Cardiac Physiology Quotes

Dyspnea during pregnancy may be “physiologic” but still requires evaluation insofar as it may represent respiratory or cardiac illness.

■Skeletal and smooth muscle cells (but not cardiac muscle cells) are elongated, and for this reason, they are called muscle fibers.

Cardiac muscle tissue occurs only in the heart (the body’s blood pump), where it constitutes the bulk of the heart walls. Like skeletal muscle cells, cardiac muscle cells are striated (see Figure 4.9b, p. 139), but cardiac muscle is not voluntary. Indeed, it can and does contract without being stimulated by the nervous system. Most of us have no conscious control over how fast our heart beats.

with every beat—about 20 percent less cardiac output than men. Less oxygenated blood means we have to breathe more often, and as a consequence, our respiratory muscles—such as the diaphragm and intercostals between our ribs—need to work harder and use a lot of energy. Like other skeletal muscles, the contracting respiratory muscles require enough blood flow to meet oxygen demand. If you have a greater oxygen cost of breathing, you also likely dedicate a greater amount of blood flow toward your respiratory muscles during maximal exercise.