Deterioration of Left Ventricular Chamber Performance After Bed Rest
To the Editor:
Perhonen et al1 estimate changes in the left ventricular (LV) diastolic rest volume before and after bed rest. By definition, diastolic rest volume is that volume which exists at zero transmural LV diastolic pressure (LVDPtm). Although they acknowledge the potential role of pericardial constraint in their discussion, they ignore this effect by assuming LVDPtm is approximately equal to pulmonary capillary wedge pressure (PCWP) in their analysis. When intracardiac and extracardiac diastolic pressures are both carefully measured, the resulting curves relating LVDPtm to LV volume have a relatively flat portion near zero pressure.2 The diastolic pressure-volume curves presented by Perhonen et al1 do not show this characteristic, suggesting an error in their assumption that pericardial constraint pressure is negligible. This methodological concern raises doubts about the main findings of their study.
Right atrial pressure (RAP) may be used to approximate LVDPtm as PCWP−RAP.3 Although this method remains controversial,4 if simultaneous RAP data are available to the authors, it would be worthwhile to repeat their analysis using this approximation.
Perhonen MA, Zuckerman JH, Levine BD. Deterioration of left ventricular chamber performance after bed rest: “cardiovascular deconditioning” or hypovolemia? Circulation. 2001; 103: 1851–1857.
Baker AE, Dani R, Smith ER, et al. Quantitative assessment of independent contributions of pericardium and septum to direct ventricular interaction. Am J Physiol. 1998; 275: H476–H483.
Smiseth OA, Refsum H, Tyberg JV. Pericardial pressure assessed by right atrial pressure: a basis for calculation of left ventricular transmural pressure. Am Heart J. 1983; 108: 603–605.
Santamore WP, Constantinescu M, Little WC. Direct assessment of right ventricular transmural pressure. Circulation. 1987; 75: 744–747.