Inotropic agents improve the peripheral microcirculation of patients with end-stage chronic heart failure

Renal macro- and microcirculatory perturbations in acute kidney injury and chronic kidney disease associated with heart failure and cardiac surgery

Chronic kidney disease (CKD) affects 50% of patients with heart failure. The pathophysiology of CKD in heart failure is proposed to be driven by macrocirculatory hemodynamic changes, including reduced cardiac output and elevated central venous pressure. However, our understanding of renal microcirculation in heart failure and CKD remains limited. This is largely due to the lack of noninvasive techniques to assess renal microcirculation in patients. Moreover, there is a lack of clinically relevant animal models of heart failure and CKD to advance our understanding of the timing and magnitude of renal microcirculatory dysfunction. Patients with heart failure and CKD commonly require cardiac surgery with cardiopulmonary bypass (CPB) to improve their prognosis. However, acute kidney injury (AKI) is a frequent unresolved clinical complication in these patients. There is emerging evidence that renal microcirculatory dysfunction, characterized by renal medullary hypoperfusion and hypoxia, plays a critical role in the pathogenesis of cardiac surgery-associated AKI. In this review, we consolidate the preclinical and clinical evidence of renal macro- and microcirculatory perturbations in heart failure and cardiac surgery requiring CPB. We also examine emerging biomarkers and therapies that may improve health outcomes for this vulnerable patient population by targeting the renal microcirculation.

Microvascular Reactivity Is Greater Following Blood Flow Restriction Resistance Exercise Compared with Traditional Resistance Exercise

ABSTRACT

Perlet, MR, Hosick, PA, Licameli, N, and Matthews, EL. Microvascular reactivity is greater following blood flow restriction resistance exercise compared with traditional resistance exercise. J Strength Cond Res 38(10): e553-e562, 2024-Chronic blood flow restriction (BFR) resistance exercise can improve muscular strength, hypertrophy, and microvasculature function, but the acute microvascular effects are unknown. We aimed to test the effects of acute BFR resistance exercise on postexercise microvascular reactivity in an exercising muscle and nonexercising muscle compared with traditional resistance exercise (TRE). Twenty-five adults (men = 14, women = 11, age: 22 ± 3 years, body mass: 71.69 ± 14.49 kg, height: 170 ± 10 cm) completed barbell back squat 1-repetition maximum (1RM) testing followed by 2 randomized and counterbalanced resistance exercise visits separated by ≥48 hours. The 2 visits involved either BFR (4 sets of 30-15-15-15 repetitions at 30% 1RM, with 60-second rest intervals) or TRE (4 sets of 10 repetitions at 70% 1RM, 60-second rest intervals). During each exercise visit, a pre- and postbarbell back squat vascular occlusion test was performed using near-infrared spectroscopy to measure skeletal muscle oxygen (SmO 2 ) in the vastus lateralis (VL) and flexor carpi radialis (FCR). Two-way repeated-measures ANOVA found an interaction effect ( p = 0.020) for SmO 2 reactivity in the VL. Post hoc analysis found greater reactive hyperemia postexercise in the VL for the BFR condition ( p < 0.001) but not the TRE condition ( p ≥ 0.05). There were no time, condition, or interaction effects (all p > 0.05) for the same analysis in the FCR. This analysis suggests that BFR, but not TRE, lead to acutely improved microvasculature function. Moreover, it suggests that the effects of BFR resistance exercise are local to the exercised or occluded limb and not systemic.

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.

Young healthy adults with a family history of hypertension have increased microvascular reactivity but decreased macrovascular function

OBJECTIVE

To determine whether, like hypertensives, normotensive adults with a family history of hypertension (+FHH) display lower microvascular reactivity and conduit artery function than normotensive adults without a family history of hypertension (-FHH).

METHODS

A forearm vascular occlusion test was performed on healthy normotensive adults while resting in the supine position. A near-infrared spectroscopy sensor placed on the forearm measured skeletal muscle oxygen saturation kinetics to determine microvascular reactivity. Simultaneously, an ultrasound probe placed on the brachial artery above the occlusion cuff was used to assess flow-mediated dilation; a test of macrovascular function.

RESULTS

Twenty-two participants were included in this investigation (-FHH n = 13, +FHH n = 9). Following cuff release, the resaturation slope (1st 10 s median ± SD, -FHH 2.76 ± 2.10, +FHH 5.59 ± 2.47%/s; p = .036) was greater in +FHH when accounting for the magnitude and rate of the decrease in skeletal muscle oxygen saturation during occlusion. Conversely, flow-mediated dilation (median ± SD, -FHH 5.96 ± 5.22, +FHH 4.10 ± 3.17%∆; p = .031) was lower in +FHH when accounting for baseline artery diameter and shear rate.

CONCLUSIONS

Young +FHH adults have altered microvascular and macrovascular reactivity compared with young -FHH adults.

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.

Effect of assuming constant tissue scattering on measured tissue oxygenation values during tissue ischemia and vascular reperfusion

The purpose of this study was to determine the effects of assuming constant tissue scattering properties on tissue oxygenation measurements during a vascular occlusion test (VOT). Twenty-one subjects (21.8 ± 1.9 yr) completed a VOT [1 min baseline (BL), 5 min of tissue ischemia (TI), and 3 min of vascular reperfusion (VR)]. Absolute concentrations of oxygenated heme (oxy-[heme]), deoxygenated heme (deoxy-[heme]), total heme (total [heme), tissue oxygen saturation (StO2), and heme difference [heme]diff) were measured using frequency domain near-infrared spectroscopy (FD-NIRS) while 1) continuously measuring and incorporating tissue scattering ([Formula: see text]) and 2) assuming scattering remained constant. FD-NIRS measured [Formula: see text] increased during TI at 692 nm ( P < 0.001) and decreased at 834 nm ( P < 0.001). During VR, [Formula: see text] decreased at 692 nm ( P < 0.001) and increased at 834 nm ( P < 0.001). When assuming constant scattering, oxy-[heme] was significantly less at TIpeak ( P < 0.05) while deoxy-[heme] and StO2 were significantly altered at BL, TIpeak, and VRpeak (all P < 0.001). Total [heme] did not change during the VOT. Absolute changes in deoxy-[heme], oxy-[heme], and StO2 in response to TI and VR were significantly exaggerated (all P < 0.001) and the rates of change during TI ( slope 1) and VR ( slope 2) in deoxy-[heme], oxy-[heme], StO2, and [heme]diff were significantly increased (all P < 0.05) when constant tissue scattering was assumed. These findings demonstrate the need for caution when interpreting NIRS data without continuously measuring tissue optical properties. Further, assuming tissue optical properties remain constant may have important consequences to experimental data and clinical conclusions made using NIRS.

NEW & NOTEWORTHY NIRS measurements provide significant experimental and clinical insight. We demonstrate that absolute changes in tissue oxygenation measurements made with NIRS are overestimated and the kinetic responses of NIRS measurements are exaggerated by varying degrees among individuals if tissue scattering characteristics are assumed to remain constant during vascular occlusion tests.

Microvascular reactivity, assessed by near-infrared spectroscopy and a vascular occlusion test, is associated with patient outcomes following cardiac surgery: A prospective observational study

BACKGROUND

Microvascular dysfunction in patients admitted to the ICU following cardiac surgery may be related to perioperative complications and increased resource utilisation even in the presence of acceptable systemic haemodynamic variables.

OBJECTIVES

To assess the relationship between microvascular impairment using peripheral near-infrared spectroscopy at ICU admission and 6 h postadmission and the duration of mechanical ventilatory support, length of stay in ICU and in hospital.

DESIGN

Prospective, observational cohort study.

SETTING

Single-centre, tertiary-level cardiac ICU.

PATIENTS

Sixty-nine adult patients following elective cardiac surgery excluding patients with on-going extracorporeal support or in whom tissue haemoglobin oxygen saturation (StO2) measurements were not feasible.

MAIN OUTCOME MEASURES

Thenar and forearm StO2 in response to a vascular occlusion test to calculate desaturation and reperfusion slopes. A logistic regression model was used to ascertain the associations between StO2, desaturation and reperfusion slopes as well as cardiac index, mean arterial pressure, arterial lactate concentrations and prolonged (≥75th percentile) duration of mechanical ventilation, ICU length of stay and hospital length of stay.

RESULTS

A reduced reperfusion slope at ICU admission was associated independently with prolonged mechanical ventilation at thenar (OR 0.08; 95% CI [0.02 to 0.47], P = 0.003) and forearm [OR 0.2 (0.04 to 0.59), P = 0.006] sites. Similarly, a reduced Rres was associated with prolonged ICU LOS at both thenar [OR 0.3 (0.13 to 0.77), P = 0.007] and forearm [OR 0.2 (0.05 to 0.62), P = 0.007] sites at ICU0 h, as well as ICU6 h [OR 0.2 (0.05 to 0.66), P = 0.004 and OR 0.05 (0.008 to 0.34), P = 0.002]. An increased Rdes was associated with prolonged hospital LOS at the thenar eminence at ICU0 h [OR 1.9 (1.4 to 2.3), P = 0.004] and ICU6 h [OR 6.7 (2.0 to 23), P = 0.002] as well as the forearm at ICU0 h [OR 1.5 (1.3 to 1.9), P = 0.004] and ICU6 h [OR 1.6 (1.3 to 2.1), P = 0.004].

CONCLUSION

In the early postoperative period following cardiac surgery, changes in thenar and forearm tissue oxygenation variables are associated with patient resource utilisation outcomes.

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).

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.

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.

The effect of aging on the cutaneous microvasculature

Aging is associated with a progressive loss of function in all organs. Under normal conditions the physiologic compensation for age-related deficits is sufficient, but during times of stress the limitations of this reserve become evident. Explanations for this reduction in reserve include the changes in the microcirculation that occur during the normal aging process. The microcirculation is defined as the blood flow through arterioles, capillaries and venules, which are the smallest vessels in the vasculature and are embedded within organs and tissues. Optimal strategies to maintain the microvasculature following surgery and other stressors must use multifactorial approaches. Using skin as the model organ, we will review the anatomical and functional changes in the microcirculation with aging, and some of the available clinical strategies to potentially mitigate the effect of these changes on important clinical outcomes.

Changes in skeletal muscle microcirculation after a hemodialysis session correlates with adequacy of dialysis

Background

Monitoring of the microcirculation may add additional information in terms of improving the adequacy of hemodialysis (HD) for patients. Withdrawal of liquid and complement activation during a HD session reduces the external pressure on the microcirculation and leads to an increased dilatation of the peripheral capillaries. The purposes of this study were to assess the effect of a single HD or hemodiafiltration session on the thenar microcirculation in patients with end-stage renal disease (ESRD) with or without diabetes, investigate the possible relationship between changes in the microcirculation and adequacy of dialysis (including Kt/V and parameters indicating secondary hyperparathyroidism), and compare microcirculation measurements obtained from patients with ESRD and those from healthy controls.

Methods

This pilot prospective observational study including eleven patients with ESRD on maintenance HD (nine men of mean age 73±10.5 years, ten [91%] with hypertension), nine patients with ESRD on maintenance hemodiafiltration (six men of mean age 65.5±13.2 years, five [55.5%] with diabetes and four [44.5%] with hypertension), and eight healthy volunteers. Two paired microcirculation assessments were recorded for each HD patient before and after a dialysis session. Near infrared spectroscopy and the vascular occlusion test were used to assess the microcirculation, and blood work samples were collected before and after dialysis when the pump slowed down.

Results

Patients with ESRD showed an increase in thenar cell metabolism at rest after a 4-hour HD session, and changes in cell metabolism correlated with the Kt/V of the session. Pre-dialysis tissue oxygen saturation over the 4-hour HD session correlated with pre-dialysis serum calcium and parathyroid hormones. Vascular reactivity was lower in ESRD patients receiving HD or hemodiafiltration than in healthy controls.

Conclusion

Improvement in skeletal muscle microcirculation noted after a HD session was related to adequacy of dialysis. Evaluation of the microcirculation may provide additional information for management of patients on HD and identify novel targets for treatment. These preliminary findings need to be tested using a larger data set.

Monitoring the microcirculation in critically ill patients

Alterations in microvascular perfusion have been identified in critically ill patients, especially in sepsis but also in cardiogenic shock, after cardiac arrest, and in high-risk surgery patients. These alterations seem to be implicated in the development of organ dysfunction and are associated with outcome. Even though microvascular perfusion can sometimes be homogenously decreased as in acute hemorrhage or in non-resuscitated cardiogenic shock, heterogeneity of perfusion is observed in sepsis and in resuscitated hemorrhagic/cardiogenic shock. Heterogeneity of perfusion has major implications for monitoring, as many techniques cannot detect microcirculatory alterations when heterogeneity of flow is present in significant amount. Indeed, devices such as laser Doppler or O2 electrodes and near-infrared spectroscopy have a relatively large sampling volume and measurements are affected by the highest values in the field. Using these techniques during a vascular occlusion test may help to characterize microvascular reactivity; however, microvascular reactivity sometimes fails to represent actual microvascular perfusion. Videomicroscopic techniques can nowadays be applied at bedside but are still restricted to some selected patients (quiet or sedated patients). Tissue PCO2 is an elegant alternative but is not yet broadly used. In this manuscript, we discuss the main advantages and limitations of the techniques available for bedside evaluation of the microcirculation in critically ill patients.

Noninvasive assessment of hemodynamic variables using near-infrared spectroscopy in patients experiencing cardiogenic shock and individuals undergoing venoarterial extracorporeal membrane oxygenation

PURPOSE

The relationship between near-infrared spectroscopy cerebral oximetry (CrSO2), peripheral oximetry (PrSO2) and hemodynamic variables is not fully understood.

METHODS

The relationship between CrSO2/PrSO2 and cardiac index (CI), systemic vascular resistance index (SVRI) and mean arterial pressure (MAP) in patients experiencing cardiogenic shock and those undergoing venoarterial extracorporeal membrane oxygenation (ECMO) was retrospectively analyzed; in patients on ECMO, total circulatory index (TCI) was calculated from the sum of CI and extracorporeal blood flow index.

RESULTS

In patients experiencing cardiogenic shock (n=10), significant correlations between PrSO2 values and CI (Spearman r=0.81; P<.0001), SVRI (r=-0.45; P<.0001), and MAP (r=0.58; P<.0001) were found. Significant correlations between CrSO2 and CI (r=0.55; P<.0001) and SVRI (r=-0.47; P<.0001), but not MAP, were observed. Linear regression analysis revealed that CI could be calculated using the following equation: CI=PrSO2/24.0. In patients on VA ECMO (n=12), significant correlations were found between PrSO2 and TCI (r=0.68; P<.0001), SVRI (r=-0.47; P<.0001), and MAP (r=0.27; P=.025). Significant correlations were also found between CrSO2 and TCI (r=0.68; P<.0001) and SVRI (r=-0.51; P<.0001), but not MAP.

CONCLUSIONS

Results of the present study suggest that CrSO2 and PrSO2 in particular can be used for noninvasive estimation and monitoring of global circulatory status in patients experiencing cardiogenic shock and individuals undergoing ECMO.

Peripheral muscle microcirculatory alterations in patients with pulmonary arterial hypertension: a pilot study

BACKGROUND

Pulmonary microcirculation abnormalities are the main determinants of pulmonary arterial hypertension (PAH) pathophysiology. We hypothesized that PAH patients have peripheral tissue microcirculation alterations that might benefit from hyperoxic breathing. We evaluated peripheral muscle microcirculation with near-infrared spectroscopy, before and after hyperoxic breathing.

METHODS

Eight PAH subjects, 8 healthy subjects (controls) matched for age, sex, and body mass index, and 16 subjects with chronic heart failure and matched for functional capacity with the PAH subjects underwent near-infrared spectroscopy. Tissue O(2) saturation, defined as the hemoglobin saturation (%) in the microvasculature compartments, was measured on the thenar muscle. Then the 3-min brachial artery occlusion technique was applied before, during, and after 15 min of breathing 100% O(2). We calculated the oxygen consumption rate (%/min), the reactive hyperemia time, and the time needed for tissue O(2) saturation to reach its baseline value after the release of the occlusion.

RESULTS

Compared to the controls, the PAH subjects had a significantly lower resting tissue O(2) saturation (65.8 ± 14.9% vs 82.1 ± 4.0%, P = .005), a trend toward a lower oxygen consumption rate (35.3 ± 9.1%/min vs 43.4 ± 19.7%/min, P = .60), and a significantly higher reactive hyperemia time (3.0 ± 0.6 min vs 2.0 ± 0.3 min, P < .001). The PAH subjects also had lower tissue O(2) saturation (P = .08), lower peripheral arterial oxygen saturation (P = .01), and higher reactive hyperemia time (P = .02) than the chronic heart failure subjects. After hyperoxic breathing, the PAH subjects had increased tissue O(2) saturation (65.8 ± 14.9% to 71.4 ± 14.5%, P = .01), decreased oxygen consumption rate (35.3 ± 9.1%/min to 25.1 ± 6.6%/min, P = .01), and further increased reactive hyperemia time (3.0 ± 0.6 min to 4.2 ± 0.7 min, P = .007).

CONCLUSIONS

The PAH subjects had substantial impairments of peripheral muscle microcirculation, decreased tissue O(2) saturation (possibly due to hypoxemia), slower reactive hyperemia time, (possibly due to endothelium dysfunction), and peripheral systemic vasoconstriction. Acute hyperoxic breathing improved resting tissue O(2) saturation (an expression of higher oxygen delivery) and decreased the oxygen consumption rate and reactive hyperemia time during reperfusion, possibly due to increased oxidative stress and evoked vasoconstriction.

Home-Based Advance Care Programme is Effective in Reducing Hospitalisations of Advanced Heart Failure Patients: A Clinical and Healthcare Cost Study

Introduction: In end-stage heart failure (HF) that is not eligible for mechanical assist device or heart transplant, palliative care serves to maximise symptom control and quality of life. We sought to evaluate the impact of home-based advance care programme (ACP) on healthcare utilisation in end-stage HF patients. Materials and Methods: Prospectively collected registry data on all end-stage HF recruited into ACP between July 2008 and July 2010 were analysed. Chart reviews were conducted on HF database and hospital electronic records. Phone interview and home visit details by ACP team were extracted to complete data entry. HF and all-cause hospitalisations 1 year before, and any time after ACP inception were defined as events. For the latter analysis, follow-up duration adjustment to event episodes was performed to account for death less than a year. Results: Forty-four patients (mean age 79 years, 39% men) were followed up for 15±8 months. Fifty-seven percent had diabetes, 80% ischaemic heart disease, and 60% chronic kidney disease. All reported functional class III/IV at enrolment. Mean serum sodium was 136±6 mmol/L, and creatinine 186±126 mmol/L. Thirty (68%) died within the programme. Mean time to death was 5.5 months. Mean all-cause and HF hospitalisations were 3.6 and 2.0 per patient before enrolment, but improved to 1.0 and 0.6 respectively after ACP. Thirty-six (71%) patients had fewer HF hospitalisations. When only those who survived more than a year were considered (n = 14), 10 (71%) and 9 (64%) experienced reduced HF (mean: 1.4 episodes per patient) and all-cause hospitalisations (mean: 2.2 episodes per patient) respectively. Conclusion: Home-based advance care programme is potentially effective in reducing healthcare utilisation of end-stage HF patients, primarily by reducing HF rehospitalisations, and in probably saving costs as well. Key words: Palliative care, End-stage heart failure

Reproducibility of near-infrared spectroscopy parameters measured during brachial artery occlusion and reactive hyperemia in healthy men

Near-infrared spectroscopy (NIRS) is a noninvasive technique evaluating microvascular function. The aim of this study was to assess the reproducibility of NIRS parameters during reactive hyperemia induced by a 5 min brachial artery occlusion. Twenty-four healthy young males (mean 34 ± 8 years old) had two microvascular function evaluations by NIRS over a 7 to 30-day period (mean 16 ± 10 days). Intra-subject and inter-observer reproducibility were evaluated with intraclass correlation coefficient (ICC), coefficient of variation (CV), and standard error of measurement (SEM%) for every parameter. Mean NIRS parameters did not differ between both evaluations. Reproducibility was greatest for muscle oxygen consumption (ICC: 0.84; CV: 6.51%; SEM: 7.11%), time to basal O(2)Hb (ICC: 0.63, CV: 20.04%, SEM 27.22%), time to maximal O(2)Hb (ICC: 0.71; CV: 15.61%; SEM: 19.27%), peak of O(2)Hb (ICC: 0.63, CV: 6.68%, SEM 8.53%), time to maximal tHb (ICC: 0.73, CV: 19,61%, SEM 24.56%) and area under the O(2)Hb and tHb curves (ICC: 0.68, CV: 16.15%, SEM 22.93% and ICC: 0.62, CV: 18.59%, SEM 26.64%, respectively). Moreover, inter-observer reproducibility ranged from excellent to perfect (ICC from 0.85 to 1.00) for every parameter. NIRS parameters during reactive hyperemia are highly reproducible which enables their repeated measurement to study microvascular function in healthy subjects.

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.

Near infrared spectroscopy (NIRS) of the thenar eminence in anesthesia and intensive care

Near infrared spectroscopy of the thenar eminence (NIRS_th) is a noninvasive bedside method for assessing tissue oxygenation. The NIRS probe emits light with several wavelengths in the 700- to 850-nm interval and measures the reflected light mainly from a predefined depth. Complex physical models then allow the measurement of the relative concentrations of oxy and deoxyhemoglobin, and thus tissue saturation (StO₂), as well as an approximation of the tissue hemoglobin, given as tissue hemoglobin index.

Here we review of current knowledge of the application of NIRS_th in anesthesia and intensive care.

We performed an analytical and descriptive review of the literature using the terms “near-infrared spectroscopy” combined with “anesthesia,” “anesthesiology,” “intensive care,” “critical care,” “sepsis,” “bleeding,” “hemorrhage,” “surgery,” and “trauma” with particular focus on all NIRS studies involving measurement at the thenar eminence.

We found that NIRS_th has been applied as clinical research tool to perform both static and dynamic assessment of StO₂. Specifically, a vascular occlusion test (VOT) with a pressure cuff can be used to provide a dynamic assessment of the tissue oxygenation response to ischemia. StO₂ changes during such induced ischemia-reperfusion yield information on oxygen consumption and microvasculatory reactivity. Some evidence suggests that StO₂ during VOT can detect fluid responsiveness during surgery. In hypovolemic shock, StO₂ can help to predict outcome, but not in septic shock. In contrast, NIRS parameters during VOT increase the diagnostic and prognostic accuracy in both hypovolemic and septic shock. Minimal data are available on static or dynamic StO₂ used to guide therapy.

Although the available data are promising, further studies are necessary before NIRS_th can become part of routine clinical practice.

Skeletal muscle microcirculatory abnormalities are associated with exercise intolerance, ventilatory inefficiency, and impaired autonomic control in heart failure

BACKGROUND

Several skeletal muscle abnormalities have been identified in patients with chronic heart failure (CHF), including endothelial dysfunction. We hypothesized that skeletal muscle microcirculation, assessed by near-infrared spectroscopy (NIRS), is impaired in CHF patients and is associated with disease severity.

METHODS

Eighty-three stable patients with mild-moderate CHF (72 males, mean age 54 ± 14 years, body mass index 26.7 ± 3.4 kg/m(2)) and 8 healthy subjects, matched for age, gender and body mass index, underwent NIRS with the vascular occlusion technique and cardiopulmonary exercise testing (CPET) evaluation on the same day. Tissue oxygen saturation (StO(2), %), defined as the percentage of hemoglobin saturation in the microvasculature compartments, was measured in the thenar muscle by NIRS before, during and after 3-minute occlusion of the brachial artery. Measurements included StO(2), oxygen consumption rate (OCR, %/min) and reperfusion rate (RR, %/min). All subjects underwent a symptom-limited CPET on a cycle ergometer. Measurements included VO(2) at peak exercise (VO(2)peak, ml/kg/min) and anaerobic threshold (VO(2)AT, ml/kg/min), VE/VCO(2) slope, chronotropic reserve (CR, %) and heart rate recovery (HRR(1), bpm).

RESULTS

CHF patients had significantly lower StO(2) (75 ± 8.2 vs 80.3 ± 6, p < 0.05), lower OCR (32.3 ± 10.4 vs 37.7 ± 5.5, p < 0.05) and lower RR (10 ± 2.8 vs 15.7 ± 6.3, p < 0.05) compared with healthy controls. CHF patients with RR ≥9.5 had a significantly greater VO(2)peak (p < 0.001), VO(2)AT (p < 0.01), CR (p = 0.01) and HRR(1) (p = 0.01), and lower VE/VCO(2) slope (p = 0.001), compared to those with RR <9.5. In a multivariate analysis, RR was identified as an independent predictor of VO(2)peak, VE/VCO(2) slope and HRR(1).

CONCLUSIONS

Peripheral muscle microcirculation, as assessed by NIRS, is significantly impaired in CHF patients and is associated with disease severity.

Perioperative management of the pediatric cardiac transplantation patient

OPINION STATEMENT

The major diagnoses carried by children undergoing cardiac transplantation worldwide are congenital heart defects, cardiomyopathies, and retransplantation. The leading diagnosis in infancy is congenital heart disease, whereas cardiomyopathy predominates in older children. In view of this wide spectrum of diagnoses, the perioperative management of these children requires medical, interventional, and surgical expertise in treatment of complex congenital heart defects, end-stage heart failure, and cardiac transplantation. According to the Pediatric Heart Transplantation Survey database, the majority of children listed for cardiac transplantation eventually require higher levels of cardiac support before transplantation. The team caring for these children should be prepared to escalate support in a timely fashion in order to avoid end-organ dysfunction or a catastrophic event that will remove the patient from the cardiac transplantation list. The first step is advanced hemodynamic monitoring in a specialized pediatric cardiac intensive care unit and initiation of inotropic support. Further escalation of care should be based on careful analysis of the hemodynamic profile, end-organ function, and biochemical markers of perfusion and myocardial stress. A patient who continues to deteriorate in spite of inotropic support requires positive pressure ventilation, and if deterioration continues, mechanical circulatory support is initiated. Cardiac transplantation is a challenging operation, and even more so in children with complex congenital heart defects. The abnormal cardiovascular anatomy requires planning and anticipation of possible pitfalls as hypoplasia of the aortic arch, abnormal pulmonary arteries, and abnormal systemic and pulmonary venous connections. The time required to remove adhesions in children with prior cardiac operations increases the ischemic time of the graft and the risk of primary graft dysfunction. Assessment of pulmonary vascular resistance in children with congenital heart defects is problematic, and even children with a normal transpulmonary gradient and pulmonary vascular resistance are at increased risk of postoperative pulmonary hypertension and right ventricular graft failure. The postoperative course is directly linked to the patient's preoperative physical condition and perioperative course. The induction of immunosuppression and the use of plasmapheresis in children with a positive cross-match may lead to further hemodynamic compromise. If severe primary graft dysfunction evolves, early initiation of extracorporeal membranous oxygenator is indicated to avoid irreversible end-organ dysfunction.

Effects of levosimendan/furosemide infusion on plasma brain natriuretic peptide, echocardiographic parameters and cardiac output in end-stage heart failure patients

BACKGROUND

Acute decompensation heart failure (ADHF) remains a cause of hospitalization in patients with end-stage congestive HF. The administration of levosimendan in comparison with a standard therapy in CHF patients admitted for ADHF was analysed.

MATERIAL/METHODS

Consecutive patients admitted for ADHF (NYHA class III-IV) were treated with levosimendan infusion 0.1 µg/kg/min or with furosemide infusion 100-160 mg per day for 48 hours (control group). All subjects underwent determination of brain natriuretic peptide (BNP), non-invasive cardiac output (CO), and echocardiogram at baseline, at the end of therapy and 1 week after therapy.

RESULTS

Seven patients admitted for 20 treatments in 16 months (age 66 years; mean admission/year 5.4) were treated with levosimendan and compared with 7 patients admitted for 15 treatments (age 69.1 years; mean admission/year 6.1). At the end of levosimendan therapy, BNP decreased (from 679.7 ± 512.1 pg/ml to 554.2 ± 407.6 pg/ml p = 0.03), and 6 MWT and LVEF improved (from 217.6 ± 97.7 m to 372.2 ± 90.4 m p = 0.0001; from 22.8 ± 9.1% to 25.4 ± 9.8% p = 0.05). Deceleration time, E/A, E/E', TAPSE, pulmonary pressure and CO did not change significantly after levosimendan therapy and after 1 week. At follow-up, only 6-min WT and NYHA class showed a significant improvement (p = 0.0001, p = 0.001 respectively). The furosemide infusion reduced NYHA class and body weight (from 3.4 ± 0.6 to 2.3 ± 0.5 p = 0.001; from 77.5 ± 8.6 kg to 76 ± 6.6 kg p = 0.04), but impaired renal function (clearances from 56.3 ± 21.9 ml/min to 41.2 ± 10.1 ml/min p = 0.04).

CONCLUSIONS

Treating end-stage CHF patients with levosimendan improved BNP and LVEF, but this effect disappeared after 1 week. The amelioration of 6 MWT and NYHA class lasted longer after levosimendan infusion.

Near-infrared spectroscopy during stagnant ischemia estimates central venous oxygen saturation and mixed venous oxygen saturation discrepancy in patients with severe left heart failure and additional sepsis/septic shock

Introduction

Discrepancies of 5-24% between superior vena cava oxygen saturation (ScvO₂) and mixed venous oxygen saturation (SvO₂) have been reported in patients with severe heart failure. Thenar muscle tissue oxygenation (StO₂) measured with near-infrared spectroscopy (NIRS) during arterial occlusion testing decreases slower in sepsis/septic shock patients (lower StO₂ deoxygenation rate). The StO₂ deoxygenation rate is influenced by dobutamine. The aim of this study was to determine the relationship between the StO₂ deoxygenation rate and the ScvO₂-SvO₂ discrepancy in patients with severe left heart failure and additional sepsis/septic shock treated with or without dobutamine.

Methods

Fifty-two patients with severe left heart failure due to primary heart disease with additional severe sepsis/septic shock were included. SvO₂ and ScvO₂ were compared to the thenar muscle StO₂ before and during arterial occlusion.

Results

SvO₂ correlated significantly with ScvO₂ (Pearson correlation 0.659, P = 0.001), however, Bland Altman analysis showed a clinically important difference between both variables (ScvO₂-SvO₂ mean 72 ± 8%, ScvO₂-SvO₂ difference 9.4 ± 7.5%). The ScvO₂-SvO₂ difference correlated with plasma lactate (Pearson correlation 0.400, P = 0.003) and the StO₂ deoxygenation rate (Pearson correlation 0.651, P = 0.001). In the group of patients treated with dobutamine, the ScvO₂-SvO₂ difference correlated with plasma lactate (Pearson correlation 0.389, P = 0.011) and the StO₂ deoxygenation rate (Pearson correlation 0.777, P = 0.0001).

Conclusions

In patients with severe heart failure with additional severe sepsis/septic shock the ScvO₂-SvO₂ discrepancy presents a clinical problem. In these patients the skeletal muscle StO₂ deoxygenation rate is inversely proportional to the difference between ScvO₂ and SvO₂; dobutamine does not influence this relationship. When using ScvO₂ as a treatment goal, the NIRS measurement may prove to be a useful non-invasive diagnostic test to uncover patients with a normal ScvO₂ but potentially an abnormally low SvO₂.

Trial Registration

NCT00384644 ClinicalTrials.Gov.

Assessment of tissue oxygen saturation during a vascular occlusion test using near-infrared spectroscopy: the role of probe spacing and measurement site studied in healthy volunteers

Introduction

To assess potential metabolic and microcirculatory alterations in critically ill patients, near-infrared spectroscopy (NIRS) has been used, in combination with a vascular occlusion test (VOT), for the non-invasive measurement of tissue oxygen saturation (StO₂), oxygen consumption, and microvascular reperfusion and reactivity. The methodologies for assessing StO₂ during a VOT, however, are very inconsistent in the literature and, consequently, results vary from study to study, making data comparison difficult and potentially inadequate. Two major aspects concerning the inconsistent methodology are measurement site and probe spacing. To address these issues, we investigated the effects of probe spacing and measurement site using 15 mm and 25 mm probe spacings on the thenar and the forearm in healthy volunteers and quantified baseline, ischemic, reperfusion, and hyperemic VOT-derived StO₂ variables.

Methods

StO₂ was non-invasively measured in the forearm and thenar in eight healthy volunteers during 3-minute VOTs using two InSpectra tissue spectrometers equipped with a 15 mm probe or a 25 mm probe. VOT-derived StO₂ traces were analyzed for base-line, ischemic, reperfusion, and hyperemic parameters. Data were categorized into four groups: 15 mm probe on the forearm (F_{15 mm}), 25 mm probe on the forearm (F_{25 mm}), 15 mm probe on the thenar (T_{15 mm}), and 25 mm probe on the thenar (T_{25 mm}).

Results

Although not apparent at baseline, probe spacing and measurement site significantly influenced VOT-derived StO₂ variables. For F_{15 mm}, F_{25 mm}, T_{15 mm}, and T_{25 mm}, StO₂ ownslope was -6.4 ± 1.7%/minute, -10.0 ± 3.2%/minute, -12.5 ± 3.0%/minute, and -36.7 ± 4.6%/minute, respectively. StO₂ upslope was 105 ± 34%/minute, 158 ± 55%/minute, 226 ± 41%/minute, and 713 ± 101%/minute, and the area under the hyperemic curve was 7.4 ± 3.8%·minute, 10.1 ± 4.9%·minute, 12.6 ± 4.4%·minute, and 21.2 ± 2.7%·minute in these groups, respectively. Furthermore, the StO₂ parameters of the hyperemic phase of the VOT, such as the area under the curve, significantly correlated to the minimum StO₂ during ischemia.

Conclusions

NIRS measurements in combination with a VOT are measurement site-dependent and probe-dependent. Whether this dependence is anatomy-, physiology-, or perhaps technology-related remains to be elucidated. Our study also indicated that reactive hyperemia depends on the extent of ischemic insult.

Physical exercise improves the peripheral microcirculation of patients with chronic heart failure

PURPOSE

Patients with chronic heart failure (CHF) present with microcirculation alterations, partially attributed to endothelial dysfunction. Exercise training has been shown to induce beneficial effects in CHF patients. The aim of our study was to assess the effect of physical exercise on the microcirculation of CHF patients by near-infrared spectroscopy (NIRS).

METHODS

Sixteen consecutive stable CHF patients (men, n = 10; mean age = 50 +/- 12 years) participated in a 3-month rehabilitation program (3 sessions per week). All patients performed symptom-limited, ramp-incremental cardiopulmonary exercise testing on a cycle ergometer before and after the completion of the program. Measurements included peak oxygen uptake (VO2peak), VO2 at anaerobic threshold (AT), and first-degree slope of VO2 during the first minute of recovery (VO2/t slope). Tissue oxygen saturation was continuously measured by NIRS at the thenar muscle during a 3-minute vascular occlusion with a pneumatic cuff (occlusion technique) before and after the rehabilitation program.

RESULTS

The oxygen reperfusion rate (%/min) following the release of vascular occlusion increased significantly after the rehabilitation program (450 +/- 105 to 532 +/- 151, P = .004) as did vascular reactivity (from 27 +/- 13%/min to 39 +/- 21%/min, P = .006). In addition, there was a significant increase in VO2peak and AT (from 14.3 +/- 4.7 mL . kg . min to 16.7 +/- 6.3 mL . kg . min and from 9.5 +/- 3.6 mL . kg . min to 11.3 +/- 4 mL . kg . min, P = .007 and P = .012, respectively) as well as in VO2/t slope (from 0.35 +/- 0.17 to 0.51 +/- 0.07 mL . kg . min, P = .005).

CONCLUSIONS

Peripheral microcirculation of CHF patients measured by NIRS improved after the rehabilitation program. NIRS is a noninvasive technique that could be used to evaluate the effect of rehabilitation on the peripheral microcirculation of CHF patients.

Short-term systemic effect of electrical muscle stimulation in critically ill patients

BACKGROUND

Our study assessed the short-term effect of electrical muscle stimulation (EMS) of the lower extremities on the thenar muscle microcirculation of patients who are critically ill.

METHODS

Twenty-nine hospital ICU patients (19 men; mean [+/- SD] age, 58 +/- 19 years; mean acute physiology and chronic health evaluation score, 17 +/- 5; mean sequential organ failure assessment score, 9 +/- 3) underwent a 45-min session of EMS of the lower extremities. BP and heart rate were measured, and blood samples were retrieved. Tissue oxygen saturation (Sto(2)) was assessed with near infrared spectroscopy at the thenar muscle with a vascular occlusion before and after EMS. A control group of six patients who were critically ill (4 men; mean age, 50 +/- 19 years) also were included in the study.

RESULTS

The mean Sto(2) did not differ significantly before and after the EMS session (81 +/- 16% vs 83 +/- 16%, respectively). The oxygen consumption rate during vascular occlusion differed significantly before the beginning and at the end of the session (20 +/- 9%/min vs 22 +/- 9%/min, respectively; p < 0.05). The reperfusion rate differed significantly before the beginning and at the end of the session (299 +/- 177%/min vs 375 +/- 182%/min, respectively; p < 0.05). Heart rate increased significantly at the end of the session (94 +/- 16 beats/min vs 99 +/- 16 beats/min, respectively; p < 0.05) as did systolic BP (127 +/- 21 mm Hg vs 133 +/- 23 mm Hg; p < 0.05, respectively). The Sto(2) value did not differ between the two measurements in control patients.

CONCLUSION

The data suggest that EMS has a systemic effect on microcirculation. These results suggest that further studies are needed to explore the potential use of EMS as a preventive and rehabilitation tool in critically ill patients.