The mechanisms that are put into action as a part of the diving reflex have effects upon the organism’s body in addition to oxygen conservation.

Blood

Arterial pressure is maintained in most diving birds and mammals by the counteracting effects of bradycardia and peripheral vasoconstriction. Cardiac output decreases due to bradycardia, yet the stroke volume remains constant (Butler, 1982; Manley, 1990). In opposition, there is an increase in resistance from the constriction of capillaries. These two effects offset each other so there is no change in central blood pressure (Jones and Butler, 1997). In addition, there is an increase in red blood cell mass and blood volume (Ramirez et al., 2007).

Inhibition of Homeostasis

Due to the nature of diving and submersion, organisms often experience asphyxia: restricted gas exchange with the environment. This leads to ischemia, the state of a tissue receiving insufficient blood. Ischemia thus produces hypoxia, in which a deficient amount of oxygen is delivered to the tissue. Diving is therefore a “hypoxic condition”. Hypoxia indicates a drastic change in partial pressures within the blood, as the concentration of oxygen decreases and carbon dioxide increases (Ramirez et al., 2007).
In addition to the changing partial pressures, there is a substantial build up of lactic acid in the blood. An organism’s aerobic dive limit is defined as the point at which the body must transition from aerobic to anaerobic metabolism. This switch allows the formation of lactic acid to reach a concentration above the resting level, also lowering the pH of the blood (Dahms et al., 2010).

Fig.5 from (Ross and Steptoe, 1980) with permission from the author. Lactic acid content in the muscles over time diving, with the lactic acid concentration of the arterial blood for comparison.

Hypoxia and acidity normally induce an increase in ventilation within organisms, however research rats exposed to these conditions made no attempt to gasp or breathe when submerged (Panneton et al., 2010). The principal chemoreceptors for respiration are found in the carotid body and central nervous system, and these receptors showed gross activation when the animal is submerged. Yet despite this recognition of the stimulants, the appropriate response of hyperventilation does not occur. The diving reflex is hypothesized to actually inhibit these chemoreceptors, thus disrupting the normal homeostatic process (Speck and Bruce, 1978).