Negative extrathoracic pressure ventilation--evaluation of the neck seal.

The effect of the neck seal used in the application of negative extra-thoracic pressure ventilation was studied using near infrared spectroscopy. Changes in cerebral blood volume (CBV) were monitored during discontinuation of negative pressure and during removal of the neck seal. CBV increased by 0.17 ml 100 ml brain-1 (95% CI +0.0875 to +0.481) when negative pressure was discontinued. Removal of the neck seal had no significant effect on CBV. It is concluded that the neck seal does not cause significant jugular venous occlusion.