9 Junie 1956 S.A. TYDSKRIF VIR GENEESKUNDE 535 exercise their time-honoured function of dispensing cited as an argument in favour of the clause. Ca!l it for their patients, within a certain distance of a chemist's be in the interests of the poor to require that the patIent shop, would in our opinion be an affront to an honour­ shall not only be responsible to the doctor for his fee, able profession. Nor would it be in the public interest. but shall pay a chemist as well? And might it !lot No doubt as many towns and villages as possible well be a hardship to enforce a journey up to 10 miles ought to have the amenity of a pharmacy, but not or more to obtain the medicine which the doctor has by legislation of this .kind. Besides, the chemist and ordered? druggist is by no means exclusively dependent on Finally, is it just or reasonable that a doctor who doctors' prescriptions. Most chemists sell household is earning his living by carrying on a dispensing pra~tice remedies, patent medicines, and any other medicine within the 5-mile limit should suddenly be reqUIred not forbidden by law to be sold, and are ready to by law to cease; and that oqtside that limit dispen~ing give advice about. treatment from the patients' symp­ doctors should be exposed to permanent uncertamty toms; and their trade is usually not confined to medica­ lest a chemist's shop should be opened in his neighbour­ ments. The' interests of the non-Europeans have been hood. SOME ASPECTS OF THE MECHANICS OF THE ABDOMEN· J. AnNO, M.B., CH.B., DIP. (Q. & G.) (RAND) Temporary Assistant Obstetrician and Gynaecologist, University of the Witwatersrand and Johannesburg General Hospital The understanding of intra-abdominal mechanics has no actual pressure-readings were taken and the con­ eluded research since the very early days of medical clusions were mostly assumptions. science. During the 19th century and up to the time of Goffe,6 in 1912, attempted to define intra-abdominal World War I, substantial investigation into abdominal pressure, and I think his definition is, as good as any dynamics was made. These researches fell into decline I have come across. He defined it as 'the pressure because of the difficulty of the project generally,- and within the abdomen due t9 external atmospheric because it was regarded as impracticable to measure pressure, "to gravity, to muscular contraction of its intra-abdominal pressures. However, during the walls, to intravisceral pressure'. Rushmer3 would add World War IT the subject obtruded itself again, pre­ to this 'the head of pressure provided by the mass of sumably because of war wounds and the problems of the movable organs within'the peritoneal cavity' (which 3 aviation medicine.1- It would be misleading to say in fact is the same as gravity). that workers are lacking who have concerned them­ In those days, as today, the general impression selves with abdominal mechanics. We have been prevailed that intra-abdominal pressure is negative and unable, though, to discover much in the way of new that under certain circumstances there is a tendency to publications of significance after 1950. produce vacuums. With this in mind, it was said that The lar~e hiatus in our present-day knowledge is the organs in the abdominal cavity were held in place certainly· noticeable when we attempt to explain the by this negative pressure, although the various liga­ etiology of conditions such as paralytic ileus, acute ments might have something to do with it. 5lilatation of tIle stomach, uterine prolapse and displace­ Sturmdorf1 said that there was no muscle or ligament ments~ enterocele, hernias, the mechanisms of parturition, that could withstand the continuous force of the intra­ defaecation arid micturition, visceroptosis (if such a abdominal pressure. These ligaments, according to­ condition exists), oesophageal regurgitation and dys­ him, support the organs not by virtue of their textural pepsia, board-like rigidity 0'£ the abdomen, etc. resistahce, but by deflecting the displacing force ofintra­ CoffeY,4 in 1917, said, 'Except in chronic processes, abdominal pressure. such as the development of a tumour by cellular increase, If it were true that the intra-abdominal organs a cyst or ascites which has behind it the blood pressure maintained their relative positions by virtue of de­ or pregnancy, there is but little change in the capacity flective forces pushing down on the one hand and of the abdomen of an otherwise normal· person'. In supporting on the other, then one must postulate a 1922 CoffeyS was still of the opinion that the abdominal central area in the abdominal cavity exerting pressure walls were relatively inelastic. This he assumed to in all directions. Obviously the force supporting the be an important factor in the 'splinting' ofthe abdominal under-surface of the liver must be diametrically opposed contents and so increasing the intra-abdominal pressure; to that pressing down on the superior surface of the particularly when the deposition of intra-abdominal uterus. The answer is still unknown. Clearly there is fat occurred, for instance, in obesity or in the West­ no single factor which is solely responsible for the Mitchell technique of the rest cure and fo(ced feeding position of the viscer~; but ligaments, intra-abdominal for neurasthenics and visceroptotics. Unfortunately pressure and support from adjacent organs seem to •A paper presented at the South Mrican. Medical Congress, be the most important. Pretoria, 1955. In the strict physical sense the question may well be 536 S.A. MEDICAL JOURNAL 9 June )956 , . asked.: Is there such a thing as intra-abdominal pressure? walls .of the abdominal" and pelvic cavities form one ,Can the abdominal cavity be considered as one physical somewhat complex organ in themselves· and that, to unit? First of all, there is no abdominal cavity in the a major degree, the functions of 'the orglins encased physical sense, except in the case of ascites, pneumo­ therein depend upon its state, and vice versa. peritoneum or peritonitis, where there is a cavity One may compare the abdomen to a sealed cylindrical filled with liquid, air, or both. rubber bag which is being· suspended by its upper Unless there is fluid in the peritoneal cavity, the margins. This bag is also partially filled with liquid , abdominal wall surrounds a multitude of organs tightly and the remaining air draw.n off: The rubber wall is adjacent to each other and tightly adjacent to 'the regarded as being the counterpart of the abdominal wall; the interspaces between two organs, or between wall, and the liquid as simulating the abdominal con­ an organ and the abdomin!11 wall, are merely potential. tents. The serosa with its moisture, sees to it that no fricti.on One will find that no matter what the.position of the takes place on the one hand and that no spaces are bag is, the fluid will always find its own level. This created on the other: will alter the 'shape of the bag accordingly.• For the present, I will consider the abdominal cavity - In, tIie vertical position the fluid will gravitate to as including the pelvic region as well. Thus the limits - the lower part of the cylinder and the rubber bag will of the cavity are the very mobile diaphragm above, assume a pear shape. The pressure above will then be the pelvic floor below, the rather rigid spinal column much less than that at the bottom of the cylinder. behind, and in front and at the sides the fairly flexible This difference in pressure is due entirely to the differ­ and elastic muscular abdominal wall.. Within these ence of the leve s of the water colmnn measured. This boundaries are the abdominal and pelvic organs, both . increased pressure at the lower level has been shown solid and hollow, surrounded by their fat and peri- to exist in both animals and the human being. Rushriier .toneum. The retroperitoneal plane, with its spongy showed that this state existed in dogs. In our experi­ connective tissue, fat and kidneys, does not participate ments we have shown that in the supine position intra­ to any degree in the present problem, the exceptions gastric and intrarectal pressures are identical, but that being retroperitoneal tumours encroaching on the in the erect posture the intragastric pressure is less than capacity of the abdominal cavity. the intrarectal pressure. This difference in pressure is One then assUJpes that. the capacity of the abdomen equa-l to the pressure of a colu.mn, of water between is .very variable, differing from subject to subject ac­ the tWQ levels at which the-readings were taken (Fi~ 1). cording to body build, II1uscular tone, obesity, posture, In ,the horizontal position one finds that the bag.. etc. flattens and tends to bulge at the sides. Obviously Being a striated muscle, the diaphragm is subject to . the degree .of distension, bulging and flattening will cortical impulses and can be moved "at will. However, depend upon the elasticity of the rubber wall; and in unlike all other striated muscles, it retains its full the human being upon the muscular tone of the antero­ coordinated function at a time when our voluntary lateral abdominal wall. An anaesthetized patient, with control of striated muscles has partially or en~irely a relaxed abdominal wall, in the sup.ine position, will ceased-<luring general anaesthesia and in coma: The also tend to bulge in the flanks. This tension is the cessation" of diaphragmatic function causes death. reason Why air rushes into the peritoneal cavity ·when There are many theories which attempt to explain the the peritoneum is opened.