22.6 Modifications in Respiratory Functions

Breathing isn't just automatic—it adapts to our needs. When we exercise or climb mountains, our lungs work harder to keep up. These changes help us get more oxygen and get rid of extra carbon dioxide.

Our bodies are smart and can adjust to new situations. Over time, we can breathe better at high altitudes or during workouts. These tweaks in our breathing help us stay healthy and active in different environments.

Respiratory Function Modifications

Hyperpnea vs hyperventilation

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• Hyperpnea involves increased depth and rate of breathing in response to increased metabolic demand (exercise) while maintaining normal blood gas levels (O2 and CO2) and not causing respiratory alkalosis
• Hyperventilation involves increased rate and depth of breathing beyond metabolic needs due to anxiety, stress, or voluntary actions, leading to excessive removal of CO2 from the blood, causing respiratory alkalosis (increased blood pH), and resulting in symptoms (dizziness, lightheadedness, tingling sensations)

Exercise effects on respiration

• Breathing rate increases during exercise controlled by the respiratory center in the medulla oblongata as chemoreceptors detect changes in blood CO2, O2, and pH levels to meet the higher oxygen demand of working muscles
• Breathing depth increases during exercise as tidal volume (volume of air inhaled and exhaled during normal breathing) rises, allowing for greater oxygen uptake and CO2 removal achieved through increased contraction of the diaphragm and external intercostal muscles
• Gas exchange improves during exercise due to:
  • Increased ventilation-perfusion matching as more alveoli are recruited and perfused with blood
  • Increased diffusion of oxygen from alveoli to blood and CO2 from blood to alveoli
  • Higher cardiac output enhancing gas exchange efficiency
• Minute ventilation, the total volume of air breathed per minute, increases to meet the elevated oxygen demand of working muscles

Respiratory adaptations at altitude

• Hypoxic ventilatory response increases ventilation in response to low oxygen levels (hypoxia) mediated by peripheral chemoreceptors (carotid and aortic bodies) to maintain adequate oxygen delivery to tissues
• Increased red blood cell production stimulated by erythropoietin (EPO) secretion from the kidneys in response to hypoxia enhances oxygen-carrying capacity of the blood but takes several weeks to develop fully
• Increased capillary density in tissues improves oxygen delivery to cells and facilitates better gas exchange between blood and tissues
• Enhanced oxygen affinity of hemoglobin caused by increased levels of 2,3-bisphosphoglycerate (2,3-BPG) in red blood cells allows hemoglobin to bind oxygen more tightly, improving oxygen delivery to tissues in hypoxic conditions
• The partial pressure of oxygen in the blood decreases at higher altitudes, leading to adaptations in the respiratory system to maintain adequate oxygenation

Acclimatization and respiratory function

• Acclimatization is the gradual physiological adaptation to high altitude environments over a period of days to weeks involving multiple organ systems, including the respiratory system
• Respiratory adaptations during acclimatization include:
  1. Increased ventilation as the hypoxic ventilatory response becomes more sensitive and efficient to maintain adequate oxygen levels in the blood
  2. Enhanced oxygen uptake and delivery through increased red blood cell production and capillary density improving oxygen-carrying capacity and delivery to tissues, and higher oxygen affinity of hemoglobin facilitating oxygen loading in the lungs and unloading at the tissues
  3. Improved carbon dioxide removal as increased ventilation helps remove excess CO2 from the blood and prevents respiratory acidosis
• Effects on respiratory function at altitude after acclimatization include improved oxygen saturation levels in the blood, better tolerance to physical exertion, and reduced risk of altitude sickness symptoms (acute mountain sickness AMS, high altitude pulmonary edema HAPE, high altitude cerebral edema HACE)

Respiratory Challenges and Adaptations

• Respiratory rate, the number of breaths taken per minute, increases in response to various stimuli such as exercise, stress, or changes in blood gas levels
• Hypoxemia, a condition of low oxygen levels in the blood, can occur at high altitudes or in certain respiratory diseases, triggering compensatory mechanisms like increased ventilation
• Hypercapnia, an elevated level of carbon dioxide in the blood, stimulates the respiratory center to increase ventilation and restore normal CO2 levels
• Lung compliance, the ability of the lungs to expand and contract, can be affected by various factors such as age, disease, or environmental conditions, influencing overall respiratory function