Comparisons were made in 10 patients scheduled for thoracotomy between a prototype of a low-compressive system (Bronchovent Special) for volume-controlled, high-frequency positive-pressure ventilation (HFPPV; fixed frequency of 60/min; fixed relative insufflation time of 22%), and a conventional respirator (SV-900) for intermittent positive-pressure, volume-controlled ventilation at a frequency of 20/min, after induction of anesthesia, but before surgery. With both ventilator systems intratracheal, intrapleural, systolic, diastolic, and mean arterial systemic and central venous pressures were measured at normoventilation (normocarbia). Mean intratracheal pressure and mean intrapleural pressure were significantly lower with volume-controlled HFPPV (1.3 +/- 0.5 and -4.0 +/- 2.1 (SD) cm H2O, respectively) than with conventional volume-controlled ventilation with SV-900 (2.1 +/- 1.2 and -3.0 +/- 1.5 cm H2O, respectively). No significant differences between the two ventilators were found with respect to arterial systemic and central venous pressures, arterial oxygen and carbon dioxide tensions, or alveolar-arterial oxygen tension difference. With the thorax open, during volume-controlled HFPPV the exposed lung was moderately expanded and exhibited only minor movements during insufflation. Repeated blood gas analyses during surgery showed normocarbia and good oxygenation even during compression of the exposed lung. After compression the lung was readily re-expanded with the aid of a brief period of positive end-expiratory pressure (PEEP). Thus, even relatively low intrapulmonary pressures during volume-controlled HFPPV without PEEP are adequate to keep the open-chest lung expanded during intrathoracic surgery. This creates optimal conditions for the surgeons.