Deadspace breathing as a screening test for early lung damage

Breathing through added external deadspace (V/sub Dext/) was found to increase the tidal volume of normal dogs in order to achieve alveolar ventilation adequate for gas exchange. Addition of V/sub Dext/ did not alter alveolar-arterial gas gradients or cardiovascular function. Respiratory patterns during V/sub Dext/ breathing were compared with variables measured during treadmill exercise to investigate deadspace breathing as an indicator of early lung dysfunction caused by radiation pneumonitis in dogs. Dogs were evaluated clinically, radiographically and by pulmonary function tests at rest before and after inhaling 144Ce in fused aluminosilicate particles. By 4 mo after inhalation of 32 to 50 μCi/kg 144Ce, there were increases in respiratory frequency and minute volume during V/sub Dext/ breathing and in minute volume and the ventilatory equivalent for O2 while running. No other significant functional, radiographic or clinical changes were noted. The dogs were sacrificed and scattered foci of inflammation were found in their lungs. Deadspace testing detected early, subclinical lung alterations with a sensitivity and at a time identical to treadmill testing and did not require whole-body exercise or training