Racial Equity in Family Approach for Patients Medically Suitable for Deceased Organ Donation.

OBJECTIVES: To conduct a contemporary analysis of the association between family approach of medically suitable potential organ donors and race/ethnicity. DESIGN: Retrospective review of data collected prospectively by Organ Procurement Organizations (OPOs). SETTING: Ten OPOs representing eight regions of the Organ Procurement and Transplantation Network and 26% of all deceased donor organs recovered in the United States. SUBJECTS: All hospitalized patients on mechanical ventilation and referred to OPOs as potential donors from January 1, 2018, to December 31, 2022. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: OPOs provided data on referral year, race, sex, donor registration status, screening determination, donation medical suitability, donation type (brain death, circulatory death), and family approach. We evaluated factors associated with family approach to discuss donation using descriptive statistics and multivariable logistic models. Of 255,429 total cases, 138,622 (54%) were screened-in for further evaluation, with variation by race/ethnicity (50% White, 60% Black, 69% Hispanic, and 60% Asian). Among those screened-in, 31,253 (23%) were medically suitable for donation, with modest variation by race/ethnicity (22% White, 26% Black, 23% Hispanic, and 21% Asian). Family approach rate by OPOs of medically suitable cases was 94% ( n = 29,315), which did not vary by race/ethnicity (94% White, 93% Black, 95% Hispanic, and 95% Asian). Family approach by OPOs was lower for circulatory death (95%) vs. brain death (97%) cases but showed minimal differences in approach rate based on race/ethnicity between medically suitable patients with different death pathways. In contrast, donor registration status of medically suitable potential donors was highly variable by race/ethnicity (37% overall; 45% White, 21% Black, 29% Hispanic, and 25% Asian). Multivariable models indicated no significant difference of family approach between White and Black (odds ratio [OR], 1.09; 95% CI, 0.95-1.24) or Asian (OR, 1.23; 95% CI, 0.95-1.60) patients. CONCLUSIONS: Findings indicate racial equity in OPO family approach rates among patients who were medically suitable for organ donation.

Effect of mesenchymal stem cells on the host response in severe community-acquired pneumonia.

Mesenchymal stem cells (MSC) have immune regulatory properties that may ameliorate pathophysiological processes in sepsis. We determined the effect of allogeneic adipose-derived MSCs (Cx611) on the host response during sepsis due to community-acquired bacterial pneumonia (CABP) by measuring 29 plasma biomarkers and blood transcriptomes at six time points in 82 patients randomised to two intravenous infusions of Cx611 or placebo. Cx611 treatment enhanced several endothelial cell and procoagulant response plasma biomarkers, and led to increased expression of pathways related to innate immunity, haemostasis and apoptosis. Cx611 infusion in sepsis due to CABP is associated with broad host response alterations.

Characterisation of molecular mechanisms for PLCγ2 disease-linked variants.

The phospholipase C enzyme PLCγ2 is best characterised in the context of immune cell regulation. Furthermore, many mutations discovered in PLCγ2 have been linked to the development of complex immune disorders as well as resistance to ibrutinib treatment in chronic lymphocytic leukaemia. Importantly, it has also been found that a rare variant of PLCγ2 (P522R) has a protective role in Alzheimer's disease (AD). Despite initial characterisation of these disease-linked variants, a comprehensive understanding of their differences and underpinning molecular mechanisms, needed to facilitate therapeutic efforts, is lacking. Here, we used available structural insights for PLCγ enzymes to further analyse PLCγ2 M1141K mutation, representative for mutations in immune disorders and cancer resistance, and the AD-protective variant, PLCγ2 P522R. Together with several other mutations in the autoinhibitory interface, the PLCγ2 M1141K mutation was strongly activating in a cell-based assay, under basal and stimulated conditions. Measurements of PLC activity in various in vitro assays demonstrated enhanced activity of PLCγ2 M1141K while the activity of PLCγ2 P522R was not significantly different from the WT. Similar trends were observed in several other assays, including direct liposome binding. However, an enhanced rate of phosphorylation of a functionally important tyrosine by Btk in vitro was observed for PLCγ2 P522R variants. To further assess implications of these in vitro findings in a cellular context relevant for the PLCγ2 P522R variant, microglia (BV2) stable cell lines were generated and analysed under growth conditions. The PLC activity in cells expressing PLCγ2 P522R at physiologically relevant levels was clearly enhanced compared to the WT, and differences in cell morphology observed. These data, combined with the structural insights, suggest that the PLCγ2 P522R variant has subtle, localised structural changes that do not directly affect the PLC activity by compromising autoinhibition, as determined for PLCγ2 M1141K. It is also likely that in contrast to the PLCγ2 M1141K, the functional impact of the P522R substitution completely depends on further interactions with upstream kinases and other regulatory proteins in a relevant cellular context, where changes in the PLCγ2 P522R variant could facilitate processes such as phosphorylation and protein-protein interactions.

Sex dependence of postoperative pulmonary complications - A post hoc unmatched and matched analysis of LAS VEGAS.

STUDY OBJECTIVE: Male sex has inconsistently been associated with the development of postoperative pulmonary complications (PPCs). These studies were different in size, design, population and preoperative risk. We reanalysed the database of 'Local ASsessment of Ventilatory management during General Anaesthesia for Surgery study' (LAS VEGAS) to evaluate differences between females and males with respect to PPCs. DESIGN, SETTING AND PATIENTS: Post hoc unmatched and matched analysis of LAS VEGAS, an international observational study in patients undergoing intraoperative ventilation under general anaesthesia for surgery in 146 hospitals across 29 countries. The primary endpoint was a composite of PPCs in the first 5 postoperative days. Individual PPCs, hospital length of stay and mortality were secondary endpoints. Propensity score matching was used to create a similar cohort regarding type of surgery and epidemiological factors with a known association with development of PPCs. MAIN RESULTS: The unmatched cohort consisted of 9697 patients; 5342 (55.1%) females and 4355 (44.9%) males. The matched cohort consisted of 6154 patients; 3077 (50.0%) females and 3077 (50.0%) males. The incidence in PPCs was neither significant between females and males in the unmatched cohort (10.0 vs 10.7%; odds ratio (OR) 0.93 [0.81-1.06]; P = 0.255), nor in the matched cohort (10.5 vs 10.0%; OR 1.05 [0.89-1.25]; P = 0.556). New invasive ventilation occurred less often in females in the unmatched cohort. Hospital length of stay and mortality were similar between females and males in both cohorts. CONCLUSIONS: In this conveniently-sized worldwide cohort of patients receiving intraoperative ventilation under general anaesthesia for surgery, the PPC incidence was not significantly different between sexes. REGISTRATION: LAS VEGAS was registered at clinicaltrial.gov (study identifier NCT01601223).

Risk Factors of Post-Traumatic Stress in Pediatric Solid Organ Transplant Recipients.

BACKGROUND: Life with end-stage organ failure is accompanied by an accumulation of traumatic medical or surgical experiences. Despite recovery after solid organ transplantation (SOT), many children and adolescents develop post-traumatic stress symptoms (PTSS). PTSS remain underappreciated as a major comorbidity in SOT programs, despite their association with decreased quality of life. METHODS: We conducted a retrospective, cross-sectional study of 86 pediatric SOT recipients (17 heart, 44 kidney, and 25 liver) to evaluate potential determinants of PTSS. Trauma symptoms were measured by the Child Trauma Screening Questionnaire (CTSQ). Demographic, baseline, and contemporaneous factors were tested for independent association with CTSQ scores. RESULTS: The median post-transplant CTSQ score was 2 (IQR 1-4), and 22% were identified as high risk (score ≥5) for PTSD. Higher CTSQ scores were independently associated with the number of ICU days within the previous 12 months, the number of medications (complexity), and involvement with foster care in the primary model (R2 [adj.] = 0.26). The addition of the Family Impact Module improved the overall model (R2 [adj.] = 0.33), wherein higher family functioning was independently associated with lower CTSQ scores. An exploratory analysis of pre-transplant patients (n = 34) found a median pre-transplant CTSQ of 2 (IQR 1-6), suggesting that PTSS are onset before transplant and persist afterward. CONCLUSIONS: PTSS are highly prevalent in the SOT population. Risk factors include recent adverse medical experiences and complexity, whereas family stability may be protective. Additional research is needed to improve early ascertainment and support for patients at high risk of developing PTSS throughout their transplant journey.

Single-Sided Peak Nasal Inspiratory Flow as an Adjunct Objective Measure in Functional Septorhinoplasty.

OBJECTIVE: Nasal obstruction can negatively impact patient quality of life, which can be alleviated by functional nasal surgery. Quantification of improvement is most commonly evaluated with the use of validated survey instruments but lacks widely utilized objective measures. Herein, we evaluate the utility of single-sided peak nasal inspiratory flow (PNIF) as an objective outcome measure in the evaluation and management of nasal obstruction. METHODS: Adults presenting with nasal obstruction who were recommended septorhinoplasty were included in the study. Single-sided and bilateral PNIF measures, nasal obstruction symptom evaluation (NOSE) scores, surgeon-rated percent nasal obstruction, and nasal obstruction visual analog scale (VAS) scores were recorded preoperatively with Spearman's correlation coefficients (ρ) calculated. Correlation coefficients were also calculated between the change in the above variables from the pre- to postoperative state. RESULTS: One Hundred Fifteen patients were enrolled in the study and underwent septorhinoplasty. Significant correlations between single-sided PNIF and the associated VAS scores of the same laterality were found for the worse (ρ = -0.366; p < 0.001) and better (ρ = -0.313; p < 0.001) breathing sides. Correlations between postoperative improvement in single-sided PNIF and improvement in VAS scores were also found (ρ = -0.330; p = 0.007, ρ = -0.354; p = 0.004). No correlation between NOSE scores and single-sided PNIF was found except in the subgroup of patients presenting with bilateral asymmetric nasal obstruction, in who NOSE scores correlated with worse side PNIF (ρ = -0.369; p = 0.038). CONCLUSIONS: Single-sided PNIF has a better correlation to patients' symptoms as rated by VAS score than bilateral PNIF and may be a useful adjunct objective measure in the evaluation and quantification of improvement in patients undergoing septorhinoplasty. LEVEL OF EVIDENCE: Level III Laryngoscope, 2024.

An acidic loop in the forkhead-associated domain of the yeast meiosis-specific kinase Mek1 interacts with a specific motif in a subset of Mek1 substrates.

The meiosis-specific kinase Mek1 regulates key steps in meiotic recombination in the budding yeast, Saccharomyces cerevisiae. MEK1 limits resection at double-strand break (DSB) ends and is required for preferential strand invasion into homologs, a process known as interhomolog bias. After strand invasion, MEK1 promotes phosphorylation of the synaptonemal complex protein Zip1 that is necessary for DSB repair mediated by a crossover-specific pathway that enables chromosome synapsis. In addition, Mek1 phosphorylation of the meiosis-specific transcription factor, Ndt80, regulates the meiotic recombination checkpoint that prevents exit from pachytene when DSBs are present. Mek1 interacts with Ndt80 through a 5-amino acid sequence, RPSKR, located between the DNA-binding and activation domains of Ndt80. AlphaFold Multimer modeling of a fragment of Ndt80 containing the RPSKR motif and full-length Mek1 indicated that RPSKR binds to an acidic loop located in the Mek1 FHA domain, a noncanonical interaction with this motif. A second protein, the 5'-3' helicase Rrm3, similarly interacts with Mek1 through an RPAKR motif and is an in vitro substrate of Mek1. Genetic analysis using various mutants in the MEK1 acidic loop validated the AlphaFold model, in that they specifically disrupt 2-hybrid interactions with Ndt80 and Rrm3. Phenotypic analyses further showed that the acidic loop mutants are defective in the meiotic recombination checkpoint and, in certain circumstances, exhibit more severe phenotypes compared to the NDT80 mutant with the RPSKR sequence deleted, suggesting that additional, as yet unknown, substrates of Mek1 also bind to Mek1 using an RPXKR motif.

Sulfated vitamin D metabolites represent prominent roles in serum and in breastmilk of lactating women.

BACKGROUND: Concentrations of vitamin D (VitD) and 25-hydroxyvitamin D (25OHD) in breastmilk are low despite the essential role of VitD for normal infant bone development, yet additional metabolic forms of vitamin D may be present. This study evaluates the contribution of sulfated vitamin D metabolites, vitamin D3-sulfate (VitD3-S) and 25-hydroxyvitamin D3-sulfate (25OHD3-S) for lactating women and assesses the response to high-dose VitD3 supplementation. METHODS: Serum and breastmilk were measured before and after 28 days with 5000 IU/day VitD3 intake in 20 lactating women. Concentrations of VitD3-S and 25OHD3-S in milk, and 25OHD2, 25OHD3, 25OHD3-S, VitD3 and VitD3-S in serum were determined by mass spectrometry. RESULTS: Baseline vitamin D status was categorized as sufficient (mean ± SD serum 25OHD3 69 ± 19 nmol/L), and both serum VitD3 and 25OHD3 increased following supplementation (p < 0.001). 25OHD3-S was 91 ± 19 nmol/L in serum and 0.47 ± 0.09 nmol/L in breastmilk. VitD3-S concentrations were 2.92 ± 0.70 nmol/L in serum and 6.4 ± 3.9 nmol/L in breastmilk. Neither sulfated metabolite significantly changed with supplementation in either serum or breastmilk. CONCLUSIONS: Sulfated vitamin D metabolites have prominent roles for women during lactation with 25OHD3-S highly abundant in serum and VitD3-S distinctly abundant in breastmilk. These data support the notion that 25OHD3-S and VitD3-S may have physiological relevance during lactation and nutritional usage for nursing infants.

A common mechanism for recruiting the Rrm3 and RTEL1 accessory helicases to the eukaryotic replisome.

The eukaryotic replisome is assembled around the CMG (CDC45-MCM-GINS) replicative helicase, which encircles the leading-strand DNA template at replication forks. When CMG stalls during DNA replication termination, or at barriers such as DNA-protein crosslinks on the leading strand template, a second helicase is deployed on the lagging strand template to support replisome progression. How these 'accessory' helicases are targeted to the replisome to mediate barrier bypass and replication termination remains unknown. Here, by combining AlphaFold structural modelling with experimental validation, we show that the budding yeast Rrm3 accessory helicase contains two Short Linear Interaction Motifs (SLIMs) in its disordered N-terminus, which interact with CMG and the leading-strand DNA polymerase Polε on one side of the replisome. This flexible tether positions Rrm3 adjacent to the lagging strand template on which it translocates, and is critical for replication termination in vitro and Rrm3 function in vivo. The primary accessory helicase in metazoa, RTEL1, is evolutionarily unrelated to Rrm3, but binds to CMG and Polε in an analogous manner, revealing a conserved docking mechanism for accessory helicases in the eukaryotic replisome.

CMG helicase disassembly is essential and driven by two pathways in budding yeast.

The CMG helicase is the stable core of the eukaryotic replisome and is ubiquitylated and disassembled during DNA replication termination. Fungi and animals use different enzymes to ubiquitylate the Mcm7 subunit of CMG, suggesting that CMG ubiquitylation arose repeatedly during eukaryotic evolution. Until now, it was unclear whether cells also have ubiquitin-independent pathways for helicase disassembly and whether CMG disassembly is essential for cell viability. Using reconstituted assays with budding yeast CMG, we generated the mcm7-10R allele that compromises ubiquitylation by SCFDia2. mcm7-10R delays helicase disassembly in vivo, driving genome instability in the next cell cycle. These data indicate that defective CMG ubiquitylation explains the major phenotypes of cells lacking Dia2. Notably, the viability of mcm7-10R and dia2∆ is dependent upon the related Rrm3 and Pif1 DNA helicases that have orthologues in all eukaryotes. We show that Rrm3 acts during S-phase to disassemble old CMG complexes from the previous cell cycle. These findings indicate that CMG disassembly is essential in yeast cells and suggest that Pif1-family helicases might have mediated CMG disassembly in ancestral eukaryotes.

An acidic loop in the FHA domain of the yeast meiosis-specific kinase Mek1 interacts with a specific motif in a subset of Mek1 substrates.

The meiosis-specific kinase Mek1 regulates key steps in meiotic recombination in the budding yeast, Saccharomyces cerevisiae. MEK1 limits resection at the double strand break (DSB) ends and is required for preferential strand invasion into homologs, a process known as interhomolog bias. After strand invasion, MEK1 promotes phosphorylation of the synaptonemal complex protein Zip1 that is necessary for DSB repair mediated by a crossover specific pathway that enables chromosome synapsis. In addition, Mek1 phosphorylation of the meiosis-specific transcription factor, Ndt80, regulates the meiotic recombination checkpoint that prevents exit from pachytene when DSBs are present. Mek1 interacts with Ndt80 through a five amino acid sequence, RPSKR, located between the DNA binding and activation domains of Ndt80. AlphaFold Multimer modeling of a fragment of Ndt80 containing the RPSKR motif and full length Mek1 indicated that RPSKR binds to an acidic loop located in the Mek1 FHA domain, a non-canonical interaction with this motif. A second protein, the 5'-3' helicase Rrm3, similarly interacts with Mek1 through an RPAKR motif and is an in vitro substrate of Mek1. Genetic analysis using various mutants in the MEK1 acidic loop validated the AlphaFold model, in that they specifically disrupt two-hybrid interactions with Ndt80 and Rrm3. Phenotypic analyses further showed that the acidic loop mutants are defective in the meiotic recombination checkpoint, and in certain circumstances exhibit more severe phenotypes compared to the NDT80 mutant with the RPSKR sequence deleted, suggesting that additional, as yet unknown, substrates of Mek1 also bind to Mek1 using an RPXKR motif.

Mechanism of human PINK1 activation at the TOM complex in a reconstituted system.

Loss-of-function mutations in PTEN-induced kinase 1 (PINK1) are a frequent cause of early-onset Parkinson's disease (PD). Stabilization of PINK1 at the translocase of outer membrane (TOM) complex of damaged mitochondria is critical for its activation. The mechanism of how PINK1 is activated in the TOM complex is unclear. Here, we report that co-expression of human PINK1 and all seven TOM subunits in Saccharomyces cerevisiae is sufficient for PINK1 activation. We use this reconstitution system to systematically assess the role of each TOM subunit toward PINK1 activation. We unambiguously demonstrate that the TOM20 and TOM70 receptor subunits are required for optimal PINK1 activation and map their sites of interaction with PINK1 using AlphaFold structural modeling and mutagenesis. We also demonstrate an essential role of the pore-containing subunit TOM40 and its structurally associated subunits TOM7 and TOM22 for PINK1 activation. These findings will aid in the development of small-molecule activators of PINK1 as a therapeutic strategy for PD.

Direct Neck Lift for Men.

Direct neck lift offers an excellent surgical technique for men seeking to rejuvenate the neck and avoid a full rhytidectomy. In this chapter, we provide an overview of direct submentoplasty techniques, as well as clinical pearls to consider in the preoperative, intraoperative, and postoperative periods. Different surgical incisions and resultant scars in the anterior neck are discussed and illustrated with figures. Given the degree of variation of submental fullness with which patients present, it is beneficial to be familiar with several different techniques to address the submental and submandibular areas.

Serial cardiac biomarkers, pulmonary artery pressures and traditional parameters of fluid status in relation to prognosis in patients with chronic heart failure: Design and rationale of the BioMEMS study.

AIMS: Heart failure (HF), a global pandemic affecting millions of individuals, calls for adequate predictive guidance for improved therapy. Congestion, a key factor in HF-related hospitalizations, further underscores the need for timely interventions. Proactive monitoring of intracardiac pressures, guided by pulmonary artery (PA) pressure, offers opportunities for efficient early-stage intervention, since haemodynamic congestion precedes clinical symptoms. METHODS: The BioMEMS study, a substudy of the MONITOR-HF trial, proposes a multifaceted approach integrating blood biobank data with traditional and novel HF parameters. Two additional blood samples from 340 active participants in the MONITOR-HF trial were collected at baseline, 3-, 6-, and 12-month visits and stored for the BioMEMS biobank. The main aims are to identify the relationship between temporal biomarker patterns and PA pressures derived from the CardioMEMS-HF system, and to identify the biomarker profile(s) associated with the risk of HF events and cardiovascular death. CONCLUSION: Since the prognostic value of single baseline measurements of biomarkers like N-terminal pro-B-type natriuretic peptide is limited, with the BioMEMS study we advocate a dynamic, serial approach to better capture HF progression. We will substantiate this by relating repeated biomarker measurements to PA pressures. This design rationale presents a comprehensive review on cardiac biomarkers in HF, and aims to contribute valuable insights into personalized HF therapy and patient risk assessment, advancing our ability to address the evolving nature of HF effectively.

Adrenal insufficiency in pediatric kidney transplantation recipients.

BACKGROUND: Immunosuppression of pediatric kidney transplant (PKT) recipients often includes corticosteroids. Prolonged corticosteroid exposure has been associated with secondary adrenal insufficiency (AI); however, little is known about its impact on PKT recipients. METHODS: This was a retrospective cohort review of PKT recipients to evaluate AI prevalence, risk factors, and adverse effects. AI risk was assessed using morning cortisol (MC) and diagnosis confirmed by an ACTH stimulation test. Potential risk factors and adverse effects were tested for associations with MC levels and AI diagnosis. RESULTS: Fifty-one patients (60.8% male, age 7.4 (IQR 3.8, 13.1) years; 1 patient counted twice for repeat transplant) were included. Patients at risk for AI (MC < 240 nmol/L) underwent definitive ACTH stimulation testing, confirming AI in 13/51 (25.5%) patients. Identified risk factors for AI included current prednisone dosage (p = .001), 6-month prednisone exposure (p = .02), daily prednisone administration (p = .002), and rejection episodes since transplant (p = .001). MC level (2.5 years (IQR 1.1, 5.1) post-transplant) was associated with current prednisone dosage (p < .001), 6-month prednisone exposure (p = .001), daily prednisone administration (p = .006), rejection episodes since transplant (p = .003), greater number of medications (ß = -16.3, p < .001), 6-month hospitalization days (ß = -3.3, p = .013), creatinine variability (ß = -2.4, p = .025), and occurrence of acute kidney injury (ß = -70.6, p = .01). CONCLUSION: Greater corticosteroid exposure was associated with a lower MC level and confirmatory diagnosis of AI noted with an ACTH stimulation test. Adverse clinical findings with AI included greater medical complexity and kidney function lability. These data support systematic clinical surveillance for AI in PKT recipients treated with corticosteroids.

Pulmonary artery pressure monitoring in chronic heart failure: effects across clinically relevant subgroups in the MONITOR-HF trial.

BACKGROUND AND AIMS: In patients with chronic heart failure (HF), the MONITOR-HF trial demonstrated the efficacy of pulmonary artery (PA)-guided HF therapy over standard of care in improving quality of life and reducing HF hospitalizations and mean PA pressure. This study aimed to evaluate the consistency of these benefits in relation to clinically relevant subgroups. METHODS: The effect of PA-guided HF therapy was evaluated in the MONITOR-HF trial among predefined subgroups based on age, sex, atrial fibrillation, diabetes mellitus, left ventricular ejection fraction, HF aetiology, cardiac resynchronization therapy, and implantable cardioverter defibrillator. Outcome measures were based upon significance in the main trial and included quality of life-, clinical-, and PA pressure endpoints, and were assessed for each subgroup. Differential effects in relation to the subgroups were assessed with interaction terms. Both unadjusted and multiple testing adjusted interaction terms were presented. RESULTS: The effects of PA monitoring on quality of life, clinical events, and PA pressure were consistent in the predefined subgroups, without any clinically relevant heterogeneity within or across all endpoint categories (all adjusted interaction P-values were non-significant). In the unadjusted analysis of the primary endpoint quality-of-life change, weak trends towards a less pronounced effect in older patients (Pinteraction = .03; adjusted Pinteraction = .33) and diabetics (Pinteraction = .01; adjusted Pinteraction = .06) were observed. However, these interaction effects did not persist after adjusting for multiple testing. CONCLUSIONS: This subgroup analysis confirmed the consistent benefits of PA-guided HF therapy observed in the MONITOR-HF trial across clinically relevant subgroups, highlighting its efficacy in improving quality of life, clinical, and PA pressure endpoints in chronic HF patients.

Larger spleens and greater splenic contraction during exercise may be an adaptive characteristic of Nepali Sherpa at high-altitude.

OBJECTIVES: The Sherpa ethnic group living at altitude in Nepal may have experienced natural selection in response to chronic hypoxia. We have previously shown that Sherpa in Kathmandu (1400 m) possess larger spleens and a greater apnea-induced splenic contraction compared to lowland Nepalis. This may be significant for exercise capacity at altitude as the human spleen responds to stress-induced catecholamine secretion by an immediate contraction, which results in transiently elevated hemoglobin concentration ([Hb]). METHODS: To investigate splenic contraction in response to exercise at high-altitude (4300 m; Pb = ~450 Torr), we recruited 63 acclimatized Sherpa (29F) and 14 Nepali non-Sherpa (7F). Spleen volume was measured before and after maximal exercise on a cycle ergometer by ultrasonography, along with [Hb] and oxygen saturation (SpO2). RESULTS: Resting spleen volume was larger in the Sherpa compared with Nepali non-Sherpa (237 ± 62 vs. 165 ± 34 mL, p < .001), as was the exercise-induced splenic contraction (Δspleen volume, 91 ± 40 vs. 38 ± 32 mL, p < .001). From rest to exercise, [Hb] increased (1.2 to 1.4 g.dl-1), SpO2 decreased (~9%) and calculated arterial oxygen content (CaO2) remained stable, but there were no significant differences between groups. In Sherpa, both resting spleen volume and the Δspleen volume were modest positive predictors of the change (Δ) in [Hb] and CaO2 with exercise (p-values from .026 to .037 and R2 values from 0.059 to 0.067 for the predictor variable). CONCLUSIONS: Larger spleens and greater splenic contraction may be an adaptive characteristic of Nepali Sherpa to increase CaO2 during exercise at altitude, but the direct link between spleen size/function and hypoxia tolerance remains unclear.