Structural readaptation of systemic resistance-sized arterioles in response to an elevated blood pressure reduces the forearm vasodilator reserve in patients with essential hypertension. The development of a similar process at the coronary microvascular level has frequently been hypothesized, but little information about coronary remodeling during the uncomplicated stage of hypertension has been obtained, and the relationship with concomitant changes in forearm blood flow reserve is not known.
To assess the minimal myocardial resistance and its relationship with the minimal forearm resistance in a group of male patients with mild-to-moderate uncomplicated hypertension and carefully matched controls.
Material and methods
The minimal myocardial resistance (Rminmyocardial, the mean arterial pressure: hyperemic myocardial flow ratio after administration of 0.84 mg/kg dipyridamole, measured by using positron emission tomography and [13N]-ammonia), minimal forearm vascular resistance (Rminforearm, a hemodynamic index of arteriolar structure derived from the mean blood pressure and maximal postischemic forearm blood flow by venous plethysmography), echocardiographic cardiac mass and wall thickness were measured in 25 male patients with mild-to-moderate uncomplicated essential hypertension, most of whom had previously been treated, and in seven sex- and age-matched normotensive controls.
Rminmyocardial (and hyperemia: baseline myocardial flow ratios) did not differ significantly between the two groups, whereas Rminforearm was significantly higher in hypertensives. There was no significant intraindividual correlation between the two parameters. The left ventricular mass index was greater in patients and was related positively to Rminforearm but not to Rminmyocardial for the overall sample. In a subgroup analysis, Rminforearm values were 2SD above control values in nine patients and within the normal range in the remaining 16. The myocardial reserve was very similar in the two subgroups.
The myocardial vasodilator reserve appeared to be preserved in these mild-to-moderate uncomplicated hypertensive patients, whereas the forearm vasodilator capacity was reduced, suggesting that the hypertensive readaptation process was not distributed homogeneously over the two vascular beds.