Pulse Oxygen Readings During Exercise

During exercise your body alters the function of multiple systems to meet the physical demands placed on it. One of the most fundamental adaptations under these conditions involves the delivery of oxygen to cells throughout the body. As muscles contract and consume energy, they require increased oxygen delivery. Pulse oxygen readings are lowered in a predictable manner because of the properties of red blood cells and the changes that occur in skeletal muscle during exercise.

Red Blood Cells and Hemoglobin

Your body has evolved highly effective mechanisms for oxygen transport and delivery to cells. Rather than simply carrying dissolved oxygen in your circulation, red blood cells are equipped with a highly specialized molecule known as hemoglobin. This protein is capable of binding up to four molecules of oxygen and thus significantly increases the capacity of your blood to carry oxygen.

Hemoglobin-Oxygen Dissociation

Several factors regulate hemoglobin's attraction to oxygen; these factors determine how many oxygen molecules will bind hemoglobin at any given time. For instance, hemoglobin will release all bound oxygen molecules when it enters a highly active tissue, such as skeletal muscle during exercise. However, it will readily bind to the maximum number of oxygen molecules possible as it passes through the lungs. The structure of hemoglobin gives it these characteristics, making it an ideal oxygen transporter; it efficiently binds oxygen when the concentration is high but rapidly drops it off when the concentration is low.

Factor Effecting Hemoglobin Dissociation

The affinity, or binding potential, of hemoglobin for oxygen is controlled by several important variables. The pH of your blood is a major factor, with lower pH, or more acidic blood, leading to the release of oxygen molecules. Another important factor is heat; with increasing temperature hemoglobin will bind less avidly to oxygen. Both of these factors are dramatically changed during periods of exercise.

Effect of Exercise

During exercise, your body is using large amounts of oxygen to fuel your muscles. The byproduct of muscle activity is lactic acid, which lowers the pH of your blood. Therefore, exercise can be expected to lower the pH of your blood, which lowers the attraction of hemoglobin for oxygen. Increased muscle activity also generates heat, increasing the temperature of these tissues. This complements the effects of lactic acid by further decreasing hemoglobin-oxygen binding. When the attraction is decreased, oxygen is released into solution and can be absorbed by the contracting muscle to support its activity.