A study of cerebral Vasoreactivity : middle cerebral artery (MCA)‎ versus ophthalmic artery (OPA)‎

Abstract EN

Background : Recently, cerebral autoregulatory capacity in humans can be studied noninvasively by TCD.

The degree of cerebral vasodilatation can be measured by the increased middle cerebral artery (MCA) blood flow in response to hypercapnea induced by either administration of 5 % CO2 or I.V acetazolamide ; few studies available on breath hold induced cerebral vasodilatation.

Cerebral vasoconstriction can be measured by the decreased MCA blood flow in response to hypo apnea induced by hyperventilation.

However, conflicting reports exist on the modulatory effect of hypercapnea (induced by breath holding) or hypocapnea (Induced by hyperventilation) on the Ophthalmic artery (OPA) blood flow. Objective : To demonstrate changes in MCA & OPA blood flow using physiological stimuli : Hypercapnea (induced by breath hold) and hypocapnea (induced by hyperventilation).

Secondly, to investigate whether or not OPA would respond in a similar fashion to MCA, to the forementioned stimuli Methods : 30 healthy individuals were enrolled, using a TCCD sonography ; the MCA and OPA were insonated utilizing transtemporal and transorbital windows respectively.

A mean of 10 cardiac cycles were used to estimate the base line control of Doppler derived spectral wave forms regarding mean flow velocities (MFV) and resistant indices (RI).

The response of change of MCA flow or OPA flow to hyper apnea induced by breath hold (BH) was measured during the last 5 seconds and that to hypocapnea induced by hyperventilation (HV) was measured during 1.5 min.

Breath holding index (BHI) and full range of vasodilatation of both arteries were also calculated. Results : In 30 Middle cerebral arteries examined, during breath hold, the MFV (mca) was significantly increased from a mean of 41.15 ± 2.00cm /s (range : 22- 54.33) to a mean of 55.22 ± 2.66 cm / s(range : 27.33-84.42) (p < 0.001).

No significant increase of RI obtained (P > 0.05)..

When performing hyperventilation, the MFV(mca) significantly decreased from a mean of 41.15 ± 2.00cm / s (range : 22- 54.33) to a mean of 26.72 ± 1.72cm / s (range : 8.92- 53.33), (p < 0.001).

There was significant increase in RI from a mean of 0.54 ± 0.011 (range 0.38-0.68) to a mean of 0.63 ± 0.015 (range 0.38-0.8), (p < 0.001).

The calculated MCA full range of vasodilatation was of a mean of 60 ℅ ± 3.51 (range 133 ℅-03℅).

In 30 ophthalmic arteries examined, during breath hold, The MFV(opa) significantly decreased from a mean of 18.49 ± 1.12cm / s (range : 7.33-32.33) to a mean of 14.55 ± 1.20cm/s (range : 7.67- 37.00), (p < 0.001).

No statistical significant decrease of RI during breath hold obtained.

When performing hyperventilation, the MFV (opa) significantly increased from a mean of 18.49 ± 1.12cm / s (range : 7.33-32.33) to a mean of 24.09 ± 1.27cm / s (range : 8.67-40.73), (p < 0.001).

There was no statistical increase of RI, (P : 0.05).

The calculated OPA full range of vasodilatation was of a mean of 57.03 % ± 4.53 (range : 22 %-104 %). Conclusion : Ophthalmic artery flow behaves in a different and opposite manner to that of MCA in response to Hypercapnea and hypo apnea. cerevasoreactivity, breath bral hold, hyperventilation, Transcranial Doppler Abbreviations : MCA, middle cerebral artery, OPA, ophthalmic artery, CBF, cerebral blood flow, MFV, mean flow velocity, PSV, peaked systolic velocity, DV, diastolic velocity, RI, resistant index, BH, breath hold, BHI, breath hold index, HV, hyperventilation, TCD, Transcranial Doppler, TCCD, Transcranial Colored Doppler.