Decompression sickness: a review.
Work in compressed air is a dangerous activity, whether it is carried on under water in a conventional diving suit, in self-contained breathing apparatus or in a diving bell, or in relatively dry conditions in a caisson or an underwater tunnel. Surprisingly large numbers of men have worked at one time or another in compressed air in tunnels or caissons and it is the dangers which arise to the health of these men that are considered here. When a tunnel is driven through water-logged strata or through porous ground under a river, the open end of the tunnel must be sealed off and air pumped in to balance the hydrostatic pressure, should there be any danger of water flooding in and bringing with it unmanageable quantities of silt or sand. A pier of a bridge may be constructed in deep water by means of a caisson (Fr. caisse, a box), which is a compressed air chamber in which a gang of men excavate foundations. In both tunnels and caissons men come and go through an air lock and must be compressed on entering and decompressed at the end of the work period. Although working conditions in these circumstances have much improved over the last 6o years, our understanding of the reactions of the human body to atmospheric pressures greater than the normal and of the pathogenesis of decompression sickness is still insufficient to prevent illness completely. In engineering practice it is customary for working pressure to be expressed as gauge pressure in pounds per square inch (p.s.i.g.) which is the pressure over and above the normal atmospheric pressure of I4-7 p.S.i. (I 03 kg./cm.2). For certain calculations absolute pressure (gauge pressure plus atmospheric pressure) is used, and for clarity it must always be stated whether gauge or absolute pressure is referred to. In naval practice it is usual to think in terms of feet of sea water, each 33 feet of depth corresponding to about one atmosphere or approximately I5 p.s.i. Sometimes the unit of pressure used is the atmosphere (atm.). On the
Decompression sickness: paradoxical response to recompression therapy.
Eight days previously, during the rehearsal for a military funeral, A. B. was acting as a member of a coffin-bearing detail, being on the left-hand side of the coffin. He therefore had his right arm abducted until parallel with the ground, with the hand round the back of his opposite number's neck, his own neck being slightly flexed to the left. Unfortunately the latter stumbled and the extra weight of the coffin was suddenly transmitted to A. B.'s shoulder at a place midway between the point of the shoulder and the junction with the neck. He continued with the rehearsal for a further two hours in some discomfort, and noticed later in the day that he had pins-and-needles in the arm. Next day there was weakness of the limb, and a small transient bruise had appeared on the shoulder. This was the day of the actual ceremony, .so he was replaced by C. D., who fared little better: the same individual on the opposite side of the coffin repeated his mistake of the previous day and lost his balance, with precisely the same effect. C. D. continued with his duty for a further 15 minutes, but after this he immediately observed weakness of his right arm. When seen, neither lad had noted any return of function over the succeeding week. There was no clinical evidence of the injury to the shoulder or cervical spine in either patient, though x-ray films showed a fracture of the tip of the spinous process of C 7 in one of them (A. B.). A. B. showed the features of a right C. 5 to 8 lesion with marked weakness and wasting of biceps and triceps and to a lesser degree of the deltoid and forearm muscles, with some weakness of grip. There was sensory blunting (and subjective paraesthesiae) of the thumb and index finger. No tendon reflex could be elicited on the affected side. There was no sympathetic involvement. C. D. had a more extensive and severe defect. The weakness and wasting extended from C 6 to T 1 inclusive, the pectoralis major being slightly wasted. Abduction of the arm was initiated by the " trick movement " of swinging it outwards with his body, suggesting weakness of the supraspinatus, though the deltoid appeared to function normally once the arm was up. Biceps, triceps, forearm, and hand muscles showed varying degrees of weakness and wasting, and apart from a rather feeble triceps jerk the tendon reflexes were absent. The superficial sensory deficit was more severe, and extended from the sixth cervical to the first thoracic dermatome inclusive. There was again no evidence of Homer's syndrome. The clinical features were those of a subtotal brachial plexus injury in each case. Fortunately, recovery began some three weeks after the injury, so no actual avulsion of nerve roots had occurred. Nerve-conduction studies and electromyographic findings suggested that the type of damage was predominantly axonotInesis in A. B. and neurapraxia in C. D. Three months later recovery was almost complete in all muscle groups in both subjects.
Thermal properties of the Florida Current as related to Ocean Thermal Energy Conversion (OTEC)
The thermal properties of the Florida Current are presented and analyzed for the available ocean thermal energy. For a cold water intake depth equal to or greater than 600 m, potential sites for Ocean Thermal Energy Conversion (OTEC) power plants appear to exist in the Straits of Florida and, to a lesser extent, off the coasts of Georgia and South Carolina. The maximum thermal differences occur on the continental shelf because of the geostrophic motion of the Gulf Stream. An estimate of the total available ocean thermal energy from the Florida Current, delivered in the form of electricity, is 3.5 × 1012 kWh yr−1. For a cold water suction depth of 600 m or more, seasonal variability in the ocean thermal resource is approx. ±35 per cent of average annual output.