Role of aortic input impedance in the decreased cardiovascular response to exercise with aging in dogs.

The diminished cardiac output response to exercise with advancing age may be attributable to intrinsic inability of the old ventricle to respond appropriately and/or to an additional loading imposed upon the ventricle by the aged vascular system. The steady (resistance) and pulsatile (characteristic impedance) load components together comprise the vascular load faced by the ejecting ventricle. To study the effect of exercise on both vascular components of load, the aortic input impedance was measured in chronically instrumented young and old beagle dogs during graded treadmill exercise before and after beta blockade. Ascending aortic flow was measured by a cuff electromagnetic flow probe, and pressure was measured by a high-fidelity semiconductor transducer. At low levels of exercise the old animals demonstrated a striking 20% increase in characteristic impedance and a 28% decrease in peripheral resistance with no increase in stroke volume. This vascular loading and limitation in stroke volume persisted across the higher exercise levels. In contrast, the young group demonstrated no increase in characteristic impedence, a progressive decrease in peripheral resistance, and a progressive increase in stroke volume across the same exercise levels. These age differences in vascular response and ventricular output were abolished by beta blockade. The groups did not demonstrate a difference in heart rate response, but the young had a greater increase in external left ventricular power than the old across exercise. These data demonstrated a profound difference in the response of young and old vasculature to exercise. At low and intermediate exercise levels the pulsatile vascular load appeared to be a major factor in the limitation of stroke volume in old dogs. At high levels of exercise, the limited exercise response in the old dog may be caused in part by a diminished inotropic responsiveness as well as by the vascular loading.

[1]  B JONSSON,et al.  CIRCULATION IN HEALTHY OLD MEN, STUDIED BY RIGHT HEART CATHETERIZATION AT REST AND DURING EXERCISE IN SUPINE AND SITTING POSITION. , 2009, Acta medica Scandinavica.

[2]  R H Jones,et al.  Effect of age on the response of the left ventricular ejection fraction to exercise. , 1980, The New England journal of medicine.

[3]  T. Takishima,et al.  Effects of changes in the aortic input impedance on systolic pressure-ejected volume relationships in the isolated supported canine left ventricle. , 1980, Cardiovascular research.

[4]  W. Nichols,et al.  Aortic input impedance during nitroprusside infusion. A reconsideration of afterload reduction and beneficial action. , 1979, The Journal of clinical investigation.

[5]  J. Ross,et al.  Effects of Alterations in Aortic Input Impedance on the Force‐Velocity‐Length Relationship in the Intact Canine Heart , 1979, Circulation research.

[6]  E. Lakatta,et al.  Age-associated decrease in heart rate response to isoproterenol in dogs , 1979, Mechanisms of Ageing and Development.

[7]  E. Lakatta,et al.  Diminished Inotropic Responsiveness to Ouabain in Aged Rat Myocardium , 1979, Circulation research.

[8]  E. Lakatta,et al.  Age-associated decrease in ventricular response to haemodynamic stress during beta-adrenergic blockade. , 1978, British heart journal.

[9]  G. Motté,et al.  Evaluation of the elasticity and characteristic impedance of the ascending aorta in man. , 1978, Cardiovascular research.

[10]  W E Walker,et al.  Input Impedance of the Systemic Circulation in Man , 1977, Circulation research.

[11]  R. Miller,et al.  Pharmacological Mechanisms for Left Ventricular Unloading in Clinical Congestive Heart Failure: Differential Effects of Nitropmsside, Phentolamine, and Nitroglycerin on Cardiac Function and Peripheral Circulation , 1976, Circulation research.

[12]  J. Fleisch,et al.  The Relationship between Age and Relaxation of Vascular Smooth Muscle in the Rabbit and Rat , 1976, Circulation research.

[13]  J. Kennedy,et al.  BLOOD FLOW IN ARTERIES (2nd ed) , 1975 .

[14]  E. Lakatta,et al.  Diminished Inotropic Response of Aged Myocardium to Catecholamines , 1975, Circulation research.

[15]  J. A. Snow,et al.  Chronic vasodilator therapy in the management of cardiogenic shock and intractable left ventricular failure. , 1974, Annals of internal medicine.

[16]  C. E. Martin,et al.  Autonomic mechanisms in hemodynamic responses to isometric exercise. , 1974, The Journal of clinical investigation.

[17]  N. Westerhof,et al.  Pressure and Flow Generated by the Left Ventricle against Different Impedances , 1973, Circulation research.

[18]  R. Sannerstedt,et al.  Sympathetic nervous activity during exercise in relation to age. , 1971, Cardiovascular research.

[19]  J. Ross,et al.  Effects of decreased aortic compliance on performance of the left ventricle. , 1968, The American journal of physiology.

[20]  M. O'Rourke.  Steady and pulsatile energy losses in the systemic circulation under normal conditions and in simulated arterial disease. , 1967, Cardiovascular research.

[21]  J. D. Bargainer,et al.  Hydraulic Power Associated with Pulmonary Blood Flow and its Relation to Heart Rate , 1966, Circulation research.

[22]  A. Guz,et al.  Effects of Alterations in Aortic Impedance on the Performance of the Ventricles , 1964, Circulation research.

[23]  T. Strandell.  HEART RATE, ARTERIAL LACTATE CONCENTRATION AND OXYGEN UPTAKE DURING EXERCISE IN OLD MEN COMPARED WITH YOUNG MEN. , 1964, Acta physiologica Scandinavica.

[24]  D. J. Patel,et al.  Hydraulic input impedance to aorta and pulmonary artery in dogs. , 1963, Journal of applied physiology.