In-Depth Notes on Breathing Regulation and Related Disorders

Regulation of Breathing

Overview of Breathing Regulation

Breathing regulation is essential for maintaining proper gas exchange in the body. Two primary mechanisms control ventilation during exercise: neurogenic and humoral factors.

Effect of Exercise on Respiratory Function

• Hyperpnea: When exercising, breathing becomes deeper and faster to match the body's increased oxygen demand and carbon dioxide production. This change is characterized by increased tidal volume and minute volume.
• Neurogenic Mechanisms: During exercise, sensory nerve activity from active muscles stimulates respiration through spinal reflexes or brain stem respiratory centers. The cerebral cortex also plays a role by stimulating respiratory centers, explaining the initial surge in ventilation at the start of exercise.
• Humoral Mechanisms: Even after stopping exercise, rapid and deep breathing persists due to chemical factors, such as changes in PCO2 and blood pH.

Lactate Production in Early Exercise

At the onset of exercise, the body may not supply enough oxygen to the muscles, leading to anaerobic respiration until adequate oxygen levels are achieved after several minutes. The onset of lactate production signals this anaerobic phase.

Lactate Threshold

• Defines the maximum rate of oxygen consumption before lactic acid accumulates in the bloodstream.
• Typically occurs at 50-70% of maximum oxygen uptake, indicating that aerobic limitations arise from the muscles rather than cardiovascular factors (since oxygen saturation remains high).
• Endurance training enhances the muscles' aerobic capacity by increasing the number of mitochondria and boosting Krebs cycle enzyme activity.

Changes in Respiratory Function During Exercise

Acclimatization to High Altitude

Adapting to high altitude includes several physiological adjustments due to lower atmospheric PO2:

• Increased ventilation as a direct response to hypoxia.
• Increased hemoglobin affinity for oxygen and total hemoglobin concentration.
• Decreased blood volume to ensure proper gas exchange despite low oxygen levels.

Changes in Ventilation

• Hypoxic Ventilatory Response: Decreased PO2 levels stimulate carotid bodies to increase ventilation, although hyperventilation can lead to respiratory alkalosis by reducing PCO2. The kidneys respond by excreting bicarbonate to restore balance.
• Hemoglobin Affinity: The affinity for oxygen decreases, allowing for a greater release of oxygen to tissues, facilitated by elevated levels of 2,3-DPG.

Acute Mountain Sickness (AMS)

AMS can occur in individuals unacclimatized to elevations over 2500 m:

• Symptoms often include headache, malaise, nausea, dizziness, and disrupted sleep.
• The underlying cause is typically hypoxia, leading to increased blood flow and pressure in the brain, which results in headaches.

Common Pulmonary Disorders

1. Asthma

• Characterized by dyspnea and wheezing caused by inflamed and constricted bronchioles.
• Triggered by allergens, exercise, and environmental factors.

Treatment for Asthma

• Quick-acting bronchodilators (e.g., Albuterol).
• Long-acting beta agonists combined with glucocorticoids.
• Leukotriene receptor antagonists for long-term management.

2. Emphysema

• Defined by the destruction of alveoli, resulting in reduced gas exchange surface area.
• Primarily associated with smoking, leading to inflammation and alveolar damage.

3. Chronic Obstructive Pulmonary Disease (COPD)

• Encompasses chronic inflammation, airway narrowing, and alveolar destruction.
• Mainly caused by smoking, leading to excessive mucus production and airway remodeling.

4. Pulmonary Fibrosis

• Accumulation of fibrous tissue in the lungs due to damage from inhaled particles, e.g., black lung disease in miners.

Acid-Base Balance of Blood

Acids and Bases

• Acids dissociate into H+ ions, while bases yield OH- ions. A neutral pH is preferred for bodily functions.

Buffer Systems in Blood

• Buffers, primarily bicarbonate, maintain stable pH by neutralizing acids and bases.
• Carbonic acid can convert to CO2 and be exhaled, which makes it a volatile acid regulated by respiratory activity.

pH Regulation

• Blood pH ranges from 7.35 to 7.45. Deviations can result in acidosis (pH < 7.35) or alkalosis (pH > 7.45).
• Respiratory Acidosis: Results from hypoventilation and increased CO2 levels.
• Respiratory Alkalosis: Results from hyperventilation and decreased CO2 levels.