Effect of extension tube length on the damping coefficient and natural frequency in normotensive dogs

Abstract

© Veterinary Emergency and Critical Care Society 2022.Objective: To establish an acceptable extension tube length (ETL) to measure direct blood pressure (BP) in dogs. Design: Prospective, experimental study. Setting: University-based small animal research facility. Animals: Eight healthy Beagle dogs: 6 males and 2 females. Interventions: Each extension tube with lengths of 25, 50, 75, 115, 145, 205, and 275 cm were connected after the catheterization with a 22-Ga catheter in the dorsal pedal artery in sternal recumbency. A square wave from the fast-flush test was consecutively recorded 5 times to analyze the system's dynamic response characteristics according to the ETL. After recording the square wave, the ETL was converted to a Latin square. The dynamic response was analyzed using natural frequency (NF) and the damping coefficient (DC), both of which affect the damping factor. The average values of NF and DC were plotted against a graph showing the damping factor. Linear regression was used to evaluate the between-group changes in NF and DC. Measurements and Main Results: The DC gradually increased from 0.21 to 0.29 ξ, and the NF gradually decreased from 38 to 14 Hz according to the increase in ETL (P < 0.05). The dynamic response showed adequate damping with all ETLs. Conclusion: With an increase in ETL, the NF decreased significantly, while the DC demonstrated a less significant change. Therefore, NF had a greater influence on the damping factor of arterial BP measurement. There was no difference between ETLs from 25 to 275 cm lines for measuring BP. An ETL of less than 275 cm is recommended as the damping amount is adequate. Moreover, an ETL less than 275 cm does not meaningfully affect BP measurement in dogs.