Nitrogen narcosis

SCUBA DIVING

1. NITROGEN NARCOSIS Aarti Sareen MSPT honours III sem .

2. NARCOSIS: a state of stupor, unconsciousness, or arrested activity produced by the influence of narcotics or other chemicals or physical agents

3. NITROGEN NARCOSIS A state of euphoria and confusion similar to that of alcohol intoxication which occurs when nitrogen in normal air enters the bloodstream at increased partial pressure (as in deepwater diving) Divers typically begin to experience the effects of nitrogen narcosis at depths of 100 feet( 30m)—called also rapture of the deep

4. NITROGEN NARCOSIS Air is 79% nitrogen At high partial pressures (>1 kPa ), nitrogen has depressant effect on CNS Usually occurs at depths > 30 m Effects mimics alcohol Symptoms: light-headedness, tendency to laugh, poor concentration , short attention span, impaired judgement , impaired motor coordination, impaired cognitive function

5. GAS LAWS Boyle’s law Charles’s law D alton’s law Henry’s law

6. BOYLE’S LAW At constant temperature, the volume of a gas varies inversely with the pressure, while the density of a gas varies directly with pressure . P 1 V 1 = P 2 V 2 = constant

7. BOYLE’S LAW P 1 V 1 = P 2 V 2 = constant

8. T he law becomes particularly important on deep dives; it predicts that the inhaled air will become denser the deeper one goes. As a result of increasing air density, deep divers often notice greater difficulty breathing.

9. CHARLE’S LAW At a constant volume, the pressure of gas varies directly with absolute temperature. Charles's law is not as important for scuba divers because temperature under water seldom changes enough to seriously affect air pressure. However, the law is useful to keep in mind when filling air tanks, especially when there is a large difference between air and water temperatures.

10. DALTON’S LAW The total pressure exerted by a mixture of gases is equal to the sum of the pressures that would be exerted by each of the gases if it alone were present and occupied the total volume. Simplified: The pressure of any gas mixture (e.g., air) is equal to the sum of pressures exerted by the individual gases (e.g., oxygen, nitrogen, and each of the minor gases). P total = P 1+ P 2 ……… where P TOTAL is the total pressure of a gas mixture (e.g., air), and P 1 and P 2 are the partial pressures of component gases (e.g., oxygen and nitrogen)..

11. HENRY LAW The amount of any gas that will dissolve in a liquid at a given temperature is a function of the partial pressure of the gas in contact with the liquid and the solubility coefficient of the gas in that particular liquid. Simplified: As the pressure of any gas increases, more of that gas will dissolve into any solution with which it is in free contact. Amount of nitrogen dissolved in plasma depends on depth and duration. Rate of nitrogen pressure equilibration depends on the affinity of the tissue for nitrogen and the rate of blood flow to that tissue

12. HOW DOES THE INCREASED PRESSURE AT DEPTH AFFECT GAS IN THE BODY? The increased pressure of each gas component at depth means that more of each gas will dissolve into the blood and body tissues, a physical effect predicted by Henry's Law. Inhaled gases are in close contact with blood entering the lungs. Hence, the greater the partial pressure of any inhaled gas, the more that gas will diffuse into the blood. Together, Boyle's and Henry's laws explain why, as a diver descends while breathing compressed air: 1) inhaled PO 2 and PN 2 increase and 2) the amount of nitrogen and oxygen entering the blood and tissues also increase.

13. Unlike oxygen and carbon dioxide, nitrogen (N 2 ) is inert; it is not metabolized by the body. At sea level the amount of N 2 inhaled and exhaled is the same. This is not the case for O 2 and CO 2 , which are not inert gases but instead participate in metabolism; as a result less O 2 is exhaled than inhaled, and more CO 2 is exhaled than inhaled. When breathing compressed air at depth, more gas molecules of air are inhaled because the air is at a higher pressure, and hence denser, than at sea level. Both the pressure and amount of inhaled nitrogen and oxygen are greater at depth than at sea level

14. Most of the extra oxygen is metabolized and doesn't pose any problem at recreational depths. But what about nitrogen, which is inert? The extra nitrogen that is inhaled has nowhere to go but into the blood and tissues, where it is stays in the gas phase ("dissolved") at the higher pressure, until the ambient pressure is reduced; then it starts to dissolve back out, and is excreted in the exhaled air. Two important problems relate to the increased quantity and pressure of nitrogen from inhaling compressed air: nitrogen narcosis and decompression sickness . Although both problems are related to too much nitrogen, they are distinct.

15. At 10m the nitrogen partial pressure doubles the sea level value to 1200 mmHg. With each additional 10m depth, nitrogen partial pressure increase by 600mmHg Nitrogen narcosis when persists more then 5-6 min. may leads to paralysis, coma or death.

16. Martini’s law Is a well known dictum states that every 50 feet (15.2m) of seawater produces effects equal to one dry martini on an empty stomach.

17. Complex reasoning decreases 33% and manual dexterity decreases by 7.3%. Till now dopamine& glutamate levels in prefrontal lobe is considered as the cause of nitrogen narcosis but yet the exact cause with evidence is lacking.

18. EFFECT OF NITROGEN ON CNS

19. Dopamine is neurotransmitter in the brain that plays vital roles in a variety of different behaviors. The major behaviors dopamine affects are movement, cognition, pleasure, and motivation . Dopamine is an essential component of the basal ganglia motor loop, as well as the neurotransmitter responsible for controlling the exchange of information from one brain area to another . However, it is the role that dopamine plays in pleasure and motivation

20. REVIEW OF LIETERATURE

21. Comparison between subjective feelings to alcohol and nitrogen narcosis: a pilot study Monteiro MG , Hernandez W , Figlie NB , Takahashi E , Korukian M Nitrogen narcosis is often compared to alcohol intoxication, but no actual studies have been carried out in humans to test the comparability of these effects. If a common mechanism of action is responsible for the behavioral effects of these substances, biological variability of response to alcohol should correlate to that of nitrogen in the same individual. To test this hypothesis, subjective feelings were assessed in two separate occasions in 14 adult male, healthy volunteers, nonprofessional divers. In one occasion, each subject received 0.75 ml/kg (0.60 g/kg) alcohol 50% (v/v PO) and in another day underwent a simulated dive at 50 m for 30 min in a hyperbaric chamber. There was a significant correlation between reported feelings in the two sessions; subjects who felt less intoxicated after drinking also felt less nitrogen narcosis during the simulated dive. The results, although preliminary, raise the hypothesis that ethanol and nitrogen may share the same mechanisms of action in the brain and that biological differences might account for interindividual variability of responses to both ethanol and nitrogen.

22. Does inert gas narcosis have an influence on perception of pain ? Kowalski JT , Seidack S , Klein F , Varn A , Röttger S , Kähler W , Gerber WD , Koch A . Source German Armed Forces Hospital, Research Center of Psychotraumatology , Berlin, Germany The effect of an increased nitrogen partial pressure under hyperbaric conditions is known as nitrogen narcosis (NN). At an ambient pressure of about 4 bar, reduced cognitive performance as well as euphoric effects are reported. We examined the effect of NN on pain perception. 22 subjects completed an experimental (50 meters = 6 bar) and a simulated control dive (0 m = 1 bar) in a hyperbaric chamber. Before and during each dive a standardized cold pressure test was performed. The intensity of pain perceived was assessed with the help of a visual analogue scale; additionally, subjects assessed the subjective effect of NN . The study showed that the perceived pain intensity is significantly reduced under nitrogen narcosis conditions (F1.21 = 5.167, p < 0.034) when compared to the perceived pain intensity under the control dive conditions (F1.21 = 0.836, p = 0.371). A connection between perceived pain intensity and subjects experience of the NN was not found under the experimental dive condition (r = 0.287, p = 0.195). We could show that even relatively moderate hyperbaric conditions may have an influence on the perception of pain. The results are highly relevant since nitrogen narcosis occurs in divers as well as in medical personnel or construction workers, working under hyperbaric conditions.

23. Measuring manual dexterity and anxiety in divers using a novel task at 35-41 m. Kneller W , Higham P , Hobbs M . Source University of Winchester, West Hill, Winchester, Hampshire SO22 4NR, UK METHODS: There were 45 subjects who were given a test of manual dexterity once in shallow water (1-10 m/3-33 ft) and once in deep water (35-41 m/115-135 ft). Subjective anxiety was concurrently measured in 33 subjects who were split into 'non-anxious' and 'anxious' groups for each depth condition. RESULTS: Subjects took significantly longer (seconds) to complete the manual dexterity task in the deep (mean = 52.8; SD = 12.1) water compared to the shallow water (mean = 46.9; SD = 8.4). In addition, anxious subjects took significantly longer to complete the task in the deep water (mean = 48.6; SD = 6.8) compared to non-anxious subjects (mean = 53.2; SD = 9.9), but this was not the case in the shallow water. DISCUSSION: This selective effect of anxiety in deep water was taken as evidence that anxiety may magnify narcotic impairments underwater. It was concluded that the test of manual dexterity was sensitive to the effects of depth and will be a useful tool in future research.

24. Mechanism of action of nitrogen pressure in controlling striatal dopamine level of freely moving rats is changed by recurrent exposures to nitrogen narcosis. Lavoute C , Weiss M , Risso JJ , Rostain JC . In rats, a single exposure to 3  MPa nitrogen induces change in motor processes, a sedative action and a decrease in dopamine release in the striatum. These changes due to a narcotic effect of nitrogen have been attributed to a decrease in glutamatergic control and the facilitation of GABAergic neurotransmission involving NMDA and GABA(A) receptors, respectively. After repeated exposure to nitrogen narcosis, a second exposure to 3  MPa increased dopamine levels suggesting a change in the control of the dopaminergic pathway. We investigated the role of the nigral NMDA and GABA(A) receptors in changes in the striatal dopamine levels. Dopamine-sensitive electrodes were implanted into the striatum under general anesthesia, together with a guide- cannula for drug injections into the SNc . Dopamine level was monitored by in vivo voltammetry . The effects of NMDA/GABA(A) receptor agonists (NMDA/ muscimol ) and antagonists (AP7/ gabazine ) on dopamine levels were investigated. Rats were exposed to 3  MPa nitrogen before and after five daily exposures to 1  MPa . After these exposures to nitrogen narcosis, gabazine , NMDA and AP7 had no effect on the nitrogen-induced increase in dopamine levels. By contrast, muscimol strongly enhanced the increase in dopamine level induced by nitrogen. Our findings suggest that repeated nitrogen exposure disrupted NMDA receptor function and decreased GABAergic input by modifying GABA(A) receptor sensitivity. These findings demonstrated a change in the mechanism of action of nitrogen at pressure.

25. Anxiety and psychomotor performance in divers on the surface and underwater at 40 m. Hobbs M , Kneller W METHODS: The effects of self-reported anxiety (anxious vs. not anxious) and depth (surface vs. underwater) on performance on the digit letter substitution test (DLST) were measured in 125 divers. RESULTS: Change from baseline scores indicated that divers performed significantly worse on the DLST underwater (mean = 3.35; SD = 4.2) compared to the surface (mean = 0.45-0.73; SD = 4.0-4.2). This decrement was increased when divers reported they were also anxious (mean = 7.11; SD = 6.1). There was no difference on DLST performance at the surface between divers reporting they were anxious and those reporting they were not anxious. DISCUSSION: The greater decrement in performance at depth in divers reporting anxiety compared to those not reporting anxiety and the lack of this effect on the surface suggested that anxiety may magnify performance deficits presumed to be caused by narcosis.

26. Behavioral temperature regulation in humans during mild narcosis induced by inhalation of 30% nitrous oxide . Yogev D , Mekjavi IB n this study, we investigated the influence of mild narcosis on temperature perception, thermal comfort, and behavioral temperature regulation in humans. Twelve subjects (six males and six females) participated in two trials, during which they wore a water- perfused suit (WPS). The temperature of the WPS (TWPS) fluctuated sinusoidally from 27 degrees to 42 degrees C, at a heating and cooling rate of 1.2 degrees C x min(-1). In the first trial, the subjects had no control over TWPS: They determined their thermal comfort zone (TCZ) by providing a subjective response whenever they perceived the temperature changing from a comfortable to an uncomfortable level and vice versa; in addition, they provided subjective ratings of temperature perception and thermal comfort on a 7-point and 4-point scale, respectively, at each 3 degrees C change in TWPS. In the second trial, subjects could change the direction of TWPS whenever it became uncomfortable by depressing a button on a manual control. The protocols were conducted with subjects breathing either room air (AIR), or a normoxic breathing mixture containing 30% N2O. Subjects perceived increasing TWPS as equally warm and the decreasing TWPS as equally cold with AIR or N2O . However, equal changes in TWPS were perceived as significantly less discomforting (P<0.05) during N2O, and the magnitude of the TCZ significantly (P<0.01) increased. Thus, narcosis did not alter thermal sensation, but it significantly changed the perception of comfort. These changes were not reflected in the behavioral response. Subjects produced similar TWPS damped-oscillation patterns in the AIR and N2O trials. We conclude that the narcosis-induced alteration in the perception of thermal comfort does not change the preferred temperature, or the ability to behaviorally maintain thermal comfort.

27. Effect of nitrogen narcosis on free recall and recognition memory in open water . Hobbs M , Kneller W . METHODS: Using a repeated measures design, the free recall and recognition memory of 20 divers was tested in four learning-recall conditions: shallow-shallow (SS), deep-deep (DD), shallow-deep (SD) and deep-shallow (DS). The data was collected in the ocean offDahab , Egypt with shallow water representing a depth of 0-10m (33ft) and deep water 37-40m (121-131ft). The presence of narcosis was independently indexed with subjective ratings. RESULTS: In comparison to the SS condition there was a clear impairment of free recall in the DD and DS conditions, but not the SD condition. Recognition memory remained unaffected by narcosis. CONCLUSIONS: It was concluded narcosis-induced memory decrements cannot be explained as simply an impairment of input into long term memory or of self-guided search and it is suggested instead that narcosis acts to reduce the level of processing/encoding of information.

28. Recent neurochemical basis of inert gas narcosis and pressure effects. recently, protein theories are in increasing consideration since results have been interpreted as evidence for a direct anaesthetic -protein interaction. The question is to know whether inert gases act by binding processes on proteins of neurotransmitter receptors. Compression with breathing mixtures where nitrogen is replaced by helium which has a low narcotic potency induces from 1 MPa , the high pressure nervous syndrome which is related to neurochemical disturbances including changes of the amino-acid and monoamine neurotransmissions. The use of narcotic gas (nitrogen or hydrogen) added to a helium-oxygen mixture, reduced some symptoms of the HPNS but also had some effects due to an additional effect of the narcotic potency of the gas. The researches performed at the level of basal ganglia of the rat brain and particularly the nigro-striatal pathway involved in the control of the motor, locomotor and cognitive functions, disrupted by narcosis or pressure, have indicated that GABAergic neurotransmission is implicated via GABAa receptors.

29. EEG patterns associated with nitrogen narcosis (breathing air at 9 ATA). Pastena L , Faralli F , Mainardi G , Gagliardi R . METHODS: The authors observed the electroencephalogram (EEG) of 10 subjects, ages 22-27 yr, who breathed air during a 3-min compression to a simulated depth of 80 msw (9 ATA). The EEG from a 19-electrode cap was recorded for 20 min while the subject reclined on a cot with eyes closed, first at 1 ATA before the dive and again at 9 ATA. Signals were analyzed using Fast Fourier Transform and brain mapping for frequency domains 0-4 Hz, 4-7 Hz, 7-12 Hz, and 12-15 Hz. Student's paired t-test and correlation tests were used to compare results for the two conditions. RESULTS: Two EEG patterns were observed. The first was an increase in delta and theta activity in all cortical regions that appeared in the first 2 min at depth and was related to exposure time. The second was an increase in delta and theta activity and shifting of alpha activity to the frontal regions at minute 6 of breathing air at 9 ATA and was related to the narcotic effects of nitrogen. DISCUSSION: If confirmed by studies with larger case series, this EEG pattern could be used to identify nitrogen narcosis for various gas mixtures and prevent the dangerous impact of nitrogen on diver performance.

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