Each participant will be required to attend the laboratory on three occasions. The first of
these will be an initial screening/training visit, within 14 days of the first active study
visit. During the initial visit participants will be provided with written informed consent
and screened with regards the study exclusion/inclusion criteria. Training will be given on
the cognitive tasks and familiarisation with the study procedures will be provided.
Study days: Forty - eight hours prior to each study day, participants will begin dietary
restrictions. Participants will then attend the first study day following an overnight fast.
A cannula will be inserted and baseline blood samples obtained, baseline measures of cerebral
blood flow will be examined using near infrared spectroscopy and its effect on cognitive
function using a cognitive demand battery. The relevant drink will then be provided and blood
samples and blood flow measures will be taken at hourly intervals (1, 2, 3, and 5h). No
additional food or drink will be provided during the study period except for low-nitrate
mineral water. After a minimum of 2 weeks, participants will be asked to return to the lab
and repeat the procedure with the other drink.
Cerebrovascular Responses
Cerebral oxygenation will be assessed using near - infrared spectroscopy . Two near-infrared
sensors will be placed on the skin over the right and left prefrontal cortex region of the
forehead, and the signals were averaged to determine cerebral oxygenation. The sensors will
be secured to the skin using double-sided adhesive tape and shielded from ambient light using
an elastic bandage. The sensors alternately emit near-infrared light at wavelengths of 730
and 810 nm. Each sensor contains two detectors located at 3 and 4 cm from the emitting source
that detect oxygenated and deoxygenated states of Hb to estimate regional O2 saturation based
on internal algorithms (Rasmussen et al. 2007).
Blood velocity in the middle cerebral artery (MCAV) will be determined using transcranial
Doppler sonography. A 2 MHz Doppler probe was positioned over the right middle cerebral
artery using previously described search techniques (Aaslid et al. 1982) and will be secured
with an adjustable headset (DiaMon, Compumedics DWL). The mean depth for Doppler signals was
51 ± 3 mm. Arterial blood pressure will be recorded with a transducer located at heart level
(TruWave, Edwards Lifesciences, Nyon, Switzerland).
