Problems with the heart and blood vessels are popularly thought to be an inevitable part of ageing. But in fact most have a pathological origin or owe more to lifestyle than to ageing.
A change in one part of the cardiovascular system affects other parts. As a result, some problems may lead to others or else two different problems may have the same end results, such as heart failure. This often makes it hard to locate the site of a cardiovascular problem without extensive tests.
The normal structure and functioning of the cardiovascular system
The heart as a pump – mechanical aspects
Functionally, the heart can be thought of as two pumps. The right side pumps blood to the lungs, to take up oxygen, and the left side pumps the oxygenated blood to blood vessels that take it to the rest of the body.
Structurally, the heart comprises four chambers with muscle cells that contract mechanically. The upper two chambers are the atria. They receive blood from the main veins (the right side) and the lungs (the left side). The atria contract and force blood through the mitral and tricuspid valves, to the lower chambers (ventricles). These contract in turn, to squeeze blood out into the main artery (the aorta) from the left ventricle and to the lungs from the right ventricle. The heart as a pump - electrical activity
Cardiac muscle cells can contract mechanically, but they can also fire and conduct electrical action potentials. Each beat the heart makes is triggered by electrical impulses initiated at natural pacemaker cells (P cells) in the sino-atrial node. The impulses pass down the atrial walls, converge on the atrio-ventricular node, and from there move down the Bundle of His and so to the ventricle walls. The electrical activity of the heart can be detected by attaching conducting leads and electrodes to the skin at the chest. The electrical activity is directly plotted on a graph, the electrocardiograph (ECG). Heart sounds
Two sounds are heard with each beat of the heart:
* Lub – at closure of the mitral and tricuspid valves. * Dub – at closure of the aortic and pulmonary valves.
When the valves are diseased, the character of these sounds is altered and often distinctive murmurs can be heard.
Cardiac output
In this section we consider a few of the factors which affect normal cardiac output (the amount of blood ejected from the ventricle every minute).
Peripheral vascular resistance
Peripheral vascular resistance opposes steady blood flow at a blood vessel. It is:
* Related to the size of the blood vessel lumen (the smaller the lumen, the greater the resistance). * Measured by dividing mean arterial pressure by cardiac output.
Aortic impedance and arterial compliance
Aortic impedance opposes pulsatile blood flow. It is:
* Dynamic. * Related to the distensibility of the artery wall (arterial compliance).
Myocardial compliance is the distensibility of the heart muscle wall; it declines with age.
Preload
The filling volume of the left ventricle, preload, is affected by:
* Factors that influence blood return to the heart. * Mechanical properties of the heart.
Afterload
Afterload, or resistance to ejection of blood by the left ventricle, is affected by:
* A 75 year-old has only 10% of the pacemaker cells present in the sinus node of the heart of a healthy 20 year-old. This makes cardiac arrhythmias more likely in the older person.
* The left ventricle wall thickens and becomes stiffer. So its compliance decreases and its relaxation phase is prolonged. The end result is that early diastolic filling of the left ventricle reduces with age.
* The reduction in early diastolic filling of the left ventricle increases left ventricular end diastolic pressure, both at rest and during exercise. The left atrium enlarges as a result. So filling during atrial contraction increases. This compensates for the changes at the left ventricle, so that resting preload does not appear to change with age. However, older people are more susceptible to the effects of drugs and disease states that reduce preload (e.g. vasodilators, diuretics, nitrates – all used to treat conditions of the cardiovascular system). This is why drugs that affect preload are more likely to lead to orthostatic hypotension in the older person.
* The arteries become dilated and stiffen with age because of calcium deposits and changes in the amount and nature of elastin and collagen in their walls. (This is not to be confused with atherosclerosis.) This means that their compliance decreases.
* Peripheral vascular resistance also increases. As a result, afterload increases.
* An increase in afterload can result in a slight rise in systolic blood pressure. Untreated, this may increase the risk of heart problems.
* In the oldest-olds, diastolic blood pressure may slightly decrease. This occurs because as the aorta becomes more rigid, vascular resistance adjusts to compensate.
Physical work capacity (e.g. exercise), and the Frank-Starling mechanism
Cardiac output is increased during exercise, by the Frank-Starling mechanism, the name given to a sequence of physiological events.
1. This mechanism causes increases in diastolic filling of the left ventricle. 2. This leads to increases in venous return to the heart. 3. This in turn contributes to an increase in the ejected stroke volume.
Common cardiovascular problems in old age
Worldwide, cardiovascular problems are the most common causes of morbidity and mortality among people aged 65 years and over.
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Problems with the heart and blood vessels are popularly thought to be an inevitable part of ageing. But in fact most have a pathological origin or owe more to lifestyle than to ageing.
A change in one part of the cardiovascular system affects other parts. As a result, some problems may lead to others or else two different problems may have the same end results, such as heart failure. This often makes it hard to locate the site of a cardiovascular problem without extensive tests.
The normal structure and functioning of the cardiovascular system
The heart as a pump – mechanical aspects
Functionally, the heart can be thought of as two pumps. The right side pumps blood to the lungs, to take up oxygen, and the left side pumps the oxygenated blood to blood vessels that take it to the rest of the body.
Structurally, the heart comprises four chambers with muscle cells that contract mechanically. The upper two chambers are the atria. They receive blood from the main veins (the right side) and the lungs (the left side). The atria contract and force blood through the mitral and tricuspid valves, to the lower chambers (ventricles). These contract in turn, to squeeze blood out into the main artery (the aorta) from the left ventricle and to the lungs from the right ventricle. The heart as a pump - electrical activity
Cardiac muscle cells can contract mechanically, but they can also fire and conduct electrical action potentials. Each beat the heart makes is triggered by electrical impulses initiated at natural pacemaker cells (P cells) in the sino-atrial node. The impulses pass down the atrial walls, converge on the atrio-ventricular node, and from there move down the Bundle of His and so to the ventricle walls. The electrical activity of the heart can be detected by attaching conducting leads and electrodes to the skin at the chest. The electrical activity is directly plotted on a graph, the electrocardiograph (ECG).
Heart sounds
Two sounds are heard with each beat of the heart:
* Lub – at closure of the mitral and tricuspid valves.
* Dub – at closure of the aortic and pulmonary valves.
When the valves are diseased, the character of these sounds is altered and often distinctive murmurs can be heard.
Cardiac output
In this section we consider a few of the factors which affect normal cardiac output (the amount of blood ejected from the ventricle every minute).
Peripheral vascular resistance
Peripheral vascular resistance opposes steady blood flow at a blood vessel. It is:
* Related to the size of the blood vessel lumen (the smaller the lumen, the greater the resistance).
* Measured by dividing mean arterial pressure by cardiac output.
Aortic impedance and arterial compliance
Aortic impedance opposes pulsatile blood flow. It is:
* Dynamic.
* Related to the distensibility of the artery wall (arterial compliance).
Myocardial compliance is the distensibility of the heart muscle wall; it declines with age.
Preload
The filling volume of the left ventricle, preload, is affected by:
* Factors that influence blood return to the heart.
* Mechanical properties of the heart.
Afterload
Afterload, or resistance to ejection of blood by the left ventricle, is affected by:
* Peripheral vascular resistance.
* Aortic impedance.
Cardiovascular changes with age
* A 75 year-old has only 10% of the pacemaker cells present in the sinus node of the heart of a healthy 20 year-old. This makes cardiac arrhythmias more likely in the older person.
* The left ventricle wall thickens and becomes stiffer. So its compliance decreases and its relaxation phase is prolonged. The end result is that early diastolic filling of the left ventricle reduces with age.
* The reduction in early diastolic filling of the left ventricle increases left ventricular end diastolic pressure, both at rest and during exercise. The left atrium enlarges as a result. So filling during atrial contraction increases. This compensates for the changes at the left ventricle, so that resting preload does not appear to change with age. However, older people are more susceptible to the effects of drugs and disease states that reduce preload (e.g. vasodilators, diuretics, nitrates – all used to treat conditions of the cardiovascular system). This is why drugs that affect preload are more likely to lead to orthostatic hypotension in the older person.
* The arteries become dilated and stiffen with age because of calcium deposits and changes in the amount and nature of elastin and collagen in their walls. (This is not to be confused with atherosclerosis.) This means that their compliance decreases.
* Peripheral vascular resistance also increases. As a result, afterload increases.
* An increase in afterload can result in a slight rise in systolic blood pressure. Untreated, this may increase the risk of heart problems.
* In the oldest-olds, diastolic blood pressure may slightly decrease. This occurs because as the aorta becomes more rigid, vascular resistance adjusts to compensate.
Physical work capacity (e.g. exercise), and the Frank-Starling mechanism
Cardiac output is increased during exercise, by the Frank-Starling mechanism, the name given to a sequence of physiological events.
1. This mechanism causes increases in diastolic filling of the left ventricle.
2. This leads to increases in venous return to the heart.
3. This in turn contributes to an increase in the ejected stroke volume.
Common cardiovascular problems in old age
Worldwide, cardiovascular problems are the most common causes of morbidity and mortality among people aged 65 years and over.
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