Multi-omics in nasal epithelium reveals three axes of dysregulation for asthma risk in the African Diaspora populations.

Asthma has striking disparities across ancestral groups, but the molecular underpinning of these differences is poorly understood and minimally studied. A goal of the Consortium on Asthma among African-ancestry Populations in the Americas (CAAPA) is to understand multi-omic signatures of asthma focusing on populations of African ancestry. RNASeq and DNA methylation data are generated from nasal epithelium including cases (current asthma, N = 253) and controls (never-asthma, N = 283) from 7 different geographic sites to identify differentially expressed genes (DEGs) and gene networks. We identify 389 DEGs; the top DEG, FN1, was downregulated in cases (q = 3.26 × 10-9) and encodes fibronectin which plays a role in wound healing. The top three gene expression modules implicate networks related to immune response (CEACAM5; p = 9.62 × 10-16 and CPA3; p = 2.39 × 10-14) and wound healing (FN1; p = 7.63 × 10-9). Multi-omic analysis identifies FKBP5, a co-chaperone of glucocorticoid receptor signaling known to be involved in drug response in asthma, where the association between nasal epithelium gene expression is likely regulated by methylation and is associated with increased use of inhaled corticosteroids. This work reveals molecular dysregulation on three axes - increased Th2 inflammation, decreased capacity for wound healing, and impaired drug response - that may play a critical role in asthma within the African Diaspora.

Shifting the HIV Paradigm from Care to Cure: Proceedings from the Caribbean Expert Summit in Barbados, August 2017.

The CCAS EXPERT SUMMIT convened an array of international experts in Barbados on August 27-31, 2017 under the theme "From Care to Cure-Shifting the HIV Paradigm." The Caribbean Cytometry & Analytical Society (CCAS) partnered with the Joint United Nations Programme on HIV/AIDS (UNAIDS) to deliver a program that reviewed the advances in antiretroviral therapy and the public health benefits accruing from treatment as prevention. Particular emphasis was placed on reexamining stigma and discrimination through a critical appraisal of whether public health messaging and advocacy had kept pace with the advances in medicine. Persistent fear of HIV driving discriminatory behavior was widely reported in different regions and sectors, including the healthcare profession itself; continued fear of the disease was starkly misaligned with the successes of new medical treatments and progress toward the UNAIDS 90-90-90 targets. The summit therefore adopted the mantra "Test-Treat-Defeat" to help engage with the public in a spirit of optimism aimed at creating a more conducive environment for persons to be tested and treated and, thereby, help reduce HIV disease and stigma at the individual and community levels.

Sacrificial Crystal Templated Hyaluronic Acid Hydrogels As Biomimetic 3D Tissue Scaffolds for Nerve Tissue Regeneration.

Pores are key features of natural tissues and the development of tissues scaffolds with biomimetic properties (pore structures and chemical/mechanical properties) offers a route to engineer implantable biomaterials for specific niches in the body. Here we report the use of sacrificial crystals (potassium dihydrogen phosphate or urea) that act as templates to impart pores to hyaluronic acid-based hydrogels. The mechanical properties of the hydrogels were analogous to the nervous system (in the Pascal regime), and we investigated the use of the potassium dihydrogen phosphate crystal-templated hydrogels as scaffolds for neural progenitor cells (NPCs), and the use of urea crystal-templated hydrogels as scaffolds for Schwann cells. For NPCs cultured inside the porous hydrogels, assays for the expression of Nestin are inconclusive, and assays for GFAP and BIII-tubulin expression suggest that the NPCs maintain their undifferentiated phenotype more effectively than the controls (with glial fibrillary acidic protein (GFAP) and BIII-tubulin expression at ca. 50% relative to the chemically/mechanically equivalent not templated control hydrogels). For Schwann cells cultured within these hydrogels, assays for the expression of S100 protein or Myelin basic protein confirm the expression of both proteins, albeit at lower levels on the templated hydrogels (ca. 50%) than on the chemically/mechanically equivalent not templated control hydrogels. Such sacrificial crystal templated hydrogels represent platforms for biomimetic 3D tissue scaffolds for the nervous system.

20 Years On: Is It Time to Redefine the Systemic Inflammatory Response to Cardiothoracic Surgery?

The "systemic inflammatory response" has never been defined from a cardiothoracic surgery perspective, but borrowed its definition from the critical care field at a landmark 1992 definition conference on sepsis. It is unclear why the diagnostic criteria for the Systemic Inflammatory Response Syndrome (SIRS) were adopted in isolation, ignoring other potentially more useful definitions for Severe Septic Shock or Secondary Multiple Organ Dysfunction Syndrome. The 1992 SIRS definition for sepsis has since been updated at a conference in 2001 advocating PIRO (Predisposition, Infection, host Response, Organ dysfunction) as a hypothetical model to better link sepsis with clinical outcome. PIRO is readily adaptable to cardiothoracic surgery and provides the precedent and road map for how to update a definition. The need is obvious since the current definition of SIRS is widely disregarded in heart surgery: a dwindling proportion (14%) of articles on the systemic inflammatory response even mention SIRS and 0% monitored SIRS criteria in the past decade in an evidence-based review of anti-inflammatory interventions. The name "inflammatory response" is also problematic; it is too narrow and might be replaced with host response (the R in PIRO) to better convey the wide spectrum of host defensive pathways activated during heart surgery (i.e., complement, coagulation, fibrinolysis, kinins, cytokines, proteases, hemolysis, oxidative stiess). A variant on PIRO could allow these elements of the host Response (R) to be anchored within the context of Premorbid conditions (P) and the inevitable Insult (I) from surgery, to better link risk exposures to Organ dysfunction (O) in heart surgery. The precedent of PIRO suggests the following steps will be required to redefine the systemic inflammatory response: 1) buy-in from the leading societies for cardiothoracic surgery, anesthesia, and perfusion on the need for a re-definition conference, 2) assigning relative risk scores to different premorbid exposures, operative insults, and host response factors on clinical outcome, 3) validation of the risk model in a prospective cohort, and 4) development of algorithms or "apps" to facilitate rapid diagnosis and staging of care at bedside.

Intravenous infusion of haptoglobin for the prevention of adverse clinical outcome in Sickle Cell Disease.

Sickle Cell Disease (SCD) is a genetic condition which manifests as altered hemoglobin (Hb) protein that can aggregate under hypoxic conditions. The resultant sickled erythrocytes experience premature hemolysis, releasing an estimated 10g of free Hb (fHb) into the intravascular space. FHb participates in redox reactions creating various reactive oxygen species which rapidly and irreversibly scavenge nitric oxide, thereby attenuating its vasodilatory, antithrombotic, and anti-inflammatory properties. FHb also induces endothelial expression of adhesion molecules, triggering leukocyte margination at the vessel wall. These mechanisms participate in diverse SCD-associated clinical events including nephropathy, pulmonary hypertension, chronic leg ulceration, and ischemic events. FHb also exerts a direct reno-toxic effect contributing to albuminuria which is an early, frequent manifestation of glomerular injury. Under normal conditions, fHb is effectively scavenged by the Hb-scavenging mechanism (HSM); this involves binding to haptoglobin (Hp), uptake via the Hb-scavenging receptor (CD163) on monocytes and metabolism by heme-oxygenase-1. This culminates in increased CD163 expression and release of anti-inflammatory by-products e.g. interleukin-10 (IL-10). In SCD, the Hb-binding capacity is overwhelmed by chronic hemolysis; our previous research shows serum Hp as the depleted component. This deficiency could result in the harmful consequences of circulating fHb going unbridled. The hypothesis we explore here is that Hp infusions, in excess of fHb concentration, will allow the HSM to remain functional, and thereby achieve improved clinical outcomes, tracking albuminuria as a sentinel. Albuminuria was selected because of its high prevalence in SCD and its relative ease of diagnosis and monitoring. The hypothesis may be evaluated in four phases: Phase 1 will determine the concentration of Hp needed to trigger the HSM as measured by induction of CD163 and IL-10 and the recovery of hemopexin. Phase 2 will investigate the half-life of HSM induction by analyzing the time-course of CD163 expression and IL-10 and hemopexin serum concentration. Phase 3 will determine patient eligibility for therapy, whether as treatment or prevention. Phase 4 will test the efficacy of Hp transfusions in a randomized control trial as measured by correction of albuminuria. Angiotensin converting enzyme inhibitors (ACEi) are currently the first-line treatment for SCD nephropathy, however hyperkalemia limits its use. Hydroxyurea, which has therapeutic value in many SCD adverse events, has yielded inconsistent effects on albuminuria. We are proposing the addition of an intervention more proximal in the hemolytic cascade. Boosting the exhausted Hb-scavenging capacity via Hp replacement therapy has the potential to modify multiple downstream clinical events.

HIV Viral Load Trends in Six Eastern Caribbean Countries Utilizing a Regional Laboratory Referral Service: Implications for Treatment as Prevention.

OBJECTIVE: Since 2009, seven countries in the Organization of Eastern Caribbean States (OECS), Antigua & Barbuda, Dominica, Grenada, Montserrat, St. Kitts & Nevis, Saint Lucia, and St. Vincent & the Grenadines, have been utilizing a laboratory referral service for HIV-1 viral load (VL) offered by The Ladymeade Reference Unit (LRU) Laboratory, Barbados. The objective of this study was to evaluate 5 year VL trends in the six larger OECS countries participating in this regional referral service. METHODS: Blood samples were collected in source countries and transported to Barbados as frozen plasma according to a standardized protocol. Plasma specimens were amplified by RT PCR on a Roche TaqMan 48 analyser (Roche Diagnostics, Panama City, Panama). VL was considered optimally suppressed below a threshold level of < 200 HIV-1 copies/mL of blood. The same threshold was used as a binary indicator in an analysis of the secular change in VL suppression. Montserrat was excluded due to insufficient number of samples. RESULTS: A steady rise in VL referrals from OECS countries was recorded, rising from 312 samples in 2009 to 1,060 samples in 2013. A total of 3,543 samples were tested, with a sample rejection rate (9.2%) mostly due to breaks in the cold chain. Aggregate VL data showed the odds of VL suppression in the Eastern Caribbean improved by 66% for each additional year after 2009 (Odds Ratio 1.66 [95% CI 1.46 to 1.88]; p<0.001). CONCLUSION: We demonstrate the feasibility of establishing a regional laboratory referral service for HIV VL monitoring in the Eastern Caribbean. Aggregate VL trends showed a significant year-on-year improvement in VL suppression, implying public health benefits through treatment as prevention in the OECS. VL provides a powerful monitoring & evaluation tool for strengthening HIV programs at country level among the small island states participating in this regional referral network.

Clinical findings associated with homozygous sickle cell disease in the Barbadian population--do we need a national SCD registry?

BACKGROUND: Comprehensive care in homozygous sickle cell disease (HbSS) entails universal neonatal screening and subsequent monitoring of identified patients, a process which has been streamlined in the neighbouring island of Jamaica. In preparation for a similar undertaking in Barbados, we have developed a database of persons with known HbSS, and have piloted processes for documenting clinical manifestations. We now present a brief clinical profile of these findings with comparisons to the Jamaican cohort. METHODS: HbSS participants were recruited from clinics and support groups. A history of select clinical symptoms was taken and blood and urine samples and echocardiograms were analysed. A re-analysis of data from a previous birth cohort was completed. RESULTS: Forty-eight persons participated (32 F/16 M); age range 10-62 yrs. 94% had a history of ever having a painful crisis. In the past year, 44% of participants had at least one crisis. There were >69 crises in 21 individuals; 61% were self-managed at home and the majority of the others were treated and discharged from hospital; few were admitted. The prevalence of chronic leg ulceration was 27%. Forty-two persons had urinalysis, 44% were diagnosed with albuminuria (urinary protein/creatinine ratio ≥30 mg/g). Thirty-two participants had echocardiography, 28% had a TRJV ≥ 2.5 m/s. Re-analysis of the incidence study revealed a sickle gene frequency (95% CI) of 2.01% (0.24 to 7.21). CONCLUSION: Although we share a common ancestry, it is thought that HbSS is less common and less severe in Barbados compared to Jamaica. The Jamaican studies reported a sickle gene frequency of 3.15 (2.81 to 3.52); the prevalence of chronic leg ulcers and albuminuria was 29.5% and 42.5% respectively. These comparisons suggest that our initial thoughts may be speculative and that HbSS may be an underestimated clinical problem in Barbados. A prospective neonatal screening programme combined with centralized, routine monitoring of HbSS morbidity and outcomes will definitively answer this question and will improve the evidence-based care and management of HbSS in Barbados.

Attenuating the Systemic Inflammatory Response to Adult Cardiopulmonary Bypass: A Critical Review of the Evidence Base.

A wide range of pharmacological, surgical, and mechanical pump approaches have been studied to attenuate the systemic inflammatory response to cardiopulmonary bypass, yet no systematically based review exists to cover the scope of anti-inflammatory interventions deployed. We therefore conducted an evidence-based review to capture "self-identified" anti-inflammatory interventions among adult cardiopulmonary bypass procedures. To be included, trials had to measure at least one inflammatory mediator and one clinical outcome, specified in the "Outcomes 2010" consensus statement. Ninety-eight papers satisfied inclusion criteria and formed the basis of the review. The review identified 33 different interventions and approaches to attenuate the systemic inflammatory response. However, only a minority of papers (35 of 98 [35.7%]) demonstrated any clinical improvement to one or more of the predefined outcome measures (most frequently myocardial protection or length of intensive care unit stay). No single intervention was supported by strong level A evidence (multiple randomized controlled trials [RCTs] or meta-analysis) for clinical benefit. Interventions at level A evidence included off-pump surgery, minimized circuits, biocompatible circuit coatings, leukocyte filtration, complement C5 inhibition, preoperative aspirin, and corticosteroid prophylaxis. Interventions at level B evidence (single RCT) for minimizing inflammation included nitric oxide donors, C1 esterase inhibition, neutrophil elastase inhibition, propofol, propionyl-L-carnitine, and intensive insulin therapy. A secondary analysis revealed that suppression of at least one inflammatory marker was necessary but not sufficient to confer clinical benefit. The most effective interventions were those that targeted multiple inflammatory pathways. These observations are consistent with a "multiple hit" hypothesis, whereby clinically effective suppression of the systemic inflammatory response requires hitting multiple inflammatory targets simultaneously. Further research is warranted to evaluate if combinations of interventions that target multiple inflammatory pathways are capable of synergistically reducing inflammation and improving outcomes after cardiopulmonary bypass.

Prevalence and risk factors for inter-generational sex: a cross-sectional cluster survey of Barbadian females aged 15-19.

BACKGROUND: The aim of this study was to establish the prevalence and risk factors for intergenerational (IG)-sex in females aged 15-19 residing in Barbados. METHODS: This cross sectional cluster survey was conducted in a 2.6% national sample in the age range (n = 261) recruited from multiple polling districts chosen with a probability proportional to size. Consent was obtained from participants aged ≥18 years or from parents/guardians of participants <18 years, with participant assent. The prevalence of age at first sex was analyzed using a life table approach and risk factors for IG sex (defined as sexual relations with a male 10 or more years older) were analyzed by logistic regression, adjusting for age. RESULTS: 51.0% of adolescent females in the survey reported ever having had sex, among whom prevalence of IG-sex was 13.2% (95% CI: 6.7-19.8) at first sex, 29.0% (22.3-35.7) within the preceding twelve months, and 34.8% (24.3-45.4) ever. Condom use at first sex was positively related to willingness to have sex (F statistic = 9.8, p = 0.001). The strongest determinant for IG-sex was age of sexual debut (age adjusted Odds Ratio [95% CI]: 0.58[0.41-0.83]), followed by money or gifts received from the partner (2.91[1.17-7.23] and self-esteem (0.33[0.11-0.95]). CONCLUSIONS: The survey establishes a high rate of IG-sex in Barbados, a 'high income' country. Most insightful is that risk of IG-sex nearly halved for every year at which first sex was delayed. A high proportion of coerced sex was reported at first sexual experience and this was linked to poor condom use. Affirmative prevention approaches are recommended to boost self-acclamation of adolescent women within less coercive relationships, especially during their first sexual encounter.

Comparison of the systemic lupus erythematosus activity questionnaire and the systemic lupus erythematosus disease activity index in a black barbadian population.

In Barbados, use of the Systemic Lupus Erythematosus (SLE) Disease Activity Index (SLEDAI) is limited by the unavailability of serologic markers. The SLE Activity Questionnaire (SLAQ) excludes laboratory measurements and is therefore more accessible. Here, we investigate the agreement between the SLAQ, the SLEDAI, and the physician global assessment (PGA). A pilot of 32 participants completed the SLAQ and SLEDAI. The tools were compared (1) in their original format, (2) limited to common indices, and (3) limited to the same patient recall period. We compared the proportions of persons reporting disease activity and the concordance between calculated activity scores for SLAQ versus SLEDAI and for SLAQ versus PGA. Seventy-eight percent versus 59% of participants reported disease activity with the original SLEDAI versus SLAQ, respectively. The relationship was reversed to 22% versus 59% when the matched item tools were compared. Concordance was 0.62 (95% CI 0.42-0.81) between the original scores, 0.70 (0.57-0.83) when restricted by matched items, and 0.72 (0.59-0.84) when further restricted by recall period. Concordance between the SLAQ and PGA was 0.56 (0.32-0.80). Reversal of the disease activity percentage in the matched items comparison highlights the inadequacy of tools that exclude laboratory measurements and suggests that the subjective nature of SLAQ may contribute to over-reporting. Further work is needed to produce a robust disease activity tool apt for resource-constrained environments.

Preoperative white blood cell count and risk of 30-day readmission after cardiac surgery.

Approximately 1 in 5 patients undergoing cardiac surgery are readmitted within 30 days of discharge. Among the primary causes of readmission are infection and disease states susceptible to the inflammatory cascade, such as diabetes, chronic obstructive pulmonary disease, and gastrointestinal complications. Currently, it is not known if a patient's baseline inflammatory state measured by crude white blood cell (WBC) counts could predict 30-day readmission. We collected data from 2,176 consecutive patients who underwent cardiac surgery at seven hospitals. Patient readmission data was abstracted from each hospital. The independent association with preoperative WBC count was determined using logistic regression. There were 259 patients readmitted within 30 days, with a median time of readmission of 9 days (IQR 4-16). Patients with elevated WBC count at baseline (10,000-12,000 and >12,000 mm(3)) had higher 30-day readmission than those with lower levels of WBC count prior to surgery (15% and 18% compared to 10%-12%, P = 0.037). Adjusted odds ratios were 1.42 (0.86, 2.34) for WBC counts 10,000-12,000 and 1.81 (1.03, 3.17) for WBC count > 12,000. We conclude that WBC count measured prior to cardiac surgery as a measure of the patient's inflammatory state could aid clinicians and continuity of care management teams in identifying patients at heightened risk of 30-day readmission after discharge from cardiac surgery.

Evolution of the Macrophage CD163 Phenotype and Cytokine Profiles in a Human Model of Resolving Inflammation.

Cantharidin skin blisters were examined over two days to model the acute and resolving phases of inflammation in human skin. Four blisters were created by topical administration of cantharidin (0.1% v/v) to the forearm of healthy volunteers, with IRB approval. Duplicate skin blisters were aspirated at 16 and 40 hours to model the proinflammatory and resolving phases, respectively. There was a significant increase in leukocyte infiltrate at 40 h with appearance of a "resolving macrophage" phenotype CD14(+)CD163(+) by flow cytometry. Neutrophils acquired apoptotic markers at 40 h and were observed to be phagocytosed by macrophagic "Reiter's" cells. Multiplex cytokine analysis demonstrated that monocyte chemoattractant protein (MCP-1/CCL2), interleukin- (IL-) 6, IL-8/CXCL8, macrophage inflammatory protein (MIP1 α /CCL3), MIP-1 ß /CCL4, tumor necrosis factor- (TNF-) α , and eotaxin (CCL11) were all significantly upregulated at 16 h compared with 40 h. In contrast, immunoregulatory transforming growth factor- (TGF-) ß , macrophage-derived chemokine (MDC/CCL22), and interferon-inducible protein (IP-10/CXCL10) were significantly elevated at 40 h. Our results demonstrate that the phases of inflammation and resolution can be discriminated in a two-day model of dermal wound healing. This confirms and extends our understanding of wound repair in humans and provides a powerful research tool for use in clinical settings and to track the molecular benefits of therapeutic intervention.

Haptoglobin Genotype-Dependent Anti-Inflammatory Signaling in CD163(+) Macrophages.

Intraplaque hemorrhage causes adaptive remodelling of macrophages towards a protective phenotype specialized towards handling iron and lipid overload, denoted Mhem. The Mhem phenotype expresses elevated levels of hemoglobin (Hb) scavenger receptor, CD163, capable of endocytosing pro-oxidant free Hb complexed to acute phase protein haptoglobin (Hp). It is notable that individuals homozygous for the Hp 2 allele (a poorer antioxidant) are at increased risk of cardiovascular disease compared to the Hp 1 allele. In this study, we examined whether scavenging of polymorphic Hp:Hb complexes differentially generated downstream anti-inflammatory signals in cultured human macrophages culminating in interleukin (IL)-10 secretion. We describe an anti-inflammatory signalling pathway involving phosphatidylinositol-3-kinase activation upstream of Akt phosphorylation (pSer473Akt) and IL-10 secretion. The pathway is mediated specifically through CD163 and is blocked by anti-CD163 antibody or phagocytosis inhibitor. However, levels of pSer473Akt and IL-10 were significantly diminished when scavenging polymorphic Hp2-2:Hb complexes compared to Hp1-1:Hb complexes (P < 0.05). Impaired anti-inflammatory macrophage signaling through a CD163/pAkt/IL-10 axis may thus represent a possible Hp2-2 disease mechanism in atherosclerosis.

Ten year trends in community HIV viral load in Barbados: implications for treatment as prevention.

BACKGROUND: Treatment as prevention is a paradigm in HIV medicine which describes the public health benefit of antiretroviral therapy (ART). It is based on research showing substantial reductions in the risk of HIV transmission in persons with optimally suppressed HIV-1 Viral Loads (VL). The present study describes ten year VL trends at the national HIV treatment unit and estimates VL suppression at a population level in Barbados, a Caribbean island with a population of 277,000, an estimated adult HIV prevalence of 1.2%, and served by a single treatment unit. METHODS: The national HIV treatment centre of the Barbados Ministry of Health has a client VL database extending back to inception of the clinic in 2002 (n = 1,462 clients, n = 17,067 VL measurements). Optimal VL suppression was defined at a threshold value of ≤200 viral copies/mL. RESULTS: Analysis of VL trends showed a statistically significant improvement in VL suppression between 2002 to 2011, from 33.6% of clients achieving the 200 copies/mL threshold in 2002 to 70.3% in 2011 (P<0.001). Taking into account the proportion of clients alive and in care and on ART, the known diagnosed HIV population in Barbados, and estimates of unknown HIV infections, this translates into an estimated 26.2% VL suppression at a population level at the end of 2010. CONCLUSIONS: We have demonstrated a significant trend towards optimal VL suppression in clients utilizing the services of the national HIV treatment program in Barbados over a 10-year period. Estimates of VL suppression at a population level are similar to reports in developed countries that applied similar methodologies and this could suggest a public health benefit of ART in minimizing the risk of sexual transmission of HIV. Continued efforts are warranted to extend HIV testing to hidden populations in Barbados and linking infected persons to care earlier in their disease.

Plasmin Activation of Glial Cells through Protease-Activated Receptor 1.

The objective of this study was to determine whether plasmin could induce morphological changes in human glial cells via PAR1. Human glioblastoma A172 cells were cultured in the presence of plasmin or the PAR1 specific activating hexapeptide, SFLLRN. Cells were monitored by flow cytometry to detect proteolytic activation of PAR1 receptor. Morphological changes were recorded by photomicroscopy and apoptosis was measured by annexinV staining. Plasmin cleaved the PAR1 receptor on glial cells at 5 minutes (P = 0.02). After 30 minutes, cellular processes had begun to retract from the basal substratum and by 4 hours glial cells had become detached. Similar results were obtained by generating plasmin de novo from plasminogen. Morphological transformation was blocked by plasmin inhibitors aprotinin or epsilon-aminocaproic acid (P = 0.03). Cell viability was unimpaired during early morphological changes, but by 24 hours following plasmin treatment 22% of glial cells were apoptotic. PAR1 activating peptide SFLLRN (but not inactive isomer FSLLRN) promoted analogous glial cell detachment (P = 0.03), proving the role for PAR1 in this process. This study has identified a plasmin/PAR1 axis of glial cell activation, linked to changes in glial cell morophology. This adds to our understanding of pathophysiological disease mechanisms of plasmin and the plasminogen system in neuroinjury.

Skin SO2 measurement using visible lightguide spectrophotometry in a black population: a feasibility study.

The aim of the study was to investigate the influence of melanin content on the visible wavelength range spectrophotometric measurement of SO(2) in the skin of normal healthy black and white volunteers. The reactive hyperaemia induced by a 5-minute period of tourniquet occlusion of the brachial artery, as manifested in the change in skin SO(2), was compared with the reactive hyperaemia index (RHI) and arterial stiffness index (AI) as measured using the Endo-PAT2000® peripheral arterial tonometry device. Further measurements were carried out on a diabetic patient with critical ischaemia. The measurements in the normal volunteers and the patient showed that there that there was no correlation between SO(2) and melanin index (r(2) = 0.02). There was a poor correlation between the degree of reactive hyperaemia as assessed using tissue SO(2) measurement and the parameters derived using the Endo-PAT2000® device. Measurements on the critically ischaemic lower limb of the diabetic patient revealed a mean medial/lateral SO(2) of 26.3% and a degree of tissue hypoxia (the percentage of recordings with an SO(2) of 15% or less) of 16.2%. This pilot study demonstrated that the measurement of tissue SO(2) in the skin of black subjects is feasible, not only under conditions of normal perfusion, but also in critical limb ischaemia.