Pulse contour model
Stroke volume (SV) was determined from the following algorithm:
SV=k.AUCsys where AUCsys is the area under curve of the arterial
pressure signal from the DAP (start of systolic ejection) up to the
start of the dichrotic wave (closure of sigmoid valves). Its principle
is based on the proportionality of AUCsys to the SV (Kouchoukos et al.,
1970). This model has been demonstrated to provide accurate and reliable
results for SV assessments versus the thermodilution technique in
anaesthetised dogs (Briganti et al., 2018). Since the location at which
arterial pressure is measured might influence the reliability of the
model, a thorough validation was conducted in anesthetised dogs (n=6) by
placing the tip of the pressure sensor of telemetric transmitter at the
same location as in experiments conducted in conscious dogs, i.e. the
caudal portion of the abdominal aorta. Reliability and pharmacological
robustness of the model were tested in anaesthetised dogs following
various pharmacological challenges expected to induce changes in SV:
nitroprusside (30 µg/kg, iv), phenylephrine (10 µg/kg, iv), dobutamine
(30 µg/kg, iv), verapamil (100 µg/kg, iv) and hexamethonium (1 mg/kg,
iv). The Pulse Contour model was compared to the ultrasonic Doppler flow
method as reference method. Ultrasonic probes (PAX transit time
ultrasonic flow probes and Ultrasonic transit-time flowmeter T402,
Transonic Systems, NY, USA ) were placed around the ascending aorta
close to the sigmoid valves. The pulse contour model has never been
published in the context of telemetry in beagle dogs. So, results of the
validation study are presented as supplemental material 1. This
validation demonstrated the reliability and pharmacological robustness
of the pulse contour model in healthy dogs when compared to the
ultrasonic flow method whatever the pharmacological challenges (bias:
+0.1 mL, agreement: ± 1.5 mL according to Bland & Altman analysis).