G. Palagi

Blood pressure evaluation based on arterial pulse wave velocity

Pulse wave transit time assessment and peripheral pressure waveform analysis are being developed for noninvasive estimation of arterial blood pressure. In the present work we investigate the dependence of the pulse wave velocity from the aortic pressure by an appropriate mathematical model and by an ad hoc developed computerised acquisition system of blood pressure waveform and sphygmic wave during cath-lab session. The relationship between the ECG, the peripheral plethysmographic wave and the intra-aortic pressure have been studied in detail. The pulse wave has been detected by means of a transmission photo-plethysmographic device (located at the ear lobe) while the aortic pressure waveform is acquired by means of a fluid-filled pressure transducer. The selected operative condition allows signal acquisition in different controlled situations following specified experimental protocols (rest condition, hand grip and Valsalvas manoeuvre). The acquisition system is composed of a PC equipped with an acquisition board. The signals, acquired at a sampling frequency of 2000 Hz, to assure the necessary time resolution, and on-line displayed are: one lead ECG, the peripheral pulse wave and the aortic pressure. An algorithm has been properly developed for the delay evaluation between R wave, aortic pressure and pulse wave onset. Beat to beat systolic, diastolic and mean aortic pressure values have been carried out. The collected data have been investigated from the statistical point of view looking for appropriate correlation between the pressure and two delays: R wave - aortic pulse; aortic pulse - peripheral pulse wave. The diastolic pressure seems more estimable in the arterial path.

The effect of mitral annuloplasty on left ventricular regional diastolic function: a finite element model

The surgical procedure of mitral valve repair is often accompanied by the insertion of a semirigid or flexible annular ring. An important effect of the insertion of small rings is a major reduction of the chamber volume and then a better ventricular performance. To evaluate this effect, a finite element model of the left ventricle has been developed. The geometry of the 3D ventricular structure has been modelled with a truncated ellipsoid. The diastolic mechanical properties of the ventricular walls have been modelled by means of a nonlinear isotropic hyperelastic material; the parameters of the constitutive equations have been chosen on the basis of the expected end diastolic pressure-volume relations. The simulations showed a reduction in the end diastolic volumes with an increase in diastolic wall stress in the equatorial and basal regions. The results suggest that a tailored annuloplasty results to be more effective.

Cardioreduction and mitral valve repair in dilated cardiomyopathy: a model-based study

Cardiac transplantation is the treatment of reference for refractory cardiac failure but the limited number of donors, the complication inherent to transplantation and the relative and absolute contra-indications has made it necessary to find alternative surgical solutions. For the surgical treatment of dilated cardiomyopathy two different procedures are used, together or separately: mitral valve repair and left ventricular volume reduction (Batista procedure). The first procedure consists in the correction of the mitral insufficiency and has its target in the reduction of the volume overload supported by the dilated ventricle. The second procedure consists in the excision of a portion of the free wall of the dilated ventricle and has its target in the reduction of wall shear stress. In order to investigate the single importance and the interaction between the two procedures, a lumped parameters, non-linea< timevarying model of global cardiovascular system, during the ejection phase of the cardiac cycle, has been developed. The eflect of the Batista procedure has been taken into account by a viscoelastic two compartments model of the left ventricle. A dilated ventricle underwent three separate procedure: 1. mitral repair; 2. Batista procedure, 3. mitral repair and Batista procedure. All the procedures reduced wall stress: the stroke volume was maintained by the mitral repair and decreased by the Batista procedure. The best option seems to be a mitral repair with a localized reduction of the ventricular volume.

A computerized multiparametric approach for the evaluation of cardiovascular risk in hypertensive patients

In order to evaluate the factor of cardiovascular risk in hypertensive patients, the most common measured physiological parameter is the arterial blood pressure (BP), often leaving out of considerations other important cardiovascular parameters, such as mechanical arterial compliance. To better evaluate the inherent variability of blood pressure, with respect to the control of cardiovascular system and situational determinants, a computerised system has been developed. By means of a PC, equipped with a 12 bits A/D board, BP, heart rate patient voice and posture and external temperature have been acquired. The systolic, diastolic, and mean values of BP and the heart rate have been continuously, beat-to-beat, acquired with a Finapres, while ad hoc developed sensors have been used to acquire the other parameters. The signals, acquired in the different detected situations, have been processed by means of a software developed in LabView environment. A linear regression of systolic blood pressure and RR interval in agreement with the Karemaker equation, is carried out, evaluating the baroceptorial system sensitivity. The developed system may be usefully exploited in the investigation of the baroceptorial reflex and the of control mechanism of cardiovascular system. Moreover, the multiparametric accomplished analysis method could be used in the evaluation and in the setting up of pharmacological interventions.

Diagnostic errors in automatic ECG analysis of signals reconstructed by irreversible compressors

Data compression techniques are mostly applied to electrocardiogram (ECG) digital transmission over a low-capacity channel. The authors consider irreversible compressors that are more efficient than reversible compressors. Many effective compression techniques have been studied and described in the literature. In the past few years the SCP/AIM project set up an ad hoc commission that prepared an analysis of some popular methods. The purpose is to evaluate some compression methods already studied by the SCP/AIM project. An evaluation is given of the errors on the wave measurements and on the diagnostic stability in the reconstruction of the ECG signal using an irreversible compression technique.<<ETX>>