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 (and 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 now at rest and during exercise. Many other studies, as well as our own: h ave shown that in uncomplicated hypertension, exercise endurance is signifi cantly reduced during beta-blockade, but is not disturbed and may even be i ncreased, during treatment with verapamil or diltiazem. Furthermore, studie s of a controlled-onset extended-release formulation of verapamil (commerci ally known as COER-24(TM) verapamil HCl) have demonstrated that the agent r esults in better control of the early morning blood pressure and heart rate than that of the conventional type of verapamil.