Retinal Arteriolar Reactivity Response Characteristics Assessed Using a Sinusoidal Hyperoxic Provocation

Abstract

Purpose: : To investigate the vascular reactivity response characteristics of the retinal arterioles to hyperoxic provocation.

Methods: : Four healthy volunteers were subjected to steady baseline (PETO2 100mmHg) and then sinusoidal hyperoxic provocation (PETO2 varied according to a sinusoid waveform between 100 and 500mmHg) using the RespirActTM gas sequencer. The Canon Laser Blood Flowmeter (CLBF-100) was used to repeatedly measure retinal arteriole reactivity. Sinusoidal end-tidal O2 and retinal arteriole reactivity data were fitted with a sine wave curve. The fitting procedure was assisted by specially-written analysis programs (National Instruments Inc, LabVIEW) that used the Levenberg-Marquardt algorithm. The phase lag, time constant, response time, gain, and "cut-off period" of the arteriole reactivity measurements to the sinusoidal hyperoxic provocation was computed.

Results: : The average correlation coefficient for the sinusoidal hyperoxic and diameter fits were r=0.999±0.0009 and r=0.730±0.1735, respectively, while for velocity and blood flow the fit values were r=0.452±0.1687 and r=0.530±0.1621, respectively. For diameter, the mean phase lag, time constant and response time were 1.30±0.59 min, 1.30±0.59 min, and 3.89±1.78 min, respectively. The mean diameter "cutoff period", the sinusoidal period that gives the corresponding vascular response of the time constant during a 500 mmHg step change, was 8.15±3.72 min. The average gain defined by the mean maximal Δ diameter/Δ 100 mmHg O2 was -1.92±0.37. Based on the sinusoidal diameter fit, the average maximal change in diameter was -7.69±1.50 µm.

Conclusions: : Assuming first order linear dynamics, we demonstrate a novel method of calculating the response time of the retinal arterioles to hyperoxic provocation.

Keywords: blood supply • oxygen • retina