2 Journal of Feline Medicine and Surgery 0(0)
defined by the American Association of Medical
Instrumentation (AAMI)4 or modified criteria suggested
by an American College of Veterinary Internal Medicine
(ACVIM) consensus panel3 for validation of automated
non-invasive blood pressure devices. More recently, a
new method of indirect BP measurement, high-definition
oscillometry (HDO), has been developed. As with other
indirect methods, the BP is measured at the level of a
peripheral artery with a cuff placed on a forelimb or the
tail, and these methods provide SBP, diastolic BP (DBP)
and mean BP (MBP), which are obtained from the analysis of the waveforms of recorded
pressure oscillations. In
cats, only one evaluation study of HDO has been published at present.5
This evaluation was performed by
comparison of measurements obtained by a Doppler
ultrasonic device with direct BP measurements undertaken in anaesthetised animals. The authors concluded
that discrepancies between the techniques were
achieved. However, in this study, many of the comparisons were
made in anaesthetised animals and are thus of
questionable applicability to conscious cats. In conscious
cats6 and dogs,7 comparisons of an indirect oscillometric
device and a Doppler ultrasonographical device with
direct BP measurements have shown that neither met the
criteria for validation of AAMI4 or the ACVIM consensus panel.3
The purpose of this study was to compare
SBP and DBP values obtained by HDO measurements
with values achieved simultaneously using a well-
recognised direct method,6-13 using radio-telemetry, in
conscious healthy cats. In addition, to reproduce the
recording conditions expected in hypertensive, normotensive and
hypotensive animals, this evaluation was
performed at ranges of BP corresponding to low, normal
and high BP levels.
Material and methods
Animals
All animals used in this study were handled and cared
for in accordance with the Directive 86/609/EEC
European Convention for the Protection of Vertebrate
Animals used for Experimental and Other Scientific
Purposes.14 The study protocol related to this experiment was reviewed
and approved by the internal ethics
committee.
Purpose-bred European cats (four males and two
females, aged 6-8 months old and weighing 2.4-3.7 kg)
were used in this study. During the acclimatisation period
of 2 weeks, and apart from the recording sessions, animals of the same sex were
group-housed. Toys (balls,
scraper or other), as well as different floors, were used for
enrichment. The animals were placed in a temperatureregulated
(15-21°C) animal house kept at a relative
humidity between 45% and 65% (except during the cleaning slot) with non-recycled
filtered air changed approximately 10 times per hour.
Tap water was provided at libitum. Likewise, food (Special Diets Services (SDS), reference:
Diet F for cat) was available ad libitum.
Telemetry device description and implantation
The telemetry device and the method used for instrumentation of cats were
derived from the method
described previously by Miller et al.9 The telemetry
device (model TL11M2D70PCT; Data Sciences
International, St Paul, MN, USA) includes a hermetically-sealed transmitter body,
containing an electronics
module, sensor and battery that is attached to a fluidfilled catheter.
After instrumentation, the battery can be
turned on and off through the skin with a magnet. The
catheter consists of polyethylene tubing coated with
anti-thrombogenic film and a thin-walled, gel-filled tip.
The gel prevents blood diffusion and conveys pressure
changes to the sensor in the transmitter body.
During the instrumentation, all procedures were
conducted according to aseptic surgical methods.
Anaesthesia was induced using propofol (Rapinovet)
administered at 8 mg/kg (IV) and was maintained by
a continuous intravenous (IV) infusion at 0.04-0.06
ml/kg/min throughout the surgery. Buprenorphine
(Temgesic) at 0.01 mg/kg was administered intramuscularly before
the start of the surgery to avoid surgical
pain. Radio-telemetry transmitters were implanted
subcutaneously. The sensor of the transmitter was
introduced into a femoral artery up to the abdominal
aorta. Postsurgical analgesia was provided by administration of meloxicam 0.07 mg/kg (Metacam) given
orally, once a day for 2-5 days after the surgery.
Prophylactic antibiotic therapy, 30 mg/kg amoxicillin
(SC), was administered daily for 1 week after surgery.
At least 2 weeks of recovery were allowed after the surgery before
starting the experiment to ensure BP
reached a steady state, as observed after cat instrumentation with the telemetry device.9
Experimental design
The BP was measured in each cat to collect at least 25 SBP
and DBP readings per animal and per range, and for the
five sub-ranges respectively (SBP: ≤109, 110-129, 130-
149, 150-169, ≥170 mmHg; DBP: ≤69, 70-89, 90-109, 110-
129, ≥130 mmHg). According to this study design, a total
of at least 750 SBP/DBP readings were generated. Two
vasoactive agents, amlodipine (1 mg/kg, PO) and phenylephrine (0.1, 0.3, 1, 3 and 10 mg/kg, PO) were
administered
in order to reach the lower and the upper parts of
the SBP/DBP ranges defined above. Amlodipine was
chosen because this calcium channel blocker induces a
stable and long lasting hypotension related to peripheral
vasodilatation with only minor reflex tachycardia.
Phenylephrine produces a peripheral vasoconstriction
resulting in relatively stable hypertension after oral
administration. The oral route was chosen because a