Immediate and Habitual Low Oxygen Adaptation

 

Immediate and Habitual Low Oxygen Adaptation.

P.K.Ghatak, MD

No.48.

Oxygen in the air is 21 % and exert 160 mm of mercury (Hg) partial pressure at the sea level. The pressure falls as we climb higher and higher from the sea level. At 10,000 ft the partial oxygen pressure is 110 mm Hg, at 20,000 ft it is 73 mm Hg and at 30,000 ft it is only 48 mm Hg.

Oxygen moves from higher presser to lower pressure. Inside the body, the oxygen is carried in the arterial blood, about 20 ml per 100ml, almost all of it is in a loose combination with hemoglobin as oxyhemoglobin, and only 0.31 ml per 100 ml dissolved in the plasma. In the venous blood, the oxygen is 15 ml /100 ml. The dissolved oxygen exerts pressure for oxygen molecules to move out of blood to the tissue where O2 pressure is lower. When the body at rest, it uses 250 ml of oxygen in an hour. The brain uses 50 ml/hr., the heart 40ml/hr. and the Kidneys 40 ml/hr.

Immediate Adaptive Mechanism to Low Oxygen conditions:

In an Olympic 100-meter event, a runner completes the run in less than 10 seconds. The skeletal muscles do the work, and ATP supplies the energy. The demand for oxygen during the run by the working muscles, is very high and not enough ATP can be generated by oxidation of glucose in 10 seconds. In the anaerobic condition glucose turned to Pyruvic acid then to Lactic acid. At the finish line the runner pants and hyperventilates in order to supply oxygen debts. Lactic and Pyruvic acids are oxidized to CO2 and ATPs generated and replaced fully.

What else happens here.

The heart beats faster, BP is elevated, as a result the cardiac output increases. By increasing depth and rate of breathing, the oxygen partial pressure in the hung alveoli increases as CO2 is driven away and fully saturated arterial blood ready to supply skeletal muscles with more oxygen. Volume of dissolved oxygen increases and extraction of oxygen by muscle and other tissues from the arterial blood increase, and the venous blood, contains less oxygen. Kidneys increase the GFR, urine volume increases and the blood pH turn back to normal from the acidic range due to Lactic acid accumulation.

By regular practice the Olympic athletes habitue themselves to temporary and short anaerobic metabolism and show less changes of their cardiovascular system to metabolic stress. A contestant has more chance to win the race when he/she is fully adapted to this metabolic stress.

Habitual low Oxygen environment Adaptation:

Tibetan plateau is 11,000 ft elevated from the sea level. The partial pressure of O2 is 110mmHg. People living in Tibet over 7,000 years and they are well adapted to low oxygen. The hypoxic stimuli from the carotid and aortic body are muted. No hyperventilation is manifested during daily laborious chores. Total hemoglobin is not high. The pulmonary arterial pressure is normal. No muscular hypertrophy of the pulmonary artery and the right ventricular takes place. The newborn babies have normal weight at birth. The incidence of miscarriage and post -partem complications are not high.

These Adaptec changes were possible due to mutation of EGLN1 and EPAS genes.

People living in high Andes Mountain are also living in lower O2 environment, but they are living in this condition, only about 1,000 years. Their cardiovascular system is not so well adapted like the Tibetan people but better than visitors.  The adaptive efforts in the cardiovascular system and pregnancy and childbirth are only partly achieved so far

Adverse Effects of Hypoxia on Recent Arrivals:

Acute Mountain Sickness.

On the very day of arrival, symptoms of cerebral anoxia develop. The main symptoms are headaches, dizziness, nausea, anorexia, fatigue and shortness of breath on minimal activities, difficulty sleeping and a mild dry cough. Swelling of the face, hands, and feet develops.

High Altitude Pulmonary Edema (HAPE).

From day 2 to day 4 of arrival, the symptoms are more severe. The shortness of breath at rest develops. The temperature rises to 101F degrees. Palpitation and rapid breathing, mental confusion, loss of coordination and prostration soon appear. The cough becomes productive of pink frothy sputum and occasionally becomes bloody, labored breathing with gurgling sounds on breathing is heard, cyanosis, a slow heart rate and BP began to fall. Acute respiratory distress and Acute Pulmonary edema set in.

High Altitude Cerebral Edema (HACE).

Anoxia of the brain cells is responsible for increased fluid accumulation in between brain cells and produces persistent headache, dizziness, nausea, the sensation of pins and needles, lethargy, loss of coordination, loss of sleep, tinnitus, violent behavior and loss of consciousness and seizures.

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Footnote:

Partial pressure of O2:  760 / 21 = 160 mm Hg

In the airway of the lungs.760 - 47 mm Hg water vapor = 713/2 1 = 150 mm Hg partial pressure of O2

In the alveoli of the lungs. 149 - 40 mm Hg CO2 =110 mmHg partial pressure of O2.

The fractional concentration of O2 remains the same in the atmosphere as one climb up and up. The partial O2 pressure falls due to decrease in the Barometric Pressure. 

ATP is adenosine Tri Phosphate. A molecule which is a ready to supply energy to any tissues and in turns become ADP -adenosine Diphosphate. And finally, to Creatin phosphate. In reverse enzymatic process ATP is fully regenerated and some more from burning glucose molecules.

The normal pH of the arterial blood is 7.4 that is an alkaline pH in chemistry. In biology 7.4 pH is called a normal pH. When Lactic or carbonic acid accumulate, the pH of blood becomes 7.1 or lower that is less alkaline in chemistry but considered acidic in Biology.

GFR is glomerular filtration rate.

Carbonic Anhydrase (CA) is an enzyme present in the RBC, which in oxygen rich environment accelerates carboxyhemoglobin formation. The same CA enzyme in CO2 rich environment accelerates    carboxyhemoglobin generation and help remove CO2 form tissues. As blood takes up more and more CO2 from the tissues, the local pH of the tissues shifts from 7.4 towards 6.9 due to carbonic acid formation. This activates another enzyme 2,3 Diphosphoglycerate (2,3DPG) which helps release of Oxygen from oxyhemoglobin and more and more O2 is released as CO2 enters blood.

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