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Effect of acute decreases of perfusion pressure on choroidal blood flow in humans
Insights
Choroidal blood flow (ChBF) shows autoregulation in response to moderate changes in ocular perfusion pressure. This regulation appears to be a neural or passive hemodynamic process, not myogenic or metabolic.
Area of Science:
- Ophthalmology
- Physiology
- Biomedical Engineering
Background:
- The choroid is a vascular layer in the eye responsible for supplying oxygen and nutrients to the outer retina.
- Understanding choroidal circulation dynamics is crucial for diagnosing and managing various ocular diseases.
- Ocular perfusion pressure (OPP) significantly influences ocular hemodynamics.
Purpose of the Study:
- To investigate the relationship between choroidal blood velocity (ChBVel), blood volume (ChBVol), and blood flow (ChBF) in the foveal region.
- To determine the correlation between these choroidal circulation parameters and ocular perfusion pressure (OPP).
- To assess the autoregulatory capacity of the choroidal circulation.
Main Methods:
- Laser Doppler flowmetry was used to measure ChBVel, ChBVol, and ChBF in healthy subjects.
- Intraocular pressure (IOP) was incrementally increased using scleral suction to alter OPP.
- Pulsatility of flow parameters was analyzed during the cardiac cycle.
Main Results:
- The relationship between mean ChBF (ChBFm) and mean OPP was non-linear, indicating autoregulation.
- ChBFm was less affected by pressure decreases at high pressures than expected in a passive system.
- A significant increase in ChBFm over baseline was observed upon release of suction.
Conclusions:
- Choroidal blood flow exhibits a bilinear relationship with mean ocular perfusion pressure.
- The choroidal circulation demonstrates autoregulatory capacity for moderate decreases in perfusion pressure.
- The observed temporal response suggests a neural or passive hemodynamic mechanism for autoregulation.
Purpose:
To investigate the relationship between choroidal blood velocity (ChBVel), blood volume (ChBVol) and blood flow (ChBF) in the foveal region of the human ocular fundus and ocular perfusion pressure and to determine whether the choroidal circulation has some autoregulatory capacity.
Methods:
Measurements of ChBVel, ChBVol and ChBF were obtained by laser Doppler flowmetry in healthy subjects (age range, 21 to 57 years) with normal eye examination results. Measurements were performed at normal intraocular pressure (IOP) and during successive step increases in IOP induced by scleral suction. In experiment 1, in six eyes (five subjects), the IOP was increased rapidly, in steps of 50 to 100 mm Hg of suction pressure, which each lasted approximately 10 seconds to a level above diastolic ophthalmic artery blood pressure (IOP = approximately 72 mm Hg). In experiment 2, in 14 eyes (seven subjects), the IOP was increased slowly in four successive steps at 2-minute intervals to a level of approximately 42 mm Hg. We also determined the pulsatility of the flow parameters during the heart cycle, pulsatility = 1 - diast value/syst value.
Results:
For both rates of suction cup increase, the relationship between ChBFm (mean ChBF over the heart cycle) and mean perfusion pressure was not linear. At high pressure, ChBFm was less affected by decreases in the pressure than expected from a passive vascular system. In some cases, no change in ChBFm was detectable, although significant changes in PChBF occurred. Further decreases in perfusion pressure resulted in a proportional decrease in ChBFm. On release of suction, a significant increase in ChBFm over baseline value was detectable in experiment 1.
Conclusions:
The relationship between ChBFm and ocular mean perfusion pressure appears to be bilinear and reveals some autoregulation for moderate step decreases in perfusion pressure. The temporal characteristics of the ChBFm-response suggest a neural or passive hemodynamical process rather than a myogenic or metabolic compensatory mechanism.