Aging of the Adult Heart. In: Sperelakis N, editor. Physiology and Pathophysiology of the Heart. Boston: Springer US; 1984. pp. 575-92. [DOI: 10.1007/978-1-4757-1171-4_27]

Hemodynamic adaptations to stress with advancing age

With advancing adult aging an increase in vascular stiffness, an increase in systolic, pulse and mean arterial pressure, modest left ventricular hypertrophy, and a moderate decline in early diastolic filling rate have uniformly been observed. In some individuals these changes are not associated with enhanced systemic resistance if arterial pressure remains within the normotensive range. End-systolic volume, stroke volume, ejection fraction, velocity of ejection, and cardiac output are preserved in these elderly subjects. In other individuals both aortic impedance and peripheral vascular resistance are increased with age and modest declines in resting stroke volume and cardiac output have been observed. During maximal exercise a diminished heart rate and a diminished reduction of end-systolic volume occur in elderly subjects. In some, an enhanced end-diastolic volume prevents a reduction in or enhances stroke volume (Starling mechanism); this adaptation bears a striking resemblance to that observed during exercise when the beta-adrenergic system is pharmacologically inhibited. In other elderly subjects, stroke volume during exercise does not increase to the extent that it does in younger subjects. Even in these subjects in whom peak cardiac output during exercise declines, however, it is not entirely clear that the central circulation limits peak oxygen consumption (VO2). The nonuniformity of results of studies that have investigated the effect of aging on cardiac function and vascular resistance suggests that variables that impact on cardiovascular function other than aging per se, i.e. life style variables, e.g. nutrition, smoking, physical conditioning status, or the prevalence of occult coronary disease, differed among the various subjects studied.

The transverse tubular system of the hypertrophic myocardium: morphology and morphometry in spontaneous hypertensive rats (SHR)

We reported previously on a modified Golgi stain that, in conjunction with high voltage electron microscope stereoscopy, gives striking views of the elaborate network of the transverse tubular system (T system) in rat myocardium. In this report we used the same techniques to study three-dimensional arrangements of the T system in the left ventricular myocardium of spontaneous hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). High voltage electron microscope stereoscopy revealed distinctive morphological characteristics of the T system, such as undulating running, short dead-end branches, and labyrinth-like tubular aggregates in the hypertrophic myocardium of SHR. Quantitative analysis of the SHR T system indicated a surface area greater than that of WKY. These findings may support the hypothesis that making an additional T system membrane will compensate for the smaller surface-to-volume ratio. However, the normal regulatory mechanism required to maintain the surface-to-volume ratio does not function properly in SHR, resulting in morphological abnormalities and functional disturbances of the myocardium.

Morphometric analysis of cardiac hypertrophy during development, maturation, and senescence in spontaneously hypertensive rats

Hypertrophy of the mammalian heart, regardless of the initiating event, results in architectural remodeling of ventricular components that maintain structural and functional characteristics of this organ. Ventricular components that vary their morphology and morphometry in a hypertrophic state are the muscle cells, connective tissue elements, vasculature, or a combination of some or all of the above. Morphologic quantification of the progressive tissue changes occurring throughout the natural life span of the spontaneously hypertensive and normotensive Wistar-Kyoto rats has not been thoroughly documented. Using perfused-fixed tissue from both strains at 1, 6, 12, 18, and 24 months of age, we have determined the morphometric changes that occurred in the subepicardial and midwall regions of the left ventricle. Myocyte cell size, wall thickness, and arterial blood pressure were elevated in 1-month-old spontaneously hypertensive rats, reached significance by 6 months, and remained significantly greater throughout the 24 months examined. Tissue morphometry demonstrated significant tissue component volumetric differences at 6 months in the spontaneously hypertensive rat. Age-related morphometric tissue changes occurred in both strains yet were exacerbated (percent volume of myocytes) or diminished (percent volume interstitial space) in the mature and aging spontaneously hypertensive rat. Capillary density of SHR left ventricle showed a drastic decline so that 6-month-old SHR had the same density as a senescent Wistar-Kyoto. Tissue morphometry and capillary density data strongly support the hypothesis that tissue oxygenation is diminished in the spontaneously hypertensive rat, and as a result, tissue necrosis and myocyte cell death occur.