Postgraduate Medical Journal (December 1975) M1, 848-850. Postgrad Med J: first published as 10.1136/pgmj.51.602.848 on 1 December 1975. Downloaded from Some problems of high speed travel D. C. READER B.Sc., M.B., B.S., M.R.C.S., Ph.D. RAF Institute ofAviation Medicine, Farnborough, Hants Summary and persists with some changes throughout life. It Some aspects of high speed flight are examined to affects practically the whole physiological machine; investigate whether increase in speed implies any respiration, thermal regulation, cardiovascular func- lowering of safety standards. The problem of circadian tion, adrenocortical activity, the reticulo-endothelial dysrhythmia is discussed and methods of attenuating and renal systems, even the parasites we may have in its effects are explained and some new hypnotic drugs our bodies respond to our own circadian rhythm. are mentioned. The risk of decompression has been Pathology also follows a rhythm, mortality rate is quantified and predictions have been made for risks in highest very early in the morning and psychotic commercial service. Cosmic radiation in supersonic episodes show inherent periodicity. With such a aircraft is unlikely to limit commercial operation or widespread control on so many functions, little significantly increase risks to passengers and crew. wonder that well-being is easily lost when one's The supersonic boom is to the circadian likely limit terrain over rhythm is forced to change. Protected by copyright. which supersonic aircraft can operate and regulations How can one minimize these effects? Passengers covering engine noise on the ground could restrict some should start longjourneys well rested and emplaning flights. drills should be minimized, vaccinations and other medical procedures should be completed some 2 Introduction weeks before the journey. Smoking and alcohol This paper will examine some civil problems affect- ingestion in flight should be minimized and only ing both crew and passengers of high speed aircraft. light meals taken. The appropriate clothing should It used to be a 6-8 week sea cruise by liner to be worn and passengers should be encouraged to Australia but in 1974 one can fly from London to sleep when possible by the extinction of lights. At Sydney in 281 hr. When Concorde starts operating the destination, one should allow at least a day or a commercially, the flight time is expected to be 15 hr. full night to permit some acclimatization to the Then New York will be only 3J hr away and local time and the knowledge that physical fatigue Buenos Aires 91 hr away, flying at Mach 2-2 is a potent sleep inducer can be of assistance. (1350 m.p.h.). Travel at this speed will accentuate Indoctrination on the hazards of circadian dysrhy- some of the problems experienced in jet aircraft in thmia can help but this aspect is seldom mentioned. 1974. Probably the most widespread of these is With crews, lack of sleep can become cumulative. http://pmj.bmj.com/ circadian dysrhythmia, colloquially called 'jet lag'. Preston, Ruffell-Smith and Sutton-Mattocks (1973) found progressive sleep loss in cabin crews on long Circadian dysrhythmia flights, and older personnel tended to lose sleep more Circadian dysrhythmia is caused by the desyn- than others. Transmeridian routes were more likely chronization of the normal sleep and wakefulness to produce gross sleep disruption and sleep periods cycle of the body with local time. The problem pre- soon became fragmented. The authors found that sents itself to travellers as lowered efficiency and hotel managements could assist in serving breakfast on October 4, 2021 by guest. malaise, the inability to sleep during local sleeping in the -evening, dinner in the morning and by hours after a journey and fatigue when one is re- avoiding disturbance from hotel cleaning staff, sleep quired to be alert. This problem is even more press- was not disrupted. One solution for this problem is to ing for the crew who have to rest in an allotted time base crews abroad for periods of up to 3 months but so as to be fit to fly the aircraft again. this has drawbacks usually of a managerial or trade Physiologically there is good evidence for an union nature. endogenous circadian rhythm (Mills, 1966). The The use of hypnotics is more contentious. It has rhythm persists under constant conditions of light been shown (Borland and Nicholson, 1974; 1975; and dark, e.g. underground, and the rhythm tends Borland, Nicholson and Wright, 1974) that nitraze- to persist even when new phases or cycles are im- pam (mogadon) is not a drug of choice for aircrew posed. Circadian rhythm is acquired early in infancy as it has a long half-life (30 hr), and one can Some problems ofhigh speed travel 849 Postgrad Med J: first published as 10.1136/pgmj.51.602.848 on 1 December 1975. Downloaded from demonstrate residual effects on skilled perform- to similar decompression profiles as would occur in ance some 19 hr after the ingestion of 10 mg. a supersonic aircraft with these defects in the cabin Flurazepam (dalmane), although it has a shorter wall. With a 4-in. diameter hole, the animals became half-life, also has residual effects for 16 hr after the unconscious but made a normal recovery. With the ingestion of 30 mg. Heptabarbitone (medomin, 6-in. diameter hole, unconsciousness supervened 200 mg) and methaqualone (melsedin, 150 mg) are early at 40,000 ft and three of the four animals either better, but not without some disadvantages. Hepta- succumbed then or died later. The animals that barbitone is a barbiturate with a short half-life survived initially showed gross neurological and (10 hr), and does affect performance for at least this behavioural abnormalities before death which sug- period. Methaqualone is excreted at a variable rate gested widespread brain damage. With the 8-in. but can persist for 10 hr and affect reaction time, diameter hole, the animals failed to recover. although little effect on skilled performance can be The requirements for the Concorde state that demonstrated 10 hr after ingestion. It is better for cabin altitude should not exceed 15,000 ft following aircrew to try to sleep without the use of hypnotics a failure in the pressurization system which would or alcohol but, if drugs must be used, heptabarbitone occur once in 103-105 flying hours. The cabin altitude and methaqualone are probably the best to use, after should not exceed 25,000 ft after a remote failure an adequate trial has been instituted off duty. For (1 in 105-107 flying hr) and should only exceed 25,000 passengers the problems are less severe and some after an extremely remote failure (less than 1 in 107 non-habit-forming hypnotic could be used with flying hr). Recent investigations into the integrity of good effect to alleviate the fatigue of long aircraft the Concorde fuselage indicate that the failures which journeys. are likely to be hazardous will be extremely remote (Preston, 1972). Multiple air supplies to the cabin High altitude together with small discharge valves and small dia- Protected by copyright. In order to fly fast, aircraft must fly high where the meter windows (less than 6 in diameter) should air density and aerodynamic drag are less. Modern further safeguard the passengers. For the crew, jet aircraft cruise just below the tropopause (38,000 special quick donning mask assemblies that will ft) but supersonic aircraft will fly considerably higher, supply oxygen at high pressure have been devised up to 60,000 ft. At this altitude loss of cabin pressure and these will maintain the oxygenation of the crew is likely to be more dramatic. Breathing 100% oxygen so that the appropriate descent manoeuvres can be will give protection up to 40,000 ft and above this executed. The passengers will be supplied with altitude, oxygen under pressure must be admini- drop-down oxygen masks automatically lowered stered to maintain oxygenation. At 63,000 ft oxygen when the pressure in the cabin falls below the at a high pressure is required with counter pressure equivalent of 14,000 ft. to the body by means of a special garment. With a pressure in the cabin equivalent to 8,000 ft altitude, Radiation the sequelae of explosive decompression caused by The atmosphere functions as an extremely efficient defects in the cabin walls were examined byNicholson attenuator of the most harmful radiation that strikes and Ernsting (1967). Assuming that the aircraft had the earth. Galactic radiation consists of high energy initiated a descent one minute after cabin pressure particles (protons and helions) and heavy particles http://pmj.bmj.com/ was lost, a 4-in. diameter hole would cause the (Fe., Mg., etc.) These normally disintegrate as they cabin altitude to rise to 30,000ft. This is unlikely meet the upper atmosphere and few reach the surface. to be serious; transient unconsciousness could occur The distribution of cosmic radiation is affected by if oxygen was not breathed immediately, but con- the earth's magnetic field, thus the density of the sciousness would soon be regained on the descent. radiation is greatest at the magnetic poles. Crew and With a 6-in. diameter hole, the cabin altitude would passengers on supersonic aircraft at altitudes above rise to 42,500 ft and the altitude would exceed 60,000 ft could run some risk of radiation, albeit on October 4, 2021 by guest. 25,000 ft for 61 min. If oxygen was administered very slight. It has been estimated that an average immediately, severe hypoxia would be avoided dosage of 1-5 mrem/hr can be expected on trans- although unconsciousness would be likely. With an atlantic routes.