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Effects of Gas Compression on Mammals Loren Greenway Ph.D. FCCP MFAWM Wilderness Medical Society 1 Dive and Hyperbaric Medicine: Practical Experience for.

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Presentation on theme: "Effects of Gas Compression on Mammals Loren Greenway Ph.D. FCCP MFAWM Wilderness Medical Society 1 Dive and Hyperbaric Medicine: Practical Experience for."— Presentation transcript:

1 Effects of Gas Compression on Mammals Loren Greenway Ph.D. FCCP MFAWM Wilderness Medical Society 1 Dive and Hyperbaric Medicine: Practical Experience for Scuba Divers

2 Financial Disclosure Loren Greenway: Has No Financial Encumberments from any Manufacturer, Vendor, Service or Product discussed in the Lecture. 2

3 Course Outline Objectives 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 3

4 Course Outline Topics 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 4

5 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 5

6 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 6

7 Gas Filled Compartments Henrys 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. 7

8 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 8

9 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) 9

10 Basic Physiology of Gas Compression Theories of Nitrogen Narcosis Alveolar Hypoventilation – C02 Retention Electro-Physiologic Disruption Cellular and Membrane Mechanism Dysfunction Neurotransmitter Disruption 10

11 Basic Physiology of Gas Compression Effects on Human Performance – 1937 Shilling & Willgate Impairment of Physical and Mental Performance FSW, 46 Men, Impairment – Addition – Multiplication – Subtraction – Division – Recording Times – Reaction Time 11

12 Basic Physiology of Gas Compression Haldane & Case – FSW 2 minutes elapsed time – Marked Impairment of practical Ability – Impaired Judgment 12

13 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 – Bean – 1960 – Seusing &Drube – Buhlman – 1971 – Vail 13

14 Basic Physiology of Gas Compression Hypoventilation and Hypercarbia is not the cause – 1955 Rashbass – 1959, 1964, 1966 – Cabarrou – 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 14

15 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 15

16 In vivo frog sciatic nerve was not effected by any inert gases at pressure as high as (96.2 ATA) 1954 – Campbell – ATA – Argon Blocked conduction of isolated peripheral nerve in frogs and mice. – However, considerably lower pressure protected mice from electroshock convulsions 16 Basic Physiology of Gas Compression

17 1953, – 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 – Bennett – Inhibitory synaptic mechanisms – Anterior Horn Cells of the synapse were specifically Effected. 17

18 Basic Physiology of Gas Compression Further studies that support Electro- Physiologic Mechanisms are: – 1964 Bennett – Auditory Induced Evoke Potentials – 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. 18

19 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 19

20 Basic Physiology of Gas Compression Biochemical Disruption – No data supports this theory 1955 – Carpenter 1960 – Leon & Cook Levy & Featherstone 1973 – Schatte & Bennett Thomas 20

21 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 fsw ( ATA) – Submersion Time from 1-5 minutes 21

22 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 22

23 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 ml/kg Sea Otter – 345 ml/kg – Surfaced Buoyancy ` 23

24 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 % of Inspiration 24

25 Cardiovascular Adaptations Anatomy – Enlarged Capacitance Spleens and Venous Sinuses Venous Sphincter Muscles Aortic Windkessels Vascular Retia 25

26 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 26

27 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 27

28 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 28

29 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 29

30 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 30

31 Gas Filled Compartments The body has many gas filled compartments – Sinuses – Gi Tract – Ear Cannels – Teeth 31


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