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G R a V I T Y a N D Ma N Part I . Studies on the Effect Of GRAVITY AND MAN PART I . STUDIES ON THE EFFECT OF INCREASED GRAVITATIONAL FORCE ON MAN. PART I I . THE EFFECTS OF OTHER PHYSIOLOGICAL STRESSES ON MAN'S TOLERANCE TO INCREASED GRAVITATIONAL FORCE. MATTHEW KENNEDY BROWNE THESIS PRESENTED FOR THE DEGREE OF DOCTOR OF MEDICINE IN THE UNIVERSITY OF GLASGOW. MARCH 1959. ProQuest Number: 13850369 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a com plete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest ProQuest 13850369 Published by ProQuest LLC(2019). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States C ode Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 CONTENTS. PAST I . Page CHAPTER I* INTRODUCTION. 1 " I I . METHODS AND MATERIALS. 10 " I I I . PHYSIOLOGY. PI " IV. HUMAN TOLERANCE TO ACCELERATION. 35 “ v. THE ELECTROCARDIOGRAM DURING POSITIVE 50 ACCELERATION. " VI. CHANGES IN THE ELECTRICAL AXIS AND THE VECTORCARDIOGRAM DURING 66 ACCELERATION. VII. THE ELECTRO-ENCEPHALOGRAM DURING 80 POSITIVE ACCELERATION. K V III. THE OCCURRENCE OP CONVULSIVE EPISODES 86 ON THE CENTRIFUGE. XI. A METHOD FOR THRESHOLD DETERMINATION 91 IN THE HUMAN CENTRIFUGE. PART I I . CHAPTER I . INTRODUCTION. 107 " I I . THE EFFECT OF HEAT ON TOLERANCE TO POSITIVE ACCELERATION. 136 " I I I . THE EFFECT OF BREATHING OXYGEN AT ATMOSPHERIC PRESSURE ON TOLERANCE 157 TO ACCELERATION. IV. THE EFFECT OF HYPE RGLYCAEMIA ON 183 TOLERANCE TO ACCELERATION. Page CHAPTER V. THE EFFECT OF INSULIN HYPOGLYCAEMIA 189 ON TOLERANCE TO ACCELERATION. M VI. THE EFFECT OF THE DEGREE OF FILLING OF THE STOMACH ON TOLERANCE TO P l6 ACCELERATION. It V II. THE EFFECTS OF INGESTION OF ETHYL. ,c__ ALCOHOL ON TOLS RANCE TO ACCELERATION. tt V III. THE EFFECT OF HYPERVENTILATION ON TOLERANCE TO ACCELERATION. tl IX. MULTIPLE STRESS SUMMATION. 264 H X. GENERAL DISCUSSION AND CONCLUSIONS. 277 It XI. SUMMARY. ACKNOWLEDGEMENTS. 291 REFERENCES. 252 APPENDIX. 288 INTRODUCTION. The immediate human problems of high speed flight are acceleration, environmental temperature and mental stress. All occur to some extent in every sortie, their relative importance depending on the flight pattern. In order to predict the human limitations it is necessary to determine man’s tolerance to these stresses and to examine any other factors which may influence their effect. This thesis presents the results of a number of experiments designed to examine human tolerance to positive acceleration. This type of acceleration, which will be more closely defined in the following paragraphs, may be considered as that which produces a force acting from the head to the feet, i.e. an increase in gravitational force. The simplest subjective example is the impression of increased weight which is felt when ascending in an express lift. The latter part of this thesis is the results of studies on the influence of other physiological factors which commonly occur in f lig h t on human to lera n ce to in creased gravitational force. These factors are heat, hypoglycaemia, hyperventilation, breathing pure oxygen, the after effects of alcohol and the degree of filling of the stomach. It is appreciated that most of the experiments performed deserve f u lle r examination and that many other physiological parameters require to be measured. This work however was of an applied nature and the requirement ms fo r an urgent survey of the whole prohlen rather than a detailed analysis of any one facet. Force is defined by Newton's first law as that which modifies, or tends to modify, either the state of rest of a body or its uniform motion in a straight line. Newton's second law provides the fundamental basis for the measurement of force and, when the units of measurement have been suitably chosen, may be reduced to the equation; F = m a (l) where a is the acceleration produced in a body of mass m by the action of a force F. This equation can be applied to calculate not only the forces producing linear accelerations, but also the forces involved when a body is made to traverse a curved path. Here, the direction of motion is being- changed continually, and, by Newton's first law, a force is required to do this. When a body traverses a curve, radius r, with velocity v, it can be shown that the continuous change of direction is eq uivalent to an a c c e le r a tio n o f amount v ^ /r (c a lle d th e centripetal acceleration) directed towards the centre of the curve; i.e. perpendicular to the direction of motion at any particular instant. Hence the force required to provide such an acceleration for a body of mass m is m v^/r. This force acts in the same direction as the acceleration (towards the curve's centre) and is called the centripetal force. The effect of inertia is to introduce a force exactly equal in magnitude, but opposite in direction, to the centripetal force. This opposing force, called the centrifugal force, would cause the body to fly off at a tangent to its curved path if the centripetal force were to be suddenly eliminated. It is this centrifugal force which is of importance in flight. Forces due to acceleration, whether linear or centripetal, can never act in isolation except in the hypothetical case of an object removed to an infinite distance from all other matter. In practice, whatever other forces there may be, the force of gravity is always present. The q u a n tita tiv e b a sis o f Newton’s work on g ra v ita tio n a l attraction was his assumption that ’’every particle of matter in the universe attracts every other particle with a force inversely proportional to the square of the distance between the two particles”. He also showed that a sphere of uniform density acts on an external body as if all its mass were concentrated at its centre. For the gravitational force, W, between the earth, mass M, and a comparatively small body, mass m, distant R from its centre, Newton’s law of attraction gives the equation W = G Mm (2) R2 where G is the 'constant gravitation'; when the other quantities are measured in e.g.s. units (i.e. M and m in g., R in cm. and w in dynes), G = 6,670 x 10“®. The force with which any body is attracted by gravity towards the earth's centre is defined as the weight of that body. Equation (2), thus, gives the weight of a body of mass m, situated at the earth's surface, in terms of the earth's radius and mass. It has been established that, if the effects of other forces such as air resistance can be excluded, all bodies fall to the ground with the same acceleration, irrespective of their mass. Thus it has been demonstrated that a very light body and a heavy one f a l l with th e same a c c e le r a tio n when the experiment is done in vacuo: This acceleration for free fall is a characteristic of the locality at which it is measured. It is called the 'acceleration due to gravity’ and is represented by the symbol g. The conventional value of 32.2 f t . / s e c . 2 is sufficiently accurate for normal use. By Newton's second law of motion (equation (l)) the weight w of a body of mass m may be expressed in terms of g as: W = mg. Since g is also the force with which gravity acts upon unit mass, it is sometimes referred to as the 'intensity of gravity' at a given point. If one equates the weight of unit mass in terms of the earth's mass and G (equation (2)) with the weight of unit mass in terms of g, then at the surface of the earth:- 5. M £ = G1 R? (3) H "being th e ea rth ’ s rad iu s. That £ i s the same fo r a ll "bodies at the same locality, is therefore demonstrated to "be a consequence of Newton’s laws of motion and his law of universal gravitation. Equation (3) is approximate to the extent that the distribution of the earth's mass is not completely symmetrical with respect to its centre. Also the relatively small centrifugal force due to the earth's rotation has been ignored. The magnitude of this force depends on latitude, but its effect never reduces true gravity by more than a few parts in a thousand. The main purpose of this/digression on gravity has been 1 to explain what it meant by the term 'weight* in its usual sense and by 'acceleration due to gravity'. Also it will be clear from equation (2), that, with the range of altitudes p o ssib le at present w ith manned a ir c r a ft, o v e r a ll v a r ia tio n s in the force of gravity due to change of distance from the 9 ' earth's centre cannot exceed 1 per cent and are therefore insignificant from a physiological point of view. For example, the error of assuming £ to be that at the earth's surface for an aircraft flying at an altitude of 100 mis.
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