Showing papers by "Nigel H. Lovell published in 1994"
TL;DR: It is concluded that although exogenous AVP induces profound changes in cardiovascular function, it does not alter carotid baroreflex control of MAP, TPR, CO, and HR.
Abstract: Arginine vasopressin (AVP) has profound effects on the cardiovascular system, yet has minimal pressor activity at physiological levels in intact subjects. We designed an investigation to delineate the effects of AVP on open-loop carotid baroreflex control of mean arterial pressure (MAP), total peripheral resistance (TPR), and cardiac output (CO) in conscious, chronically instrumented dogs. During graded infusions of AVP (0.5-2.0 ng.kg-1.min-1), the open-loop hemodynamic responses to controlled changes in isolated carotid sinus pressure (CSP) were determined. Increasing levels of AVP infusion led to significant increases in plasma AVP levels (P < 0.01). Increasing doses of AVP led to significant increases in TPR at all levels of CSP (P < 0.01). The overall range and gain of the response were not significantly different at any level of AVP infusion. Despite this increase in systemic resistance, there was no significant change in the MAP-CSP relationship. Infusion of AVP led to a dose-dependent depression in CO (P < 0.01) and heart rate (HR; P < 0.05) at all levels of CSP with no significant effect on open-loop baroreflex control. We conclude that although exogenous AVP induces profound changes in cardiovascular function, it does not alter carotid baroreflex control of MAP, TPR, CO, and HR.
6 citations
03 Nov 1994
TL;DR: The authors report on the design and development of an integrated clinical workstation for primary health care that is modular and expandable both in its software and hardware components so that users may select only those modules appropriate to their own roles, clinical practice and levels of expertise.
Abstract: The authors report on the design and development of an integrated clinical workstation for primary health care. The workstation is Windows based, has a sophisticated user interface and supports a wide range of computing platforms from desktop to laptop to handheld notebook computers. The workstation is modular and expandable both in its software and hardware components so that users may select only those modules appropriate to their own roles, clinical practice and levels of expertise. The design focuses on the provision of clinical services and integrates the following key components. 1) Patient records and basic practice management. 2) Clinical records; based on ICD 10, ICPC or Read Code classifications. 3) Clinical measurements; blood pressure, spirometry, ECG and basic haematology and biochemistry. 4) Clinical decision support; based on epidemiological data, protocols and medical expert systems. 5) Domiciliary care and evaluation of functional health status of the elderly. 6) Communications and networks; wireless LAN, ISDN, modem and fax. 7) Clinical reporting; morbidity profiles, prescribing profiles and laboratory services and procedures.
2 citations
03 Nov 1994
TL;DR: The single pacemaker cell model of Wilders et.
Abstract: The single pacemaker cell model of Wilders et. al. (1991) has been modified to simulate the complex negative chronotropic response of cardiac period to brief vagal stimulation. Equations have been added to describe the muscarinic K/sup +/ current i/sub K,ACh/ the [ACh]-modulated pacemaker current i/sub f/, and acetylcholine uptake and release by vagal stimulation. The resulting model is able to reproduce the experimentally observed triphasic response of cardiac period following brief vagal stimulation.
1 citations
03 Nov 1994
TL;DR: The hardware and software which was designed and implemented to perform this study, and a present brief report on the results obtained from the study, are described.
Abstract: The purpose of the present study was to assess carotid baroreflex control of left ventricular contractility in the conscious dog. The authors describe the hardware and software which was designed and implemented to perform this study, and a present brief report on the results obtained from the study. Custom designed software, written in the ASYST language, was used to acquire, display and analyze the hemodynamic data. Variables recorded include mean arterial pressure, carotid sinus pressure, cardiac output, heart rate, left ventricular pressure and left ventricular volume. In order to obtain quantitative data on left ventricular contractility, the conductance catheter technique was employed to measure left ventricular volume. The preload recruitable stroke work was calculated as an index of ventricular contractility. >
03 Nov 1994
TL;DR: The Wilders-Jongsma-van Ginneken single cell model of sinoatrial node electrical activity was found to be unsuitable for simulating autonomic modulation of sinai node rhythm, so the equations were modified by reducing the effects of the large sarcoplasmic reticulum calcium store, and modifying the activation curve of the hyperpolarizing-activated current.
Abstract: The Wilders-Jongsma-van Ginneken single cell model of sinoatrial node electrical activity was found to be unsuitable for simulating autonomic modulation of sinoatrial node rhythm. The equations were modified by reducing the effects of the large sarcoplasmic reticulum calcium store, altering the kinetics of the L-type calcium current, and modifying the activation curve of the hyperpolarizing-activated current i/sub f/. The resulting model was able to reproduce the chronotropic responses of cardiac period to sympathetic and parasympathetic stimulation.