Effect of systemic hyperoxia on optic nerve head blood flow in normal subjects, as measured by laser speckle flowgraphy

Abstract

 

Purpose

 

To evaluate the capability of laser speckle flowgraphy (LSFG) to assess optic nerve head (ONH) blood flow (BF) changes in response to hyperoxia.

 

Methods

 

This study included 30 healthy volunteers (mean age: 28.5 ± 4.0, male: female = 13: 17). The testing protocol had three phases: in the baseline phase, the subjects inhaled room air for 5 minutes; in the hyperoxic phase, pure oxygen (6L/min) for 15 minutes; and in the recovery phase, room air again for 15 minutes. LSFG measurements of mean blur rate (MBR), which represents ONH BF, were taken every minute. The MBR ratio in the hyperoxic and recovery phase was calculated with reference to this baseline. Clinical parameters including systemic blood pressure, diastolic blood pressure, pulse rate, respiratory rate, saturation of pulse-oximetry oxygen (SpO2) and end-tidal carbon dioxide (EtCo2) were measured with an automated monitor every two and a half minutes.

 

Results

 

SpO2 increased significantly during hyperoxia, from 97.3% ± 1.1 to 99.0% ± 0.7 (P < 0.001), and then returned to baseline during recovery. EtCO2, by contrast, decreased significantly during hyperoxia, from 40.7 ± 2.1 to 37.2 ± 2.6 mmHg (P = 0.03), and then returned to baseline during recovery. Among the other clinical parameters, there were no significant differences between hyperoxia and baseline. In addition, we saw no adverse events from oxygen inhalation. A significant decrease in MBR was already detectable after 1 minute of hyperoxia (93.1% ± 8.2, P = 0.02), with the greatest decrease after 5 minutes, when it reached 84.6% ± 6.5 (P < 0.001). The average decrease during hyperoxia was 13.4%. MBR returned to baseline 2 minutes after recovery (94.2% ± 6.9, P = 0.11).

 

Conclusions

 

These results suggest that LSFG is a safe and convenient method to assess ONH BF changes in response to hyperoxia. This new approach for evaluating vasoreactivity may be useful for screening certain ocular diseases.

 

 

Representative images of ONH BF, taken using LSFG, in the baseline phase. The color-coded area around the ONH (white circle #1) is automatically tracked in the images at each time point.

 

 

Representative images of ONH BF, taken using LSFG, in the hyperoxic phase. When the subject begins to inhale pure oxygen, the color images of ONH become bluer,indicating a decrease in ONH BF.

 

Keywords: 436 blood supply • 629 optic nerve • 552 imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)