Suppression of the cardiac electric field artifact from the heart action evoked potential

The study of heart action-related brain potentials is strongly disrupted by the presence of an inherent cardiac electric artifact. The hypothesis is presented that most of the electric current coupled to the cardiac field surrounds the skull and flows through the scalp tissue without crossing the cranial cavity. This pseudo two-dimensional conduction model contrasts with the volumetric conduction of the brain electrical activity, and this property is exploited to cancel the cardiac electric artifact. QRS loop vector-cardiographic projections on saggital planes were recorded in 11 healthy subjects in the head and neck areas. Comparative analysis of the projection eccentricities, estimated by the correlation coefficients of the paired data on each area, supported the hypothesis and allowed the handling of the cardiac electric field at the scalp as if enclosed in a two-dimensional wrapped space. This approach permitted the combination of different heart action-related brain potentials recorded at different electrode positions to cancel the cardiac electric artifact. The cancellation method, applied to the subjects' EEG data, yielded a slow cortical potential with a negligible cardiac electric residue and an amplitude of about 1.5-2 microV, with a maximum around 150 ms and a minimum at 400 ms post-R wave.

Quantification of intracranial contribution to rheoencephalography by a numerical model of the head

OBJECTIVES

Partial contributions of intracranial and extracranial circulation to rheoencephalography (REG) remain uncertain. The main goal of this work is to determine theoretically the capability of REG techniques to reflect intracranial blood flow.

METHODS

Head and current injection electrodes were computationally modeled to assess REG sensitivity to brain and scalp conductivity changes. Data obtained were related to tissue perfusions to calculate the partial contribution of cerebral blood perfusion to REG I, REG II and monopolar REG and to assess their amplitudes.

RESULTS

When REG I and monopolar REG were used, the theoretical maximum of intracranial contribution was reached with large current injection electrodes, being 8% for REG I and 12% for monopolar REG. However, some specific REG II electrode arrangements showed a nil contribution of the extracranial circulation and a minimum influence of the electrode size.

CONCLUSIONS

These results may explain the disagreement on REG origin and suggest a theoretically optimum electrode arrangement.

The effect of fibrin glue patch in an in vitro model of postdural puncture leakage

We studied the possibility of stopping a continuing transdural leakage with fibrin glue, a biologic adhesive, in an in vitro model. The model was made by sealing the bottom of a tube filled with saline to a height of 50 cm with a human lyophilized dural specimen. Dural punctures were performed with a 17-gauge Tuohy needle. The needle was then withdrawn, and 0.8 mL of fibrin glue was injected through the same needle to seal the defect. The column was refilled 3 min after sealing. The pressure in the intrathecal chamber was measured during the procedure. Macroscopic and microscopic histological studies of the dura and the fibrin plug were performed. In the five cases studied, the leak was sealed by the fibrin plug at closing pressures of 25-35 cm H2O, and no further leakage was detected after refilling. The dural specimens showed a fibrin glue plug stuck at the edges of the hole. We conclude that fibrin glue stops leakage of fluid from dural holes created by a 17-gauge Tuohy needle in an in vitro pressurized model.

IMPLICATIONS

We explored the possibility of repairing a cerebrospinal fluid leak produced by an accidental dural puncture during epidural anesthesia by percutaneously injecting tissue adhesive in vitro. This technique seems promising for the prophylaxis and treatment of the headache associated with this leakage but requires further study in vivo.