Relationships of cardiac function and structure to blood pressure rhythms

It is well known that hemodynamic load is one of the most important determinants of cardiac structure and function. Circadian variations in blood pressure (BP) values are usually accompanied by consensual changes in peripheral resistance and/or cardiac output. In recent years, in hypertensive patients with left ventricular hypertrophy (LVH), a reduction in the circadian variations of BP and, in particular, a lack of nocturnal decline were observed; patients with only a small reduction in BP or none at all during the night were considered "non-dippers." In patients in whom a regression of LVH was obtained after prolonged antihypertensive therapy, restoration of the circadian rhythm of BP was also observed. However, the division of patients into "dippers" and "non-dippers" is arbitrary and poorly standardized and repeatable, and in the recent SAMPLE study, most hypertensive patients with LVH were dippers. Therefore, we should be particularly cautious about the conclusions drawn using this index. On the other hand, in patients with LVH, reduced activity of the low pressure cardiopulmonary baroreceptors and impaired day-to-night modulation of autonomic nervous system activity were observed. Therefore, cardiac structural alterations may possibly impair BP modulation; on the other hand, the opposite could also be true: a primarily altered BP modulation, through a persistently elevated afterload, could increase cardiac mass. Therefore, the interrelationships between cardiac structure and BP modulation are complex, and as a result, new and more specific methods of evaluation circadian changes in BP are needed to better clarify their reciprocal influences.