Nitrite and S -Nitrosohemoglobin Exchange Across the Human Cerebral and Femoral Circulation: Relationship to Basal and Exercise Blood Flow Responses to Hypoxia
Authors' conclusion
These findings suggest that hypoxia and, to a far greater extent, exercise independently promote arterial-venous delivery gradients of intravascular nitric oxide, with deoxyhemoglobin-mediated reduction identified as the dominant mechanism underlying hypoxic vasodilation.
Study context
- Population
- Ten healthy participants (5 men, 5 women) aged 24±4 years
- Participants
- Ten participants
- Comparison
- Normoxia vs hypoxia, at rest and during exercise; cerebral vs femoral circulation
- Outcome
- Arterial-venous concentration gradients of nitrite and SNO-Hb across the cerebral and femoral circulation
- Follow-up
- At rest and after 30 minutes of cycling
Methodological detailsrandomised order of trials, crossover, Blood sampled simultaneously from brachial artery and internal jugular and femoral veins, Plasma and red blood cell (RBC) nitric oxide metabolites measured by tri-iodide reductive chemiluminescence, Blood flow by transcranial Doppler ultrasound (cerebral) and constant infusion thermodilution (femoral); net exchange by Fick principle
- Randomised order of trials
- Crossover
- Blood sampled simultaneously from brachial artery and internal jugular and femoral veins
- Plasma and RBC nitric oxide metabolites measured by tri-iodide reductive chemiluminescence
- Blood flow by transcranial Doppler ultrasound (cerebral) and constant infusion thermodilution (femoral); net exchange by Fick principle
Main finding
As reported in the abstract
Arterial-venous nitric oxide metabolite gradients
- Plasma gradients reflecting consumption (arterial>venous)
- P<0.05
- RBC iron nitrosylhemoglobin formation (venous>arterial) at rest in normoxia, during hypoxia and especially during exercise
- P<0.05
- Hypoxia vs normoxia for these gradients
- P<0.05
- Exercise vs rest for these gradients
- P<0.05
- Most pronounced gradients across the femoral circulation vs cerebral
- P<0.05
- No gradients consistent with RBC S-nitrosohemoglobin (SNO-Hb) consumption and corresponding delivery of plasma S-nitrosothiols
- P>0.05
Further findings
- Mild increase in both cerebral and femoral blood flow in hypoxia vs normoxia
- P < 0.05
- Further, more pronounced increases in femoral blood flow during exercise vs rest
- P < 0.05
- Correlation with reduction in RBC oxygenation
- r=0.680-0.769, P<0.001
Original publication
Nitrite and S -Nitrosohemoglobin Exchange Across the Human Cerebral and Femoral Circulation: Relationship to Basal and Exercise Blood Flow Responses to Hypoxia. Circulation. Published 15 November 2016. doi:10.
Summarised from the published abstract; every number is checked against it