This article details a method for measuring cerebral blood flow velocity (CBFV) using Doppler ultrasound technology. The procedure involves monitoring blood flow in the middle cerebral artery (MCA) during breath-holding to assess changes in blood velocity.
To measure cerebral blood flow velocity, or CBFV, begin with a human participant with a secured Doppler ultrasound transducer.
Pre-applied ultrasound gel on the transducer facilitates efficient wave transmission.
The transducer is positioned over the middle cerebral artery, or MCA, which delivers oxygenated blood to the brain.
The transducer emits sound waves reflected by moving blood cells in the MCA. The motion of these cells alters the reflected wave frequency, known as a Doppler shift.
Record these frequencies, generating a CBFV baseline spectrum.
Now, instruct the participant to hold his breath while the recording continues.
During breath-holding, blood CO2 levels rise, causing MCA dilation and increasing blood flow with a higher Doppler shift. This generates a broader spectral profile, confirming elevated CBFV.
After the breath-hold ends, blood CO2 levels and MCA diameter normalize, and CBFV returns to baseline.
The Doppler ultrasound measures real-time blood velocity, acting as a functional imaging tool.
Adjust the fixation device to the subject's approximate head size. Alert the subject before placing the headset on his or her head. After placing the headset, adjust the fixation devices fit and ask the subject if the device is too tight. Loosen the mechanism of the fixation device so that the transducer can move freely. Apply enough ultrasound gel to the transducer to cover the face of the transducer. Adjust the fixation device so that the transducer is located over the top of the previously made Mark.
Search for the optimal MCA spectral signal, striving for the highest velocity spectral signal possible. When the optimal MCA spectral signal is found, tighten the mechanism of the fixation device to lock the transducer in place. Note the depth and all other settings.
Decrease the power as much as possible, while still maintaining a spectral envelope that traces the maximum velocity accurately. Begin recording on the TCD software. Instruct the subject to breathe normally for three minutes to achieve a good baseline recording, and allow cerebral blood flow velocity to stabilize from any previous experiments or stimuli.
Count down slowly from three. On the count of 1, ask the subject to begin breath holding after a normal inspiration. Place a marker in the TCD recording to signify the start of breath holding. Have the subject hold their breath for 30 seconds, or until they're no longer comfortable holding their breath.
The subject inhales. Place a marker in the TCD recording to signify the end of breath holding. Continue monitoring cerebral blood flow velocity using TCD for at least 30 seconds following the end of breath holding, to ensure that the velocity returns to baseline values.
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