Protective effects of low respiratory frequency in experimental ventilator-associated lung injury

Objective: To determine whether ventilator-associated lung hyperinflation injury can be attenuated by a reduction in respiratory frequency. Design: Prospective comparative laboratory investigation. Setting: University medical center research laboratory. Subjects: Male Sprague-Dawley rats. Interventions: Eight groups of isolated, perfused rat lungs were exposed to cyclic ventilation at different respiratory frequencies and tidal volumes. Each group of six to eight lung preparations was assigned to one of four respiratory frequencies (10, 20, 40, or 80 breaths/min) and one of two tidal volumes (5 or 20 mL(.)kg(-1)). Measurement of capillary filtration coefficient (K-f,K-c), a sensitive index of lung microvascular permeability and injury, was made at baseline and at 30, 60, and 90 mins of the experimental conditions. Measurements and Main Results: Lungs exposed to 5 mL(.)kg(-1) tidal volume had no elevation in K-f,K-c at any time point regardless of respiratory frequency. Lungs exposed to 20 mL(.)kg(-1) tidal volume and a respiratory frequency of 80 had significant elevations in K-f,K-c at all times after baseline compared with lungs exposed to respiratory frequencies of 10, 20, or 40 (0.14 +/- 0.03, 0.16 +/- 0.02, 0.31 +/- 0.05 vs. 0.76 +/- 0.16). Furthermore, the K-f,K-c at 90 mins was significantly higher than permeability at baseline in this group (1.53 +/- 0.45 vs. 0.12 +/- 0.02 mL(.)min(-1.)cm H(2)O(-1.)100 g of lung tissue(-1)). Conclusions: Reduction in respiratory frequency to values much lower than normal ameliorated experimental ventilator-induced hyperinflation lung injury as determined by pulmonary capillary filtration coefficient.