Detection of Very Low Frequency Modulation in Renal Autoregulation

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Detection of Very Low Frequency Modulation in
Renal Autoregulation

• Kin L. Siu1
• Leon C. Moore2
• Aija Birzgalis2
• Ki H. Chon1

1Department of Biomedical Engineering, SUNY at
Stony Brook 2Department of Physiology and
Biophysics, SUNY at Stony Brook
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3rd Autoregulatory Mechanism

• Originally proposed by Just and Arendshorst1
• 100 seconds (0.01 Hz)
• Used time domain methods
• How do you find it (spectrally)?
• Want to examine and quantify the dynamics of this
  mechanism

1Am J Physiol Regul Integr Comp Physiol. 2003
Sep285(3)R619-31.
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Overall Objective

• Detect the very low frequency (VLF) component
• - SDR vs. SHR
• - Telemetry, Whole kidney, cortical
  measurements

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Challenges

• Operating frequency of 0.01 Hz
• Near the frequency of TGF (0.02-0.05 Hz)
• Resolution
• Need long data sets
• Other novel methods are needed
• Spectral analysis inconclusive in detecting 0.01
  Hz oscillations

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SDR
SHR
SHR
SDR
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Indirect Detection

• Non-linear interactions exists between TGF and
  MYO1
• Possible interactions between 3rd mechanism and
  TGF and MYO
• Indirectly detect 3rd mechanism by detecting
  interactions
• Amplitude and frequency modulation
• Wavelet analysis to detect interactions between
  MYO TGF (Sosnovtseva et al., Phys. Rev. E.,
  2004).

1Am J Physiol. 1994 Jul267(1 Pt 2)F160-73.
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Background AM FM
AM
FM
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Detection of Modulation
Variable Frequency Complex Demodulation1 to
obtain Time-Frequency Representation
Extract peak amplitude or frequency from MYO and
TGF frequency bands across time
FFT or Time-Frequency on resulting time series
Compare the resultant peaks with surrogate data
generated peak
1Ann Biomed Eng. 2006 Feb34(2)326-38.
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Time-Frequency Analysis
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Time-Frequency Amplitude Estimation
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Detection of Modulation
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Experimental Methods
Whole Kidney (telemetry anesthetic)
Cortical
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Results
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Hypertensive Studies

• Observe modulation in SHR
• N-nitro-L-arginine methyl ester (LNAME)
• Nitric oxide synthesis inhibitor
• Vasoconstricts

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Results
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Conclusions

• Statistically significant amplitude modulation by
  a VLF component detected in MYO and TGF
• Observed in SDR and SHR
• Magnitude differ
• LNAME did not affect the presence of VLF

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Electrohydraulic pump-driven closed-loop
pressure regulatory system
1Jae Mok Ahn, 2Kin Siu, 2Leon C. Moore, 2Ki H.
Chon 1Dept. of Electrical Engineering, Hallym
University, Korea 2Dept. of Biomedical
Engineering, SUNY at Stony Brook, Stony Brook, NY
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Background

• To investigate a blood pressure-dependent
  physiological variability including renal
  autoregulation mechanisms, a sophisticated BP
  regulation system required.
• BP regulation systems constructed by other groups
• Pneumatic servo-control system (Benn Nafz, et al,
  1992)
• Bidirectional DC motor syringe pump system
  (Hester R.L., et al, 1983)
• Unidirectional occlusive mechanical system (morff
  R.J., et al, 1978)
• Limitations and disadvantages
• Longer control latencies
• Less accurate pressure control
• Less steady-state stabilization
• Bulky system due to hardware-oriented
  implementation

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Objectives

• To develop an electrohydraulic (EH) configuration
  for BP (step) regulation using PI controller
• Assess efficiency of autoregulation
• Pressure ramp predicts the rate of progression of
  hypertensive renal disease (Bidani et al., AJP,
  2005)
• To develop a user-friendly interface monitor
  program using the LabVIEW program

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Electrohydraulic (EH) Configuration
Flow-mediated vascular occlusion
Double Y- tube size (LS17, ID6.4 mm)
Bidirectional flow
RS232
water
Distal Aorta
Vascular Occluder (OC4) Cuffs width 5 mm Cuffs
thickness 2 mm Cuffs lumen 4 mm
Peristaltic pump
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Basic Occlusion principle

• Flow-mediated occlusion (cuffs inflation) or
  release (cuffs deflation)
• For complete occlusion, cuffs inflation must be
  at least 50 mmHg higher than systolic pressure
• For BP maintenance, continuous constant fluid
  hydraulic pressure required

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Occlusion/release time (ORT) determination

• Occluders dimension and the pump tube inside
  diameter are key factors
• Y-tubing size 6.4 mm (ID)
• Occluders cuff OC4 (4 mm, lumen diameter)

Lumen diameter
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Estimation of ORT using Simulink
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Main subroutines of LabVIEW
Serial comm. sub.
PI control sub.
DAQ sub.
FFT sub.
Data logging sub.
Display sub.
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LabVIEW-based user-friendly interface monitor
program
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Schematic diagram of the EH proportional plus
integral (PI) control
Anti-windup
e-st
E(s)
U(s)
KI/s
EH flow pump
Animal model


BP reference
KP
BP feedback
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PI Controller
Tuned Parameters
1000
25
rad/s
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Results of in vivo performance
PI termination
PI start
BP (mmHg)
10 min
Release response
Occlusive response
Maintenance response
BP (mmHg)
10 min
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Conclusions

• BP was servo-controlled by using a vascular cuff
  connected to the optimal electrohydraulic pump
  drive.
• LabVIEW based user-friendly interface monitor
  program developed
• Release time with approximately 300 ms
• Optimal PI compensation developed (error 3)
• The PI control in conjunction with the EH pump
  for any blood pressure-dependent studies could be
  applied even in non-linear experimental model.

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Acknowledgements

• Kin Siu
• Dr. Jae Mok Ahn
• Dr. Leon Moore
• Aija Birzgalis
• Support by NIH HL 69629