Comparative plethysmography; evidence for a hydrostatic effect on foot blood flow

Area of Science:

• Physiology
• Biomedical Engineering

Background:

• Accurate measurement of peripheral blood flow is crucial for diagnosing and monitoring various vascular conditions.
• Existing methods for measuring foot blood flow have limitations in accuracy and scope.

Purpose of the Study:

• To compare the efficacy of a strain gauge and water displacement plethysmography in measuring foot blood flow.
• To investigate the impact of hydrostatic pressure on blood flow measurements in the foot.

Main Methods:

• Simultaneous measurement of right foot blood flow using a strain gauge and water displacement plethysmography in 11 subjects.
• Assessing the correlation between the two methods across a range of blood flow values.
• Evaluating the effect of plethysmograph emptying/refilling and applied hydrostatic pressure on strain gauge readings.

Main Results:

• A strong linear correlation (r = 0.88) was observed between strain gauge and plethysmography measurements.
• Strain gauge measurements represented only about 30% of total foot blood flow measured by plethysmography.
• Strain gauge estimates increased significantly (2-3 fold) when the plethysmograph was emptied, an effect reversed upon refilling.
• Hydrostatic pressure applied within the plethysmograph proportionally reduced blood flow measurements.

Conclusions:

• Strain gauges provide a reliable measure of mid-metatarsal blood flow but do not capture total foot perfusion.
• Hydrostatic pressure within plethysmography systems can significantly artifactually alter blood flow measurements, necessitating careful consideration of experimental setup.
• Proposed mechanisms for pressure-induced reduction include increased venous leakage, decreased arterial inflow, and enhanced capillary filling.