Mechanical activities of trachea as measured in vitro and in vivo

The phenomenon of spontaneous contractions as measured in vivo and in vitro (isolated guinea pig trachea) is described. In vitro contractility is defined in terms of active tension (AT), the maximum rate of tension development (dT/dt) and time to peak tension (TTP). The length-tension relationship was established for spontaneous contractions of isolated guinea pig trachea. The effect of the temperature on spontaneous activities was also studied. An increase in temperature from 37.5 to 41.5C produced an increase in the maximum rate of tension development (dT/dt( and a decrease in the time to peak tension (TTP). A comparable decrease in temperature, from 37.5 to 33.5C produced slight but not statistically significa-nt increases in active tension, dT/dt and TTP. Frequency of the spontaneous contractions varied directly with changes in temperature. Employing a micro-strain-gauge transducer a rhytmic change of tracheal diameter has been observed in vivo in both guinea pigs and rabbits. Administration of atropine and isoproterenol in those experiments transiently abolished the appearance of these rhythmic changes of tracheal diameter.