Sociodemographic and Lifestyle Factors and Epigenetic Aging in US Young Adults: NIMHD Social Epigenomics Program.

Importance: Epigenetic clocks represent molecular evidence of disease risk and aging processes and have been used to identify how social and lifestyle characteristics are associated with accelerated biological aging. However, most research is based on samples of older adults who already have measurable chronic disease. Objective: To investigate whether and how sociodemographic and lifestyle characteristics are associated with biological aging in a younger adult sample across a wide array of epigenetic clock measures. Design, Setting, and Participants: This cohort study was conducted using data from the National Longitudinal Study of Adolescent to Adult Health, a US representative cohort of adolescents in grades 7 to 12 in 1994 followed up for 25 years to 2018 over 5 interview waves. Participants who provided blood samples at wave V (2016-2018) were analyzed, with samples tested for DNA methylation (DNAm) in 2021 to 2024. Data were analyzed from February 2023 to May 2024. Exposure: Sociodemographic (sex, race and ethnicity, immigrant status, socioeconomic status, and geographic location) and lifestyle (obesity status by body mass index [BMI] in categories of reference range or underweight [<25], overweight [25 to <30], obesity [30 to <40], and severe obesity [≥40]; exercise level; tobacco use; and alcohol use) characteristics were assessed. Main Outcome and Measure: Biological aging assessed from banked blood DNAm using 16 epigenetic clocks. Results: Data were analyzed from 4237 participants (mean [SD] age, 38.4 [2.0] years; percentage [SE], 51.3% [0.01] female and 48.7% [0.01] male; percentage [SE], 2.7% [<0.01] Asian or Pacific Islander, 16.7% [0.02] Black, 8.7% [0.01] Hispanic, and 71.0% [0.03] White). Sociodemographic and lifestyle factors were more often associated with biological aging in clocks trained to estimate morbidity and mortality (eg, PhenoAge, GrimAge, and DunedinPACE) than clocks trained to estimate chronological age (eg, Horvath). For example, the ß for an annual income less than $25 000 vs $100 000 or more was 1.99 years (95% CI, 0.45 to 3.52 years) for PhenoAgeAA, 1.70 years (95% CI, 0.68 to 2.72 years) for GrimAgeAA, 0.33 SD (95% CI, 0.17 to 0.48 SD) for DunedinPACE, and -0.17 years (95% CI, -1.08 to 0.74 years) for Horvath1AA. Lower education, lower income, higher obesity levels, no exercise, and tobacco use were associated with faster biological aging across several clocks; associations with GrimAge were particularly robust (no college vs college or higher: ß = 2.63 years; 95% CI, 1.67-3.58 years; lower vs higher annual income: <$25 000 vs ≥$100 000: ß = 1.70 years; 95% CI, 0.68-2.72 years; severe obesity vs no obesity: ß = 1.57 years; 95% CI, 0.51-2.63 years; no weekly exercise vs ≥5 bouts/week: ß = 1.33 years; 95% CI, 0.67-1.99 years; current vs no smoking: ß = 7.16 years; 95% CI, 6.25-8.07 years). Conclusions and Relevance: This study found that important social and lifestyle factors were associated with biological aging in a nationally representative cohort of younger adults. These findings suggest that molecular processes underlying disease risk may be identified in adults entering midlife before disease is manifest and inform interventions aimed at reducing social inequalities in heathy aging and longevity.

The Sociodemographic and Lifestyle Correlates of Epigenetic Aging in a Nationally Representative U.S. Study of Younger Adults.

Importance: Epigenetic clocks represent molecular evidence of disease risk and aging processes and have been used to identify how social and lifestyle characteristics are associated with accelerated biological aging. However, most of this research is based on older adult samples who already have measurable chronic disease. Objective: To investigate whether and how sociodemographic and lifestyle characteristics are related to biological aging in a younger adult sample across a wide array of epigenetic clock measures. Design: Nationally representative prospective cohort study. Setting: United States (U.S.). Participants: Data come from the National Longitudinal Study of Adolescent to Adult Health, a national cohort of adolescents in grades 7-12 in U.S. in 1994 followed for 25 years over five interview waves. Our analytic sample includes participants followed-up through Wave V in 2016-18 who provided blood samples for DNA methylation (DNAm) testing (n=4237) at Wave V. Exposure: Sociodemographic (sex, race/ethnicity, immigrant status, socioeconomic status, geographic location) and lifestyle (obesity status, exercise, tobacco, and alcohol use) characteristics. Main Outcome: Biological aging assessed from blood DNAm using 16 epigenetic clocks when the cohort was aged 33-44 in Wave V. Results: While there is considerable variation in the mean and distribution of epigenetic clock estimates and in the correlations among the clocks, we found sociodemographic and lifestyle factors are more often associated with biological aging in clocks trained to predict current or dynamic phenotypes (e.g., PhenoAge, GrimAge and DunedinPACE) as opposed to clocks trained to predict chronological age alone (e.g., Horvath). Consistent and strong associations of faster biological aging were found for those with lower levels of education and income, and those with severe obesity, no weekly exercise, and tobacco use. Conclusions and Relevance: Our study found important social and lifestyle factors associated with biological aging in a nationally representative cohort of younger-aged adults. These findings indicate that molecular processes underlying disease risk can be identified in adults entering midlife before disease is manifest and represent useful targets for interventions to reduce social inequalities in heathy aging and longevity. Key Points: Question: Are epigenetic clocks, measures of biological aging developed mainly on older-adult samples, meaningful for younger adults and associated with sociodemographic and lifestyle characteristics in expected patterns found in prior aging research?Findings: Sociodemographic and lifestyle factors were associated with biological aging in clocks trained to predict morbidity and mortality showing accelerated aging among those with lower levels of education and income, and those with severe obesity, no weekly exercise, and tobacco use.Meaning: Age-related molecular processes can be identified in younger-aged adults before disease manifests and represent potential interventions to reduce social inequalities in heathy aging and longevity.

EPAS1 expression contributes to maintenance of the primordial follicle pool in the mouse ovary.

Oxygen availability can have profound effects on cell fate decisions and survival, in part by regulating expression of hypoxia-inducible factors (HIFs). In the ovary, HIF expression has been characterised in granulosa cells, however, any requirement in oocytes remains relatively undefined. Here we developed a Hif2a/Epas1 germline-specific knockout mouse line in which females were fertile, however produced 40% fewer pups than controls. No defects in follicle development were detected, and quality of MII oocytes was normal, as per assessments of viability, intracellular reactive oxygen species, and spindle parameters. However, a significant diminishment of the primordial follicle pool was evident in cKO females that was attributed to accelerated follicle loss from postnatal day 6 onwards, potentially via disruption of the autophagy pathway. These data demonstrate the importance of HIF signalling in oocytes, particularly at the primordial follicle stage, and lend to the importance of controlling oxygen tension in the development of in vitro growth and maturation approaches for assisted reproduction.

Mechanochromic polymer blends made with an excimer-forming telechelic sensor molecule.

The ability to monitor mechanical stresses and strains in polymers via an optical signal enables the investigation of deformation processes in such materials and is technologically useful for sensing damage and failure in critical components. We show here that this can be achieved by simply blending polymers of interest with a small amount of a mechanochromic luminescent additive (Py-PEB) that can be accessed in one step by end-functionalizing a telechelic poly(ethylene-co-butylene) (PEB) with excimer-forming pyrenes. Py-PEB is poorly miscible with polar polymers, such as poly(ε-caprolactone) and poly(urethane), so that blends undergo microphase separation even at low additive concentrations (0.1-1 wt%), and the emission is excimer-dominated. Upon deformation, the ratio of excimer-to-monomer emission intensity decreases in response to the applied stress or strain. The approach appears to be generalizable, although experiments with poly(isoprene) show that it is not universal and that the (in)solubility of the additive in the polymer must be carefully tuned.

From Sheltered in Place to Thriving in Place: Pandemic Places of Aging.

BACKGROUND AND OBJECTIVES: Response to the coronavirus disease 2019 pandemic required rapid changes to physical, social, and technological environments. There is a need to understand how independent-living older adults are adapting to pandemic-borne transformations of place and how environmental factors may shape experiences of aging well in the context of a public health emergency response. RESEARCH DESIGN AND METHODS: We conducted a photovoice study to examine the characteristics associated with aging in place. Our study investigated how independent-living older adults characterized aging in a "right" place approximately 1 year after the onset of the pandemic. RESULTS: Six themes categorized into 2 groups capture how older adults describe a "right" place to age. The first category, "places as enactors of identity and belonging," describes the significance of places contributing to intimate relationships, social connections, and a sense of personal continuity. The second category, "places as facilitators of activities and values," recognizes environments that promote health, hobbies, goals, and belief systems. Participants reported modifying their daily living environments with increased use of technology and more time outdoors. DISCUSSION AND IMPLICATIONS: Our findings emphasize older adults' active engagement with place and strategies used to maintain healthy aging despite public health restrictions. The results also identify place-based characteristics that may help overcome stressful circumstances from older adults' perspectives. These findings inform pathways to pursue to facilitate resiliency for aging in place.

The hypoxia-inducible factor EPAS1 is required for spermatogonial stem cell function in regenerative conditions.

In this study we explored the role of hypoxia and the hypoxia-inducible transcription factor EPAS1 in regulating spermatogonial stem cell (SSC) function in the mouse testis. We have demonstrated that SSCs reside in hypoxic microenvironments in the testis through utilization of the oxygen-sensing probe pimonidazole, and by confirming the stable presence of EPAS1, which is degraded at >5% O2. Through the generation of a germline-specific Epas1 knockout mouse line, and through modulation of EPAS1 levels in primary cultures of spermatogonia with the small drug molecule Daprodustat, we have demonstrated that EPAS1 is required for robust SSC function in regenerative conditions (post-transplantation and post-chemotherapy), via the regulation of key cellular processes such as metabolism. These findings shed light on the relationship between hypoxia and male fertility and will potentially facilitate optimization of in vitro culture conditions for infertility treatment pipelines using SSCs, such as those directed at pediatric cancer survivors.

Sleep Duration Differences by Education from Middle to Older Adulthood: Does Employment Stratification Contribute to Gendered Leveling?

Sleep duration changes across the life course and differs by education in the United States. However, little research has examined whether educational differences in sleep duration change over age-or whether sleep duration trajectories over age differ by education. This study uses a life course approach to analyze American Time Use Survey data (N = 60,908), examining how educational differences in weekday sleep duration change from middle to older adulthood (ages 40-79). For men only, differences in total sleep time between individuals with less than a high school degree and those with more education converge in older adulthood. Results suggest that this leveling is explained by decreasing educational stratification in work hours as men enter older adulthood. Findings highlight the importance of employment for shaping gendered socioeconomic differences in sleep and demonstrate differences by education in how sleep duration changes over age, with possible implications for health disparities.

Retinal Responses to Visual Stimuli in Interphotoreceptor Retinoid Binding-Protein Knock-Out Mice.

Interphotoreceptor retinoid-binding protein (IRBP) is an abundant glycoprotein in the subretinal space bound by the photoreceptor (PR) outer segments and the processes of the retinal pigmented epithelium (RPE). IRBP binds retinoids, including 11-cis-retinal and all-trans-retinol. In this study, visual function for demanding visual tasks was assessed in IRBP knock-out (KO) mice. Surprisingly, IRBP KO mice showed no differences in scotopic critical flicker frequency (CFF) compared to wildtype (WT). However, they did have lower photopic CFF than WT. IRBP KO mice had reduced scotopic and photopic acuity and contrast sensitivity compared to WT. IRBP KO mice had a significant reduction in outer nuclear layer (ONL) thickness, PR outer and inner segment, and full retinal thickness (FRT) compared to WT. There were fewer cones in IRBP KO mice. Overall, these results confirm substantial loss of rods and significant loss of cones within 30 days. Absence of IRBP resulted in cone circuit damage, reducing photopic flicker, contrast sensitivity, and spatial frequency sensitivity. The c-wave was reduced and accelerated in response to bright steps of light. This result also suggests altered retinal pigment epithelium activity. There appears to be a compensatory mechanism such as higher synaptic gain between PRs and bipolar cells since the loss of the b-wave did not linearly follow the loss of rods, or the a-wave. Scotopic CFF is normal despite thinning of ONL and reduced scotopic electroretinogram (ERG) in IRBP KO mice, suggesting either a redundancy or plasticity in circuits detecting (encoding) scotopic flicker at threshold even with substantial rod loss.

Microscopic strain mapping in polymers equipped with non-covalent mechanochromic motifs.

The mechanical failure of polymers remains challenging to understand and predict, as it often involves highly localised phenomena that cannot be probed with bulk characterisation techniques. Here, we present a generalisable protocol based on optical microscopy, tensile testing, and image processing that permits the spatially resolved interrogation of mechanical deformation at the molecular level around defects in mechanophore-containing polymers. The approach can be applied to a broad range of polymeric materials, mechanophores, and deformation scenarios.

Aging in Place Through the COVID-19 Pandemic: Perspectives from Aging Service Providers.

Formal and informal networks of resources are critical to supporting the growing number of older adults aging in place (AIP). Data are needed from aging-service providers about assets and barriers that impact their abilities to support AIP during the pandemic, as well as emergent needs resulting from response measures. A series of World Café workshops were conducted with aging-service providers in Salt Lake City, Utah, to understand supportive factors, service gaps, and future needs. Novel domains to support AIP in the context of the pandemic were identified: digital access and literacy, social isolation and mental health, and emergency preparedness. Issues related to access, equity, and affordability were identified as overarching themes across domains. Issues reflect concern over how the pandemic exacerbated socioeconomic and cultural disparities impacting older adults who benefit from aging services. Networks of advocacy and support are needed to bolster resources for older adults, caregivers, and aging-service providers.

Hierarchically Structured Deformation-Sensing Mechanochromic Pigments.

Mechanochromic materials alter their color in response to mechanical force and are useful for both fundamental studies and practical applications. Several approaches are used to render polymers mechanochromic, but they generally suffer from limitations in sensing range, capacity to provide quantitative information, and their capability to enable broad and simple implementation. Here, is it reported that these problems can be overcome by combining photonic structures, which alter their reflection upon deformation, with covalent mechanophores, whose spectral properties change upon mechanically induced bond scission, in hierarchically structured mechanochromic pigments. This is achieved by synthesizing microspheres consisting of an elastic polymer with spiropyran-based cross-links and non-close-packed silica nanoparticles. A strain of less than 1% can be detected in a shift of the reflection band from the photonic structure, while the onset strain for the conversion of the spiropyran into fluorescent merocyanine ranges from 30% to 70%, creating a broad strain detection range. The two responses are tailorable and synergistic, permitting the activation strain for the mechanophore response to be tuned. The mechano-sensing photonic pigments are demonstrated to be readily incorporated into different polymeric materials of interest and quantitatively probe spatially heterogeneous deformations over a large strain range.

Systematics of the Central African Spiny Reed Frog Afrixalus laevis (Anura: Hyperoliidae), with the description of two new species from the Albertine Rift.

The geographically widespread species Afrixalus laevis (Anura: Hyperoliidae) currently has a disjunct distribution in western Central Africa (Cameroon, Equatorial Guinea, Gabon, and possibly adjacent countries) and the area in and near the Albertine Rift in eastern Democratic Republic of the Congo and neighboring countries. At least two herpetologists have previously suggested that these disjunct populations represent distinct species, and herein, we utilize an integrative taxonomic approach with molecular and morphological data to reconcile the taxonomy of these spiny reed frogs. We sequenced 1554 base pairs of the 16S and RAG1 genes from 34 samples of A. laevis and one sample of A. orophilus (sympatric with eastern populations of A. laevis), and combined these data with previously sequenced GenBank Afrixalus samples via the bioinformatics toolkit SuperCRUNCH. Phylogenetic trees, dated phylogenetic analyses, and species-delimitation analyses were generated with RAxML, BEAST, and BPP, respectively. Eleven mensural characters were taken from multiple specimens of A. laevis and A. orophilus, and compared with paired t-tests and analyses of covariance. These combined results suggested populations of A. laevis in western Central Africa (Cameroon and Bioko Island, Equatorial Guinea) represent one species, whereas populations from the Albertine Rift and nearby forests represent two undescribed taxa that are sister to A. dorsimaculatus. The two new species (A. lacustris sp. nov. and A. phantasma sp. nov.) are distinguished by our phylogenetic and species-delimitation analyses, significant differences in several mensural characters, qualitative morphological differences, and by their non-overlapping elevational distribution.

Paranormal experiences, sensory-processing sensitivity, and the priming of pareidolia.

This investigation tested the effect of priming on pareidolia (the hearing of illusory words in ambiguous stimuli). Participants (41 women, 20 men, mean age 29.95 years) were assigned to primed (n = 30) or unprimed (n = 31) groups: the former were told the study was of 'purported ghosts voices', the latter 'voices in noisy environments.' Participants were assessed for perception of human voices within recordings of purported electronic voice phenomena (EVP), degraded human speech, normal human speech, and white noise. The primed group had significantly higher perception of voices within EVPs than in degraded speech, this difference was not found for unprimed participants. In contrast to the previous use of this design, the primed group did not have higher perception of voices in EVPs and degraded speech than did the unprimed group. The Aesthetic Sensitivity dimension of the Highly Sensitive Person Scale (HSPS) was associated with detection of degraded stimuli, but not with accuracy of stimulus identification. HSPS score was related to lifetime reporting of anomalous and paranormal experiences. This study partially replicates a paranormal priming effect and shows relationships between HSPS and detection of ambiguous stimuli and anomalous and paranormal experiences.

Changes in Attachment to Parents and Peers and Relations With Mental Health During the COVID-19 Pandemic.

Using a longitudinal design, we examined changes in parent and peer attachment among college students, and their predictive and protective roles in relation to mental health problems during the COVID-19 pandemic. College students (N = 106) rated their parent and peer attachment, and self-reported anxiety, loneliness, and depressive symptoms 1 year before and during the pandemic. Participants also rated the impact of COVID-19 related stressors (CRS). Results demonstrate significant increases in loneliness and depression and a decrease in peer attachment security during the pandemic. Increases in peer attachment security were negatively correlated with loneliness during the pandemic. Parent attachment buffered the relationship between the impact of CRS and mental health problems during the pandemic. Guided by the integrated framework from attachment theory and life course theory, the current study discussed findings and practices regarding the important role of attachment for college students and their adjustment to the pandemic.

A slicing mechanism facilitates host entry by plant-pathogenic Phytophthora.

Phytophthora species, classified as oomycetes, are among the most destructive plant pathogens worldwide and pose a substantial threat to food security. Plant pathogens have developed various methods to breach the cuticle and walls of plant cells. For example, plant-pathogenic fungi use a 'brute-force' approach by producing a specialized and fortified invasion organ to generate invasive pressures. Unlike in fungi, the biomechanics of host invasion in oomycetes remains poorly understood. Here, using a combination of surface-deformation imaging, molecular-fracture sensors and modelling, we find that Phytophthora infestans, Phytophthora palmivora and Phytophthora capsici slice through the plant surface to gain entry into host tissues. To distinguish this mode of entry from the brute-force approach of fungi that use appressoria, we name this oomycete entry without appressorium formation 'naifu' invasion. Naifu invasion relies on polarized, non-concentric, force generation onto the surface at an oblique angle, which concentrates stresses at the site of invasion to enable surface breaching. Measurements of surface deformations during invasion of artificial substrates reveal a polarized mechanical geometry that we describe using a mathematical model. We confirm that the same mode of entry is used on real hosts. Naifu invasion uses actin-mediated polarity, surface adherence and turgor generation to enable Phytophthora to invade hosts without requiring specialized organs or vast turgor generation.

Body mass and the epidemic of chronic inflammation in early mid-adulthood.

OBJECTIVES: Chronic inflammation is a potentially important mechanism through which social inequalities may contribute to health inequalities over the life course. Excess body fat contributes to chronic inflammation, and younger adults in the US have come of age during a pronounced secular increase in body mass index (BMI). We aim to document levels of chronic inflammation in a nationally representative sample of 33-to-44 year-old adults in the US, and to describe associations with BMI, race/ethnicity, and education. METHODS: High sensitivity C-reactive protein (CRP) was measured in Wave V (2016-18) of the National Longitudinal Study of Adolescent to Adult Health, with complete data available for 4349 participants. Sex-stratified weighted regression models were implemented to investigate CRP in association with education, race/ethnicity, and BMI. RESULTS: Geometric mean CRP was 1.9 mg/L, and 35.4% of the sample had CRP >3 mg/L. Females had significantly higher CRP than males. Body mass index was a strong positive predictor of CRP, and education level was negatively associated with CRP. Associations between education and CRP were substantially attenuated after adjusting for BMI. High risk CRP increased linearly with BMI even among the obese: 87.0 percent of females and 74.1 percent of males with class 3 obesity (BMI ≥40) were predicted to have high risk CRP > 3 mg/L. CONCLUSIONS: The obesity epidemic is producing an epidemic of chronic inflammation in early mid-adulthood in the US. Strong associations between BMI and chronic inflammation portend high risk for future disease-and inequitable distribution of disease-as the cohort ages.

Bedtime Schedules and Sleep Regulation among Children of Incarcerated Parents.

OBJECTIVES: To investigate variation by parental incarceration history in the bedtime schedules set for elementary-age children and whether sleep was effectively regulated. STUDY DESIGN: We ran multivariate regression models estimating the relationship between parental incarceration and 6 measures of bedtime schedules and sleep regulation. Our sample included 9-year-olds in the Fragile Families and Child Wellbeing Study (n = 3246), a survey of children born in large US cities between 1998 and 2000 that has an oversample of unmarried mothers. RESULTS: Children's bedtime schedules did not differ at a statistically significant level by parental incarceration history, but children of ever- vs never-incarcerated fathers had lower odds of consistently adhering to a set bedtime. Children of ever-incarcerated fathers also slept for less time on average than did children of never-incarcerated fathers, and they had lower odds of obtaining sufficient sleep. Bedtime consistency partly mediated the association between paternal incarceration and total sleep duration. CONCLUSIONS: Although caregivers set appropriate bedtime schedules for children of ever-incarcerated fathers, consistent adherence to those schedules may be particularly challenging given the structural hardships of paternal incarceration. Policymakers, researchers, and practitioners working to improve sleep among children of incarcerated fathers should focus on helping families to develop strategies for implementing bedtime schedules as consistently and effectively as possible.

Failure to replicate a robust Down syndrome advantage for maternal well-being.

BACKGROUND: Family members caring for children with intellectual disability (ID) routinely report heightened levels of psychological distress. However, families of children with Down syndrome typically report better outcomes (known as the Down syndrome advantage). We examined whether the Down syndrome advantage would be present for maternal psychological distress, impact of caregiving, life satisfaction and perceived positive impact of the child with ID when controlling for external variables. METHODS: Mothers of children with Down syndrome (n = 111) and mothers of children with ID of mixed aetiologies (n = 196) completed measures about their own mental health, perceived impact of caregiving, life satisfaction and perceived positive impact of their child on themselves and the family unit. RESULTS: A series of group comparisons revealed small to moderate differences supporting the presence of a putative Down syndrome advantage in relation to personal maternal well-being outcomes. However, when child-related characteristics and external variables were controlled, the Down syndrome advantage was no longer present, with reduced, small effect sizes observed for all maternal outcomes. CONCLUSIONS: Initial group differences in psychological distress and life satisfaction were largely associated with family poverty, indicating that the Down syndrome advantage may be less robust than previously thought. Future research should seek to move beyond examining the existence of the putative Down syndrome advantage and focus on how families of children with Down syndrome experience family life, including longitudinal research exploring responses to life cycle and transition challenges.

Mechanochromism in Structurally Colored Polymeric Materials.

Mechanochromic effects in structurally colored materials are the result of deformation-induced changes to their ordered nanostructures. Polymeric materials which respond in this way to deformation offer an attractive combination of characteristics, including continuous strain sensing, high strain resolution, and a wide strain-sensing range. Such materials are potentially useful for a wide range of applications, which extend from pressure-sensing bandages to anti-counterfeiting devices. Focusing on the materials design aspects, recent developments in this field are summarized. The article starts with an overview of different approaches to achieve mechanochromic effects in structurally colored materials, before the physical principles governing the interaction of light with each of these materials types are summarized. Diverse methodologies to prepare these polymers are then discussed in detail, and where applicable, naturally occurring materials that inspired the design of artificial systems are discussed. The capabilities and limitations of structurally colored materials in reporting and visualizing mechanical deformation are examined from a general standpoint and also in more specific technological contexts. To conclude, current trends in the field are highlighted and possible future opportunities are identified.

Bioaerosol sampling of a ventilated patient with COVID-19.

Bioaerosol samples were collected in an airborne infection isolation room, bathroom, and anteroom of a ventilated patient with coronavirus disease 2019. Twenty-eight samples were negative for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleic acid, possibly due to the patient being on a closed-circuit ventilator or the efficiency of the air exchanges in the room.