17637
document
Intravenously administered histamine increases choroidal but not retinal blood flow . PURPOSE To determine the effect of intravenously administered histamine on both retinal and choroidal blood flow in humans . METHODS A randomized , double-masked , two-way crossover study was performed in 14 healthy volunteers . Placebo or histamine was administered intravenously in stepwise increasing doses ( 0.08 microg/kg/min , 0.16 microg/kg/min , and 0.32 microg/kg/min ) . Retinal vessel diameters were measured with a retinal vessel analyzer , and retinal venous blood speed was assessed by bi-directional laser Doppler velocimetry . Using these parameters retinal blood flow was calculated . Subfoveal and pulsatile choroidal blood flow were measured with laser Doppler flowmetry and laser interferometry , respectively . RESULTS After infusion of histamine pulsatile choroidal blood flow increased by 5 +/- 3 % , 9 +/- 8 % , and 14 +/- 7 % ( P = 0.001 , ANOVA ) and subfoveolar choroidal blood flow by 8 +/- 11 % , 13 +/- 11 % , and 13 +/- 12 % ( P = 0.003 , ANOVA ) . Retinal arterial and venous vessel diameter significantly increased by 3 +/- 4 % , 2 +/- 4 % , and 3 +/- 5 % ( P = 0.047 , ANOVA ) and 1 +/- 2 % , 3 +/- 2 % , and 3 +/- 2 % ( P = 0.015 , ANOVA ) , respectively . Red blood cell velocity in major retinal veins tended to decrease by -9 +/- 12 % , -9 +/- 20 % , and -13 +/- 12 % , but this effect did not reach levels of significance . Calculated retinal blood flow was not changed by administration of histamine ( -7 +/- 14 % , -4 +/- 20 % , and -8 +/- 12 % , P = 0.28 , ANOVA ) . CONCLUSIONS Intravenous histamine in the selected doses increased choroidal blood flow . Retinal vessels showed a small diameter increase , whereas red blood cell speed decreased , resulting in an unchanged total retinal blood flow . This may result from local differences in the receptor distribution in the posterior part of the eye .
17638
Intervention_Pharmacological
Intravenously administered histamine
17639
Intervention_Pharmacological
intravenously administered histamine
17640
Intervention_Pharmacological
Placebo
17641
Intervention_Pharmacological
histamine
17642
Intervention_Pharmacological
histamine
17643
Intervention_Pharmacological
histamine
17644
Intervention_Pharmacological
Intravenous histamine
17645
Outcome_Physical
Retinal vessel diameters
17646
Outcome_Physical
retinal venous blood speed
17647
Outcome_Physical
retinal blood flow
17648
Outcome_Physical
choroidal blood
17649
Outcome_Physical
pulsatile choroidal blood flow
17650
Outcome_Physical
subfoveolar choroidal blood flow
17651
Outcome_Physical
Retinal arterial and venous vessel diameter
17652
Outcome_Physical
Red blood cell velocity in major retinal veins
17653
Outcome_Physical
Calculated retinal blood flow
17654
Outcome_Physical
choroidal blood flow
17655
Outcome_Physical
small diameter increase
17656
Outcome_Physical
red blood cell speed
17657
Outcome_Physical
total retinal blood flow