The document discusses how mild narcosis induced by inhalation of 30% nitrous oxide affects temperature perception, thermal comfort, and behavioral temperature regulation in humans. While narcosis did not change perceptions of warmth and cold, it significantly increased perceptions of thermal comfort. However, this change in comfort perception did not alter subjects' behavioral responses for regulating temperature.

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
• Dalton’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.
• P1V1 = P2V2 = constant

7. BOYLE’S LAW P1V1 = P2V2 = constant

8. • The 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= P1+P2………
• where PTOTAL is the total pressure of a gas mixture (e.g., air),
and P1 and P2 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 PO2 and PN2 increase and
• 2) the amount of nitrogen and oxygen entering the blood
and tissues also increase.

14. • Unlike oxygen and carbon dioxide, nitrogen (N2) is inert; it is not
metabolized by the body.
• At sea level the amount of N2 inhaled and exhaled is the same. This
is not the case for O2 and CO2, which are not inert gases but instead
participate in metabolism; as a result less O2 is exhaled than
inhaled, and more CO2 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

15. • 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.

16. • 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.

17. 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.

18. • 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.

19. EFFECT OF NITROGEN ON CNS

20. • 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

21. • Increase nitrogen concentration cause excitation of cortex and thalamus.
• Increase dopamine and glutamate levels due to inability to get recycled completely
Excitatory
after due to lack of oxidation in absence of oxygen.
neurotransmitter s • Thus there is a buildup of dopamine and glutamate , and it floods certain neural areas
• Increased level of dopamine and glutamate will then stimulates the inhibitory centres of
thalamus and striatum.
• The thalamus and straitum will further enhance the release of inhibitory synaptic
neurotransmitters .
• This will further leads reduce synapsis.
Inhibitory effect

22. REVIEW OF LIETERATURE

23. 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.

24. 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.

25. 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.

26. 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.

27. 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.

28. 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.

29. 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.

30. 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.

31. 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.

32. •
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