Showing papers on "Pulsatile flow published in 1974"

Effects of hypothalamic deafferentation on the pulsatile rhythm in plasma concentrations of luteinizing hormone in ovariectomized rats.

Abstract: Plasma LH concentrations were measured by radioimmunoassay in blood collected at 10-min intervals through atrial cannulas implanted in long-term ovariectomized rats. Regular fluctuating levels of the hormone were recorded in which plasma LH concentration rose rapidly to a peak every 20–40 min. Interruption of the anterior nerve projections to the medial basal hypothalamus (MBH) by deafferentation with a small stereotaxic knife rendered rats acyclic and resulted in a persistently cornified vaginal epithelium (constant estrus). Although these neural afferents were necessary for an ovulatory discharge of LH, the anterior deafferentation procedure did not block either the post-castration rise in plasma LH or the pulsatile discharge of hormone in the same rats when they were ovariectomized 4–6 weeks after deafferentation.Similarly, an extended frontal or an anterior-lateral cut resulted in constant estrus and permitted the pulsatile circulating levels of LH after ovariectomy. Posterior-lateral deafferentation ...

Pulsatile Growth Hormone Secretion: Suppression by Hypothalamic Ventromedial Lesions and by Long-Acting Somatostatin

Abstract: Sequential blood samples, obtained from freely behaving, nonstressed male rats, showed a pulsatile pattern of growth hormone secretion with a mean interval between peaks of 68 minutes. The bursts of secretion were blocked by lesions of the hypothalamic ventromedial nuclei and by administration of a longacting preparation of synthetic somatostatin.

Pulsatile flow in pulmonary artery, capillary, and vein in the dog.

Abstract: The temporal relationship of flow pulses in the pulmonary artery, capillaries, and veins was investigated in 10 chronic dog preparations with pulsed ultrasonic flowmeters and a nitrous oxide-body plethysmograph for capillary flow. Implanted pressure transducers in the left atrium provided reference to the conventional atrial pulses: A, C, X-descent, V, and Y-descent. Left atrial contraction produced an A-wave pressure transient followed by retrograde flow up the veins. The C-pressure pulse occasionally produced a minimal trough in the venous flow pattern. Early in ventricular systole, X-descent in left atrial pressure preceded a venous flow pulse of modest amplitude, which began prior to the onset of the pulse of capillary flow. On average, right ventricular ejection was followed in 37 msec by the major flow pulse in the capillaries, which in turn was followed 68 msec later by the onset of venous flow. This venous flow pulse was simultaneous with a rise in left atrial pressure, the V-wave. With the onset of diastole, the Y-descent in atrial pressure preceded a major venous flow pulse. With accelerated heart rate, separation of the V and Y venous flow pulses was lost, and a monophasic pulse was found.

Localization of the inhibitory actions of ovulation-blocking drugs on release of luteinizing hormone in ovariectomized rats.

Abstract: Plasma LH concentrations were meas-ured by radioimmunoassay in blood withdrawn through atrial cannulas at 10-min intervals in longterm ovariectomized rats. Urethane (1.5 g/kg body wt) or phenobarbital (75 mg/kg body wt) injected ip inhibited the pulsatile discharge of the hormone and depressed plasma LH concentration for over 2 hr. Partial or total deafferentation of the medial basal hypothalamus 4–6 weeks prior to ovariectomy did not interfere with the pulsatile rhythm in high plasma LH concentration after ovariectomy and injection of urethane or phenobarbital inhibited LH release in these deafferented rats as effectively as in nondeafferented animals. An ip injection of pen-tobarbital (32 mg/kg body wt) caused a marked but temporary depression in plasma LH concentration. Within 1 hr after administration of pentobarbital, the pulsatile fluctuations in plasma LH had re-sumed. Continuous deep ether anesthesia sup-pressed the pulsatile rhythm in plasma LH but levels remained steady in the low range of pretr...

Network model of pulsatile hemodynamics in the microcirculation of the rabbit omentum

Abstract: GROSS, JOSEPH F., MARCOS INTAGLIETTA, AND BENJAMIN W. ZWEIFACH. Network model of pulsatile lzemodynamics in the microcirculation of the rabbit omentum. Am. J. Physiol. 226(5) : 1117-l 123. 1974.-Pulsatile pressure and red cell velocities were measured throughout the microvasculature of the rabbit omentum as a function of the order of branching. The data were analyzed in terms of a network model that incorporates known structural properties of the microvessels at each level of branching. Pulsatile effects are described by a “pressure diffusion” equation, where the diffusion coefficient is determined by the dimensions and mechanical properties of the . microvessels at each order of branching. Experimental and theoretical results show that measurable pressure and velocity pulsatile effects persist through this microvascular bed. Pressure and flow amplitudes were found to decay and the corresponding phase was found to increase, which indicates that this microcirculatory network behaves as a relatively compliant system. Effects in the semipermeable microvessels could be accounted for by compliance due to exchange as well as by compliance due to elasticity. Pressure amplitude and phase were found to be a more sensitive index of changes in structural properties in the microcirculation than corresponding velocity effects.

Quantitation of valvular insufficiency by computerized radionuclide angiocardiography

Abstract: Linear differential equation techniques for modeling tracer dynamics that assume constant flow rates and fixed chamber volumes are not totally suitable for describing the pulsatile conditions of cardiac tracer dynamics. In this paper, z-transformation methods for solving finite difference equations have resulted in a set of solutions for a pulsatile flow model of the atrial-ventricular-arterial system that accurately describes the cardiac dynamics associated with valvular insufficiency. This model can be applied to data extracted from radionuclide angiocardiographic studies on patients with mitral or aortic insufficiency as well as tricuspid or pulmonary insufficiency. Application of the model requires that the proximal atrium be labeled by a discrete bolus injection of radionuclide. Rapid sequential scintigraphic images are then recorded by an Anger camera-computer system, and the time-activity curves extracted from the resulting dynamic data are representative of the activity in the atrium and ventricle as functions of time. Determination of at most four parameters from this pair of curves then permits quantitation of total, forward and regurgitant ejection fractions and regurgitant fractions. In addition, end-diastolic and end-systolic cardiac chamber volumes can be computed from forward stroke volume. These quantities, determined by radionuclide angiocardiographic methods in 12 patients with mitral or aortic insufficiency, are compared with results from conventional contrast angiographic studies.

An esophageal Doppler probe for aortic flow velocity monitoring.

Abstract: An ultrasonic Doppler transducer suitable for intra-esophageal use in humans has been constructed, tested, and its function as a flow monitoring device assessed on a series of 15 unselected anaesthetized human subjects undergoing surgery. Doppler flow signals from the descending thoracic aorta have been obtained in all cases. Once correctly positioned, the probe can give continuous qualitative monitoring of pulsatile aortic blood flow velocity for extended periods. It is possible to observe flow waves in the descending thoracic aorta from the aortic arch distally for about 20 cm and observe the change from disturbed to laminar flow patterns over this length.

Stiffness of cerebral arteries--its role in the pathogenesis of cerebral aneurysms.

Abstract: Distensibility of human cerebral arteries was compared quantitatively with extracranial arteries using a parameter which was obtained from the pressure-radius data. It was found that cerebral arteries were much stiffer than the extracranial arteries of comparative sizes. The stifiness of cerebral arteries reached nearly maximum at the middle age and did not progress thereafter. Effect of arterial stiffness on blood flow was also examined using pulsatile flow in polymer tubes with different distensibility under the influence of sinusoidally oscillating pressure. The stiffer the tube was, the higher was pulsatile pressure. It is concluded that much larger fluctuation of pressure may occur in the cerebral arteries compared with extracranial arteries and induce the degenerative change or structural weakness in the wall, especially at the apex of bifurcation, which may play important roles in the pathogenesis of cerebral aneurysms and the mechanism of their growth and rupture.

Central flow prosthetic cardiac valve

Abstract: A central flow prosthetic cardiac valve for disposition in the heart and the aorta for controlling the pulsatile flow of blood into and from the heart, having a plurality of valve flaps for positive opening and closing of the valve during pulsatile flow of the blood.

Hydromechanical simulation of systemic circulation.

Abstract: A hydromechanical model is developed for the simulation of the arterial systemic circulation. The geometry and elastic properties of arteries, the pulse-rate and stroke volume of the left ventricle, the design of peripheral resistances and the viscosity of the model fluid are approximated to physiological conditions.

Pulsatile Plasma LH Rhythms in Normal and Androgen-Sterilized Ovariectomized Rats: Effects of Estrogen Treatment

Abstract: SummaryPlasma LH was determined in sequential venous samples obtained at 10-min intervals from rats which had been ovariectomized 20 days earlier. Normal (nonandrogenized) castrates exhibited pulsatile rhythms in plasma LH with a peak to peak time of approximately 30 min. Castrated androgen-sterilized rats (ASR) also exhibited pulsatile plasma LH rhythms, but most were of the 40-60-min peak to peak type. In normal rats, when either 0.1 or 1.0 μg estradiol benzoate (EB) was administered on Day 17 and sequential blood collections were obtained on Day 20 after ovariectomy, the pulsatile rhythm was still present; however, pulse amplitudes were reduced and the average plasma LH concentration for individual animals over a 2-hr collection period was progressively lowered as the EB dosage was increased. Pituitary LH concentration increased in these EB-treated normal castrates. Administration of either 0.1 or 1.0 μg EB to castrated ASR markedly decreased average plasma LH concentrations and, in the 1.0-μg EB group...

Ultraradian fluctuations of gonadotropins.

Abstract: Some of those using a 3-6 hour sampling frequency have reported a diurnal variation for both luteinizing hormone (LH) and follicle stimulating hormone (FSH); others have not confirmed these findings Studies were initiated to determine the presence of short-term rhythms by frequent sampling with a time interval of less than the biologica half-life of the hormone being studied Within the cyclic rhythm gonadotropin levels were not maintained by continuous rates of secretion but represent the integration of episodic bursts of pituitary discharge with a frequency and magnitude that varies with different phases of the cycle The acyclic gonadotropin levels found in eugonadal males were similarly composed of episodic pituitary releases When sampling frequency of 10-15 minute intervals was used a pattern of episodic fluctuation of LH was disclosed It is thought that the pulsatile componenet of LH release was superimposed on a continuous secretion which may account for the slower decay A periodicity of about 90 minutes was noted in all phases of the cycle except during the mid and late luteal phases when a diminished frequency of 3-4 hours was observed The magnitude of the LH pulses was greatest during the midcycle surge Infusion of 17beta-estradiol induced a rapid conversion of the pulsatile pattern to a pattern of oscillations Administration of progesterone had a dampening effect It seemed that all pituitary hormones are secreted in episodic fashion and that at least 4 hypothalam ic-pituitary systems had patterns of secretion closely linked to the 24-hour sleep-wake activity in humans At puberty during a transient p eriod of sex maturation LH release may also be linked with the sleep-wake cycle In humans general anesthesia was shown to have a dampening effect on the central mechanism of pulsatile regulation of gonadotropin release The effects of phentolamine an alpha-adrenergic blocking agent and propanol a beta-adrenergic blocking agent were evaluated in 6 patients Negative findings resulted Others using 10 times larger doses in monkeys have reported positive effects Administration of androstenedione testosterone or progesterone by infusion failed to elicit change in the pulsatile pattern of 5 subjects Infusion of 17beta-estradiol abolished the pulsatile pattern of LH and converted it to a pattern of oscillations for 5-6 hours despite the rapid disappearance of the circulating E2 Clomid increased the amplitude of the pulsatile release more for LH than FSH From these studies it was thought that an inherent ultraradian rhythm of central nervous system/pituitary gonadotropin regulation exists