Changes in short-term variability of blood pressure and heart rate during the development of obesity-associated hypertension in high-fat fed dogs

Objective To investigate the nature and time course of autonomic nervous sy stem changes elicited by a 21-week ad libitum high-fat diet (HFD) in dogs. Results The HFD increased body weight (+22.0 +/- 2.8% at week 21) with an a bdominal circumference gain significantly more elevated than the thoracic o ne. The increases in insulin and free fatty acid plasma levels were correla ted with body weight changes, Systolic and diastolic blood pressures and he art rate significantly increased (+23 +/- 6, +28 +/- 5 and 19 +/- 9% respec tively). Arterial hypertension was characterized by an increase in cardiac output (+22.3 +/- 7.7%), in left ventricular mass (+18.1 +/- 5.0% at week 2 1) and a decrease in spontaneous baroreflex efficiency (-55 +/- 6%). The ti me course of autonomic changes (using spectral analysis of systolic blood p ressure and heart rate) showed the existence of time-dependent modification s, which were linked with food intake. The initial rise in arterial blood p ressure during body weight increment (observed between the 1st and 8th week of HFD) was associated with a transient increase in the low frequency band of systolic blood pressure variability and noradrenaline plasma levels ass ociated with a long-lasting decrease in the high frequency band of heart ra te variability. Early changes in short-term variability were significantly correlated with free fatty acid plasma levels. In contrast, the steady-stat e of obesity-related hypertension was associated with a decreased high freq uency band of heart rate variability, without significant changes in noradr enaline plasma levels. Conclusions This study shows that the HFD induces abdominal obesity, hyperi nsulinaemia and arterial hypertension, with a left ventricular hypertrophy associated with a biphasic changes in autonomic activity: an early and long -lasting decrease in parasympathetic nervous system activity and an early b ut transient increase in sympathetic activity, The present data suggest tha t autonomic nervous system changes are dependent on the time course of obes ity development, J Hypertens 1999, 17:1135-1143 (C) Lippincott Williams & W ilkins.