physiology of high altitude & high pressure

DR NILESH KATE

MBBS,MD ASSOCIATE PROF

DEPT. OF PHYSIOLOGY

PHYSIOLOGY OF HIGH ALTITUDE &

HIGH PRESSURE

OBJECTIVES High altitude physiology.

Hypoxia at high altitude. Other effects of high altitude.

High atmospheric pressure physiology. Physiological problems under depth. Physiological problems of ascent. Prevention of these problems.

Wednesday, May 3, 2023

INTRODUCTION. Atmosphere -- Medium

in which aerospace physiology occurs.

Major zones Troposphere (0-18km) Stratosphere (18-50) Mesosphere.(50-85) Thermosphere(85-700) Exosphere. (above 700)


CRITICAL ALTITUDE. Up to 10000 ft – no signs

& symptoms, but mild hypoxia. Can acclimatize. So high altitude called above 10000ft.

18,000 ft highest altitude where permanent inhabitation possible


CRITICAL ALTITUDE. Above 20,000 ft

hypoxia endanger life so O2 needed.

About 35,000 ft modern aircrafts fly, pressurized cabins provide environment similar to sea level.

Above 40,000 ft – Ozone layer.


COMPOSITION OF AIR & EFFECT OF ALTITUDE ON IT.


GAS ATMOSPHERE AIR ALVEOLAR AIR

CONC PARTIAL PRESSURE

CONC PARTIAL PRESSURE.

NITROGEN 78.62 597 74.9 569

OXYGEN 20.84 159 13.6 104

CARBON DIOXIDE

0.04 0.3 5.3 40

WATRE VAPOUR

0.50 3.7 6.2 47

TOTAL 100 760 100 760

BAROMETRIC PRESSURE & PARTIAL PRESSURE OF GASES.

According to Dalton’s law – total pressure of air = sum of partial pressure of all gases.

P = pO2+pCO2+pN2+pH2O pH2O & pCO2 determined by

body so does not change with altitude.

Only pO2 & pN2 changes.


BAROMETRIC PRESSURE & PARTIAL PRESSURE OF GASES.


Level of altitude

Barometric pressure

Atmospheric pressure

pO2

Alveolar air Po2

pCO2 % O2 saturation

of Hb

Sea level 760 159 104 40 100

5000 630 130 80 40 95

10000 520 110 60 40 90

15000 480 90 50 36 80

18000 400 80 40 30 70

20000 350 70 <40 <30 <70

40000 140 30 12 24 15

HYPOXIA AT HIGH ALTITUDE. Hypoxia – decrease in

PO2 at high altitude. Effects depend on –

Level of altitude Rate of development –

acute, subacute Duration of exposure

to Hypoxia – acute, chronic.


CLINICAL TYPES OF HYPOXIC HYPOXIA AT HIGH ALTITUDE.

Fulminating hypoxia Acute hypoxia Chronic hypoxia.


CLINICAL SYNDROMES CAUSED BY HIGH ALTITUDE.

High altitude pulmonary oedema. (HAPO)

Acute mountain sickness.

Chronic mountain sickness.


HIGH ALTITUDE PULMONARY EDEMA(HAPO).

Above 10000 ft. Seen in

75-80% in persons doing heavy physical work in first 3-4 days

Persons who acclimatized to high altitude, stay at sea levels for > 2wks& again rapidly reascend.


MECHANISM OF DEVELOPMENT OF HAPO


ACUTE MOUNTAIN SICKNESS. Occurs when person

from sea level ascend to high altitude within 1-2 days for the first time

Develop within 8-24 hrs & lasts for 4-8 days.


ACUTE MOUNTAIN SICKNESS. Cause – cerebral oedema


ACUTE MOUNTAIN SICKNESS. Treatment – Large dose of Glucocorticoids. Decreasing alkalosis by giving Acetazolamide

– as it decreases H+ ion excretion by kidney by inhibiting carbonic anhydrase.


CHRONIC MOUNTAIN SICKNESS. Monge’s disease Occurs in long term

residents of high altitude.

Develop – Polycythemia, cyanosis, malaise, fatigue & exercise intolerance.


PHYSIOLOGICAL COMPENSATORY RESPONSES TO HIGH ALTITUDE HYPOXIA.

2 types of Physiological Compensatory Mechanisms occurs Accommodation Acclimatization.


ACCOMMODATION Immediate reflex

adjustment of RS & CVS system to hypoxia. Hyperventilation.- Tachycardia- due to

peripheral chemoreceptors stimulation.

Increase in 2,3-DPG – due to Hypoxia & Alkalosis.


ACCLIMATIZATION. Changes in body tissue in

response to long term exposure. Polycythemia due to

hypoxia & renal erythropoietic factor

Tachypnoea – loss of breaking effect of CO2

CVS – Tachycardia, increase in CO & force of contraction.


ACCLIMATIZATION. Pulmonary hypertension –

due to hypoxic pulmonary vasoconstriction.

Increase in total lung capacity & diffusing capacity of lung.

Cellular & tissue acclimatization – increase in oxidative enzyme conc, mitochondrial density.

Decrease respiratory drive.


OTHER EFFECTS OF HIGH ALTITUDE.

Effects of expansion of gases. Effects of fall in atmospheric temperature. Effects of light rays.


EFFECTS OF EXPANSION OF GASES.

According to Boyle’s law of gases

P α 1/V At 18000 atmospheric

pressure – 400 mmHg volume – 2L

At 30000, P – 225mmHg, volume – 3L


RAPID DECOMPRESSION When body exposed to

sudden low pressure all body gases expand.

Effects are GIT – painful distension of

stomach & intestine RS- destroy alveoli Paranasal sinuses – tissue

damage. Decompression sickness.


EFFECTS OF FALL IN ATMOSPHERIC TEMPERATURE.

Every 1000 ft increase in altitude – temp decreases by 20c

At 10,000 ft – 00c At 20000ft - -220c At 40,000ft - -440c Effect also depend on

wind velocity & humidity.


EFFECTS OF LIGHT RAYS. Skin irritation.


PHYSIOLOGY OF HIGH ATMOSPHERIC PRESSURE.

Atmospheric pressure of 760 mm Hg at sea level is – 1 atmospheric pressure.

For every 33ft descend it increases by 1 atmospheric pressure.

High atm pressure seen in Deep sea diving Submarines Caisson’s workers.


PHYSIOLOGICAL PROBLEMS UNDER DEPTH.

Due to mechanical effects Due to effect of high pressure on respiratory

gases.


PHYSIOLOGICAL PROBLEMS DUE TO MECHANICAL EFFECTS OF HIGH

ATMOSPHERIC PRESSURE.

At a depth of more than 30 meters (100 ft)

Caving of the chest Damage to the face Squeezing of air in the

Paranasal sinuses & middle ear.


PHYSIOLOGICAL PROBLEMS DUE TO EFFECT OF HIGH PRESSURE ON

RESPIRAATORY GASES.

Effect of increases PO2 Effect of increased Pn2 (nitrogen narcosis) Effect of carbon dioxide build up.


EFFECT OF INCREASED PO2 Acute oxygen toxicity –

disorientation, dizziness, convulsions & coma

Chronic oxygen toxicity Irritation of airways Pulmonary oedema &

atelectasis Bronchopneumonia.


EFFECT OF INCREASED PN2 (NITROGEN NARCOSIS)


EFFECT OF CARBON DIOXIDE BUILD UP.


PHYSIOLOGICAL PROBLEMS OF ASCENT.

Decompression Sickness Air Embolism


DECOMPRESSION SICKNESS Caisson’s

disease/Dysbarism/compression of air sickness/the bends/diver’s palsy.

Cause – under high pressure nitrogen in the breathed air dissolved in the body fluids & fats.


DECOMPRESSION SICKNESS When individual

ascend rapidly to sea level, nitrogen is decompressed & escapes from the tissue in the form of bubbles

These bubbles block the blood vessels – ischemia & infarction.


SYMPTOMS. Pain in joints & muscles

– Bends Sensation of numbness The chokes Paralysis of muscles Coronary ischemia & MI Neurological symptoms

– dizziness, collapse, unconsciousness


TREATMENT Tank Decompression. Diver in pressurised

tank & recompression is done to dissolve bubbles.

Pressure lowered back to normal.


AIR EMBOLISM Due to entry of air into

blood circulation following rupture of pulmonary capillaries, arteries & veins due to sudden expansion of gases in lungs due to sudden fall in atmospheric pressure.

Occurs in Caisson’s workers & in Rockets.


AIR EMBOLISM SYMPTOMS Chest pain, tachypnoea,

systemic hypotension, hypoxemia

Sometimes air emboli to systemic circulation – death.


PREVENTION OF PHYSIOLOGICAL PROBLEMS OCCURING AT DEPTH &

ASCENT.

Measures for short duration dive up to 20 meters.

Take rapid & deep breaths before diving – CO2 washes out – N2 does not get enough time to dissolve – O2 toxicity not occur.



ASCENT. Measures for deeper &

longer dives. Use of breathing

apparatus – gives gas to breath & either dissolves CO2 ( close circuits) or bubbles out in water (open circuits)

SCUBA DIVING ( Self-Contained-Underwater-Breathing-Apparatus)



ASCENT. Use of breathing

mixtures containing helium & low oxygen concentration – prevent O2 toxicity.

Slow ascent or use of Decompression Tank.


THANK YOU.


physiology of high altitude & high pressure

Health & Medicine