Blood Volume following Operations in Man. 



421 



the average vaso-motor tone, the increased heart output more than com- 

 pensating for the vaso-dilatation, and so raising the systolic pressure. This 

 agrees with the fact that during exercise the diastolic pressure may fall. 



In the curves of diurnal variations the lag of the haemoglobin changes in 

 the capillary blood behind the blood pressure changes is very evident, and 

 the haemoglobin change is therefore probably secondary. On the other 

 hand, the concentration seen in the capillary blood immediately after a meal 

 occurs quickly, is transient, and has no parallel in the blood pressure 

 changes ; it is probably a local and temporary change due to a local con- 

 striction of the blood vessels. By reference to the Tables of Case IV it will 

 be seen that an estimation of the haemoglobin of venous blood immediately 

 after a meal showed it to be almost 10 per cent, more dilute than the 

 capillary blood, while the capillary blood itself showed this dilution a little 

 later. So that all the figures seem explicable, if it be assumed tliat any 

 change in the haemoglobin percentage of the capillary blood, imless it he a 

 transient one, indicates a corresponding change in the blood volume. In 

 cases where the periplieral circulation is reduced to a low level (as in 

 Case III), a considerable degree of stasis may result, and then the change in 

 the capillary blood may lag far behind the general circulation changes. 



One case of spinal anaesthesia (Case X) is included, and though an exami- 

 nation of the blood changes was not possible in this case, yet the changes 

 -observed are easily explicable when analysed by the formula — the stovaine 

 inducing a fall of blood pressure through a partial vasomotor paralysis, and 

 this being compensated for by an increased heart output until the resistance 

 is raised by vaso-constriction in other parts. One case (Case XII) of pure 

 traumatic shock uncomplicated by haemorrhage or anaesthesia is also included 

 for comparison. In this case collapse occurred with great dilution of the 

 blood, and this is paralleled by a calculated great loss of vasomotor tone. 



This formula is therefore put forward tentatively as of value in the 

 analysis of the circulatory changes in most clinical conditions. It is not 

 ■claimed that its truth is absolute, and it can probably be improved. 



In conclusion, my thanks are due to Prof. Dreyer and Prof. Bayliss for 

 much valuable advice, to Lt.-Col. Waring, D.S.O., for the facilities he gave 

 me to carry on this research, and to Captain Wagstaffe, F.E.C.S., for assistance 

 in many of the cases, and for access to all his patients. 



