A new, lightweight (2.3 kg), ambulatory pulmonary assist system (PAS) underwent preliminary evaluation in ambulatory sheep. The PAS was purposefully designed for long-term extracorporeal respiratory support for chronic lung disease and utilizes a novel, small (0.9 m2 surface area) gas exchanger, the pulmonary assist device, with a modified Heart Assist 5 pump fitting in a small wearable pack. Prototype PAS were attached to two sheep in venovenous configuration for 7 and 14 days, evaluating ability to remain thrombus free; maintain gas exchange and blood flow resistance; avoid biocompatibility-related complications while allowing safe ambulation. The PAS achieved 1.5 L/min of flow at 10.8 kRPM with a 24 Fr cannula in sheep one and 2.0 L/min at 10.5 kRPM with a 28 Fr cannula in sheep 2 without significant change. Both sheep walked freely, demonstrating the first application of truly ambulatory ECMO in sheep. While in vitro testing evaluated PAS oxygen transfer rates of 104.6 ml/min at 2 L/min blood flow, oxygen transfer rates averaged 60.6 ml/min and 70.6 ml/min in studies 1 and 2, due to average hemoglobin concentrations lower than humans (8.9 and 10.5 ;g/dl, respectively). The presented cases support uncomplicated ambulation using the PAS.
