Application of a tourniquet during venous blood collection from the forearm reduces plasma nitrite concentration

Chris Easton*, Luke Liddle, Mia C. Burleigh, Chris Monaghan, David J. Muggeridge

*Corresponding author for this work

Research output: Contribution to journalMeeting Abstract

Abstract

Dietary nitrate (NO3-) supplementation increases nitric oxide (NO) availability and can reduce blood pressure and improve exercise performance. While plasma nitrite [NO2-] provides the best marker of NO availability, the use of a tourniquet during blood collection may be problematic due to the established effects of hypoxia on NO metabolism.

PURPOSE

This study compared measurements of plasma NO2- and NO3- where blood was collected via venepuncture and from an indwelling intravenous cannula.

METHODS
Fifteen participants (mean ± standard deviation: age 27 ± 4 years, body mass 71 ± 11 kg) completed two experimental trials in a randomized order. In one trial, participants ingested 140 ml of NO3--rich beetroot juice (BR; ˜8.4 mmol NO3-) 2.5 h prior to sample collection. No supplementation was given in the other (CON). In both trials, a blood sample was collected from a forearm vein using a venepuncture needle 40 s after the application of a tourniquet to the upper arm. Simultaneously, a blood sample was collected from the opposite arm via an indwelling intravenous cannula with no restriction to blood flow. A second blood sample was collected from the cannula 40 s after a tourniquet was attached to the upper arm. Near-infrared spectroscopy was used to assess deoxygenation of the flexor muscles through changes in total (tHb), deoxy- (HHb), and oxy- (HbO2) haemoglobin. Samples of plasma were analyzed for [NO2-] and [NO3-] using gas-phase chemiluminescence.

RESULTS
The application of a tourniquet increased tHb, HHb, and HbO2 suggesting deoxygenation of the local forearm muscles (all P<0.05). Plasma [NO2-] was significantly higher when sampled from the unrestricted cannula (CON: 179 ± 67 nM, BR: 473 ± 164 nM) in comparison to venepuncture (CON 112 ± 51 nM, P=0.03; BR 387 ± 136 nM, P<0.001) and the cannula during tourniquet application (CON 109 ± 43 nM, P=0.02; BR 384 ± 124 nM, P<0.001). Plasma [NO3-] was not different between sample sites in either trial (all P>0.05).

CONCLUSIONS
The application of a tourniquet for venous blood sampling causes ischemia, localized hypoxia, and reduces plasma [NO2-], possibly due to an increased conversion to NO or greater uptake of NO2- by the tissue. Researchers should ensure consistency in blood collection methodologies and consider how the use of a tourniquet may influence NO metabolism.
Original languageEnglish
Article number2428
Pages (from-to)665-665
Number of pages1
JournalMedicine & Science in Sports & Exercise
Volume51
Issue number6
DOIs
Publication statusPublished - Jun 2019

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