The Effects of the diving response on breath-hold divers

In contrast to the common findings cited above, elite divers appear to have a significantly increased ability to hold their breaths compared to average athletes. A study done by Heusser, K. and his colleagues (2009) revealed that elite divers, during voluntary apnea, have longer apnea time that is coupled with a five old increase in sympathetic nerve activity. Vascular resistance also increased markedly in elite divers explaining their ability to hold their breaths for several minutes. Since the sympathetic vasoconstrictor activity of these athletes is activated by excessive chemoreflex, their vital organs are supplied with an adequate oxygen supply. This finding is applicable during periodic apnea of elite divers but is difficult to observe in untrained athletes who undergo voluntary apnea.
Meanwhile, the quest to break the current world record in breath-hold competition (10:12 min) at a depth of 214 meters has been the main goal of competitive breath-hold divers (Lindholm, P. and Lundgren, C., 2009). However, physiological reactions and pathophysiological mechanisms need to be breached by each diver attempting to prolong the minutes underwater and at deeper lengths. For less-trained divers, they fall victims to decreased oxygen in the brain called hypoxia (Hiebert, S. & Burch, E., 2003) as well as pulmonary edema and hemorrhage in the alveolar sac after diving (Leuenberger, U. et al, 2001). Divers who fall victims to hypoxia underwater are in extreme danger of drowning once they lose consciousness (Lindholm, P. and Lungdren, C., 2009). Other factors related to increased risk of mortality while diving include having an existing cardiac problem (Lindholm, P. et al, 2002); or divers who have experienced earlier alternobaric vertigo (Lindholm, P. and Lungdren, C., 2009). Researches have shown that the common effects of diving response include bradycardia (Shiraishi, M. et al, 2002); hypertension (Irgens, A. et al, 2007), arrhythmia (Kroenke, K. et al, 2002) along with contraction of the spleen (Lindholm, P. and Lungdren, C., 2009). The respiratory system also experiences a host of problems once the diver prolongs his/her stay underwater. Some examples include intrapulmonary hemorrhage (McCaul, C. et al, 2006), edema (Leuenberger, U. et al, 2001) and insufflation and exsufflation of the glossopharynx (Lindholm, P. and Lungdren, C., 2009). These divers are also at risk of blackout during ascent (Shiraishi, M. et al, 2002), nitrogen narcosis (Irgens, A. et al, 2007) and decompression sickness.
Since breath-holding or apnea diving is considered as an extreme sport, divers do not only have to deal with physiological and pathophysiological problems associated with this type of diving as cited above, but they also have to utilize certain body maneuvers to allow them to breach the theoretic physiologic limit (Muth, C. et al, 2005). This maneuver called lung-packing maneuver (Muth, C. et al, 2005) allows divers to dive deeper at a longer interval. While this maneuver allows the heart rates of divers to fall, this could lead to a higher incidence of arrhythmia in the ventricles (Ferrigno, M. et al, 1997). This maneuver can be adapted in breath-holding divers sand allow them to conserve oxygen (Muth, C. et al, 2005). Another mechanism employed by the body to allow longer breath-hold diving is the lowering of oxygen consumption as a result of increased concentration of carbon dioxide in the lung alveoli (Ferreti, G., 2001). However, Ferreti (2001) noted that this would invariably result to anaerobic glycolysis or accumulation of lactate in the blood. Eight years ago, the current world record for depth in breath-hold diving was 150 m (Ferreti, G., 2001). Today, it now stands at 214 meters (Lindholm, P. and Lungdren, C., 2009). Ferreti explained then in 2001 that the world record can be improved depending on the following factors; “how far the equilibrium between starting oxygen stores, the overall rate of energy expenditure, the fraction of energy provided by anaerobic metabolism and the diving speed can be pushed, with consciousness upon emersion. The ultimate limit to breath-hold diving records may indeed be imposed by an energetic constraint.” (p. 254).
While only immediate effects of the diving-response have been recorded, there are some studies that have recognized the long-term health effects of a career in diving (Ross, J. et al., 2007). For example, aside from the common problems such as dysbaric bone necrosis and decompression illness (Ross, J. et al, 2007) associated with a long career in diving, studies have also noted that these divers may experience musculoskeletal symptoms (Pingitore, A. et al, (2007; Kroenke, K. et al. 2002); cognitive dysfunction (Muth, C. et al, 2005); difficulties in concentration (Taylor, C., et al, 2006) and forgetfulness (Kroenke, K. et al, 2002; Taylor, C., et al, 2006) along with hearing impairment. However, it is imperative to acknowledge that diving animals are more adapted to longer and deeper breath-hold diving (Mori, Y., 1999). While the immediate physiologic effects such as bradycardia, peripheral vasoconstriction, conservation of oxygen and a decrease in CO or cardiac output are the same effects observed in diving mammals, humans are still less adapted to longer breath-hold diving (Ferrigno, M., et al, 1997). The main deterrents in humans are the presence of arrhythmias and increase in blood pressure (Ferrigno, M. et al, 1997).
In conclusion, the effects of the diving response on breath-hold divers include various physiological impacts such as arrhythmia, increased blood pressure and cardiac output, bradycardia and conservation of oxygen with resulting anaerobic glycolysis. However, the most dangerous effect of prolonged breath-hold diving is hypoxia- which may result to loss of consciousness and eventually drowning of inexperienced divers. While breath-hold diving has elicited wide attention as an extreme sport, the desire to breach current world records in terms of longevity under water and depth submerged by breath-hold divers has always been present. A number of researchers have acknowledged that the theoretical limits have already been surpassed and apparently, the ability to breach current records may lie on the amount of energy a well-trained diver possess to achieve his goal of breaking world records. If a diver can conserve more oxygen and produce more energy without losing consciousness, this might significantly improve his/her time to hold his breath underwater and at the same time allow him to reach deeper into the water.