Ensayo cardiovalscular

CARDIOVASCULAR RESPONSE TO EXERCISE
M. Harold Laughlin
Department of Veterinary Biomedical Sciences, Department of Physiology, and Dalton
Cardiovascular Research Center, University of Missouri, Columbia, Missouri 65211
This article is intended for instructors who teach cardiovascular physiology. In our
physiology course exercise physiology is used as a tool to review and integratecardiovascular and respiratory physiology. It is assumed that the students already
have mastered the fundamentals of cardiovascular and respiratory physiology. Because
this paper is part of a cardiovascular refresher course, I have deleted much of the
respiratory physiology. The objectives of this presentation are for the student to 1)
understand the relationship between maximal oxygen consumption andendurance
during sustained exercise and be able to define ‘‘maximal oxygen consumption’’; 2)
understand the determinants of maximal oxygen consumption; 3) understand the effects
of dynamic exercise on the cardiovascular system and mechanisms for these effects; 4)
understand the relationships between exercise intensity and major cardiorespiratory
parameters, including heart rate, cardiacoutput, blood flow distribution, left ventricular
stroke volume, arterial pressures, total peripheral resistance, and arterial and venous
blood oxygen content; 5) be able to compare and contrast the cardiovascular effects of
dynamic and isometric exercise in man and the mechanisms responsible for the major
differences; and 6) be able to apply knowledge of the cardiovascular effects of exercise tounderstanding causes of cardiovascular symptoms in disease and in diagnosis of disease
states. This material contains many areas that stimulate discussion with students and
allow exploration of concepts that are challenging for the student. This give and take
between teachers and student is difficult to summarize in an article of this sort.
Therefore, subjects that in my experience oftenstimulate questions and discussion with
the students are indicated in the text.
AM. J. PHYSIOL. 277 (ADV. PHYSIOL. EDUC. 22): S244–S259, 1999.
Dynamic exercise produces the most striking burden
on the cardiorespiratory systems of any of the various
stresses encountered in normal life. The study of
exercise physiology provides an excellent method to
improve understanding of how the circulatoryand
respiratory systems respond and interact. Exercise
stress is also used clinically to evaluate and quantify the
severity of cardiovascular and/or respiratory disease.
Most of the cardiorespiratory effects of exercise are
related to supplying adequate oxygen and nutrients to
the working muscles. This task becomes more difficult
when the exercise is performed in a hot environment.
In thislecture we will only consider exercise in a
thermal-neutral environment. There are many forms
of physical activity that can be considered as exercise.
These can be grouped into two general types of
exercise: dynamic exercise (walking, running, cycling,
and swimming) and isometric exercise. We will
consider the cardiovascular effects of these two general
types of exercise separately. Indynamic exercise
there is a linear relationship between oxygen consumption
and exercise intensity up to the maximal amount
of oxygen a subject can consume.
A P S R E F R E S H E R C O U R S E R E P O R T
1043 - 4046 / 99 – $5.00 – COPYRIGHT r 1999 THE AMERICAN PHYSIOLOGICAL SOCIETY
VOLUME 22 : NUMBER 1 – ADVANCES IN PHYSIOLOGY EDUCATION – DECEMBER 1999
S244
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DETERMINANTS OF MAXIMAL OXYGEN
CONSUMPTION IN DYNAMIC EXERCISE
Figure 1A illustrates the time course of changes in
oxygen consumption from initiation of exercise. At
the onset of dynamic exercise, oxygen consumption
begins to increase, continues to increase over the first
minute of sustained exercise, and then plateaus as the
oxygen uptake and transport are increased...