Effect of Changing Heart Rate and Body Posture on the Ocular Pulse Amplitude and Optic Nerve Head Deformations

Abstract

Purpose : To use finite element (FE) analysis to model the effect of changing heart rate and body posture on the ocular pulse amplitude and lamina cribrosa (LC) deformations.

Methods : An FE model of a healthy eye was reconstructed. The choroid was biphasic and consisted of a solid phase (connective tissues) and a fluid phase (blood). The LC was viscoelastic as characterized by a stress-relaxation test. We applied arterial pressures at 18 entry sites (posterior ciliary arteries) and venous pressures at 4 exit sites (vortex veins). The heart rate was varied from 60 bpm to 120 bpm (increment: 10 bpm). Two body positions were considered: supine with a cerebrospinal fluid pressure (CSFP) of 11.3 mmHg, and standing with a CSFP of -0.8 mmHg. We reported the ocular pulse amplitude (OPA), pulse volume, and diastole-to-systole LC strains (i.e. deformations).

Results : With an increasing heart rate, the OPA decreased by 0.30 mmHg (Supine) and 0.25 mmHg (Standing) linearly for every 10bpm increase (Figure 1). The pulse volume also exhibited a linear relationship with heart rate, and decreased by more than 2L for both supine (2.01 L) and standing (2.45 L) positions. Diastole-to-systole LC strains reduced by 0.0063% (Standing) and 0.0043% (Supine) for every 10 bpm increase in heart rate.

Conclusions : Our model predicted that both OPA and pulse volume decreased with an increasing heart rate. Optic nerve head deformations were also affected by heart rate, which was in agreement with clinical observations that showed the decreased fundus pulsation amplitude during isometric exercise. Our results may help us better understand the role of blood pressure and heart rate on vascular dysregulation for glaucoma detection.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.