Objectives: Cognitive dysfunction from high altitude exposure is a major cause of civilian and military air disasters. Pilot training improves recognition of the early symptoms of altitude exposure so that countermeasures may be taken before loss of consciousness. Little is known regarding the nature of cognitive impairments manifesting within this critical window when life-saving measures may still be taken. Prior studies evaluating cognition during high altitude simulation have predominantly focused on measures of reaction time and other basic attention or motor processes. Memory encoding, retention, and retrieval represent critical cognitive functions that may be vulnerable to acute hypoxic/ischemic events and could play a major role in survival of air emergencies, yet these processes have not been studied in the context of high altitude simulation training. Methods: In a series of experiments, military aircrew underwent neuropsychological testing before, during, and after brief (15 min) exposure to high altitude simulation (20,000 ft) in a pressure-controlled chamber. Results: Acute exposure to high altitude simulation caused rapid impairment in learning and memory with relative preservation of basic visual and auditory attention. Memory dysfunction was predominantly characterized by deficiencies in memory encoding, as memory for information learned during high altitude exposure did not improve after washout at sea level. Retrieval and retention of memories learned shortly before altitude exposure were also impaired, suggesting further impairment in memory retention. Conclusions: Deficits in memory encoding and retention are rapidly induced upon exposure to high altitude, an effect that could impact life-saving situational awareness and response. (JINS, 2017, 23, 1–10)

Escherichia coli JM109 (Gram-negative) and Bacillus subtilis (Gram-positive) were grown under hypobaric conditions for 19 days at 25 °C to study the effects of 33 and 67 kPa low pressures on selected physiological responses; growth, cytoplasmic membrane polarization (measure of cytoplasmic membrane fluidity) and total cellular fatty acids. In the first experiment, cytoplasmic membrane polarization in B. subtilis increased under both hypobaric conditions, indicating the membrane became more rigid or less fluid. This experiment was repeated and the effect of the hypobaric conditions was not evident as in the first experiment with B. subtilis. In addition, total cellular fatty acids analysis for B. subtilis showed that hypobaric conditions did not alter the ratio of saturated to unsaturated fatty acids. The cytoplasmic membrane remained in the same fluid state in hypobaric grown E. coli cell cultures as in the 101 kPa ambient control cells in both experiments. However, the saturated to unsaturated ratios were altered in E. coli under hypobaric conditions. It is important to note the ratios for E. coli were less than 1, while the ratios for Bacillus were in the 28–50 range. Growth of both species was also measured by colony forming units at the termination of the 19 day experiment. Both bacterial species were capable of growth under hypobaric conditions and no distinct trend emerged as to the effect of hypobaric pressure on bacterial growth and cytoplasmic membrane fluidity.

The increasing use of ambulatory surgery requires methods of anaesthesia that allow patients to be discharged soon after the operation is completed. Spinal anaesthesia is usually simple and quick, and the incidence of post-spinal headache has been reduced by using non-cutting small-gauge needles. Limiting the spread of spinal anaesthesia, as long as it still provides analgesia for surgery, should reduce the haemodynamic effects and speed recovery. Restricted spinal anaesthesia, intended to be unilateral using 0.18% hypobaric bupivacaine via a 25G or 27G Whitacre unidirectional needle, was compared with epidural anaesthesia (using a mixture of lignocaine and prilocaine) in 64 matched-pair patients undergoing ambulatory arthroscopy. Motor blockade, assessed for the specific myotomes L2 to S1, was significantly more unilateral in the spinal group. Two patients in the spinal group and nine patients in the epidural group were treated for hypotension (P < 0.05). One patient in the spinal group developed a post-spinal headache. One patient in the epidural group rated the anaesthesia poor.