What is Breath Holding Test?
The Breath Holding (BH) test is a specific test for evaluation of Vasomotor Reactivity (VMR) and cerebral autoregulatory capacity.
Identification of exhausted VMR can be a good indication for high risk for stroke. The 3 main methods to induce and test the VMR capacity include:
- The CO2 Reactivity Test, which requires installation and operation of a special CO2 hookup,
- Acetazolamide Testing, which requires intravenous (IV) medication, and
- The Breath Holding Test, which is a simple and non-invasive test that can be performed on any patient that is capable of holding a breath for at least 30 seconds.
How to use TCD for the Breath Holding Test
The purpose of the BH test is to induce a temporary increase in CO2, which in turn results in cerebral vasodilation. The BH test is quick and simple and can be performed unilaterally or bilaterally. Once the patient is relaxed and breaths normally for a few minutes, they are instructed to hold their breath for at least 30 seconds. TCD measurements are continuously monitored during the duration of the test, and typically the MCA velocities are monitored. Measurements are made specifically at baseline prior to the patient initiating breath-holding and when the patient starts to breathe again. There are various methods to calculate the Breath Holding Index (BHI), with the most common method being based on the formula:
It is expected that with an intact vasomotor reactivity the mean blood flow velocity (MFV) will increase as the duration of breath-holding progresses. An increase in mean or peak blood flow velocities during breath-holding indicates different levels of patent autoregulatory capacity. On the other hand, the absence of flow increase during the BH test indicates the diminished physiological vasodilatory capacity and potentially high risk for stroke and other detrimental conditions.
Using Dolphin for Breath Holding Test
The Viasonix Dolphin is ideal for performing the Breath Holding Test quickly and effectively with a dedicated breath-holding protocol. The BH protocol was originally developed for the Sonara TCD systems after visiting the laboratories of Dr. Alexandrov. It has since been significantly improved with the dolphin systems.
This Breath Holding protocol guides the examiner in a simple way along the different stages of the BH test, with the use of only a single control button. The control Baseline and the Doppler Spectrum at the end of the test are automatically captured and displayed alongside a table that details the velocity and pulsatility parameters for Control and end of breath-holding, along with the relative percentage change in each parameter value. In addition, the BHI (Breath Holding Index) as well as the duration of breath-holding by the patient are automatically calculated and displayed for immediate clinical determination.
During the breath-holding process, a large digital timer is displayed on the screen to help both the patient and the examiner in keeping track of the duration of the procedure. This timer greatly helps the patient to be aware of how much longer is required to hold the breath and get through the test successfully. The Dolphin automatically places unique markers to identify the start and end of the test. The Doppler waveforms during the complete test process, as well as the trends of the velocity or pulsatility parameters, are displayed in a special monitoring trends screen.
Impaired VMR is considered when the BHI value is less than 0.69 when calculated based on the standard formula above.
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