Endothelial cell responses to castor oil-based polyurethane substrates functionalized by direct laser ablation.

Surface-induced thrombosis and lack of endothelialization are major drawbacks that hamper the widespread application of polyurethanes for the fabrication of implantable cardiovascular devices. Endothelialization of the blood-contacting surfaces of these devices may avoid thrombus formation and may be implemented by strategies that introduce micro and submicron patterns that favor adhesion and growth of endothelial cells. In this study, we used laser radiation to directly introduce topographical patterns in the low micrometer range on castor oil-based polyurethane, which is currently employed to fabricate cardiovascular devices. We have investigated cell adhesion, proliferation, morphology and alignment in response to these topographies. Reported results show that line-like and pillar-like patterns improved adhesion and proliferation rate of cultured endothelial cells. The line-like pattern with 1 µm groove periodicity was the most efficient to enhance cell adhesion and induced marked polarization and alignment. Our study suggests the viability of using laser radiation to functionalize PU-based implants by the introduction of specific microtopography to facilitate the development of a functional endothelium on target surfaces.

Particle-image velocimetry study of a pediatric ventricular assist device.

Particle-image velocimetry (PIV) was used to visualize the flow within an optically transparent pediatric ventricular assist device (PVAD) under development in our laboratory. The device studied is a diaphragm type pulsatile pump with an ejection volume of 30 ml per beating cycle intended for temporary cardiac assistance as a bridge to transplantation or recovery in children. Of particular interest was the identification of flow patterns, including regions of stagnation and/or strong turbulence that often promote thrombus formation and hemolysis, which can degrade the usefulness of such devices. For this purpose, phase-locked PIV measurements were performed in planes parallel to the diaphragm that drives the flow in the device. The test fluid was seeded with 10 microm polystyrene spheres, and the motion of these particles was used to determine the instantaneous flow velocity distribution in the illumination plane. These measurements revealed that flow velocities up to 1.0 m/s can occur within the PVAD. Phase-averaged velocity fields revealed the fixed vortices that drive the bulk flow within the device, though significant cycle-to-cycle variability was also quite apparent in the instantaneous velocity distributions, most notably during the filling phase. This cycle-to-cycle variability can generate strong turbulence that may contribute to greater hemolysis. Stagnation regions have also been observed between the input and output branches of the prototype, which can increase the likelihood of thrombus formation.

Critical analysis of autoregressive and fast Fourier transform markers of cardiovascular variability in rats and humans

The autonomic nervous system plays an important role in physiological and pathological conditions, and has been extensively evaluated by parametric and non-parametric spectral analysis. To compare the results obtained with fast Fourier transform (FFT) and the autoregressive (AR) method, we performed a comprehensive comparative study using data from humans and rats during pharmacological blockade (in rats), a postural test (in humans), and in the hypertensive state (in both humans and rats). Although postural hypotension in humans induced an increase in normalized low-frequency (LFnu) of systolic blood pressure, the increase in the ratio was detected only by AR. In rats, AR and FFT analysis did not agree for LFnu and high frequency (HFnu) under basal conditions and after vagal blockade. The increase in the LF/HF ratio of the pulse interval, induced by methylatropine, was detected only by FFT. In hypertensive patients, changes in LF and HF for systolic blood pressure were observed only by AR; FFT was able to detect the reduction in both blood pressure variance and total power. In hypertensive rats, AR presented different values of variance and total power for systolic blood pressure. Moreover, AR and FFT presented discordant results for LF, LFnu, HF, LF/HF ratio, and total power for pulse interval. We provide evidence for disagreement in 23 percent of the indices of blood pressure and heart rate variability in humans and 67 percent discordance in rats when these variables are evaluated by AR and FFT under physiological and pathological conditions. The overall disagreement between AR and FFT in this study was 43 percent.

Critical analysis of autoregressive and fast Fourier transform markers of cardiovascular variability in rats and humans.

The autonomic nervous system plays an important role in physiological and pathological conditions, and has been extensively evaluated by parametric and non-parametric spectral analysis. To compare the results obtained with fast Fourier transform (FFT) and the autoregressive (AR) method, we performed a comprehensive comparative study using data from humans and rats during pharmacological blockade (in rats), a postural test (in humans), and in the hypertensive state (in both humans and rats). Although postural hypotension in humans induced an increase in normalized low-frequency (LFnu) of systolic blood pressure, the increase in the ratio was detected only by AR. In rats, AR and FFT analysis did not agree for LFnu and high frequency (HFnu) under basal conditions and after vagal blockade. The increase in the LF/HF ratio of the pulse interval, induced by methylatropine, was detected only by FFT. In hypertensive patients, changes in LF and HF for systolic blood pressure were observed only by AR; FFT was able to detect the reduction in both blood pressure variance and total power. In hypertensive rats, AR presented different values of variance and total power for systolic blood pressure. Moreover, AR and FFT presented discordant results for LF, LFnu, HF, LF/HF ratio, and total power for pulse interval. We provide evidence for disagreement in 23% of the indices of blood pressure and heart rate variability in humans and 67% discordance in rats when these variables are evaluated by AR and FFT under physiological and pathological conditions. The overall disagreement between AR and FFT in this study was 43%.

A low-cost transmittance transducer for measurement of blood oxygen saturation in extracorporeal circuits.

Designs for a low-cost dual wavelength transducer based on light transmittance and a disposable cuvette for monitoring oxygen saturation (SO2) in extracorporeal arterial and venous blood are presented. The transducer utilizes red and infrared light-emitting diodes and a large photodiode; it is designed to attach to a flow-through cuvette modified from 3/8-in x3/8-in bypass-circuit connectors. A mock extracorporeal circulation system was assembled to evaluate operation of the transducer at a controlled blood SO2 and the relationship between light transmittance and hemodilution. SO2 was calculated based on multiple linear regression analyses. The results show a high correlation between the SO2 obtained with the equipment designed and values measured with commercial gasometric equipment in the range of 50% to 100% (r2 = 0.976, error <2%). The method presented allows continuous and real time measurement of whole blood SO2 with a low-cost transmittance transducer.

Real time monitoring of oxygen saturation in extracorporeal circulation using an optical reflectance transducer.

A novel optical reflectance transducer for continuous and real time monitoring of oxygen saturation (So2) in extracorporeal tubings during cardiopulmonary bypass (CPB) is described. The optical transducer integrates 2 light-emitting diodes and a photodiode. The transducer is attached to the extracorporeal tubing by a transparent flow through a 3/8 x 3/8 inch connector/cuvette. Four transducers were built and evaluated in vitro in a mock extracorporeal system at a controlled So2. The correlation index (r2) between the So2 measured by the transducers and values determined by a commercial blood gas analyzer was 0.998 with an absolute difference < 0.5%. The performance of the transducer was also evaluated during 16 CPB surgeries in patients with an r2 of 0.873 and an absolute difference < 3.5%. The results obtained demonstrate the applicability of the optical reflectance transducer for monitoring So2 in the tubings of the CPB circuit.

Pulsatile ventricular assist device with pericardial inner lining.

Preserved pericardium in contact with blood is not thrombogenic, therefore avoiding the use of anticoagulants, and has excellent mechanical properties. Our objective is to take advantage of these characteristics and build a pulsatile ventricular assist device (VAD) with pericardium used as the inner lining of the blood chamber. A mold is used for the tanning of the pericardium, rendering it with an exact shape. A flexible polymeric structure is designed to serve as a base for the pericardium, guiding it and limiting its rate of strain. It consists of two halves, which when outfitted with the interior pericardium lining and connected to each other, form the blood chamber. This assembly is housed in rigid polyvinyl chloride (PVC) shells making up the air chamber for the pneumatic activation. Valves are likewise made of pericardium. Sealing of the chambers was tested statically up to 300 mm Hg with no air or fluid leakage. The device was tested for 60 continuous days in a mock loop, demonstrating hydrodynamic performance adequate for ventricular assist. Micrographs (confocal laser and scanning electron microscopy) were obtained of several pericardium areas, especially on the flexing regions that are a transition between the wet and dry regions. No sign of damage to the pericardium was observed either with the naked eye or at the microscopic level. From the hydraulic performance and materials viewpoints, a completely pericardium-lined pulsatile VAD displaying a polymeric structure that avoids unpredictable bending and limits strain is feasible. The results warrant further studies regarding biocompatibility and strength advantages.

Mechanical behavior and stability of the internal membrane of the InCor ventricular assist device.

This paper describes and analyzes the mechanical behavior of the internal membrane of the InCor VAD (Heart Institute [InCor], University of São Paulo, Brazil), applying the knowledge and tools of structural engineering analysis. This membrane plays an important role in the operation of the ventricular assist device (VAD) because it separates the blood chamber from the pneumatic one, transmitting the pneumatic load to the blood, thus making the desired blood flow possible. The loading repeats itself every time the VAD beats. Therefore the performance, reliability, and durability of the membrane are critical for the performance of the VAD. The mathematical model is based on the large deflection theory of thin shells and on the finite element method. The snap-through instability phenomenon, which is responsible for transmission of the pneumatic load to the blood, was observed in the membrane both when modeled mathematically and experimentally. Principal stresses and strain distributions were obtained with this model at certain load levels along the pre- and postbuckling paths.

A new approach to the study of latissimus dorsi muscle vasoreactivity in rats.

In this paper we describe a new approach to the study of changes in latissimus dorsi (LD) muscle microcirculation in rats. The experiments were carried out under anesthesia in normal male Wistar rats (C, n = 6) and in diabetes-induced rats (D, streptozotocin, 50 mg/kg, i.v., n = 6). The left LD muscle was exposed in order to preserve the proximal tendon with its thoracodorsal nerve and artery. The animal was kept in lateral decubitus over a heating board attached to the mechanical stage of the intravital microscope. The ventral surface of the muscle was exposed over a transparent plate and fixing. The image of the LD vascularization was transferred to the camera system, which was connected to a microcomputer equipped with software (KS-300, Kontron Elektronik, Munich, Germany) for image storage. The vasoreactivity of LD was analyzed by changes in arteriole diameter after topically administered noradrenaline (0.3 microg/ml) and acetylcholine (300 microg/ml). The microscopic image provided by the described optical setup permitted clear resolution of capillary vessels and a stable preparation over a period of 3-4 h. D rats showed increased vasodilatation (29 +/- 2% vs. 18 +/- 2.6% in C) and similar vasoconstriction (25.5 +/- 3% vs. 27.5 +/- 3.3% in C) as compared to C rats. The method described in this paper is suitable for the study of changes in responsiveness of LD arterioles, vessels which represent the major site of vascular resistance and are most actively involved in the control of tissue perfusion.

Nonstimulated cardiomyoplasty improves hemodynamics in myocardial-infarcted rats.

Cardiomyoplasty has been proposed as an alternative surgical treatment for congestive heart failure. The girdling effect of the muscle wrap is believed to reduce diastolic wall stress. We tested the hypothesis that nonstimulated or passive cardiomyoplasty (CDM) would reduce hemodynamic deficits in rats with experimentally induced myocardial infarction (MI). Four groups of animals were studied: intact (C, n = 6), CDM (n = 6), MI by ligation of the left coronary artery (n = 6), and left latissimus dorsi CDM performed 14 days post-MI (MI + CDM, n = 6). All groups were studied 8 weeks after MI and/or CDM or from the beginning of the experiment in controls. MI rats had a lower mean arterial pressure and higher end-diastolic pressure (EDP) compared with controls. End-diastolic pressure (EDP) and the left ventricular-body weight ratio (LV/BW) were reduced in the MI group after CDM. These data suggest that passive girdling of the heart provided by CDM may improve post-MI cardiac function.

Acute AT1 receptor blockade does not improve the depressed baroreflex in rats with chronic renal hypertension.

To assess the role of angiotensin II in the sensitivity of the baroreflex control of heart rate (HR) in normotensive rats (N = 6) and chronically hypertensive rats (1K1C, 2 months, N = 7), reflex changes of HR were evaluated before and after (15 min) the administration of a selective angiotensin II receptor antagonist (losartan, 10 mg/kg, iv). Baseline values of mean arterial pressure (MAP) were higher in hypertensive rats (195 +/- 6 mmHg) than in normotensive rats (110 +/- 2 mmHg). Losartan administration promoted a decrease in MAP only in hypertensive rats (16%), with no changes in HR. During the control period, the sensitivity of the bradycardic and tachycardic responses to acute MAP changes were depressed in hypertensive rats (approximately 70% and approximately 65%, respectively) and remained unchanged after losartan administration. Plasma renin activity was similar in the two groups. The present study demonstrates that acute blockade of AT1 receptors with losartan lowers the MAP in chronic renal hypertensive rats without reversal of baroreflex hyposensitivity, suggesting that the impairment of baroreflex control of HR is not dependent on an increased angiotensin II level.

Acute AT1 receptor blockade does not improve the depressed baroreflex in rats with chronic renal hypertension

To assess the role of angiotensin II in the sensitivity of the baroreflex control of heart rate (HR) in normotensive rats (N = 6) and chronically hypertensive rats (1K1C, 2 months, N = 7), reflex changes of HR were evaluated before and after (15 min) the administration of a selective angiotensin II receptor antagonist (losartan, 10 mg/kg, iv). Baseline values of mean arterial pressure (MAP) were higher in hypertensive rats (195 ± 6 mmHg) than in normotensive rats (110 ± 2 mmHg). Losartan administration promoted a decrease in MAP only in hypertensive rats (16 percent), with no changes in HR. During the control period, the sensitivity of the bradycardic and tachycardic responses to acute MAP changes were depressed in hypertensive rats (~70 percent and ~65 percent, respectively) and remained unchanged after losartan administration. Plasma renin activity was similar in the two groups. The present study demonstrates that acute blockade of AT1 receptors with losartan lowers the MAP in chronic renal hypertensive rats without reversal of baroreflex hyposensitivity, suggesting that the impairment of baroreflex control of HR is not dependent on an increased angiotensin II level

Oxidative stress in the latissimus dorsi muscle of diabetic rats

The purpose of the present study was to investigate the effects of experimental diabetes on the oxidant and antioxidant status of latissimus dorsi (LD) muscles of male Wistar rats (220 +/- 5 g, N = 11). Short-term (5 days) diabetes was induced by a single injection of streptozotocin (STZ, 50 mg/kg, iv; glycemia >300 mg/dl). LD muscle of STZ-diabetic rats presented higher levels of thiobarbituric acid reactive substances (TBARS) and chemiluminescence (0.36 +/- 0.02 nmol/mg protein and 14706 +/- 1581 cps/mg protein) than LD muscle of normal rats (0.23 +/- 0.04 nmol/mg protein and 7389 +/- 1355 cps/mg protein). Diabetes induced a 92 percent increase in catalase and a 27 percent increase in glutathione S-transferase activities in LD muscle. Glutathione peroxidase activity was reduced (58 percent) in STZ-diabetic rats and superoxide dismutase activity was similar in LD muscle of both groups. A positive correlation was obtained between catalase activity and the oxidative stress of LD, as evaluated in terms of TBARS (r = 0.78) and by chemiluminescence (r = 0.89). Catalase activity also correlated inversely with glutathione peroxidase activity (r = 0.79). These data suggest that an increased oxidative stress in LD muscle of diabetic rats may be related to skeletal muscle myopathy

Oxidative stress in the latissimus dorsi muscle of diabetic rats.

The purpose of the present study was to investigate the effects of experimental diabetes on the oxidant and antioxidant status of latissimus dorsi (LD) muscles of male Wistar rats (220 +/- 5 g, N = 11). Short-term (5 days) diabetes was induced by a single injection of streptozotocin (STZ, 50 mg/kg, iv; glycemia >300 mg/dl). LD muscle of STZ-diabetic rats presented higher levels of thiobarbituric acid reactive substances (TBARS) and chemiluminescence (0.36 +/- 0.02 nmol/mg protein and 14706 +/- 1581 cps/mg protein) than LD muscle of normal rats (0.23 +/- 0.04 nmol/mg protein and 7389 +/- 1355 cps/mg protein). Diabetes induced a 92% increase in catalase and a 27% increase in glutathione S-transferase activities in LD muscle. Glutathione peroxidase activity was reduced (58%) in STZ-diabetic rats and superoxide dismutase activity was similar in LD muscle of both groups. A positive correlation was obtained between catalase activity and the oxidative stress of LD, as evaluated in terms of TBARS (r = 0.78) and by chemiluminescence (r = 0.89). Catalase activity also correlated inversely with glutathione peroxidase activity (r = 0.79). These data suggest that an increased oxidative stress in LD muscle of diabetic rats may be related to skeletal muscle myopathy.

Aging and baroreflex control of RSNA and heart rate in rats.

Aging is associated with altered autonomic control of cardiovascular function, but baroreflex function in animal models of aging remains controversial. In this study, pressor and depressor agent-induced reflex bradycardia and tachycardia were attenuated in conscious old (24 mo) rats [57 and 59% of responses in young (10 wk) Wistar rats, respectively]. The intrinsic heart rate (HR, 339 +/- 5 vs. 410 +/- 10 beats/min) was reduced in aged animals, but no intergroup differences in resting mean arterial blood pressure (MAP, 112 +/- 3 vs. 113 +/- 5 mmHg) or HR (344 +/- 9 vs. 347 +/- 9 beats/min) existed between old and young rats, respectively. The aged group also exhibited a depressed (49%) parasympathetic contribution to the resting HR value (vagal effect) but preserved sympathetic function after intravenous methylatropine and propranolol. An implantable electrode revealed tonic renal sympathetic nerve activity (RSNA) was similar between groups. However, old rats showed impaired baroreflex control of HR and RSNA after intravenous nitroprusside (-0.63 +/- 0. 18 vs. -1.84 +/- 0.4 bars x cycle(-1) x mmHg(-1) x s(-1)). Therefore, aging in rats is associated with 1) preserved baseline MAP, HR, and RSNA, 2) impaired baroreflex control of HR and RSNA, and 3) altered autonomic control of resting HR.

A simplified single pump circuit for cardiac bypass with autogenous oxygenation.

A simplified extracorporeal circulation (ECC) assemblage with autogenous oxygenation (AO) using a single centrifugal pump was tested in dogs. The transpulmonary gradient was obtained by increasing pressure in the right atrium through volume expansion and decreasing it in the left atrium by collecting the blood from the pulmonary veins in a reservoir placed below the level of the animal, generating a siphon effect. This arrangement dispenses with a right side pump. The heart was electrically fibrillated after perfusion was started and defibrillated at the end of the bypass. This ECC circuit allowed the maintenance of adequate hemodynamic and blood gas parameters during the bypass. The operating field and the mobility of the heart were equivalent to that of conventional cardiopulmonary bypass (CPB). We conclude that the use of a single centrifugal pump simplifies the autogenous oxygenation approach, making it a practical choice for the coronary artery bypass graft (CABG) procedure.

Canine latissimus dorsi muscle: an apparatus for isometric force measurements.

This paper describes a device used to measure the isometric forces generated during electrical stimulation of the canine latissimus dorsi muscle in vivo with a preserved neurovascular supply. This device uses 2 strain gauge force sensors linked to a movable alignment frame to which the muscle is attached. The muscle length is controlled by the application of known weights to the system. The device has a frequency of response of 17.5 Hz and compliance of approximately 0.1 mm N(-1), and its experimental performance was tested in the anesthetized mongrel dog.

Relaçäo temporal entre atividade neurogênica dos pressoreceptores e atividade simpática periférica e labilidade da pressäo arterial / Temporal relation between neurogenic activity of pressoreceptors and peripheral sympathetic activity and arterial pressure lability

O objetivo desse estudo foi avaliar a atividade neurogênica dos pressoreceptores (APR, registrada no nervo aórtico) e a atividade simpática periférica (ASR, registrada no nervo simpático renal), considerando-se a ocorrência e distribuição nos ciclos cardíacos e nas fases sistólica e diastólica. Foram estudados ratos normais anestesiados e ratos acordados submetidos à desnervação sino-aórtica (DSA) nas fases aguda e crônica após a desnervação. Os resultados obtidos sugerem que a falta de sincronismo entre a atividade simpática e os ciclos da pressão arterial contribuem para as alterações encontradas na pressão sanguínea na ausência dos pressoreceptores

Abstract - The aim of this study was to analyze the neurogenic activity of baroreceptors (recorded on the aortic nerve, APR) and peripheral sympathetic activity (recorded on the renal nerve. AsR ) with regard to its occurence and distribution in relation to the cardiac cycle and the systolic and diastolic phases of it. Normal anesthetized rats and awaken sino aortic denervated (SAD) rats were studied. The analysis showed that the existing synchronism between sympathetic activity and arterial pressure pulses found in normal rats was absent in SAD rats. These results suggest that the Jack of synchronism between sympathetic activity and cardiac cycles may contribute to the alterations in blood pressure observed in the absence of baroreceptors

Changes of renal sympathetic activity in acute and chronic conscious sinoaortic denervated rats.

The arterial pressure level attained in sinoaortic denervated rats depends on the net effect of eliminating excitatory and inhibitory influences (chemoreceptor and baroreceptor elimination, respectively). After sinoaortic denervation is completed, the hypertension usually observed within the first few days is followed by normotension at the chronic stages. In this work renal sympathetic nerve activity was measured in conscious, unrestrained rats 6 hours (acute) and 20 days (chronic) after sinoaortic denervation. Increased arterial pressure (154 +/- 10 versus 114 +/- 3 mm Hg in controls) and renal sympathetic nerve activity (32 +/- 5 versus 13 +/- 2 bars per cycle in controls) with no changes in heart rate (404 +/- 17 vs 380 +/- 26 beats per minute) were observed in rats with acute sinoaortic denervation. In rats with chronic sinoaortic denervation, arterial pressure (119 +/- 8 mm Hg) and renal sympathetic nerve activity (13 +/- 6 bars per cycle) returned to control levels. Bradycardiac and tachycardiac responses to changes in blood pressure were reduced to 88% and 89%, respectively, in rats with acute sinoaortic denervation and 76% and 74%, respectively, in rats with chronic sinoaortic denervation. The reflex control of renal sympathetic nerve activity after acute and chronic sinoaortic denervation showed an impairment of sympathoinhibition (0.13 +/- 0.02 and 0.25 +/- 0.1 bars per cycle, respectively, versus 0.9 +/- 0.17 bars per cycle in controls). Sympathoexcitatory responses also were impaired in rats with acute and chronic sinoaortic denervation (0.08 +/- 0.03 and 0.37 +/- 0.1 bars per cycle, respectively, compared with 0.98 +/- 0.2 bars per cycle in controls).(ABSTRACT TRUNCATED AT 250 WORDS)