Which method is employed by positive pressure ventilators to ventilate the lungs?

Positive pressure ventilators operate by delivering air or oxygen into the lungs under elevated pressures. This method ensures that the inspiratory pressure generated by the ventilator exceeds the pressure within the patient's lungs. As a result, air is effectively pushed into the airways and lungs, facilitating the exchange of gases (oxygen and carbon dioxide).

The use of elevated pressures is crucial in situations where a patient is unable to breathe on their own or requires assistance in maintaining adequate ventilation. The ventilator can be adjusted to provide the appropriate tidal volume and pressure settings to meet the patient's respiratory needs, ensuring adequate oxygenation and ventilation.

In contrast, other methods listed, such as low atmospheric pressure, high humidity levels, or a vacuum seal, do not align with the mechanism of positive pressure ventilation. Low atmospheric pressure would not provide the necessary force to ventilate the lungs, humidity is typically a consideration for comfort and mucus clearance rather than a primary mechanism for ventilation, and a vacuum seal does not apply in the context of delivering air into the lungs. Thus, the method of using elevated pressures is fundamental to how positive pressure ventilators function effectively.