Monday, May 28, 2007
Teaser Appetizer: Why Does BIL Breathe?
My brother-in- law (BIL) has been breathing all his life but is unaware of the amount of air he has sucked in - over 200 million liters! He has inhaled 500 ml per breath - a little less during childhood - 15 times every minute to keep his body working for 51 years.
“Now, that is lot of air.” he exclaims.
BIL, an affable, portly man of liberal bend feels guilty of this enormous selfish appropriation. The guilt probably is also an overflow from his job – he manages a hedge fund.
When I ask him, “ What do you do?”
He mumbles, “I work for a hedge fund.”
“But what do you actually do to be so rich?”
He just smiles.
I try to assuage his hedge-fund-guilt by telling him that he did not hoard all that air, but exhaled an equal volume. But as a blue blood liberal - who thrives on a staple of guilt - this disconcerts him even more: he exhaled 200 million liters of pollution.
He cajoles me, "If you explain what happened to all that air, I will tell you about the hedge fund."
So, here I go: Neurons in the brain stem (brain–spinal cord junction) regulate the autonomous respiratory rhythm; some neurons control the rate, while others control the depth of breathing. These neurons are sensitive to carbon dioxide (CO2) level in the blood; when the CO2 level crosses a threshold, sensors (chemoceptors) in the neck vessels and brain alert the respiratory neurons to initiate a breath. While cerebral cortex can direct the autonomous respiratory center to hold a breath for some time, it cannot override the chemical stimulus of CO2, which is why you cannot voluntarily hold your breath indefinitely.
With each breath, the diaphragm muscle, that partitions the chest from the abdomen, descends and the rib cage expands, which creates a negative pressure inside the chest cavity. The air from higher atmospheric pressure gushes in, fills the respiratory passages and reaches the small gas exchange sacs (alveoli). When the lung pressure equals the atmospheric pressure, the breath ends. The lung tissue also has stretch sensors, which send signals to the respiratory center to terminate lung expansion, which prevents over inflation and rupture.
About 500 ml of air rush into the chest, of which, 300 ml fill up the non breathing spaces like trachea and bronchial tubes. About 200 ml travel to alveoli - the active breathing sacs at the end of the breathing passages. About 60% of the inhaled air at rest, does not participate in gas exchange and occupies the dead space. During exercise and deep breathing more lung alveoli open up to accommodate increased inhaled volume of air.
During exhalation the diaphragm ascends, rib cage contracts, increasing the pressure inside the chest, which pushes out the air.
The walls of alveoli lay in apposition to the walls of the thin capillary blood vessels, which together form a respiratory membrane for exchange of gases. The gases diffuse from higher to lower pressure gradient. Thus, oxygen crosses from alveolar air into the blood and carbon dioxide moves in reverse.
Hemoglobin, the oxygen-loving-red-protein in blood, clutches oxygen in its quaternary embrace and swishes to the farthest tissues, where it unloads its valuable cargo to allow the oxygen-depleted cells breathe and thrive. Low tissue oxygen tension, acidic ph and some enzymes stimulate oxygen release from hemoglobin. Oxygen again follows the simple rule of diffusing from higher tension to lower and crosses the cell membrane into the interior, where it ignites the energy combustion by working as the terminal electron acceptor in the electron transport chain (ETC) near the mitochondrial membrane. ETC uses oxygen to generate adenosine triphosphate (ATP), the storehouse of cellular energy. All food components - fats, carbohydrates, and proteins - participate in the manufacture of ATP, which works as a ‘battery’ that powers the cell. The uncoiling of the high-energy phosphate bonds of the ATP provides the energy for metabolism and muscular activity.
“BIL are you listening?” I shout as I see him yawning.
“Yes, I am, go on. And what about the toxins and pollutants we produce?”
I continue: we produce CO2 during metabolism, which diffuses from the cells into the blood, mixes with plasma and travels back to the alveoli and forms major portion of the exhaled air.
We also form damaging ‘free oxygen radicals’ during metabolism. An atom is in a stable state when all the electrons in the outer orbit have a complimentary electron spinning in opposite direction. A ‘free radical’ has at least one unpaired electron in the outer orbit, which makes it highly reactive. To achieve stability, the atom ‘ steals’ an electron from a neighboring molecule converting it into to a free radical. To restore its own stability, this newly formed radical, in turn, captures an electron from another surrounding molecule thus setting up a chain reaction. Oxygen radicals - with two unpaired electrons in the outer shell - are readily formed in the cell during metabolism. These roving radicals snatch electrons from fatty acids of the cell membrane (lipid per-oxidation) causing decay and senescence. Approximately 2 to 5% of the total oxygen intake has the ability to form the highly damaging radicals by electron escape. During exercise, oxygen consumption can increase up to 20 times; electron escape from the ETC multiplies, generating considerably more damaging radicals.
“BIL, are you there?”
“Yes, I am. Energy giver oxygen is also a toxic radical. With each gasp of life comes a whiff of death.”
BIL could be right but for the antioxidants - the molecules with ability to mop up roving radicals. Body produces its own protective antioxidants and it extracts some from food, such as vegetables, fruits, nuts, seeds, oil and meats. . These antioxidants readily donate their electrons to unstable radicals and electron depleted antioxidants are not harmful themselves. The fat-soluble antioxidants, Vitamin E, beta-carotene and coenzyme Q line the cell membrane and the water-soluble antioxidants like vitamin C, glutathione peroxidase and catalase scavenge the interior of the cell. Under normal circumstances these suffice, but during increased oxygen use, like exercise, excessive radical production may overwhelm body defense causing lipid per-oxidation and cellular damage.
I summarize for BIL, ”The respiratory cycle involves, autonomous breathing, carrying oxygen to the needy tissue which extract it to use it for metabolism and produce unwanted by products like CO2 and free radicals. CO2 exits through the lungs and antioxidants neutralize the radicals.”
BIL demands, “Now tell me more about that dead space you talked earlier.”
I repeat, “ Even though we inhale about 500 ml with each breath, only 200ml actively participate in gas exchange. The rest just fills up the space in the air passages.”
BIL looks into the sky and pontificates, “That is the nature of human action: most of the human endeavor lands in dead space, seemingly futile. But that is the good news. The better news is that very little of human action is of any consequence, which unfortunately generates all the bad news.”
Now, BIL gets earnest and adds “Every living person consumes air every few seconds. That must make air the largest consumption good in the world and that is a huge market opportunity – bigger than food, water, oil, religion or war. But where is the business?”
I remind him that respiratory therapy for ‘the breathing - challenged’ is a big business, but BIL reminds me that the normal non- ailing healthy lungs form a much bigger market. I tell him that the Yoga peddlers have exploited the ‘business of normal breath’ and quote some data that I read recently, “The US Patent and Trademark Office has granted 150 yoga-related copyrights, 134 patents on yoga accessories and 2,315 yoga trademarks.”
Unimpressed, he remarks, “The opportunity has not been exploited enough.”
I loose my patience, “Then go to moon and mine oxygen! Oxygen is the most abundant element in lunar soil, constitutes nearly half of it by weight. Your mined oxygen from the moon can play big in space ventures.”
“How do we arbitrage this?” he enquires.
I stare at him with dumb expression; I don’t even understand his question.
“Arbitrage is like diffusion of oxygen across gradients; it equilibrates the gradient of the financial markets.”
Now, confusion contorts my dumb expression. He notices my silence and says,” You wanted to know what I do for my living; I will tell you. For my detractors I am a selfish free radical who steals from others; for my supporters I am an anti-oxidant bringing stability to the inherently inefficient systems; but I think, I am like the cushion of air in the dead respiratory space, mostly futile, but ready to pounce when action erupts.”
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