How do capnographic waveforms differ between open and closed breathing systems?

• A. Open systems have rounded waves; closed systems have square waves
• B. Open systems have square waves; closed have rounded
• C. Both have rounded waves
• D. Capnography waveforms are not distinct

Answer: (A)

The main idea is that the breathing system design changes how quickly CO2 concentrations change in the circuit, which shapes the capnography waveform. In open systems, fresh gas continuously dilutes exhaled CO2, so the rise and fall of CO2 during the respiratory cycle are smoother, giving rounded, curved waveform segments. In closed systems, there is more rebreathing and less dilution, which makes the transitions sharper and the end-tidal plateau appear more square or flat at the top. So open systems tend to produce rounded waves, while closed systems tend to produce square-shaped plateaus.