Effects of water temperature on some noninvasively measured components of the human dive reflex: an experimental response-topography analysis

The human dive reflex (DR) essentially consists of HR deceleration (HRD) and peripheral vasoconstriction. The dominant view of the DR's mechanism is (adaptive) oxygen conservation such that the DR is often referred to as the oxygen-conserving reflex. However, this and other issues have not been resolved because the literature has lacked precise measurement quantification and experimental control. The present study was designed to test the oxygen conservation hypothesis in a controlled laboratory setting and varied temperature between three groups of 16 subjects (10°, 20° and 40° C). The range was chosen to produce maximal variation in the rate of trigeminal cold-fibre activity, and minimal pain-fibre activity. The response-topography results were consistent with an earlier study, and also yielded evidence that the DR varied inversely with temperature. This seems contrary to the oxygen-conservation view, and indirectly implicates the role of the trigeminal nerves in the afferent mechanisms of the human DR. A physiological analysis of these results is offered.