Altitude sickness, Part 1
Posted: Wed Apr 07, 2021 11:17 am
Since it's slow around here, and since someone posted something about altitude sickness and Diamox last week, I thought I would offer this.
Altitude sickness has a lot to do with the acid/base properties of blood. The chemistry scale for acid/base solutions is a function called "pH". A neutral solution, neither acidic nor basic, has a pH of 7.00. An acidic solution has a pH of less the 7.00, and a basic solution has a pH greater than 7.00. The scale is logarithmic, so pH 9.00 is ten times more basic the pH = 8.00. A solution with a pH of 4.00 is ten times more acidic than pH 5.00 and one hundred times less acidic than pH = 2.00.
Human blood has a pH of 7.40, very slightly basic, and is very intolerant of changes in that value. Changes in blood pH by only a few tenths of a unit can cause severe illness or death. Metabolic processes generate waste byproducts that are acidic, and the most important of these is carbon dioxide, CO2. You might be surprised to learn that CO2 is an acid, but in water (i.e. blood), carbon dioxide produces a small amount of carbonic acid, like this:
CO2 + H20 ⇄ H2CO3 ⇄ H3O+ + HCO3-
The double arrows mean the reaction runs both directions, continuously, but the relative amounts of each chemical species do not change in value if the system is in the stable state of "chemical equilibrium". Chemical equilibrium means the specified reactions run in both directions at the same time and the same rate, so there is no net change in the system over time.
CO2 produced by metabolism is transported from tissue through the blood to the lungs for exhalation. In the absence of a regulatory mechanism, dissolved CO2 is acidic enough to drop the pH of blood to about 5.6, a value that would result in rapid death. The condition of acidosis results from a blood pH that drops below normal limits. Acidosis can result from diabetes, kidney failure or persistent diarrhea. Temporary acidosis can result from prolonged vigorous exercise, via excess CO2 produced by amped up metabolism. The opposite condition, alkalosis, results from blood pH higher than the normal range. Alkalosis can result from hyperventilation or severe vomiting.
Fortunately, the blood does have a regulatory mechanism for holding a constant pH. It's a complex system, but much of it involves the CO2/H2O chemistry shown in the equation above. In chemistry terms, we say the blood is "buffered" against pH changes. (Anyone who has taken a year of college general chemistry will have given an involuntary shudder upon reading the word "buffer".
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This will do for an introduction. if the topic is relevant and of interest, I will continue in Part 2 with how this applies to altitude sickness and about what Diamox does to prevent the condition.
Altitude sickness has a lot to do with the acid/base properties of blood. The chemistry scale for acid/base solutions is a function called "pH". A neutral solution, neither acidic nor basic, has a pH of 7.00. An acidic solution has a pH of less the 7.00, and a basic solution has a pH greater than 7.00. The scale is logarithmic, so pH 9.00 is ten times more basic the pH = 8.00. A solution with a pH of 4.00 is ten times more acidic than pH 5.00 and one hundred times less acidic than pH = 2.00.
Human blood has a pH of 7.40, very slightly basic, and is very intolerant of changes in that value. Changes in blood pH by only a few tenths of a unit can cause severe illness or death. Metabolic processes generate waste byproducts that are acidic, and the most important of these is carbon dioxide, CO2. You might be surprised to learn that CO2 is an acid, but in water (i.e. blood), carbon dioxide produces a small amount of carbonic acid, like this:
CO2 + H20 ⇄ H2CO3 ⇄ H3O+ + HCO3-
The double arrows mean the reaction runs both directions, continuously, but the relative amounts of each chemical species do not change in value if the system is in the stable state of "chemical equilibrium". Chemical equilibrium means the specified reactions run in both directions at the same time and the same rate, so there is no net change in the system over time.
CO2 produced by metabolism is transported from tissue through the blood to the lungs for exhalation. In the absence of a regulatory mechanism, dissolved CO2 is acidic enough to drop the pH of blood to about 5.6, a value that would result in rapid death. The condition of acidosis results from a blood pH that drops below normal limits. Acidosis can result from diabetes, kidney failure or persistent diarrhea. Temporary acidosis can result from prolonged vigorous exercise, via excess CO2 produced by amped up metabolism. The opposite condition, alkalosis, results from blood pH higher than the normal range. Alkalosis can result from hyperventilation or severe vomiting.
Fortunately, the blood does have a regulatory mechanism for holding a constant pH. It's a complex system, but much of it involves the CO2/H2O chemistry shown in the equation above. In chemistry terms, we say the blood is "buffered" against pH changes. (Anyone who has taken a year of college general chemistry will have given an involuntary shudder upon reading the word "buffer".
)This will do for an introduction. if the topic is relevant and of interest, I will continue in Part 2 with how this applies to altitude sickness and about what Diamox does to prevent the condition.