Sunrise on the pines.

As the sun rises above a mountain ridge populated with pine trees, a short-lived but spectacular light scattering effect off the pine needles is visible. It was noted by the Victorian physicist and mountaineer John Tyndall in his two mountaineering books, and this paper describes Tyndall's observations, discusses his and Professor Necker's descriptions, and illustrates the effect with a modern photographic image, as well as commenting on possible explanations of the phenomenon. A rarely cited reference to a memorandum of Babinet has been found that gave Necker's description as a spectacular example to illustrate his theorem "Babinet's Principle."

Decreased Nursing Staffing Adversely Affects Emergency Department Throughput Metrics.

INTRODUCTION: The effect of nurse staffing on emergency department (ED) efficiency remains a significant area of interest to administrators, physicians, and nurses. We believe that decreased nursing staffing adversely affects key ED throughput metrics. METHODS: We conducted a retrospective observational review of our electronic medical record database from 1/1/2015 to 12/31/2015 at a high-volume, urban public hospital. We report nursing hours, door-to-discharge length of stay (LOS) and door-to-admit LOS, and percentage of patients who left without being seen (LWBS). ED nursing hours per day was examined across quartiles with the effect evaluated using analysis of covariance and controlled for total daily ED volume, hospital occupancy and ED admission rate. RESULTS: From 1/1/15-12/31/15, 105,887 patients presented to the ED with a range of 336 to 580 nursing hours per day with a median of 464.7. Independent of daily ED volume, hospital occupancy and ED admission rate, days in the lowest quartile of nursing hours experienced a 28.2-minute increase per patient in door-to-discharge LOS compared to days in the highest quartile of nursing hours. Door-to-admit LOS showed no significant change across quartiles. There was also an increase of nine patients per day who left without being seen by a provider in the lowest quartile of nursing hours compared to the highest quartile. CONCLUSION: Lower nursing hours contribute to a statistically significant increase in door-to-discharge LOS and number of LWBS patients, independent of daily ED volume, hospital occupancy and ED admission rate. Consideration of the impact of nursing staffing is needed to optimize throughput metrics for our urban, safety-net hospital.

Host inactivation of bacterial lipopolysaccharide prevents prolonged tolerance following gram-negative bacterial infection.

A transient state of tolerance to microbial molecules accompanies many infectious diseases. Such tolerance is thought to minimize inflammation-induced injury, but it may also alter host defenses. Here we report that recovery from the tolerant state induced by Gram-negative bacteria is greatly delayed in mice that lack acyloxyacyl hydrolase (AOAH), a lipase that partially deacylates the bacterial cell-wall lipopolysaccharide (LPS). Whereas wild-type mice regained normal responsiveness within 14 days after they received an intraperitoneal injection of LPS or Gram-negative bacteria, AOAH-deficient mice had greatly reduced proinflammatory responses to a second LPS injection for at least 3 weeks. In contrast, LPS-primed Aoah- knockout mice maintained an anti-inflammatory response, evident from their plasma levels of interleukin-10 (IL-10). LPS-primed Aoah-knockout mice experiencing prolonged tolerance were highly susceptible to virulent E. coli challenge. Inactivating LPS, an immunostimulatory microbial molecule, is thus important for restoring effective host defenses following Gram-negative bacterial infection in animals.

A host lipase detoxifies bacterial lipopolysaccharides in the liver and spleen.

Much of the inflammatory response of the body to bloodborne Gram-negative bacteria occurs in the liver and spleen, the major organs that remove these bacteria and their lipopolysaccharide (LPS, endotoxin) from the bloodstream. We show here that LPS undergoes deacylation in the liver and spleen by acyloxyacyl hydrolase (AOAH), an endogenous lipase that selectively removes the secondary fatty acyl chains that are required for LPS recognition by its mammalian signaling receptor, MD-2-TLR4. We further show that Kupffer cells produce AOAH and are required for hepatic LPS deacylation in vivo. AOAH-deficient mice did not deacylate LPS and, whereas their inflammatory responses to low doses of LPS were similar to those of wild type mice for approximately 3 days after LPS challenge, they subsequently developed pronounced hepatosplenomegaly. Providing recombinant AOAH restored LPS deacylating ability to Aoah(-/-) mice and prevented LPS-induced hepatomegaly. AOAH-mediated deacylation is a previously unappreciated mechanism that prevents prolonged inflammatory reactions to Gram-negative bacteria and LPS in the liver and spleen.