BLOOD PRESSURE IN THE TROPICS. 327 



DISCUSSION. 



If the figures shown in this report should, after more extensive work, 

 prove to be representative facts, two very important points immediately 

 suggest themselves for solution: (a) The cause or causes for this very 

 decided decrease in blood pressure in the Tropics; and (&) its significance 

 in tropical pathology. 



At the present time, our understanding of the physics and physiology 

 of normal blood pressure in general is too incomplete to allow the use 

 of available data as premises for the explanation of the phenomena of 

 lowered blood pressure in warm countries. 



The energy of the heart, the peripheral resistance, the elasticity of the 

 arterial walls, and the volume of the circulating blood are the four chief 

 factors generally accepted as the principal forces governing the normal 

 blood pressure. All these factors are subject to considerable individual 

 physiologic variation, and, what is more important, as well as more 

 difficult to measure in instituting comparisons, they are so closely con- 

 nected and interdependent through vasomotor and other nervous influences 

 that changes in one may produce marked secondary effects in the others. 



However, in analyzing these four major factors which influence blood 

 pressure with the view of securing an explanation of the lowered tension 

 in the Tropics, it seems probable that the influence of the energy of the 

 heart and of the elasticity of the blood vessels may be eliminated. While 

 heart and arterial diseases are sufficiently prevalent in the Tropics, all 

 our work in the clinics and autopsy room are against the conclusion that 

 these organs are factors in the general tendency toward lowered arterial 

 tension. 



The volume and viscosity of the blood have not been studied sufficiently 

 in Manila and we are not familiar with reliable observations upon these 

 factors in other parts of the Tropics. This important subject should 

 be investigated carefully. The literature of tropical medicine seems to 

 support the general opinion that anaemia is almost universally prevalent 

 among people who have lived for some years in the Tropics; but this 

 is by no means proved. 



The clinical appearances of pallor of the skin and mucous membranes 

 which are so prevalent are probably responsible for this opinion, but 

 such observations do not necessarily prove that anaemia is actually present. 

 These appearances may be explained in other ways, and work on the 

 blood does not support the conclusions of any such general prevalence 

 of anaemia. The estimation of hsemaglobin by percentage methods shows 

 an average which will compare favorably with that of temperate climates 

 and the number of erythrocytes per cubic millimeter of blood will show an 

 equally normal average. 



