Conditioned Heart Rate Deceleration Under Different Dimensions of Respiratory Control

Both accelerative and decelerative cardiac responses have been observed in studies on human heart rate conditioning. An interpretation of the contradictory responses regarded as conditioned seems to remain equivocal. Experiments generally have used shock or loud sound as the US, so that effects of respiratory and pressor reflexes on heart rate appeared to be implicated in the conditioning process. In the present experiment, the period following a simple non‐aversive signal‐detection task established a heart rate deceleration as the UR. During this period, subjects of three experimental groups controlled part of their respiratory cycle for 20 seconds. Respiratory control was either sustained inhalation, sustained exhalation or maintained shallow resting cycle, while control subjects exercised no respiratory restraint. The non‐aversive stimulation excluded excessive heart rate acceleration and permitted a CS to coincide with onset of relaxation in the postdecision period. Only in experimental subjects was a significant conditional deceleration of heart rate found. Conditional deceleration occurred in addition to a gradual drop in heart rate level during the experiment. When respiratory activity was not controlled, a biphasic response of heart rate was observed.