Whelan Resp. Summary

More of an audutory learner? Click the link to listen to a podcast on part 1 of this summary, material covered on the midterm exam:

https://notebooklm.google.com/notebook/a2a0cdc3-278e-4aa1-9c7d-dff86d441177/audio

Click here to listen to Part 2 of this summary, material covered after the midterm exam: 

https://notebooklm.google.com/notebook/eb060fb1-554a-4fda-886d-00dc69908863/audio

I've taken the liberty of making flashcards from Part 1 of this summary, material covered on Midterm exam.

Here you can find a condensed flashcard deck focusing only on information that  I feel isn't intuitive and needs straight memorization:

https://quizlet.com/ca/955570095/overview-of-respiratory-physiology-and-mechanics-flash-cards/

Summary of the Lecture: Respiratory Physiology #1

1. Overview of Respiration:

• Respiration involves the intake of oxygen (O₂) and expulsion of carbon dioxide (CO₂) in animals. This is essential for oxygenating tissues and removing metabolic waste.

• Respiration can be divided into external (air exchange in the lungs) and internal (gas exchange between blood and tissues).

2. Anatomy of the Respiratory System:

• The nasal cavity warms and humidifies air. Different animals have variations in nasal structure, such as pigs (rigid nares) and horses (pliable nares), to accommodate breathing needs.

• The trachea, surrounded by cartilaginous rings, prevents airway collapse.

• The bronchi and alveoli are key structures where gas exchange occurs. The bronchoalveolar lavage (BAL) is a diagnostic technique to detect diseases like pneumonia in the bronchioles of animals.

3. Ventilation:

• Ventilation refers to the movement of air into and out of the lungs.

• Minute ventilation (VE) is the total volume of gas exchanged in the respiratory system over a period. It is calculated as: 

VE= (f)(VT)

where f is the number of breaths per minute and VT is the tidal volume.

• Tidal Volume (VT) is the volume of air brought into body per breath, typically ~15 mL/kg in animals

• Dead space (VD) is the portion of tidal volume where no gas exchange occurs, often in the upper airways (e.g., trachea). 

• Alveolar Ventilation (VA) is the volume of gas that actually participates in gas exchange over a period of time. It is calculated as:

(VA) = (f)(VT - VD)

4. Ventilation Terms:

• Normoventilation: Normal breathing with CO₂ levels in the normal range (~40 mmHg).

• Hyperventilation: Increased alveolar ventilation, leading to low CO₂ (<40 mmHg), potentially causing respiratory alkalosis.

• Hypoventilation: Decreased alveolar ventilation, resulting in elevated CO₂ (>40 mmHg), which can lead to respiratory acidosis.

• Panting: Increases dead space ventilation to regulate temperature without affecting CO₂ levels.

5. Respiratory Pressures:

• Intrapulmonary pressure is the pressure in the alveoli. It equalizes with atmospheric pressure but drops slightly during inspiration, allowing air to flow in, and becomes slightly positive during expiration, forcing air out.

• Intrapleural pressure is the pressure in the space around the lungs, always slightly negative, ensuring the lungs stay adhered to the thoracic wall.

6. Respiratory Cycle:

• The breathing cycle consists of two phases: inspiration (active process) and expiration (passive process). Contraction of the diaphragm and intercostal muscles expands the thorax, creating a negative pressure that draws air into the lungs.

7. Types of Breathing:

• Abdominal breathing: Normal breathing visible in the abdomen, especially during inspiration.

• Costal breathing: Breathing with prominent rib movements, seen in conditions like dyspnea (labored breathing).

Summary of Respiratory Physiology #2

1. Lung Volumes and Capacities

• Tidal Volume (VT): The air inhaled or exhaled in a normal breath, approximately 15 mL/kg for most domestic species.

• Residual Volume (RV): The air that remains in the lungs after a complete expiration, which cannot be expelled.

• Inspiratory Reserve Volume: Extra air that can be inhaled beyond a normal breath.

• Expiratory Reserve Volume: Extra air that can be exhaled after a normal breath.

• Vital Capacity (VC): The maximum volume of air that can be inhaled and exhaled with maximal effort (i.e., Inspiratory Reserve Volume + Expiratory Reserve Volume + Tidal Volume).

• Total Lung Capacity (TLC): The sum of Vital Capacity and Residual Volume.

• Functional Residual Capacity (FRC): The sum of Residual Volume and Expiratory Reserve Volume, representing the air remaining in the lungs after normal expiration.

• Affected by diseases (pneumothorax, diaphramatic hernia)

3. Surface Tension and Surfactant

• Laplace’s Law explains that smaller alveoli require higher pressure to overcome surface tension and expand. Formula:

P = 2T/r

where P is the pressure inside the alveolus, T  is the tension on inner surface and r is the internal radius of the alveolus.

SO, smaller alveoli would have higher internal pressures and empty into larger alveoli - not effiecent and wouldn'd direct air where it needs to go. Resolution: 

• Surfactant, produced by Type II alveolar cells, reduces surface tension and stabilizes alveoli, preventing collapse during expiration and making inspiration easier. This counteracts the effects of small radius and prevents small alveoli from amptying into larger alveoli. Insufficient surfactant can lead to conditions like Respiratory Distress Syndrome.

4. Airway Resistance

• Poiseuille’s Law dictates that resistance is primarily affected by the radius of the airway. A small decrease in radius significantly increases resistance, making airflow more difficult. 

Resistance =  8nl/(π r^4)

where n is viscosity of the fluid/gas, l is the length of the tube and r is the radius of the tube.

• Although airways get progressively smaller with each branching, total cross-sectional area increases, reducing resistance overall in the respiratory zone and increasing area for gas exchange. Therefore, resistance in the conducting zone (trachea) is greater than the respiratory zone (terminal bronchioles) 

5. Gas Diffusion

• Gases move across membranes by simple diffusion, governed by Fick’s Law: 

Vgas = A x D x (P1 – P2) / T, where:

• • A = surface area of memebrane

  • D = diffusion coefficient (depends on gas solubility and size)

  • P1 and P2 = partial pressures on either side of the membrane

  • T = membrane thickness

• Oxygen (O2) and Carbon Dioxide (CO2) follow their own pressure gradients and diffuse accordingly. Oxygen diffuses quickly due to a high pressure gradient, while CO2 diffuses slower.

6. Gas Laws and Partial Pressures

• Dalton’s Law: In a gas mixture, each gas exerts its own pressure, known as partial pressure (P). Sum of all individual gas pressures is equal to the total gas pressure.

  1. • Pa: arterial pressure of a gas

     • Pv: venous pressure of a gas 

     • PA: Alveolar pressure of a gas

• The movement of gases depends on these partial pressures, with oxygen diffusing from high-pressure alveoli to low-pressure blood, while CO2 diffuses from blood to alveoli.

7. Optimal gas exchange conditions

• Surface Area (SA): A large surface area (e.g., alveoli in the lungs) increases the amount of gas that can diffuse across the membrane.

• Diffusion Coefficient: This depends on the gas's solubility and molecular weight. Gases like oxygen and carbon dioxide have high diffusion coefficients, allowing them to diffuse more efficiently.

• Difference in Partial Pressures: A larger difference in partial pressures of the gas across the membrane (e.g., higher oxygen in the alveoli than in the blood) drives faster diffusion due to the pressure gradient.

• Membrane Thickness: A thinner membrane facilitates faster diffusion, as gases have less distance to travel.

Part 2 (Material on MT 2)

Summary of Respiratory Physiology (Lecture 3)

Podcast: https://notebooklm.google.com/notebook/ff656f90-9c27-4e5c-95f7-df6d874baaa2/audio

1. Pathologies that impose diffusion limitations

• Pulmonary edema: gas echange cant occur b/c alveoli become fluid filled

• Interstitial fibrosis: thickenings in alveloar walls prevent efficient diffusion

2.  Oxygen Transport and Hemoglobin Saturation

• Oxygen is primarily transported by hemoglobin in red blood cells, with only a small portion (~0.003 mL per 100 mL of plasma) dissolved in the blood.

• each of the 4 heme protein subunits of Hemoglobin (Hb)  have an iron atom that can carry molecules of oxygen. Oxygen binds loosely and reversibly to Hb, which allows for easy oxygen release in tissues with low oxygen pressure (PO2).

• Hemoglobin saturation describes the percentage of Hb molecules bound to oxygen. It remains high (near 100%) across a wide range of oxygen pressures in the lungs (60-100 mmHg), which is critical for oxygen loading. Hb + Oxygen = Oxyhemoglobin = red.

• In tissues, oxygen pressure decreases (30-50 mmHg), leading to significant Hb desaturation (from 90% to 50%)—this facilitates oxygen unloading. Hb - Oxygen = Deoxyhemoblobin = purple.

In action: In the lungs, the high oxygen pressure ensures efficient oxygen loading, while in peripheral tissues, the lower oxygen pressure allows hemoglobin to release oxygen where it's needed.

3. Oxygen Affinity and Hemoglobin

• Hemoglobin’s affinity for oxygen changes depending on conditions like temperature and pH. 

  1. Right shift: In tissues (where it's warmer and more acidic), Hb releases more oxygen, reducing its affinity. 

  2. Left shift: Conversely, in the cooler, less acidic lungs, Hb increases its affinity to take up more oxygen.

Example: When exercising, muscles produce more CO2, increasing acidity and temperature locally. This causes Hb to release more oxygen to these active tissues (a shift of the oxygen dissociation curve to the right).

4. Oxygen Uptake and Alveolar Gas Equation

• Oxygen uptake in the alveoli depends on the partial pressure of oxygen (PAO2), which is influenced by factors like altitude and inspired oxygen concentration. The alveolar gas equation estimates how much oxygen can be present in the alveoli at a given time:

Where FiO2 is the fraction of inspired oxygen, barometric pressure (PB) at sea level is 760 mmHg, water vapor pressure (PH2O) is 47 mmHg and PaCO2 is 40 mmHg at normal ventilation. Therefore, 

PAO2 = 0.21 (760 mmHg - 47 mmHg) - (40/0.8)

PAO2 = ~100 mmHg at sea level

• PaO2 (arterial oxygen pressure) should be = to PAO2 (alveolar oxygen pressure) under normal conditions.

Example: At sea level, breathing room air (21% O2), PAO2 should be around 100 mmHg. This decreases with altitude, e.g., in Calgary, where PB is 670 mmHg, PAO2 would be 80 mmHg.

5. Oxygen Content and Delivery

• The total oxygen content in the blood is a combination of oxygen bound to hemoglobin and dissolved oxygen. Oxygen content is calculated as:

• Oxygen delivery depends on both oxygen content and cardiac output: 

• Adequate oxygen delivery is crucial for maintaining tissue oxygenation.

6.  Hypoxemia and Hypoxia

• Hypoxemia refers to low arterial oxygen saturation, measured via blood gas analysis or pulse oximetry. Hypoxia is low oxygen at the tissue level and can result from inadequate oxygen delivery or uptake - blood still has oxygen, but it's not being transferred to tissues.

• Causes of hypoxemia include:

  • Low inspired oxygen (e.g., high altitude)

  • Hypoventilation

  • Diffusion impairment (e.g., pulmonary edema)

  • Ventilation/perfusion mismatch

  • Right-to-left shunts (e.g., congenital heart defects)

Example: A patient on nasal oxygen therapy showing low oxygen saturation (PaO2 lower than expected) might be evaluated for a ventilation-perfusion mismatch or shunt.

Summary Respiration 4 Lecture:

Podcast: https://notebooklm.google.com/notebook/b7be8e77-e4e4-4502-8de8-be4fae557f6b/audio

1. Ventilation/Perfusion (V/Q) Ratios

• V/Q Ratio Definition: A measure of the balance between air entering the lungs (ventilation) and blood reaching the alveoli (perfusion).

• V/Q = 1: Optimal gas exchange occurs when ventilation matches perfusion.

• V/Q Mismatch: Occurs in pathological conditions, leading to inefficient gas exchange. Examples include:

  • V/Q = 0: No ventilation (e.g., airway collapse), resulting in a "shunt" where blood bypasses the lung without gas exchange.

• Alveolar hypoxia: If the partial pressure of oxygen in the alveolus <70mmHG the arterioles with constrict to divert blood away from poorly ventilated areas, reducing shunt effect

• V/Q = Infinity: No perfusion (e.g., blood clot), causing "dead space" where air moves without gas exchange.

2. CO₂ Transport Mechanisms

CO2 is produced during cell metabolism and readily crosses cell membranes and physical barriers. Methods of transport include:

• CO₂ in Plasma: A small fraction dissolves in plasma due to CO₂’s high solubility (dependent on partial pressure of CO2). Also combine with water in plasma to form H2CO3.

• Carbamino Compounds: CO₂ combines with plasma proteins, forming carbamino compounds.

Majority of CO2 captured by:

• Bicarbonate Ions: The primary transport form, created by the reaction of CO₂ with water in red blood cells (facilitated by carbonic anhydrase). This accounts for the majority of CO₂ transport.

  • Why does this work? CO₂ diffuses from tissues into red blood cells (RBCs). Inside RBCs, CO₂ reacts with water to form carbonic acid (H₂CO₃) via the enzyme carbonic anhydrase.H₂CO₃ then dissociates into bicarbonate ions (HCO₃⁻) and hydrogen ions (H⁺).The HCO₃⁻ ions are transported out of RBCs into the plasma, while chloride ions (Cl⁻) move into RBCs to maintain electrical neutrality, a process known as the chloride shift.

  • When blood reaches the lungs, the reverse process occurs. HCO₃⁻ reenters RBCs and combines with H⁺ to reform H₂CO₃. Carbonic anhydrase then converts H₂CO₃ back to CO₂ and water. CO₂ diffuses out of the RBCs, into the alveoli, and is expelled through exhalation.

CO2 levels can be determined by taking blood samples and using a blood gas analyzer or with expired air using a capnograph.

4. Chemoreceptors in Respiratory Control

Sensors gather information about CO2, O2, pH and movement. Their overall goal is to maintain normal levels of O2/CO2 in arterial blood by acting on the inspiratory center (DRG) in the brain.

• Central Chemoreceptors (70% of ventilatory drive): Located in the medulla, respond to H+ concentration changes in the brain's interstitial fluid. Respiration rate and tidal volume are indirectly influenced by CO₂ levels (more CO2 = more H+ ions) to increase. Remember: the blood brain barrier is not permeable to H+, these receptors are looking at interstitial fluid. 

• Peripheral Chemoreceptors (30% of ventilatory drive): Located in aortic and carotid bodies (areas w/ high arterial blood), and are sensitive to blood levels of O₂, CO₂, and pH, with a primary role in hypoxia responses. They have an excitatory response (increase ventilation) on the respiration center through the vagus (aortic) and glossopharyngeal (carotid) nerve.

• Usually quiet, main response is to changes in CO2 levels in arterial blood. Can react to low arterial O2 levels as a last effort to bring O2 into body.

5. Gas Exchange and Regulation Mechanisms

• Oxygen and CO₂ Partial Pressures: Maintain partial pressures at specific levels in arterial blood (O₂ at ~100 mmHg, CO₂ at ~40 mmHg).

• Hypoxic Pulmonary Vasoconstriction: In response to alveolar hypoxia, arterioles constrict, reducing blood flow to poorly ventilated areas and optimizing oxygen delivery.