Respiratory System Lecture (L28)

Respiratory System Lecture (L28)

• The lecture was presented by Dr. Pugazhandhi Bakthavatchalam, an Assistant Professor of Anatomy and Physiology at AUACAS, American University of Antigua.

Learning Outcomes

• Students will describe lung function tests and their significance.
• Students will describe physiological changes in respiratory system pressures and lung expansion.

Question

• People born and living at sea level usually have smaller lung capacities than those who live at high altitudes.

Lung Function Tests (PFTs)

• Also called pulmonary function tests (PFTs).
• Measure how well lungs work.
• Determine how much air lungs can hold, how quickly air moves in and out, and how well lungs exchange oxygen and carbon dioxide.
• Used to diagnose and assess severity of lung diseases.

Indications for PFTs

• Evaluating patients with dyspnea (shortness of breath).
• Assessing disease severity and monitoring treatment response.
• Determining fitness for surgery (e.g., thoracic surgery/lung resection).

Clinical Significance of PFTs

• Assess lung compliance/elasticity.
• Evaluate airway resistance.
• Measure respiratory muscle strength.
• These factors determine the amount of air a person can move into their lungs per unit of time.

PFTs: Available Measures

• Spirometry: Measures airflow (how much and how fast air moves in and out of lungs).
  • Static Lung Volumes: Measures lung volumes (how much air).
  • Diffusing Capacity: Measures gas exchange (how effective gas exchange is).
• Other testing: Airway responsiveness, respiratory muscle strength testing, and lung compliance.

Spirometry

• First lung function test performed.
• Measures how much and how quickly air is exhaled from the lungs.
• Involves breathing into a mouthpiece connected to a spirometer (recording device).
• Two types of spirometers: Mechanical (incentive spirometer) and electronic.

Respiratory Volumes

• Total lung capacity is divided into volumes based on their function during inhalation and exhalation of air.
• Average total lung capacity for an adult male is about 6 liters.
• A small fraction of this capacity is used during typical breathing.
• Average respiratory rate is 30-60 breaths/minute at birth, decreasing to 12-20 breaths/minute in adults.
• Air volume in lungs can be divided into four volumes:

[1] Tidal Volume (TV)

• Volume of air inspired or expired in each normal breath.
• Approximately 500 ml in an average young adult male.

[2] Inspiratory Reserve Volume (IRV)

• Extra air that can be inspired beyond tidal volume.
• Approximately 3000 ml.

[3] Expiratory Reserve Volume (ERV)

• Amount of air that can be exhaled after a normal exhalation.
• Approximately 1100 ml.

[4] Residual Volume (RV)

• Volume of air remaining in lungs after the most forceful exhalation.
• Approximately 1200 ml. Cannot be measured directly by spirometry; indirect methods are used (e.g., helium dilution).

Lung Capacities

• Combined volumes are used to calculate lung capacities:
  • Inspiratory Capacity (IC) = TV + IRV = ~3500 ml (amount of air a person can breathe in from their normal expiratory level, filling the lungs to max extent)
  • Functional Residual Capacity (FRC) = ERV + RV = ~2300 ml (amount of air remaining in lungs at end of normal exhalation)
  • Vital Capacity (VC) = TV + IRV + ERV = ~4600 ml (max amount of air a person can expel from the lungs after filling and then emptying to max extent)
  • Total Lung Capacity (TLC) = VC + RV = ~5800 ml (max volume to which lungs can be expanded with most forceful inhalation)

Peak Expiratory Flow (PEF)

• Maximum rate of exhalation after a deep breath (velocity).
• Measured by Wright peak flow meters.
• PEF is higher when lungs are full than when they are almost empty.
• More convenient for lung diagnosis than spirometry.

Is Spirometric Assessment and Peak Flow Measurement Identical?

• No. Peak flow measures fastest exhaled air rate while spirometry encompasses broader tests of lung function.

Factors Affecting Lung Volume

• Several factors influence lung volumes (some controllable, some not):
  • Larger: Males, taller people, non-smokers, professional athletes, and people living at high altitudes.
  • Smaller: Females, shorter people, heavy smokers, non-athletes, and people living at altitudes.

Restrictive and Obstructive Pulmonary Diseases

• Obstructive: Characterized by a reduced expiratory airflow rate (e.g., asthma, COPD).
• Restrictive: Characterized by reduced lung volumes and decreased lung compliance (e.g., interstitial fibrosis, scoliosis, obesity, and lung resection).

Spirometries Risk Assessment

• Generally low-risk test, however, certain conditions might prevent it:
  • Unstable angina, prior pneumothorax, recent heart attack/stroke, recent eye/abdominal surgery, or unexplained blood coughing.

Obsructive Vs. Restrictive Disorders

• Obstructive: Airflow limitation but normal/increased total lung capacity.
  • Examples: Asthma Emphysema, Cystic Fibrosis, bronchitis.
• Restrictive: Reduced lung volumes with decreased lung compliance.
  • Examples: Interstitial fibrosis, scoliosis, obesity, lung resection, neuromuscular disease.

Additional Considerations

• Higher altitudes necessitate increased oxygen diffusing capacity to process more air.

Explore the functions and tests of the respiratory system in this lecture by Dr. Pugazhandhi Bakthavatchalam. Understand lung function tests, their significance, and how physiological changes affect lung expansion and pressures. Perfect for students studying Anatomy and Physiology.