- In contrast to action potentials in neurons,
the spike in cardiac action potentials is followed by a plateau
phase that lasts 0.2–0.3 s. Whereas the action potential
for skeletal muscle and nerves is due to the abrupt opening of fast
sodium channels in the cell membrane, in cardiac muscle it is due
to the opening of both fast sodium channels (the spike) and slower
calcium channels (the plateau).
- Halothane, enflurane, and isoflurane depress
sinoatrial (SA) node automaticity. These agents appear to have only
modest direct effects on the atrioventricular (AV) node, prolonging
conduction time and increasing refractoriness. This combination
of effects likely explains the frequent occurrence of junctional
tachycardia when an anticholinergic is administered for sinus bradycardia
during inhalation anesthesia; junctional pacemakers are accelerated
more than those in the SA node.
- Studies suggest that all volatile anesthetics
depress cardiac contractility by decreasing the entry of Ca2+ into
cells during depolarization (affecting T- and L-type calcium channels),
altering the kinetics of its release and uptake into the sarcoplasmic
reticulum, and decreasing the sensitivity of contractile proteins
- Because the normal cardiac index (CI) has a wide
range, it is a relatively insensitive measurement of ventricular
performance. Abnormalities in CI therefore usually reflect gross
- In the absence of hypoxia or severe anemia, measurement
of mixed venous oxygen tension (or saturation) is the best determination
of the adequacy of cardiac output.
- Because the atrial contribution to ventricular
filling is important in maintaining low mean ventricular diastolic
pressures, patients with reduced ventricular compliance are most
affected by loss of a normally timed atrial systole.
- Cardiac output in patients with marked right
or left ventricular impairment is very sensitive to acute increases
- The ventricular ejection fraction, the fraction
of the end-diastolic ventricular volume ejected, is the most commonly
used clinical measurement of systolic function.
- Left ventricular diastolic function can be assessed
clinically by Doppler echocardiography on a transthoracic or transesophageal
- Because the endocardium is subjected to the
greatest intramural pressures during systole, it tends to be most
vulnerable to ischemia during decreases in coronary perfusion pressure.
- The failing heart becomes increasingly dependent
on circulating catecholamines. Abrupt withdrawal in sympathetic
outflow or decreases in circulating catecholamine levels, such as
can occur following induction of anesthesia, may lead to acute cardiac
Anesthesiologists must have a thorough understanding of cardiovascular
physiology both for its scientific significance in anesthesia and
for its practical applications to modern patient management. This
chapter reviews the physiology of the heart and the systemic circulation
and the pathophysiology of heart failure. The pulmonary circulation
and the physiology of blood and nutrient exchange are discussed
in Chapters 22 and 28,
The circulatory system consists of the heart, the blood vessels,
and the blood. Its function is to provide oxygen and nutrients to
the tissues and to carry away the by-products of metabolism. The heart
propels blood through two vascular systems arranged in series. In
the pulmonary ...