A model for pulsatile and steady ocular blood flow.

BACKGROUND

The aim was to elucidate two controversial questions. (1) is the pulsatile inflow dominant or is there a sizeable steady inflow component? (2) Is the outflow of blood steady or pulsatile in induced and in glaucomatous hypertension?

METHODS

The OBF system (Langham) was used for pulse recording. A simple electric flow model was conceived and analysed in terms of Fourier series, using linear circuit theory.

RESULTS AND CONCLUSIONS

Possible explanations of the seemingly inconsistent observations are indicated by the model. (1) A steady inflow of similar magnitude to the pulsatile one is predicted. The total flow can be determined at present theoretically from recordings of the pulsatile inflow and of the systolic and diastolic intraocular blood pressure. Some methodological improvements are desirable in order to obtain reliable estimates in practice. (2) The outflow is normally steady, probably even in ocular hypertension and glaucoma. In hypertension induced with the suction cup this may be doubted. The eye has similarities with the device called the Starling resistor which describes the behaviour of collapsible vessels. Acute pressure increase (plus the pulsations of the IOP) may put the collapsible vessels into a state which disturbs the steady outflow. The effects of changes in IOP and in other components on the size and shape of the flow curve are demonstrated.