Pain

Abstract

Lewis, 1 by an ingenious method, studied the time factor in the production of pain following temporary complete obstruction of the brachial artery. After an interval of 70 to 75 seconds, obstruction of the brachial artery caused unbearable pain. He thinks that during this interval a change in metabolites may be the factor in producing pain and has called this the “P-factor”. Lewis used as a criterion of pain, that unbearable end point in order to eliminate the psychic factor. In our earlier experiments when the coronary artery was temporarily occluded, pain was observed immediately. 2 , 3 The question raised by Lewis as to the discrepancy apparent between the results by different methods of study suggested further investigation.

Method. 20 dogs were used. Briefly, the chest was opened under ether anesthesia, and artificial respiration given at once. The pericardium was exposed, opened, and a tough linen suture passed around the ramus descendens branch of the left coronary artery as close to its origin as was technically possible. This suture was passed through a flanged glass tube, a purse string suture held the tube firmly in place in the pericardium and prevented an open pneumothorax. The chest wall with the tube projecting was tightly sutured. After a period of not less than 4 hours following the completion of the operation, traction on the suture will occlude the vessel and produce a painful response. At the conclusion of all experiments the animals were sacrificed and the position of the ligature verified by postmortem examination.

Results. The typical result is that of immediate pain response to slowing of blood flow during constriction. The time interval is too short to be easily accurately measured.