TY - JOUR

T1 - Coherence and coupling functions reveal microvascular impairment in treated hypertension

AU - Ticcinelli, Valentina

AU - Stankovski, Tomislav

AU - Iatsenko, Dmytro

AU - Bernjak, Alan

AU - Bradbury, Adam

AU - Gallagher, Andrew

AU - Clarkson, Peter B M

AU - McClintock, Peter Vaughan Elsmere

AU - Stefanovska, Aneta

PY - 2017/10/13

Y1 - 2017/10/13

N2 - The complex interactions that give rise to heart rate variability (HRV) involve coupled physiological oscillators operating over a wide range of different frequencies and length-scales. Based on the premise that interactions are key to the functioning of complex systems, the time-dependent deterministic coupling parameters underlying cardiac, respiratory and vascular regulation have been investigated at both the central and microvascular levels. Hypertension was considered as an example of a globally altered state of the complex dynamics of the cardiovascular system. Its effects were established through analysis of simultaneous recordings of the electrocardiogram, respiratory effort, and microvascular blood flow (by laser Doppler flowmetry). The signals were analysed by methods developed to capture time-dependent dynamics, including the wavelet transform, wavelet-based phase coherence, nonlinear mode decomposition and dynamical Bayesian inference, all of which can encompass the inherent frequency and coupling variability of living systems. Phases of oscillatory modes corresponding to the cardiac (around 1.0~Hz), respiratory (around 0.25~Hz) and vascular myogenic activities (around 0.1~Hz) were extracted and combined into two coupled networks describing the central and peripheral systems respectively. The corresponding spectral powers and coupling functions were computed. The same measurements and analyses were performed for three groups of subjects: healthy young (Y group, 24.4 +/- 3.4 y), healthy aged (A group, 71.1 +/- 6.6 y), and aged treated hypertensive patients (ATH group, 70.3 +/- 6.7 y). It was established that the degree of coherence between low-frequency oscillations near 0.1~Hz in blood flow and in HRV time series differs markedly between the groups, declining with age and nearly disappearing in treated hypertension. Comparing the two healthy groups it was found that the couplings to the cardiac rhythm from both respiration and vascular myogenic activity decrease significantly in aging. Comparing the data from A and ATH groups it was found that the coupling from the vascular myogenic activity is significantly weaker in treated hypertension subjects, implying that the mechanisms of microcirculation are not completely restored by current anti-hypertension medications.

AB - The complex interactions that give rise to heart rate variability (HRV) involve coupled physiological oscillators operating over a wide range of different frequencies and length-scales. Based on the premise that interactions are key to the functioning of complex systems, the time-dependent deterministic coupling parameters underlying cardiac, respiratory and vascular regulation have been investigated at both the central and microvascular levels. Hypertension was considered as an example of a globally altered state of the complex dynamics of the cardiovascular system. Its effects were established through analysis of simultaneous recordings of the electrocardiogram, respiratory effort, and microvascular blood flow (by laser Doppler flowmetry). The signals were analysed by methods developed to capture time-dependent dynamics, including the wavelet transform, wavelet-based phase coherence, nonlinear mode decomposition and dynamical Bayesian inference, all of which can encompass the inherent frequency and coupling variability of living systems. Phases of oscillatory modes corresponding to the cardiac (around 1.0~Hz), respiratory (around 0.25~Hz) and vascular myogenic activities (around 0.1~Hz) were extracted and combined into two coupled networks describing the central and peripheral systems respectively. The corresponding spectral powers and coupling functions were computed. The same measurements and analyses were performed for three groups of subjects: healthy young (Y group, 24.4 +/- 3.4 y), healthy aged (A group, 71.1 +/- 6.6 y), and aged treated hypertensive patients (ATH group, 70.3 +/- 6.7 y). It was established that the degree of coherence between low-frequency oscillations near 0.1~Hz in blood flow and in HRV time series differs markedly between the groups, declining with age and nearly disappearing in treated hypertension. Comparing the two healthy groups it was found that the couplings to the cardiac rhythm from both respiration and vascular myogenic activity decrease significantly in aging. Comparing the data from A and ATH groups it was found that the coupling from the vascular myogenic activity is significantly weaker in treated hypertension subjects, implying that the mechanisms of microcirculation are not completely restored by current anti-hypertension medications.

KW - Hypertension

KW - Ageing

KW - Heart rate variability

KW - Nonlinear oscillator

KW - Wavelet Transform

KW - coherence analysis

KW - Bayesian inference

KW - Coupling functions

KW - microvascular blood flow oscillations

KW - vascular myogenic activity

KW - cardiovascular regulation

U2 - 10.3389/fphys.2017.00749

DO - 10.3389/fphys.2017.00749

M3 - Journal article

VL - 8

JO - Frontiers in Physiology

JF - Frontiers in Physiology

SN - 1664-042X

M1 - 749

ER -