Physiological Responses to Cold Water Stimulation

Exercise Physiology I - AS24

• Course is about exercise physiology, specifically focusing on hyperbaric conditions (diving).
• Professor Christina M. Spengler, PhD, MD, teaches the course.
• The course covers physiological changes associated with water immersion (cold) and increasing hyperbaric environments (depth).
• Students will critically analyze the physiological similarities and differences free diving and scuba diving, including accident risks and preventative measures.

Learning Objectives

• Physiological changes during immersion and diving depth
• Similarities and differences between free diving and scuba diving
• Potential risks and safety measures for diving accidents
• Critically reflect on pathophysiological changes during diving

Cardio-Respiratory changes with Partial Water Immersion

• Venous return increases (↑)
• Stroke volume increases (↑) and heart rate decreases (↓), but overall, cardiac output increases (↑)
• Pulmonary blood volume increases (↑)
• Respiratory muscle work increases (↑)
• Diuresis increases (↑) in response to the above.

Cardio-Respiratory response to Cold Water Immersion (The Cold Shock)

• Combination of reflexes triggered by cold water (<25°C) on the body (excluding the head)
• Initial deep inspiration leads to substantial hyperventilation (the colder the water, the more pronounced the stimulus; peaks at approximately 10°C).
• Functional residual capacity (FRC) increases
• Increased air hunger.

Cardio-Respiratory changes with Full Water Immersion (The Diving Reflex)

• Physiological response to cold water stimulation of the face and eyes: Includes apnea, bradycardia, and peripheral vasoconstriction.
• Aim: Reduce oxygen consumption (VO2) and extend underwater survival time.
• Diving mammals demonstrate a more effective diving reflex compared to humans (children show a less effective response than adults)

Effects of Cold Water - Thermoregulation

• Heat transfer in water is significantly greater (26x) than in air..
• Overall, heat loss in water is 4x faster than in air.
• Immersion in 15°C water leads to body temperature decrease at a rate of -2.1°C/hour.

Effects of Cold Water - Muscle Function and Metabolism

• Contraction velocity decreases(↓)
• Neuromuscular coordination decreases(↓)
• Fatigue increases(↑)
• Increased risk of cardiac arrhythmia in cold water.
• Epinephrine and norepinephrine secretion increases(↑↑)
• Lipolysis increases (↑) leading to increased free fatty acids in the blood.
• Anaerobic glycolysis (muscle glycogen use) increases(↑)

Effects of Hyperbaric Conditions on Air-Filled Cavities

• Boyle's Law applies, impacting air-filled cavities (like sinuses, ears, lungs, and intestines) during diving
• Lung volume decreases with depth
• Lung volume is shown across depths in a graph

Barotrauma in Response to Hypobaric Conditions

• Equalize pressure or risks injuries
• The blockage may lead to pain, rupture of small vessels and membranes in the middle ear or sinuses, or rupture of the ear drum.
• Without proper equalization, blood vessels in the eyes and skin may be damaged, and eyes may even be displaced.
• Swim goggles provide no assistance to equalize pressure.
• Facemasks should include a nose opening to enable pressure equalization.

Free Diving (Apnea Diving) - Limits and Risks

• Breathhold limitations:
• Effects of hyperbaric conditions on lungs
• Snorkel considerations

Static Apnea - Guinness Book of World Records

• World records in breath-holding (e.g., Robert Foster, Budimir Sobat)
• Factors that influence apnea duration

Static Apnea - World Records (without oxygen breathing):

• Natalia Molchanova holding her breath for 9.02 minutes, and Stephane Mifsud for 11.35 minutes.

Limits to apnea

• Changes in blood gases (increase in PaCO2 and decrease in PaO2)
• Suppression of the respiratory drive and feedback.
• Motivation of the individual is an important factor.

Risk of Hyperventilation prior to Apnea

• Lower pCO2 levels can delay the stimulus to breathe.
• Reduced stimulus to breathe leads to the risk of unconsciousness

Diving depth and lung volume

• Lung volume decreases with increasing depth.
• Calculations for lung volume (L) at depths.

Diving depth and lung volume (Male and Female)

• Average Total Lung Capacity (TLC)
• Average Residual Volume (RV)
• Average Peak Expiratory flow (Pmax)
• Maximum depth according to these variables

Free diving (no limits) - World records (NLT)

• World records without any limitations other than those set by the athlete Tanya Streeter (160m) and Herbert Nisch (214m) world records

SCUBA Diving

• Invention of SCUBA by Jacques Cousteau and Emile Gagnan
• Incidents/risks in diving

SCUBA Diving - Additional Risks

• Oxygen poisoning
• Nitrogen narcosis
• Lung Injury
• Problems with decompression

Open-circuit demand SCUBA

• Detailed explanation of equipment and volume of air
• Calculation for time it takes to use air supplies at different depths

Gases under pressure during hyperbaric conditions

• O2 poisoning
• N2 narcosis
• Decompression complications
• Preventative and treatment methods

SCUBA Diving - additional risk: Oxygen poisoning

• Symptoms (visual distortion, rapid/shallow breathing, convulsions, seizures)
• Cause: Reduced oxygen removal from hemoglobin, decreased carbon dioxide uptake. This results in high oxygen pressure that causes vasoconstriction to cerebral vessels.

SCUBA Diving - additional risk: Nitrogen narcosis

• Nitrogen acts as anaesthetic.
• Symptoms worsen with increasing depth and pressure.
• Mitigation of symptom with different breathing gasses.

SCUBA Diving - additional risk: Lung injury

• Lung rupture during ascent (pneumothorax) due to rapidly decreasing pressure.

SCUBA Diving - additional risks: Bubbles, Emboli and Decompression sickness

• Bubbles, emboli and decompression sickness cause pain.
• Ascending too quickly releases dissolved nitrogen from liquid, causing bubbles that can cause various problems

SCUBA Diving - additional risk: Decompression sickness (special risk)

• Increased risk of N2-embolus to brain in divers with open foramen ovale (25% prevalence in population), is magnified threefold.

Prevention of decompression sickness

• Charts and dive computers that provide safe times for divers to ascend
• Treatment using hyperoxia and recompression chambers

Hyperbaric chambers

• Medical facilities that treat divers experiencing decompression sickness

Air-Rescue of divers with decompression sickness — a Challenge

• Air rescue procedures for divers
• Rega-Helicopter deployment in case of diver emergencies

Diving — Risks-Summary

• Summarize the overall risks of diving (free diving or SCUBA)

After this Lecture, ask yourself "Can I ...."

• List of potential questions to ask about diving