Dear Editor
We read with great interest the well-crafted article by Kim et al. [1], which reported that presyncopal symptoms during nitrate-stimulated tilt-testing could be explained by decreased systemic vascular resistance (SVR) rather than reduced cardiac output (CO). The study setup is sound, but being accustomed to this methodology [2], [3], we noticed inaccuracies in Tables 2 and 3. The SVR values appear correct, whereas the systemic vascular resistance index (SVRI) values presented seem incorrect. SVR is calculated as 80*(MAP-CVP)/CO, where MAP is mean arterial pressure and CVP is central venous pressure. The normal values of SVR range from 800 to 1200 dynes s/cm5 [4], consistent with the original article [1]. SVRI is calculated as 80*(MAP-CVP)/CI, where CI is cardiac index [5]; and the formula equals 80*(MAP-CVP)/(CO/BSA), where BSA is body surface area. This formula may also be presented as SVRI=SVR*BSA, and the normal values of SVRI range from 1900 to 2400 dynes s m2/cm5 [2], [3], [5]. Notably, the reported SVRI values in the article by Kim et al. [1] range from 612 to 683 and the units are given as dynes s/cm5/m2, indicating that the SVR values were divided and not multiplied by BSA. The correct SVRI units should be presented as either dynes s/(cm5/m2) or dynes s*m2/cm5. We estimated that the proper SVRI values in the study conducted by Kim et al. [1] would range from 1900 to 2300 dynes s m2/cm5. We agree with the general results and conclusions of the article; however, the SVRI results should be recalculated.
Conflict of interest
All authors declare no conflict of interest related to this study.
Acknowledgements
Work in the laboratory was supported by the Competitive State Research Financing of the Expert Responsibility Area of Tampere University Hospital, the Finnish Foundation for Cardiovascular Research, the Sigrid Jusélius Foundation, and the Pirkanmaa Fund of Finnish Cultural Foundation.
References
- 1.Kim B.G., Cho S.W., Lee H.Y. Reduced systemic vascular resistance is the underlying hemodynamic mechanism in nitrate-stimulated vasovagal syncope during head-up tilt-table test. J Arrhythm. 2015;31(4):196–200. doi: 10.1016/j.joa.2014.11.008. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Tahvanainen A.M., Tikkakoski A.J., Leskinen M.H. Supine and upright haemodynamic effects of sublingual nitroglycerin and inhaled salbutamol: a double-blind, placebo-controlled, randomized study. J Hypertens. 2012;30(2):297–306. doi: 10.1097/HJH.0b013e32834e4b26. [DOI] [PubMed] [Google Scholar]
- 3.Tikkakoski A.J., Tahvanainen A.M., Leskinen M.H. Hemodynamic alterations in hypertensive patients at rest and during passive head-up tilt. J Hypertens. 2013;31(5):906–915. doi: 10.1097/HJH.0b013e32835ed605. [DOI] [PubMed] [Google Scholar]
- 4.Stamler J.S., Loh E., Roddy M.A. Nitric oxide regulates basal systemic and pulmonary vascular resistance in healthy humans. Circulation. 1994;89(5):2035–2040. doi: 10.1161/01.cir.89.5.2035. [DOI] [PubMed] [Google Scholar]
- 5.Borlaug B.A., Melenovsky V., Redfield M.M. Impact of arterial load and loading sequence on left ventricular tissue velocities in humans. J Am Coll Cardiol. 2007;50(16):1570–1577. doi: 10.1016/j.jacc.2007.07.032. [DOI] [PubMed] [Google Scholar]