The cardiac effects of hyperbaric oxygen at 243 kPa using inchamber echocardiography

The adverse effects of hyperbaric oxygen (HBO) on cardiac physiology are considered a potential hazard during the treatment of some patients. The haemodynamic effects of HBO are poorly understood and the incompatibility of electrical equipment inside the chamber has made assessment difficult. At Fremantle Hyperbaric Unit, we have modified an ultrasound machine (Logiq™ e) for safe use within the hyperbaric environment. The aim of this study was to evaluate the cardiac changes that occur during HBO using in-chamber transthoracic echocardiography (TTE) in subjects without evidence of active cardiac disease.

Eleven patients and nine members of staff underwent comprehensive TTE examinations before and during HBO administered at a pressure of 243 kPa. The TTE examinations were reported by two independent cardiologists and statistically evaluated using paired Student's t-tests.

There was a significant decrease in heart rate during HBO (65 vs. 70 bpm on air at atmospheric pressure, P = 0.002) resulting in a decrease in cardiac output (5.3 vs. 5.9 L·min⁻¹, P = 0.003). Left ventricular outflow tract (LVOT) dimension was larger during HBO than baseline imaging (2.30 vs. 2.23 cm, P = 0.0003). LVOT velocity time integrals (VTI) decreased (19.9 vs. 21.5 cm, P = 0.009) and therefore a similar stroke volume was maintained (61 vs. 65 ml, P = 0.5). Ventricular and atrial volumes, intracardiac flows and minor valvular abnormalities were not significantly affected by HBO. No adverse cardiac effects were observed.

TTE can be safely performed within a hyperbaric chamber. Cardiac physiology is not adversely affected by HBO in individuals without active cardiac disease.