Divers underwent two Doppler echographic examinations with a 1-week interval: the first examination in basal conditions, and the second examination 1 h after the investigational scuba dive. The ultrasonographic examinations were carried out by an experienced investigator (A.B.) using a commercially available Doppler echocardiograph (Diasonics Vingmed CFM 750 A; GE Medical Systems; Milwaukee, WI) connected to a transducer array of 2.5 to 3.5 MHz. Investigations were performed in a quiet room with a stable environmental temperature (25°C). Subjects stayed at rest for 10 min before the ultrasonographic examination. HR was recorded by echocardiogram, and the rate was averaged over 60 s. Sphygmomanometric BP measurements on the right arm were obtained after each echographic examination. Two-dimensional (2D) echography and Doppler studies were used to detect circulating bubbles after diving and to assess cardiac function. so
Circulating bubbles were screened using 2D echography and pulsed Doppler. Bubble detection was performed 1 h after diving and before cardiac function assessment. Images were obtained from the parasternal view (long axis and short axis) and from the apical four-chamber view (Fig 1). Gas bubbles appear as high intensity “blobs” in the images. A quantitative evaluation of circulating bubbles was performed using 2D images. Each view was recorded for 30 s on videotape. Circulating bubbles were also detected with pulsed Doppler echography. The sample volume was placed in the outflow area of the right ventricle (RV) 1 to 2 cm below the pulmonary valve to record pulmonary artery blood flow. Circulating bubbles could be visualized in the flow spectrum as bright spots (Fig 2). Circulating bubbles were graded according to a specific echocar-diographic Doppler bubbles grade (Table 1) built by our team and derived from the scale of Spencer.
Apical four-chamber view and aortic blood flow study were systematically obtained to detect circulating bubbles in the left cavities. The total duration for each examination was 3 to 5 min. 2D echocardiography and pulsed Doppler studies were analyzed by two independent investigators (A.B., D.C.). Interobserver variability was < 5%. In case of discrepancy, a consensus was obtained.
Figure 1. Apical four-chamber view: circulating bubbles in the RV (arrows).
Figure 2. Circulating bubbles (arrows) detected in the pulmonary arterial blood flow using pulsed-Doppler echography.
Table 1—2D Echocardiographic and Pulsed Doppler Grade
|0||No detectable bubble signal (2D echocardiography and pulsed Doppler ultrasonography)|
|1||Occasional bubbles; the great majority of cardiac cycles are free of bubbles (2D echocardiography and pulsed Doppler ultrasonography)|
|2||Flow of bubbles (2D echocardiography); many but less than half of the cardiac periods contain bubble signals singularly or in group (pulsed Doppler ultrasonography)|
|3||Flow of bubbles (2D echocardiography); the majority of the cardiac periods contain bubble signals singularly or in group (pulsed Doppler ultrasonography)|
|4||Bubbles fill cardiac chambers (2D echocardiography); all the cardiac periods contain bubble signals in group (pulsed Doppler ultrasonography)|