Page 314 - Clinical Application of Mechanical Ventilation

280 Chapter 10

TABLE 10-3 Conditions Leading to High Pulse Pressure

Condition Example

High stroke volume Hypervolemia

Noncompliant blood vessel Arteriosclerosis
Abnormal heart rate Bradycardia
Heart Block
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systolic and diastolic pressures are affected by stroke volume and vascular compli-
ance, pulse pressure can be used to assess the gross changes in stroke volume and
blood vessel compliance. High pulse pressure may occur in conditions where the
stroke volume is high, blood vessel compliance is low, or heart rate is low. Low
pulse pressure may occur in conditions where the stroke volume is low, blood vessel
compliance is high, or heart rate is high (Christensen, 1992a, 1992b).
High (Wide) Pulse Pressure. High pulse pressure (.40 mm Hg) can occur with an
Pulse pressure is the
difference between arterial increasing systolic pressure or a decreasing diastolic pressure. The systolic pressure
systolic and diastolic pressures may be increased when the stroke volume is increased or the blood vessel compli-
(normal 30 mm Hg to
40 mm Hg). ance is decreased. As long as the diastolic pressure does not increase by the same
proportion, a high pulse pressure results. Bradycardia may also lead to a higher
pulse pressure because a slow heart rate allows the blood volume more time for
diastolic runoff and causes a lower diastolic pressure. The conditions that may lead
to a high pulse pressure are summarized in Table 10-3.
High pulse pressure may be an important risk factor for heart disease. In elderly
patients, a 10 mm Hg rise in pulse pressure increases the risk of major cardiovascular
complication and mortality by about 20% (Blacher et al., 2000).
Low (Narrow) Pulse Pressure. By the same mechanism, a decreased stroke volume or
an increased blood vessel compliance leads to a corresponding decrease in systolic
pressure. A low pulse pressure (,30 mm Hg) is seen as long as the diastolic pres-
sure does not decrease by the same proportion. Tachycardia may also lead to a lower
pulse pressure because a high heart rate provides less time for diastolic runoff and
causes a higher diastolic pressure. The conditions leading to a low pulse pressure are
summarized in Table 10-4.

TABLE 10-4 Conditions Leading to Low Pulse Pressure

Condition Example

Low stroke volume Congestive Heart Failure

High compliance blood vessel Septic Shock
Abnormal heart rate Tachycardia
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