Utilizing the vascular occlusion technique with NIRS technology

Noninvasive estimation of skeletal muscle oxygen consumption rate and microvascular reactivity in chronic stroke survivors using near-infrared spectroscopy

Understanding post-stroke changes in skeletal muscle oxidative metabolism and microvascular reactivity could help create therapeutic targets that optimize rehabilitative interventions. Due to disuse atrophy, we hypothesized that basal muscle oxygen consumption rate and microvascular endothelial function would be impaired in the tibialis anterior (TA) muscle of the affected leg of chronic stroke survivors compared with the nonaffected leg and versus matched controls. Fifteen chronic stroke survivors (10 females) and 15 matched controls (9 females) completed this study. A near-infrared spectroscopy oximeter measured tissue oxygen saturation (StO2) of the TA in both legs of stroke survivors and the dominant leg of controls. A cuff was placed around the thigh and inflated to 225 mmHg for 5 min while StO2 was continuously measured. The rate of change in StO2 was calculated during cuff occlusion and immediately post-cuff release. The rate of oxygen desaturation was similar between the legs of the stroke survivors (paretic -0.12 ± 0.04%·s-1 vs. nonparetic -0.16 ± 011%·s-1; P = 0.49), but the paretic leg had a reduced desaturation rate versus controls (-0.25 ± 0.18%·s-1; P = 0.007 vs. paretic leg). After cuff release, there was a greater oxygen resaturation rate in the nonparetic leg compared with the paretic leg (3.13 ± 2.08%·s-1 vs. 1.60 ± 1.11%·s-1, respectively; P = 0.01). The control leg had a similar resaturation rate versus the nonparetic leg (control = 3.41 ± 1.79%·s-1; P = 0.69) but was greater than the paretic leg (P = 0.003). The TA in the paretic leg had an impaired muscle oxygen consumption rate and reduced microvascular endothelial function compared with controls.NEW & NOTEWORTHY Secondary consequences of stroke are not well described. In this study, we show that basal muscle oxidative consumption and microvascular endothelial function are reduced in the paretic tibialis anterior muscle of chronic stroke survivors compared with matched controls using near-infrared spectroscopy and the vascular occlusion technique. There was a moderately strong correlation between microvascular endothelial function and paretic leg strength.

NIRS-Derived Muscle-Deoxygenation and Microvascular Reactivity During Occlusion-Reperfusion at Rest Are Associated With Whole-Body Aerobic Fitness

Purpose: Near-infrared spectroscopy (NIRS) indices during arterial occlusion-reperfusion maneuver have been used to examine the muscle's oxidative metabolism and microvascular function-important determinants of whole-body aerobic-fitness. The association of NIRS-derived parameters with whole-body VO2max was previously examined using a method requiring exercise (or electrical stimulation) followed by multiple arterial occlusions. We examined whether NIRS-derived indices of muscle deoxygenation and microvascular reactivity assessed during a single occlusion-reperfusion at rest are (a) associated with maximal/submaximal indices of whole-body aerobic-fitness and (b) could discriminate individuals with different VO2max. We, also, investigated which NIRS-parameter during occlusion-reperfusion correlates best with whole-body aerobic-fitness. Methods: Twenty-five young individuals performed an arterial occlusion-reperfusion at rest. Changes in oxygenated- and deoxygenated-hemoglobin (O2Hb and HHb, respectively) in vastus-lateralis were monitored; adipose tissue thickness (ATT) at NIRS-application was assessed. Participants also underwent a maximal incremental exercise test for VO2max, maximal aerobic velocity (MAV), and ventilatory-thresholds (VTs) assessments. Results: The HHbslope and HHbmagnitude of increase (occlusion-phase) and O2Hbmagnitude of increase (reperfusion-phase) were strongly correlated with VO2max (r = .695-.763, p < .001) and moderately with MAV (r = .468-.530; p < .05). O2Hbmagnitude was moderately correlated with VTs (r = .399-.414; p < .05). After controlling for ATT, the correlations remained significant for VO2max (r = .672-.704; p < .001) and MAV (r = .407; p < .05). Individuals in the high percentiles after median and tritile splits for HHbslope and O2Hbmagnitude had significantly greater VO2max vs. those in low percentiles (p < .01-.05). The HHbslope during occlusion was the best predictor of VO2max. Conclusion: NIRS-derived muscle deoxygenation/reoxygenation indices during a single arterial occlusion-reperfusion maneuver are strongly associated with whole-body maximal indices of aerobic-fitness (VO2max, MAV) and may discriminate individuals with different VO2max.

Muscle oxygenation of the paretic and nonparetic legs during and after exercise in chronic stroke: Implications for mobility

BACKGROUND

Oxygen delivery and demand are reduced in the paretic leg of individuals after stroke. However, it is unknown how muscle oxygenation, the balance between delivery and utilization of oxygen at the muscle, is altered post-stroke during aerobic exercise and how it relates to mobility.

OBJECTIVE

To monitor muscle oxygenation changes between the paretic and nonparetic legs of individuals after stroke during treadmill exercise and the 6-minute walk test and analyze the association with mobility.

DESIGN

Cross-sectional study.

SETTING

Cardiac rehabilitation program.

PATIENTS

Eleven male participants were enrolled in the study. Ten men (30.8 ± 4.1 months post-stroke; age 63.9 ± 13.9 years) with hemiparetic gait pattern finished the study.

METHODS OR INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Muscle oxygenation was measured with near-infrared spectroscopy placed on the vastus lateralis of each leg during treadmill exercise at the first ventilatory threshold and during a 6-minute walk test.

RESULTS

The desaturation slope during treadmill exercise was significantly steeper (p = .047) in the paretic (-0.7 ± 0.6%/s) compared to the nonparetic leg (-0.3 ± 0.2%/s). There was no other significant difference between legs. The 6-minute walk test distance was not correlated with 6-minute walk test muscle oxygenation in either leg (paretic: r = 0.20, p = 0.590; nonparetic: r = 0.42, p = .232).

CONCLUSIONS

At the onset of treadmill exercise, the paretic leg was unable to effectively match the oxygen demand and extraction of the nonparetic leg, suggesting the need for an immediate cardiovascular warmup prior to initiating moderate intensity exercise in this population. Because the exercise desaturation rate is thought to indicate increased anaerobic metabolism and lactate production, efforts to delay rapid desaturation could improve the sustainability of activities of daily living and exercise.

The utility of the reperfusion rate of tissue oxygen saturation as a measure of vascular endothelial function in adolescents: reliability, validity and sensitivity

Introduction: The near-infrared spectroscopy (NIRS)-derived reperfusion rate of tissue oxygen saturation (slope 2 StO2) may provide a surrogate measure of vascular function, however, this has yet to be examined in a paediatric population. This study investigated in adolescents: 1) the between-day reliability of NIRS-derived measurements; 2) the relationship between slope 2 StO2 and macro- (flow-mediated dilation, FMD) and microvascular (peak reactive hyperaemia, PRH) function; and 3) the effect of high-intensity interval exercise (HIIE) on slope 2 StO2, FMD, and PRH. Methods: Nineteen boys (13.3 ± 0.5 y) visited the laboratory on two occasions, separated by ∼ 1 week. On visit 1, participants underwent simultaneous assessment of brachial artery FMD and slope 2 StO2 and PRH on the internal face of the forearm. On visit 2, participants completed a bout of HIIE with slope 2 StO2, FMD and PRH measured pre-, immediately post- and 1.5 h post-exercise. Results: Slope 2 StO2 showed no mean bias (p = 0.18) and an intraclass correlation coefficient of 0.67 (p = 0.003) between visits. No significant correlation between slope 2 StO2 and FMD or PRH was observed on visit 1 (r = -0.04, p = 0.89 and r = -0.30, p = 0.23, respectively) or visit 2 pre-exercise (r = -0.28, p = 0.25 and r = -0.31, p = 0.20, respectively). Compared to pre-exercise, FMD decreased immediately post-exercise (p < 0.001) and then increased 1.5 h post-exercise (p < 0.001). No significant change was detected for slope 2 StO2 (p = 0.30) or PRH (p = 0.55) following HIIE. Conclusion: In adolescents, slope 2 StO2 can be measured reliably, however, it is not correlated with FMD or PRH and does not follow the acute time course of changes in FMD post-exercise. Hence, the use of slope 2 StO2 as a surrogate measure of vascular function in youth must be refuted.

Partial-body cryostimulation does not impact peripheral microvascular responsiveness but reduces muscular metabolic O2 consumption (mV˙O2) at rest

This study aimed to investigate the effect of partial-body cryostimulation (PBC) on microvascular responsiveness and muscular metabolic O2 consumption rate (mV˙O2). Twenty healthy young adults (ten males and ten females) underwent a post-occlusive reactive hyperemia (PORH) test at the flexor digitorum superficialis area before and after a 3-min PBC session and a 3-min control session. Using near-infrared spectroscopy, occlusion and reperfusion slopes were calculated: oxyhemoglobin ([HbO2]) decrease rate ([HbO2] slope 1), deoxyhaemoglobin ([HHb]) increase rate ([HHb] slope 1), [HbO2] increase rate ([HbO2] slope 2), and [HHb] increase rate ([HHb] slope 2. Using HbO2 kinetics during the occlusion, mV˙O2 was also calculated to characterize myocytes' metabolic O2 consumption. HbO2 slope 1 value was lower after PBC than before PBC (-0.15 ± 0.08 vs -0.24 ± 0.11 s-1; respectively; P < 0.05) in male participants only. A lower [HHb] slope 1 was also observed after PBC compared to before PBC (0.18 ± 0.10 vs 0.24 ± 0.16 s-1; P < 0.05) with no interaction for sex categories. mV˙O2 was significantly lower after PBC than before (pre values 14.75 ± 3.94 vs 18.47 ± 5.73 μMO2Hb.s-1; respectively; P < 0.01) with no interaction between sex categories. No changes in the calculated slope 2 were observed. These findings suggest that a single session of PBC reduces the muscular metabolic O2 needs at rest; however, it does not alter the vascular ability to provide O2 to the myocytes.

Spatial-Temporal Oxygenation Mapping Using a Near-Infrared Optical Scanner: Towards Peripheral Vascular Imaging

Near-infrared spectroscopy (NIRS)-based peripheral perfusion, or microcirculation, can be used to assess the severity of peripheral vascular dysfunction. A low-cost, portable non-contact near-infrared optical scanner (NIROS) was developed for spatio-temporal mapping of tissue oxygenation and perfusion in tissues. In vivo validation studies were carried out on control subjects (n = 3) to assess the ability of NIROS to measure real-time oxygenation changes in response to an occlusion paradigm on the dorsum of the hand. NIROS captured real-time tissue oxygenation changes with 95% correlation when compared to a commercial device. A feasibility peripheral imaging study was performed in a mouse model (n = 5) of chronic kidney disease (CKD) induced vascular calcification to assess differences in microcirculatory peripheral tissue oxygenation. The tissue oxygenation (in terms of oxy-, deoxy-, and total hemoglobin changes) due to the occlusion paradigm was distinctly different prior to (week-6) and after the onset of vascular calcification (week-12) in the murine tails. Future work will involve extensive studies to correlate these microcirculatory tissue oxygenation changes in the peripheral tail to the vascular calcification in the heart.

Unraveling the pathophysiology of lower-limb postthrombotic syndrome in adolescents: a proof-of-concept study

A better understanding of the pathophysiology of pediatric postthrombotic syndrome (PTS) is needed to develop strategies to treat this condition. We investigated calf pump function, exercise capacity, balance in power output, and changes in limb muscle oxygen saturation (SmO2) and fluid content during exercise in 10 pediatric patients with unilateral lower-limb PTS, and in age- and sex-matched controls (1:1-1:2 ratio). Outcomes were investigated using bioimpedance spectroscopy, torque-sensing pedals, and near-infrared spectroscopy during incremental- and constant-load cycling tests. The median age at participation was 17 years (25th-75th percentile, 15-18 years); 68% of participants were females. The median CAPTSure score in the affected leg of affected participants was 35 points (25th-75th percentile, 24-46 points), indicating moderate/severe PTS; 20% of patients had a history of central venous catheter-related thrombosis. Increasing PTS severity was associated with higher calf pump venous volume and higher ejection volume, leading to compensated calf pump performance. We found no evidence of PTS impact on exercise capacity. Leg contribution to power output was similar in affected and unaffected legs. However, the PTS-affected legs showed lower SmO2 during active cycling and recovery with increasing PTS severity, indicating impaired microvascular function in the muscle. These findings suggest that PTS severity is associated with impaired blood flow, presumably from elevated venous pressure during and after exercise. The fact that microvascular function is impaired in young patients with PTS underscores the relevance of developing strategies to mitigate the effects of this chronic vascular disease to minimize its deleterious effects as children grow older.

Characterizing tourniquet induced hemodynamics during total knee arthroplasty using diffuse optical spectroscopy

Tourniquet use creates a reduced blood surgical field during total knee arthroplasty (TKA), however, prolonged ischemia may cause postoperative tourniquet complications. To understand the effects of tourniquet-induced ischemia, we performed a prospective observational study using quantitative broadband diffuse optical spectroscopy (DOS) to measure tissue hemodynamics and water and lipid concentrations before, during, and after tourniquet placement in subjects undergoing TKA. Data was collected for 6 months and, of the total subjects analyzed (n = 24), 22 were primary TKAs and 2 were revision TKA cases. We specifically investigated tourniquet-induced hemodynamics based upon subject-specific tissue composition and observed a significant relationship between the linear rate of deoxygenation after tourniquet inflation and water/lipid ratio (W/L, p < 0.0001) and baseline somatic tissue oxygen saturation, StO2 (p = 0.05). Subjects with a low W/L ratio exhibited a lower tissue metabolic rate of oxygen consumption, (tMRO2 ) (p = 0.008). Changes in deoxyhemoglobin [HbR] (p = 0.009) and lipid fraction (p = 0.001) were significantly different between high and low W/L subject groups during deoxygenation. No significant differences were observed for hemodynamics during reperfusion and total tourniquet time was neither significantly related to the hemodynamic hyperemic response (p = 0.73) nor the time to max StO2 after tourniquet release (p = 0.57). In conclusion, we demonstrate that DOS is capable of real-time monitoring of tissue hemodynamics distal to the tourniquet during TKA, and that tissue composition should be considered. DOS may help surgeons stratify hemodynamics based upon tissue composition and eventually aid the preoperative risk assessment of vascular occlusions from tourniquet use during TKA.

Muscle Oxygenation of the Paretic and Nonparetic Legs During and After Arterial Occlusion in Chronic Stroke

Oxygen delivery and demand are reduced in the paretic leg post-stroke, reflecting decreased vascular function and reduced muscle quantity and quality. However, it is unknown how muscle oxygenation, the balance between muscle oxygen delivery and utilization, is altered in chronic stroke during and after occlusion-induced ischemia.

OBJECTIVES

The objective was to determine muscle oxygen consumption rate, microvascular responsiveness and reactive hyperemia in the paretic and nonparetic legs during and after arterial occlusion post-stroke.

MATERIALS AND METHODS

Muscle oxygen saturation was measured with near-infrared spectroscopy on the vastus lateralis of each leg during 3-minute arterial occlusion and recovery (3 min). Muscle oxygen consumption was derived from the desaturation slope during ischemia, microvascular responsiveness was derived from the resaturation slope after ischemia and reactive hyperemia was derived from the area under the curve above baseline after ischemia.

RESULTS

Eleven subjects (91% male; 32.2±6.1 months post-stroke; age 62.9±13.6 years) with a hemiparetic gait pattern participated. There was no significant between-leg muscle oxygenation difference at rest (paretic: 64.9±16.6%; nonparetic: 70.6±15.6%, p = 0.13). Muscle oxygen consumption in the paretic leg (-0.53±0.24%/s) was significantly reduced compared to the nonparetic leg (-0.70±0.36%/s; p = 0.03). Microvascular responsiveness was significantly reduced in the paretic leg compared to the nonparetic leg (paretic: 4.6±1.8%/s; nonparetic: 5.7±1.6%/s, p = 0.04). Reactive hyperemia was not significantly different between legs (paretic:4384±2341%·s; nonparetic: 3040±2216%·s, p = 0.07).

CONCLUSION

Muscle oxygen consumption and microvascular responsiveness are impaired in the paretic compared to the nonparetic leg, suggesting both reduced skeletal muscle aerobic function and reduced ability to maximally perfuse muscle tissue.

Performance Assessment of a Commercial Continuous-Wave Near-Infrared Spectroscopy Tissue Oximeter for Suitability for Use in an International, Multi-Center Clinical Trial

Despite the wide range of clinical and research applications, the reliability of the absolute oxygenation measurements of continuous wave near-infrared spectroscopy sensors is often questioned, partially due to issues of standardization. In this study, we have compared the performances of 13 units of a continuous wave near-infrared spectroscopy device (PortaMon, Artinis Medical Systems, NL) to test their suitability for being used in the HEMOCOVID-19 clinical trial in 10 medical centers around the world. Detailed phantom and in vivo tests were employed to measure the precision and reproducibility of measurements of local blood oxygen saturation and total hemoglobin concentration under different conditions: for different devices used, different operators, for probe repositioning over the same location, and over time (hours/days/months). We have detected systematic differences between devices when measuring phantoms (inter-device variability, <4%), which were larger than the intra-device variability (<1%). This intrinsic variability is in addition to the variability during in vivo measurements on the forearm muscle resulting from errors in probe positioning and intrinsic physiological noise (<9%), which was also larger than the inter-device differences (<3%) during the same test. Lastly, we have tested the reproducibility of the protocol of the HEMOCOVID-19 clinical trial; that is, forearm muscle oxygenation monitoring during vascular occlusion tests over days. Overall, our conclusion is that these devices can be used in multi-center trials but care must be taken to characterize, follow-up, and statistically account for inter-device variability.

In vivo Measurement of Intraosseous Vascular Haemodynamic Markers in Human Bone Tissue Utilising Near Infrared Spectroscopy

Objective: Poor vascular health is associated with reduced bone strength and increased risk of fragility fracture. However, direct measurement of intraosseous vascular health is difficult due to the density and mineral content of bone. We investigated the feasibility of using a commercially available continuous wave near infrared spectroscopy (NIRS) system for the investigation of vascular haemodynamics in human bone in vivo.

Approach: An arterial occlusion (AO) protocol was developed for obtaining haemodynamic measurements of the proximal tibia and lateral calf, including assessment of the protocol’s intra operator reproducibility. For 36 participants, intraosseous haemodynamics derived by NIRS were compared to alternative tests of bone health based on dual x-ray absorptiometry (DXA) testing and MRI.

Main Results: Near infrared spectroscopy markers of haemodynamics of the proximal tibia demonstrated acceptable reproducibility, comparable with reproducibility assessments of alternative modalities measuring intraosseous haemodynamics, and the use of NIRS for measuring muscle. Novel associations have been demonstrated between haemodynamic markers of bone measured with NIRS and body composition and bone mineral density (BMD) measurements obtained with both DXA and MRI.

Significance: Near infrared spectroscopy provides inexpensive, non-invasive, safe, and real time data on changes in oxygenated and deoxygenated haemoglobin concentration in bone at the proximal tibia. This study has demonstrated the potential for NIRS to contribute to research investigating the pathophysiological role of vascular dysfunction within bone tissue, but also the limitations and need for further development of NIRS technology.

Altered microvascular reactivity assessed by near-infrared spectroscopy after hepato-pancreato-biliary surgery

Little is known about microcirculatory dysfunction following abdominal surgeries. This study aimed to evaluate changes in microvascular reactivity (MVR) before and after major abdominal surgery, assessed by near-infrared spectroscopy in conjunction with a vascular occlusion test. This prospective observational study included 50 adult patients who underwent hepato-pancreato-biliary surgery lasting ≥ 8 h. MVR was assessed by tissue oxygen saturation (StO₂) changes in the plantar region of the foot during 3 min of vascular occlusion and subsequent release under general anesthesia before and after surgery. The primary outcome was alteration in the recovery slope of StO₂ (RecStO₂) and recovery time (tM) between the preoperative and postoperative values. Postoperative short-term outcome was represented by the Post-operative Morbidity Survey (POMS) score on the morning of postoperative day 2. After surgery, RecStO₂ was reduced (0.74% [0.58-1.06]/s vs. 0.89% [0.62-1.41]/s, P = 0.001), and tM was longer (57.0 [42.9-71.0] s vs. 41.3 [35.5-56.5] s, P < 0.001), compared to the preoperative values. Macrohemodynamic variables such as cardiac index, arterial pressure, and stroke volume during postoperative measurement did not differ with or without relative MVR decline. In addition, the POMS score was not associated with postoperative alterations in microcirculatory responsiveness. MVR in the plantar region of the foot was reduced after major hepato-pancreato-biliary surgery regardless of macrocirculatory adequacy. Impaired MVR was not associated with short-term outcomes as long as macrocirculatory indices were well maintained. The impact of relative microcirculatory changes, especially combined with inadequate macrocirculation, on postoperative complications remains to be elucidated.Clinical Trial Registrations UMIN-CTR trial ID: 000033461.

Measurement of peripheral muscle oxygen saturation in conscious healthy horses using a near-infrared spectroscopy device

OBJECTIVE

Maintaining adequate muscle tissue oxygenation is of paramount importance during equine general anesthesia. The objectives of this study were to assess the feasibility, reliability and repeatability of near-infrared spectroscopy (NIRS) muscle oximetry using the Inspectra m650 in conscious healthy adult horses.

STUDY DESIGN

Prospective, observational study.

ANIMALS

A group of 30 healthy client-owned adult horses admitted to the equine hospital between July 2017 and July 2018.

METHODS

The probe of an Inspectra m650 NIRS tissue oximeter was placed on the hairless surface of five muscle sites (omotransversarius, triceps long head, extensor carpi ulnaris, vastus lateralis and lateral digital extensor) on the left side of the body of each standing, unsedated horse. Each site had muscle oxygenation (StO₂) recordings measured in triplicate and statistical modeling used to assess the reading reliability and repeatability within and between muscle sites.

RESULTS

The readings acquired at the vastus lateralis and extensor carpi ulnaris muscle sites had highly repeatable values [mean (90% confidence interval): StO₂, 95% (93.8%, 96.5%) and 93% (91.6%, 93.9%), respectively; intraclass correlation coefficients, 0.92 and 0.80, respectively]. These two sites also had high reliability (represented by the percentage of successful readings; 70% and 86%, respectively).

CONCLUSIONS AND CLINICAL RELEVANCE

The use of NIRS muscle oxygenation technology is a clinically feasible means to assess tissue oxygenation in horses. The vastus lateralis and extensor carpi ulnaris muscle sites provided the most reliable and repeatable readings when using the Inspectra m650 machine in horses.

Thenar Muscle Oxygen Saturation Using Vascular Occlusion Test: A Novel Technique to Study Microcirculatory Abnormalities in Pediatric Heart Failure Patients

Heart failure (HF) is associated with microcirculatory changes secondary to neuro-humoral imbalance, vascular stiffness and increased sympathetic tone. Near Infra-Red Spectroscopy (NIRS) derived Thenar muscle tissue oxygenation levels (StO₂) can provide an estimate of the functional status of microcirculation. There is a paucity of literature regarding evaluation of microcirculation in pediatric subjects with HF. We hypothesized that microcirculation and oxygen saturation dynamics as assessed by Thenar StO₂ levels using vascular occlusion test (VOT) would be altered in HF subjects and that these changes may correlate with the severity of heart failure. We prospectively enrolled 60 pediatric subjects (29 healthy control, 31 HF). Baseline StO₂ levels were measured using InSpectra™ StO₂ probe placed over the Thenar eminence of right hand, followed by a VOT for 3 min, during which the changes in StO₂ levels during the occlusion phase and post occlusion phase were recorded. Baseline Thenar StO₂ levels (72 ± 8 vs 76 ± 5, p = 0.02) and time to baseline StO₂ in seconds (150 ± 70 vs 200 ± 70, p = 0.007) were significantly lower in HF group compared to healthy control (HC). In addition, HF patients had a significantly lower trough StO₂ (37 ± 9 vs 42 ± 11%, p =  0.04) and peak StO₂ compared to HC (87 ± 8 vs 91 ± 5%, p = 0.01). However, there was no difference in the rate of desaturation, rate of resaturation or time to peak StO₂ levels in between the 2 groups. Significant correlation was present between baseline Thenar StO₂ levels and NYU Pediatric Heart Failure Index Score (NYU-PHFI) (p = 0.003). This study is the first to report an objective assessment of microcirculation and Thenar tissue oxygen dynamics in pediatric subjects with HF in comparison with HC. Our study suggests altered microcirculation and oxygenation patterns in these subjects as well as correlation with a validated pediatric heart failure clinical score. Large-scale prospective studies are needed to further study the utility of this novel technology in HF subjects.

Reliability of microvascular responsiveness measures derived from near-infrared spectroscopy across a variety of ischemic periods in young and older individuals

BACKGROUND

Cardiovascular disease (CVD) is associated with impairments in microvascular responsiveness. Therefore, reliably assessing microvascular function is clinically relevant. Thus, this study aimed to examine the reliability of the near-infrared spectroscopy (NIRS)-derived oxygen saturation (StO₂) reperfusion slope, a measure of microvascular responsiveness, to four different vascular occlusion tests (VOT) of different durations in young and older participants.

METHODS

Eight healthy young (29 ± 5 yr) and seven older (67 ± 4 yr) men participated in four NIRS combined with VOT (NIRS-VOT; 30 s, 1, 3, and 5 min) in the leg microvasculature on two visits separated by 1-2 weeks. Vascular responsiveness was determined by the StO₂ reperfusion slope. The coefficient of variation (CV), repeatability, reliability (ICC), and the limits of agreement (LOA) were calculated for the NIRS-derived reperfusion slopes for each occlusion duration and visit.

RESULTS

CV for the StO₂ reperfusion slope following 30 s, 1, 3 and 5 min of occlusion were 33 ± 29%, 19 ± 21%, 14 ± 12%, and 12 ± 10%, respectively. Repeatability values following 30 s, 1, 3 and 5 min occlusions were 20%, 1%, 4% and 21%, respectively. The ICC for the StO₂ reperfusion slopes for each occlusion duration were 0.29, 0.42, 0.84, and 0.88 following 30 s, 1, 3 and 5 min of occlusion, respectively. LOA values between visit 1 and 2 for occlusions were not different from zero. There were no age-related differences for all variables of the study.

CONCLUSION

NIRS-derived StO₂ reperfusion slope, has good reliability across a range of occlusion durations with the strongest reliability during longer occlusion durations.

Microvascular reactivity monitored with near-infrared spectroscopy is impaired after induction of anaesthesia in cardiac surgery patients: An observational study

BACKGROUND

Induction of anaesthesia causes significant macrohaemodynamic changes, but little is known about its effects on the microcirculation. However, alterations in microvascular perfusion are known to be associated with impaired tissue oxygenation and organ dysfunction. Microvascular reactivity can be assessed with vascular occlusion testing, which evaluates the response of tissue oxygen saturation to transient ischaemia and reperfusion.

OBJECTIVE

The aim of the current study was to evaluate the effects of an opioid-based anaesthesia induction on microvascular reactivity. We hypothesised that despite minimal blood pressure changes, microvascular function would be impaired.

DESIGN

Prospective, observational study.

SETTING

Single-centre, tertiary university teaching hospital, Belgium.

PATIENTS

Thirty-five adult patients scheduled for elective coronary artery bypass grafting surgery.

INTERVENTION

Microvascular reactivity was assessed before and 30 min after anaesthesia induction by means of vascular occlusion testing and near-infrared spectroscopy.

MAIN OUTCOME MEASURES

Tissue oxygen saturations, desaturation rate, recovery time (time from release of cuff to the maximum value) and rate of recovery were determined.

RESULTS

Data are expressed as median (minimum to maximum). Tissue oxygen saturation was higher after induction of anaesthesia [70 (54 to 78) vs. 73 (55 to 94)%, P = 0.015]. Oxygen consumption decreased after induction, appreciable by the higher minimum tissue oxygen saturation [45 (29 to 69) vs. 53 (28 to 81)%, P < 0.001] and the slower desaturation rate [11 (4 to 18) vs. 9 (5 to 16)% min, P < 0.001]. After induction of anaesthesia, recovery times were longer [40 (20 to 120) vs. 48 (24 to 356) s, P = 0.004] and the rate of recovery was lower [114 (12 to 497) vs. 80 (3 to 271)% min, P < 0.001].

CONCLUSION

After induction of anaesthesia, oxygen consumption was decreased. The longer recovery times and slower rates of recovery indicate impaired microvascular reactivity after induction of anaesthesia.

TRIAL REGISTRATION

The research project was registered at ClinicalTrials.gov (NCT02034682).

Assessment of hand superficial oxygenation during ischemia/reperfusion in healthy subjects versus systemic sclerosis patients by 2D near infrared spectroscopic imaging

BACKGROUND AND OBJECTIVE

Patients affected by systemic sclerosis (SSc) develop functional and structural microcirculatory dysfunction, which progressively evolves towards systemic tissue fibrosis (sclerosis). Disease initially affects distal extremities, which become preferential sites of diagnostic scrutiny. This pilot investigation tested the hypothesis that peripheral microcirculatory dysfunction in SSc could be non-invasively assessed by 2D Near Infrared Spectroscopic (NIRS) imaging of the hand associated with Vascular Occlusion Testing (VOT). NIRS allows measurement of hemoglobin oxygen saturation (StO₂) in the blood perfusing the volume tissue under scrutiny.

METHODS

In five normal volunteers and five SSc patients we applied a multispectral oximetry imaging device (Kent camera, Kent Imaging, Calgary, Canada) to acquire StO₂ 2D maps of the whole hand palm during baseline, ischemia and reperfusion phase.

RESULTS

We found significant differences between controls and SSc patients in basal StO₂ (82.80 ± 2.51 vs 65.44 ± 7.96%, p = 0.0016), minimum StO₂ (59.35 ± 4.29 vs 40.73 ± 6.47%, p = 0.0007), final StO₂ (83.83 ± 4.09 vs 68.84 ± 11.41%, p = 0.02) and time to maximum StO₂ (40 ± 12.25 vs 62 ± 4.47 s, p = 0.005).

CONCLUSIONS

This is, to our knowledge, the first application of 2D NIRS imaging of the whole hand to the investigation of microvascular dysfunction in systemic sclerosis. The image processing presented here considered the StO₂ in the entire hand allowing a comprehensive view of the spatial heterogeneity of microvascular dysfunction.

Dorsiflexor Muscle Oxygenation During Low, Moderate and Submaximal Sustained Isometric Contraction

Sustained isometric contractions of skeletal muscles produce intramuscular pressures that lead to blood flow restriction. Thus, we have the paradox of rising O₂ demand due to muscle activity and at the same time reduced blood flow. The aim was to assess muscle oxygenation during sustained isometric low (30%), moderate (60%) and submaximal [90% of maximal voluntary contraction (MVC)] contraction of the dorsiflexor muscle. Experiments were conducted on the dominant (right) leg of 8 male students (age 19 ± 2 years, weight 75 ± 6 kg). Tissue oxygen saturation (StO₂) was recorded from the tibialis anterior using near-infrared spectroscopy. StO₂ was higher at 30% compared to both 60% and 90% MVC at all time points after the start of the exercise and higher at 60% than 90%. This indicates that the supply of O₂ did not keep up with its consumption. During arterial occlusion the minimal StO₂ reached 52%, which is significantly higher than StO₂ during 60% and 90% MVC. After each contraction there was a large and immediate hyperemic response, whose resaturation rate continuously increased from 30% to 60% to 90% MVC. The StO₂ resaturation rate was positively correlated with the MVC, indicating a vasodilation depending on the intensity of the exercise.

Muscle microcirculation alterations and relation to dipping status in newly diagnosed untreated patients with arterial hypertension-A pilot study

OBJECTIVE

The importance of abnormalities observed in the microcirculation of patients with arterial hypertension (AH) is being increasingly recognized. The authors aimed to evaluate skeletal muscle microcirculation in untreated, newly diagnosed hypertensive patients with NIRS, a noninvasive method that evaluates microcirculation.

METHODS

We evaluated 34 subjects, 17 patients with AH (13 males, 49±13 years, BMI: 26±2 kg/m² ) and 17 healthy controls (12 males, 49±15 years, BMI: 25±3 kg/m² ). The thenar muscle StO₂ (%) was measured by NIRS before, during and after 3-minutes vascular occlusion to calculate OCR (%/min), EF (%/min), and RHT (minute). The dipping status of hypertensive patients was assessed.

RESULTS

The RHT differed between AH patients and healthy subjects (2.6±0.3 vs 2.1±0.3 minutes, P<.001). Dippers had higher EF than nondippers (939±280 vs 710±164%/min, P=.05).

CONCLUSIONS

The study suggests an impaired muscle microcirculation in newly diagnosed, untreated AH patients.

Assessing muscular oxygenation during incremental exercise using near-infrared spectroscopy: comparison of three different methods

Using continuous-wave near-infrared spectroscopy (NIRS), this study compared three different methods, namely the slope method (SM), the amplitude method (AM), and the area under the curve (AUC) method to determine the variations of intramuscular oxygenation level as a function of workload. Ten right-handed subjects (22+/-4 years) performed one isometric contraction at each of three different workloads (30 %, 50 % and 90 % of maximal voluntary strength) during a period of twenty seconds. Changes in oxyhemoglobin (delta[HbO(2)]) and deoxyhemoglobin (delta[HHb]) concentrations in the superficial flexor of fingers were recorded using continuous-wave NIRS. The results showed a strong consistency between the three methods, with standardized Cronbach alphas of 0.87 for delta[HHb] and 0.95 for delta[HbO(2)]. No significant differences between the three methods were observed concerning delta[HHb] as a function of workload. However, only the SM showed sufficient sensitivity to detect a significant decrease in delta[HbO(2)] between 30 % and 50 % of workload (p<0.01). Among these three methods, the SM appeared to be the only method that was well adapted and sensitive enough to determine slight changes in delta[HbO(2)]. Theoretical and methodological implications of these results are discussed.

Effect of acute nitrate and citrulline supplementation on muscle microvascular response to ischemia-reperfusion in healthy humans

Nitric oxide (NO) is implicated in vasomotor control mechanisms altering the diameter of the vessels under various physiological and pathological conditions. There are 2 main NO production pathways, 1 NO synthase (NOS) independent (nitrate-nitrite-NO) and the other is NOS dependent (citrulline-arginine-NO). The objective of the study was to evaluate the effect of acute nitrate and citrulline supplementation on post-ischemic vascular response in healthy subjects. Fourteen subjects performed 2-leg vascular occlusion tests, 3 days apart. They were randomly assigned to consume a drink containing 1200 mg (19.4 mmol) of nitrate and 6 g of citrulline (N+C) or a placebo (Pl). Changes in total hemoglobin (Hbtot) and oxyhemoglobin (HbO₂) concentrations were recorded by near-infrared spectroscopy on the thigh and calf muscles. No differences between N+C and Pl were observed during the ischemic period. Hbtot increased to a larger extent during the reperfusion period for the thigh (e.g., area under the curve, 821 ± 324 vs. 627 ± 381 mmol·s^-1, p = 0.003) and the calf (515 ± 285 vs. 400 ± 275 mmol·s^-1, p = 0.029) in the N+C versus Pl conditions. Similar results were found regarding HbO₂ for the thigh (e.g., area under the curve, 842 ± 502 vs. 770 ± 491 mmol·s^-1, p = 0.077) and the calf (968 ± 536 vs. 865 ± 275 mmol·s^-1, p = 0.075). The larger postocclusive Hbtot and HbO₂ responses observed after N+C intake suggests a greater post-ischemic vasodilation, which may be due to increased NO availability, via the activation of the 2 main NO production pathways.

Oxygenation dynamics of sepsis patients undergoing far-infrared intervention based on near-infrared spectroscopy

Near-infrared spectroscopy (NIRS; continuous wave type) is a noninvasive tool for detecting the relative change of oxyhemoglobin and deoxyhemoglobin. To make this change, intervention methods must be applied. This study determined the hemodynamics of 44 healthy participants and 35 patients with sepsis during exposure to FIR as a novel physical intervention approach. Local microcirculation of their brachioradialis was monitored during exposure and recovery through NIRS. The variations in blood flow and microvascular reaction were determined by conducting paired and unpaired t tests. The oxyhemoglobin levels of the healthy participants increased continuously, even during recovery. In contrast to expextations, the oxyhemoglobin levels of the patients plateaued after only 5 min of FIR illumination. The proposed method has potential applications for ensuring efficient treatment and facilitating doctors in diagnosing the functions of vessels in intensive care units. Mapping diagrams of HbO₂ in healthy males and males with sepsis illustrated unique scenarios during the process.

Vascular responsiveness measured by tissue oxygen saturation reperfusion slope is sensitive to different occlusion durations and training status

What is the central question of this study? Is the near-infrared spectroscopy-derived measure of tissue oxygen saturation (StO2) reperfusion slope sensitive to a range of ischaemic conditions, and do differences exist between trained and untrained individuals? What is the main finding and its importance? The StO2 reperfusion rate is sensitive to different occlusion durations, and changes in the reperfusion slope in response to a variety of ischaemic challenges can be used to detect differences between two groups. These data indicate that near-infrared spectroscopy-derived measures of StO2, specifically the reperfusion slope following a vascular occlusion, can be used as a sensitive measure of vascular responsiveness. The reperfusion rate of near-infrared spectroscopy-derived measures of tissue oxygen saturation (StO2) represents vascular responsiveness. This study examined whether the reperfusion slope of StO2 is sensitive to different ischaemic conditions (i.e. a dose-response relationship) and whether differences exist between two groups of different fitness levels. Nine healthy trained (T; age 25 ± 3 years; maximal oxygen uptake 63.4 ± 6.7 ml kg^-1  min^-1 ) and nine healthy untrained men (UT; age 21 ± 1 years; maximal oxygen uptake 46.6 ± 2.5 ml kg^-1  min^-1 ) performed a series of vascular occlusion tests of different durations (30 s, 1, 2, 3 and 5 min), each separated by 30 min. The StO2 was measured over the tibialis anterior using near-infrared spectroscopy, with the StO2 reperfusion slope calculated as the upslope during 10 s following cuff release. The reperfusion slope was steeper in T compared with UT at all occlusion durations (P < 0.05). For the T group, the reperfusion slopes for 30 s and 1 min occlusions were less than for all longer durations (P < 0.05). The reperfusion slope following 2 min occlusion was similar to that for 3 min (P > 0.05), but both were less steep than for 5 min of occlusion. In UT, the reperfusion slope at 30 s was smaller than for all longer occlusion durations (P < 0.05), and 1 min occlusion resulted in a reperfusion slope that was less steep than following 2 and 3 min (P < 0.05), albeit not different from 5 min (P > 0.05). The present study demonstrated that the reperfusion rate of StO2 is sensitive to different occlusion durations, and that changes in the reperfusion rate in response to a variety of ischaemic challenges can be used to detect differences in vascular responsiveness between trained and untrained groups.

Near infrared image processing to quantitate and visualize oxygen saturation during vascular occlusion

The assessment of microcirculation spatial heterogeneity on the hand skin is the main objective of this work. Near-infrared spectroscopy based 2D imaging is a non-invasive technique for the assessment of tissue oxygenation. The haemoglobin oxygen saturation images were acquired by a dedicated camera (Kent Imaging) during baseline, ischaemia (brachial artery cuff occlusion) and reperfusion. Acquired images underwent a preliminary restoration process aimed at removing degradations occurring during signal capturing. Then, wavelet transform based multiscale analysis was applied to identify edges by detecting local maxima and minima across successive scales. Segmentation of test areas during different conditions was obtained by thresholding-based region growing approach. The method identifies the differences in microcirculatory control of blood flow in different regions of the hand skin. The obtained results demonstrate the potential use of NIRS images for the clinical evaluation of skin disease and microcirculatory dysfunction.

Attenuated Microcirculatory Response to Maximal Exercise in Patients With Chronic Heart Failure

PURPOSE

Exercise training programs improve microcirculatory alternations in patients with chronic heart failure (CHF). However less is known about the acute effect of maximum exercise on the skeletal muscle microcirculation. We aimed to assess the effect of acute exercise on peripheral microcirculation of patients with CHF, as assessed by near-infrared spectroscopy with vascular occlusion technique.

METHODS

Tissue oxygenation was evaluated in 8 stable patients with CHF (7 males; mean age, 60 ± 9 years; body mass index, 26.3 ± 3.8 kg/m) and 8 healthy subjects (matched for age, sex, and body mass index) before and after cardiopulmonary exercise testing. Tissue oxygen saturation (StO2), StO2peak, oxygen consumption rate, and endothelial function (reperfusion rate), before and after maximum exercise, were assessed.

RESULTS

Patients with CHF had lower StO2 and reperfusion rate compared with healthy subjects (71.4% ± 9.8% vs 81.0% ± 5.4% and 9 ± 1 %/min vs 13.9 ± 5.8%/min, respectively; P < .05) at rest. Oxygen consumption rate increased after exercise in patients with CHF and healthy subjects (from -31.7 ± 8.2 to -43.7 ± 12.7 and from -35.7 ± 6.7 to -42.4 ± 6.4, respectively; P < .05). StO2 decreased significantly after maximal exercise in patients with CHF (from 71.4 ± 9.8 to 65.2 ± 12.7; P < .05), whereas it returned to the preexercise values in healthy subjects (from 81.0 ± 5.4 to 80.3 ± 7.0). There was a significant between-group difference (P < .05).

CONCLUSIONS

Patients with CHF present microcirculatory alternations. Acute exercise exerts an effect on microcirculation in peripheral, nonexercising muscles, with altered response in patients with CHF compared with healthy subjects.

The use of skeletal muscle near infrared spectroscopy and a vascular occlusion test at high altitude

Microcirculatory function, central to tissue regulation of oxygen flux, may be altered by the chronic hypoxemia experienced at high altitude. We hypothesized that at high altitude, adaptations within skeletal muscle would result in reduced oxygen consumption and reduced microcirculatory responsiveness, detectable by near infrared spectroscopy (NIRS) during a vascular occlusion test (VOT). The VOT comprised 3 min of noninvasive arterial occlusion; thenar eminence tissue oxygenation (Sto2) was measured by NIRS during the VOT at sea level, 4900 m and 5600 m (after 7 and 17 days at altitude, respectively) in 12 healthy volunteers. Data were derived from Sto2 time-curves using specifically designed computer software. Mean (±SD) resting Sto2 was reduced at 4900 m and 5600 m (69.3 (± 8.2)% (p=0.001) and 64.2 (± 6.1)% (p<0.001) respectively) when compared to sea level (84.4 (± 6.0)%. The rate of Sto2 recovery after vascular occlusion (Sto2 upslope) was significantly reduced at 4900 m (2.4 (± 0.4)%/sec) and 5600 m (2.4 (± 0.8)%/sec) compared to sea level (3.7 (± 1.3)%/sec) (p=0.021 and p=0.032, respectively). There was no change from sea level in the rate of desaturation during occlusion (Sto2 downslope) at either altitude. The findings suggest that in resting skeletal muscle of acclimatizing healthy volunteers at high altitude, microvascular reactivity is reduced (Sto2 upslope after a short period of ischemia) but that oxygen consumption remains unchanged (Sto2 downslope).

Microcirculation and macrocirculation in cardiac surgical patients

Background. The aim of our study was to investigate the relationship between microcirculatory alterations after open cardiac surgery, macrohemodynamics, and global indices of organ perfusion. Methods. Patients' microcirculation was assessed with near-infrared spectroscopy (NIRS) and the vascular occlusion technique (VOT). Results. 23 patients undergoing open cardiac surgery (11 male/12 female, median age 68 (range 28-82) years, EuroSCORE 6 (1-12)) were enrolled in the study. For pooled data, CI correlated with the tissue oxygen consumption rate as well as the reperfusion rate (r = 0.56, P < 0.001 and r = 0.58, P < 0.001, resp.). In addition, both total oxygen delivery (DO(2), mL/min per m(2)) and total oxygen consumption (VO(2), mL/min per m(2)) also correlated with the tissue oxygen consumption rate and the reperfusion rate. The tissue oxygen saturation of the thenar postoperatively correlated with the peak lactate levels during the six hour monitoring period (r = 0.50, P < 0.05). The tissue oxygen consumption rate (%/min) and the reperfusion rate (%/min), as derived from the VOT, were higher in survivors compared to nonsurvivors for pooled data [23 (4-54) versus 20 (8-38) P < 0.05] and [424 (27-1215) versus 197 (57-632) P < 0.01], respectively. Conclusion. Microcirculatory alterations after open cardiac surgery are related to macrohemodynamics and global indices of organ perfusion.