Physics Units and Concepts Quiz

Units of Measurement

• Mass is measured in grams (g).
• Length is measured in meters (m).
• Volume is measured in liters (L).
• Time is measured in seconds (sec).

Force

• Force is defined as the amount of energy required to change an object's state of rest to motion.
• Force is calculated using the formula: F = mass (m) x acceleration (a).
• Force is measured in Newtons.
• One Newton is the energy needed to move 1 kg of mass 1 meter.
• Gravity is a force: a force of attraction between masses.
• Larger molecules attract other molecules through gravity.
• Hydrostatic pressure is affected by gravity and distance from the heart.

Pressure

• Pressure is defined as the amount of force applied per unit area.
• Pressure is measured in Pascals (Pa) and Kilopascals (kPa).
• Bourdon Gauge: directly measures pressure, used on compressed gas cylinders.
• Absolute pressure = atmospheric pressure + gauge pressure.
• Gauge pressure = absolute pressure - atmospheric pressure.

Energy

• Energy is measured in Joules.
• Potential energy (PE): stored energy that can be converted to work.
• Kinetic energy (KE): the exertion of force.
• PE and KE exist in equilibrium.
• KE and Work are essentially the same.
• Law of Conservation of Energy: energy cannot be destroyed or created, only transferred or converted.

Work

• Work is calculated as Force x Distance.
• KE and Work are essentially the same.

Laplace's Law

• Laplace's Law describes the relationship between the pressure of a fluid inside a closed container, the radius of the container, and the tension of the container's wall.
• Cylinders: the pressure inside a cylinder is inversely proportional to the radius of the cylinder.
• Spheres: the pressure inside a sphere is inversely proportional to the radius of the sphere.

Pascal's Principle

• Pascal's Principle states that the pressure applied to an enclosed fluid is transmitted equally to every point within the fluid.

Surface Tension

• Surface Tension is the force that exists at the interface between a liquid and a gas.
• Surface Tension is influenced by the cohesive forces between liquid molecules, adhesion forces between the liquid and another surface, and the temperature.

Venturi Effect

• The Venturi Effect describes the decrease in pressure that occurs when a fluid flows through a narrowing space, resulting in an increase in velocity.

Fluid Mechanics

• Fluids are susceptible to pressure and gravity.
• Fluids include liquids and gases.
• Fluid dynamics are defined by the response to stress.
• Perpendicular stress is resistance to compression.
• Liquids resist compression while gases are compressible and expandable.
• Tangential stress: resistance to flow due to surface interaction.
• Friction is proportional to viscosity.
• Viscosity is the inherent property of a fluid that resists flow.

Types of Flow

• Laminar flow: predictable, with less tangential stress at the center of the flow and more stress on the bottom and outside.
• Transitional flow: most common type of flow in the body.
• Turbulent flow: irregular, swirling flow that occurs at high velocities, sharp bends, angles, and irregularities.

Poiseuille's Law

• Poiseuille's Law predicts the rate of flow through a pipe.
• Flow is exponentially proportional to the radius of the pipe.
• Flow is directly proportional to the pressure gradient.
• Flow is inversely proportional to viscosity.
• Flow is inversely proportional to the length of the pipe.

Reynold's Number

• Index that combines Poiseuille's Law and fluid density to determine whether a given flow will be laminar or turbulent.
• Flow is directly proportional to velocity, diameter, and density.
• Flow is inversely proportional to viscosity.
• Laminar flow: Reynold's number < 2000.

Bernoulli's Principle

• As fluid flows through a constriction, velocity increases and pressure decreases.
• Velocities and pressures exist in an inverse relationship, Velocity takes away KE from pressure (Law of Conservation).

Gas Analysis

• Oxygen (O2) Analysis
  • Electro-Galvanic Cell (Fuel Cells): Oxygen passes through a semipermeable membrane and dissolves into an electrolyte solution, generating electrical potential measured by a voltmeter.
  • Polarographic Electrode (Clark Electrode): Applied voltage causes oxygen to reduce at the cathode, creating a current proportional to O2 partial pressure.
  • Paramagnetic Oxygen Analyzer: Oxygen's paramagnetic properties are used to measure its concentration by analyzing pressure differences caused by rapidly alternating electromagnetic fields.
  • Fluorescence-Quenching: Oxygen absorbs photons, preventing emitted light, allowing concentration analysis through the amount of emitted photons.
• Carbon Dioxide (CO2) Analysis
  • Severinghaus PCO2 electrode: CO2 diffuses into a bicarbonate solution and reacts with water producing carbonic acid, measured by a voltmeter.
  • Colorimetric Sensor: CO2 dissolves into a solution, altering pH and activating a pH-sensitive dye, creating a color change which can be measured.
• Other Gas Analysis
  • Mass Spectrometry: Ionized gas molecules are deflected by a magnetic field, creating electrical currents measured at collectors.
  • Infrared analysis: Gases absorb infrared radiation at distinct wavelengths, allowing measurement by analyzing changes in the infrared beam.
  • Raman Scattering Analysis: analyzes scattered light from molecules hit by a laser beam.

Beer-Lambert Law

• The Beer-Lambert Law describes the relationship between the absorption of electromagnetic radiation and the concentration of the absorbing substance.
• Absorption is determined by the thickness and absorbing properties of the substance.

Capnography

• Capnography is a tool that measures the concentration of carbon dioxide (CO2) in exhaled air.
• Capnographs use a specific waveform to display the amount of CO2 in exhaled tidal volume over time.
• Phases of Capnography Waveform:
  • Phase 0: Inspiratory phase.
  • Phase 1: Exhalation of dead space, minimal to no CO2.
  • Phase II: Exhalation of mixed alveolar and dead space gas, expired CO2 from the upper airways.
  • Phase III: Alveolar plateau, represents alveolar pCO2.
  • Phase IV: End-tidal CO2, measured at this point.
• Angles of Capnography Waveform:
  • Alpha Angle: between phases II and III, represents transition to just alveolar air exhalation.
  • Beta Angle: between phases III and IV, represents transition to inspiration.

Pulse Oximetry

• Pulse oximetry is a non-invasive tool that measures the percentage of hemoglobin in the blood that is saturated with oxygen (SpO2).
• Pulse oximeter probe emits red and infrared light, which is absorbed differently by oxyhemoglobin and deoxyhemoglobin, allowing for SpO2 calculation.
• Advantages:
  • Non-invasive.
  • Easy to apply.
  • Continuous monitoring.
  • Earlier detection of desaturation.
  • Inexpensive.
• Disadvantages:
  • Prone to artifact.
  • Delayed measurements (30-60 seconds).
  • Inaccurate at SpO2 values below 70%.
  • Rare risk of burns in poor perfusion states.
• Inaccuracies:
  • Falsely high readings: carbon monoxide poisoning, methemoglobinemia.
  • Underestimated readings: dyes such as methylene blue.
  • Other sources of error: ambient light, skin pigmentation, electrosurgery, motion artifact, nail polish.

Cerebral Oximetry

• Cerebral oximetry measures the oxygen saturation of the blood in the brain.
• It relies on the scattering and reflection of radiation, which is highly unpredictable and influenced by venous and arterial blood.
• The Beer-Lambert Law does not apply directly, so modified equations are used.

Lasers

• Lasers are high-energy light beams that are concentrated and directional.
• Components of a laser:
  • Energy source (example: electricity)
  • Brewster Angle- mirrors that determine directionality.
  • Resonant chamber: contains the laser medium where the laser light amplifies.
  • Electrodes (anode and cathode).
• Lasers are classified based on their wavelengths which correspond to their energy levels.
• Risks and Dangers:
  • Protective eyewear is crucial for all personnel.
  • Reflected radiation is as hazardous as direct radiation.
  • Laser beams do not decay with distance: distance from the source has minimal safety effects.
• Types of Lasers:
  • Carbon Dioxide Laser: superficial penetration, used for ENT surgeries and some neurosurgeries, infrared wavelength, not fiberoptic compatible.
  • Nd-YAG laser: deeper penetration, wavelengths are better absorbed by water, used for distal airway surgeries, good coagulation, can cause delayed swelling.
• Anesthesia Considerations:
  • Laser in standby mode when not in use.
  • Secondary light beams for aiming assistance.
  • Monitor the location of instruments and flammable materials.
  • Laser safety goggles for all personnel.
  • Clear communication and a planned approach for crisis response.
  • Patient should wear laser safety goggles.
  • Monitor EtO2 (end-tidal oxygen) levels.

Fire Risks & Emergency Precautions

• Use laser safety goggles for all staff members.
• Minimize flammable materials in the room where a laser is in use.
• Have a plan for emergency response to fires.
• Be prepared to extinguish a fire with appropriate equipment and resources.