Methods and consequences of lowering the blood pressure / by W.D.M. Paton.

  • Paton, William D. M.
Date:
[1957?]
Catalogue details

Licence: In copyright

Credit: Methods and consequences of lowering the blood pressure / by W.D.M. Paton. Source: Wellcome Collection.

    16/24 (page 32)
    records were obtained. The outstanding- thing- about this experiment is that every student had a different pattern of autonomic block. Some would have a postural hypotension, to the verge of fainting-, without any effect on the pupil or the reaction to accommodation. Others would have quite a marked effect on the e^es and yet very little effect on the blood pressure. It was remarkable that even in a single ganglion, the ciliary ganglion, you might find paralysis of the pupil and not of accommodation, or paralysis of accommodation and not of the pupil; it seemed as though you could produce a sort of Argyll-Robertson pupil or inverse Argyll- Robertson pupil according to the individual. One has therefore to allow for a substantial variation from one individual to another, and from one ganglion to another. An analogous point is this, that it is difficult to produce complete block with these drugs. If, for instance, you give maximum doses of hexamethonium to an anaesthetised animal, you will still fail to lower its blood pressure as far as can be done by destroying the spinal cord; and there are other examples illustrating the difficulty of paralysing all the ganglia in the body. Now there is an analogous clinical situation here, in the difficulty met by the surgeon undertaking sympathectomy. There are many ganglia in the sympathetic system which are not located in the sympathetic chains normally drawn in the text books, but are hidden away in spinal nerves, in rami communicantes, sometimes found approaching the spinal canal itself (cf. Boyd and Monro, 1949). Now we know that hexa¬ methonium, and quaternary salts like it, penetrate into the cerebrospinal fluid only with great difficulty, so that it cannot reach structures which are definitely within the cerebrospinal axis. But we know also that it can reach ganglion cells in the superior cervical ganglion, and in the heart and in the intestine, and so on. The interesting question arises as to where the barrier to diffusion of these quaternary salts disappears as you move out from the central nervous system to the peripheral nervous tissue. It seems quite possible that the change of accessibility of ganglia to compounds of this sort is not abrupt as you come through the vertebral laminae, but may actually occur somewhere along a nerve trunk; so that any ganglion cells which have not been fully extruded into the normal sympathetic chains may, in fact, be simultaneously inaccessible, and for the same reason, not only to the surgeon’s knife but also to the pharmacologist’s syringe. The Response to Sympathectomy. This brings me to a rather different topic. I mentioned that one of. the surgeon’s difficulties in sympathectomy is that he cannot remove all the sympathetic ganglia. It was shown quite a long time ago by Simeone, Cannon, and Rosenblueth that if you cut the majority, but not all, of the preganglionic fibres to a ganglion there is a remarkably rapid recovery of function. Recently Murray and Thompson (1957), in my laboratory, have been re-examining this phenomenon. Figure 11 illustrates what happens. Supposing you cut down the number of fibres in the preganglionic trunk of the cervical sympathetic in the neck by sectioning the rami where they leave the spinal nerves from the thoracic 1, 2, and 3 segments. This means that the remaining fibres, contributed by segments T4-7, now are the only ones