1181

Preliminary Communication

LEVITATION

JOHN T. SCALESM.R.C.S.

Department of Biomechanics andSurgical Materials.

Institute of Orthopædics(University of London),

Royal National Orthopædic HospitalLondon, W.C.1

IT occurred to me that supporting a patient on air mightsolve some of the problems of nursing patients whoseillness necessitates the avoidance of contact with their

beds-e.g., patients with severe burns of the trunk orpatients with spinal paraplegia.At first it seemed that a patient could be supported on

air by using ducted air from a centrifugal blower passingthrough a porous membrane approximately the size ofthe average adult trunk. In other words it seemed thatthe most fruitful approach was to use air at high pressureand low volume. In the early stages it was calculatedfrom estimations of the weight and area of the averageadult trunk that a pressure of l-4rLO’4 lb. per sq. in. ofair would be required to support the trunk of a patient.Using these figures for the high-pressure, low-volumemethod of supporting the trunk on air, it was found thatas soon as the subject was lifted from the " bed " the airpressure fell so much that the subject fell back on the" bed "-a most disconcerting experience, particularly asthis ascent and descent occurred at a very high frequency.At this stage it was thought that it would be wise to

look more closely at the principle of operation of theHovercraft. In brief, this principle is that a heavy bodycan be kept aloft on a cushion of air which is preventedfrom leaking out through the edges by means of a curtainof air. Both the curtain of air and the supporting cushionof air can be provided by a low-pressure, high-volumefan system. As the result of discussions with somemembers of the Hovercraft research team of the NationalResearch Development Corporation, it was decided thatthis low-pressure, high-volume system was likely to bea better way of supporting patients.This principle has been applied by means of the

apparatus illustrated in fig. 1. Both the curtain and thecushion of air are provided by means of suitably arrangedjets positioned in a rectangular form. In the apparatusillustrated, which has been designed to

" levitate "domestic pigs whose total weight is equivalent to thetrunk weight of the average adult, 12 jets, 6 in. wide

by 1/2 in. deep, are employed. Approximately 2000 c.ft.of air per minute are supplied by means of a paddle fanat a nressure nf 1R in. water.

It t was s

found that byusing this ap-paratus "pigscan fly " (fig.2). In all

experimentsthere are in-evitable prob-lems, and sofar we havestudied onlysome of themore obviousones. The

problems swhich imme-

diately come

to mind are

(a) the pos-sible damageFig. 1-Arrangement of apparatus

to tissues produced by the air pressure, and (b) the possibleextreme and rapid cooling by the high air-flow rates.To study the problem of tissue damage, a 2 in. x 2 in.

dermal wound was made on the back of an anaesthetised

pig in such a position that it was exposed to the jetpressure of unsterilised air. The piece of skin removedfrom the pigwas left ex-

posed to nor-mal laboratoryair conditions,and in a cer-tain senseserved as a

control. The

pig was then" levitated "until the der-mal woundwas dry-aperiod of onehour. Afterthis time theexcised pieceof skin was

wet andshowed nosigns of co-

agulation (fig.3). My col-league, G. D.Winter, whois studyingthe problemof normalwound heal-

ing in the domestic pig, has found that a comparablewound in normal conditions dries in approximately24 hours.

In the days following this " levitation " the pig showedno observable difference from its normal state; thewound was not clinically infected and was healingnormally.As far as the cooling of the pig was concerned, the

rectal temperature was recorded at a depth of 5 in. fromthe anus and during the hour of exposure it fell by 7°F.This fall in body temperature was thought to be a factorcontributing to the postoperative wellbeing of the animal.From the experiments conducted so far, it seems that

low-pressure, high-volume " levitation " may offer thefollowing advantages in treatment: (a) reduction inshock, (b) prevention of tissue-fluid loss, (c) rapid creationof a dry antibacterial shield, and (d) a possibility ofavoiding bedsores.My thanks are due to the R.A.M.C., who have generously provided

staff and equipment; and to Mr. H. J. Seddon and the Institute ofOrthopaedics for having encouraged this work. I must also acknow-

ledge the cooperation and advice of the following companies: Abreyand Gerratt, Avica Equipment, Benham and Sons, Keith Blackman,Brook Motors, Burgess Products, Flexible Ducting, Horace Green,W. C. Holmes, the worth Thames Gas Board, Porous Plastics, L.Robinson, Rotameter, Triplex, Martin Walter, Allen West, W. H.Willcox, and Zerny Engineering. I am particularly grateful for thehelpful advice of the research team of Hovercraft Development, Ltd.,and for the interest displaved bv the Medical Research Council.

Fig. 2-Pig " floating".

(A) (B)Fig. 3-A, Appearance of wound one hour after

"levitation"; and B, removed tissue placedbeside wound for comparison.