (EF) are computed from the monitored data and used as the traditional measures of LV contractility. When our computed peak active elastance (E(a,max)) is compared against these traditional indices by linear regression, a high degree of correlation is obtained. As regards E(p), it constitutes a volume-dependent stiffness property of the LV, and is deemed to represent resistance-to-filling. CONCLUSIONS: Passive and active ventricular elastance formulae can be evaluated from a single-beat P-V data by means of a simple-to-apply LV model. The active elastance (E(a)) can be used to characterize the ventricle's contractile state, while passive elastance (E(p)) can represent a measure of resistance-to-filling

Randomized controlled trial of supervised exercise to evaluate changes in cardiac function in patients with peripheral atherosclerotic disease

Introduction: Peripheral atherosclerotic disease (PAD) is a condition characterized by low functional capacity which is associated with impaired free living, ambulation and low exercise tolerance. The purpose of this randomized controlled study was to evaluate whether changes in maximal walking time are associated with adaptations in cardiovascular function following supervised exercise. Methods: After ethics approval, 28 patients (63±11 years) completed a graded treadmill test (2min stages, 3.2 kmh-1, with gradient increasing 2% every 2min) until they reached level three or four on the claudication pain scale. Peak oxygen consumption was assessed on a breath-by-breath basis, by online expiratory gas analysis. Following a 40-min recovery period, peak cardiac output was measured using the non-invasive carbon dioxide rebreathing method described by Defares (J Appl Physiol, 13, 1958, 159). Peak cardiac power output was then computed using the equation described by Cooke et.al. (Heart, 1998, 79, 289). Patients were randomly assigned to one of two groups: supervised, who exercised at the hospital twice weekly for 12weeks or control, who received normal treatment which included encouragement to walk regularly. Results: After 12 weeks, there were no significant changes in body mass, peak oxygen consumption, peak cardiac output, peak heart rate, peak cardiac power output, respiratory exchange ratio or rating of perceived exertion in both the supervised and control group. There was a significant improvement (91%) in maximal walking distance following the supervised exercise programme. Although patients'peak cardiovascular measurements were unchanged, the patients in the supervised exercise group were able to complete a higher workload at the end of the 12 weeks of exercise, for the equivalent demands on the circulation system. Conclusions: The findings from this study suggest that a short-term period of supervised exercise training results in an improved walking time in patients with limiting claudication because of PAD. It also demonstrated that the cardiovascular system becomes more efficient in meeting the demands of exercise. It is recommended that individuals with PAD should undertake exercise as a form of treatment. © 2007 The Authors Journal compilation © 2007 Blackwell Publishing Ltd