Role of the prefrontal lobe in young normotensives with a family history of hypertension and hypertensives.

Accumulating evidence has demonstrated a significant relationship between prefrontal lobe and hypertension. Elevated blood pressure is usually associated with a prefrontal hemodynamic abnormality. However, the detailed process is still unclear. In this study, we designed a startle protocol and tested the response of the cerebral cortex and cardiovascular system in young normotensive subjects with a family history of hypertension (FH+). Additionally, the cold forehead test (CFT) was performed in hypertensive subjects. In total, 40 young normotensive subjects (21 with FH+ and 19 without a family history of hypertension (FH-)) and 49 middle-aged subjects (21 normotensives (NT) and 28 hypertensives (HT)) were recruited. Our results showed that the magnitude of startle-evoked alpha oscillation at the parasympathetic-related prefrontal cortex (FP1 and FP2) in the FH+ group was significantly smaller than in the FH- group. Acute bradycardia (RRI increase) was observed in FH- subjects but disappeared in the FH+ group. The coupling between instant cardiac acute response (increased RRI) and prefrontal arousal (magnitude of evoked oscillation) was significantly weakened in the FH+ group compared with the FH- group. Furthermore, the decrease in HR induced by parasympathetic outflow during CFT was absent in HT subjects. Hence, we concluded that the impairment of parasympathetic outflow derived from the prefrontal lobe occurs in both healthy young offspring of hypertensive and hypertensive patients.

Increased Respiratory Modulation of Blood Pressure in Hypertensive Patients.

OBJECTIVE: Although the important role of respiratory modulation of the cardiovascular system in the development of hypertension has been demonstrated in animal studies, little research has assessed this modulation in essential hypertensive patients. We aimed to explore whether respiratory-related variations in cardiovascular variables are changed in hypertensive patients and their potential relationships with the respiratory pattern. METHODS: Respiration, ECG, and beat-to-beat blood pressure (BP) were simultaneously measured in 46 participants (24 hypertensive patients and 22 normotensive participants) during rest and a mental arithmetic task (MAT). Respiratory-triggered averaging and orthogonal subspace projection methods were used to assess the respiratory modulations of BP and heart rate (HR). Respiratory parameters including inspiratory time, expiratory time, respiratory rate and their variabilities were also characterized. RESULTS: The inspiratory time, expiratory time, respiratory rate and their variabilities were not different between hypertensive and normotensives. Additionally, the modulation of HR by respiration was also similar between the two groups. Hypertensive patients exhibited an amplified respiratory modulation of systolic BP (SBP), as assessed from the amplitude of respiratory-related changes and the percentage of the power of respiratory-related variation, and also reflected from the temporal pattern of respiratory modulation of SBP. The exaggerated respiratory-related variation of SBP in hypertensive patients accounted for ≈23% of the total power of SBP, producing an absolute change of ≈4.5 mmHg in SBP. MAT was characterized by decreased inspiratory time and increased variabilities of expiratory time and respiratory rate with no changes in the amplitude of respiratory modulations. CONCLUSION: Hypertensive patients had excessive respiratory modulation of SBP, despite having similar respiratory pattern with normotensives. These findings highlight the importance of respiratory influence in BP variation and suggest that respiratory modulation of SBP may have prognostic information for cardiovascular events in hypertensive patients.

An improved method to evaluate heart rate variability based on time-variant cardiorespiratory relation.

Frequency domain analysis of heart rate variability (HRV) is a noninvasive method to evaluate the autonomic nervous system (ANS), but the traditional parameters of HRV, i.e., the power spectra of the high-frequency (HF) and low-frequency bands (LF), cannot estimate the activity of the parasympathetic (PNS) and sympathetic nervous systems (SNS) well. The aim of our study was to provide a corrected method to better distinguish the contributions of the PNS and SNS in the HRV spectrum. Respiration has a gating effect on cardiac vagal efferent activity, which induces respiration-locked heart rate (HR) changes because of the fast effect of the PNS. So the respiration-related heart rate (HRr) is closely related to PNS activity. In this study, HR was decomposed into HRr and the respiration-unrelated component (HRru) based on empirical mode decomposition (EMD) and the relationship between HR and respiration. Time-frequency analysis of HRr and HRru was defined as HFr and LFru, respectively, with specific adaptive bands for every signal. Two experimental data sets, representing SNS and PNS activation, respectively, were used for efficiency analysis of our method. Our results show that the corrected HRV predicted ANS activity well. HFr could be an index of PNS activity, LFru mainly reflected SNS activity, and LFru/HFr could be more accurate in representing the sympathovagal balance.NEW & NOTEWORTHY This study includes the time-varying relationship between respiration and heart rate in the analysis of heart rate variability. Correction for low-frequency and high-frequency components based on respiration significantly improved evaluation of the sympathetic and parasympathetic nervous systems.