Effects of different mechanical ventilation strategies on the mucociliary system.

OBJECTIVE: To evaluate the effects of different mechanical ventilation (MV) strategies on the mucociliary system. DESIGN AND SETTING: Experimental study. SUBJECTS: Twenty-seven male New Zealand rabbits. INTERVENTIONS: After anesthesia, animals were tracheotomized and ventilated with standard ventilation [tidal volume (Vt) 8 ml/kg, positive end expiratory pressure (PEEP) 5 cmH(2)O, flow 3 L/min, FiO(2) 0.4] for 30 min. Next, animals were randomized into three groups and ventilated for 3 h with low volume (LV): Vt 8 ml/kg, PEEP 5 cmH(2)O, flow 3 L/min (n = 6); high volume (HV): Vt 16 ml/kg, PEEP 5 cmH(2)O, flow 5 L/min (n = 7); or high pressure (HP): Ppeak 30 cmH(2)O, PEEP 12 cmH(2)O (n = 8). Six animals (controls) were ventilated for 10 min with standard ventilation. Vital signals, blood lactate, and respiratory system mechanics were verified. Tracheal tissue was collected before and after MV. MEASUREMENTS: Lung and tracheal tissue sections were stained to analyze inflammation and mucosubstances by the point-counting method. Electron microscopy verified tracheal cell ultrastructure. In situ tracheal ciliary beating frequency (CBF), determined using a videoscopic technique, and tracheal mucociliary transport (TMCT), assessed by stereoscopic microscope, were evaluated before and after MV. RESULTS: Respiratory compliance decreased in the HP group. The HV and HP groups showed higher lactate levels after MV. Macroscopy showed areas of atelectasis and congestion on HV and HP lungs. Lung inflammatory infiltrate increased in all ventilated groups. Compared to the control, ventilated animals also showed a reduction of total and acid mucus on tracheal epithelium. Under electron microscopy, injury was observed in the ciliated cells of the HP group. CBF decreased significantly after MV only in the HP group. TMCT did not change significantly in the ventilated groups. CONCLUSIONS: Different MV strategies induce not only distal lung alterations but also morphological and physiological tracheal alterations leading to mucociliary system dysfunction.

Short-term effects of nCPAP on nasal mucociliary clearance and mucus transportability in healthy subjects.

Nasal mucociliary clearance is a primary defense mechanism of the upper airways and may be acutely affected by nasal continuous positive airway pressure (nCPAP). nCPAP treatment is effective and safe. However, it can cause nasal side effects and contribute to a low compliance to the treatment. The aim of this study was to investigate the short-term effects of nCPAP on nasal mucociliary clearance and on mucus transportability of healthy subjects. Eleven healthy subjects were submitted to 20 min of nCPAP (10 cm H2O). Five subjects were also evaluated before and after 20 min of rest on the consecutive study day. Nasal mucociliary clearance was measured by the saccharin nasal transit time test and nasal mucus was collected for the in vitro study of mucus transportability by the frog palate model, both before and after the nCPAP challenge. Saccharin nasal transit time decreased significantly after nCPAP (9.29+/-6.06 min and 4.83+/-5.57 min; P=0.002 before and after nCPAP respectively). No significant changes were observed on the control day (11.66+/-7.57 min and 12.40+/-5.62 min; P=0.70). Mucus transportability was not significantly affected by nCPAP. Our results suggest that nCPAP can acutely increase nasal mucociliary clearance but does not affect in vitro mucus transportability in healthy subjects.

Sputum induction as a research tool for the study of human respiratory mucus.

The study objectives were to compare in vitro transportability and physical properties of respiratory mucus, obtained invasively by direct collection (DC) right after endotracheal intubation and non-invasively by sputum induction with 3% hypertonic saline solution inhalation (SI) 24 h before the anesthesia. Twenty-two patients with no pulmonary disease scheduled for elective abdominal surgical procedures were studied. The parameters analyzed and the main results are as follows. (1) Transportability by cilia (MCT), SI was higher than DC (0.94+/-0.25 and 0.62+/-0.25; P<0.001). There was a significant correlation between the two methods and DC could be estimated by: DC=0.21+(0.44 SI) (r=0.44; P<0.001). (2) Transportability by cough (CC), SI was higher than DC (68.23+/-32.1 and 33.58+/-19.04 mm; P=0.002). (3) Contact angle (CA), SI was lower than DC (10+/-3 degrees and 22+/-14 degrees ; P=0.025). (4) Rheological properties (no significant difference obtained between SI and DC). These results indicated that SI changes mucus physical properties and transportability in non-expectorators.