Daily Heart Rate Variability Indices in Subjects with and Without Metabolic Syndrome Before and After the Elimination of the Influence of Day-time Physical Activity

• Main Authors: Anžela Slušnienė, Aleksandras Laucevičius, Petras Navickas, Ligita Ryliškytė, Vytautas Stankus, Albinas Stankus, Rokas Navickas, Ieva Laucevičienė, Vytautas Kasiulevičius
• Format: Article
• Language: English
• Published: MDPI AG 2019-10-01
• Series: Medicina
• Subjects: metabolic syndrome; heart rate variability; physical activity; hypertension
• Online Access: https://www.mdpi.com/1010-660X/55/10/700

<i>Background and Objectives:</i> The available research shows conflicting data on the heart rate variability (HRV) in metabolic syndrome (MetS) subjects. The discrepancy suggests a methodical shortcoming: due to the influence of physical activity, the standard measuring of HRV at rest is not comparable with HRV assessment based on 24 h Holter monitoring, which is preferred because of its comprehensiveness. To obtain a more reliable measure and to clarify to what extent HRV is altered in MetS, we assessed a 24 h HRV before and after the elimination of the influence of physical activity. <i>Materials and Methods:</i> We investigated 69 metabolic syndrome (MetS) and 37 control subjects, aged 50&#8722;55. In all subjects, 24 h monitoring of electrocardiogram, blood pressure, and actigraphy profiles were conducted. To eliminate the influence of day-time physical activity on RR intervals (RRI), a linear polynomial autoregressive model with exogenous terms (ARX) was used. Standard spectral RRI analysis was performed. <i>Results:</i> Subjects with MetS had blunted HRV; the diurnal SDNN index was reliably lower in the MetS group than in control subjects. The elimination of the influence of physical activity did not reveal a significant HRV change in long-term indices (SDNN, SDANN, and SD2), whilst adjacent RRI values (RMSSD, pNN50, and SD1) and SDNN index significantly increased (<i>p</i> &lt; 0.001). An increase in the latter indices highlighted the HRV difference between the MetS and control groups; a significant (<i>p</i> &lt; 0.001) decrease of all short-term HRV variables was found in the MetS group (<i>p</i> &lt; 0.01), and low-frequency spectral components were less pronounced in the MetS group. <i>Conclusion:</i> The application of a polynomial autoregressive model in 24 h HRV assessment allowed for the exclusion of the influence of physical activity and revealed that MetS is associated with blunted HRV, which reflects mitigated parasympathetic tone.