Hindawi Publishing Corporation Cardiology Research and Practice Volume 2012, Article ID 961423, 2 pages doi:10.1155/2012/961423 Letter to the Editor Procedural Aspects and Physiologic Mechanisms of the Deep Inspiratory Maneuver Simon Tilma Vistisen,1 Peter Juhl-Olsen,2 Christian Alcaraz Frederiksen,2 and Hans Kirkegaard1, 2 1 Research Centre for Emergency Medicine, Aarhus University Hospitals, Nørrebrogade 42, Building 30, 8000 Aarhus, Denmark 2 Department of Anaesthesiology & Intensive Care, Aarhus University Hospitals, Skejby, Denmark Correspondence should be addressed to Simon Tilma Vistisen, vistisen@ki.au.dk Received 16 February 2012; Accepted 27 February 2012 Copyright © 2012 Simon Tilma Vistisen et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Sir, we have read the paper by S. Preau et al. “Hemodynamic changes during a deep inspiration maneuver predict ﬂuid res- ponsiveness in spontaneously breathing patients” with great interest. Based on the fundamental ideas of dynamic hemo- dynamic monitoring, inducing cardiac preload variations and monitoring corresponding pulse pressure variations [1], the paper presents a novel technique of varying cardiac pre- load in spontaneously breathing (SB) patients that does not necessitate specialised equipment apart from routine clinical monitoring. The paper is indeed relevant because it is, to our knowledge, the ﬁrst to present the feasibility of a deep breath- ing method (deep inspiratory maneuver, DIM) for inducing preload changes. For the purpose of better understanding the presented technique, we wish to pose the following questions for the authors. (1) Concerning compliance and applicability in terms of intention-to-treat: it is not clear which proportion of SB patients with acute circulatory failure was able to comply with the DIM. Can compliance be expected to be as high as 87% (26 of 30) for this generally deﬁned patient group? (2) Concerning the calculations: DIM-induced changes are deﬁned by the authors as. DIM-induced changes = (maximal value during DIM − minimal value dur- ing quiet SB prior to DIM)/((maximal value during DIM − minimal value during quiet SB prior to DIM)/ 2). (a) How large was the time window when estimat- ing the minimal value during quiet SB prior to DIM? Did the time window vary or was it ﬁxed? (b) The maximal value during DIM was found in either phase 2 or phase 4 of the DIM. In which phase was the maximal value typically found? Were the maximal values during the two phases generally of the same magnitude? (3) Instructing the patients to perform the DIM: this is important should the technique be validated by other study groups and in turn gain widespread use. (a) Did the authors in any way evaluate if the slow continuous inspiration strain was associated with a more or less constant inspiratory ﬂow or was most air generally inspired in the ﬁrst phase of inspiration, perhaps amplifying maximal value during DIM phase 2? How were instructions given on inspiratory ﬂow rate? (b) Did you make any instructions to the pa- tients (directly or indirectly) what tidal volume should be during DIM? Did they inspire to, for example, maximal or convenient lung volume? (4) Concerning the physiological mechanisms: did you experience any patients with signiﬁcant heart rate variability (HRV)? The respiratory part of HRV (with its subsequent varying passive ﬁlling time of the