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Background: Hypoxia challenges the regulation of arterial oxygenation (SaO 2 ), eliciting a compensatory increase in ventilation ([Formula: see text]E) to preserve blood-gas homeostasis. However, the ability to maintain blood-gas homeostasis during hypoxic exercise may differ between sexes due to differences in chemoreflex drive and the mechanical capacity to augment ventilation. The purpose of this study was to evaluate sex differences in ventilatory and blood-gas responses to progressive hypoxia during moderate walking exercise. Specifically, we asked whether females would be more susceptible to hypoxemia. We hypothesized that females would exhibit a smaller ventilatory response and a less steep ventilatory CO 2 -response (Δ[Formula: see text]E/ΔPaCO 2 ) compared with males, resulting in a greater reduction in SaO 2 during progressive hypoxia. Methods: Twenty-six physically active adults (15M: age 35.3±9.4; [Formula: see text]O 2 max 54.3±15.5 mL/kg/min, 11F: age 36.2±9.0; [Formula: see text]O 2 max 44.6±5.2 mL/kg/min) were studies during two visits. Visit 1: we determined the participants’ maximal oxygen uptake ([Formula: see text]O 2 max) during an incremental treadmill test. Visit 2: participants walked at ~50% of their [Formula: see text]O 2 max while we reduced the fraction of inspired oxygen (FiO 2 ) progressively every 5 minutes (0.21, 0.19, 0.17, 0.15, 0.13, 0.12, 0.11). Arterial blood samples were collected from a brachial artery catheter during the final 30 seconds of each stage; cardiometabolic and ventilatory data were averaged over the final minute of each stage. The test ended when peripheral oxygen saturation (SpO 2 ) fell below 70%. Because 0.13 FiO 2 was the lowest stage completed by all participants, Δ responses were calculated from 0.21 to 0.13 FiO 2 . Independent t-tests compared Δ responses between sexes; data are mean±SD, significance was set at p < 0.05. Results: There was no significant difference in ΔSaO 2 between sexes across hypoxia (M: −22.0±3.7%; F: −22.8±5.5%; p = 0.89). Males had higher arterial oxygen content (CaO 2 ) than females across all stages (M: 20.6±1.2 to 16.0±1.4 mL O 2 ·dL -1 ; F: 18.5±1.1 to 13.8±2.0 mL O 2 ·dL -1 ), but the ΔCaO 2 during hypoxia was not significantly different between sexes (M: −4.6±0.7; F: −4.7±1.4 mL O 2 ·dL -1 ; p = 0.86). Similarly, there was no significant difference in the change in arterial CO 2 (ΔPaCO 2 ) between sexes (M: −5.8±1.5 mmHg; F: −6.5±3.6 mmHg, p = 0.51). In contrast, males exhibited a significantly greater increase in ventilation (Δ[Formula: see text]E: +13.9±4.2 L·min -1 ) than females (+8.6±2.7 L·min -1 ; p = 0.003). Consequently, the ventilatory CO 2 -response (Δ[Formula: see text]E/ΔPaCO 2 ) was steeper in males (−2.46±0.66 L·min -1 ·mmHg -1 ) compared with females (−1.57±0.68 L·min -1 ·mmHg -1 ; p = 0.004). However, when Δ[Formula: see text]E was expressed relative to maximal ventilatory capacity (%[Formula: see text]Emax), there was no sex difference (M: 8.8±2.6% vs F: 8.3±2.8%; p = 0.68). Conclusion: Females were not more susceptible to hypoxemia than males; both sexes showed comparable reductions in SaO 2 during moderate exercise in progressive hypoxia. Reductions in PaCO 2 were also similar, indicating comparable ventilatory drive. Although males exhibited a larger absolute increase in [Formula: see text]E and a steeper ventilatory CO 2 -response, this difference disappeared when Δ[Formula: see text]E was expressed relative to %[Formula: see text]Emax. These findings indicate that apparent sex differences in ventilation during hypoxia largely reflect differences in ventilatory capacity rather than true differences in oxygenation or ventilatory drive. Taken together, these findings challenge the assumption that females are inherently more susceptible to hypoxemia or have a lower ventilatory drive than males during moderate hypoxic exercise. Funding: NIH T32 DK007352, UL1 TR002377 This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

Background: During hypoxic exercise, oxygen transport becomes increasingly challenged as oxygen availability decreases. As the inspired oxygen fraction (FiO 2 ) decreases, peripheral oxygen saturation (SpO 2 ) gradually declines, then drops rapidly upon reaching the steepest point of the sigmoidal shaped, oxyhemoglobin dissociation curve. This reduction in FiO 2 creates a distinct SpO 2 “breakpoint,” which likely represents the threshold at which compensatory mechanisms, such as increases in ventilation and cardiac output, can no longer maintain arterial oxygenation. Several physiological factors may modulate this breakpoint, including hemoglobin concentration, blood volume, and ventilatory capacity. This study aimed to determine the SpO 2 breakpoint during steady-state, submaximal, hypoxic exercise and examine whether factors like sex, age, and fitness level influence the SpO 2 breakpoint. We hypothesized that SpO 2 breakpoints would differ by sex, age, and fitness level, with earlier breakpoints visible in females, older adults, and those with higher aerobic fitness. Methods: Twenty-six physically active adults (15M: age 35±9 yrs, [Formula: see text]O 2 max 54.3±15.5 mL/kg/min, 11F: age 38±10 yrs, [Formula: see text]O 2 max 44.6±5.2 mL/kg/min) participated in a two-day study. Day one: participants performed a treadmill [Formula: see text]O 2 max test. Day two: participants walked at a steady state of ~50% of their [Formula: see text]O 2 max, for 40 minutes, while FiO 2 was progressively reduced every 5 minutes in a stepwise fashion (0.25, 0.21, 0.19, 0.17, 0.15, 0.13, 0.12, 0.11). The test was terminated when SpO 2 dropped below 70%. SpO 2 was measured continuously using a clinical-grade oximeter. Analysis was performed in RStudio by first determining each participant’s individual SpO 2 vs time breakpoint. Male and Female breakpoints were compared to assess sex-based differences. To evaluate whether SpO 2 breakpoint timing differed by age or fitness level, participants were then divided into tertiles for each variable. Age tertiles were derived from the sample distribution of chronological age, and fitness tertiles were defined using [Formula: see text]O 2 max (L/min). Mean breakpoint times were compared between the highest and lowest tertiles for both age and fitness. Mean SpO 2 breakpoints were compared between groups using independent sample t-tests. Significance was set to p< 0.05. Results: The overall mean breakpoint occurred at an SpO 2 of 90.7±2.8% during the 0.17 FiO 2 stage. No significant sex differences were observed in breakpoint SpO 2 and timing (M: SpO 2 = 90.7±2.7%, time = 18.6 min; F: SpO 2 = 90.7±3.0%, time = 17.7 min; p = 0.961). Age did not significantly influence breakpoint (younger tertile [21-30 yrs] SpO 2 = 91.0±2.4%, time = 18.4 min; older tertile [41-60 yrs] SpO 2 = 91.1±2.4%, time = 17.2 min, p = 0.953). Additionally, fitness level showed no significant difference on breakpoint (low fitness [1.91-3.01 L/min]: SpO 2 = 90.3±3.1%, time = 17.8 min; high fitness [4.38-5.25 L/min]: SpO 2 = 90.4±2.9%, time = 19.2 min; p = 0.992). Conclusion: During a hypoxic, steady state walking exercise, at ~50% [Formula: see text]O 2 max, we observed no difference in the peripheral oxygen saturation breakpoint, across sex, age, and fitness level. This may suggest that moderate exercise in hypoxia does not sufficiently challenge the cardiopulmonary system for individual variations in oxygen transport to influence the breakpoint. These findings imply that the SpO 2 breakpoint, during hypoxic exercise, may represent a physiological marker of the upper limit for maintaining oxygen saturation in healthy adults. Applying this protocol to identify SpO 2 breakpoints may offer insights for improving pharmacological interventions and our understanding of clinical populations with impaired oxygen transport. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

Abstract Females likely experience larger performance benefits from androgenic‐anabolic steroids than males. We set out to determine if there were temporal differences in select athletics (track and field) records between females and males. Exploratory aims included: (1) evaluating the improvements in female and male world records over time, and (2) investigating the influence of doping programs on male and female world records before and after 1990, when sports governing bodies began to implement random out‐of‐competition and systematic in‐competition drug testing. We collected the top 500 performances of all time for both sexes from an online database (worldathletics.org) in four running events (100, 200, 400 and 800 m) and two throwing events (discus throw and shot‐put). Data were stratified into quintiles based on world record ranking (1st to 100th, 101st to 200th, etc.). The temporal distribution of the top 100 female performers was significantly earlier than the top 100 male performers (year: 2000 ± 1 vs. 2005 ± 1, respectively; P < 0.0001). Within the event, the top performances occurred significantly earlier for females in the 800 m (year: 1995 ± 15 vs. 2003 ± 12; P = 0.0007) and shot‐put (year: 1992 ± 14 vs. 2003 ± 17; P = 0.0004). Among females, world records rapidly improved through the 1980s, but following 1990, the world records ceased to improve. Geographically, there was a greater representation of countries with state‐sponsored doping programs, specifically among female performances. We postulate these sex differences in the temporal distribution of top performances are likely associated with enhanced effectiveness of exogenous androgens (steroid doping) among female athletes with lower endogenous androgen hormones compared to males.

Introduction: Multiple Valvular Heart Disease (VHD), defined as at least moderate stenotic or regurgitant lesions in ≥2 valves, mixed VHD as combination of lesions in the same valve and mitral annular calcification (MAC) are common conditions. Association between multiple-mixed VHD (MMVHD), MAC and MACE in patients exposed to Radiation Therapy (RT) and/or chemotherapy (CT) who underwent Transcatheter Aortic Valve Replacement (TAVR) has not been studied. Aim: Assess the presence of MMVHD and MAC in cancer patients with prior RT and/or CT and their correlation with MACE (cardiovascular death, myocardial infarction, revascularization, stroke and hospitalization for heart failure) after TAVR. Methods: 544 patients were included and divided into 3 groups: 187 with prior chest RT and CT (RT/CT), 155 CT only, and 202 without CT/RT as controls (Table 1). Data was obtained from the pre-procedure echocardiogram and quantified in a 1-6 scale (none, mild, mild/moderate, moderate, moderate/severe and severe). Fisher’s exact test or chi-square were used to compare categorical. Multiple VHD-MACE correlation was evaluated through multivariable Cox analysis using a proportional hazards model. Results: The prevalence of Multiple VHD was 37.4% in RT/CT, 23.2% in CT, and 13.9% in controls p<0.001(Figure 1). The RT/CT group had a significantly higher prevalence of severe MAC. Multiple VHD predicted MACE at 18 months after TAVR in RT/CT (HR 3.42, CI 1.93-6.08, p<0.001) and in CT (HR 2.55, CI 1.39-4.66, p=0.002) (Table 2). In RT/CT, severe MAC also predicted MACE (HR 3.68, CI 2.13-6.37, p<0.001), while it was not a predictor in the other groups. Stenotic or regurgitant VHD was more prevalent in the RT/CT group (Figure 2). Conclusions: Multiple VHD was found higher in RT/CT and predicted MACE at 18 months post-TAVR, including CT only patients. Severe MAC was also a strong predictor of the outcome in RT/CT patients. Pre-TAVR evaluation of MMVHD lesions is crucial for optimal patient management.

Introduction: Assessing baseline cardiovascular (CV) risk factors is crucial for identifying cancer patients at higher risk of cardiotoxicity (CT). While both CT specific scores, including Heart Failure Association-International Cardio Oncology Society (HFA-ICOS) and our institutional score, as well as general CV scores like Atherosclerotic cardiovascular disease (ASCVD), have been used to assess CT risk; in lymphoma patients undergoing anthracycline therapy, their utility remains unknown. Aim: Evaluate the performance of each risk score to predict CT in a cohort of newly diagnosed lymphoma patients undergoing anthracycline treatment, followed for a median of 5.4 years. Methods: 326 Hodgkin and non-Hodgkin lymphoma patients treated and followed from 2013 to 2021 were prospectively assessed. Baseline measurements of the three risk scores were obtained. ASCVD score was not assessed in patients >80 or <40 years old or without baseline cholesterol. CT was defined during or after one year of chemotherapy as severe, moderate, or mild according to 2022 ESC guidelines. Logistic regression and AUC were used to assess the association of each score and compare the models. Results: Among 326 patients, 78 developed CT (8 severe, 21 moderate, 49 mild). A high-risk score from HFA-ICOS was significantly associated with severe and moderate CT(OR: 6.1, p=0.001), sensitivity 37%, and specificity 88%. A very high-risk classification of the institutional score was associated with severe and moderate CT (OR: 8.4, p=0.006), sensitivity 44%, and specificity 81%. No association was found between the ASCVD score stratification and CT. When mild CT was included in the analysis, the AUC values were lower (see Table 1). Conclusions: Cardio-oncology risk scores were associated with severe and moderate CT, outperforming ASCVD, but their predictive capacity was weak. Incorporating other serum or imaging biomarkers into the models may improve the predictive accuracy of CT risk assessment.

Background: CD19 CAR T-cell therapy is a novel cancer treatment for B-cell malignancies. Systemic inflammation due to Cytokine Release Syndrome (CRS) can occur. Elevated levels of cytokines have been linked to valve damage. Hypothesis: Evaluate changes in valve morphology or progression of valvular heart disease in adult patients after CD19 CAR T-cell therapy and by clinical CRS grade. Methods: Patients that underwent CD19 CAR T-cell therapy with both a baseline and a post-treatment transthoracic echocardiogram (TTE) were included. Patient characteristics and outcomes were abstracted from the electronic medical record. CRS was categorized as CRS<2 and CRS ≥2 for all patients using the ASTCT 2019 criteria. Valve thickening was graded as a dichotomous variable. Valve disease (regurgitation or stenosis) was ranked on a 1-to-6-point numeric scale (none, mild, mild-moderate, moderate, moderate-severe, severe) and grade point value difference was calculated. Variables were compared by Chi Squared and Student’s t tests. Results: 114 patients were included with a median TTE follow-up of 44 days, 54% developed CRS ≥2 (Table 1a). Overall, no statistically significant changes in valve morphology and valve disease progression were observed in the cohort (Figure 1a, 1b). Among CRS groups, valve morphology changes and valve disease progression were similarly distributed (21% in CRS <2 vs 19% in CRS ≥2, p=0.623 and 28% in CRS <2 vs 24% in CRS ≥2, p=0.62 respectively) (Fig. 1a). In the cases that progression was observed, it was mostly mild, and regurgitation was the most common pattern (Fig. 1c). Conclusions: This is the first study to evaluate the incidence of cardiac valve disease progression or thickening in patients treated with CD19 CAR T therapies. We can conclude that no progression of valve disease or changes in valve morphology were observed in its entirety or by CRS groups. Longer follow up is needed to validate these findings.

Abstract Background Exercise stress echocardiography (ESE) is a non-invasive, radiation-free, and widely available technique that has demonstrated a reliable accuracy for the detection of coronary artery disease (CAD). Chest radiotherapy (RT) is associated with accelerated age-related atherosclerosis and fibrosis in a dose-dependent manner. ESE plays a role as a screening tool of RT induced heart disease, however, the prognostic value of changes in regional wall motion abnormalities in this population during ESE has not been evaluated. Methods This is a retrospective cohort study of breast cancer survivors treated with adjuvant RT that underwent ESE from 2000-2020 after treatment completion. Outcomes evaluated were: major adverse cardiovascular events (MACE: cardiovascular death, myocardial infarction, revascularization and stroke); and all-cause mortality. A univariate analysis was performed to characterize the population. Continuous variables were presented as means ± standard deviation (SD) or median with quartile 1 and 3 (Q1, Q3), and categorical variables as numbers and percentages. A Cox regression model adjusted by age and cardiovascular risk factors was used to evaluate variables associated with outcomes, and a time to first event approach was used. A p-value of &lt;0.05 was considered statistically significant. Results From 2000-2020, 507 patients, with a mean age 66 ± 10 years, underwent ESE at a median of 5.8 years after RT completion. The most prevalent comorbidities were dyslipidemia (59%), HTN (55%) and obesity (37%). 55% underwent RT for left-sided breast cancer and 45% for right-sided, and median RT dose was 6000 cGy. Baseline characteristics are presented in Table 1. Most patients underwent Bruce Protocol (92%). Patients exercised a mean time of 6.6 minutes achieving 7.3 METS and 109% of functional aerobic capacity (Table 2). At a median follow up of 7.8 years, 61 MACE events occurred. Predictors of MACE were double product, baseline and stress EF, baseline and peak regional wall motion abnormalities (RWMA), development of new ischemic RWMA, inability to reach 85% of maximum HR, and an abnormal EF response with stress after adjusting for age, HTN, DM, smoking history, dyslipidemia, obesity, prior MI and cancer staging (Fig 1). Predictors of all-cause mortality were METS, LV mass index, baseline and peak RWMA, development of new ischemic RWMA and an abnormal EF change with stress even after adjusting for variables described previously (Fig 2). Conclusions The development of new or worsening RWMA of just 2 segments with stress, was a significant predictor of MACE and all-cause mortality in a large cohort of breast cancer survivors undergoing multidisciplinary management including adjuvant RT. Special emphasis on management of cardiovascular comorbidities and closer surveillance are recommended for these patients.