The origin of inverted waveforms in the reflection plethysmogram

Area of Science:

• Biomedical Engineering
• Physiology
• Medical Instrumentation

Background:

• Reflection plethysmography is a technique used to measure blood volume changes.
• Inverted pulse waves are an observed artifact in finger plethysmography, particularly during anesthesia when arterial pressure is monitored concurrently.
• The origin of these inverted pulse waves requires elucidation for accurate physiological measurements.

Purpose of the Study:

• To investigate the underlying causes of inverted pulse waves observed in reflection plethysmography of the finger.
• To determine the influence of external pressures on the plethysmographic signal.
• To differentiate between systemic and local factors contributing to pulse wave inversion.

Main Methods:

• Two series of experiments were conducted with human volunteers.
• Experiment 1: Investigated the effect of upper arm cuff pressure on finger plethysmography.
• Experiment 2: Examined the impact of transducer application pressure on the finger.

Main Results:

• Inverted pulse waves are a localized phenomenon specific to the reflection plethysmography method.
• The inversion results from a relative increase in the optical density of surrounding tissues compared to arterial vessels.
• Venous engorgement in the finger, influenced by applied pressure, is identified as the primary cause of inversion.

Conclusions:

• The observed inversion of plethysmographic pulse waves is a local artifact of the reflection technique.
• Applied pressure, leading to venous engorgement, is the critical factor causing signal inversion in the finger.
• Understanding these factors is crucial for accurate interpretation of plethysmographic data.