EFFECT OF CAFFEINE ON VENTILATION DURING POST-NATAL MATURATION OF BREATHING IN AWAKE LAMBS

Abstract

Caffeine is an efficient respiratory stimulant during the neonatal period, but its action on respiration beyond this period remains unclear. This study was performed to evaluate the effect of caffeine on ventilation in relation to post-natal maturation. Nineteen lambs divided in 3 groups of different ages were studied;I: 7 lambs with a mean age of 1 week;II: 6 lambs, mean age of 2 1/2 months and III: 6 sheep, 6 months old. After a baseline period, saline (as a control infusion) then, 10 minutes later, caffeine 10 mg/kg I.V. were injected to the animals. Ventilation was measured using a mask adapted to the animal's facial contour and connected to a pneumotachograph; on-line values of VE (minute ventilation), Vt/Ti, (mean inspiratory flow) and Ti/Ttot (timing of respiration) were derived from the flow signal using a computerized system.No response was seen after saline;but in all three groups, VE (ml/min/kg) increased significantly after caffeine; this increase was 36% in group I; 46% in group II; and was 48% in group III. This increase in VE was due mainly to an increase in Vt/Ti (ml/sec/kg), which increased in groups I,II,III by 36,41 and 26%. Ti/Ttot did not change significantly at any time. The plasma concentrations were 9.7,8.8,10.0 mg/1 in groups I,II,III. We conclude that: the magnitude of the ventilatory response and the strategy of breathing in response to the therapeutic blood concentration of caffeine persists without major difference between 1 week to 6 months of age in lambs.