COVID-19 has been declared a global pandemic by the World Health Organization and is responsible for hundreds of thousands of deaths worldwide. COVID-19 is caused by SARS-CoV-2, and common clinical symptoms include fever, cough, sore throat, headache, and fatigue. Myocardial injury is relatively common in patients with COVID-19, accounting for 7%-23% of cases, and is associated with a higher rate of morbidity and mortality. There is a discrepancy in the literature about

Pregnancy produces rapid, dramatic volume-overload changes to the maternal circulation. This paper examines pregnancy-induced structural-mechanical changes in bovine aortic and mitral heart valve leaflets. Valve leaflets were harvested from non-pregnant heifers and pregnant cows. Dimensions, biaxial extensibility and creep resistance were assessed and related to changes in the collagen network: histological leaflet and anatomic layer thicknesses plus collagen crimp, and biochemical collagen content. Collagen stability and crosslinking were assessed thermomechanically. Pregnancy altered both aortic and mitral valve leaflets. Both valves demonstrated biphasic changes in leaflet stretch, decreasing in early pregnancy and recovering by late pregnancy. Creep in leaflets from both valves was minimal and decreased even further with pregnancy in the mitral valve. There were valve-specific changes in preconditioning areal extension with pregnancy: increasing in the aortic valve and decreasing in the mitral valve. Leaflet area increased dramatically (84% aortic, 56% mitral), with thickening mainly in the fibrosa, accompanied by increases in collagen content (8% aortic, 16% mitral): together suggesting synthesis of new collagen. Collagen crimp was almost completely lost in pregnancy, with the denaturation temperature decreased by approximately 2 °C. Mature and total crosslinking increased, curiously without a significant increase in immature crosslinking. Mature aortic and mitral heart valve leaflets in the maternal cardiovascular system remodel substantially and similarly-despite their different embryological origins.

There is growing evidence that heart valves are not passive structures but can remodel with left ventricular dysfunction. To determine if these tissues remodel under nonpathological conditions, we examined the mirtal valve anterior leaflet during the volume loading and cardiac expansion of pregnancy using a bovine model. We measured leaflet dimensions, chordal attachments, and biaxial mechanical properties of leaflets collected from never-pregnant heifers and pregnant cows (pregnancy duration estimated from fetal length). Hydrothermal isometric tension (HIT) tests were performed to assess the denaturation temperature (T(d)) associated with collagen molecular stability and the load decay half-time (t(1//2)) associated with intermolecular cross-linking. Histological changes were examined using Verhoeff-van Gieson and picrosirius red staining with polarized light. We observed striking changes to the structure and material properties of the mitral anterior leaflet during pregnancy. Leaflet area was increased 33%, with a surprising increase (nearly 25%) in chordae tendinae attachments. There was a biphasic change in leaflet extensibility: it rapidly decreased by 30% and then reversed to prepregnant values by late pregnancy. The 2°C decrease in T(d) in pregnancy was indicative of collagen remodeling, whereas the 70% increase in HIT t(1/2) indicated an increase in collagen cross-linking. Finally, histological results suggested transient increases in leaflet thickness and transient decreases in collagen crimp. This remodeling may compensate for the increased loading conditions associated with pregnancy by normalizing leaflet stress and maintaining coaptation. Understanding the mechanisms of mitral valve physiological remodeling in pregnancy could contribute to alternative treatments of pathological remodeling associated with left ventricular dysfunction.

BackgroundResident duty hours have recently been under criticism, with concerns for resident and patient well-being. Historically, call shifts have been long, and some residency training programs have now restricted shift lengths. Data and opinions about the effects of such restrictions are conflicting. The Internal Medicine Residency Program at Dalhousie University recently moved from a traditional call structure to a day float/night float system. This study evaluated how this change in duty hours affected resident perceptions in several key domains.MethodsSenior residents from an internal medicine training program in Canada responded to an anonymous online survey immediately before and 6 months after the implementation of duty hour reform. The survey contained questions relating to three major domains: resident wellness, ability to deliver quality health care, and medical education experience. Mean pre- and post-intervention scores were compared using the t-test for paired samples.ResultsTwenty-three of 27 (85 %) senior residents completed both pre- and post-reform surveys. Residents perceived significant changes in many domains with duty hour reform. These included improved general wellness, less exposure to personal harm, fewer feelings of isolation, less potential for error, improvement in clinical skills expertise, increased work efficiency, more successful teaching, increased proficiency in medical skills, more successful learning, and fewer rotation disruptions.ConclusionsSenior residents in a Canadian internal medicine training program perceived significant benefits in medical education experience, ability to deliver healthcare, and resident wellness after implementation of duty hour reform.Electronic supplementary materialThe online version of this article (doi:10.1186/s12909-016-0703-4) contains supplementary material, which is available to authorized users.