ŒDEMA AND HEART-FAILURE IN THE TROPICS

A mechanism is outlined to explain why oedema forms so readily in hot climates. A continual cutaneous vasodilation produces a low total peripheral resistance so that the mean arterial pressure cannot be raised except by increasing cardiac output. This inability to raise the arterial pressure as efficiently as usual will lead to difficulties in dealing with excess sodium and water loads, because the mean arterial pressure is the major determinant of urinary output. Anything which favours the retention of sodium and water in hot climates must therefore make things worse. This mechanism will also explain the post-partum cardiac failure syndrome which occurs in Northern Nigeria, since Hausa women take high-sodium diets and lie on heated beds during the post-partum period. The necessity for a further increase of cardiac output to excrete excess sodium and water in hot climates causes stress in persons with vulnerable myocardia and produces the symptoms and signs of cardiac failure more rapidly.