Regulation of rest, rather than activity, underlies day-night activity differences in mice

The suprachiasmatic nucleus (SCN), which serves as the central pacemaker in mammals, regulates the 24-h rhythm in behavioral activity. However, it is currently unclear whether and how bouts of activity and rest are regulated within the 24-h cycle (i.e., over ultradian time scales). Therefore, we used passive infrared sensors to measure temporal behavior in mice housed under either a light-dark (LD) cycle or continuous darkness (DD). We found that a probabilistic Markov model captures the ultradian changes in the behavioral state over a 24-h cycle. In this model, the animal's behavioral state in the next time interval is determined solely by the animal's current behavioral state and by the "toss" of a proverbial "biased coin." We found that the bias of this "coin" is regulated by light input and by the phase of the clock. Moreover, the bias of this "coin" for an animal is related to the average length of rest and activity bouts in that animal. In LD conditions, the average length of rest bouts was greater during the day compared to during the night, whereas the average length of activity bouts was greater during the night compared to during the day. Importantly, we also found that day-night changes in the rest bout lengths were significantly greater than day-night changes in the activity bout lengths. Finally, in DD conditions, the activity and rest bouts also differed between subjective night and subjective day, albeit to a lesser extent compared to LD conditions. The ultradian regulation represented by the model does not result in ultradian rhythms, although some weak ultradian rhythms are present in the data. The persistent differences in bout length over the circadian cycle following loss of the external LD cycle indicate that the central pacemaker plays a role in regulating rest and activity bouts on an ultradian time scale.Circadian clocks in health and diseas

Impact of COVID-19 pandemic on cardiovascular testing in Asia: the IAEA INCAPS-COVID study

BACKGROUND The coronavirus disease-2019 (COVID-19) pandemic significantly affected management of cardiovascular disease around the world. The effect of the pandemic on volume of cardiovascular diagnostic procedures is not known. OBJECTIVES This study sought to evaluate the effects of the early phase of the COVID-19 pandemic on cardiovascular diagnostic procedures and safety practices in Asia. METHODS The International Atomic Energy Agency conducted a worldwide survey to assess changes in cardiovascular procedure volume and safety practices caused by COVID-19. Testing volumes were reported for March 2020 and April 2020 and were compared to those from March 2019. Data from 180 centers across 33 Asian countries were grouped into 4 subregions for comparison. RESULTS Procedure volumes decreased by 47% from March 2019 to March 2020, showing recovery from March 2020 to April 2020 in Eastern Asia, particularly in China. The majority of centers cancelled outpatient activities and increased time per study. Practice changes included implementing physical distancing and restricting visitors. Although COVID testing was not commonly performed, it was conducted in one-third of facilities in Eastern Asia. The most severe reductions in procedure volumes were observed in lower-income countries, where volumes decreased 81% from March 2019 to April 2020. CONCLUSIONS The COVID-19 pandemic in Asia caused significant reductions in cardiovascular diagnostic procedures, particularly in low-income countries. Further studies on effects of COVID-19 on cardiovascular outcomes and changes in care delivery are warranted

Impact of COVID-19 on cardiovascular testing in the United States versus the rest of the world

Objectives: This study sought to quantify and compare the decline in volumes of cardiovascular procedures between the United States and non-US institutions during the early phase of the coronavirus disease-2019 (COVID-19) pandemic. Background: The COVID-19 pandemic has disrupted the care of many non-COVID-19 illnesses. Reductions in diagnostic cardiovascular testing around the world have led to concerns over the implications of reduced testing for cardiovascular disease (CVD) morbidity and mortality. Methods: Data were submitted to the INCAPS-COVID (International Atomic Energy Agency Non-Invasive Cardiology Protocols Study of COVID-19), a multinational registry comprising 909 institutions in 108 countries (including 155 facilities in 40 U.S. states), assessing the impact of the COVID-19 pandemic on volumes of diagnostic cardiovascular procedures. Data were obtained for April 2020 and compared with volumes of baseline procedures from March 2019. We compared laboratory characteristics, practices, and procedure volumes between U.S. and non-U.S. facilities and between U.S. geographic regions and identified factors associated with volume reduction in the United States. Results: Reductions in the volumes of procedures in the United States were similar to those in non-U.S. facilities (68% vs. 63%, respectively; p = 0.237), although U.S. facilities reported greater reductions in invasive coronary angiography (69% vs. 53%, respectively; p < 0.001). Significantly more U.S. facilities reported increased use of telehealth and patient screening measures than non-U.S. facilities, such as temperature checks, symptom screenings, and COVID-19 testing. Reductions in volumes of procedures differed between U.S. regions, with larger declines observed in the Northeast (76%) and Midwest (74%) than in the South (62%) and West (44%). Prevalence of COVID-19, staff redeployments, outpatient centers, and urban centers were associated with greater reductions in volume in U.S. facilities in a multivariable analysis. Conclusions: We observed marked reductions in U.S. cardiovascular testing in the early phase of the pandemic and significant variability between U.S. regions. The association between reductions of volumes and COVID-19 prevalence in the United States highlighted the need for proactive efforts to maintain access to cardiovascular testing in areas most affected by outbreaks of COVID-19 infection

Entrainment of cell division in phytoplankton with dynamic energy budgets

We explore the entrainment behavior of cell division in phytoplankton in the context of Dynamic 25 Energy Budget (DEB) theory. In particular, we explore the range of DEB and environmental 26 parameter values within which a cell divides at regular intervals in a periodic light environment 27 with abundant nutrients and investigate the impact of parameter values on the phase of cell 28 division. We consider three types of cells that differ in the evolution of surface area to volume 29 ratio during the cell cycle: cells with a constant shape (isomorphs), cells with a constant surface 30 area (V0-morphs) and cells with a constant surface area to volume ratio (V1-morphs), the latter 31 being the default choice in studies on the population dynamics of unicellular organisms because 32 of its desirable mathematical implications. Only in isomorphs and V0-morphs, however, cell 33 division can be entrained to a periodic light. Regular cell division in V1 is purely coincidental, as 34 it depends on exact choices for parameter values. We attribute this to the fact that V1-morphs 35 lack the negative feedback of size on the dynamics of reserves in V0-morphs and isomorphs. 36 Because entrained isomorphs and V0-morphs divide during the dark hours in our simulations, 37 these two shapes can represent the division behavior of phytoplankton species that complete the 38 cell cycle during the night, such as dinoflagellates and coccolithophores. A description of the 39 division behavior of species completing the cell cycle during the day, such as silicon dependent 40 diatoms and cyanobacteria, requires a more complex model than used in this paper. 41 Furthermore, we explore the robustness of our findings by randomizing model parameters and 42 introducing unevenness in biomass separation between daughter cells during cell division. We 43 conclude that especially the entrainment in V0-morphs is relative insensitive to perturbations