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 the opposing arm. 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.

中文翻译：

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血液收集过程中的静脉阻塞会降低血浆中的亚硝酸盐，但不会降低人体中的硝酸盐浓度。

背景

为了在减少组织氧合作用时保持血管张力和血流量，将亚硝酸根阴离子还原为一氧化氮（NO）。从实际的角度来看，尚不清楚在采血时使用止血带会如何影响NO代谢物的测量。因此，本研究评估了静脉血收集过程中静脉阻塞对血浆亚硝酸盐和硝酸盐的影响。

方法

15名健康参与者完成了两项试验，之后摄入了富含硝酸盐的甜菜根汁（BRJ；硝酸盐总量约为8.4 mmol）或不补充（对照组）。在这两个试验中，在将止血带施加于上臂并使用留置的静脉插管从对侧臂上使用静脉穿刺针采血。在闭塞后35 s收集静脉穿刺样品。使用近红外光谱法评估前臂屈肌的氧合变化。使用气相化学发光法分析血浆亚硝酸盐和硝酸盐。

结果

在对照试验中，与静脉穿刺术（112±51 nM，P  = 0.03）相比，通过套管收集的血浆亚硝酸盐（179±67 nM）显着升高。与静脉穿刺术相比，从插管中取样时，BRJ的摄入使血浆亚硝酸盐增加，并且值保持较高（473±164 nM）（387±136 nM，P  <0.001）。在任何一项试验中，硝酸盐血浆在两种收集方法之间均无差异（所有P  > 0.05）。与采血管时的插管样品相比，在静脉穿刺样品期间总血红蛋白，脱氧血红蛋白和血红蛋白血红蛋白的变化都明显更大（所有P  <0.05）。

结论

静脉穿刺采血期间的静脉阻塞会降低血浆亚硝酸盐浓度，这可能是由于血红蛋白浓度的局部变化和/或内源性NO合成的抑制。因此，研究人员应仔细考虑并始终如一地报告采血方法以测量NO代谢产物。