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Introduction
It is believed that general vascular dysfunction and defective cardiovascular neuroregulation may play a major pathogenetic role in patients with normal tension glaucoma (NTG). A higher incidence of cardiovascular disorders 1 and ischaemic cerebral lesions 2 has been reported in patients with NTG compared to patients with primary open angle glaucoma or ocular hypertension. 3
Variables such as arterial blood pressure (BP) and heart rate (HR) depend on the autonomic nervous system (ANS). Sympathetic neural activity (SNA) causes an increase of HR, stroke volume and vasoconstriction. SNA regulates the circadian variation of BP and is closely linked to nocturnal dipping. Chronic increased SNA can lead to arterial and cardiac remodelling, endothelial dysfunction, increased tissue oxygen demand and subsequent decreasing of the ischaemia threshold in all organs, including the eye. 4 It has been postulated that optic nerve head (ONH) circulation is not purely autoregulated but may also be affected by the systemic ANS and circulating vasoactive hormones. 5 High sympathetic drive may constrict the microvasculature nourishing the ONH and lead to a decrease of the ocular blood flow.
There is evidence that nitric oxide (NO) is a major modulator of the autonomic control of HR and acts as a sympatholytic factor. 6 Reduced levels or bioavailability of NO in patients with glaucoma 7 may therefore shift an ANS balance to a sympathetic tension.
Heart rate variability (HRV) and BP variability (BPV) represent reliable and non-invasive tools to assess the ANS modulation under physiological conditions. HRV describes variation of HR and RR intervals whereas BPV is defined in terms of SD of the BP readings and is a clinical marker to describe the adaptation of the systemic vascular resistance to the fluctuation in cardiac output.
The purpose of the present study was to evaluate the activity of the central ANS by defining 24-h HR modulation, 24-h BPV and nocturnal dipping status in patients with NTG.
Materials and methods
Patients newly and previously diagnosed as having early and middle-stage NTG and control subjects of either sex were included in this prospective study. The study was performed according to the tenets of the Declaration of Helsinki and was approved by an institutional review board at the Military Institute of Medicine in Warsaw. The study is listed...