THE CIRCULATORY SYSTEM. 429 



HYPERTROPHY. 



Hypertrophy may involve the walls of one or more or all the cavities 

 of the heart. While the wall of a ventricle is thickened, its cavity may 

 retain its normal size simple hypertrophy ; or be dilated excentrlc hyper- 

 trophy ; or it may be contracted concentric hypertrophy. 



Care should always be exercised in judging of this condition, for a 

 firmly contracted heart seems to have a small cavity and thick walls. 

 The existence of such a condition as concentric hypertrophy is denied by 

 some authors. Excentric hypertrophy is the most common form. Sim- 

 ple hypertrophy is not common, but may occur in connection with the 

 atrophied kidneys of chronic diffuse nephritis. The muscle tissue in 

 hypertrophied hearts is firmer and denser than normal, and is apt to have 

 a darker color. Fatty degeneration may, however, be associated with 

 it, giving the walls a lighter appearance. It is probable that the increase 

 of tissue in the hypertrophied heart wall is the result of increase both in 

 size and uumber of the muscle fibres. ' 



Hypertrophy of both ventricles increases both the length and breadth 

 of the heart. Hypertrophy of the left ventricle (alone) increases its 

 length. The apex is then lower and farther to the left than usual. Hy- 

 pertrophy of the right ventricle (alone) increases the breadth of the 

 heart toward the right side ; but sometimes the right edge of the heart 

 retains its normal situation and the apex is displaced to the left. With 

 large hypertrophy of both ventricles, the base of the heart may sink, so 

 that its long axis approaches a horizontal direction. 



Hypertrophied hearts may weigh from forty to fifty ounces, or even 

 more. 



Hypertrophy of the heart may depend upon a variety of conditions 

 which increase its work. 



1. Changes in the valves; either insufficiency or stenosis in the 

 valves leading from a cavity, and insufficiency in valves leading to a 

 cavity, may induce hypertrophy of its walls. 



2. Obstruction to the passage of blood through the arterial system, 

 as in arterio-sclerosis and other lesions of the arteries; congenital or 

 acquired stenosis of the aorta or other vessels, pressure of tumors, etc. , 

 on vessels. Certain forms of chronic diffuse nephritis, especially atro- 

 phied kidneys, lead to hypertrophy of the left ventricle, and sometimes 

 secondarily to hypertrophy of the right ventricle. 



3. Obstruction to the passage of blood through the pulmonary artery 

 by stenosis or by certain diseases of the lungs, particularly emphysema 

 and chronic phthisis, may lead to hypertrophy of the right ventricle, 

 and, secondarily, of the right auricle and left ventricle. 



4. Any cause, whether muscular or nervous, which increases the ra- 

 pidity and force of the heart's contractions, may induce hypertrophy. 



1 For a suggestive study of cardiac hypertrophy see Welch, " Adaptation in Patho- 

 logical Processes." Trans. Congr. of American Physicians and Surgeons, vol. iv., 1807. 



