Laboratory #6: Respiratory Physiology

Objectives

• Measure chest dimensions during the respiratory cycle to understand lung mechanics and capacity.

• Study the effects of changes in end-expiratory pressure (Peo), end-inspiratory pressure (Po), and pleural pressure (pll) on breathing movements to assess respiratory function.

• Perform Valsalva's maneuver to explore circulatory and respiratory responses to intrathoracic pressure changes.

• Examine neural input to respiration to see how the nervous system regulates breathing patterns.

• Determine respiratory volumes and capacities using iWorx technology to quantify lung function.

Recommended Reading

• Chapter 17: All sections - Overview of respiratory anatomy and physiology.

• Chapter 18: All sections - Functions of the respiratory system in health and disease.

• Chapter 25: Section on Ventilatory Responses to Exercise - Understanding how exercise influences breathing mechanics and gas exchange.

Demonstrations

Surface Tension and Pressure

• Law of LaPlace: Describes how the pressure (P) within a balloon—and by extension, alveoli—is influenced by surface tension (T) and radius (r) through the formula: P = \frac{2T}{r}.

• In the lungs, surfactant decreases alveolar surface tension from approximately 50 dynes/cm³ to about 2 dynes/cm, preventing alveolar collapse, especially in smaller air sacs.

• The variation in surfactant concentration across alveoli highlights its critical role in maintaining proper lung function.

"Squirt Bottle" Demonstration

• This demonstration illustrates how negative pressure in the chest cavity facilitates air filling in the lungs during inhalation.

• The loss of this negative pressure can lead to conditions such as pneumothorax (collapsed lung) due to the failure of lung expansion.

A. Chest Measurements

• Two main motions fill the lungs: 1. Diaphragm contraction lowers the chest cavity, increasing internal volume. 2. External intercostal muscles expand the ribcage, allowing for larger air intake.

• Measure anteroposterior and lateral diameters using calipers at the nipple line during different phases of breathing:

  • Quiet expiration: Measure sitting calmly, mouth closed.

  • Quiet inspiration: Inhale gently without force.

  • Forced expiration: Exhale completely with effort.

  • Forced inspiration: Inhale deeply with maximal effort.

• Plot results against a fixed spine point to evaluate lung's structural changes during different respiratory phases.

B. Regulation of Ventilation

• The body's gas exchange and ventilation adjust according to carbon dioxide (CO₂) levels rather than oxygen levels, which is crucial for maintaining acid-base balance.

• Increased CO₂ concentration in the blood leads to acidosis (lower pH).

• Chemoreceptors:

  • Central chemoreceptors are located in the brain and directly detect changes in CO₂ levels.

  • Peripheral chemoreceptors, found in the aorta and carotid arteries, respond to blood acidity changes caused by CO₂.

• The body initiates a compensatory mechanism—negatively feedback loop—by increasing the depth and rate of breathing to expel excess CO₂.

Overventilation

• Results in decreased hydrogen ion concentration in the blood, potentially leading to dizziness and cerebral hypoxia due to insufficient oxygen delivery to the brain.

• Forced deep breathing may inadvertently lead to apnea (temporary cessation of breathing), highlighting the body's balance in breath control.

C. The Valsalva Maneuver

• Definition: This maneuver is a forced expiration against a closed glottis, which temporarily raises intrathoracic pressure, impacting hemodynamics.

• Physiological consequences include decreased venous return leading to reduced cardiac output, resulting in fluctuations in blood pressure and might cause reflex tachycardia as the body attempts to maintain adequate blood flow.

• Symptoms such as cyanosis may occur, indicating diminished oxygen delivery to vital organs, particularly the brain.

Experiment Procedure

• Note radial pulse before and after performing the Valsalva maneuver to assess cardiovascular responses.

• Observe for cyanosis in the face and neck post-maneuver as a sign of oxygen deficiency.

• Measure any resulting changes in pulse rate or force to analyze the cardiovascular response.

D. Neural Control of Respiration

• The respiratory centers in the brainstem regulate breathing rhythm using a complex interplay of excitatory and inhibitory impulses to respiratory muscles.

• This regulation is influenced by sensory inputs from stretch receptors in the lungs, higher brain centers (associated with emotional responses), and stimuli from activities such as coughing and speech, showcasing the integration of various neural pathways.

Hering-Breuer Reflex

• Inflation Reflex: Acts as a protective mechanism preventing over-inflation of the lungs by inhibiting the inspiratory center when lung receptors sense excessive stretching.

• Deflation Reflex: Activates the inspiratory center during lung deflation, promoting inhalation when lung volume decreases.

Exercise Effects

• Strenuous exercise leads to the production of carbon dioxide and lactic acid, resulting in increased acidity and stimulating respiratory drive.

• This results in immediate increases in ventilation rates, initiated by muscle impulses as the body strives to meet heightened oxygen demands.

E. Respirometry (iWorx)

Background

• Key definitions include:

  • Tidal volume (TV): The volume of air inhaled or exhaled per breath.

  • Inspiratory reserve volume (IRV): The additional air that can be inhaled after a normal inspiration.

  • Expiratory reserve volume (ERV): The additional air that can be forcibly exhaled after a normal expiration.

  • Residual volume: The volume of air remaining in the lungs after maximal exhalation.

• Purpose: Assess and measure various breathing parameters at rest and following exercise to evaluate lung capacity and function.

Procedure for Measuring Breathing at Rest

• Record the resting subject's breathing using the spirometer to gather baseline data.

• Measure tidal volume, maximum inspiratory flow rate, and breath period consistently across multiple trials to ensure reliability in results.

F. Data Analysis

• After collecting data, calculate mean values, flow rates, and other relevant metrics to evaluate respiratory parameters.

• Key ratios include:

• FEV1/FVC ratio: A crucial indicator of potential obstructive lung diseases, where healthy values typically range around 0.80 for FEV1/FVC and 0.95 for FEV3/FVC in adults.

• Discussion on the correlation between tidal volume, vital capacity, and variables like age, gender, or fitness levels illustrates the dynamic nature of respiratory physiology.

• Document expected physiological changes such as increased tidal volume or respiratory rate post-exercise to understand the body's adaptive mechanisms.

Questions for Reflection

• Compare lung volumes across students to analyze individual physiological variations.

• Examine physiological changes in tidal volume, IRV, and ERV in response to exercise to gain insights into lung capacity and endurance.

• Discuss the differences in airflow rates during inhalation and exhalation pre- and post-exercise to assess the impact of physical activity on respiratory function.

• Evaluate changes in minute ventilation in relation to exercise intensity and duration, highlighting the physiological adaptations of the respiratory system.

• Assess the overall implications of exercise on respiratory function changes, linking to aspects such as training adaptations and health benefits.