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External Work (external + work)

Distribution by Scientific Domains
Medical Sciences80%

Selected Abstracts

Prediction of the External Work of the Native Heart From the Dynamic H-Q Curves of the Rotary Blood Pumps During Left Heart Bypass

ARTIFICIAL ORGANS, Issue 9 2010
Yoshimasa Yokoyama
Abstract The ventricular performance is dependent on the drainage effect of rotary blood pumps (RBPs) and the performance of RBPs is affected by the ventricular pulsation. In this study, the interaction between the ventricle and RBPs was examined using the pressure-volume (P-V) diagram of the ventricle and dynamic head pressure-bypass flow (H-Q) curves (H, head pressure: arterial pressure minus ventricular pressure vs. Q, bypass flow) of the RBPs. We first investigated the relationships in a mock loop with a passive fill ventricle, followed by validation in ex vivo animal experiments. An apical drainage cannula with a micro-pressure sensor was especially fabricated to obtain ventricular pressure, while three pairs of ultrasonic crystals placed on the heart wall were used to derive ventricular volume. The mock loop-configured ventricular apical,descending aorta bypass revealed that the external work of the ventricle expressed by the area inside the P-V diagrams (EWHeart) correlated strongly with the area inside dynamic H-Q curves (EWVAD), with the coefficients of correlation being R2 = 0.869 , 0.961. The results in the mock loop were verified in the ex vivo studies using three Shiba goats (10,25 kg in body weight), showing the correlation coefficients of R2 = 0.802 , 0.817. The linear regression analysis indicated that the increase in the bypass flow reduced pulsatility in the ventricle expressed in EWHeart as well as in EWVAD. Experimental results, both mock loop and animal studies, showed that the interaction between cardiac external work and H-Q performance of RBPs can be expressed by the relationships "EWHeart versus EWVAD." The pulsatile nature of the native heart can be expressed in the area underneath the H-Q curves of RBPs EWVAD during left heart bypass indicating the status of the level of assistance by RBPs and the native heart function. [source]

Hypervolaemia improves global and local function and efficiency in postischaemic myocardium

CLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 8 2001
FY Du
SUMMARY 1. In the present study, we investigated the effects of blood volume on postischaemic function and efficiency. In 14 anaesthetized dogs, following recovery from a period of 15 min occlusion of the left anterior descending coronary artery, the effects of hypervolaemia (HYPER; 15% increased volume produced by fast infusion of Hespan; B Braun Medical, Irvine, CA, USA), normovolaemia (NORMO) and hypovolaemia (HYPO) were studied. 2. Although myocardial O2 consumption was not significantly increased by volume (6.37±0.94 vs 6.89±1.1 mL/min per 100 g for HYPO and HYPER, respectively), local work of the stunned myocardium was markedly elevated (8.8±1.7 vs 22.5±3.5 g·mm/ beat, for HYPO and HYPER, respectively; P < 0.05). External work of the heart was also significantly improved (71.8±12.7 vs 139.5±16.2 mmHg·L/min for HYPO and HYPER, respectively). These data indicate markedly improved efficiency produced by volume, because work was increased with no change in myocardial O2 consumption. 3. Local dysfunction was characterized by several parameters, including systolic bulge, end-diastolic length, delay to onset of shortening, end shortening time delay (EST) and tail work ratio. Hypervolaemia reduced EST compared with hypovolaemia (98.6±18.3 vs 110.7±14.9 msec, respectively; P < 0.05) and improved tail work ratio (28.0±7.0 vs 36.0±7.0%, respectively; P < 0.05), with no effects on systolic bulge, end-diastolic length and delay to onset of shortening. 4. Thus, even in the postischaemic myocardium, increasing work by volume is energetically efficient and is accompanied by partial improvement of local dysfunction. [source]

Engineering investigations on the potentiality of the thermoformability of HDPE charged by wood flours in the thermoforming part

POLYMER ENGINEERING & SCIENCE, Issue 8 2009
F. Erchiqui
A dynamic finite element method is used to analyze the thermoformability of composites containing wood and a thermoplastic matrix for five different proportions of wood flour. Linear viscoelastic properties can be obtained by small amplitude oscillatory shear tests and the viscoelastic behavior is characterized using the Lodge model. To account for enclosed gas volume, which inflates the thermoplastic composite membrane, a thermodynamic approach is used to express the external work in terms of a closed volume. Pressure load is deduced by thermodynamic law using the Redlich,Kwong gas equation. The Lagrangian method together with the assumption of membrane theory is used in the finite element implementation. In addition, the influence of air flow on thickness and stress and the energy required to form a thin polymeric part in the thermoforming process are analyzed for five different proportions of wood flour in the HDPE material. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers [source]

Prediction of the External Work of the Native Heart From the Dynamic H-Q Curves of the Rotary Blood Pumps During Left Heart Bypass

ARTIFICIAL ORGANS, Issue 9 2010
Yoshimasa Yokoyama
Abstract The ventricular performance is dependent on the drainage effect of rotary blood pumps (RBPs) and the performance of RBPs is affected by the ventricular pulsation. In this study, the interaction between the ventricle and RBPs was examined using the pressure-volume (P-V) diagram of the ventricle and dynamic head pressure-bypass flow (H-Q) curves (H, head pressure: arterial pressure minus ventricular pressure vs. Q, bypass flow) of the RBPs. We first investigated the relationships in a mock loop with a passive fill ventricle, followed by validation in ex vivo animal experiments. An apical drainage cannula with a micro-pressure sensor was especially fabricated to obtain ventricular pressure, while three pairs of ultrasonic crystals placed on the heart wall were used to derive ventricular volume. The mock loop-configured ventricular apical,descending aorta bypass revealed that the external work of the ventricle expressed by the area inside the P-V diagrams (EWHeart) correlated strongly with the area inside dynamic H-Q curves (EWVAD), with the coefficients of correlation being R2 = 0.869 , 0.961. The results in the mock loop were verified in the ex vivo studies using three Shiba goats (10,25 kg in body weight), showing the correlation coefficients of R2 = 0.802 , 0.817. The linear regression analysis indicated that the increase in the bypass flow reduced pulsatility in the ventricle expressed in EWHeart as well as in EWVAD. Experimental results, both mock loop and animal studies, showed that the interaction between cardiac external work and H-Q performance of RBPs can be expressed by the relationships "EWHeart versus EWVAD." The pulsatile nature of the native heart can be expressed in the area underneath the H-Q curves of RBPs EWVAD during left heart bypass indicating the status of the level of assistance by RBPs and the native heart function. [source]