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Pulsatile flow

About: Pulsatile flow is a research topic. Over the lifetime, 6278 publications have been published within this topic receiving 149638 citations.


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Journal ArticleDOI
TL;DR: Pulsatile secretion is the more efficient means for islet A cells to stimulate hepatic glucose production and, in the dose range equivalent to concentrations in portal plasma, pulsed glucagon enhanced glucose production twofold.
Abstract: We have compared the effects of pulsatile and continuous glucagon administration on hepatocyte glucose production in order to clarify the physiological role of pulsatile hormone secretion. Two identical columns containing freshly isolated rat hepatocytes mixed with polyacrylamide gel beads were perifused with oxygenated tissue culture medium. A fixed total amount of glucagon was delivered to one column as a continuous 90-min infusion and to the other column as a series of six 3-min pulses. A 15-min interpulse interval was chosen in order to approximate the 10- to 12-min interval observed in primates while permitting the resolution of individual hepatocyte responses. With this protocol, the EC50 values for pulsatile and continuous glucagon administration were 186 +/- 41 and 884 +/- 190 (SD) pg/ml, respectively. For glucagon concentrations less than 1,000 pg/ml, pulsatile administration always led to greater hepatocyte glucose production than continuous administration (P = 0.008) and, in the dose range equivalent to concentrations in portal plasma, pulsed glucagon enhanced glucose production twofold. The data suggest that pulsatile secretion is the more efficient means for islet A cells to stimulate hepatic glucose production.

44 citations

Journal ArticleDOI
TL;DR: Pulsatile insulin delivery has advantageous metabolic effects compared to continuous hormone administration in patients with noninsulin-dependent diabetes mellitus and significantly reduced plasma triglyceride, very low density lipoprotein lipid levels, and FFA levels and increased high densitylipoprotein cholesterol and apolipoprotein-B levels.
Abstract: This study was done to compare the actions of pulsatile and continuous insulin administration in eight noninsulin-dependent diabetic patients. Human insulin was delivered in a pulsatile manner (1.3 mU/kg.min for 2 min, followed by 11 min during which no insulin was infused) or continuously (0.2 mU/kg.min) for 325 min. Endogenous hormone secretion was inhibited by somatostatin (125 micrograms/h), and glucagon was replaced at rate of 3.5 micrograms/h. Under these conditions plasma C-peptide levels fell progressively to extremely low values at the end of the experiment. Continuous insulin infusion resulted in steady plasma insulin levels, averaging 86 pmol/L, while during intermittent insulin administration plasma insulin levels were 5.7 and 158 pmol/L before and 3 min after the start of the insulin injection, respectively. Basal plasma glucagon [mean 158 +/- 11 (+/- SE) vs. 163 +/- 21 ng/L; P = NS] levels were similar on both occasions. During replacement peripheral plasma glucagon levels were no different whatever the mode of insulin administration, nor did they differ from the basal values. The mean plasma glucose concentrations were similar before both studies and rose to 9.5 and 8.6 mmol/L in the first 65 min during continuous and pulsatile insulin administration, respectively. In contrast, during the last 65 min, plasma glucose averaged 6.2 mmol/L during both studies. The glucose infusion rate initially increased, but then rapidly fell to values close to zero at the end of the first 65 min during the continuous insulin infusion, whereas during this time it averaged 0.59 +/- 0.10 mg/kg.min (32.5 +/- 5.5 mumol/kg.min) during pulsatile insulin administration. In the last 65 min the glucose infusion rate was significantly higher during pulsatile than during continuous insulin delivery. Furthermore, pulsatile rather than continuous insulin administration significantly reduced plasma triglyceride, very low density lipoprotein triglyceride, and FFA levels and increased high density lipoprotein cholesterol and apolipoprotein-B levels. We conclude that pulsatile insulin delivery has advantageous metabolic effects compared to continuous hormone administration in patients with noninsulin-dependent diabetes mellitus.

44 citations

Journal ArticleDOI
TL;DR: The present novel testosterone add-back clinical experimental paradigm indicates that 1) remarkably different 24-h mean serum free testosterone concentrations can result from continuous vs. pulsatile testosterone delivery into the bloodstream; 2) androgen negative feedback can exert frequency- as well as amplitude-dependent suppression of pulsatile LH release; and 3) testosterone is required to maintain an orderly 24-H LH release process in young men.
Abstract: To investigate the neuroendocrine mechanisms underlying the negative feedback actions of testosterone on both the pulsatile mode of LH release and the entropy or disorderliness of the LH release process, we blocked testicular androgen biosynthesis using oral high dose ketoconazole treatment with concomitant low dose glucocorticoid replacement for 48 h in six healthy young men. Volunteers were then infused iv with saline or a total of 8.0 mg testosterone base over the second 24 h via either a continuous or a pulsatile (90-min boluses) delivery pattern. Discrete peak detection (Cluster analysis) was applied to obtain a model-independent estimate of the frequency of serum LH concentration peaks, maximal and incremental LH peak amplitudes, peak area, and interpeak nadir serum LH concentrations. Approximate entropy was used to quantify the relative orderliness/disorderliness of the LH release process over 24 h. Ketoconazole treatment markedly lowered 24-h mean serum total and free testosterone concentrations (by 17- and 9-fold respectively), and significantly increased LH pulse frequency, maximal LH peak height, and interpeak nadir serum LH concentrations. Continuous iv testosterone add-back increased 24-h pooled serum free testosterone concentrations 3-fold more and concomitantly reduced mean (24-h) serum LH concentrations by at least 2-fold more than pulsatile delivery of the same total daily amount of androgen. Both modes of testosterone infusion suppressed pulsatile LH release, but the effects were distinguishable; namely, treatment with continuous vs. intermittent androgen add-back, respectively, decreased LH pulse frequency and incremental LH pulse amplitude. Ketoconazole treatment alone also significantly increased approximate entropy values, indicating greater disorderliness of LH release during androgen removal. Approximate entropy/orderliness was restored to baseline by continuous, but not pulsatile, iv testosterone replacement. In conclusion, the present novel testosterone add-back clinical experimental paradigm indicates that 1) remarkably different 24-h mean serum free testosterone concentrations can result from continuous vs. pulsatile testosterone delivery into the bloodstream; 2) androgen negative feedback can exert frequency- as well as amplitude-dependent suppression of pulsatile LH release; and 3) testosterone is required to maintain an orderly 24-h LH release process in young men.

44 citations

Journal ArticleDOI
TL;DR: The hypothesis that the planar flow visualization techniques, when integrated with traditional point-to point techniques, provide significantly more insight into the complex pulsatile flow past MHVs is reinforced.
Abstract: This study investigates the transient regurgitant flow downstream of a prosthetic heart valve using both laser Doppler velocimetry (LDV) and particle image velocimetry (PIV) Until now, LDV has been the more commonly used tool in investigating the flow characteristics associated with mechanical heart valves The LDV technique allows point-by-point velocity measurements and provides enough information about the temporal variations in the flow The main drawback of this technique is the time consuming nature of the data acquisition process in order to assess an entire flow field area The PIV technique, on the other hand, allows measurement of the entire flow field in space in a plane at a given instant In this study, PIV with spatial resolution of 0 (1 mm) and LDV with a temporal resolution of 0 (1 ms) were used to measure the regurgitant flow proximal to the Bjork-Shiley monostrut (BSM) valve in the mitral position With PIV, the ability to measure 2 velocity components over an entire plane simultaneously provides a very different insight into the flow field compared to a more traditional point-to-point technique like LDV In this study, a picture of the effects of occluder motion on the fluid flow in the atrial chamber is interpreted using an integration of PIV and LDV measurements Specifically, fluid velocities in excess of 30 m/s were recorded in the pressure-driven jet during valve closure, and a 15 m/s sustained regurgitant jet was observed on the minor orifice side Additionally, the effects of the impact and subsequent rebound of the occluder on the flow also were clearly recorded in spatial and temporal detail by the PIV and LDV measurements, respectively The PIV results provide a visually intuitive way of interpreting the flow while the LDV data explore the temporal variations and trends in detail This analysis is an integrated flow description of the effects of valve closure and leakage on the pulsatile regurgitation flow field past a tilting-disc mechanical heart valve (MHV) It further reinforces the hypothesis that the planar flow visualization techniques, when integrated with traditional point-to point techniques, provide significantly more insight into the complex pulsatile flow past MHVs

44 citations

Journal ArticleDOI
TL;DR: Study of dynamic events associated with the pulsatile flow of blood in the pulmonary arterial system of six healthy men in the supine position found changes in the pattern of inflow pulse were detectable in the capillary flow pulse.
Abstract: We studied a number of dynamic events associated with the pulsatile flow of blood in the pulmonary arterial system of six healthy men in the supine position. We used the nitrous oxide-body plethysmograph method to record the pulmonary capillary blood flow pulse and the phonocardiogram to determine the time of opening and closing of the pulmonary valve. The pattern of right ventricular ejection was modified by administration of atropine and isoproterenol and by exercise. The time of conduction of the flow pulse from the pulmonary valve to the lung capillaries averaged 120 msec. Acceleration of capillary blood during systole averaged 8.2 ml/sec/msec. The fraction of stroke volume which distended the pulmonary arterial system during systole averaged 67.2%. The peak flow rate averaged 186 ml/sec. Tachycardia resulted in a decrease in the fraction of the stroke volume stored in the arterial tree during systole. Isoproterenol and exercise resulted in an increase in average capillary blood acceleration. Conducti...

44 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023274
2022641
2021170
2020181
2019171
2018189