Near infrared spectroscopy (NIRS) to assess the effects of local ischemic preconditioning in the muscle of healthy volunteers and critically ill patients

Microvascular reactivity is altered early in patients with acute respiratory distress syndrome

“…These patients had diminished capillary density in the sublingual area, with a low proportion of perfused vessels and a reduced microvascular flow index. In the thenar muscle, post-occlusive reactive hyperemia was impaired, as manifest by low values of the Asc slope, similar to those found in septic patients in other studies [ 29 – 31 ]. Our current study extends these data to a larger and more heterogeneous population of patients with ARDS.…”

“…Half of the patients in our study had sepsis, but microcirculatory alterations detected by NIRS are not pathognomonic of septic conditions. Numerous studies have shown alterations of the Asc slope in septic populations, especially in the presence of shock [ 20 , 29 , 30 ], but low values of the Asc slope have also been observed in other acute conditions (normal values of 288 and 323 %/min have been reported [ 20 , 22 ]): Gomez et al reported values of 172 ± 103 %/min in trauma patients [ 22 ]; Petroni et al reported values of 77 ± 42 %/min in patients with severe acute heart failure requiring veno-arterial extracorporeal membrane oxygenation (ECMO) support [ 23 ]; Morel et al reported values of 144 (126–228) %/min 6 h after cardiopulmonary bypass in patients who had undergone cardiac surgery [ 24 ]; Donadello et al reported values of 68 ± 32 %/min in resuscitated cardiac arrest patients after cessation of therapeutic hypothermia [ 25 ]; and we previously reported values of 186 ± 89 %/min in patients with circulatory shock of different etiologies [ 31 ]. In the present study, patients with septic shock had similar Asc slope values to patients with ARDS of non-septic causes.…”

“…In the present study, patients with septic shock had similar Asc slope values to patients with ARDS of non-septic causes. Although the mechanisms involved in the control of post-occlusive reactive hyperemia (NIRS Asc slope) have not been completely identified and are sometimes controversial [ 32 , 33 ], it is well known that multiple vasodilator pathways (e.g., nitric oxide and prostaglandins) are necessary to obtain the transient increase in local blood flow [ 32 ] and complex inflammatory alterations will have been present in all the populations studied above [ 20 , 22 – 25 , 31 ]. Thus, the NIRS VOT is a functional test of the microcirculation, which measures its reserve (recruitability) under controlled ischemia, and involves multiple pathways.…”

“…Third, our control group was comprised of healthy younger individuals who may have different vascular reactivity to that of ARDS patients. However, we have previously reported that NIRS values are quite similar in control cohorts of patients and in healthy younger volunteers [ 20 , 31 ]. Our comparison enables the whole spectrum from the normal values of health to those in severe ARDS patients to be considered.…”

Oral Nitrate Increases Microvascular Reactivity and the Number of Visible Perfused Microvessels in Healthy Volunteers

“…Third, we only tested a single dose of nitrate, so we cannot comment on the effects of repeated or prolonged doses. Fourth, repetition of a VOT may induce ischemic preconditioning and change the local metabolism, thus reducing the Asc slope, but in a previous study, we showed that repeated VOT had no effect on the Asc slope [51]. Fifth, some experimental data have shown a reversible inhibition of cytochrome c oxidase, especially in situations of decreased O 2 availability, thus diminishing mitochondrial respiration [36].…”