Question

\- Control of Blood pll by Respiratory Rate a. The partial pressure of \(\mathrm{CO}_{2}\left(\mathrm{~T} \mathrm{CO}_{2}\right)\) in the lungs can be varied rapadly by the rate and depth of breathing. For example, a common remedy to alleviate hiccups is to increase the concentration of \(\mathrm{CO}_{2}\) in the lungs. This can be achieved by holding one's breath, by very slow and shallow breathing (hypoventilation), or by breathing in and out of a paper bag. Under such conditions, \(\mathrm{p} \mathrm{CO}_{2}\) in the air space of the lungs rises above normal. How would increasing \(\mathrm{pCO}_{2}\) in the air space of the lungs affect blood pH?b. It is common practice among competitive shortdistance runners to breathe rapidly and deeply (hyperventilate) for about half a minute to remove \(\mathrm{CO}_{2}\) from their lungs just before a race begins. Under these conditions, blood pH may rise to \(7.6\). Explain how hyperventilation elicits an increase in blood pH. c. During a short-distance run, the muscles produce a large amount of lactic acid \(\left(\mathrm{CH}_{3} \mathrm{CH}(\mathrm{OH}) \mathrm{COOH} ; K_{\mathrm{a}}=1.38 \times 10^{-4} \mathrm{M}\right)\) from their glucose stores. Why might hyperventilation before a short-distance run be useful?

Short answer

Increasing \( \mathrm{pCO}_{2} \) decreases pH, hyperventilation increases pH, and pre-run hyperventilation buffers against lactic acid's effect on pH.

Step-by-step solution

Understanding Carbon Dioxide's Effect on Blood pH

When the partial pressure of carbon dioxide (\( \mathrm{pCO}_{2} \)) in the lungs rises, due to mechanisms like hypoventilation or breath-holding, the concentration of dissolved \( \mathrm{CO}_{2} \) in the blood increases. This additional \( \mathrm{CO}_{2} \) reacts with water to form carbonic acid (\( \mathrm{H}_2\mathrm{CO}_3 \)), which dissociates into hydrogen ions (\( \mathrm{H}^+ \)) and bicarbonate ions (\( \mathrm{HCO}_3^- \)). The increase in \( \mathrm{H}^+ \) leads to a decrease in blood pH, causing acidosis.

How Hyperventilation Increases Blood pH

Rapid and deep breathing, or hyperventilation, lowers \( \mathrm{pCO}_{2} \) in the lungs. This decreased concentration of \( \mathrm{CO}_{2} \) means less carbonic acid is formed, decreasing the \( \mathrm{H}^+ \) concentration in the blood. As a result, the blood pH rises, creating a state known as respiratory alkalosis. This is what happens when blood pH rises to 7.6 during hyperventilation.

Benefits of Pre-run Hyperventilation Against Lactic Acid

During a short-distance run, your body produces lactic acid, which can lower blood pH, leading to acidosis. Hyperventilation before a race helps to raise the blood pH by reducing \( \mathrm{CO}_{2} \), providing a "buffered" starting point so that once lactic acid is produced during exertion, the resulting drop in pH is not as pronounced. Essentially, this method offers a temporary increase in pH to counteract the acid load from lactic acid.

Key concepts

Respiratory Rate

The respiratory rate refers to the number of breaths you take per minute. It's a crucial factor in maintaining the right balance of gases in your blood. By adjusting this rate, your body regulates the levels of carbon dioxide (CO2) in the blood, which is vital for keeping your blood pH within a healthy range.
When you breathe in, you take in oxygen, and when you breathe out, you expel CO2. The faster and deeper you breathe, the more CO2 you remove from your lungs. Conversely, slower and shallower breathing retains CO2.

• Faster Respiratory Rate: Lowers CO2 levels.
• Slower Respiratory Rate: Increases CO2 levels.

This ability to adjust your respiratory rate gives your body a dynamic way to regulate blood pH in response to various physiological conditions.

Carbon Dioxide (CO2)

Carbon dioxide, often abbreviated as CO2, plays a critical role in the regulation of blood pH. It is a waste product of cellular metabolism and is expelled from the body through exhalation. The level of CO2 in the blood influences the acidity of the blood. When CO2 levels rise, they react with water to form carbonic acid, which then dissociates into hydrogen ions. These hydrogen ions increase the acidity of the blood, effectively lowering the pH.
Conversely, when CO2 levels decrease, there is less carbonic acid formation, leading to a rise in pH. This delicate balance underscores why controlling CO2 concentrations through breathing is vital for maintaining proper blood pH.

Hyperventilation

Hyperventilation occurs when someone breathes faster and more deeply than normal. This rapid breathing expels CO2 from the lungs at a quicker rate, thereby reducing the CO2 concentration in the blood. As a result, less carbonic acid is formed, and the concentration of hydrogen ions in the blood decreases. This process leads to an increase in blood pH, a condition known as alkalosis.
Common in situations where there's an acute need to improve oxygenation or remove excess CO2, hyperventilation can sometimes occur naturally during stress or intense exercise. Short-distance athletes often employ a strategy known as pre-race hyperventilation to create a buffer against the lactic acid generated during a race.

Acidosis and Alkalosis

Acidosis and alkalosis are conditions characterized by an imbalance in the pH level of the blood. Acidosis occurs when the blood pH drops below 7.35, leading to an acidic state, often a result of increased CO2 levels due to slow breathing or excessive production of acids, such as lactic acid during intense exercise.
On the other hand, alkalosis refers to a situation where the blood becomes too alkaline, with a pH level above 7.45. This can be caused by a rapid decrease in CO2 levels from hyperventilation.
Both states can be detrimental to health if not properly managed, illustrating the vital role of breathing and CO2 regulation in maintaining pH balance. Understanding these conditions helps in developing strategies like controlled breathing to prevent or mitigate their effects.