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Biomedical subjects

I A Cestari

Publications and source records attributed to I A Cestari.

At least 19 recordsLinked to original sources
PubMed2001

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.

Extracorporeal Circulation↗
PubMed2001

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.

Animals↗
PubMed2001

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.

Equipment Design↗
PubMed2001

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.

Biocompatible Materials↗
PubMed2001

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.

Animals↗
PubMed2001

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.

Animals↗
PubMed2000

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.

Aging↗
PubMed2000

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.

Animals↗
PubMed2000

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.

Angiotensin II↗
PubMed1999

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.

Animals↗
PubMed1997

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.

Animals↗
PubMed1995

Effects of muscle length, frequency of stimulation, and fatigue on the isometric tension in canine latissimus dorsi.

An experimental protocol was designed to study the mechanical response of the canine latissimus dorsi muscle stimulated to contract isometrically. Active and passive tensions were measured with the muscle's initial length varying within 10% of its physiologic length in situ. The force-frequency relationship was obtained at frequencies of stimulation of 1, 10, 15, 30, and 60 Hz. Muscle fatigability was assessed during 3 min of successive contractions. Tests were performed in pedicled muscles of anesthetized mongrel dogs (n = 10). Force-length characteristics were found to affect evoked tension markedly. Maximal active tension was generated near the muscle length in situ. Specific isometric tension measured with unit pulse stimulation was 2 +/- 0.4 N/cm2, and the time to peak twitch was 92.8 +/- 2.67 ms. With 60 Hz of stimulation frequency, the tension was 9.31 +/- 0.32 N/cm2, and the time to peak tension was 216.05 +/- 16.28 ms. After the fatigue test, the tension generated decreased to 62.5% of its initial value, and this decline was paralleled by the rate of tension development and tension relaxation.

Animals↗
PubMed1995

Extracorporeal circulation with autogenous oxygenation: hemodynamic and gasometric parameters.

Ten experimental perfusions with autogenous oxygenation were performed in mongrel dogs to evaluate the efficacy of the procedure in maintaining normal hemodynamic the efficacy of the procedure in maintaining normal hemodynamic conditions and adequate blood gases for 1 h. Blood was drained from the right and left atria and pumped to the pulmonary artery and aorta, respectively. Two closed circuits containing compliant chambers and roller pumps were utilized. Artificial ventilation with an FiO2 of 50% were used in 5 animals and with an FiO2 level of 30% in the other 5. EKG, cardiac output, aortic, pulmonary artery, and left atrium pressures were registered. Pulmonary tissue was biopsied after perfusion. The heart was electrically fibrillated after perfusion was established and defibrillated at the end of the bypass. The procedure was able to maintain blood gases and pulmonary, aortic, and left atrial pressures within normal ranges during the perfusion. The mobility of the heart and the access to all coronary arteries was excellent. Clinical central nervous system evaluation, EKG tracings, and pulmonary histological exams showed no adverse effects of perfusion. We conclude that the technique employed may present a suitable proceeding for extracorporeal circulation in closed heart surgeries, and its clinical application should be evaluated as a safe and economical alternative.

Animals↗
PubMed1995

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)

Analysis of Variance↗
PubMed1994

Restoration of arterial blood oxygen tension increases arterial pressure in sinoaortic-denervated rats.

The objective of the present study was to analyze whether the hypoxemia produced by chemoreceptor elimination influences the arterial pressure level after sinoaortic denervation (SAD) in rats. Hypoxemia and hypercapnia were observed in acute (1 day) and chronic (20 days) SAD rats [arterial PO2 (PaO2) = 65 +2- 1.6 and 71 +2- 2.2 mmHg and arterial PCO2 (PaCO2) = 46 +/- 1.3 and 37 +/- 1.8 mmHg, respectively] compared with control rats (PaO2 = 85 +/- 1.6 mmHg, PaCO2 = 31 +/- 1.07 mmHg). Increasing inspired PO2 (PIO2) from 138 mmHg (room air) to 155 mmHg restored the PaO2 of SAD rats to control levels (acute = 81 +/- 2.21 mmHg, chronic = 85 +/- 2.35 mmHg). PaO2. restoration produced pronounced elevation of mean arterial pressure (MAP) of acute (from 121 +/- 4 to 147 +/- 3.5 mmHg) and chronic (from 121 +/- 3 to 134 +/- 3.5 mmHg) SAD rats. Progressive stepwise increase of PIO2 (from 138 to 175, 210, and 235 mmHg) produced no additional elevation of MAP of acute (113 +/- 4, 137 +/- 5, 143 +/- 5, and 147 +/- 5 mmHg) and chronic (111 +/- 3.6, 131 +/- 7.4, 130 +/- 8.7, and 130 +/- 7 mmHg) SAD rats. Otherwise, the arterial pressure of control rats remained unchanged to progressive stepwise increase of PIO2 (118 +/- 5, 117 +/- 4, 118 +/- 4, 116 +/- 4 mmHg). These data suggest that the elimination of chemoreceptors in SAD rats produces hypoxemia responsible for hypotensive influences that counteract the pressor effects produced by baroreceptor elimination.

Animals↗
PubMed1991

Alternative parameters for evaluating the performance of skeletal muscle in cardiac assistance.

This article describes a system designed to study the force, intramuscular pressure (IP), thickening (TH), and electromyographic (EMG) activity of the latissimus dorsi muscle in response to electrical stimulation. Experiments were carried out on fresh unconditioned muscles freed from the left flank insertion and fixed to contract isometrically. Statistical analysis of the data obtained demonstrated that IP and EMG activity were linearly related to force. The thickening of the muscle was found to be sensitive only to large variations in force, in a linear fashion.

Animals↗
PubMed1991

The relationship between renal sympathetic nerve activity and arterial pressure after selective denervation of baroreceptors and chemoreceptors.

The relationship between an acute increase in arterial pressure and renal sympathetic nerve activity produced in rats under chloralose anesthesia after carotid and sinoaortic denervation was analyzed by quantifying the nerve activity associated with arterial pressure changes. After sinus denervation there was no change in arterial pressure (125 +/- 2.3 vs 124.6 +/- 5 mmHg, N = 6), but the renal sympathetic nerve activity (10.8 +/- 0.9 vs 8.0 +/- 1.1 bars s-1 cycle-1, N = 6) was significantly decreased. In spite of this, baroreflex control of renal sympathetic nerve activity was the same as during the control period. After sinoaortic denervation, there were simultaneous increases in arterial pressure (from 124 +/- 2.3 to 188 +/- 6 mmHg, N = 6) and renal sympathetic nerve activity (from 10.8 +/- 0.9 to 13.7 +/- 2.9 bars s-1 cycle-1) with marked attenuation of the baroreflexes. Spectral analysis of arterial blood pressure after sinus denervation showed a shift of a 1-Hz peak to 0.7 Hz, probably related to a decrease in respiratory frequency. The results suggest that after sinoaortic denervation the acute increase in arterial pressure is only due to aortic denervation.

Animals↗