scholarly journals Analysis of nonstationarity in renal autoregulation mechanisms using time-varying transfer and coherence functions

2008 ◽  
Vol 295 (3) ◽  
pp. R821-R828 ◽  
Author(s):  
Ki H. Chon ◽  
Yuru Zhong ◽  
Leon C. Moore ◽  
Niels H. Holstein-Rathlou ◽  
William A. Cupples
Keyword(s):  
Transfer Functions ◽  
Low Frequency ◽  
Time Varying ◽  
Frequency Range ◽  
Sprague Dawley ◽  
Dynamic Complexity ◽  
Spontaneously Hypertensive ◽  
Renal Autoregulation ◽  
Blood Flow Dynamics ◽  
Frequency Coherence

The extent to which renal blood flow dynamics vary in time and whether such variation contributes substantively to dynamic complexity have emerged as important questions. Data from Sprague-Dawley rats (SDR) and spontaneously hypertensive rats (SHR) were analyzed by time-varying transfer functions (TVTF) and time-varying coherence functions (TVCF). Both TVTF and TVCF allow quantification of nonstationarity in the frequency ranges associated with the autoregulatory mechanisms. TVTF analysis shows that autoregulatory gain in SDR and SHR varies in time and that SHR exhibit significantly more nonstationarity than SDR. TVTF gain in the frequency range associated with the myogenic mechanism was significantly higher in SDR than in SHR, but no statistical difference was found with tubuloglomerular (TGF) gain. Furthermore, TVCF analysis revealed that the coherence in both strains is significantly nonstationary and that low-frequency coherence was negatively correlated with autoregulatory gain. TVCF in the frequency range from 0.1 to 0.3 Hz was significantly higher in SDR (7 out of 7, >0.5) than in SHR (5 out of 6, <0.5), and consistent for all time points. For TGF frequency range (0.03–0.05 Hz), coherence exhibited substantial nonstationarity in both strains. Five of six SHR had mean coherence (<0.5), while four of seven SDR exhibited coherence (<0.5). Together, these results demonstrate substantial nonstationarity in autoregulatory dynamics in both SHR and SDR. Furthermore, they indicate that the nonstationarity accounts for most of the dynamic complexity in SDR, but that it accounts for only a part of the dynamic complexity in SHR.

Frequency domain of renal autoregulation in the conscious dog

1995 ◽  
Vol 269 (3) ◽  
pp. F317-F322 ◽  
Author(s):  
U. Wittmann ◽  
B. Nafz ◽  
H. Ehmke ◽  
H. R. Kirchheim ◽  
P. B. Persson
Keyword(s):  
Blood Flow ◽  
Phase Shift ◽  
Transfer Function ◽  
Arterial Pressure ◽  
Dynamic Range ◽  
Transfer Functions ◽  
Driving Pressure ◽  
Acute Administration ◽  
Frequency Range ◽  
Renal Autoregulation

The dynamic range in which renal blood flow (RBF) autoregulation occurs was determined in eight conscious foxhounds chronically catheterized in the abdominal aorta and implanted with a transit-time flow probe over the renal artery. Sinusoidal driving pressures (amplitude of 10 mmHg) were forced on the renal arterial pressure at different frequencies by a servo-control device, and transfer functions were calculated. Only one frequency range was found below which the gain of the transfer function declined and in which the phase angle increased (n = 8). This indicates the presence of a potent mechanism for renal autoregulation in the examined frequency range between 0.0031 and 0.08 Hz, which buffers changes in blood flow < 0.02 Hz. After furosemide treatment, one indicator for autoregulation (phase shift of transfer function) was significantly blunted at low frequencies (n = 6). Furosemide, however, did not reduce the phase shift to zero, suggesting that some autoregulation still remained in the frequency range between 0.04 and 0.08 Hz. In conclusion, autoregulation of RBF during sinusoidal changes in driving pressure between 0.0031 and 0.02 Hz is mediated by a single mechanism, which can be blocked by the acute administration of furosemide. The residual phase shift between arterial pressure and RBF in the transfer function observed during sinusoidal changes in driving pressure between 0.04 and 0.08 Hz suggests the presence of a second mechanism for RBF autoregulation.

Interactions between TGF-dependent and myogenic oscillations in tubular pressure and whole kidney blood flow in both SDR and SHR

2006 ◽  
Vol 290 (3) ◽  
pp. F720-F732 ◽  
Author(s):  
Ramakrishna Raghavan ◽  
Xinnian Chen ◽  
Kay-Pong Yip ◽  
Donald J. Marsh ◽  
Ki H. Chon
Keyword(s):  
Blood Flow ◽  
Tubuloglomerular Feedback ◽  
Nonlinear Interactions ◽  
Time Varying ◽  
Nonlinear Coupling ◽  
Flow Data ◽  
Sprague Dawley ◽  
Spontaneously Hypertensive ◽  
Kidney Blood Flow ◽  
Time Invariant

We previously showed that nonlinear interactions between the two renal autoregulatory mechanics (tubuloglomerular feedback and the myogenic mechanism) were observed in the stop flow pressure (SFP) and whole kidney blood flow data from Sprague-Dawley rats (SDR) using time-invariant bispectrum analysis ( 3 , 4 ). No such nonlinear interactions were observed in either SFP or whole kidney blood flow data obtained from spontaneously hypertensive rats (SHR). We speculated that the failure to detect nonlinear interactions in the SHR data may be related to our observation that these interactions were not continuous and therefore had time-varying characteristics. Thus the absence of such nonlinear interactions may be due to an inappropriate time-invariant method being applied to data that are especially time varying in nature. We examine this possibility in this paper by using a time-varying bispectrum approach, which we developed for this purpose. Indeed, we found significant nonlinear interactions in SHR ( n = 18 for SFP; n = 12 for whole kidney blood flow). Moreover, the duration of nonlinear coupling is found statistically to be longer ( P = 0.001) in SFP data from either SDR or SHR than it is in whole kidney data from either type of rat. We conclude that nonlinear coupling is present at both the single nephron as well as the whole kidney level for SDR and SHR. In addition, SHR data at the whole kidney level exhibit the most transient nonlinear coupling phenomena.

Agility Comparison of Stabilizer and Direct Head Systems Mounted on an Unmanned Agricultural Helicopter

2018 ◽  
Vol 61 (6) ◽  
pp. 1813-1821
Author(s):  
Sung Bo Shim ◽  
Yeonghwan Bae ◽  
Young Mo Koo
Keyword(s):  
Time Delay ◽  
Transfer Functions ◽  
Low Frequency ◽  
Frequency Range ◽  
New Paradigm ◽  
Aerial Application ◽  
Attitude Stability ◽  
Equivalent Time ◽  
Pitch Direction ◽  
Direct Head

Abstract. Recently, there has been increasing interest in using unmanned aerial vehicles (UAVs) to reduce the labor required for pest control and to protect farmers from exposure to pesticides. Unmanned aerial application has become a new paradigm in pesticide application; however, a uniform speed must be maintained within a short accelerating distance when spraying small plots, and this depends on the skill of the operator, which is difficult to rely on. In this study, the agility of a direct head system mounted on an unmanned agricultural helicopter was compared with that of a conventional stabilizer head system by using a pitch sweep test in CIFER, a dynamic analysis software program. The controllable frequency range of the unmanned agricultural helicopter with the direct head was analyzed to range between 0.06 and 5 Hz, and the responsiveness of the helicopter with the conventional stabilizer head was observed in a relatively low frequency range of 0.06 to 1.6 Hz. In addition, in comparing the equivalent time delay between the representative transfer functions from the pitch direction input to the surge acceleration obtained using NAVFIT analysis, the time delay of the direct head was shorter than that of the stabilizer head, although the extent of the enhancement was not satisfactory because of the tail gyroscope used for intrinsic attitude stability. Keywords: Agility, Agricultural unmanned helicopter, CIFER, Flight dynamics, Swash head system.

Responses of mesenteric and renal blood flow dynamics to acute denervation in anesthetized rats

1998 ◽  
Vol 275 (5) ◽  
pp. R1543-R1552 ◽  
Author(s):  
Isam Abu-Amarah ◽  
David O. Ajikobi ◽  
Hélène Bachelard ◽  
William A. Cupples ◽  
Fred C. Salevsky
Keyword(s):  
Blood Flow ◽  
Renal Blood Flow ◽  
Wistar Rats ◽  
Function Analysis ◽  
Renal Nerves ◽  
Dynamic Regulation ◽  
Spontaneously Hypertensive ◽  
Renal Autoregulation ◽  
Transfer Function Analysis ◽  
Blood Flow Dynamics

Previous studies have shown that renal autoregulation dynamically stabilizes renal blood flow (RBF). The role of renal nerves, particularly of a baroreflex component, in dynamic regulation of RBF remains unclear. The relative roles of autoregulation and mesenteric nerves in dynamic regulation of blood flow in the superior mesenteric artery (MBF) are similarly unclear. In this study, transfer function analysis was used to identify autoregulatory and baroreflex components in the dynamic regulation of RBF and MBF in Wistar rats and young spontaneously hypertensive rats (SHR) anesthetized with isoflurane or halothane. Wistar rats showed effective dynamic autoregulation of both MBF and RBF, as did SHR. Autoregulation was faster in the kidney (0.22 ± 0.01 Hz) than in the gut (0.13 ± 0.01 Hz). In the mesenteric, but not the renal bed, the admittance phase was significantly negative between 0.25 and 0.7 Hz, and the negative phase was abrogated by mesenteric denervation, indicating the presence of an arterial baroreflex. The baroreflex was faster than autoregulation in either bed. The presence of sympathetic effects unrelated to blood pressure was inferred in both vascular beds and appeared to be stronger in the SHR than in the Wistar rats. It is concluded that a physiologically significant baroreflex operates on the mesenteric, but not the renal circulation and that blood flow in both beds is effectively stabilized by autoregulation.

Evaluation of Special Hearing Aids for Deaf Children

1971 ◽  
Vol 36 (4) ◽  
pp. 527-537 ◽  
Author(s):  
Norman P. Erber
Keyword(s):  
Hearing Aids ◽  
High Frequency ◽  
Hearing Aid ◽  
Low Frequency ◽  
Acoustic Stimulation ◽  
Deaf Children ◽  
Frequency Range ◽  
Frequency Limit ◽  
Unpublished Studies ◽  
Published Research

Two types of special hearing aid have been developed recently to improve the reception of speech by profoundly deaf children. In a different way, each special system provides greater low-frequency acoustic stimulation to deaf ears than does a conventional hearing aid. One of the devices extends the low-frequency limit of amplification; the other shifts high-frequency energy to a lower frequency range. In general, previous evaluations of these special hearing aids have obtained inconsistent or inconclusive results. This paper reviews most of the published research on the use of special hearing aids by deaf children, summarizes several unpublished studies, and suggests a set of guidelines for future evaluations of special and conventional amplification systems.

Dynamic Damping and Stiffness Characteristics of the Rolling Tire

2001 ◽  
Vol 29 (4) ◽  
pp. 258-268 ◽  
Author(s):  
G. Jianmin ◽  
R. Gall ◽  
W. Zuomin
Keyword(s):  
Dynamic Behavior ◽  
Variable Parameter ◽  
Low Frequency ◽  
Vertical Load ◽  
Frequency Range ◽  
Inflation Pressure ◽  
Vehicle Simulation ◽  
Dynamic Damping ◽  
Speed Range ◽  
Stiffness Characteristics

Abstract A variable parameter model to study dynamic tire responses is presented. A modified device to measure terrain roughness is used to measure dynamic damping and stiffness characteristics of rolling tires. The device was used to examine the dynamic behavior of a tire in the speed range from 0 to 10 km/h. The inflation pressure during the tests was adjusted to 160, 240, and 320 kPa. The vertical load was 5.2 kN. The results indicate that the damping and stiffness decrease with velocity. Regression formulas for the non-linear experimental damping and stiffness are obtained. These results can be used as input parameters for vehicle simulation to evaluate the vehicle's driving and comfort performance in the medium-low frequency range (0–100 Hz). This way it can be important for tire design and the forecasting of the dynamic behavior of tires.

scholarly journals An Improved Time Integration Method Based on Galerkin Weak Form with Controllable Numerical Dissipation

2021 ◽  
Vol 11 (4) ◽  
pp. 1932
Author(s):  
Weixuan Wang ◽  
Qinyan Xing ◽  
Qinghao Yang
Keyword(s):  
High Frequency ◽  
Integration Method ◽  
Time Integration ◽  
Low Frequency ◽  
Weak Form ◽  
High Accuracy ◽  
Numerical Dissipation ◽  
Frequency Range ◽  
Time Integration Method ◽  
Numerical Damping

Based on the newly proposed generalized Galerkin weak form (GGW) method, a two-step time integration method with controllable numerical dissipation is presented. In the first sub-step, the GGW method is used, and in the second sub-step, a new parameter is introduced by using the idea of a trapezoidal integral. According to the numerical analysis, it can be concluded that this method is unconditionally stable and its numerical damping is controllable with the change in introduced parameters. Compared with the GGW method, this two-step scheme avoids the fast numerical dissipation in a low-frequency range. To highlight the performance of the proposed method, some numerical problems are presented and illustrated which show that this method possesses superior accuracy, stability and efficiency compared with conventional trapezoidal rule, the Wilson method, and the Bathe method. High accuracy in a low-frequency range and controllable numerical dissipation in a high-frequency range are both the merits of the method.

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