TRANSCRANIAL DOPPLER ULTRASOUND IN COMMERCIAL AIR DIVERS - A FIELD-STUDY INCLUDING CASES WITH RIGHT-TO-LEFT SHUNTING

Many cases of decompression illness occur in divers using recommended decompression tables. Doppler ultrasound has been used for over 20 yr and has shown the presence of venous bubbles in asymptomatic divers wo rking well, within decompression limits. Previous studies have demonst rated an increased prevalence of patent foramen ovale in divers who ha ve suffered neurologic decompression illness. It has been postulated t hat right-to-left shunting through a patent foramen ovale could allow arterialization of these bubbles, causing symptoms and signs of acute decompression illness and possibly chronic subclinical neurologic impa irment. We set out to determine the incidence of bubbles in the cerebr al circulation of commercial divers decompressing from air dives. Usin g transcranial Doppler ultrasound (TCD), the middle cerebral arteries of 17 divers were monitored after surfacing from depths ranging betwee n 3 and 50 m. Peripheral contrast injection with simultaneous transtho racic echocardiography and TCD was used to screen for right-to-left sh unting. Right-to-left shunting was detected in four divers by TCD (one at rest, two after a Valsalva maneuver, and one only after coughing); however, echocardiography was positive in only one of these subjects after a Valsalva maneuver (TCD was positive at rest in this subject). Seventy-three TCD recordings were performed in four settings: 41 after underwater decompression, 18 after surface decompression, 10 in the i nterval between surfacing and entering the decompression chamber, and 4 after a chamber dive. Twenty-three of these recordings were in four subjects with right-to-left shunting; no bubbles were detected in any of these recordings. Commercial air divers with demonstrated right-to- left shunting did not have detectable arterial bubbles when using reco mmended decompression tables.