ABC | Volume 110, Nº4, April 2018

Original Article Silva et al Postural hypotension: spectral analysis Arq Bras Cardiol. 2018; 110(4):303-311 Figure 5 – Receiver operating characteristic curve of heart rate in the supine position (blue line), considering the stable variable postural response without orthostatic hypotension. 1.0 1.0 0.8 0.8 0.6 0.6 0.4 0.4 0.2 0.0 0.0 0.2 Sensitivity 1 – Specificity Figure 4 – Spectral analysis of a female patient (62 years of age) without orthostatic hypotension (the same of Figure 3) in orthostatic position, showing an increase in low frequency (LF) component and in the LF/high frequency (HF) ratio, in relation to supine position. VLF: very low frequency; RR: number of QRS in sinus rhythm; VLF: very low frequency; HFnu: HF normalized unit. 26 K 19 K 13 K 6 K 0 0,0 0,1 0,2 0,3 0,4 0,5 Frequency (c/b) Duration: 5 min Total RR: 410 corrected: 0 RR average: 732 ms 82 bpm Total potential: 1201 VLF Power: 628 (0,00–0,04)Hz LF Power: 548 (0,04–0,15)Hz LFnu: 95,8 HF Power: 17 (0,15–0,40)Hz HFnu: 3,0 LF/HF: 32,16 dysfunction 20 may be associated with reduced HR in supine position in elderly patients, regardless of OH. In the study population, when this variablewas analyzed,medianHR in supine position in the case group was significantly lower than in control group. In addition to the changes already described, another factor that may be associatedwith differences between the groups would be the use of beta-blockers. These medications have a negative chronotropic effect on HR. 21 However, in the present study, no difference was found in the use of most of these drugs between the groups. Significant difference was found in the use of ACE inhibitors, which decrease vascular resistance but have no substantial effect on HR, despite restoration of parasympathetic tone with the use of the drug in hypertensive patients. 22 In light of this, analysis of HRV was important for the study of HR profile in elderly subjects with OH in supine position. With change of position, as expected, 10 there was a decrease in HF and increase in LF/HF in all patients, without an increase in the LF component. There is a decline in baroreflex and HRV with age in both sexes, resulting in autonomic dysfunction. 6,8,13 A U-curve has been used to describe the progressive decrease of HRV with aging, which reaches its nadir in the sixth or seventh decade of life, followed by progressive increase, which is determinant for longevity from those decades on. 23‑26 Therefore, to avoid age bias, the case and control groups were matched by age. Although previous studies on OH and HRV 11-13,27 have shown different results, it is possible to 308