History of Research

The history of research surrounding the diving reflex in mammals and birds is relatively short, yet in that brief time a number of different conclusions have been reached. Researchers Irving and Scholander are credited for uncovering the mechanisms of the “classic response” with their experiments upon the forced submersion of birds. Their discoveries supplied the first hypothesis for why the diving reflex is needed and how it is employed, providing the premises that later work was built upon (Jones and Butler, 1997). I will outline below the nature of each of their observations and the implications of the research. Their general conclusions were that prolonged dives characterize the behavior of most diving mammals and birds, with bradycardia and vasoconstriction as the primary mechanisms (Butler, 1982).

However, their classic view of the diving response was challenged in the late 1970’s with evidence provided by observations of the weddell seal and tufted duck. Weddell seals showed no increase in lactic acid after dives of up to 25 minutes, and the tufted duck supported the growing realization that birds generally only perform very short dives (Fiegel and Folkow, 1963). A paper released by a researcher named Eliassen proposed that most dives performed voluntarily are actually aerobic, and that vasoconstriction does not occur in muscles but in viscera alone (Jones and Butler, 1997).

Despite these opposing views, more recent studies of a wider range of species (such as elephant seals, emperor penguins, gray seals, thick billed murres) have brought the theory back full circle (Jones and Butler, 1997). Analysis of the diving behavior and response revealed that at some point in the dive all of these species, low aerobic metabolic rates and accumulation of lactate were exhibited. This is supported by the observation that marine mammals generally consume oxygen at less than half of the pre-dive rate (Gooden, 1992).

Classic Response

• Scholander’s conclusion (Scholander, 1940)
• Observed that diving mammals and birds can survive submersion much longer than would be expected based on oxygen stores
• Ventilation must stop immediately to avoid drowning, causing the arterial carbon dioxide content increases while oxygen content decreases



Fig. 1 from (Ramirez et al., 2007) with permission from the author. Relative arterial concentrations of oxygen and carbon dioxide with volume of carbond dioxide constantly increaseing over time (lower graph), and volume of oxygen constantly decreasing over time (upper graph). Data was collected from grey seals and hooded seals.

 

• Irving’s conclusion (Irving, 1934)
• To survive asphyxia and conserve oxygen in the blood, cardiovascular adjustments must be made
• Reduction of blood flow to all tissues and organs that can stand lack of oxygen supply in short term
• Blood redirected to maintain continual flow towards necessary tissues
• There must be a switch to anaerobic metabolism due to the lack of oxygen, would produce lactic acid

• 	Pre-Dive	Sections of 20 min. dive
  Time (min)	5	0-5	5-10	10-15	15-20
  Oxygen used per kilo in muscle (cc)	50	45	3	1	0
  Lactic acid formed per kilo in muscle (gm)	0	0.1	0.35	0.9	1.2

  Table 1 adapted from (Irving 1934). Assume that 5 gm calories are formed by the concumption of 1 cc of oxygen and 385 gm, the calculated average of oxygen decrease and lactic acid increase in teh muscle tissue during diving.