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1. Gases and Gas Laws: Fundamentals and Applications Understanding Gas Behavior & Their Relevance to Physical Therapy

2. Introduction to Gases and Their Properties • Gases were the first pure substances studied.
• More difficult to handle than solids/liquids.
• Collected using liquid displacement methods.
• Gases have no fixed shape or volume.
• Volume depends on pressure and temperature.

3. Boyle’s Law: Pressure-Volume Relationship • Published by Robert Boyle in 1662.
• Product of pressure and volume is constant: $PV = k$.
• Pressure and volume inversely related.
• Temperature must remain constant.
• Useful in understanding lung volume changes.

4. Measuring Gas Pressure: Units and Equivalents • Common units: atm, psi, mmHg, Torr, Pascal.
• 1 atm = 14.7 psi = 760 mmHg = 101,325 Pa.
• Atmospheric pressure at sea level exerts 14.7 psi.
• Pressure measurement crucial in respiratory therapy.
• Understanding units aids accurate patient monitoring.

5. Torricelli’s Barometer and Atmospheric Pressure • Evangelista Torricelli invented mercury barometer.
• Demonstrated atmospheric pressure using mercury column.
• Introduced concept of vacuum (Torricellian vacuum).
• Partial pressures explained by mercury height.
• Barometers help monitor environmental pressure in therapy settings.

6. Limitations of Suction Pumps and Atmospheric Pressure • Suction pumps cannot raise water >10 meters.
• Atmospheric pressure limits pump height.
• Explains why negative pressure in lungs is limited.
• Essential concept for respiratory therapy devices.
• Relates to patient ventilation and oxygen delivery.

7. Amontons’ Law: Pressure-Temperature Relationship • Pressure divided by temperature is constant: $P/T = k$.
• Temperature measured in Kelvin to avoid negatives.
• Explains pressure changes in closed gas systems with temp.
• Relevant for understanding gas behavior in body cavities.
• Helps optimize physical therapy involving respiratory gases.

8. Charles’ Law: Volume-Temperature Relationship • Volume divided by temperature is constant: $V/T = k$.
• Charles’ hydrogen balloon experiment demonstrated gas expansion.
• Volume increases as temperature rises at constant pressure.
• Important in managing lung inflation during therapy.
• Supports understanding of temperature effects on respiratory devices.

9. Combined Gas Law: Integrating Pressure, Volume, Temperature • Formula: $P1V1/T1 = P2V2/T2$.
• Combines Boyle’s, Charles’, and Amontons’ laws.
• Calculates gas changes under varying conditions.
• Useful in physical therapy for gas delivery adjustments.
• Helps predict lung volume changes during treatment.

10. Kinetic Molecular Theory: Gas Particle Behavior • Gases consist of tiny particles in constant motion.
• Large distances between particles compared to size.
• Particles have elastic collisions without chemical reactions.
• Temperature relates to kinetic energy and velocity.
• Applies to gas exchange and diffusion in lungs.

11. Avogadro’s Law: Volume and Number of Particles • Equal volumes of gases contain equal particles at same T, P.
• Formula: $V/n = k$.
• Clarified molecular composition of gases (e.g., $N2$, $O2$).
• Important for calculating oxygen delivery in therapy.
• Supports dosing of medical gases in treatments.

12. Ideal Gas Law: Comprehensive Gas Behavior Model • Equation: $PV = nRT$.
• Combines all individual gas laws.
• $R$ is gas constant: 0.0821 L·atm/mol·K.
• Predicts gas behavior in closed systems.
• Vital for respiratory therapy equipment calibration.

13. Dalton’s Law of Partial Pressures • Total pressure equals sum of individual gas pressures.
• $P{total} = p{oxygen} + p{nitrogen} + p{water} + ...$
• Explains gas mixtures in the atmosphere and lungs.
• Partial pressures influence oxygen diffusion.
• Critical for managing mixed gas therapies.

14. Vapor Pressure: Equilibrium Between Liquid and Gas • Water molecules constantly escape and re-enter liquid phase.
• Vapor pressure is partial pressure of water vapor at equilibrium.
• Depends only on temperature for constant pressure.
• Important in understanding humidity in therapy environments.
• Affects patient comfort and respiratory conditions.

15. Saturation Vapor Pressure and Boiling Point • Vapor pressure equals atmospheric pressure at boiling point.
• For water, boiling at 100°C at 1 atm.
• Lower pressure decreases boiling temperature.
• Explains boiling changes at high altitude therapy.
• Relevant for sterilization and humidification techniques.

16. High Altitude Effects on Vapor Pressure and Boiling • Lower pressure at altitude lowers boiling point.
• Requires longer cooking and sterilization times.
• Pressure cookers increase local pressure to raise boiling point.
• Analogous to oxygen delivery challenges in therapy at altitude.
• Guides therapy adjustments in mountainous regions.

17. Relative Humidity and Vapor Pressure Misconceptions • Relative humidity = actual vapor pressure / saturation vapor pressure.
• Warm air does not “hold” more moisture chemically.
• Vapor pressure fixed at given temperature regardless of gas type.
• Important for humidified oxygen therapy management.
• Clarifies misconceptions in respiratory care environments.

18. Application of Gas Laws in Physical Therapy: Respiratory Care • Boyle’s law explains lung volume changes during breathing.
• Charles’ law relates to temperature effects on inhaled gases.
• Dalton’s law critical in oxygen therapy and gas mixtures.
• Vapor pressure affects humidification in respiratory devices.
• Ideal gas law helps calculate gas delivery and volumes.

19. Boyle’s Law in Lung Mechanics and Physical Therapy • Inhalation: diaphragm lowers, thoracic volume increases.
• Lung pressure decreases, air flows in (Boyle’s law).
• Exhalation: volume decreases, pressure increases, air flows out.
• Therapists use this principle in breathing exercises.
• Supports mechanical ventilation settings.

20. Dalton’s Law and Oxygen Delivery in Therapy • Oxygen’s partial pressure drives diffusion into blood.
• Mixtures of gases affect total and individual pressures.
• Therapists adjust oxygen concentration based on partial pressures.
• Understanding vapor pressure prevents underestimation of oxygen levels.
• Essential for safe and effective respiratory treatments.

21. Vapor Pressure and Humidification in Physical Therapy • Dry oxygen can irritate airways.
• Humidifiers add water vapor to oxygen.
• Vapor pressure controlled to optimize patient comfort.
• Relative humidity impacts mucous membrane health.
• Gas laws guide device design and clinical protocols.

22. Gas Laws in Mechanical Ventilation and Physical Therapy • Boyle’s law governs pressure-volume relationships in lungs.
• Temperature and pressure control gas behavior inside ventilators.
• Proper gas delivery requires understanding combined gas law.
• Ensures patient safety during assisted breathing.
• Physical therapists collaborate in ventilator management.

23. Kinetic Molecular Theory and Gas Exchange • Gas particles move rapidly and collide elastically.
• Movement explains diffusion across alveolar membranes.
• Temperature influences particle velocity and oxygen uptake.
• Therapy techniques often aim to optimize gas movement.
• Foundation for understanding respiratory physiology.

24. Avogadro’s Law and Respiratory Gas Volumes • Equal gas volumes contain equal molecules at same T, P.
• Important for measuring lung capacities.
• Helps calculate inhaled and exhaled gas volumes.
• Guides dosing of medical gases in therapy.
• Supports calibration of spirometry devices.

25. Integrating Gas Laws into Physical Therapy Curriculum • Gas laws provide scientific basis for respiratory therapies.
• Understanding gas behavior improves patient assessment.
• Facilitates effective use of oxygen and ventilation equipment.
• Encourages evidence-based treatment planning.
• Empowers therapists to optimize respiratory outcomes.

26. Summary: Gas Laws and Their Role in Physical Therapy • Boyle’s, Charles’, Dalton’s, and Ideal Gas Laws explain gas behavior.
• Gas laws impact lung function, oxygen therapy, and ventilation.
• Vapor pressure and humidity affect patient comfort and safety.
• Physical therapy utilizes these principles for treatment optimization.
• Mastery of gas laws enhances clinical decision-making.

27. Thank You • Questions and discussion
• Explore gas laws in your clinical practice
• Continue learning to improve patient care

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