Name: tilt testing with combined lower body negative pressure: a "gold standard" for measuring orthostatic tolerance
Uploaded: 2013-03-21T12:00:00
Description: Watch this Scientific Journal Video about Tilt Testing with Combined Lower Body Negative Pressure: a "Gold Standard" for Measuring Orthostatic Tolerance at JoVE.com

We would like to acknowledge Professor Roger Hainsworth, who developed this technique. We are grateful to Mr. King Hang Chao and Mr. Wang-Joe Woo for their assistance with photography.
This work is supported by Simon Fraser University and the Heart and Stroke Foundation of Canada.

Throughout testing, continuous beat-to-beat blood pressure and electrocardiogram (ECG) monitoring is paramount. This ensures subject safety, and prompt termination of the test with the onset of presyncope. Beat-to-beat blood pressure recordings can be obtained through arterial catheterization, or finger plethysmography31-33. The latter is used in this protocol because it is non-invasive and can assess the onset of presyncope with the same accuracy as catherization31,34, without the detrimental impac...

This technique is highly reproducible, has the ability to discriminate normal and abnormal responses with high sensitivity and specificity, and can provoke presyncope in all subjects, allowing for symptom recognition in patients with recurrent syncope. In a clinical setting, different types of syncope can be distinguished, allowing tailored treatment and management approaches. The impact of interventions can readily be assessed. With additional cardiovascular monitoring, reflex responses can also be evaluated.
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<table border="1">
 <tbody>
 <tr>
 <td>Equipment</td>
 <td>Manufacturer</td>
 <td>Location</td>
 </tr>
 <tr>
 <td>Tilt Table</td>
 <td>Custom-build</td>
 <td>Leeds, United Kingdom</td>
 </tr>
 <tr>
 <td>Finometer</td>
 <td>Finapres Medical Systems</td>
 <td>Amsterdam, The Netherlands</td>
 </tr>
 <tr>
 <td>Doppler Box</td>
 <td>Compumedics</td>
 <td>Singen, Germany</td>
 </tr>
 <tr>
 <td>Doppler software</td>
 <td>The DWL Doppler Company</td>
 <td>Singen, Germany</td>
 </tr>
 <tr>
 <td>Aquasonic Ultrasound gel</td>
 <td>Parker Laboratories, Inc.</td>
 <td>Fairfield, USA</td>
 </tr>
 <tr>
 <td>Headbands</td>
 <td>Lululemon</td>
 <td>Burnaby, Canada</td>
 </tr>
 <tr>
 <td>Headset</td>
 <td>Canadian Tire</td>
 <td>Burnaby, Canada</td>
 </tr>
 <tr>
 <td>ECG</td>
 <td>Finapres ECG Module, Finapres Medical Systems</td>
 <td>Amsterdam, The Netherlands</td>
 </tr>
 <tr>
 <td>Electrodes</td>
 <td>Red Dot</td>
 <td>Ontario, Canada</td>
 </tr>
 <tr>
 <td>Antiseptic Isopropyl Alcohol Pads</td>
 <td>Lernapharm</td>
 <td>Quebec, Canada</td>
 </tr>
 <tr>
 <td>O2Cap-Oxygen Analyser</td>
 <td>Oxigraph Inc.</td>
 <td>California, USA</td>
 </tr>
 <tr>
 <td>Airlife Nasal Oxygen Cannula</td>
 <td>Cardinal Health</td>
 <td>Mountainview, USA</td>
 </tr>
 <tr>
 <td>Powerlab 16/30</td>
 <td>AD Instruments</td>
 <td>Colorado Springs, USA</td>
 </tr>
 </tbody>
</table>

tilt testing with combined lower body negative pressure: a "gold standard" for measuring orthostatic tolerance

Orthostatic tolerance (OT) refers to the ability to maintain cardiovascular stability when upright, against the hydrostatic effects of gravity, and hence to maintain cerebral perfusion and prevent syncope (fainting). Various techniques are available to assess OT and the effects of gravitational stress upon the circulation, typically by reproducing a presyncopal event (near-fainting episode) in a controlled laboratory environment. The time and/or degree of stress required to provoke this response provides the measure of OT. Any technique used to determine OT should: enable distinction between patients with orthostatic intolerance (of various causes) and asymptomatic control subjects; be highly reproducible, enabling evaluation of therapeutic interventions; avoid invasive procedures, which are known to impair OT1.
In the late 1980s head-upright tilt testing was first utilized for diagnosing syncope2. Since then it has been used to assess OT in patients with syncope of unknown cause, as well as in healthy subjects to study postural cardiovascular reflexes2-6. Tilting protocols comprise three categories: passive tilt; passive tilt accompanied by pharmacological provocation; and passive tilt with combined lower body negative pressure (LBNP). However, the effects of tilt testing (and other orthostatic stress testing modalities) are often poorly reproducible, with low sensitivity and specificity to diagnose orthostatic intolerance7.
Typically, a passive tilt includes 20-60 min of orthostatic stress continued until the onset of presyncope in patients2-6. However, the main drawback of this procedure is its inability to invoke presyncope in all individuals undergoing the test, and corresponding low sensitivity8,9. Thus, different methods were explored to increase the orthostatic stress and improve sensitivity.
Pharmacological provocation has been used to increase the orthostatic challenge, for example using isoprenaline4,7,10,11 or sublingual nitrate12,13. However, the main drawback of these approaches are increases in sensitivity at the cost of unacceptable decreases in specificity10,14, with a high positive response rate immediately after administration15. Furthermore, invasive procedures associated with some pharmacological provocations greatly increase the false positive rate1.
Another approach is to combine passive tilt testing with LBNP, providing a stronger orthostatic stress without invasive procedures or drug side-effects, using the technique pioneered by Professor Roger Hainsworth in the 1990s16-18. This approach provokes presyncope in almost all subjects (allowing for symptom recognition in patients with syncope), while discriminating between patients with syncope and healthy controls, with a specificity of 92%, sensitivity of 85%, and repeatability of 1.1&plusmn;0.6 min16,17. This allows not only diagnosis and pathophysiological assessment19-22, but also the evaluation of treatments for orthostatic intolerance due to its high repeatability23-30. For these reasons, we argue this should be the "gold standard" for orthostatic stress testing, and accordingly this will be the method described in this paper.

Using this protocol, all subjects experience presyncope, and the definition of normal or abnormal responses is made largely based upon the time it takes to induce this reaction. OT is defined as the time to presyncope in minutes from the onset of upright tilting. Typical values for OT in healthy volunteers according to age and gender can be seen in Table 1. Patients with orthostatic intolerance exhibit presyncope earlier in the test, with 85% ending the test within the -20 mmHg phase compared to 23% of c...

Watch this Scientific Journal Video about Tilt Testing with Combined Lower Body Negative Pressure: a "Gold Standard" for Measuring Orthostatic Tolerance at JoVE.com

Tilt Testing with Combined Lower Body Negative Pressure: a "Gold Standard" for Measuring Orthostatic Tolerance

We describe a "gold standard" for evaluating orthostatic tolerance (OT) using tilt testing with combined lower body negative pressure (LBNP). This can be combined with non-invasive evaluations of cardiovascular reflex control. Normal and abnormal responses are defined.

Orthostatic tolerance (OT)  refers to the ability to maintain cardiovascular stability when upright,  against the hydrostatic effects of gravity, and ...

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