Very Few Exercise-Induced Arterialized Gas Bubbles Reach the Cerebral Vasculature

Arterialization of venous gas emboli (VGE) formed after surfacing from SCUBA diving can become arterial gas emboli (AGE) through intrapulmonary arterial-venous anastomoses that open with exercise.

We recruited twenty patent foramen ovale-negative SCUBA divers and conducted a field and a laboratory study with the aim of investigating the appearance of AGE in intracranial vessels. At the field, they performed a single dive to a depth of 18-m sea water with a 47-min bottom time and a direct ascent to the surface. Transthoracic echocardiography was used to score VGE and AGE, and transcranial Doppler was used to visualize middle and posterior cerebral arteries with automated objective bubble detection. Observations were conducted for 45-min after dive at rest and at the laboratory after agitated saline injection at rest and throughout an incremental cycle supine exercise test until exhaustion and for 10 min of recovery.

After resurfacing, all divers presented endogenous VGE and arterialization was present in three divers. Saline contrast injection led to AGE in nine of 19 subjects at rest. AGE that reached the cerebral arteries after dive were recorded in two divers at 60 W, three at 90 W, five at 120 W, six at 150 W, and four at 180 W and in three, four, five, nine, and nine, respectively, after saline contrast injection in the laboratory. All divers had AGE grades of 1 or 2, and only single AGE reached the cerebral vasculature.

These data suggest that few emboli of venous origin reach the brain through exercise-induced intrapulmonary arterial-venous anastomoses but cerebral embolization is not high risk in the studied population.