The hemodynamic effects of aortic clamping.

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Impact of varying diastolic pressure fitting technique for the reservoir-wave model on wave intensity analysis

The reservoir-wave model assumes that the measured arterial pressure is made of two components: reservoir and excess. The effect of the reservoir volume should be excluded to quantify the effects of forward and backward traveling waves on blood pressure. Whilst the validity of the reservoir-wave concept is still debated, there is no consensus on the best fitting method for the calculation of the reservoir pressure waveform. Therefore, the aim of this parametric study is to examine the effects of varying the fitting technique on the calculation of reservoir and excess components of pressure and velocity waveforms. Common carotid pressure and flow velocity were measured using applanation tonometry and doppler ultrasound, respectively, in 1037 healthy humans collected randomly from the Asklepios population, aged 35 to 55 years old. Different fitting techniques to the diastolic decay of the measured arterial pressure were used to determine the asymptotic pressure decay, which in turn was used to determine the reservoir pressure waveform. The corresponding wave speed was determined using the PU-loop method, and wave intensity parameters were calculated and compared. Different fitting methods resulted in significant changes in the shape of the reservoir pressure waveform; however, its peak and time integral remained constant in this study. Although peak and integral of excess pressure, velocity components and wave intensity changed significantly with changing the diastolic decay fitting method, wave speed was not substantially modified. We conclude that wave speed, peak reservoir pressure and its time integral are independent of the diastolic pressure decay fitting techniques examined in this study. Therefore, these parameters are considered more reliable diagnostic indicators than excess pressure and velocity which are more sensitive to fitting techniques

Effects Of Iabp Timing On Baroreflex Activities In A Closed Loop Cardiovascular Hybrid Model.

Abstract: Despite 50 years of research to assess the intraaortic balloon pump (IABP) effects on patients' hemodynamics, some issues related to the effects of this therapy are still not fully understood. One of these issues is the effect of IABP, its inflation timing and duration on peripheral circulation autonomic controls.This work provides a systematic analysis of IABP effects on baroreflex using a cardiovascular hybrid model, which consists of computational and hydraulic submodels. The work also included a baroreflex computational model that was connected to a hydraulic model with a 40-cm3 balloon. The IABP was operated at different inflation trigger timings (-0.14 to 0.31 s) and inflation durations (0.05-0.45 s), with time of the dicrotic notch being taken as t = 0. Baroreflex-dependent parameters- afferent and efferent pathway activity, heart rate, peripheral resistance, and venous tone-were evaluated at each of the inflation trigger times and durations considered. Balloon early inflation (0.09 s before the dicrotic notch) with inflation duration of 0.25 s generated a maximum net increment of afferent pathway activity of 10%, thus leading to a decrement of efferent sympathetic activity by 15.3% compared with baseline values.These times also resulted in a reduction in peripheral resistance and heart rate by 4 and 4.3% compared with baseline value. We conclude that optimum IABP triggering time results in positive effects on peripheral circulation autonomic controls. Conversely, if the balloon is not properly timed, peripheral resistance and heart rate may even increase, which could lead to detrimental outcomes. Key Words: Intra-aortic balloon pump- Baroreceptors-Balloon timing-Hybrid model

Influence of arterial compliance on baroreflex activity during IABP assistance. a hybrid model study.

Objectives: The aim of this work is to investigate the influence of arterial compliance on baroreflex mechanism during IABP assistance. Materials & Methods: The hybrid cardiovascular model used in this work embeds: 1) a computational model of the ascending aorta, upper body, kidneys, splanchnic, lower body, pulmonary circulations, left and right hearts, 2) a hydraulic model of the descending aorta containing a 40cc balloon, 3) a baroreflex computational model acting as a feedback control loop of blood pressure. The descending aorta was reproduced using a silicon rubber tube and connected with the computational model through two impedance transformers. Experiments were performed for two values of arterial compliance C1 and C2, each of them composed of a numerical ascending aorta (Cn1=0.5, Cn2=0.15 cm3/ mmHg), and a hydraulic descending aorta (Ch1=1.9 Ch2=1.2 cm3/mmHg). Data on afferent (ANA) and efferent (ENA) nervous activity, peripheral resistance (Ras) and heart rate (HR) were collected and analysed during control and IABP assistance. Results: during IABP assistance two volleys in ANA were observed for each cardiac cycle for both C1 and C2: one caused by left ventricular systole and the other by diastolic pressure augmentation. As a consequence, IABP induces an increment in ANA [spikes/s] of 7.8% (26.3 vs. 24.4, for C1) and 10% (28.2 vs. 25.6, for C2), a decrement in ENA [spikes/s] of 9% (5.6 vs. 6.1, for C1) and 15% (5.9 vs. 6.8, for C2), a decrement of HR [bpm] of 3% (89 vs. 92 for C1) and 6.4% (87 vs. 93 for C2), and a decrement of Ras [mmHg/(cm3/s)] in the peripheral circulatory districts, i.e. for splanchnic resistance of 3% (4.17 vs. 4.3 for C1) and 8% (4.08 vs. 4.4 for C2). Conclusions: Arterial compliance affects ANA volleys and as a consequence baroreflex activity during IABP. Compared to a higher compliance, lower the compliance induces higher increase of ANA, higher decrease in ENA, and higher decrease in Ras and HR

Effects Of Iabp Timing On Baroreflex Activities In A Closed Loop Cardiovascular Hybrid Model.

Abstract: Despite 50 years of research to assess the intraaortic balloon pump (IABP) effects on patients\u27 hemodynamics, some issues related to the effects of this therapy are still not fully understood. One of these issues is the effect of IABP, its inflation timing and duration on peripheral circulation autonomic controls.This work provides a systematic analysis of IABP effects on baroreflex using a cardiovascular hybrid model, which consists of computational and hydraulic submodels. The work also included a baroreflex computational model that was connected to a hydraulic model with a 40-cm3 balloon. The IABP was operated at different inflation trigger timings (-0.14 to 0.31 s) and inflation durations (0.05-0.45 s), with time of the dicrotic notch being taken as t = 0. Baroreflex-dependent parameters- afferent and efferent pathway activity, heart rate, peripheral resistance, and venous tone-were evaluated at each of the inflation trigger times and durations considered. Balloon early inflation (0.09 s before the dicrotic notch) with inflation duration of 0.25 s generated a maximum net increment of afferent pathway activity of 10%, thus leading to a decrement of efferent sympathetic activity by 15.3% compared with baseline values.These times also resulted in a reduction in peripheral resistance and heart rate by 4 and 4.3% compared with baseline value. We conclude that optimum IABP triggering time results in positive effects on peripheral circulation autonomic controls. Conversely, if the balloon is not properly timed, peripheral resistance and heart rate may even increase, which could lead to detrimental outcomes. Key Words: Intra-aortic balloon pump- Baroreceptors-Balloon timing-Hybrid model

Effects of baroreflex activities on IABP hemodynamics in a closed loop hybrid cardiovascular model.

Objectives: Aim of this work is the integration of the autonomic mechanism of pressure regulation during temporary IABP assistance in a hybrid circulatory model. Methods: The hybrid model is based on merging computational and hydraulic models. The lumped parameter computational model includes the upper thoracic aorta, circulatory districts (upper body, kidneys, splanchnic, lower body, pulmonary, coronary circulation) and left/right hearts. The hydraulic model provides a representation of the lower thoracic aorta by a silicon rubber tube containing a 40cc IAB. An additional numerical module provides a representation of the baroreflex mechanism in terms of afferent and efferent sympathetic nerve activity (ANA, ENA). Baroreflex model acts as a feedback control loop that regulates the blood pressure by changing heart rate (HR), peripheral resistance and venous tone of each circulatory district. Experiments were conducted applying IABP assistance to a pathological circulatory condition. Results: The increment of diastolic pressure due to IABP provides an increment of ANA (+7%) and a decrement of ENA(-9%). Operating the IABP induced a reduction in HR by -6% (90 vs. 95 bpm), in kidney and upper body resistances by -5% (5.43 vs. 5.72 and 5.17 vs. 5.44 mmHg?s/mL, respectively). IABP also induced an increment in kidney flow by +7% (0.63 vs. 0.59 L/min) and upper body flow by +6.8% (0.50 vs. 0.46 L/min). By switching the IABP assistance frequency from 1:1 to 1:2 or 1:3 the mentioned effects reduce progressively. Results indicate that the short term effects of IAB are small, even in the presence of a model including baroreflex control. Conclusions: The model provides an instrument for the assessment of IABP effects on baroreflex mechanism due to the increase of mean diastolic blood pressure. This contributes to predict and study the global evolution of hemodynamic condition after IABP activation and the resultant change in organ flows

Effects of baroreflex activities on IABP hemodynamics in a closed loop hybrid cardiovascular model.

Objectives: Aim of this work is the integration of the autonomic mechanism of pressure regulation during temporary IABP assistance in a hybrid circulatory model. Methods: The hybrid model is based on merging computational and hydraulic models. The lumped parameter computational model includes the upper thoracic aorta, circulatory districts (upper body, kidneys, splanchnic, lower body, pulmonary, coronary circulation) and left/right hearts. The hydraulic model provides a representation of the lower thoracic aorta by a silicon rubber tube containing a 40cc IAB. An additional numerical module provides a representation of the baroreflex mechanism in terms of afferent and efferent sympathetic nerve activity (ANA, ENA). Baroreflex model acts as a feedback control loop that regulates the blood pressure by changing heart rate (HR), peripheral resistance and venous tone of each circulatory district. Experiments were conducted applying IABP assistance to a pathological circulatory condition. Results: The increment of diastolic pressure due to IABP provides an increment of ANA (+7%) and a decrement of ENA(-9%). Operating the IABP induced a reduction in HR by -6% (90 vs. 95 bpm), in kidney and upper body resistances by -5% (5.43 vs. 5.72 and 5.17 vs. 5.44 mmHg?s/mL, respectively). IABP also induced an increment in kidney flow by +7% (0.63 vs. 0.59 L/min) and upper body flow by +6.8% (0.50 vs. 0.46 L/min). By switching the IABP assistance frequency from 1:1 to 1:2 or 1:3 the mentioned effects reduce progressively. Results indicate that the short term effects of IAB are small, even in the presence of a model including baroreflex control. Conclusions: The model provides an instrument for the assessment of IABP effects on baroreflex mechanism due to the increase of mean diastolic blood pressure. This contributes to predict and study the global evolution of hemodynamic condition after IABP activation and the resultant change in organ flows