Abstract
Abstract: :
Purpose:To determine the impact of intense dynamic and isometric exercise on retinal blood flow in young healthy subjects. Methods:The sample comprised 11 young, healthy subjects (mean age 24.2 yrs; range 21–29 yrs; 4 males and 7 females). Retinal blood flow was assessed using the Canon Laser Blood Flowmeter (CLBF), model 100. The CLBF measured centerline blood velocity using a 675nm diode laser Doppler velocimeter while simultaneously measuring arteriolar diameter with a 543nm eye tracking laser. Retinal blood flow values were derived from the measured velocity and diameter values. Measurements were made at a selected point along an arteriole, typically within 1 disc diameter of the optic nerve head in the superior temporal quadrant. Five baseline CLBF readings were acquired. Subjects then undertook three forms of exercise in randomized order with at least one hour of rest between each; intense dynamic exercise (using a stationary exercise bike until heart rate increased by at least 75% or for a minimum period of 5 minutes), a 5–minute isometric hand–grip exercise, and a 5–minute squatting exercise. CLBF readings were then acquired within the first minute of ceasing exercise and every minute up to 10 minutes after the cessation of exercise. Heart rate, measured using a finger sensor, and brachial artery blood pressure, measured using an arm pressure cuff, were recorded throughout the baseline and exercise periods. A repeated measures ANOVA was undertaken on the dependent variables; arteriolar diameter, blood velocity, blood flow, CLBF derived pulse rate, heart rate and mean arterial blood pressure. Results: Dynamic exercise significantly increased heart rate (p<0.001) whereas the squatting exercise significantly increased mean arterial blood pressure (p<0.005). Neither heart rate nor blood pressure changed significantly in response to the hand–grip exercise. Arteriolar diameter, blood velocity and blood flow were not significantly altered as a result of any form of exercise. The correlation between finger sensor derived heart rate and CLBF derived pulse rate was found to be 0.89 in the dynamic exercise group and 0.84 in the squatting exercise group (p<0.0001 in both cases). Conclusions:Neither increased heart rate nor increased systemic blood pressure altered retinal arteriolar blood flow. This finding suggests that retinal vascular reactivity changes rapidly in response to exercise. The high degree of correlation between the CLBF derived pulse rate and the finger sensor derived heart rate confirm that the CLBF readings are valid.
Keywords: blood supply • retina