Ventilatory support by tracheal gas insufflation and chest vibration during bronchoconstriction.
OBJECTIVE
To determine whether chest wall vibration with tracheal gas insufflation during bronchoconstriction maintains gas exchange at lower airway and intrathoracic pressures than those that occur during positive pressure ventilation.


METHODS
Prospective study.


METHODS
Experimental laboratory.


METHODS
Six anesthetized, paralyzed mongrel dogs (mean weight, 24.7+/-3.8 kg).


METHODS
Dogs were ventilated by two methods: mechanical ventilation (7 breaths/min, 25 mL/kg tidal volume); and tracheal oxygen insufflation at 0.15 L x kg(-1) x min(-1) delivered with external chest wall vibration (29 Hz, 2 mm amplitude) of the dependent hemithorax. Bronchoconstriction was induced by methacholine infusion adjusted to double and quadruple the baseline airway resistance. Proximal mean airway pressure was kept equal for both modes of ventilation.


RESULTS
Airway pressure and flow, esophageal pressure, hemodynamic variables (cardiac output, systemic and pulmonary arterial pressures, pulmonary artery occlusion pressure) and gas exchange variables (PaO2, PaCO2, pH, shunt fraction, VO2) were measured. Peak airway pressure was lower (p < .05) with insufflation and vibration than with mechanical ventilation by 83.6% at baseline resistance, by 76.9% at twice baseline resistance, and by 76.8% at four times baseline resistance. Peak esophageal pressure was lower (p < .05) during insufflation with vibration by 68.5% at baseline resistance, by 87.5% at twice baseline resistance, and by 107% at four times baseline resistance. During insufflation with vibration, mild hypercapnia (PaCO2 58+/-3 torr (7.7+/-0.4 kPa) and pH 7.28+/-0.02) developed with moderate bronchoconstriction; more profound respiratory acidosis (PaCO2 137+/-41 torr (18.2+/-5.5 kPa) and pH 6.87+/-0.11) developed with severe bronchoconstriction.


CONCLUSIONS
Tracheal gas insufflation with chest vibration supports gas exchange with permissive hypercapnia only during moderate, not severe, bronchoconstriction. Gas exchange was achieved at lower airway and intrathoracic pressures than those that developed during mechanical ventilation. The alveolar hypoventilation that occurred during insufflation with vibration indicates impaired CO2 elimination and suggests increased resistance to CO2 transport. This ventilation technique may confer therapeutic advantages over mechanical ventilation in the treatment of asthma.
Department of Anesthesia, University of Pennsylvania Medical School, and Institute for Medicine and Engineering, University of Pennsylvania, Philadelphia 19104, USA.
D M
DM
Eckmann
D000818:Animals; D001249:Asthma / Q000139:chemically induced; D016084:Bronchoconstriction / Q000502:physiology*; D004285:Dogs; D004562:Electrocardiography; D006439:Hemodynamics; D007327:Insufflation / Q000379:methods*; D007442:Intubation, Intratracheal; D008297:Male; D016210:Methacholine Chloride / Q000009:adverse effects; D011659:Pulmonary Gas Exchange; D012121:Respiration, Artificial; D014732:Vibration
D016210:Methacholine Chloride