Exploring ICP, Tissue Oxygenation and RSNA with Implantable Telemetry

Sponsored by:

Prof. Jacqueline Phillips

Professor of Neuroscience

Faculty of Medicine and Health Sciences

Macquarie University

Sydney NSW Australia

Dr. Fiona McBryde

Research Fellow,

Department of Physiology

University of Auckland

New Zealand

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and laboratory services.

Cohousing with Millar Telemetry

Dr. Sandy Lau

Scientist

Millar

Copyright 2015 S. Lau, Millar & InsideScientific. All Rights Reserved.

1. Millar Telemetry System

2. Cohousing feature (New!)

An implantable telemetry system with a difference!

Millar Telemetry System

1. Telemeters – fully implantable,

rechargeable (see www.millar.com)

2. SmartPad – wireless charger and

signal receiver

3. Configurator System –pairs telemeters and SmartPads(30 Channels), enable/disable cohousing

House 2 rats in one cage (>175g each)

Implant 2 telemeters in one large rat (>350g)

NC3Rs on telemetry…“investigators should be aware of potential sources of pain and distress within telemetry projects, including: distress induced by housing animals individually” http://3rs.ccac.ca/en/research/reduction/telemetry.html

Cohousing – reduce costs and increase research opportunity

Primary (1°) SmartPad

• Collects data from telemeter 1 only

• Monitors battery and charges two implanted telemeters

How Cohousing Works

Secondary (2°) SmartPad

• Collects data from telemeter 2 only

• Charging disabled

21

1 2

High Quality Data Recordings

Same high quality data expected from a Millar Telemetry System…

Just more of it!

Cohousing helps address ethical concerns around social isolation

Reduces housing costs

Same high quality data expected from a Millar Telemetry System!

Summary

For more information, visit www.millar.comor contact us on support@millar.com

In the lab, data gets you results. Innovation gets you noticed.

The Millar Telemetry System adds a higher level of understanding to any cardiovascular, neuroscience, toxicology or pharmacology study — bringing the accuracy and precision you expect from Millar in a fully implantable device.

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Simultaneous recordings of blood pressure, intracranial pressure and brain oxygenation

Fiona McBryde

Research Fellow,

Department of Physiology

University of Auckland

New Zealand

1. Why we want to use dual telemeters

2. Surgical techniques and tips

3. Housing dual-telemetered animals

4. Examples of Data

5. Summary

What are we going to cover today?

• Hypothesis – can the “selfish brain” cause systemic hypertension?

• Relationship between intracranial pressure, brain tissue oxygen and arterial pressure

• Simultaneous measurements require technical innovation:

• Solution = dual telemeters

Understanding the Selfish Brain

1. To implant two telemeters animal weight needs to be >350g

2. A longer surgery is required to instrument each subject:

• extra pain relief/supplemental flood and fluid after surgery

• allow longer recovery time (>7 days)

Using Two Telemeters in One Rat…

Blood Pressure Placement

BP (9cm) catheter inserted into the abdominal aorta and fixed in place using tissue adhesive and surgical mesh

BP catheter

Blood Pressure Placement

BP (9cm) catheter inserted into the abdominal aorta and fixed in place using tissue adhesive and surgical mesh

Seal around catheter with

minimal tissue adhesive

Small dab of glue

Surgical Mesh

BP catheter

Placement of Dual Telemeters

• Align telemeters in abdominal cavity, either side of the midline incision.

• Important – use suture tabs to secure in place!

Oxygen and ICP Placement

TRM54PP telemeter with one 9cm catheter (BP) and one 25cm catheter (ICP)

Oxygen and ICP Placement

19

• Tunnel ICP and Oxygen electrodes up from abdomen to head (use trocar)

• Take care not to damage sensing tips, especially ICP and p02

Sensor Placement on Skull

ICP

Auxiliary

Oxygen

electrode

Ground

• Give careful thought to electrode/screw arrangement

• Be very gentle with ICP catheter

1. Bevel back of ICP catheter hole

2. Seal all holes with Gelfoam, and seal with tissue adhesive.

3. Cover screws and catheter with rubber dental impression material (Do NOT use dental cement)

Securing sensors in place

Top view

Skull

Brain

Side view

Dura

Useful Materials

1.

4.2.

3.

Recording of intracranial pressure in conscious rats via telemetry

Although cerebral perfusion pressure (CPP) is known to be fundamental in the control of normal

brain function, there have been no previous long-term measurements in animal models. The aim

of this study was to explore the stability and viability of long-term recordings of intracranial

pressure (ICP) in freely moving rats via a telemetry device. We also developed a repeatable

surgical approach with a solid-state pressure sensor at the tip of the catheter placed under the

dura and in combination with arterial pressure (AP) measurement to enable the calculation of

CPP.

Sarah-Jane Guild, Fiona D. McBryde, Simon C. Malpas

Journal of Applied Physiology Published 1 September 2015 Vol. 119 no. 5, 576-581 DOI: 10.1152/japplphysiol.00165.2015

Intracranial Pressure Methodsclick to access

A fully implantable telemetry system for the chronic monitoring of brain tissue oxygen in freely moving rats.

The ability to monitor tissue oxygen concentration in a specific region of the brain in a freely moving

animal could provide a new paradigm in neuroscience research. We have developed a fully implantable

telemetry system for the continuous and chronic recording of brain tissue oxygen (PO(2,BR)) in

conscious animals. A telemetry system with a sampling rate of 2kHz was combined with a miniaturized

potentiostat to amperiometrically detect oxygen concentration with carbon paste electrodes.

Russell DM1, Garry EM, Taberner AJ, Barrett CJ, Paton JF, Budgett DM, Malpas SC.

J Neurosci Methods. 2012 Mar 15;204(2):242-8. doi: 10.1016/j.jneumeth.2011.11.019. Epub 2011 Nov 19.

Brain Oxygen Methods

Journal of Neuroscience Methods

click to access

• Smartpads need to be specially configured -- important to consult with Millar

• TWO smartpads per rat – one active charge field.

• Second (field off) smartpadcan be off to one side.

Housing Dual Telemeter Animals:

Opening new channels for data collection:

Simultaneous recordings of multiple inputs –allows real-time calculation of respiration rate and cerebral perfusion pressure

Other possibilities: BP, ICP and Renal SNA

Possible to combine any two telemeter types, to access a wide range of signals

• Demanding surgical set-up for both experimenter and rat

• Aseptic technique and good post-surgical care essential

• Longer recovery time (>5-7 days)

• Access to multiple signals – unique insight

• Further resources:

Millar Knowledge Centre (www.millar.com)

Papers

Collaborations

Tips, Pointers and Summary

Direct conscious telemetry recordings demonstrate increased renal sympathetic nerve activity in rats with chronic kidney disease

Professor Jacqueline Phillips

Professor of Neuroscience

Faculty of Medicine and Health Sciences

Macquarie University

Sydney NSW Australia

1. Experimental context

2. Why telemetry?

• Advantages and challenges

• Study outcomes

3. What’s next?

Conscious recording of renal sympathetic nerve activity in an animal model of disease

Salman et. al 2015 – Frontiers in Physiology

Direct conscious telemetry recordings demonstrate increased

renal sympathetic nerve activity in rats with chronic kidney disease

Chronic kidney disease (CKD) is associated with sympathetic hyperactivity and impaired blood pressure control reflex responses, yet direct evidence demonstrating these features of autonomic dysfunction in conscious animals is still lacking. Here we measured renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) using telemetry-based recordings in a rat model of CKD, the Lewis Polycystic Kidney (LPK) rat, and assessed responses to chemoreflex activation and acute stress.

Ibrahim M. Salman, Divya Sarma Kandukuri, Joanne L. Harrison, Cara M. Hildreth and Jacqueline K. Phillips*

Salman et. al 2015 – Frontiers in Physiology

Increased sympathetic nerve activity in chronic kidney disease

1. Experimental Context

Hypertension and Chronic Kidney Disease

1. Global increased sympathetic nerve activity (SNA) to the vasculature mediating increased total peripheral resistance

2. Local increase in renal SNA driving neuronal and hormonal mediators of hypertension

3. In polycystic kidney disease (PKD) increased muscle SNA and hypertension evident before renal dysfunction

Role of the sympathetic nervous system

J Am Soc Nephrol. 2001 Klein et al.

Measuring SNA

Indirect and direct approaches…

• Circulating catecholamines and noradrenaline spillover techniques

• Blood pressure response to ganglionic blockade

• Muscle SNA recordings

• Direct recording in anaesthetised animal preparations

Lewis Polycystic Kidney Rat – Histological Phenotype

100 υm100 υm

LPKLewis

Indirect evidence of increased SNA in CKD in the LPK

1. Enhanced response to ganglionic blockade

2. Increased levels of circulating catecholamines

Direct evidence of increased SNA in CKD in the LPK

Increased baseline SNA with in-vivo recordings

• animals aged 12 weeks

J Hypertension 2015, Yao. et al

Lewis n LPK n

sSNA (µV) 3.4± 0.4 14 5.7± 1* 14

rSNA (µV) 3.7± 0.6 12 8.3± 1.2* 15

lSNA (µV) 2.4± 0.3 12 5.0± 1.2* 12

* P < 0.05

Considering the advantages and technical challenges……

2. Why (dual BP and SNA) Telemetry?

Advantages:

Overcome the impact of anaesthesia on SNA

Overcomes the impact of handling/ restraint stress

Validate integrity of SNA recording

Measure haemodynamic and SNA reflex responses

Why Dual BP and SNA Telemetry?

Why Dual BP and SNA Telemetry?

Technical Challenges:

Animal size and surgical risk

One week recovery to regain circadian rhythms

Dual BP and SNA required at study end point (72%)

Data analysis (uV or % change data)

Validation of renal SNA recordings as evidenced by pulse modulation

Lewis n LPK n

rSNA (µV) 0.6 ± 0.1 8 1.2 ± 0.1* 6

* P < 0.05

…also noted increased baseline level of renal SNA in the conscious LPK animals compared to Lewis controls…

Frontiers Physiol 2015 Salman et al

Study outcomes…

2. Why Telemetry?

Correlation of increased blood pressure with increased renal SNA

Potential mechanism underlying blood pressure lowering effect of renal denervation…

Frontiers Physiol 2015 Salman et al

Impaired mean arterial pressure (MAP) and rSNAresponse to:

• Central chemoreflex activation (hypercapnia)

• Tonic activation of the reflex may impair further relative increases in SNA and BP

Reflex Responses

Frontiers Physiol 2015 Salman et al

Impaired mean arterial pressure (MAP) and rSNAresponse to:

• Stress (open field chamber 10 minutes)

• Increased baseline rSNAlimiting relative further increases?

Reflex Responses

Frontiers Physiol 2015 Salman et al

1. Confirmation of enhanced SNA

2. Impaired chemoreflex and stress induced pressor and sympathoexcitatory responses, consistent with impaired central processing of autonomic reflexes

Renal SNA in a model of CKD as determined by conscious telemetry recordings

Long term recordings looking for temporal changes in SNA with disease progression

3. What’s Next…

Long-term recordings in individual animals out to 18 weeks

Picture Label 18 week Lewis 18 week LPK

12 week LPK12 week Lewis

MA

P (

mm

Hg

R

NSA

(μV

)

RSN

A (μV

)M

AP

(m

mH

g

RN

SA (μV

)

RSN

A (μV

)

Salman et. al unpublished

Conclusion

• Conscious telemetry recording of SNA overcomes many of the limitations of other indirect and direct measures of SNA

• Technically challenging with validation of recordings required and additional considerations (eg size) when being used for disease models

• Longitudinal data is possible…

• Dream for smaller probes (mice sized)

Acknowledgements:

Dr Ibrahim Salman

Dr Cara Hildreth

Divya Sarma Kandurkuri

Dr. Sarah-Jane Guild

Dr Joanne Harrison

Thank You!

Fiona McBrydef.mcbryde@auckland.ac.nz

Jacqueline PhillipsJacqueline.Phillips@mq.edu.au

If you have questions for the presenters please contact them by email.

For additional information on Millar Telemetry solutions for physiological monitoring please visit:

http://www.millar.com