Diurnal Variations of Blood Pressure in Cats

Abstract

ABSTRACT. Blood pressure (BP) was analyzed invasively using the telemetry system in unanesthetized, unrestrained healthy adult mongrel cats. After surgical implantation of a telemetry transmitter, BP was transiently elevated due to the invasive nature of the surgery, but it was gradually decreased. BP was largely stabilized seven to ten days postsurgery. Once BP was settled, systolic, diastolic and mean BPs 2 were obtained at 5-min intervals in individual cats. Hourly averages of these BP values revealed a diurnal variation with two peaks at 8:00 and 19:00. We also found that BP was significantly higher when cats were active compared to when they were sleeping or at rest (p<0.05). The average 24-hr BP in 20 healthy cats was 118.4 ± 11.0 (systolic), 78.0 ± 8.7 (diastolic) and 94.8 ± 9.5 mmHg (mean) by the telemetry system. KEY WORDS: blood pressure, feline, diurnal variation.J. Vet. Med. Sci. 68(3): 243-248, 2006 Currently blood pressure (BP) is commonly measured in cats by noninvasive methods such as oscillometry and Doppler ultrasonography in the clinical setting [3,12,13,15]. Accurate and stable BP measurements, however, have been difficult with these indirect techniques, because cuff placement and restraint can be very stressful to animals and may interfere with BP readouts. The results may also be variable among methods and operators. In addition, because BP is constantly affected by various factors, it is difficult to reliably evaluate BP of an animal based on a single measurement. To solve these problems, it is necessary to understand the diurnal pressure pattern in cats.Circadian rhythmic or diurnal variations of BP have been known in humans and mice [1,22,23]. We have previously shown that dogs also have diurnal BP variations using a telemetry system that continuously monitors BP for 24 hr without anesthetizing or restraining the animals [16]. On the other hand, only a handful of studies have documented circadian BP patterns in healthy, unrestrained cats. Brown et al. have reported changes in diurnal BP patterns in six healthy cats after administration of certain vasoactive agents [7]. The study by Sei et al. has focused on BP changes during paradoxical sleep and slow-wave sleep in cats [19]. In this study, we monitored BP in 20 healthy cats continuously for a long term by using the stress-free telemetry system. Obtained data were analyzed for diurnal and nocturnal circadian rhythmic patterns and for influences by daily activities. We also addressed whether the 24-hr BP obtained in this study represented the baseline BP in healthy cats. MATERIALS AND METHODS Animals:Twenty adult mixed-breed cats (four males and 16 females) weighing 2.0 to 4.0 kg were used. No abnormalities were found in these animals by general physical examination and blood, serology and urinary tests. They were individually housed in cages for several months prior to the study (for acclimatization) and during the study period under a 12L/12D cycle (light on at 8:00 and off at 20:00). They were given water ad libitum and fed twice da...

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