This project was funded by the National Stroke Foundation, Hunter Medical Research Institute (HMRI) and National Health and Medical Research Council (NH&amp;MRC), Australia. Special thanks to the Faculty of Health Workshop staff at The University of Newcastle for their technical expertise.

1. Skull Penetration
<ol>
	<li>Anaesthetize rat with isoflurane (5% induction, 1.5-2% maintenance) in 70% N2 and 30% O2. Following induction of anaesthesia, place the rat prone on a warming plate, positioning the rat's nose in an anaesthetic nose cone.</li>
	<li>Whilst maintaining anaesthesia, secure the head in a stereotaxic frame, inserting the ear-bars until head is stabilised. Ensure breathing is not impaired. (Figure 2-A).</li>
	<li>Inject scalp subcutaneously with long lasting local anaesthetic, Bupivacaine 0.3 ml 0.5% (Pfizer, Australia) before making a 1.5 cm skin midline head incision. (Sterile instruments and gloves should be used.)</li>
	<li>Blunt dissect the soft tissue and surrounding muscles to clearly locate Lambda and Bregma. Retract the skin and connective tissue.</li>
	<li>Stem any bleeding by applying pressure to the exposed skull. Excessive skull bleeding may be cauterized.</li>
	<li>Using a dental drill with a 1 mm tip burr, burr a hole 2 mm wide into the right parietal bone. Burr the hole 2 mm lateral and 2 mm posterior from Bregma to avoid the superior sagittal sinus and ensure the placement of the ICP sensor is over the ischemic territory, for stroke studies. Alternative locations would be equally suitable for other applications. Burr the hole to a depth where the skull above the dura becomes translucent. (Figure 2-B).</li>
	<li>Replace the burr with a 0.5 mm tip burr to remove the skull at the base of hole.</li>
	<li>When the skull begins to crack, use 45&deg; forceps to remove all remaining skull, ensuring the base of the hole is cleared of debris. (Figure 3).</li>
</ol>
2. Screw Modification and Insertion
<ol>
	<li>Drill a 0.7 mm hole through a hexagonal-headed screw using a lathe and 0.7 mm drill bit.</li>
	<li>Insert the monitoring screw into the hole by turning it approximately 1.5 turns (use the minimum amount of turns needed to secure screw in skull so as not to damage underlying tissue). (Figure 2-C and Figure 4).</li>
	<li>Burr a second hole for an anchoring screw in the left parietal bone, 2 mm lateral and 2 mm posterior from Bregma. This hole does not require complete penetration of the skull, so the 1 mm tip burr is used to thin the skull for screw insertion.</li>
	<li>Insert a 2 x 4 mm hexagonal-headed screw into the second hole. This screw helps to anchor the dental cement and hence the monitoring screw to the skull.</li>
	<li>Use a transfer pipette to mix and apply dental cement monomer and polymer to the base of the head of the screws.</li>
	<li>Allow dental cement to dry for at least 10 minutes.</li>
</ol>
3. Intracranial Pressure Transducer Insertion
<ol>
	<li>Using white correction fluid, mark the fibre-optic sensor 4 mm from the tip.</li>
	<li>Fill the hole of the monitoring screw with sterile saline (0.9%) and ensure no air bubbles are present within the screw.</li>
	<li>Insert the ICP probe 4 mm into the screw so that the tip of the probe is level with the end of the screw. Ensure the tip does not pierce the dura.</li>
	<li>Adjust the tip of the probe within the screw until an ICP trace reflecting ventilation and blood pressure pulse waves can be observed. (Figure 5).</li>
</ol>
4. Forming an Airtight Seal
<ol>
	<li>An airtight seal is imperative to an accurate ICP reading. Mix a viscous biocompatible caulking material monomer and polymer in the ratio of 1:1. Because the pressure sensor is at the tip of the probe, and this is within the hollowed out screw, application of caulking material to the shaft of the fibre-optic probe has no effect on pressure sensitivity of the sensor.</li>
	<li>Apply a thin layer around the probe and the head of the monitoring screw. Avoid displacing the ICP probe.</li>
	<li>Allow to set for 5 minutes.</li>
	<li>Apply a second layer of caulking material around the entire monitoring screw and probe. Ensure that no liquid is leaking from any crevasses in the caulking material. (Figure 2-D).</li>
	<li>Remove ear-bars.</li>
	<li>The rat may remain in the prone position, or be carefully rotated into the supine position during ICP monitoring.</li>
	<li>A schematic of the completed procedure is depicted in (Figure 6).</li>
</ol>
5. Intracranial Pressure Transducer Removal and Reinsertion
<ol>
	<li>At the completion ICP monitoring, the ICP sensor may be removed by gently pulling the catheter from the screw and caulking material.</li>
	<li>The SAMBA sensor should be immediately place into 1 % Terg-A-Zyme solution to prevent tip corrosion.</li>
	<li>The hole remaining in the caulking material should be covered with an additional layer of caulking material. (Rat may be woken at this stage).</li>
	<li>To reinsert the SAMBA catheter for additional monitoring, slice the caulking material at the level of the head of the screw.</li>
	<li>Repeat steps 3.2 - 5.3.</li>
</ol>
6. Representative Results
Figure 5 is a representation of ICP readings over ten seconds. At baseline, the average ICP in a Wistar rat is 6 mmHg. The events of shorter periodicity depicted in Figure 5 reflect blood pressure pulse waves. The events of longer periodicity show ventilation events. Note that the SAMBA sensor reflects a ventilation amplitude of 3-4 mmHg and pulse amplitude of 1-2 mmHg.
To validate the position of the SAMBA sensor in each experiment, ICP traces should be tested for responsiveness to abdominal compressions and respiratory events, such as periods of apnoea. An abdominal compression is depicted in Figure 7.
Periods of apnoea (illustrated in Figure 8) are observed in most experiments involving spontaneously breathing animals. These events are identified on physiological records by an absence of respiratory deflections on respiratory (diaphragm transducer) and arterial pressure traces. An equivalent alteration in the ICP trace validates the ICP probe positioning.
Figure 9 depicts a typical ICP trace after the removal of the ear-bars (step 4.6). The insertion of the ear-bars in step 1.2 results in a slight compression of the skull and consequent disruption in intracranial volume and hence an increased ICP. If the sensor is positioned correctly, ICP will drop at least 4 - 5 mmHg with the removal of the ear-bars.
Histological analysis may be used to check for any damage to the cortical area immediately under the pressure sensor and screw. An example of a traumatic and non-traumatic screw insertion is depicted in Figure 4.
<img alt="Figure 1" src="/files/ftp_upload/3689/3689fig1.jpg" /> 
Figure 1. Fluid Filled Vs SAMBA ICP Traces. ICP was recorded simultaneously via the SAMBA fibre-optic catheter (top) and a fluid filled catheter (bottom). The mean ICP values were similar in both traces, however the fluid filled catheter signal was notably dampened compared to the clear respiratory and arterial pressure waveforms seen with the fibre-optic catheter.
<img alt="Figure 2" src="/files/ftp_upload/3689/3689fig2.jpg" /> 
Figure 2. Intracranial Pressure Catheter Insertion Procedure. The rat's head was secured in a stereotaxic frame with ear-bars and an anaesthetic nose cone [A]. A hole, approximately 2 mm in diameter, was drilled into the right parietal bone [B]. A 2 x 4 mm screw with a 0.7 mm hole in the shaft was inserted [C]. An anchoring screw was inserted into the left parietal bone and the skull and surgical site covered in dental cement. The ICP catheter (black arrow) was then inserted into the screw-hole and an airtight seal made with the caulking material (white arrow) [D]. Staple (for scale) = 12 mm x 5 mm.
<img alt="Figure 3" src="/files/ftp_upload/3689/3689fig3.jpg" /> 
Figure 3. Monitoring Screw Burr Hole Orientation. The skull was cleared of connective tissue to locate Lambda (black asterisk) and Bregma (white asterisk) and the hole drilled 2 mm lateral and 2 mm posterior from Bregma. The hole was cleared of debris leaving the dura and pial vessels (black arrow) intact. Staple (for scale) = 12 mm x 5 mm.
<img alt="Figure 4" src="/files/ftp_upload/3689/3689fig4.jpg" /> 
Figure 4. Histology of Rat Brain 24 Hours after Instrumentation of ICP Monitoring Screw. Haemotoxylin and Eosin staining, 6 &mu;m coronal sections. Left: Non-traumatic screw insertion. Right: Traumatic screw insertion, area of pallor depicts damaged tissue with similar cellular morphology to stroke damaged area (arrow). Inserts at 4x objective.
<img alt="Figure 5" src="/files/ftp_upload/3689/3689fig5.jpg" /> 
Figure 5. Typical ICP Trace. Pulse pressure waves are depicted by events of smaller amplitude (*). Ventilation is reflected by events of longer periodicity (#).
<img alt="Figure 6" src="/files/ftp_upload/3689/3689fig6.jpg" /> 
Figure 6. ICP Probe Insertion Schematic. Diagram illustrates placement of support screw (right) and caulking material coated ICP probe into screw (left).
<img alt="Figure 7" src="/files/ftp_upload/3689/3689fig7.jpg" /> 
Figure 7. Abdominal Compression. The abdomen was temporarily compressed (~1 sec) to validate the viability of the ICP signal. Compression results in reduced cerebral venous return, increasing intracranial volume and thus increasing ICP. Arterial pressure (Pa) dropped only after the initial ICP rise.
<img alt="Figure 8" src="/files/ftp_upload/3689/3689fig8.jpg" /> 
Figure 8. Period of Apnoea. The temporary cessation of breathing is reflected in the diaphragm transducer trace, the arterial pressure (Pa) trace and the ICP trace.
<img alt="Figure 9" src="/files/ftp_upload/3689/3689fig9.jpg" /> 
Figure 9. Ear-Bar Removal. ICP should drop with the removal of the stereotaxic frame ear-bars.

<ol>
	<li>Ng, L. K., Nimmannitya, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Massive+cerebral+infarction+with+severe+brain+swelling:+a+clinicopathological+study.">Massive cerebral infarction with severe brain swelling: a clinicopathological study.</a> Stroke. 1, 158-163 (1970).</li><li>Plum, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Brain+swelling+and+edema+in+cerebral+vascular+disease.">Brain swelling and edema in cerebral vascular disease.</a> Res. Publ. Assoc. Res. Nerv. Ment. Dis. 41, 318-348 (1966).</li><li>Ropper, A. H., Shafran, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Brain+edema+after+stroke.+Clinical+syndrome+and+intracranial+pressure.">Brain edema after stroke. Clinical syndrome and intracranial pressure.</a> Arch. Neurol. 41, 26-29 (1984).</li><li>Silver, F. L., Norris, J. W., Lewis, A. J., Hachinski, V. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Early+mortality+following+stroke:+a+prospective+review.">Early mortality following stroke: a prospective review.</a> Stroke. 15, 492-496 (1984).</li><li>Geraci, E. B., Geraci, T. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hyperventilation+and+head+injury:+controversies+and+concerns.">Hyperventilation and head injury: controversies and concerns.</a> J. Neurosci. Nurs. 28, 381-387 (1996).</li><li>Schwab, S., Aschoff, A., Spranger, M., Albert, F., Hacke, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+value+of+intracranial+pressure+monitoring+in+acute+hemispheric+stroke.">The value of intracranial pressure monitoring in acute hemispheric stroke.</a> Neurology. 47, 393-398 (1996).</li><li>Adams, H. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Guidelines+for+the+early+management+of+patients+with+ischemic+stroke:+A+scientific+statement+from+the+Stroke+Council+of+the+American+Stroke+Association.">Guidelines for the early management of patients with ischemic stroke: A scientific statement from the Stroke Council of the American Stroke Association.</a> Stroke. 34, 1056-1083 (2003).</li><li>Zhong, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Advances+in+ICP+monitoring+techniques.">Advances in ICP monitoring techniques.</a> Neurol. Res. 25, 339-350 (2003).</li><li>Aucoin, P. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Intracranial+pressure+monitors.+Epidemiologic+study+of+risk+factors+and+infections.">Intracranial pressure monitors. Epidemiologic study of risk factors and infections.</a> Am. J. Med. 80, 369-376 (1986).</li><li>Silasi, G., MacLellan, C. L., Colbourne, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Use+of+telemetry+blood+pressure+transmitters+to+measure+intracranial+pressure+(ICP)+in+freely+moving+rats.">Use of telemetry blood pressure transmitters to measure intracranial pressure (ICP) in freely moving rats.</a> Curr. Neurovasc. Res. 6, 62-69 (2009).</li><li>Crutchfield, J. S., Narayan, R. K., Robertson, C. S., Michael, L. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaluation+of+a+fiberoptic+intracranial+pressure+monitor.">Evaluation of a fiberoptic intracranial pressure monitor.</a> J. Neurosurg. 72, 482-487 (1990).</li><li>Bolander, R., Mathie, B., Bir, C., Ritzel, D., Vandevord, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Skull+Flexure+as+a+Contributing+Factor+in+the+Mechanism+of+Injury+in+the+Rat+when+Exposed+to+a+Shock+Wave.">Skull Flexure as a Contributing Factor in the Mechanism of Injury in the Rat when Exposed to a Shock Wave.</a> Ann. Biomed. Eng. , (2011).</li><li>Chavko, M., Koller, W. A., Prusaczyk, W. K., McCarron, R. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measurement+of+blast+wave+by+a+miniature+fiber+optic+pressure+transducer+in+the+rat+brain.">Measurement of blast wave by a miniature fiber optic pressure transducer in the rat brain.</a> J. Neurosci. Methods. 159, 277-281 (2007).</li><li>Chavko, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Relationship+between+orientation+to+a+blast+and+pressure+wave+propagation+inside+the+rat+brain.">Relationship between orientation to a blast and pressure wave propagation inside the rat brain.</a> J. Neurosci. Methods. 195, 61-66 (2011).</li><li>Leonardi, A. D., Bir, C. A., Ritzel, D. V., VandeVord, P. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Intracranial+pressure+increases+during+exposure+to+a+shock+wave.">Intracranial pressure increases during exposure to a shock wave.</a> J. Neurotrauma. 28, 85-94 (2011).</li></ol>

We have nothing to disclose.

The procedure presented here enables a very sensitive and accurate recording of intracranial pressure. This minimally invasive technique avoids significant brain trauma by positioning the pressure sensor in the epidural space and not the brain tissue or ventricles. 
The critical steps Include: 1) drilling through the skull &#x2013; care must be taken not to pierce the dura or damage underlying brain tissue; 2) ensuring a tight seal with the caulking material &#x2013; if there is any leak, the...

<table border="1">
 <tbody>
 <tr>
 <td>Name of the reagent</td>
 <td>Company</td>
 <td>Catalogue number</td>
 <td>Comments</td>
 </tr>
 <tr>
 <td>Dental Cement Monomer</td>
 <td>Henry Schein</td>
 <td>VX- SC500MLL</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Dental Cement Polymer</td>
 <td>Henry Schein</td>
 <td>VX- SC1000GCL4</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Dental drill burr- size 12</td>
 <td>Gunz Dental</td>
 <td>EL104S001012/10</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Dental drill burr- size 6</td>
 <td>Gunz Dental</td>
 <td>EL104S001006/10</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Metal Screw</td>
 <td>Hardware Store</td>
 <td>&nbsp;</td>
 <td>2 x 4 mm, hexagonal head. (laboratory-modified by 0.7 mm hole drilled through shaft) </td>
 </tr>
 <tr>
 <td>SAMBA Control Unit</td>
 <td>Harvard Apparatus</td>
 <td>50433102</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>SAMBA Sensor</td>
 <td>Harvard Apparatus</td>
 <td>50461122</td>
 <td>420 LP, 15cm bare fibre, radio-opaque coating</td>
 </tr>
 <tr>
 <td>Silagum AV Mono caulking material</td>
 <td>Gunz Dental</td>
 <td>RG 9152</td>
 <td>Vinylpolysiloxanes, hydrogen polysiloxanes, filler, pigments, additives, plantinum catalyst</td>
 </tr>
 <tr>
 <td>Terg-A-Zyme</td>
 <td>Alconox, Inc.</td>
 <td>1304</td>
 <td>Enzyme-active powdered detergent</td>
 </tr>
 </tbody>
</table>

epidural intracranial pressure measurement in rats using a fiber-optic pressure transducer

Elevated intracranial pressure (ICP) is a significant problem in several forms of ischemic brain injury including stroke, traumatic brain injury and cardiac arrest. This elevation may result in further neurological injury, in the form of transtentorial herniation1,2,3,4, midbrain compression, neurological deficit or increased cerebral infarct2,4. Current therapies are often inadequate to control elevated ICP in the clinical setting5,6,7 . Thus there is a need for accurate methods of ICP measurement in animal models to further our understanding of the basic mechanisms and to develop new treatments for elevated ICP.
In both the clinical and experimental setting ICP cannot be estimated without direct measurement. Several methods of ICP catheter insertion currently exist. Of these the intraventricular catheter has become the clinical 'gold standard' of ICP measurement in humans8. This method involves the partial removal of skull and the instrumentation of the catheter through brain tissue. Consequently, intraventricular catheters have an infection rate of 6-11%9. For this reason, subdural and epidural cannulations have become the preferred methods in animal models of ischemic injury. 
Various ICP measurement techniques have been adapted for animal models, and of these, fluid-filled telemetry catheters10 and solid state catheters are the most frequently used11,12,13,14,15. The fluid-filled systems are prone to developing air bubbles in the line, resulting in false ICP readings. Solid state probes avoid this problem (Figure 1). An additional problem is fitting catheters under the skull or into the ventricles without causing any brain injury that might alter the experimental outcomes. Therefore, we have developed a method that places an ICP catheter contiguous with the epidural space, but avoids the need to insert it between skull and brain. 
An optic fibre pressure catheter (420LP, SAMBA Sensors, Sweden) was used to measure ICP at the epidural location because the location of the pressure sensor (at the very tip of the catheter) was found to produce a high fidelity ICP signal in this model. There are other manufacturers of similar optic fibre technologies13 that may be used with our methodology. Alternative solid state catheters, which have the pressure sensor located at the side of the catheter tip, would not be appropriate for this model as the signal would be dampened by the presence of the monitoring screw. 
Here, we present a relatively simple and accurate method to measure ICP. This method can be used across a wide range of ICP related animal models.

Watch this Scientific Journal Video about Epidural Intracranial Pressure Measurement in Rats Using a Fiber-optic Pressure Transducer at JoVE.com

Epidural Intracranial Pressure Measurement in Rats Using a Fiber-optic Pressure Transducer

A novel technique to record the pressures within the skull is described. The minimally invasive method uses a fibre-optic pressure sensing system to accurately measure intracranial pressure (ICP) in anaesthetized rats without causing significant brain trauma. The technique may be used in a wide range of experimental models.

Elevated intracranial pressure (ICP) is a significant problem in several forms of ischemic brain injury including stroke, traumatic brain injury and ...

epidural-intracranial-pressure-measurement-rats-using-fiber-optic

Research

JoVE Journal

Medicine

20.8K Views.  The University of Newcastle. Una nuova tecnica per registrare le pressioni all'interno del cranio è descritto. Il metodo minimamente invasivo utilizza una fibra ottica sistema di rilevamento della pressione per misurare accuratamente la pressione endocranica (ICP) in ratti anestetizzati senza causare traumi significativi cervello. La tecnica può essere utilizzata in un'ampia gamma di modelli sperimentali.

Video: Epidural Intracranial Pressure Measurement in Rats Using a Fiber-optic Pressure Transducer

Automated Midline Shift and Intracranial Pressure Estimation based on Brain CT Images

In this paper we present an automated system based mainly on the computed tomography (CT) images consisting of two main components: the midline shift estimation and intracranial pressure (ICP) pre-screening system. To estimate the midline shift, first an estimation of the ideal midline is performed based on the symmetry of the skull and anatomical features in the brain CT scan. Then, segmentation of the ventricles from the CT scan is performed and used as a guide for the identification of the actual midline through shape matching. These processes mimic the measuring process by physicians and have shown promising results in the evaluation. In the second component, more features are extracted related to ICP, such as the texture information, blood amount from CT scans and other recorded features, such as age, injury severity score to estimate the ICP are also incorporated. Machine learning techniques including feature selection and classification, such as Support Vector Machines (SVMs), are employed to build the prediction model using RapidMiner. The evaluation of the prediction shows potential usefulness of the model. The estimated ideal midline shift and predicted ICP levels may be used as a fast pre-screening step for physicians to make decisions, so as to recommend for or against invasive ICP monitoring.

An automated midline shift estimation and intracranial pressure (ICP) pre-screening system based on computed tomography (CT) images for patients with traumatic brain injury (TBI) is proposed using image processing and machine learning techniques.

In this paper we present an automated system based mainly on the computed tomography (CT) images consisting of two main components: the midline shift ...

Ascending Aortic Constriction in Rats for Creation of Pressure Overload Cardiac Hypertrophy Model

Ascending aortic constriction is the most common and successful surgical model for creating pressure overload induced cardiac hypertrophy and heart failure. Here, we describe a detailed surgical procedure for creating pressure overload and cardiac hypertrophy in rats by constriction of the ascending aorta using a small metallic clip. After anesthesia, the trachea is intubated by inserting a cannula through a half way incision made between two cartilage rings of trachea. Then a skin incision is made at the level of the second intercostal space on the left chest wall and muscle layers are cleared to locate the ascending portion of aorta. The ascending aorta is constricted to 50&#8211;60% of its original diameter by application of a small sized titanium clip. Following aortic constriction, the second and third ribs are approximated with prolene sutures. The tracheal cannula is removed once spontaneous breathing was re-established. The animal is allowed to recover on the heating pad by gradually lowering anesthesia. The intensity of pressure overload created by constriction of the ascending aorta is determined by recording the pressure gradient using trans-thoracic two dimensional Doppler-echocardiography. Overall this protocol is useful to study the remodeling events and contractile properties of the heart during the gradual onset and progression from compensated cardiac hypertrophy to heart failure stage.

We describe a stepwise procedure for creating pressure overload and left ventricular hypertrophy in Wistar rats by constriction of the ascending aorta using a small metallic clip. This model is extensively used for studying remodeling changes during cardiac hypertrophy and for identifying and evaluating strategies for regression of such changes.

Ascending aortic constriction is the most common and successful surgical model for creating pressure overload induced cardiac hypertrophy and heart ...

Assessing Myogenic Response and Vasoactivity In Resistance Mesenteric Arteries Using Pressure Myography

Small resistance arteries constrict and dilate respectively in response to increased or decreased intraluminal pressure; this phenomenon known as myogenic response is a key regulator of local blood flow. In isobaric conditions small resistance arteries develop sustained constriction known as myogenic tone (MT), which is a major determinant of systemic vascular resistance (SVR). Hence, ex vivo&#160;pressurized preparations of small resistance arteries are major tools to study microvascular function in near-physiological states. To achieve this, a freshly isolated intact segment of a small resistance artery (diameter ~260 &#956;m) is mounted onto two small glass cannulas and pressurized. These arterial preparations retain most in vivo characteristics and permit assessment of vascular tone in real-time. Here we provide a detailed protocol for assessing vasoactivity in pressurized small resistance mesenteric arteries from rats; these arteries develop sustained vasoconstriction - approximately 25% of maximal diameter - when pressurized at 70 mmHg. These arterial preparations may be used to study the effect of investigational compounds on relationship between intra-arterial pressure and vasoactivity and determine changes in microvascular function in animal models of various diseases.

Pressure myography is used to assess vasoactivity of small arteries that develop sustained constriction when pressurized. This manuscript provides a detailed protocol to assess in isolated segments of small mesenteric arteries from rats, vasoactivity and the effect of intraluminal pressure on vascular diameter.

Small resistance arteries constrict and dilate respectively in response to increased or decreased intraluminal pressure; this phenomenon known as myogenic ...

Measurement of the Pressure-volume Curve in Mouse Lungs

In recent decades the mouse has become the primary animal model of a variety of lung diseases. In models of emphysema or fibrosis, the essential phenotypic changes are best assessed by measurement of the changes in lung elasticity. To best understand specific mechanisms underlying such pathologies in mice, it is essential to make functional measurements that can reflect the developing pathology. Although there are many ways to measure elasticity, the classical method is that of the total lung pressure-volume (PV) curve done over the whole range of lung volumes. This measurement has been made on adult lungs from nearly all mammalian species dating back almost 100 years, and such PV curves also played a major role in the discovery and understanding of the function of pulmonary surfactant in fetal lung development. Unfortunately, such total PV curves have not been widely reported in the mouse, despite the fact that they can provide useful information on the macroscopic effects of structural changes in the lung. Although partial PV curves measuring just the changes in lung volume are sometimes reported, without a measure of absolute volume, the nonlinear nature of the total PV curve makes these partial ones very difficult to interpret. In the present study, we describe a standardized way to measure the total PV curve. We have then tested the ability of these curves to detect changes in mouse lung structure in two common lung pathologies, emphysema and fibrosis. Results showed significant changes in several variables consistent with expected structural changes with these pathologies. This measurement of the lung PV curve in mice thus provides a straightforward means to monitor the progression of the pathophysiologic changes over time and the potential effect of therapeutic procedures.

Here we present a protocol to simply and reliably measure the lung pressure-volume curve in mice, showing that it is sufficiently sensitive to detect phenotypic parenchymal changes in two common lung pathologies, pulmonary fibrosis and emphysema. This metric provides a means to quantify the lung&#8217;s structural changes with developing pathology.

In recent decades the mouse has become the primary animal model of a variety of lung diseases. In models of emphysema or fibrosis, the essential ...

Intrauterine Telemetry to Measure Mouse Contractile Pressure In Vivo

A complex integration of molecular and electrical signals is needed to transform a quiescent uterus into a contractile organ at the end of pregnancy. Despite the discovery of key regulators of uterine contractility, this process is still not fully understood. Transgenic mice provide an ideal model in which to study parturition. Previously, the only method to study uterine contractility in the mouse was ex vivo isometric tension recordings, which are suboptimal for several reasons. The uterus must be removed from its physiological environment, a limited time course of investigation is possible, and the mice must be sacrificed. The recent development of radiometric telemetry has allowed for longitudinal, real-time measurements of in vivo intrauterine pressure in mice. Here, the implantation of an intrauterine telemeter to measure pressure changes in the mouse uterus from mid-pregnancy until delivery is described. By comparing differences in pressures between wild type and transgenic mice, the physiological impact of a gene of interest can be elucidated. This technique should expedite the development of therapeutics used to treat myometrial disorders during pregnancy, including preterm labor.

Intrauterine Telemetry to Measure Mouse Contractile Pressure In Vivo

This manuscript provides a protocol for implanting telemeters in the mouse for the purpose of measuring intrauterine pressures during pregnancy.

A complex integration of molecular and electrical signals is needed to transform a quiescent uterus into a contractile organ at the end of pregnancy. ...

Trabecular Meshwork Response to Pressure Elevation in the Living Human Eye

The mechanical characteristics of the trabecular meshwork (TM) are linked to outflow resistance and intraocular pressure (IOP) regulation. The rationale behind this technique is the direct observation of the mechanical response of the TM to acute IOP elevation. Prior to scanning, IOP is measured at baseline and during IOP elevation. The limbus is scanned by spectral-domain optical coherence tomography at baseline and during IOP elevation (ophthalmodynamometer (ODM) applied at 30 g force). Scans are processed to enhance visualization of the aqueous humor outflow pathway using ImageJ. Vascular landmarks are used to identify corresponding locations in baseline and IOP elevation scan volumes. Schlemm canal (SC) cross-sectional area (SC-CSA) and SC length from anterior to posterior along its long axis are measured manually at 10 locations within a 1 mm segment of SC. Mean inner to outer wall distance (short axis length) is calculated as the area of SC divided by its long axis length. To examine the contribution of adjacent tissues to the effect IOP elevations, measurements are repeated without and with smooth muscle relaxation with instillation of tropicamide. TM migration into SC is resisted by TM stiffness, but is enhanced by the support of its attachment to adjacent smooth muscle within the ciliary body. This technique is the first to measure the living human TM response to pressure elevation in situ under physiological conditions within the human eye.

Trabecular meshwork (TM) migration into Schlemm&#8217;s canal space can be induced by acute pressure elevation by ophthalmodynamometer, and observed by spectral domain optical coherence tomography. The goal of this method is to quantify the morphometric response of the living outflow tract to acute pressure elevation in living tissues in situ.

The mechanical characteristics of the trabecular meshwork (TM) are linked to outflow resistance and intraocular pressure (IOP) regulation. The rationale ...

Long-term Blood Pressure Measurement in Freely Moving Mice Using Telemetry

During the development of new vasoactive agents, arterial blood pressure monitoring is crucial for evaluating the efficacy of the new proposed drugs. Indeed, research focusing on the discovery of new potential therapeutic targets using genetically altered mice requires a reliable, long-term assessment of the systemic arterial pressure variation. Currently, the gold standard for obtaining long-term measurements of blood pressure in ambulatory mice uses implantable radio-transmitters, which require&#160;artery cannulation. This technique eliminates the need for tethering, restraining, or anesthetizing the animals which introduce stress and artifacts during data sampling. However, arterial blood pressure monitoring in mice via catheterization can be rather challenging due to the small size of the arteries. Here we present a step-by-step guide to illustrate the crucial key passages for a successful subcutaneous implantation of radio-transmitters and carotid artery cannulation in mice. We also include examples of long-term blood pressure activity taken from freely moving mice after a period of post-surgery recovery. Following this procedure will allow reliable direct blood pressure recordings from multiple animals simultaneously.

The goal of this protocol is to assess systemic blood pressure in conscious freely moving mice using implantable radio-telemetry devices.

During the development of new vasoactive agents, arterial blood pressure monitoring is crucial for evaluating the efficacy of the new proposed drugs. ...

Cavernous Nerve Stimulation and Recording of Intracavernous Pressure in a Rat

The stimulation of the cavernous nerve (CN) and measurement of intracavernous pressure (ICP) have been used extensively to test and evaluate therapies for erectile dysfunction. However, the methods used vary between laboratories, and pitfalls still exist. The goal of this study was to describe a surgical technique that would provide a reliable and reproducible model. By exposing the ischiocavernosus muscle at its point of insertion on the ischial tuberosity, the penile crus could be cannulated with minimal dissection and injury to the structures involved in erectile function. Repeated stimulation of the CN, without the need for lifting and drying, was achieved by using a 125 &#181;m bipolar silver electrode and biocompatible silicon glue to isolate the electrode-nerve complex. This method prevents neuropraxia by reducing stretching and drying the nerve and provides complete isolation of the nerve, negating electrical leakage and preventing stimulation of alternative pathways.

This study describes a simplified surgical procedure and technique for performing cavernous nerve stimulation with the isolation of the nerve-electrode complex using silicone glue and intracavernous pressure measurement.

The stimulation of the cavernous nerve (CN) and measurement of intracavernous pressure (ICP) have been used extensively to test and evaluate therapies for ...

Measurement of the Hepatic Venous Pressure Gradient and Transjugular Liver Biopsy

Here we provide a detailed protocol describing the clinical procedure of hepatic venous pressure gradient (HVPG) measurement in patients with advanced chronic liver disease followed by an instruction for transjugular biopsy. Under local anesthesia and ultrasound guidance, a catheter introducer sheath is placed in the right internal jugular vein. Using&#160;fluoroscopic guidance, a balloon catheter is advanced into the inferior vena cava (IVC) and inserted into a large hepatic vein. Correct and sufficient wedge position of the catheter is ensured by injecting contrast media while the balloon is blocking the outflow of the cannulated hepatic vein. After calibrating the external pressure transducer, continuous pressure recordings are obtained with triplicate recordings of the wedged hepatic venous pressure (WHVP) and free hepatic venous pressure (FHVP). The difference between FHVP and WHVP is referred to as HVPG, with values &#8805;10 mm Hg indicating clinically significant portal hypertension (CSPH). Before removing the catheter, pressure readings obtained in the IVC at the same level, as well as the right atrial pressure are recorded.
Finally, a transjugular liver biopsy can be obtained via the same vascular route. Different systems are available; however, core biopsy needles are preferred over aspiration needles, especially for cirrhotic livers. Again, under fluoroscopic guidance a biopsy needle introducer sheath is advanced into an hepatic vein. Next, the transjugular biopsy needle is gently advanced through the introducer sheath: (i) in case of aspiration biopsy, the needle is advanced into the liver parenchyma under aspiration and then removed quickly, or (ii) in case of a core biopsy, the cutting-mechanism is triggered inside the parenchyma. Several separate passages can be safely performed to obtain sufficient liver specimens via transjugular biopsy. In experienced hands, the combination of these procedures takes about 30-45 min.

Here, we present a protocol for measurement of hepatic venous pressure gradient (HVPG),the gold standard to diagnose clinically significant portal hypertension. Moreover, we describe how to perform a transjugular liver biopsy within the same session.

Here we provide a detailed protocol describing the clinical procedure of hepatic venous pressure gradient (HVPG) measurement in patients with advanced ...

Simultaneous Electrocardiography Recording and Invasive Blood Pressure Measurement in Rats

For studies related to cardiovascular physiology or pathophysiology, blood pressure (BP) and electrocardiography are basic observational parameters. Research focusing on cardiovascular disease models, potential cardiovascular therapeutic targets or pharmaceutical agents requires assessment of systemic arterial pressure and heart rhythm changes. In situations where radio telemetry systems are not available or affordable, the technique of femoral artery cannulation is an alternative way to obtain intra-arterial pressure waveform recordings and systemic BP measurements. This technique is economical and can be performed with standard equipment in animal facilities. However, invasive arterial pressure recording requires cannulation of small arteries, which can be a challenging surgical skill. Here, we present step-by-step protocols for femoral artery cannulation procedures. Key procedures include the calibration of the data acquisition system, tissue dissection and femoral artery cannulation, and setup of the arterial cannulation system for pressure recording. Surface electrocardiography recording procedures are also included. We also present examples of BP recordings from normotensive and hypertensive rats. This protocol allows reliable direct recordings of systemic BP with simultaneous electrocardiography.

Here, we describe a setup for simultaneous recording of electrocardiography and intra-arterial blood pressure (BP) in experimental rats, which can be done with standard equipment in animal facilities and can be applied to physiological or pharmacological studies to investigate pathogenic or therapeutic mechanisms in cardiovascular medicine.

For studies related to cardiovascular physiology or pathophysiology, blood pressure (BP) and electrocardiography are basic observational parameters. ...