Evolution and the cardiac patient

These essays have traced the evolution of three great convective systems of the body: ventilation, circulation and excretion. We have seen how the ventilatory system evolved with an inherent susceptibility to flooding, how the kidney came to need an enormous blood flow and how a high blood pressure grew out of the explosive demands of muscular activity. Success and survival in the animal kingdom have overwhelmingly depended on physical mobility and strength. To ensure this the body makes use of the neuro-endocrine defence reaction which is also life-saving in injury. The reaction favours the retention of water and salt by directing blood away from the kidney and by endocrine activity. When the output of the diseased heart decreases, the body reacts in the way for which nature has programmed it. It cannot distinguish. But now the neuro-endocrine response persists. But now the neuro-endocrine response persists. Over weeks or months or years the retention of saline threatens the cardiac patient with drowning in his own juice. And every hour of the day and night be is running for his life.