Wiggins, Chad C.

Abstract Hypoxia constrains cerebral oxygen availability and challenges brain function and stability. Although hypoxia-responsive functional connectivity (HR-FC) reorganizes rapidly with declining arterial oxygen partial pressure, its relationship to local neurovascular activity remains unclear. We examined time-resolved amplitude of low-frequency fluctuations (ALFF) in blood-oxygenation-level dependent (BOLD) fMRI during graded acute hypoxia in healthy adults, performing a continuous cognitive test (Go/No-go task) with concurrent physiological monitoring. Dynamic ALFF and functional connectivity were estimated using a sliding-window approach and analyzed across large-scale brain networks defined by Schaefer’s 17-network parcellation. Severe hypoxia elicited temporally dissociated responses across modalities. Functional connectivity increased monotonically, whereas ALFF exhibited pronounced nonlinear modulation, including phase-dependent divergence across networks. During hypoxic decompensation, the default mode network (DefaultA) showed marked ALFF suppression, whereas a ventral secondary somatosensory-dominant network (SomMotB) exhibited preferential preservation despite similar engagement in HR-FC. Together, these findings indicate that network-level ALFF captures a distinct yet complementary layer of functional dynamics, with a temporal profile distinct from functional connectivity. Spontaneous BOLD dynamics during acute hypoxia reflect structured network-level modulation rather than a uniform suppression attributable solely to reduced oxygen availability. These findings support a conceptual framework of cerebral oxygen budgeting , in which metabolic constraints reshape functional dynamics across brain networks.

This study investigated the first multiomics data for association with tolerance to central hypovolemia in humans. Analyzing gene expression, proteins, and genetic variants in individuals with high and low tolerance to simulated hemorrhage, the findings show that severe blood loss causes widespread transcriptional changes, including the activation of innate immune system pathways and inhibition of gas transport processes. This research can help identify molecular factors that influence individuals’ tolerance levels for progressive blood loss.

AbstractInterstitial lung disease (ILD) encompasses pulmonary disorders characterized by chronic inflammation and fibrosis that disrupt pulmonary gas exchange. While ILD‐related changes in the lung parenchyma are well‐documented, less is known about how ILD affects luminal area within the large conducting airways. This retrospective, case–control study tested the hypothesis that patients with ILD would have greater large conducting airway luminal areas than healthy matched controls. Three‐dimensional reconstructions of computed tomography images were used to quantify airway luminal areas in patients with ILD (n = 82; 54% female) and healthy controls matched for age, sex, and height. Patients with ILD had 16%–22% greater airway luminal areas across all seven measured large conducting airways compared to controls (all p < 0.001). Among patients with ILD, males had 17%–34% greater height‐normalized airway luminal areas than females (all p < 0.05). These data provide evidence that ILD is associated with greater large conducting airway luminal area, even when matched for key demographic factors. Consistent with observations in health, males with ILD exhibited greater height‐normalized airway size than females. These findings offer new insight into airway remodeling in ILD and highlight potential sex differences in airway luminal area.

AbstractFatiguing inspiratory work has been shown to evoke a sympathetically mediated reflex that has systemic cardiovascular consequences, including increases in heart rate and blood pressure and a decrease in resting limb vascular conductance. Moreover, the response to this reflex appears to be attenuated in females compared with males. It remains to be seen whether this respiratory muscle metaboreflex also exerts an effect on cerebral blood flow. Cerebral blood flow is tightly regulated to maintain homeostasis and critical function. Therefore, it stands to reason that cerebrovascular haemodynamics would not be compromised through this respiratory muscle metaboreflex. We hypothesized that fatiguing inspiratory work would reduce resting limb conductance, but cerebral blood flow would be minimally impaired. Females (34 ± 10 years old, n = 12) and males (31 ± 8 years old, n = 12) performed a 5 min, high‐intensity bout of inspiratory pressure threshold loading (IPTL) designed to evoke the respiratory muscle metaboreflex. In response to IPTL, mean arterial pressure increased in both males and females (p < 0.001), and limb vascular conductance decreased to a greater degree in males than in females (p = 0.005). The cerebrovascular conductance index was higher in females (p = 0.007) but not affected by IPTL (p = 0.417). Our findings suggest that cerebral blood flow is spared from the redistribution of blood flow in response to fatiguing inspiratory work and that this protection is true in both males and females.

Intravenous dexmedetomidine infusion (selective α 2 -adrenergic receptor agonist) 1) reduced the firing probability and strength of baroreflex control over medium-sized sympathetic action potentials in muscle sympathetic nerve activity (MSNA) and 2) attenuated the transduction of MSNA bursts to changes in blood pressure (BP) by reducing the magnitude of BP responses and increasing the time to peak BP. These data suggest that neural and vascular α 2 -adrenergic mechanisms contribute to sympathetic baroreflex regulation of human BP.

Sympathetic control of human blood pressure is mechanistically regulated by α 2 -adrenergic receptors distributed throughout the nervous system and cardiovascular end-targets. Recently, we discovered the sympathoinhibitory effects of central α 2 -adrenergic mechanisms on human sympathetic neuronal emission patterns. However, our knowledge remains incomplete regarding the impact of α 2 -adrenergic mechanisms on beat-by-beat transduction of muscle sympathetic nerve activity (MSNA) bursts to changes in blood pressure and heart rate (HR). Based on evidence of α 2 -adrenergic receptors within central and peripheral sympathetic neural sites and on the vasculature, this study tested the hypothesis that activation of α 2 -adrenergic receptors with dexmedetomidine (DEX) would reduce sympathetic transduction to blood pressure. In eight healthy participants (5 females; 28 ± 7 years), diastolic blood pressure (DBP; brachial arterial catheter), HR (ECG), and MSNA (peroneal microneurography) were recorded during a 5-minute supine baseline (BSL) and an intravenous DEX infusion consisting of a loading dose (10 minutes at 0.225 μg/kg/hr) and a maintenance dose (~0.15 μg/kg/hr). Signal averaging quantified sympathetic transduction to DBP and HR for 12 cardiac cycles following integrated MSNA bursts. We also quantified sympathetic transduction to DBP using a transduction gain estimate derived from the slope of the linear relationship between the peak DBP response and the number of cardiac cycles until peak DBP response. Data (mean ± SD) are reported for the 5-minute BSL and the last 5-minute period during the DEX infusion. Mixed-effects modeling and t -tests were performed. Non-parametric tests were performed for non-normally distributed data. DEX reduced resting MAP (BSL: 92 ± 7, DEX: 82 ± 6 mmHg: p < 0.001) but did not affect resting HR (BSL: 62 ± 14, DEX: 61 ± 14 bpm; p = 0.853). DEX reduced resting integrated MSNA burst frequency (BSL: 14 ± 6, DEX: 4 ± 3 bursts/min; p = 0.001) and total integrated MSNA (BSL: 663 ± 252, DEX: 188 ± 142 AU/min; p < 0.001). DEX attenuated the DBP transduction response, particularly for the cardiac cycle associated with peak DBP during BSL (cardiac cycle 6: BSL: 4.3 ± 3.2, DEX: 3.3 ± 2.0 mmHg; p = 0.025) and prolonged the time to peak DBP transduction (BSL: 6 ±1, DEX: 10 ± 3 cardiac cycles; p = 0.014). Also, DEX reduced DBP transduction gain (BSL: 1.6 ± 2.4, DEX: 0.9 ± 1.3 mmHg/cardiac cycle; p = 0.029). By contrast, DEX did not affect the mean transduction of MSNA bursts to changes in HR (BSL: 3.2 ± 3.1, DEX: 3.9 ± 4.6 mmHg; p = 0.668). These data suggest that α 2 -adrenergic mechanisms distributed among central and peripheral sympathetic neural regions and the cardiovascular system influence moment-to-moment sympathetic regulation of blood pressure homeostasis, but not HR, in humans. This work was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) and the National Institutes of Health (NIH). This abstract was presented at the American Physiology Summit 2025 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.

Biological sex impacts baroreflex control of integrated muscle sympathetic nerve activity (MSNA), yet our knowledge remains incomplete regarding sex differences in baroreflex regulation of the differently sized APs contributing to variations in MSNA burst frequency and size. We hypothesized that sex differences in baroreflex control of sympathetic action potential (AP) discharge contribute to higher resting AP activity in males compared to females. We measured diastolic blood pressure (DBP; Finometer or brachial arterial catheter) and MSNA (peroneal microneurography and continuous wavelet transform, APs normalized to 10 clusters) in 24 healthy individuals (aged 18-30, 12 females) during a 5-minute supine baseline. Sympathetic AP baroreflex threshold gain was measured as the slope of the linear relationship between AP discharge probability and DBP. Sympathetic AP baroreflex sensitivity gain was measured as the slope of the linear relationship between AP clusters per burst and DBP. Analyses were performed during DBP rises and falls to explore baroreflex hysteresis. Mixed-effects analyses and t-tests were performed. Data are reported as mean ± SD. In the aggregate cohort, baroreflex control of medium-sized APs exhibited hysteresis. Compared to rises in DBP, DBP falls were associated with greater AP firing probabilities (cluster 3; DBP rise: 20 ± 11, DBP fall: 26 ± 12%; p < 0.01) and greater AP baroreflex gains (cluster 3; DBP rise: -4.36 ± 2.43, DBP fall: -5.32 ± 3.09 %/mmHg; p < 0.01). In the aggregate cohort, baroreflex hysteresis was not detected for small- or large-sized AP clusters (both p ≥ 0.56). Similar observations were detected for medium-sized APs in male (M) and female (F) cohorts when analyses were stratified by sex. Compared to females, males exhibited greater medium-sized AP firing probabilities during DBP rises (cluster 3; M: 23 ± 12, F: 16 ± 8%; p < 0.01) and falls (cluster 3; M: 32 ± 13, F: 20 ± 8%; p < 0.01). However, AP baroreflex gains were not different between sexes during DBP rises (cluster 3; M: -4.87 ± 2.05, F: -3.84 ± 2.75%/mmHg; p = 0.13) and falls (cluster 3; M: -5.87 ± 2.25, F: -4.76 ± 3.77 %/mmHg; p = 0.15). In the aggregate cohort, the number of AP clusters per burst and the AP baroreflex sensitivity gain were not different between rises and falls in DBP. However, compared to females, males demonstrated a greater number of AP clusters per burst during DBP rises (M: 4 ± 0.9, F: 3 ± 0.6 clusters/burst; p < 0.01) and falls (M: 4 ± 0.8, F: 3 ± 0.7 clusters/burst; p < 0.01). No sex differences in AP baroreflex sensitivity gain were detected during DBP rises (M: -0.08 ± 0.09, F: -0.30 ± 0.07 clusters/burst/mmHg; p = 0.14) or falls (M: -0.08 ± 0.08, F: -0.02 ± 0.08 clusters/burst/mmHg; p = 0.09). These data suggest that 1) hysteresis exists in baroreflex regulation of medium-sized but not small or large sympathetic APs firing under baseline conditions and 2) in line with earlier integrated MSNA studies, compared to females, males demonstrate greater resting sympathetic outflow from greater sympathetic AP discharge and more AP clusters firing per burst in periods of rising and falling DBPs. This work was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) and the National Institutes of Health (NIH). This abstract was presented at the American Physiology Summit 2025 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 acute hypoxia, Thehuman brainemploys complex regulatory mechanisms to compensate for high O 2 demand and low O 2 blood saturation. High hemoglobin-oxygen (Hb-O 2 ) affinity improves arterial oxygen saturation (S a O 2 ) in low oxygen environments providing a potential physiologic benefit in humans. However, the impact of high Hb-O 2 affinity on cerebral blood flow (CBF) and cerebral tissue oxygenation (S t O 2 ) has yet to be examined. This work aimed to determine the influence of an acute increase in Hb-O 2 affinity from Etavopivat, a selective red blood cell pyruvate kinase activator, on CBF regulation and S t O 2 during handgrip exercise in normoxia and hypoxia. Methods: 16 healthy adults (31±8 yr, 5 females) completed two visits; before and after Etavopivat (400 mg daily, 7 days) administration,. Each visit included graded handgrip (~3 min stages each) exercise (rest, 10% maximal voluntary contraction (MVC), 20% MVC) while participants inspired normoxic (NORM, 21% O 2 ), moderate (MH, 15% O 2 ), and severe (SH, 10% O 2 ) hypoxic gas mixtures. Hb-O 2 binding affinity (P 50 ), was measured using dual-wavelength spectrophotometry (pH~7.4 and 37ºC). Blood sampling through catheterization of the non-exercising arm measured S a O 2 . CBF was approximated by the peak middle cerebral artery velocity, measured with a 2MHz transcranial doppler ultrasound through the transtemporal window. S t O 2 was measured using frequency-domain near infrared spectroscopy of the frontal cortex. CBF and S t O 2 between visits were compared using separate two-way RM ANOVA models to determine the effects of Etavopivat [before (baseline) or after 7d Etavopivat exposure (post)] and exercise intensity [rest, 10% MVC, 20% MVC] for each inspirate. Results: P 50 was reduced after Etavopivat exposure (Baseline: 28.6±1.6 mmHg, Etavo: 24.8±1.3, P <0.001) without impacting hematocrit ( P =0.97). S a O 2 was higher following Etavopivat exposure during each inspirate ( P <0.001 for each). There was no significant effect of handgrip exercise on CBF or S t O 2 within any inspirate. Cerebral S t O 2 was higher during each inspirate (all P <0.002)– NORM (Baseline: 65.3±12.3%, Post: 68.8±9.8%), MH (Baseline: 61.0±11.7 %, Post: 66.1±10.5%) and SH (Baseline: 47.7±13.5%, Post: 56.6±11.5%). In addition, CBF was increased during each inspirate (all P <0.001)– NORM (Baseline: 62.2±12.2 cm/s, Post: 69.2±12.5 cm/s), MH (Baseline: 60.8±13.1 cm/s, Post: 67.9±12.3 cm/s) and SH (Baseline: 69.8±16.3 cm/s, Post: 79.2±18.0 cm/s). Conclusion: The acute pharmacological induction of high Hb-O 2 affinity leads to increased CBF and cerebral S t O 2 during acute hypoxic exposure in conditions of mild muscular exertion. Whether the improvement of cerebral S t O 2 is associated increased S a O 2 or CBF (or both) is unclear. These findings are the first to investigate the complex determinants of cerebral S t O 2 as a function of an acute increase in Hb-O 2 affinity. These improvements in S t O 2 during hypoxic exposure may lead to a host of theoretical benefits such as improved hypoxia tolerance, and mitigated decrements in cognitive function during hypoxic exposure. This study was funded by Forma Therapeutics Inc, which was acquired by Novo Nordisk on October 14, 2022, Novo Nordisk A/S. This abstract was presented at the American Physiology Summit 2025 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.

There is a context-dependent trade-off in body size of elite runners, such that smaller body sizes are observed among longer distance runners. However, it is unclear whether this trade-off in body size is observed in other Olympic sports, such as cycling and swimming. To understand the association between body size and athletic competition, we examined metrics of body size from male and female Olympic athletes competing in swimming, running, and cycling. We collected standard anthropometrics (height, mass, body mass index (BMI), and body surface area) of elite male and female athletes competing in the London 2012 Summer Olympics from a public repository. Anthropometric data were compared between sexes (male and female); between sports (swimming, running, and cycling); and between distances within sports (shorter and longer distance). Males were taller ( P < 0.001), heavier ( P < 0.001), and had a larger BMI ( P < 0.001) compared to females. Relative to athletes competing in longer distance events, athletes competing in shorter distance were generally taller (running: P < 0.001, swimming: P ≤ 0.014) and heavier (running: P < 0.001, swimming: P = 0.002 (males) and P = 0.148 (females), cycling: P < 0.001) for both males and females. Height was not different between shorter and longer distance cyclists. There was a trade-off between body size and distance for each of the three Olympics sports, such that smaller athletes were observed in longer distance events. Although there were large sex-based differences in body size, similar trade-offs in size and event were observed for both males and females. These data suggest that there is an optimal combination of skeletal muscle mass and body size to optimize movement economy that is generally preserved across different modes of human locomotion.