Blood pressure and heart rate responses during physical stress in hypertension: modifications by drug treatment

Resting heart rate is usually increased by 10-15% in the early stages of es sential hypertension. Consequently, the systolic arterial pressure-heart ra te (SAP-HR) product may be considerably elevated. In our population-based s tudies in subjects with untreated uncomplicated essential hypertension, the SAP-MR product was increased by approximately 40-45% compared with normote nsive controls, reflecting a markedly increased myocardial oxygen need. Whi le virtually all commonly used antihypertensive agents reduce blood pressur e during physical exercise, some drugs also reduce heart rate and induce a greater reduction in the SAP-MR product land in the myocardial oxygen need) than drugs not affecting heart rate. Our invasive series of investigations was on subjects aged 40-60 years with uncomplicated previously untreated e ssential hypertension. We found that hydrochlorothiazide reduced the SAP-MR product by approximately 10% during rest and exercise, beta-blockers (incl uding timolol, atenolol and metoprolol) decreased cardiac output at rest an d during exercise by 25-30%, while increasing the systemic arteriovenous ox ygen difference, and reducing the oxygen reserve in the venous blood. In co ntrast, calcium antagonists such as verapamil and diltiazem, are known to a ffect heart rate and reduced the SAP-MR product by approximately 20%. These drugs increase stroke volume during rest and exercise compared with beta-b lockers; they compensate for the reduction in heart rate and maintain blood flow at rest and during exercise. Many other studies, as well as our own, have shown that in uncomplicated hypertension, exercise endurance is signif icantly reduced during beta-blockade, but is not disturbed and may even be increased, during treatment with verapamil or diltiazem. Furthermore, studi es of a controlled-onset extended-release formulation of verapamil (commerc ially known as GOER-24(TM) verapamil HCl) have demonstrated that the agent results in better control of the early morning blood pressure and heart rat e than that of the conventional type of verapamil.