Abstract

Although the homeostatic and pathophysiological impacts of circadian rhythms on the cardiovascular system are well-documented in the literature, the cardiovascular dynamic modulations of ultradian rhythms—which are generated by autonomous oscillators that interact with the circadian system and recur with periods shorter than 24 hours—have emerged as a novel focus of research. The cardiovascular system exhibits prominent ultradian oscillations at the levels of arterial blood pressure fluctuations, heart rate variability, and catecholamine levels. These oscillations occur through a dynamic and reciprocal interplay between peripheral sympathovagal balance and autonomous oscillator mechanisms within the central nervous system that interact with the circadian system. Current autonomic assessments based on cardiac electrical activities do not always fully reflect the vascular effects of these central discharges within peripheral effector beds. Therefore, the limitation of conventional cardiovascular autonomic tests in converting systemic microcirculatory reflections into quantitative data enhances the importance of investigating non-invasive and objective complementary methods to assess peripheral sympathetic reactivity. In this regard, the nasal mucosa, with its dense vascular structure under dual autonomic control, along with the periodic volume changes in the nasal cavity (the ultradian nasal cycle), may offer a suitable microcirculation model for evaluating the peripheral reflections of central autonomic outputs. Accordingly, it is hypothesized that acoustic rhinometry—despite its nature as a localized nasal assessment method—may serve as a potential indirect autonomic indicator model in cardiovascular research by converting instantaneous nasal geometric changes potentially associated with systemic sympathetic activity into quantitative data.