Respiration In Unusual Environments

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 sicknessfatigue, 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 HCO3Polycythemia: • 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