Arterial and Venous Systems in Essential Hypertension

The hemodynamic mechanisms of hypertension are often limited to the study of three dominant parameters: blood pressure, cardiac output and vascular resis­ tance. Accordingly, the development of hypertension is usually analyzed in terms of a 'struggle' between cardiac output and vascular resistance, resulting in the classical pattern of normal cardiac output and increased vascular resistance, thus indicating a reduction in the caliber of small arteries. However, during the past years, the clinical management of hypertension has largely modified these simple views. While an adequate control of blood pressure may be obtained with antihypertensive drugs, arterial complications may occur, involving mainly the coronary circulation and suggesting that several parts of the cardiovascular system are altered in hypertension. Indeed, disturbances in the arterial and the venous system had already been noticed in animal hypertension. The basic assumption in this book is that the overall cardiovascular system is involved in the mechanisms of the elevated blood pressure in patients with hypertension: not only the heart and small arteries, but also the large arteries and the venous system. For that reason, the following points are emphasized. First, the cardiovascular system in hypertension must be studied not only in terms of steady flow but also by taking into account the pulsatile components of the heart and the arterial systems. Second, arterial and venous compliances are altered in hypertension and probably reflect intrinsic alterations of the vascular wall.

I - Small arteries and the concept of resistance.- Hemodynamic basis for the concept of resistance and impedance in hypertension.- Structural component of vascular resistance in hypertension.- Baroreflex mechanisms and the high pressure system in hypertension.- II - Low pressure system and the concept of venous distensibility.- Venous compliance in essential hypertension.- Functional and structural components of reduced forearm venous disten- sibility in human hypertension.- Cardiac mechanoreceptors in hypertension.- Venous system, extracellular fluid volume and the kidney in essential hypertension.- III - Large vessels and the concept of arterial compliance.- Systolic hypertension in the elderly.- Large arteries in borderline and sustained essential hypertension.- Pulse wave velocity and hypertension.- Renin-angiotensin system and arterial wall in hypertension.- IV - Regional circulations.- The coronary circulation in hypertensive left ventricular hypertrophy.- Carotido-cerebral circulation in patients with sustained essential hypertension.- Renal circulation in essential hypertension.- Hepato-splanchnic circulation in human hypertension.- V - Forearm circulation as a model for the study of hypertension.- Methods for investigation of forearm blood flow.- The contribution of alpha-1 and alpha-2-adrenoceptor mediated vasoconstriction in essential hypertension as assessed by forearm venous occlusion plethysmography.- Beta-adrenergic receptors and the forearm circulation.- Converting enzyme inhibitors and hypertensive large arteries.- Calcium entry blockers and the forearm arterial bed.- Cations and the forearm circulation in hypertensive humans.- Conclusion.- Homeostatic mechanisms and structural modifications of the cardiovascular system in essential hypertension.- Listof contributors.