Validating and Extending the Three Process Model of Alertness in Airline Operations

Sleepiness and fatigue are important risk factors in the transport sector and bio-mathematical sleepiness, sleep and fatigue modeling is increasingly becoming a valuable tool for assessing safety of work schedules and rosters in Fatigue Risk Management Systems (FRMS). The present study sought to validate the inner workings of one such model, Three Process Model (TPM), on aircrews and extend the model with functions to model jetlag and to directly assess the risk of any sleepiness level in any shift schedule or roster with and without knowledge of sleep timings. We collected sleep and sleepiness data from 136 aircrews in a real life situation by means of an application running on a handheld touch screen computer device (iPhone, iPod or iPad) and used the TPM to predict sleepiness with varying level of complexity of model equations and data. The results based on multilevel linear and non-linear mixed effects models showed that the TPM predictions correlated with observed ratings of sleepiness, but explorative analyses suggest that the default model can be improved and reduced to include only two-processes (S+C), with adjusted phases of the circadian process based on a single question of circadian type. We also extended the model with a function to model jetlag acclimatization and with estimates of individual differences including reference limits accounting for 50%, 75% and 90% of the population as well as functions for predicting the probability of any level of sleepiness for ecological assessment of absolute and relative risk of sleepiness in shift systems for safety applications.     

Operations on the adrenal glands

Various conditions of the adrenal gland are amenable to surgical treatment. Removal of a pheochromocytoma is almost always indicated when the tumor is diagnosed. The results of extirpation have been excellent in cases in which patients were operated upon before the onset of chronic hypertension. Removal of the "nerve cell" tumors of the adrenal is indicated if metastasis cannot be demonstrated. Hypofunction of the adrenal cortex may be partially alleviated by the repeated implantation of pellets of desoxycorticosterone acetate. Hyperfunction of the adrenal cortex causes a variety of clinical manifestations depending upon which of the numerous hormones are affected. Removal of a cortical tumor alleviates these symptoms. These tumors are malignant in more than 50 per cent of cases, and recurrence is frequent. Bilateral hyperplasia of the glands rather than a tumor may be present. In such circumstances, resection of 95 per cent of the adrenal tissue is effective in controlling the symptoms of the disease. Total bilateral excision of the adrenals is, at present, under investigation as a means of treatment for a variety of conditions.