Autonomic response to change of posture among normal and mild-hypertensive adults: Investigation by time-dependent spectral analysis

Akselrod, Solange; Oz, O.; Greenberg, M. A.; Keselbrener, Laurence

doi:10.1016/s0165-1838(97)00011-8

Cited by 41 publications

(24 citation statements)

References 22 publications

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“…13,23 Increased SAP variability in lower frequencies has been linked to increased sympathetic modulation. 24 In hypertensive subjects, an inverse relationship has been reported between BRS and plasma catecholamine levels. 25 However, in systo-diastolic and systolic hypertension, baroreceptor modulation of sympathetic nerve traffic is still present despite impaired baroreflex control of the heart rate and increased muscle sympathetic nerve activity.…”

Section: Discussionmentioning

confidence: 99%

Increased pulse pressure is associated with reduced baroreflex sensitivity

et al. 2004

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Although pulse pressure (PP), heart rate variability (HRV) and baroreflex sensitivity (BRS) have been shown to predict cardiovascular events and mortality in various populations, their relationships have not been clarified. We examined these associations in two separate population-based samples of healthy middle-aged subjects. In population 1, data were obtained from 149 subjects (71 men and 78 women) aged 35-64 (mean 47.7) years, and in population 2, from 214 subjects (88 men and 126 women) aged 40-62 (mean 50.5) years. Increased 24-h ambulatory PP was related to decreased cross-spectral BRS independent of age and gender (b ¼ À0.28, Po0.001 for population 1; b ¼ À0.22, P ¼ 0.003 for population 2). This association remained significant when 24-h ambulatory diastolic blood pressure, body mass index, smoking and alcohol intake were added as covariates in the multivariate analysis. Increased ambulatory PP was also associated with increased beat-to-beat systolic arterial pressure variability. Associations between ambulatory PP and HRV were not significant after controlling for age and gender. Our results suggest that elevated PP does not affect overall HRV, but it interferes with baroreflex-mediated control of the heart rate. This association may be due to a common denominator, such as arterial stiffness, for PP and BRS.

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Section: Discussionmentioning

confidence: 99%

Increased pulse pressure is associated with reduced baroreflex sensitivity

et al. 2004

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“…The brain represents 2% of the total body weight in man, demands 15% of the cardiac output at rest and requires the maintenance of a stable output regardless of posture or locomotion 8 . The change from a supine posture to the orthostatic one results in a displacement of blood at the thorax level to the subdiaphragmatic venous system, a phenomenon usually called venous pooling 9 . If compensatory adjustments do not occur promptly after the change in posture, the arterial pressure decreases, and the individual can present from milder symptoms related to orthostatic intolerance to the sudden loss of consciousness 10 .…”

Section: Orthostatic Posture and Gravitational Stressmentioning

confidence: 99%

“…The hypertensive individuals present an increase in the variability of arterial pressure fl uctuation and a decreased sensitivity of the baroreceptors 9,54 . The hypertensive patient's gender also seems to be an important determinant in barorefl ex sensitivity, as the autonomic function shows to be more compromised in the female sex 54 .…”

Section: Factors That Influence the Baroreflex Sensitivitymentioning

confidence: 99%

“…In fact, the analysis of the autonomic response of hypertensive individuals to postural change, when compared to that of normal individuals, shows that, although there is a basal increase of sympathetic activity during the orthostatic posture, the sympathetic response is signifi cantly decreased, suggesting an impairment of the mean arterial pressure control by the barorefl ex in these individuals 9 .…”

Section: Factors That Influence the Baroreflex Sensitivitymentioning

confidence: 99%

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Contribuição dos grandes vasos arteriais na adaptação cardiovascular a ortostase

Neto¹

2006

Arq. Bras. Cardiol.

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“…For example, standing up from a supine position causes increased pooling of blood in the systemic venous circulation, which reduces preload to the right ventricle [25], [26].The reduced preload results in reduced RV stroke volume, ensuring that ventricular outflow matches inflow and therefore preventing the ventricle from emptying completely. Conversely, during exercise muscles contract around the veins, squeezing blood back to the right atrium and thereby increasing preload [20].…”

Section: The Frank-starling Law Of the Heartmentioning

confidence: 99%

Automatic control of dual left ventricular assist devices as a biventricular assist device

Stevens¹

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In this thesis, we investigate automated methods for the control of rotary blood pumps in the treatment of heart failure. Heart failure is a common end-point for many forms of cardiovascular disease resulting in significant morbidity and mortality. Ventricular assist devices (VADs) are blood pumps designed to assist a failing heart and are used both to support patients whilst they are awaiting a heart transplant, or as an alternative to transplantation. Small rotary VADs can provide long-term support of the left ventricle (LVAD), right ventricle (RVAD) or both ventricles of the heart simultaneously.Unfortunately, the lack of a commercially available rotary RVAD has led to the implantation of two rotary LVADs as an ad hoc biventricular assist device (BiVAD). Clinicians currently operate such dual LVADs at a constant speed, which ensures balanced left and right pump flows for inactive patients.However, changes in levels of patient activity will lead to altered cardiac output requirements, which may disturb this balance. In turn, this can lead to undesirable events such as pulmonary venous congestion or ventricular suction. A control system that automatically adjusts pump speed with changes in the required cardiac output could alleviate such events and so offer significant benefits. However, while such physiological control systems have been investigated for single LVADs, limited work has been completed on dual LVAD control. In addition, there is no generally accepted framework for the evaluation of these systems that encompasses a broad range of patient scenarios, activity levels and heart conditions. Therefore, the primary aim of this thesis was to develop and evaluate a number of physiological control systems suitable for dual rotary LVADs.The first objective was to characterise the methods that are currently used to operate dual LVADs in the clinic. Using both in-vitro and in-vivo methods, it was shown that balanced left and right flow rates could be obtained by operating the RVAD slower than the LVAD, albeit at speeds below the manufacturer's recommendations (1400 -1800 RPM), which, according to other investigators, may adversely affect impeller washout. Operating both at the same design speed is only possible in patients with high pulmonary vascular resistance (PVR), high left ventricular contractility or high RVAD outflow cannula resistance. This thesis demonstrates that if the RVAD outflow cannula is restricted to a diameter between 6.5 and 8.1 mm, suitable steady-state haemodynamics (systemic flow rate 5 L.min -1 , MAP 90mmHg and LAP less than 25mmHg) can be achieved while maintaining impeller stability and optimal device washout. It was also established that changes in pump speed or outflow graft diameter were required to overcome elevations in pulmonary vascular resistance, thereby justifying the necessity of a physiological control system for dual LVADs.The second objective was to develop an in vitro evaluation protocol for control system testing utilising a mock circulation loop (MCL). The test...

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Autonomic response to change of posture among normal and mild-hypertensive adults: Investigation by time-dependent spectral analysis

Cited by 41 publications

References 22 publications

Increased pulse pressure is associated with reduced baroreflex sensitivity

Increased pulse pressure is associated with reduced baroreflex sensitivity

Contribuição dos grandes vasos arteriais na adaptação cardiovascular a ortostase

Automatic control of dual left ventricular assist devices as a biventricular assist device

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