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Lars J Bjertnaes,1,2 Anton Hauge,3 Marianne Thoresen,3,4 Lars Walløe3 1Anesthesia and Critical Care Research Group, Department of Clinical Medicine, Faculty of Health Sciences, UiT The Arctic University of Norway, Tromsø, N-9037, Norway; 2Department of Intensive Care Medicine, University Hospital of North Norway, Tromsø, N- 9017, Norway; 3Division of Physiology, Institute of Basic Medical Sciences, University of Oslo, Oslo, 0317, Norway; 4Translational Health Sciences, University of Bristol, Bristol, UKCorrespondence: Lars J BjertnaesAnesthesia and Critical Care Research Group, Department of Clinical Medicine, Faculty of Health Sciences, UiT The Arctic University of Norway, Tromsø, N-9037, NorwayTel +47 77627001Fax +47 77626042Email lars.bjertnaes@uit.noBackground: Successful cardiopulmonary resuscitation after drowning or avalanche is often attributed to hypothermia-induced decrease in metabolism, which adapts the oxygen demand to the amount supplied under cardiac compression. Four decades ago, we speculated if oxygen-sparing mechanisms like those found in marine mammals, may improve cerebral oxygenation during acute airway blockade in humans. We investigated hemodynamic changes during steady state ergometer cycling with intermittent periods of apnea and face immersion (AFI) in ice-cold water. During AFI, heart rate (HR) dropped by 58% whereas average blood velocity (ABV) determined by means of a Doppler ultrasound velocity meter (UNIDOP University of Oslo, Oslo, Norway) fell by 85% in the radial artery and rose by 67% in the vertebral artery. Similar changes occured in radial artery ABV, albeit more slowly, when the test subject only held his breath while cycling. When he breathed via a snorkel during face immersion, HR remained unchanged while radial artery ABV fell transiently and subsequently returned to its pre-immersion level. These findings later were confirmed by other investigators. Moreover, a recent study revealed that the seal even has a system for selective brain cooling during the dive.Conclusion: Our research has confirmed prioritized cerebral circulation during AFI in cold water. We hypothesize that these changes may improve brain oxygenation due both to greater blood flow and possibly also to faster brain cooling, as demonstrated in diving seals.Keywords: apnea, breath-hold, cardiopulmonary resuscitation, diving response, hypothermia

Medical records from maternity clinics in three Norwegian cities, Oslo, Bergen and Trondheim, have been used to study the relationship between lactation and post-partum amenorrhoea during the period 1860–1964. Resumption of menses after a period of post-partum amenorrhoea has been examined separately during lactation, after cessation of lactation, and in the absence of lactation, in 5250 cases. During ongoing lactation the median duration of post-partum amenorrhoea was found by survival analysis to be 12 months for women who had given birth before 1900 and 6 months for women who had given birth after 1900. In a Cox regression analysis, age of menarche and parity were found to influence the duration of post-partum amenorrhoea, in addition to the child's birth year. With a later age of menarche there was longer amenorrhoea, and primiparae resumed menses earlier than multiparae. After cessation of breast-feeding the median duration of amenorrhoea was 1 month, the only variable significantly influencing it being the age of menarche, a younger age showing a shorter duration. In the absence of lactation the survivor function started to decline after 3–4 weeks, and had a half-life of 2 months.None of the variables indicating the woman's social condition seemed to influence the duration of amenorrhoea. The decline in the duration of post-partum amenorrhoea during ongoing lactation from 1860 until today is therefore probably caused by a changed breast-feeding pattern rather than by improved nutrition for women giving birth. [ABSTRACT FROM PUBLISHER]

Various methods of assessing infant chemoreceptor responses have been reported in the literature. However, equipment dead space, trigeminal stimulation and inherent respiratory variability may have affected the results. A method is presented which attempts to reduce the effect of these factors and thereby isolate the chemoreceptor response. Inspiratory gas was delivered into a lightweight face mask with a pliable rim, minimal dead space and a connected pneumotachograph. Ventilatory data were computed breath by breath. Computer-controlled electromagnetic valves allowed instantaneous switching between air and different gas mixtures, repeated in a randomized sequence. In 18 healthy term neonates, the mask increased ventilation by 12% (95% confidence interval 6-18%), measured by calibrated strain-gauge bands. The effect on respiratory frequency and tidal volume differed significantly between sleep states. Neonates were challenged with short-lasting hyperoxia, mild hypoxia, rebreathing and mild hypercapnia. Coherent averaging of several ventilatory responses from each sleep state reduced the variability while maintaining a high time-resolution. [ABSTRACT FROM AUTHOR]