Comparison of peripheral blood saturation with brain oxygenation in patients undergoing thoracic surgery.

Introduction: Near-infrared spectroscopy (NIRS) is a non-invasive method of regional tissue oxygenation measurement. Intraoperative use of NIRS to monitor brain oxygenation (BO) during surgery might be beneficial to identify cerebral desaturations. Aim: To compare peripheral blood saturation (SpO2) with BO measurements and evaluate the utility of BO in thoracic surgery. Material and methods: We took BO and SpO2 measurements in a group of 100 patients undergoing standard thoracic surgery. Measurements were made every 15 minutes. The Mann-Whitney U test was used to compare study groups. Spearman's rank correlation coefficient was used to determine correlation between studied parameters. Results: We found a negative correlation between patients' age and BO at the beginning of surgery. Operations lasted between 30 and 200 minutes. We found a positive correlation between BO and SpO2 between 15 and 90 minutes of surgery. Subsequently, BO remained at a low level while SpO2 returned to baseline values. Higher minimum SpO2 values were noted in patients undergoing left-sided procedures. Conclusions: Cerebral oxygenation does not return to baseline values until the end of the surgery as opposed to the SpO2. Furthermore, both SpO2 and BO correlate negatively with the overall duration of thoracic surgery. In addition, after 90 minutes of surgery, SpO2 stopped reflecting brain oxygenation.

Time-of-flight angiography at 7T using TONE double spokes with parallel transmission.

PURPOSE: To demonstrate that fast-kz spokes can be used in parallel transmission to homogenize flip angle ramp profiles (known as TONE) in slab selections, and thereby improve Time-Of-Flight angiography of the whole human brain at 7T. METHODS: B1+ and B0 maps were measured on seven human brains with a z-segmented coil connected to an 8-channel pTx system. Tailored two-spoke pulses were designed under strict hardware and SAR constraints for uniform slab profile before transforming their subpulse waveforms for linearly-increasing flip-angle ramps. Increasing angulations along the feet-head direction were prescribed in 2-slab and 3-slab TOF acquisitions. Excitation patterns were simulated and compared with RF-shimmed (single spoke) ramp pulses. Excitation performances were assessed in ~10-min TOF acquisitions by visually inspecting Maximal Intensity Projections angiograms. RESULTS: The flip-angle ramp fidelity achieved by double spokes inside slabs of interest was improved by 30-40% compared to RF-shimmed ramps. This allowed better homogenizing signal along arteries, and depicting small vessels in distal areas of the brain, in comparison with RF-shimmed ramp pulses or double-spoke uniform excitation. CONCLUSION: Ramp double spokes used in conjunction with parallel transmission yield better blood saturation compensation and more finely resolved TOF angiograms than mere double spokes or ramp single spokes at 7T.

Preoperative and postoperative measurements of retinal vessel oxygen saturation in patients with different grades of cataracts.

PURPOSE: To assess the retinal vessel blood oxygen saturation preoperatively and postoperatively in patients with different grades of cataracts. METHODS: This study included 40 eyes from 40 patients with senile cataracts ranging from grade 1 to 3. All 40 eyes received standard phacoemulsification and intraocular lens implantation. The mean retinal arterial and venular oxygen saturation (SO2 ) levels were measured using the Oxymap system prior to, immediately after and 3 months after cataract surgery. The arterial-venular difference (AVD) was calculated as the difference between the arterial and venular saturations. Linear regression analysis was performed to identify the relationship between the lens density grades and changes in the measured retina vessel SO2 . RESULTS: The mean age of the subjects was 64.1 ± 7.8 years, and 14 (35%) were male. The mean SO2 level increased in the retinal arterioles from 90.5 ± 7.8% to 95.0 ± 6.7% immediately postoperatively and to 98.3 ± 5.3% at 3 months after surgery (p < 0.001). The mean venular saturation levels were 43.4 ± 9.7%, 58.0 ± 8.5% and 61.9 ± 6.5% at baseline, immediately after and at 3 months postoperatively, respectively, with a statistically significant increase after surgery (p < 0.001). The mean AVD significantly decreased from 47.1 ± 8.9% before surgery to 37.1 ± 7.3% immediately after and 36.4 ± 6.4% 3 months after surgery (p < 0.02). A linear regression model indicated that denser lens opacity was significantly associated with a larger amplitude of the venular SO2 level and the AVD after cataract surgery: change of venous SO2  = 5.934-0.191 × Age + 13.534 × Lens Grade (age: p = 0.586; lens grade: p < 0.001); change in AVD = -7.438-0.037 × Age + 7.744 × Lens Grade (age: p = 0.917; lens grade: p = 0.031). CONCLUSIONS: Retinal arterial and venular oxygen saturation levels are significantly increased after cataract surgery, and increase rates vary with the preoperative grading of lens density.

Acute Hypoxic Test in Patients with Prediabetes.

Shatylo, Valerii B., Tetiana V. Serebrovska, Anna V. Gavalko, Egor Egorov, and Oleg V. Korkushko. Acute hypoxic test in patients with prediabetes. High Alt Med Biol. 17:101-107, 2016.-Prediabetes is a state of impaired carbohydrate metabolism when not all of the symptoms required to label a person as diabetic are present, but blood glucose is higher than in healthy subjects. Recent evidence suggests that intermittent hypoxia training (IHT) might provide a cost-effective strategy for improving metabolic functioning. One of the most important aspects of the successful IHT application is individualized approach to hypoxic dose and regimen prescription. To establish the relationships between indices of carbohydrate metabolism and individual resistance to hypoxia, the acute hypoxic test (AHT, breathing gas mixture with 12% O2 during 20 minutes) was performed in 33 healthy volunteers (mean age, 63.0, range, 44-76; fasting plasma glucose (FPG) less than 5.6 mmol/L and 2 hours postoral glucose tolerance test (OGTT) glycemia less than 7.8 mmol/L) and 30 patients with impaired glucose metabolism (mean age, 65.5, range, 44-75; FPG from 5.6 to 6.9 mmol/L and 2 hours post-OGTT glycemia from 7.8 to 11 mmol/L). Negative correlation was found between the SaO2 level at 20th minute AHT and FPG (r = -0.83; p < 0.01) and insulin (r = -0.27; p < 0.05), as well as 2 hours post-OGTT glucose and insulin levels (r = -0.75 and -0.40, respectively). Longer recovery time and less effective functioning of respiratory and cardiovascular systems were also registered in patients with prediabetes showing that their cardiovascular resilience is impaired compared to normoglycemic controls. These patterns of relationship must be considered when assigning the individual modes of IHT.

The effect of pars plana vitrectomy and nuclear cataract on oxygen saturation in retinal vessels, diabetic and non-diabetic patients compared.

PURPOSE: To determine the effect of pars plana vitrectomy (PPV) on oxygen saturation in retinal vessels in patients with diabetes and non-diabetes after a 1-year follow-up. METHODS: This was a prospective consecutive interventional case series in 82 eyes in 82 patients. The sample consisted of 25 patients with non-proliferative diabetic retinopathy with macular oedema based on vitreoretinal traction or epiretinal membrane (ERM) and 57 non-diabetic patients with macular hole and ERM. Automatic retinal oximetry (Oxymap Inc.) was used on all patients 24 hr prior to PPV, and it was also used 7 and 52 weeks after PPV (classic 20G or sutureless 23G). We analysed the data according to subgroup diagnosis and lens status. RESULTS: Arterial saturation increased significantly from 96.4 ± 2.9% at baseline to 96.6 ± 3.4% at week 7 and 97.3 ± 3.4% at week 52 (p < 0.0001; Friedman test). Vein saturation also increased significantly from 63.5 ± 7.9% at baseline to 66.1 ± 7.7% and 67.0 ± 7.2% at weeks 7 and 52 (p < 0.0001; Friedman test). The value of the arteriovenous (A-V) difference decreased significantly after vitrectomy from 32.8 ± 7.5% at baseline to 30.5 ± 7.5% and 30.3 ± 7.0% at weeks 7 and 52 (p < 0.0001; Friedman test). The subgroup analysis revealed that in patients with diabetes, there were no statistically significant changes in oxygen saturation in blood vessels or in the A-V difference after PPV. After vitrectomy, retinal vessel diameter reduced by about 3.5% in both groups of patients. Further, the analysis revealed that opacification of the lens leads to a decrease in oxygen saturation in contrast to a clear lens and pseudophakic IOLs. CONCLUSION: Oxygen saturation is higher in the retinal veins and arteries after PPV in patients with non-diabetes, and this lasts for at least 52 weeks. In contrast, in patients with diabetes, there is no increase in oxygen saturation in the retinal vessels after vitrectomy. After vitrectomy, retinal vessel diameter reduced in both groups of patients. Further, the nuclear cataract progression has substantial effect on oximetry results. Patients with nuclear cataract exhibited an increase in saturation in both arteries and veins, but the A-V difference remained the same.

The effect of pars plan vitrectomy on oxygen saturation in retinal vessels--a pilot study.

PURPOSE: To determine the effect of pars plana vitrectomy (PPV) on oxygen saturation in retinal vessels. METHODS: We performed a prospective consecutive interventional case series of 20 eyes of 20 patients with macular hole or epiretinal membrane. We performed automatic retinal oximetry (Oxymap Inc., Reykjavik, Iceland) in each patient 24 hr prior to and 45 days (range 42-49) after PPV (classic 20G or sutureless 23G). We analysed oxygen saturations in retinal arteries and veins. Vessel segments of first or second degree were selected. The same segment was analysed before and after PPV. Oximetry data were compared by paired two-tailed t-test. RESULTS: Pars plana vitrectomy did not alter arterial haemoglobin saturation with oxygen (98±2% prior to the surgery and 98±3% after the procedure, p=0.549). The mean venous haemoglobin saturation with oxygen increased after vitrectomy from 63±10% to 66±8% (p=0.012). CONCLUSIONS: Oxygen saturation is higher in retinal veins after pars plana vitrectomy. Further studies are needed to unveil the mechanism of how vitrectomy affects oxygen metabolism in the retina.