Question

A frequently recommended treat ment for hiccups is to hold one's breath. The resulting condition, hypoventilation, causes buildup of carbon dioxide in the lungs. Predict the effect on the pH of blood.

Short answer

Holding one's breath increases CO2, which lowers blood pH.

Step-by-step solution

Understand the Concept

When holding one's breath, hypoventilation occurs. This results in a buildup of carbon dioxide (CO2) in the lungs and bloodstream.

Recognize the Chemical Reaction

CO2 in the blood reacts with water (H2O) to form carbonic acid (H2CO3). The reaction is as follows: \[ \text{CO}_2 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{CO}_3 \]

Understand the Dissociation of Carbonic Acid

Carbonic acid (H2CO3) dissociates into hydrogen ions (H+) and bicarbonate ions (HCO3-): \[ \text{H}_2\text{CO}_3 \rightarrow \text{H}^+ + \text{HCO}_3^- \]

Link Increase in CO2 to pH

An increase in CO2 leads to more carbonic acid formation, which dissociates into more hydrogen ions (H+). This causes an increase in hydrogen ion concentration in the blood.

Determine the Effect on pH

An increase in hydrogen ion concentration results in a decrease in the pH of the blood, making it more acidic.

Key concepts

hypoventilation

Hypoventilation occurs when breathing is too shallow or too slow, resulting in insufficient intake of oxygen (O2) and a buildup of carbon dioxide (CO2) in the blood. When you hold your breath, this can lead to hypoventilation.

• In hypoventilation, your body isn't expelling enough CO2.
• This means more CO2 remains in your lungs and blood.

It's the opposite of hyperventilation which involves rapid or deep breathing. Hypoventilation can make your blood more acidic due to the increase in CO2.

carbon dioxide buildup

With hypoventilation, CO2 begins to accumulate in the lungs and bloodstream. Carbon dioxide buildup means the gas is not being expelled from the body effectively.

• This is often a consequence of holding your breath or breathing very slowly.
• Higher levels of CO2 in the blood can affect its chemistry.

Having more CO2 means that more is available to react with water in the blood.

carbonic acid dissociation

CO2 in the blood reacts chemically with water (H2O) to form carbonic acid (H2CO3). The equation for this reaction is:
\[ \text{CO}_2 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{CO}_3 \]
Carbonic acid is not stable and quickly dissociates into hydrogen ions (H+) and bicarbonate ions (HCO3-). The dissociation reaction can be written as:
\[ \text{H}_2\text{CO}_3 \rightarrow \text{H}^+ + \text{HCO}_3^- \]
More CO2 leads to more carbonic acid, which dissociates into more hydrogen ions, increasing the H+ concentration in the blood.

blood acidity

The acidity of blood is measured by its pH level. When there is an increase in hydrogen ions (H+), the pH decreases, making the blood more acidic.

• A normal blood pH is between 7.35 and 7.45.
• An increase in CO2 causes more H+ to form from carbonic acid.

This process lowers the pH, leading to a state known as acidosis, where the blood becomes too acidic. If hypoventilation continues, it can worsen blood acidity, which can be harmful to the body.