Venous occlusion during blood collection decreases plasma nitrite but not nitrate concentration in humans

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

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Background
To maintain vascular tone and blood flow when tissue oxygenation is reduced, nitrite anions are reduced to nitric oxide (NO). From a practical perspective, it is unclear how the application of a tourniquet during blood collection might influence measurement of NO metabolites. Accordingly, this study evaluated the effect of venous occlusion on plasma nitrite and nitrate during venous blood collection.
Methods
Fifteen healthy participants completed two trials that were preceded by the ingestion of nitrate-rich beetroot juice (BRJ; total of ∼8.4 mmol nitrate) or no supplementation (control). In both trials, blood was collected using a venepuncture needle while a tourniquet was applied to the upper arm and using an indwelling intravenous cannula, from opposing arms. The venepuncture samples were collected at 35 s post occlusion. Changes in the oxygenation of forearm flexor muscles were assessed using near-infrared spectroscopy. Plasma nitrite and nitrate were analysed using gas-phase chemiluminescence.
Results
In the control trial, plasma nitrite was significantly elevated when collected via the cannula (179 ± 67 nM) compared to venepuncture (112 ± 51 nM, P=0.03). The ingestion of BRJ increased plasma nitrite and values remained higher when sampled from the cannula (473 ± 164 nM) compared to venepuncture (387 ± 136 nM, P<0.001). Plasma nitrate did not differ between collection methods in either trial (all P>0.05). The delta changes in total-, deoxy-, and oxy-haemoglobin were all significantly greater during venepuncture sample compared to the cannula sample at the point of blood collection (all P<0.05).
Conclusions
Venous occlusion during venepuncture blood collection lowers plasma nitrite concentration, potentially due to localised changes in haemoglobin concentration and/or a suppression of endogenous NO synthesis. Accordingly, the method of blood collection to enable measurements of NO metabolites should be carefully considered and consistently reported by researchers.
Original languageEnglish
Pages (from-to)21-27
Number of pages7
JournalNitric Oxide
Volume102
Early online date11 Jun 2020
DOIs
Publication statusPublished - 1 Sep 2020

Keywords

  • beetroot juice
  • cannula
  • ischemia
  • blood flow
  • nitric oxide

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