What is Breath Holding Test?
The Breath Holding (BH) test is a specific test for evaluation of Vasomotor Reactivity (VMR) and cerebral autoregulatory capacity.
Breath holding is a simple and non-invasive method to assess cerebral vasomotor reactivity (VMR) using transcranial Doppler (TCD). In clinical settings, it is used to evaluate the cerebrovascular system’s ability to adjust to changes in carbon dioxide (CO₂) concentrations.
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 Study, 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.
Applications of the Breath Holding Study
Here’s when and why breath-holding is needed:
Assessment of Vasomotor Reactivity
Breath-holding causes an increase in arterial CO₂ (hypercapnia). The brain responds to elevated CO₂ levels by dilating cerebral blood vessels, leading to an increase in cerebral blood flow. By using TCD to monitor the blood flow velocities in cerebral arteries during breath-holding, clinicians can assess the brain’s vasomotor reactivity.
Detection of Cerebrovascular Disease
Impaired VMR may indicate cerebrovascular disease, chronic cerebrovascular insufficiency, or other disorders. Patients with cerebrovascular disease might have a blunted or delayed increase in blood flow velocity during breath holding.
Pre-surgical Evaluation
Before certain surgeries, especially carotid endarterectomy or cardiac surgery, breath-holding tests can be used to evaluate the risk of intraoperative cerebral ischemia.
Monitoring Cerebral Autoregulation
Assessing cerebral autoregulation can be crucial in conditions like traumatic brain injury or after subarachnoid hemorrhage. Breath holding can act as a challenge to assess the brain’s ability to maintain stable blood flow despite changes in systemic blood pressure or CO₂ levels.
Monitoring Chronic Cerebrovascular Effects
Breath-holding can detect early changes in cerebral vasculature due to stroke risk factors like diabetes and arteriosclerosis.
Brain Research
Due to their non-invasive nature, breath-holding tests are also used in research settings to study cerebral hemodynamics.
How to Perform Breath Holding Test with TCD
Transcranial Doppler (TCD) is an important tool in the diagnostic arsenal for assessing cerebral blood flow dynamics, and specifically for this test – the cerebral autoregulation capacity.
This step-by-step guide outlines a common protocol for the Breath Holding Test using TCD:
Step 1: Patient Evaluation
- Before initiation, assess the patient for potential contraindications, specifically elevated intracranial pressure (ICP) or cardiopulmonary disease. The test cannot be done with unresponsive patients or patients who cannot hold their breath for at least 20 seconds.
- Clearly communicate the procedure’s objectives and steps to the patient, emphasizing the breath-holding component.
Step 2: TCD Equipment Preparation
- Select a Breath Holding Protocol.
- Adjust the Doppler parameters such as Depth, Sample Volume, Power, and Gain.
- Bilateral studies are preferable. For bilateral studies, a robotic headset is recommended for precise measurements, though a manual headset can be utilized as well.
Step 3: Acquire Baseline Doppler Signal
- Begin by capturing baseline blood flow velocities, focusing on the Middle Cerebral Artery (MCA).
- Once a stable velocity is obtained, document the mean velocity, which is crucial for the Breath Holding Index (BHI) calculation at the end of the study.
- Allow the patient a brief period of regular respiration.
- Press the “Record” button on the TCD Machine to start capturing the Doppler baseline signals.
Step 4: Initiating the Breath-Holding Phase
- Instruct the patient to perform a 30-second breath hold without first taking a breath and to refrain from performing Valsalva.
- Press the “Start Breath Holding” button in the TCD Machine as soon as the patient starts breath-holding.
Step 5: During the Breath-Holding Phase
- Closely watch vital signs and patient comfort.
- Continuously observe the M Mode window. Any significant deviations observed in the M Mode may indicate patient or probe movement, which could affect results accuracy.
- Let the patient know every few seconds about how many seconds have passed or how many seconds are left. It is recommended that the patient will view the TCD display screen where the Breath Holding duration is digitally displayed to encourage the patient to keep holding their breath.
Step 6: Completing the Breath-Holding Phase
- Once the 30 seconds limit has passed, or if the patient is unable to complete the breath-holding phase, press ‘Stop Breath Holding’ button on the TCD Machine.
- Continue recording for a few more seconds until pressing Freeze on the TCD Machine to ensure that the true maximum velocity was captured.
- Document the mean velocity at the end of the breath-holding phase. Depending on your institute protocols, the mean velocity might be recorded immediately or a 2-4 seconds post breath hold.
Step 7: Data Analysis and BHI Calculation
- Verify the correctness of the envelope tracking at captured waveforms of both start and stop breath-holding waveforms. A Doppler signal with poor quality may require recalculation of the mean velocities using cursors.
- Using the documented mean velocities, calculate the Breath Holding Index (BHI) per the formula below:
Step 8: Comprehensive Documentation
- Carefully enter all relevant findings into the patient’s record, including baseline values, observed changes, and the BHI.
- Use the collected data to assess the patient’s cerebral autoregulatory capacities and potential vascular implications.
This step-by-step guide for performing a Breath Holding test is for informational purposes only. Healthcare professionals should rely on their expertise, clinical judgment, and institutional protocols for accurate administration and interpretation. Additional clinical information, patient history, physical examination, and other diagnostic tests may be necessary for comprehensive evaluation.
Using Dolphin TCD for Breath Holding Test
The Viasonix Dolphin is a robotic Transcranial Doppler machine ideal for performing the Breath Holding Test quickly and effectively.
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.
Here are some key benefits of using the Dolphin TCD for breath-holding tests:
1. Dedicated Breath Holding Protocol: A dedicated breath-holding protocol that streamlines the test procedure. This protocol guides the examiner through the various stages of the Breath Holding study using a single control button, making it easy to follow and execute.
2. Robotically Assisted Test: Use the renowned Dolphin/XF robotic probe to perform the Breath Holding test bilaterally. Benefit from enhanced comfort for the patient with the fabric headset and reduced time and effort in locating the signal.
3. Unique Spectral Display: Dolphin TCD displays the entire test in a single spectral waveform allowing you to immediately visualize the trends.
4. Immediate BHI Calculation: Automatically calculate and display the Breath Holding Index (BHI) as well as the duration of breath holding by the patient in real time.
5. Enhanced Efficiency: Capture and display Doppler waveforms with high quality spectral display and ultra sensitive Doppler probes. This ensures that the measurements taken during the Breath Holding examination are consistent, leading to easier assessment of cerebral blood flow dynamics and autoregulatory capacity.
6. Automated Data Capture: Automatically capture and display the Doppler waveforms before and after the breath-holding phase with a click of a button.
7. Large Timer Display: During the breath-holding process, a large digital timer is displayed on the screen, helping both the patient and the examiner track the duration of the procedure.
8. Multi Session Study: Repeat the breath-holding test as many times as you need in a single study. Dolphin software will automatically generate a single report that includes all breath-holding sessions.
Expected Results
It is expected that with intact vasomotor reactivity, the mean blood flow velocity (MFV) will increase as the duration of breath-holding progresses. An increase in mean 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.
Impaired VMR is considered when the BHI value is less than 0.69 when calculated based on the standard formula above.
Note that in a bilateral test, velocities on both sides are expected to trend similarly during the breath-holding phase. In case one side has a BHI that is considered normal and the other side has a BHI that is considered impaired (possibly a negative BHI), it may indicate a potential Reverse Robin Hood Syndrome (“steal phenomenon”).
Selected Literature
Assessment: transcranial Doppler ultrasonography: report of the Therapeutics and Technology Assessment Subcommittee of the American Academy of Neurology. Sloan MA et al., Therapeutics and Technology Assessment Subcommittee of the American Academy of Neurology. Neurology. 2004 May 11;62(9):1468-81
Transcranial Doppler: Techniques and advanced applications: Part 2, Sharma AK, Bathala L, Batra A, Mehndiratta MM, Sharma VK, Ann Indian Acad Neurol. 2016 Jan-Mar;19(1):102-7
Cerebrovascular ultrasound in stroke prevention and treatment, Edited by Andrei V. Alexandrov, Blackwell Publishing, 2004
Reversed Robin Hood Syndrome in Acute Ischemic Stroke Patients, Andrei V. Alexandrov et al., Stroke, 2007;38:3045-3048
Breath Holding Index in the Evaluation of Cerebral Vasoreactivity, Iris Zavoreo and Vida Demarin, Acta Clin Croat 2004; 43:15-19
Neuro-ultrasonography, Ryan Hakimi, Andrei V. Alexandrov, and Zsolt Garami, Neurol Clin 38 (2020) 215–229
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