Effects of Gas Compression on Mammals

Loren Greenway Ph.D. FCCP MFAWMWilderness Medical Society

1Dive and Hyperbaric Medicine:Practical Experience for Scuba Divers

Financial Disclosure

• Loren Greenway: Has No Financial Encumberments from any Manufacturer, Vendor, Service or Product discussed in the Lecture.

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Course OutlineObjectives

• Introduce attendees to the field of dive medicine and concepts of gas narcosis and decompression illness.

• Review aspects of underwater thermoregulation, dive safety, and accident prevention

• Review aspects of Hyperbaric Medicine

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Course OutlineTopics

• Introduction to Dive Medicine and Physiology– Loren Greenway, PhD, MFAWM, FCCP

• Marine Creature Envenomation and other injuries– James Geiling, MD FCCP

• DAN: Overview of Hyperbaric Medicine and DCI Treatment– -Nick Bird, MD

• Hyperbaric Literature Review: Top Ten Landmark Papers– Eric Johnson, MD

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Effects of Gas Compression on the Mammals - Objectives

• Understand the basic physiology of Gas Compression

• Comparative Diving Physiology• Barometer Pressure effects on Gas Filled

Spaces• Biological Effects of Pressure

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Definitions

• 1 ATA = Atmosphere Absolute = 14.7 psi• 1 ATA = 33 FSW (Feet of Sea Water)• 1 ATA = 34 FFW ( Feet of Fresh Water)• 2 ATA = Surface Pressure + 33 FSW/ 34 FFW• 3 ATA = 66 FSW / 68 FFW• 4 ATA = 99 FSW / 101 FFW

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Gas Filled Compartments

• Henry’s Law: The dissolving process for gases is an equilibrium. The solubility of a gas depends directly on the gas pressure. The number of molecules leaving the gas phase to enter the solution equals the number of gas molecules leaving the solution. If the temperature stays constant increasing the pressure will increase the amount of dissolved gas.

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Basic Physiology of Gas Compression

• The Effects of air compression at 4.0 ATA

– 1835 Junrod, Described “Nitrogen Narcosis”• ‘ The functions of the brain are activated’• ‘Imagination is lively’• ‘Thoughts have a peculiar charm’• ‘Symptoms of Intoxication’

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Basic Physiology of Gas Compression

• 1861 Green – added to the symptomology– Sleepiness– Hallucinations– Impaired Judgment

• 1878 Bert, Described:– Oxygen Toxicity– Decompression Sickness (DCS) – Decompression Illness (DCI)

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Basic Physiology of Gas CompressionTheories of Nitrogen Narcosis

• Alveolar Hypoventilation – C02 Retention• Electro-Physiologic Disruption• Cellular and Membrane Mechanism

Dysfunction• Neurotransmitter Disruption

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Basic Physiology of Gas Compression

• Effects on Human Performance– 1937 Shilling & Willgate• Impairment of Physical and Mental Performance• 90-330 FSW, 46 Men, Impairment

– Addition– Multiplication– Subtraction– Division– Recording Times– Reaction Time

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Basic Physiology of Gas Compression

• 1941- Haldane & Case– 250-300 FSW • 2 minutes elapsed time

– Marked Impairment of practical Ability– Impaired Judgment

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Basic Physiology of Gas Compression

• Why do these changes happen– Causes of inert gas narcosis are complex – They are multifactorial in nature• Hypoventilation and Hypercarbia

– 1950 - Bean– 1960 – Seusing &Drube– 1963 - Buhlman– 1971 – Vail

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Basic Physiology of Gas Compression

• Hypoventilation and Hypercarbia is not the cause– 1955 Rashbass– 1959, 1964, 1966 – Cabarrou– 1963- Lamphier– 1965 – Bennett

• Conclusively showed “No correlation between carbon dioxide retention and the degree of Narcosis”• Further supported by:

– 1974 – Bennet & Blenkam– 1971 – Hesser– 1991 – Fothergill

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Basic Physiology of Gas Compression

• Electro-Physiologic Mechanisms– 1950 – Marshall & Fenn• Frogs, Mice (Isolated Tissues)• Frog reflex preparations• Frog Brain Wave preparations

– 260 minutes – Nitrogen (16.3 ATA)– 260 minutes – Helium (9 ATA)

– Nitrogen -Reversibly Blocked in vitro frog reflex preparations

– Helium- had no effect even at 82.8 ATA

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• In vivo frog sciatic nerve was not effected by any inert gases at pressure as high as (96.2 ATA)

• 1954 – Campbell– 310-340 ATA – Argon Blocked conduction of

isolated peripheral nerve in frogs and mice.– However, considerably lower pressure protected

mice from electroshock convulsions

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Basic Physiology of Gas Compression

Basic Physiology of Gas Compression

• 1953,- 1955 – Carpenter– Inference that the site of action for inert gas narcosis,

(as with Anesthetics) is at the central synapses

• 1959 – Chun – Reflex inhibition in cats

• 1963-1966 – Bennett– Inhibitory synaptic mechanisms – Anterior Horn Cells of the synapse were specifically

Effected.

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Basic Physiology of Gas Compression

• Further studies that support Electro-Physiologic Mechanisms are:– 1964 Bennett – Auditory Induced Evoke Potentials– 1953-1955 Jullien, Morris, Rogers• Increased excitatory state of cortical neurons

– 1971 Hamilton – Visual stimuli, psychomotor testing, and arithmetic performance with auditory evoke potentials.

• These tests indicated an appreciable effect with nitrogen.

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Basic Physiology of Gas Compression

• Cellular and Membrane Mechanisms– Theories fall into two categories• Biochemical Reactions

– Effect on the respiratory enzyme system

• Physical Disruption– Interaction with part of the neuron such as the cell membrane

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Basic Physiology of Gas Compression

• Biochemical Disruption– No data supports this theory• 1955 – Carpenter• 1960 – Leon & Cook• 1963 -Levy & Featherstone• 1973 – Schatte & Bennett• 1963 - Thomas

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Comparative Diving Physiology

• Cetacea– 80 species of modern Cetaceans– 11 species of Baleen Whales (Mysrticerti)– 69 Species toothed Whales (Odontoceti)– They Inhabit all Oceans of the world– Four species live only in Fresh Water Rivers or

Lakes– Dive to depths of 984-1640 fsw ( 30-50 ATA)– Submersion Time from 1-5 minutes

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Comparative Diving Physiology

• Respiratory Adaptations– Lungs are liability in deep diving– They are a better nitrogen store than oxygen store– Structurally Modified more than any mammalian

group

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Lung Volumes

• In general Lung of Marine Mammals are:– Extremely Compressible• No Residual Capacity• Peripheral Airway Reinforcement• Exceptional short and thick airways

– Lung Volumes• TLC - 28-145 ml/kg• Sea Otter – 345 ml/kg – Surfaced Buoyancy

`

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Intermittent Breathing

• 1991 – Reynolds, Odell – Tidal Volume – 80-90% of TLC– Weddell Seals – Tidal Volume is 75% of TLC– Most Cetolgist believe• Whales and Dolphins dive during Inspiration• Pinnipeds and Sea Lions -50-75% of Inspiration

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Cardiovascular Adaptations

• Anatomy– Enlarged Capacitance• Spleens and Venous Sinuses• Venous Sphincter Muscles• Aortic Windkessels• Vascular Retia

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Hypotheses

• Windkessel functions of the Brain Blood Flow– Prevention of the ‘Bends’ by entrapping bubbles– Intrathoracic Vascular Engorgement to prevent

lung squeeze– Modification of blood composition

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Cardiovascular Physiology

• Marine Mammals are most noted for the their exquisite control of Heart Rate and Peripheral Vasculature Constriction.

• ‘Dive Reflex’– 1940 Scholander – Dive Reflex

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Dive Reflex

– Stimulation• Nasal or Upper Respiratory Receptors• Facilitated / Reinforced by:

– Cessation of Breathing– Lung Collapse– Hypoxia– Hypercapnea– Baroreceptor Response

• Trained Divers– 1965 Elsner - Cerebral Cortex Modification

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Dive Reflex

• Sea Lions rested on surface pads have been trained:– Lower Heart rate > 10 BPM– Decreased Peripheral Blood flow– Blood Oxygen Depletion (Extraction)• Decrease Splanchnic and Renal Blood Flow• Improve Oxygen Extraction

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Oxygen Stores

• Breath Hold Capacity of Diving Mammals– Thoracic Blood Volume– Muscle Compartment Blood Volume– Hemoglobin Concentration– Muscle Mass– Myoglobin Concentration– Humans 70ml/kg– Diving Mammals 3x higher stores

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Gas Filled Compartments

• The body has many gas filled compartments– Sinuses– Gi Tract– Ear Cannels– Teeth

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