Autoregulation in the ocular and cerebral arteries during the cold pressor test and handgrip exercise

Abstract

The aim of this study was to determine whether autoregulation exerts similar effects in the ocular and cerebral vessels, which are both branches of the internal carotid artery. Ocular blood flow velocities, cerebral blood flow velocity and blood pressure were measured in 11 subjects during a 2-min resting period, static handgrip exercise (HG) and a cold pressor test (CPT). Blood velocity data for the superior and inferior temporal retinal arterioles (STRA and ITRA, respectively) and the retinal and choroidal vasculature (RCV) were obtained for 4 s during the measurement using laser speckle flowmetry. Mean blood flow velocity in the middle cerebral artery (MCAVmean) was measured by transcranial Doppler ultrasound. The conductance index (CI) of each vessel was calculated by dividing blood flow by mean arterial pressure. Blood flow velocity in the RCV increased by 19 ± 9% from resting baseline level during the CPT (P < 0.05), while blood flow in the STRA, ITRA and MCAVmean did not. The CI of the MCA decreased. The RCV blood flow velocity, ITRA blood flow and MCAVmean increased by 8 ± 1, 9 ± 3 and 11 ± 4%, respectively, during the HG (P < 0.05). Conversely, STRA blood flow remained unchanged. The HG did not significantly change the CI in any of the vessels measured. These findings suggest that cerebral blood flow velocity was maintained during the CPT, but autoregulation does not work well in the RCV during the CPT and HG.

Inner ocular blood flow response to exercise in healthy humans

“…No change was reported in retinal blood flow despite an increase in MAP during a cold pressor test, whereas choroidal blood flow increased 19) . Choroidal blood flow increased with an increase in MAP during dynamic exercise, while retinal blood flow remained at resting baseline level 12) .…”

“…The authors, in turn, observed that an increase in choroidal blood flow occurred concomitantly with an increase in MAP by roughly 15% during handgrip exercise (Fig. 4) 19) . These inconsistent results can be due to different types of exercise.…”

“…Choroidal circulation does not seem to be able to stabilize its blood flow, though autoregulation in choroidal circulation is still controversial 1,18,19) . No change was reported in retinal blood flow despite an increase in MAP during a cold pressor test, whereas choroidal blood flow increased 19) .…”

Ocular blood flow decreases during passive heat stress in resting humans

“…Laser-speckle images were obtained using a laser-speckle flowgraphy (LSFG) system (SoftCare, Fukuoka, Japan), which is described elsewhere (for example, [8]). The LSFG measurements were made in triplicate at each time point and the mean of the three values was used for analysis.…”

Blood flow in non-muscle tissues and organs during exercise: Nature of splanchnic and ocular circulation

“…However, whether autoregulation exists in the human retina has yet to be established. One study found no change in the retinal circulation during either the cold pressor test or handgrip exercise, indirectly suggesting the existence of autoregulation 48) . Consistent with the presence of autoregulation, choroidal flow did not change during submaximal dynamic exercise even where there was a pressor response 45,46) .…”