Spirometry Flashcards
Compliance
Change in volume per change in pressure
Can be dynamic or static
Static Compliance
calculated using end inspiratory occlusion pressure
■ Static compliance = VT/Plateau pressure - PEEP
■ Requires zero gas flow
Reflects elastic resistance of lungs, chest wall
Total Compliance
reflects elastic properties of lungs, thorax, abdomen, breathing system
NMBA: will increase chest wall compliance but not affect lung compliance - if paralyzed, changes in compliance DT alterations in lung compliance
Resistance
Non elastic resistance to breathing: airway flow resiatcne + pulmonary tissue resistance
For given VT, high resistance overcome by lower flow for longer time or higher driving pressure
Pulmonary Tissue Resistance
Pressure required to overcome resistance to gas flow through airways during respiration
factors that Increase resistance
Increased FR
Turbulent flow
Bronchoconstriction/increased SmM
Emphysema
Obstruction
Bronchitis/spasm
Factors that Decrease Resistance
Laminar flow
Increased lung volume
Bronchodilation
Shorter Airways
Decreased Viscosity
Factors that Decrease Resistance
Laminar flow
Increased lung volume
Bronchodilation
Shorter Airways
Decreased Visocisyt
Total Airway Resistance
estimated by (Peak Pressure - Plateau Pressure)
■ Normal 2-5 cmH20
■ Increased resistance: higher peak pressure needed to produce same flow
If inspiratory flow and VT remain constant, but resistance increases, greater difference (Ppeak - PPlateau)
Respirometer
device that measures volume of gas passing during period of time through a location in flow pathway
detect obstructions, leaks, disconnections, apnea, ventilatory failure and high/low volumes in spont breathing/controlled vent
Required: expired VT, minute volume, both
Ventilator Bellows Scale
rough estimate of tidal volume delivered into breathing system
Not an accurate estimate of the volume delivered to patient
● Wasted ventilation DT gas compression, distension of components of breathing system
FGF: additive to VT during inspiration
● Will not be reflected on this scale
Wright Respirometer
Gas enters through outer casing, directed through tangential slots to strike a vane, causing rotation
Vane connected to gear system to hands on dial so that a reading corresponding to volume of gas passing through device registered
Evaluation of the Wright Respirometer
Over-reads at high flows
○ Pulsatile flow adds to over-reading
○ Higher readings with N20 as carrier gas
Under-reads at low flows
Advantages of the Wright Respirometer
● Small size, light weight
● Low dead space - use between patient and breathing system
Disadvantages
● No alarms
● Can be difficult to read
● No respiratory rate
● Does not read bidirectional flow
Spiromed
Electronic respirometer: use with North American Drager breathing systems
Gas flows through monitor forcing a pair of rotors to counter-rotate - rotate in unison with armature containing magnets
Transistors ay 7, 12 o’clock receive pulses from magnets on rotating armatures –> interface panel –> processer
Number of paired pulses related to vol of gas that passes trough sensor over time with # counted during each breath = Vt
Spiromed Accuracy
Programmed to measure TV equal or > 150 mL
○ If < 150 mL, instrument will automatically +2 or more consecutive TV’, reduce the recorded frequency
■ Minute volume remains correct
D-Lite Gas Sampler and Flow/Sensor
–Two-sided Pitot Tube
–Measuring flow via measurement of pressure difference across flow resistor via Bernoulli Equation
MOA Pitot Tube
–Placed btw breathing system and patient
–Two sensing tubes: one faces direction of flow (total pressure measurement), other = opposite flow (static pressure)
–Difference between total, static pressure = dynamic pressure –> Bernoulli equation to estimate flow
Advantages of Pitot Tube
Can determine CO2, O2, anesthetic gases
Derive flows, measured parameters, insp/expiratory VT, minute volumes
Can display FVL, PVLs
Not position dependent, allows bidirectional gas flows, able to be used in both Mapleson and Circle Systems
Variable Orifice Flow Sensory
Sensors at both connections to CO2 absorber used to measure inspiratory, expiratory flows
Can be used to generate pressure, flow volume loops
Main advantage = used by ventilator to compensate for changes in FGF
MOA Variable Flow Orifice
Sensors on both sides of circle system
Plastic (miler) flap placed across direction of gas flow - opens at increasing gas flows
Two sensors, transducer inside AxM measure proximal and distal pressure to flap
Volume calculated from these flows
Sensor on inspiratory side connected to pressure sensor so breathing system pressure is measured
Fixed Orifice Flow Sensor
■ Restrictor and two pressure sensors (on either side of the restrictor)
■ Zeroing valve compensates for pressure sensor drift
Respirometer: Ideal position in breathing system
Best location = C btw patient, breathing system (at y piece)
