Elevations in Intra-cranial blood flow velocities following a SCUBA Dive and the Influence of Post-dive Exercise

The effect that a SCUBA dive has on cerebral blood flow (CBF) at rest and during exercise is poorly understood. We examined the hypothesis that the altered hemodynamic parameters following a SCUBA dive will lead to differential changes in CBF at rest and during exercise. 16 divers completed a field-based study with a single dive at a depth of 18 m sea water with a 47-min bottom time. A follow-up laboratory based study was conducted - 1 week later. Intra-cranial velocities were measured with transcranial Doppler ultrasound (TCD) pre-dive, post-dive at rest and throughout incremental exercise until exhaustion. Following the dive at rest, middle cerebral artery velocity (MCAv) was elevated 15 and 30 min after surfacing (by 3.3±5.8 and 4.0±6.9 cm/s, respectively; p<0.05); posterior cerebral artery velocity (PCAv) was increased at 30 min after surfacing (by 3.0±4.5 cm/s; p<0.05). During exercise following the dive, both MCAv and PCAv increased up to 150W followed by a decrease towards baseline at 180W (p<0.05). We found no difference in CBV during exercise between field and laboratory studies (p<0.05). The novel finding of this study is the transient elevation in resting intra-cranial velocities within 30 min following a SCUBA dive.