Mate Sampling Behavior Determines the Density Dependence of Sexual Selection.

AbstractTheory predicts that the strength of sexual selection (i.e., how well a trait predicts mating or fertilization success) should increase with population density, yet empirical support remains mixed. We explore how this discrepancy might reflect a disconnect between current theory and our understanding of the strategies individuals use to choose mates. We demonstrate that the density dependence of sexual selection predicted by previous theory arises from the assumption that individuals automatically sample more potential mates at higher densities. We provide an updated theoretical framework for the density dependence of sexual selection by (1) developing models that clarify the mechanisms through which density-dependent mate sampling strategies might be favored by selection and (2) using simulations to determine how sexual selection changes with population density when individuals use those strategies. We find that sexual selection may increase strongly with density if sampling strategies change adaptively in response to density-dependent sampling costs, whereas within-individual plasticity in sampling over time (e.g., due to adaptation to increasing sampling costs as the breeding season progresses) produces weaker density-dependent sexual selection. Our findings suggest that density dependence of sexual selection depends on the ecological context in which mate sampling has evolved.

A micro-costing analysis of post-fracture care pathways: results from the International Costs and Utilities Related to Osteoporotic Fractures Study (ICUROS).

This study identified the costs and health-related quality of life impacts of several post-fracture multidisciplinary care pathways specific to individual skeletal site (hip, distal forearm, vertebrae, humerus). These care pathways may assist healthcare providers in allocating resources for osteoporotic fractures in more effective and cost-efficient ways. INTRODUCTION: This micro-costing study was undertaken to provide the estimated healthcare costs of several fracture site-specific health service use pathways associated with different trajectories of health-related quality of life (HRQoL) 12-months post-fracture. METHODS: The study included 4126 adults aged ≥ 50 years with a fragility fracture (1657 hip, 681 vertebrae, 1354 distal forearm, 434 humerus) from the International Costs & Utilities Related to Osteoporotic fractures Study (ICUROS). ICUROS participants were asked to recall the frequency and duration (where applicable) of their health and community care service use at 4- and 12-month follow-up visits. Patient-level costs were identified and aggregated to determine the average cost of healthcare use related to the fracture in each care pathway (presented in Australian 2021 dollars). Mean cost differences were calculated and analysed using a one-way analysis of variance (ANOVA) and post hoc Bonferroni correction to determine any statistically significant differences. RESULTS: The total direct cost of fractures was estimated at $89564, $38926, $18333, and $38461AUD per patient for hip, vertebral, wrist, and humeral participants, respectively. A Kruskal-Wallis test yielded a statistically significant difference in cost values between most care pathways (p < 0.001). Of the 20 care pathways, those associated with recovery of HRQoL had lower mean costs per patient across each fracture site. CONCLUSIONS: This study identified the costs and HRQoL impacts of several multidisciplinary care pathways for individual fracture sites based on the health service utilization of an international cohort of older adults. These care pathways may assist healthcare providers in allocating resources for fragility fractures in more effective and cost-efficient ways.

Sex differences in recovery of quality of life 12 months post-fracture in community-dwelling older adults: analyses of the Australian arm of the International Costs and Utilities Related to Osteoporotic Fractures Study (AusICUROS).

In this study of 695 Australian older adults (aged ≥50 years), we found that men and women had a similar trajectory of health-related quality of life (HRQoL) recovery following fragility fracture at any skeletal site. These results provide us with critical knowledge that improves our understanding of health outcomes post-fracture. INTRODUCTION: Mortality is higher in men than that in women following a fragility fracture, but it is unclear whether recovery of patient-reported outcomes such as health-related quality of life (HRQoL) differs between sexes. This study aimed to identify sex differences in HRQoL recovery 12 months post-fracture. METHODS: Data were from the Australian arm of the International Costs and Utilities Related to Osteoporotic Fractures Study (AusICUROS). Participants recruited to AusICUROS were adults aged ≥50 years who sustained a fragility fracture. HRQoL was measured using the EQ-5D-3L at three time-points post-fracture: within 2 weeks (including pre-fracture recall) and at 4 and 12 months. Multivariate logistic regression analyses were undertaken, adjusting for confounders including age, education, income, and healthcare utilization post-fracture. RESULTS: Overall, 695 AusICUROS participants (536 women, 77.1%) were eligible for analysis with fractures at the hip (n = 150), distal forearm (n = 261), vertebrae (n = 61), humerus (n = 52), and other skeletal sites (n = 171). At the time of fracture, men were younger, reported a higher income, and were more likely to be employed, compared with women. For all fracture sites combined, there were no differences between men and women in recovery to pre-fracture HRQoL at 12-month follow-up (adjusted OR = 1.09; 95% CI: 0.75-1.61). When stratified by fracture site, no significant sex differences were seen for hip (OR = 1.02; 95% CI: 0.42-2.52), distal forearm (OR = 1.60; 95% CI: 0.68-3.78), vertebral (OR = 2.28; 95% CI: 0.61-8.48), humeral (OR = 1.62; 95% CI: 0.16-9.99), and other fractures (OR = 1.00; 95% CI: 0.44-2.26). CONCLUSION: Community-dwelling men and women who survived the 12 months following fragility fracture had a similar trajectory of HRQoL recovery at any skeletal site.

Finite-Size Effect in Phonon-Induced Elliott-Yafet Spin Relaxation in Al.

The Elliott-Yafet theory of spin relaxation in nonmagnetic metals predicts proportionality between spin and momentum relaxation times for scattering centers such as phonons. Here, we test this theory in Al nanowires over a very large thickness range (8.5-300 nm), finding that the Elliott-Yafet proportionality "constant" for phonon scattering in fact exhibits a large, unanticipated finite-size effect. Supported by analytical and numerical modeling, we explain this via strong phonon-induced spin relaxation at surfaces and interfaces, driven in particular by enhanced spin-orbit coupling.

Lymph Liquid Biopsy for Detection of Cancer Stem Cells.

Collection of a blood sample defined by the term "blood liquid biopsy" is commonly used to detect diagnostic, prognostic, and therapeutic decision-making markers of metastatic tumors including circulating tumor cells (CTCs). Many tumors also release CTCs and other markers into lymph fluid, but the utility of lymphatic markers largely remains unexplored. Here, we introduce lymph liquid biopsy through collection of peripheral (afferent) and central (thoracic duct [TD]) lymph samples and demonstrates its feasibility for detection of stem-like CTCs potentially responsible for metastasis development and tumor relapse. Stemness of lymphatic CTCs (L-CTCs) was determined by spheroid-forming assay in vitro. Simultaneously, we tested blood CTCs by conventional blood liquid biopsy, and monitored the primary tumor size, early metastasis in a sentinel lymph node (SLN) and distant metastasis in lungs. Using a mouse model at early melanoma stage with no distant metastasis, we identified stem-like L-CTCs in lymph samples from afferent lymphatic vessels. Since these vessels transport cells from the primary tumor to SLN, our finding emphasizes the significance of the lymphatic pathway in development of SLN metastasis. Surprisingly, in pre-metastatic disease, stem-like L-CTCs were detected in lymph samples from the TD, which directly empties lymph into blood circulation. This suggests a new contribution of the lymphatic system to initiation of distant metastasis. Integration of lymph and blood liquid biopsies demonstrated that all mice with early melanoma had stem-like CTCs in at least one of three samples (afferent lymph, TD lymph, and blood). At the stage of distant metastasis, spheroid-forming L-CTCs were detected in TD lymph, but not in afferent lymph. Altogether, our results demonstrated that lymph liquid biopsy and testing L-CTCs holds promise for diagnosis and prognosis of early metastasis. © 2020 International Society for Advancement of Cytometry.

Experimental Realization of the 1D Random Field Ising Model.

We have measured magnetic-field-induced avalanches in a square artificial spin ice array of interacting nanomagnets. Starting from the ground state ordered configuration, we imaged the individual nanomagnet moments after each successive application of an incrementally increasing field. The statistics of the evolution of the moment configuration show good agreement with the canonical one-dimensional random field Ising model. We extract information about the microscopic structure of the arrays from our macroscopic measurements of their collective behavior, demonstrating a process that could be applied to other systems exhibiting avalanches.

Imaging mass spectrometry: a new way to distinguish dermal contact from administration of cocaine, using a single fingerprint.

Here we show a new and significant application area for mass spectrometry imaging. The potential for fingerprints to reveal drug use has been widely reported, with potential applications in forensics and workplace drug testing. However, one unsolved issue is the inability to distinguish between drug administration and contamination by contact. Previous work using bulk mass spectrometry analysis has shown that this distinction can only be definitively made if the hands are washed prior to sample collection. Here, we illustrate how three mass spectrometry imaging approaches, desorption electrospray ionisation (DESI), matrix assisted laser desorption ionisation (MALDI) and time of flight secondary ion mass spectrometry (ToF-SIMS) can be used to visualise fingerprints at different pixel sizes, ranging from the whole fingerprint down to the pore structure. We show how each of these magnification scales can be used to distinguish between cocaine use and contact. We also demonstrate the first application of water cluster SIMS to a fingerprint sample, which was the sole method tested here that was capable of detecting excreted drug metabolites in fingerprints, while providing spatial resolution sufficient to resolve individual pore structure. We show that after administration of cocaine, lipids and salts in the fingerprint ridges spatially correlate with the cocaine metabolite, benzoylecgonine. In contrast after contact, we have observed that cocaine and its metabolite show a poor spatial correlation with the flow of the ridges.

First Precision Measurement of the Parity Violating Asymmetry in Cold Neutron Capture on

We report the first precision measurement of the parity-violating asymmetry in the direction of proton momentum with respect to the neutron spin, in the reaction ^{3}He(n,p)^{3}H, using the capture of polarized cold neutrons in an unpolarized active ^{3}He target. The asymmetry is a result of the weak interaction between nucleons, which remains one of the least well-understood aspects of electroweak theory. The measurement provides an important benchmark for modern effective field theory and potential model calculations. Measurements like this are necessary to determine the spin-isospin structure of the hadronic weak interaction. Our asymmetry result is A_{PV}=[1.55±0.97(stat)±0.24(sys)]×10^{-8}, which has the smallest uncertainty of any hadronic parity-violating asymmetry measurement so far.

Temporal Variation in Predation Risk May Explain Daily Rhythms of Foraging Behavior in an Orb-Weaving Spider.

Daily rhythms occur in numerous physiological and behavioral processes across an immense diversity of taxa, but there remain few cases in which mechanistic links between rhythms of trait expression and organismal fitness have been established. We construct a dynamic optimization model to determine whether risk allocation provides an adaptive explanation for the daily foraging rhythm observed in many species using the orb-weaving spider Cyclosa turbinata as a case study. Our model predicts that female C. turbinata should generally start foraging at lower levels of energy reserves (i.e., should be less bold) during midday when predators are most abundant. We also find that individuals' foraging efficacy determines whether daily rates of encounters with predators or prey more strongly influences boldness under high risk. The qualitative model predictions are robust to variation in our parameter estimates and likely apply to a wide range of taxa. The predictions are also consistent with observed patterns of foraging behavior under both laboratory and field conditions. We discuss the implications of our study for understanding the evolution of daily rhythms and the importance of model predictions for interpreting empirical studies and generating additional hypotheses regarding behavioral evolution.

RESPOND: a programme to prevent secondary falls in older people presenting to the emergency department with a fall: protocol for an economic evaluation.

BACKGROUND: Falls remain common for community-dwelling older people and impose a substantial economic burden to the healthcare system. RESPOND is a novel falls prevention programme that aims to reduce secondary falls and fall injuries among older people who present to a hospital emergency department (ED) with a fall. The present protocol describes a prospective economic evaluation examining the incremental cost-effectiveness of the RESPOND programme, compared with usual care practice, from the Australian health system perspective. METHODS AND DESIGN: This economic evaluation will recruit 528 participants from two major tertiary hospital EDs in Australia and will be undertaken alongside a multisite randomised controlled trial. Outcome and costing data will be collected for all participants over the 12-month trial. It will compare the RESPOND falls prevention programme with usual care practice (current community-based falls prevention practices) to determine its incremental cost-effectiveness according to three intermediate clinical outcomes: (1) falls prevented, (2) fall injuries prevented and (3) injurious falls prevented. In addition, utilities will be derived from a generic quality-of-life measure (EQ-5D-5L) and used to calculate the 'incremental cost per quality-adjusted life years gained'. DISCUSSION: The results of this study will provide healthcare decision makers with evidence to assist with setting spending thresholds for preventive health programmes and inform selection of emergency and community service models of care. TRIAL REGISTRATION NUMBER: The protocol for this study is registered with the Australian New Zealand Clinical Trials Registry (ACTRN12614000336684); Pre-results.

Spatio-temporal analysis of foraging behaviors of Anelosimus studiosus utilizing mathematical modeling of multiple spider interaction on a cooperative web.

In this paper, we develop a model for predation movements of a subsocial spider species, Anelosimus studiosus. We expand on a previous model to include multiple spider interaction on the web as well as a latency period during predation. We then use the model to test different spatial configurations to determine the optimal spacing of spiders within a colony for successful capture during predation. The model simulations indicate that spiders uniformly spacing out along the edge of the web results in the most successful predation strategy. This is similar to the behavior observed by Ross (2013) in which it was determined to be statistically significant that during certain times of the day, spiders were positioned along the edge more than expected under complete spatial randomness.

Frailty and post-operative outcomes in older surgical patients: a systematic review.

BACKGROUND: As the population ages, increasing numbers of older adults are undergoing surgery. Frailty is prevalent in older adults and may be a better predictor of post-operative morbidity and mortality than chronological age. The aim of this review was to examine the impact of frailty on adverse outcomes in the 'older old' and 'oldest old' surgical patients. METHODS: A systematic review was undertaken. Electronic databases from 2010 to 2015 were searched to identify articles which evaluated the relationship between frailty and post-operative outcomes in surgical populations with a mean age of 75 and older. Articles were excluded if they were in non-English languages or if frailty was measured using a single marker only. Demographic data, type of surgery performed, frailty measure and impact of frailty on adverse outcomes were extracted from the selected studies. Quality of the studies and risk of bias was assessed by the Epidemiological Appraisal Instrument. RESULTS: Twenty-three studies were selected for the review and they were assessed as medium to high quality. The mean age ranged from 75 to 87 years, and included patients undergoing cardiac, oncological, general, vascular and hip fracture surgeries. There were 21 different instruments used to measure frailty. Regardless of how frailty was measured, the strongest evidence in terms of numbers of studies, consistency of results and study quality was for associations between frailty and increased mortality at 30 days, 90 days and one year follow-up, post-operative complications and length of stay. A small number of studies reported on discharge to institutional care, functional decline and lower quality of life after surgery, and also found a significant association with frailty. CONCLUSION: There was strong evidence that frailty in older-old and oldest-old surgical patients predicts post-operative mortality, complications, and prolonged length of stay. Frailty assessment may be a valuable tool in peri-operative assessment. It is possible that different frailty tools are best suited for different acuity and type of surgical patients. The association between frailty and return to pre-morbid function, discharge destination, and quality of life after surgery warrants further research.

Changes in quality of life associated with fragility fractures: Australian arm of the International Cost and Utility Related to Osteoporotic Fractures Study (AusICUROS).

UNLABELLED: We investigated change in health-related quality of life due to fracture in Australian adults aged over 50 years. Fractures reduce quality of life with the loss sustained at least over 12 months. At a population level, the loss was equivalent to 65 days in full health per fracture. PURPOSE: We aimed to quantify the change in health-related quality of life (HRQoL) that occurred as a consequence of a fracture using the EQ-5D-3 L questionnaire. METHODS: Adults aged ≥50 years with a low to moderate energy fracture were recruited from eight study centres across Australia. This prospective study included an 18-month follow-up of participants recruited within 2 weeks of a fracture (hip, wrist, humerus, vertebral and ankle). Information collected at baseline and 4, 12 and 18 months included characteristics of participants such as income level, education and prior fracture status. At 12 months post-fracture, the cumulative loss of quality of life was estimated using multivariate regression analysis to identify the predictors of HRQoL loss. RESULTS: Mean HRQoL for all participants before fracture was 0.86, with wrist fracture having the highest pre-fracture HRQoL (0.90), while vertebral fracture had the lowest (0.80). HRQoL declined to 0.42 in the immediate post-fracture period. Only participants with a wrist, humerus or ankle fracture returned to their pre-fracture HRQoL after 18 months. An increased loss of HRQoL over 12 months was associated with HRQoL prior to the fracture, hospitalisation, education and fracture site. The multiple regression explained 30 % of the variation in the cumulative HRQoL loss at 12 months post-fracture for all fractures. CONCLUSION: Low to moderate energy fractures reduce HRQoL, and this loss is sustained for at least 12 months or, in the case of hip and spine fractures, at least 18 months. At a population level, this represents an average loss of 65 days in full health per fragility fracture. This significant burden reinforces the need for cost-effective fracture prevention strategies.

Effectiveness of a multidisciplinary team approach to the prevention of readmission for acute glycaemic events.

AIMS: To describe the effect of a combined diabetes specialist/mental health team approach to prevent readmissions for acute glycaemic events among patients with diabetes. METHODS: Consecutive patients with diabetes, readmitted to a single hospital for an acute glycaemic condition, were offered one or more diabetes (including assessment, education, medication, technology use and intensive support) and mental health (including assessment, training and therapies) interventions. The pilot service took place over 11 months, with the preceding 24 months and subsequent 8 months serving as control periods. RESULTS: Of the 58 patients admitted, 50 had Type 1 diabetes and were from within the hospital catchment area, and were discharged home. Of these, 32 (64%) had a pre-existing mental health issue and 14 (28%) had a complex social situation. In all, 96% of patients were met as an inpatient by a team member, and 94% accepted at least one intervention. The mean ±sd number of admissions per patient/month dropped from 0.12 ± 0.10 to 0.05 ± 0.10 (P < 0.001) during the intervention, increasing, once the intervention ended, to 0.16 ± 0.36 (P = 0.002). The mean ± sd length of stay similarly decreased and increased (0.6 ± 0.9 to 0.2 ± 0.7 days; P < 0.001 to 0.006) to 0.6 ± 1.4 days (P = 0.003) per patient/month) across the three periods, as did the mean ±sd tariff paid per patient/month (£258.0 ± 374.0 vs £92.1 ± 245.0 vs £287.3 ± 563.8; P < 0.001 and P = 0.018, respectively). The mean ± sd HbA1c level dropped from 99 ± 22 to 92 ± 24 mmol/mol (11.2 ± 4.2% vs 10.6 ± 4.3%; P = 0.014) but did not increase after the intervention [89 ± 26 mmol/mol (10.4 ± 4.5%)]. CONCLUSIONS: The cost and long-term risks of hospitalization among patients with Type 1 diabetes and recurrent admissions can be reduced by a combined specialist diabetes/mental health team approach.

An excess of cosmic ray electrons at energies of 300-800 GeV.

Galactic cosmic rays consist of protons, electrons and ions, most of which are believed to be accelerated to relativistic speeds in supernova remnants. All components of the cosmic rays show an intensity that decreases as a power law with increasing energy (for example as E(-2.7)). Electrons in particular lose energy rapidly through synchrotron and inverse Compton processes, resulting in a relatively short lifetime (about 10(5) years) and a rapidly falling intensity, which raises the possibility of seeing the contribution from individual nearby sources (less than one kiloparsec away). Here we report an excess of galactic cosmic-ray electrons at energies of approximately 300-800 GeV, which indicates a nearby source of energetic electrons. Such a source could be an unseen astrophysical object (such as a pulsar or micro-quasar) that accelerates electrons to those energies, or the electrons could arise from the annihilation of dark matter particles (such as a Kaluza-Klein particle with a mass of about 620 GeV).

Expected and unexpected imaging features after oesophageal cancer treatment.

Oesophageal cancer is a leading cause of cancer-related mortality worldwide. Various surgical procedures are performed for oesophageal malignancies. The advancement in surgical technique as well as post-surgical care has significantly reduced the complication rate. However, various complications may still occur either immediately (infection, aspiration, anastomotic leak, ischaemic necrosis, fistulae, chylothorax) or late after surgery (strictures, tumour recurrence, fistulae, delayed emptying). The palliative treatment options of radiotherapy and stent placement may also be accompanied by complications, such as radiation necrosis, stricture, and stent ingrowth by the tumour. This review presents the expected post-surgical appearance as well as various complications after surgical and non-surgical treatments of oesophageal cancer.

Reduced activity of AMP-activated protein kinase protects against genetic models of motor neuron disease.

A growing body of research indicates that amyotrophic lateral sclerosis (ALS) patients and mouse models of ALS exhibit metabolic dysfunction. A subpopulation of ALS patients possesses higher levels of resting energy expenditure and lower fat-free mass compared to healthy controls. Similarly, two mutant copper zinc superoxide dismutase 1 (mSOD1) mouse models of familial ALS possess a hypermetabolic phenotype. The pathophysiological relevance of the bioenergetic defects observed in ALS remains largely elusive. AMP-activated protein kinase (AMPK) is a key sensor of cellular energy status and thus might be activated in various models of ALS. Here, we report that AMPK activity is increased in spinal cord cultures expressing mSOD1, as well as in spinal cord lysates from mSOD1 mice. Reducing AMPK activity either pharmacologically or genetically prevents mSOD1-induced motor neuron death in vitro. To investigate the role of AMPK in vivo, we used Caenorhabditis elegans models of motor neuron disease. C. elegans engineered to express human mSOD1 (G85R) in neurons develops locomotor dysfunction and severe fecundity defects when compared to transgenic worms expressing human wild-type SOD1. Genetic reduction of aak-2, the ortholog of the AMPK α2 catalytic subunit in nematodes, improved locomotor behavior and fecundity in G85R animals. Similar observations were made with nematodes engineered to express mutant tat-activating regulatory (TAR) DNA-binding protein of 43 kDa molecular weight. Altogether, these data suggest that bioenergetic abnormalities are likely to be pathophysiologically relevant to motor neuron disease.

Enhanced imaging of developed fingerprints using mass spectrometry imaging.

Latent fingermarks are invisible to the naked eye and normally require the application of a chemical developer followed by an optical imaging step in order to visualize the ridge detail. If the finger deposition is poor, or the fingermark is aged, it can sometimes be difficult to produce an image of sufficient quality for identification. In this work, we show for the first time how mass spectrometry imaging (in this case time-of-flight secondary ion mass spectrometry, ToF-SIMS) can be used to enhance the quality of partially recovered fingermarks. We show three examples of how chemical imaging can be used to obtain enhanced images of fingermarks deposited on aluminium foil, glass and the handle of a hand grenade compared with conventional development techniques.

Cross-cultural evaluation of the French version of the LEIPAD, a health-related quality of life instrument for use in the elderly living at home.

PURPOSE: To cross-culturally adapt a French version of the LEIPAD, a self-administered questionnaire assessing the health-related quality of life (HRQoL) in adults aged 65 years and over living at home, and to evaluate its psychometric properties. METHODS: After having translated LEIPAD in accordance with guidelines, we studied psychometric properties: reliability and construct validity-factor analysis, relationships between items and scales, internal consistency, concurrent validity with the Medical Outcome Study Short-Form 36 and known-groups validity. RESULTS: The results obtained in a sample of 195 elderly from the general population showed very good acceptability, with response rates superior to 93 %. Exploratory factor analysis extracted eight factors providing a multidimensionality structure with five misclassifications of items in the seven theoretical scales. Good internal consistency (Cronbach's alpha ranging from 0.73 and 0.86) and strong test-retest reliability (ICCs higher than 0.80 for six scales and 0.70 for one) were demonstrated. Concurrent validity with the SF-36 showed small to strong expected correlations. CONCLUSION: This first evaluation of the French version of LEIPAD's psychometric properties provides evidence in construct validity and reliability. It would allow HRQoL assessment in clinical and common practice, and investigators would be able to take part in national and international research projects.

Females without reflux symptoms or gastroesophageal reflux disease have less distal esophageal acid exposure than males without reflux symptoms or gastroesophageal reflux disease.

Ambulatory 24-hour esophageal pH monitoring is the gold standard examination to assess esophageal acid exposure. Gender-related variation is a well-recognized physiologic phenomenon in health and disease. To date, limited gender-specific 24-hour esophageal pH monitoring data are available. The aim of this study was to obtain values of esophageal pH monitoring in males and females without reflux symptoms or gastroesophageal reflux disease (GERD) to determine if gender variation exists in esophageal acid exposure among individuals without these factors. Twenty-four-hour dual esophageal pH monitoring was performed in male and female volunteers without reflux symptoms or GERD. Values for total number of reflux episodes, episodes longer than 5 minutes, total reflux time in minutes, % time with pH below 4, and longest reflux episode in the proximal/distal esophagus were obtained and recorded for both groups. The distal channel was placed 5 cm and proximal channel 15 cm above the manometrically determined lower esophageal sphincter. Means were compared using an independent sample t-test. Sixty-seven males and 69 females were enrolled. All subjects completed esophageal 24-hour pH monitoring without difficulty. There was no age or body mass difference between groups. Females had significantly fewer reflux episodes at both esophageal measuring sites and, significantly less total reflux time and % time with pH below 4 in the distal esophagus than males. All other parameters were similar. Significant gender-related differences exist in esophageal acid exposure, especially in the distal esophagus in individuals without reflux symptoms or GERD. These differences underscore the need for gender-specific reference values for 24-hour pH monitoring, allowing for an accurate evaluation of esophageal acid exposure in symptomatic patients.