Left atrial pressure in normotensive and spontaneously hypertensive rats.

The left atrial pressure in adult spontaneously hypertensive rats (SHR) of the Okamoto strain and normotensive control rat (NCR) was measured via chronically implanted catheters. In SHR left atrial pressure in end-expiration was more than twice as high (10.3 +/- 0.4 mmHg) as in NCR (4.6 +/- 0.3 mmHg). There was no difference in the intrapleural pressure between the two groups of rats, therefore the enhanced left atrial pressure in SHR represents a real rise in the diastolic filling pressure of its left ventricle. This is considered to be the most important compensation for the earlier reported rightward shift of the Frank-Starling curve in SHR (Hallbäck, Isaksson & Noresson 1975, Noresson et al. 1979a). Without this compensation the stroke volume would have been drastically reduced for the hypertrophied heart.