Respiratory Control and Hemoglobin

• Respiratory physiology concerns the body's mechanisms for proper oxygenation and ventilation.

Airway Patency

• Airway patency is the ability of the airway to remain open for adequate airflow, essential for proper oxygenation and lung ventilation.
• Compromised airway patency can result from edema, crushing injuries, foreign objects, deviated septum, nasal polyps, inflammation, allergic reactions, vocal chord changes, spasms, surfactant deficiency, or tumors.
• Observations of compromised airway patency include noisy breathing, secretions, snoring, difficulty breathing, coughing, and decreased oxygen saturation.

Lung Blood Supply

• Pulmonary arteries carry deoxygenated blood from the heart's right side to the lungs for oxygenation.
• Bronchial arteries supply oxygenated blood to the muscular walls of the bronchi and bronchioles.

Ventilation-Perfusion Coupling

• Blood flow to lung areas matches airflow to alveoli.
• Hypoxia-induced vasoconstriction moves blood from poorly ventilated to well-ventilated lung areas.
• Hypoxia in body tissues dilates blood vessels to increase blood flow.

Pulmonary Ventilation and Volume-Pressure Relationship

• Pulmonary ventilation moves air between the atmosphere and alveoli through inhalation and exhalation.
• Boyle's law states that gas pressure is inversely proportional to container volume.

Factors Affecting Pulmonary Ventilation

• Surface tension causes alveoli to minimize diameter and accounts for half of the elastic recoil during exhalation.
• Surfactant reduces surface tension to prevent alveolar collapse, a condition premature infants are prone to due to surfactant deficiency, potentially leading to respiratory distress syndrome needing CPAP.
• Compliance: Ease of lung and chest wall stretching; high compliance is easy, low compliance is difficult and is affected by elasticity and surface tension.
  • Scar tissue reduces compliance by decreasing elasticity.
  • Thin balloons have high compliance, while heavy, stiff balloons have low compliance.
• Airway resistance is determined by the pressure difference divided by airway resistance.
  • Larger airways decrease resistance.
  • Bronchioles dilate during inhalation, reducing resistance.
  • Smooth muscle controls airway diameter; sympathetic input causes relaxation and bronchodilation.
• COPD increases airway resistance.

Lung Volumes - Spirometry

• At rest, a person typically breathes 12 times per minute with a tidal volume of 500 ml (minute ventilation of 6 L/min).
• Approximately 350 ml (70%) reaches the respiratory zone with 150 ml (30%) remaining in the conducting zone (anatomic dead space); alveolar ventilation rate is ~4.2 L/min
• Factors affecting lung volumes and capacities include gender, height, age, and disease.
• Inspiratory reserve volume (IRV) is the additional air that can be inhaled beyond a normal breath.
• Expiratory reserve volume (ERV) is the additional air that can be exhaled beyond a normal breath.
• Residual volume (RV) is the air remaining in the lungs after maximal exhalation.
• Inspiratory capacity (IC = TV + IRV) is the maximum volume of air someone can inhale after a normal breath.
• Vital capacity (VC = ERV + TV + IRV) is the maximum volume of air that can be exhaled after a maximal inhalation.
• Functional residual capacity (FRC = RV + ERV) is the volume of air left in the lungs after a normal exhalation when the muscles are relaxed.
• Total lung capacity (TLC = RV + ERV + TV + IRV = FRC + IC) is the total volume of air in the lungs after maximal inspiration.

Gas Laws

• Dalton's law is important for understanding how gases move down their pressure gradients by diffusion.
• Henry's law explains how gas solubility relates to diffusion

Dalton's Law

• Each gas in a mixture exerts its own pressure (partial pressure, Px).
  • Px is calculated by multiplying the gas percentage by the total pressure.
  • The total pressure is the sum of all partial pressures.
• Partial pressures drive O2 and CO2 movement during respiration.
• Gases diffuse from high to low partial pressure areas.
• Alveolar air has decreased O2 (13.6% vs 20.9%) and increased CO2 (5.2% vs 0.04%) compared to atmospheric air.

Henry's Law

• The amount of gas dissolving in a liquid is proportional to its partial pressure and solubility.
  • The ability of a gas to stay insulated is greater when its partial pressure is higher and when it has a high solubility in water
• Carbon dioxide is more soluble in blood plasma (24x) than oxygen.

Respiration

• Partial pressure determines the movement of oxygen and carbon dioxide during: the lungs and atmosphere exchange, the gas exchange between the blood and lungs, and the gas exchange between the body cells and the blood.
• Gases diffuse across membranes from high to low partial pressure.
• Factors affecting the gas exchange rate include: partial pressure differences, surface area (reduced in emphysema), diffusion distance (increased by pulmonary edema), and gases' molecular weight and solubility.
  • Although oxygen has a lower molecular weight, carbon dioxide diffuses faster overall due to its higher solubility (24x more soluble than O2) which is why Net outward carbon dioxide diffusion occurs 20x more rapidly than net inward oxygen diffusion.

External and Internal Respiration

• External respiration is the gas exchange between the alveoli and blood.
• Internal respiration is the gas exchange between systemic capillaries and body tissues.
• Exchange refers to the movement of oxygen OR carbon dioxide NOT THE EXCHANGE OF O2 FOR CO2.
• Diffusion continues until the partial pressure in the blood matches that in the alveoli for O2 and alveoli matches the blood for CO2.

Oxygen Transport

• Some O2 dissolves in the plasma.
• Most O2 (98.5%) binds to hemoglobin (oxyhemoglobin).
• PO2 is the most important factor determining the amount of O2 that binds to hemoglobin; greater PO2, the more O2 combines with Hb.

Hemoglobin

• The percentage saturation of haemoglobin expresses the average saturation of haemoglobin with oxygen.
• Factors affecting hemoglobin affinity for O2 include PO2, acidity, carbon dioxide, temperature, and 2,3-bisphosphoglycerate (BPG). The Bohr effect is hemoglobin O2 binding affinity relates inversely to acidity and CO2 concentration
  • Acids from active tissues (lactic acid, carbonic acid) promotes O2 release.
  • Increased H+ causes haemoglobin to release O2 making it available for tissue cells
• Decreased CO2 increases pH, causing hemoglobin to pick up more O2 and Conversely.
• BPG, produced during glycolysis, reduces the O2-binding affinity of haemoglobin.
• Higher BPG levels promote O2 unloading.
• Carbon monoxide binds to haemoglobin with high affinity, increasing the affinity of other sites for O2 (left shift) preventing O2 dissociation.
• Carbon monoxide poisoning results in tissue hypoxia despite normal pO2.

Carbon Dioxide Transport

• Carbon dioxide is transported three ways: 7% dissolves in plasma, 70% converts to carbonic acid (carbonic anhydrase), and 23% binds to haemoglobin (at a non-oxygen site).

Control of Respiration

• Respiratory muscles contract and relax due to nerve impulses from brain centres.
• Neurons form a respiratory centre.
• The respiratory centre has two areas: the medullary respiratory centre (medulla oblongata) and the pontine respiratory group (pons).
• Medullary respiratory centre includes the dorsal respiratory group (DRG) & ventral respiratory group (VRG).
• DRG neurons generate impulses over 2 seconds stimulating contraction of diaphragm and intercostals muscles - inhalation.
• DRG becomes inactive the intercostals and diaphragm relax allowing the recoil of the lungs and thoracic wall - exhalation.
• VRG contains the pre-Bötzinger complex, important is setting the pace of the heart and composed of pacemaker cells for the basic rhythm of breathing.
  • Additional VRG neurons activate during forceful breathing.
• Cortical control modifies respiratory centre activity, responding to brain regions, peripheral receptors, and other factors to maintain homeostasis.
• The cerebral cortex connects with the respiratory centre, enabling voluntary breathing control, including protective breath-holding.
• The buildup of CO2 and H+ limits the ability to not breathe.
• Increased PC02 and H+ stimulate DRG neurons of the medullary respiratory centre
• Nerve impulses are sent along the phrenic and intercostal nerves to inspiratory muscles, and breathing resumes

Chemoreceptor regulation

• Chemical stimuli regulate breathing rate and depth.
• Chemoreceptors monitor CO2, H+, and O2 levels.
• Central chemoreceptors are near the medulla oblongata and respond and respond to changes in H+ concentration or Pc02 in cerebrospinal fluid
• Peripheral chemoreceptors located in the aortic bodies, clusters of chemoreceptors located in the wall of the aortic arch, and in the carotid bodies and are part of the peripheral nervous system and are sensitive to changes in P02, H+, and Pc02 in the blood.

Explore the neural control of respiration, focusing on the pre-Bötzinger complex and medullary respiratory center. Understand cortical influence on breathing and limitations of voluntary control. Learn about carbaminohemoglobin, pH effects, BPG, and carbon monoxide poisoning.