THE CORRELATION OF CARDIAC MASS WITH ARTERIAL HEMODYNAMICS OF RESISTIVE AND CAPACITIVE LOAD IN RATS WITH NORMOTENSION AND ESTABLISHED HYPERTENSION

In hypertensive animals and humans, cardiac hypertrophy may occur as a consequence of an external load on the heart. Several studies have su ggested that the non-pulsatile components of arterial haemodynamics, s uch as arterial pressure and vascular resistance, do not adequately re present the ventricular afterload and are not well correlated with the degree of cardiac hypertrophy (CH). The present study was undertaken to analyse the correlation between the degree of CH and various haemod ynamic parameters in the spontaneously hyper hypertensive rat (SHR) wi th established hypertension. A total of 36 SHRs (6-8 months) with a ta il-cuff pressure above 190 mm Hg were used. Control data were obtained from 32 age-matched normotensive Wistar Kyoto rats (WKY). Animals wer e anaesthetized with pentobarbitone sodium (40 mg/kg i.p.) and artific ially ventilated with a respirator. A Millar catheter with a high-fide lity pressure sensor was used to record the aortic pressure and an ele ctromagnetic flow transducer to monitor the aortic flow. The pressure and flow signals were subjected to Fourier transformation for the anal ysis of the arterial impedance spectrum. The left ventricular weight-t o-body weight ratio (LVW/BW) was taken as a measure of the degree of C H. The measured haemodynamic parameters in these anaesthetized, open-c hest SHRs were systolic pressure (SP) (mean +/- SE) 172 +/- 4 mm Hg, d iastolic pressure (DP), 120 +/- 3 mm Hg, pulse pressure 52 +/- 2 mm Hg , peripheral resistance (R(p)) 344,032 +/- 8,012 dyne . s . cm(-5), ch aracteristic impedance (Z(c)) 6,442 +/- 313 dyne . s . cm(-5), the imp edance modulus at the first harmonic (Z1) 26,611 +/- 1,061 dyne . s . cm(-5), mean arterial compliance (C-m) 0.87 +/- 0.04 mu l/mm Hg and LV W/BW 3.092 +/- 0.026 mg/g. These parameters were significantly greater than the corresponding values in WKY, except that C-m was much decrea sed. In SHR, the LVW/BW was not significantly correlated with the SP, DP, R(p) and steady external power. In contrast, the degree of CH was positively correlated with Z(c) (r = 0.66, P < 0.001), Z1 (r = 0.62, P < 0.001) and pulsatile external work (r = 0.41, P < 0.05). It was als o positively correlated with the backward pressure wave (r = 0.42, P < 0.05) and negatively correlated with C-m (r = -0.72, P < 0.01). Such correlations of LVW/BW with pulsatile haemodynamics were not found in the normotensive WKY. The results indicate that the degree of cardiac hypertrophy in hypertensive rats, with a high blood pressure and incre ased stiffness of the arterial tree, is more closely related to pulsat ile arterial haemodynamics than to the nonpulsatile components.