Tracheal ciliary beat frequency in baboons: effects of peripheral histamine and capsaicin

To determine if tracheal ciliary beat frequency (CBFt) in the nonhuman primate could be stimulated indirectly, either by an inhaled irritant or by a mediator potentially released from an inhalation challenge, saline (0.9%), capsaicin (3 x 10(-9) M), or histamine (8 mg/ml) were delivered for three minutes as 100 ml aerosol (0.25 micron MMAD) boluses at the beginning of each breath, followed by 10 sec breath hold. Each of five adult baboons (17-27 kg, Papio cynocephalus) underwent three studies using a randomized block design. The baboons were anesthetized and ventilated eucapnically through an endotracheal tube whose cuff was inflated in the distal trachea. CBFt was measured in the mid-trachea proximal to the cuff at one minute intervals using heterodyne laser light scattering. There was no change in CBFt from a baseline of 7.2 +/- 0.6 Hz (mean +/- SE) following inhalation of saline deposited peripherally. Capsaicin stimulated CBFt for over 80 min reaching a maximum of 14.7 +/- 6.3 Hz 46 min after aerosol delivery. Histamine stimulated CBFt for 90 minutes reaching a maximum of 19.3 +/- 9.9 Hz 67 min after aerosol delivery. The prolonged stimulatory responses of CBFt to peripherally deposited capsaicin and histamine most likely involve both cellular and neural pathways through which the tracheobronchial airways, in response to an alveolar challenge, are cleansed of secretions thus enabling the maintenance of effective gas transport.