Respiratory fluctuations in pupil size

Abstract

Regular fluctuations in pupil size of the cat were measured and the properties, nervous pathways, and origin of these oscillations were investigated. The rhythm of pupil movements under control conditions appeared to be either locked to the central respiratory cycle or to the artificial ventilatory cycle. These movements were only seen in lightly anesthetized or tranquilized cats, but not in alert or deeply anesthetized cats (ether, halothane or pentobarbital). The fluctuations proved to be independent of sympathetic innervation but related to variations in parasympathetic outflow. At least two sources for pupil oscillations appeared to be involved: central respiratory activity and respiratory blood pressure fluctuations that modulated pupil width via sinoaortic baroreceptors. Lung movements per se, as a third possible factor, did not modulate pupil width, whereas electrical stimulation of the afferent lung vagi did; therefore the role of this mechanical factor is not clear. A review of the pertinent literature shows that in the organism there are many phenomena exhibiting respiratory oscillations. It seems likely that these oscillations have the same origin as the respiratory pupil fluctuations.

Synchronization between arterial blood pressure and cerebral oxyhaemoglobin concentration investigated by wavelet cross-correlation

“…On top of that, in particular, when the test subject is drowsy, the pupil diameter shows small oscillations around the respiratory frequency, which have become known as 'the hippus'. This may also be observed under light anesthesia; it disappears when the anesthetic level deepens (experimentally studied in cats (Borgdorff 1975), but applicable to humans as well, as reviewed in Heaver (2011) and Onorati et al (2013). Borgdorff (1975) conclusively showed that the hippus reacts to baroreceptor input and is only dependent on parasympathetic activity.…”

Baroreceptor-sensitive fluctuations of heart rate and pupil diameter

“…Because the influence of blood pressure on PD can neither be mediated by an increased filling of the iris vessel nor by fluctuations in intraocular pressure [1], a neuro-mediated mechanism can be hypothesised [14]. We can speculate that signals from the carotid sinus reach not only the cardiovascular centre, but almost the entire reticular formation.…”

“…DISCUSSION To our knowledge t he contribution of baroreflex control to the spontaneous PD fluctuations was only investigated by invasive study in animals [1].…”

“…Recently, t he identification of a spectral component in the LF band in spontaneous Pupil Diameter ( PD) fluctuations has been reported by our group [5] and by others [6]. Animal studies suggested that two sources for pupil oscillations could be involved: central respiratory activity and respiratory blood pressure fluctuations that modulate pupil width via sinoaortic baroreceptors [1]. It might be hypothesized that in humans carotid and sinoaortic baroreceptors may contribute to, if not cause, the genesis of pupillary LF and HF rhythms.…”

“…The sympathetic and parasympathetic innervations of the iris muscle are supposed to be responsible for these physiologic fluctuations of the human pupil (hippus). It has been demonstrated, first in animals [1] and then in humans [2] [3], that the respiratory rhythm is one of the source of these fluctuations. In general the inspiration is accompanied by pupil dilatation, the expiration by pupil constriction.…”