Dr. Niranjan Murthy HL

Asst. Prof. of Physiology

SSMC, Tumkur

• Mt. Everest

• Deep sea divers

• Space travel

• Neonatal breathing

HIGH ALTITUDE

• Atmospheric pressure exponentially reduce as we ascend up

• Mt. Everest- 29k ft- 253 mm Hg- PO2 43 mm Hg

• 63,000 ft- 47 mm Hg- PO2 ‘0’ mm Hg

• Acclimatization is important

• >10 million live above 10k ft

Acute mountain sickness

• c/f: headache, nausea, palpitations, fatigue, dizziness, loss of appetite, insomnia.

• May be due to combination of hypoxemia and alkalosis

• Periodic breathing• Increased cerebral blood flow• Monge’s disease- chronic mountain sickness-

fatigue, polycythemia, reduced exercise tolerance, severe hypoxemia

Acclimatization Hyperventilation:

• Hypoxic stimulation of peripheral chemoreceptors

• hypoxia hyperventilation hypocapnia inhibition of central chemoreceptors hypoventilation

• Increased renal excretion of HCO3-

Polycythemia:

• Increased O2 carrying capacity

Shift to right of O2 dissociation curve:

• Increased 2,3-DPG

• O2 release increase by 10%

Increase in peripheral capillaries:

Increase in oxidative enzymes:

Increased max breathing capacity:

*Pulmonary hypertension & RVH

*Pulmonary edema

Deep sea diving

• Pressure increases by 1 atm for every 33ft descent.

• Gases compress as we descend and expand as we ascend

Decompression Sickness

• Dysbarism, Bends, Caisson’s Disease• N2 is poorly soluble• At high pressures it is forced into tissues• Fat has high N2 solubility• N2 in diver at 300 ft is 10 L• N2 removal is slower in ascent• Rapid decompression can cause bubbling

out of N2

• Bends- pain in joints

• Chokes- dyspnoea

• Deafness, impaired vision, vestibular disturbances, paralysis

• Avascular necrosis of femoral head

• Rx- recompression and decompression in a chamber

• Use of helium-oxygen mixture

• Pure oxygen is contraindicated

Inert gas narcosis

• N2 is regarded as physiologically inert

• At high PN2 it affects CNS

• At 150ft- feeling of euphoria

• Lower down- loss of co-ordination and coma

SCUBA

• SELF CONTAINED UNDERWATER BREATHING APPARATUS

• Diver should ascend with exhaling

Shallow water blackout

• Divers tend to hyperventilate before a dip

• PCO2 falls

• PaO2 should fall for respiratory drive

• With the ascent, PAO2 and subsequently PaO2 fall further and cause loss of consciousness

Drowning

• Dry drowning

• Wet drowning- (i) fresh water

(ii) salt water

• Blood gas changes- hypoxemia, hypercapnia, acidosis

• Artificial gills

• Liquid breathing

CORIXA

Oxygen toxicity

• Guinea pigs placed in 100% oxygen at atmospheric pressure will develop pulmonary edema in 48hrs

• Retrolental fibroplasia in premature infants- can be avoided by keeping O2 concentration <40%

• Absorption atelectasis- N2 and other inert gases act as splint against collapse as they have low solubility