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this shit is cool

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Brittney Young

on 17 March 2014

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Transcript of this shit is cool

Diving Response
Environmental Factors
Human Physiology of Apnea
Water Submersion & Breath Hold Diving
Greater than air, and even greater in sea water
Air-filled cavities in human body result in lower mean density, which causes body to float
Increases linearly by 1 absolute atmosphere (ATA) every 10m of depth
Temperature and thermal conductivity
Thermal neutral water allows for lowest oxygen consumption to maintain body temperature
Water is 25x more thermally conductive than air
Breath-hold diving
Static apnea
Diver floats motionless, face-down in a pool to achiever maximal breath-hold
Dynamic apnea
Diver's goal is to attain maximal underwater swimming distances
Constant weight
Diver descends along vertically suspended rope using fins
No-limits apnea
Dive is performed by descending using a weight and ascending with a floatation device
Scuba Diving
Use of Self Contained Breathing Apparatus (SCUBA)
Surface Supplied Diving
Gasses are supplied from surface via an umbilical (air hose), which can also provide a means of communication and safety line, with options of a hot water hose, a video cable and a gas reclaim line
Physiology of Breath-Hold Diving
Two main factors induce important physiological modifications:
1. Duration

2. Depth

Causes increase of hydrostatic pressure resulting in compression of the body's air-containing cavities (chest/lungs)
Extended duration of apnea has increased effects on gas concentrations
Major physiological adaptation allowing divers to endure lack of oxygen during apnea.
Can be characterized by:
A reduction in heart rate (bradycardia) due to increased cardiac parasympathetic activity
Peripheral vasoconstriction on the arterial vascular tree
Increase in sympathetic activity triggered in response to cessation of respiration
And, but not necessarily, the stimulation of facial cold receptors
Role of Diving Response
Conservation of oxygen
The diving response is controlled by the respiratory and cardiovascular systems, which integrated by a complex neural network (Foster & Sheel, 2005)
Facial Immersion
Stimulation causes inhibition of respiration and excitation of the vasomotor centers and cardiac vagal motorneurons
Potentiate diving response by further reducing heart rate and vasoconsctriction during
Most strongly excited by water temperatures from 10-15 degrees Celsius; temperaturs of 15-35 degrees have little effect
Chemoreceptors in the carotid body serve as mechanisms for detecting and eliciting response to hypoxia and changes in arterial blood pH and partial pressures of CO2
Supporting Research
Hypoxia is an important chemoreceptor stimulus for development and maintenance of bradycardia when diving, which may also be attenuated by hypercapnia
Denervation of arterial chemoreceptors eliminates heart rate response in ducks
Carotid resection in asthmatics causes tachycardia to occur when beath holding
Stimulation of chemoreceptors via injection of cyanide in ducks increases blood pressure and vasoconstriction
Pulmonary Stretch Receptors
Slowly adapting pulmonary stretch receptors help modulate the diving response
Heart rate increases during inspiration due to parasympathetic withdrawal and decreases during expiration as a result of increases parasympathetic tone
Heart rate decreases more when lung volumes are held at 60% in comparison with 85% of vital capacity
Facial Cold Receptors:
Drive to Breath
Breath holding acts as a stimulus to increase respiratory neuronal drive
The physiologic breaking point is related to hypoxic hypercapnic conditions, which produce involuntary diaphragmatic activity associated with diver's wish to breath
Breathing is avoided by tightly contracting the glottis, which blocks the upper airway
Asphyxia & Chemosensitivity
Regular participation in breath holding activities reduce chemosensitivity to progressive hypoxia and hypercapnia
Non divers can reduce arterial partial pressure of oxygen to 60 mmHg and can increase their partial pressure of carbon dioxide to 45 mmHg
Trained breath hold divers can endure partial pressures of oxygen as low as 35 mmHg and partial pressures of CO2 as high as 50 mmHg
However, not all breath hold diving activities are associated with the same stimuli...
Relationship between total lung capacity & residual lung volume:
Due to increased hydrostatic pressure with descent lung volume is gradually "squeezed" to residual volume
Why doesn't thoracic implosion occur?
Intrathoracic blood volume increases by approximately 1L in a deep breath-hold dive
Physiological Limitations of Barotrauma
Three possible outcomes of excessive ambient pressure on thoracic cavity during apnea:
Partial or full collapse or closure resulting in reduced or absent gas exchange
Fluid filtration into airways and alveolar space
Aveolocapillary membrane rupture with bleeding into void spaces

Pulmonary edema
Symptoms of pulmonary edema or swelling of the lungs have been reported post-dive due to redistribution of blood from periphery to chest
Fun Fact:
Diving into shallow water (5 m) after a complete exhalation to residual volume has been calculated to simulate the same effects of chest/lung compression at depths of 91 m experienced in deep diving!
Glossopharyngeal Insufflation & Essuflation
"Lung packing"
Glossopharyngeal insufflation (GI) or "lung packing" is a respiratory maneuver practiced by divers to add air to the lungs on top of a full inspiration
6 week study of GI in 16 healthy women (non-divers)
VC increased by 3% without GI
GI volumes were corresponding to 10-25% of VC
After each session of GI, VC was increased - warm up effect
Lung compliance lasted almost 3 minutes
GI has been reported to increase volume of air by as much as 50% of vital capacity!
Depth & Duration
Depth and duration are both effective to some extent on reductions in heart rate associated with apnea
Physiological Affects of Changes in Hydrostatic Pressure
Ascent Blackout
Barotrauma of Descent
Barotrauma of Descent
Ascent Blackout
Hypoxia of ascent is caused by reduction of water pressure acting on chest resulting in extreme decreases of lung gas pressures
Boyles Law: relationship between gas pressure and volume
At surface, pressure is 1.0 ATA, but each 10m of depth adds another 1.0 ATA
As a result, loss of conciousness is likely to occur at lesser depths during ascent as a result of increased lung volume and decreased gas pressures
Extra: Cool study!
Future Research:
Genetic and/or training effects on allowing some individuals to dive beyond 100m without apparent clinical affects
Critical factors in etiology of pulmonary edema such as cold exposure, physical exertion, and predisposing physiological traits
Trainability of CNS tolerance to hypoxia
Unfavorable long-term effects and potential micro-damage to circulatory system?
Parallels between breath-hold divers and sufferers of sleep apnea?
Explanations of short-term lung compliance following GI - is extreme stretching of chest and lungs deleterious in long-term perspective?
Brittney Young, Sarah Loreen Smith, Aly McComb
Supporting research
(Bosco et al., 2007)
(Dujic et al., 2013)
(Lindholm & Lundgren, 2009)
(Lindholm & Lungren, 2009)
(Lindholm & Lungren, 2009)
(Foster & Sheel, 2005)
Retrieved from Foster & Sheel, 2005
Retrieved from Bosco et al., 2007
(Foster & Sheel, 2005)
Retrieved from Foster & Sheel, 2005
(Foster & Sheel, 2005)
Retrieved from Anderson & Schagatay, 1998
(Foster & Sheel, 2005)
(Foster & Sheel, 2005, Bosco et al., 2007)
(Foster & Sheel, 2005)
(Lindholm & Lungren, 2009)
(Lindholm & Lundgren, 2009)
(Lindholm & Lundgren, 2009)
Retrieved from Linholm & Lundgren, 2009
(Lindholm & Lungren, 2009)
(Lindholm & Lundgren, 2009)
Anderson, J., & Schagatay, E. (1998). Effects of lung volume and involuntary breathing movements on human diving response. European Journal of Physiology, 77, 19-24.
Bosco, G., Tano, G., Zanon, V., & Fano, G. (2007). Breath-hold diving: a point of view. Sport Science Health, 2, 47-54.
Foster, G. E., & Sheel, A. W. (2005). The human diving response, its function, and its control. Scandinavian Journal of Medicine & Science in Sports, 15, 3-12.
Lindholm, P., & Lundgen, C. (2009). The physiology and pathophysiology of human breath-hold diving. Journal of Applied Physiology, 106, 284-292.
Dujic, Z., Breskovic, T., & Bakovic, D. (2013). Breath-hold diving as a brain survival response. Translational Neuroscience, 4(3), 302-313.
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