Biomedical Engineering Reference
In-Depth Information
Long-term regulation is mediated mostly by the kidneys because they regulate the
body's salt and water content, which control blood pressure. Sodium retention is controlled
by the Na pump, as regulated by the hormone aldosterone. This is in turn regulated by
the hormones rennin and angiotensin. If sodium is retained, the blood osmotic pressure
rises, which causes water to be retained. Water reabsorption in the kidney is through
water channels in the kidney tubules, and these are controlled by the antidiuretic hormone
(ADH). If ADH is present in high concentrations, water absorption will be high and blood
pressure will rise.
8.2.5 Heart Disease
Cardiovascular disease can be divided into two main categories: coronary heart disease
(CHD) and congestive heart failure (CHF).
CHD is caused primarily by hardening of the arteries within the heart. This hardening
process is due to deposits of fat and cholesterol (plaque) on the inner walls of the arteries,
which reduces their diameter and impairs blood flow. The heart tries to compensate by
pumping harder, but sufferers often exhibit symptoms of a lack of oxygen resulting in
fatigue as well as severe chest pains.
Congestive heart disease arises when the heart no longer pumps blood efficiently. This
leads to an accumulation of blood in the lungs—hence the congestion. Once again, the
heart needs to work harder to provide sufficient oxygen to the body, which can lead to
excessive wear and tear on the already enfeebled organ. As the disease progresses, patients
suffer from shortness of breath and palpitations.
Many sufferers of heart disease are ineligible for heart transplants for the following
reasons:
• Age of more than 65 years.
• High pressure in the lung arteries due to permanent changes in the lung blood
vessels.
• Irreversible kidney or liver dysfunction not caused by underlying heart failure.
• Symptomatic arterial diseases in the legs, kidneys, neck, or brain.
• Severe chronic lung disease including emphysema, asthma, and chronic bronchitis.
• Chronic infection in the blood, lung, urine, or elsewhere or open wound.
• Insulin-dependent diabetes with evidence of damage to other organs, such as kidney,
retina, or nerves.
• Cancer within the past 5 years. Exceptions may be made for some types of early
skin cancer or under other very unusual circumstances.
• Other life-threatening diseases likely to severely limit length or quality of life even
if the transplant were successful.
In some of these cases, the best alternative is a total artificial heart or a left ventricle
assist device (LVAD).
8.2.6 Biomechatronic Perspective
From a biomechatronic perspective, the cardiovascular system offers a rich environment
for measurement, stimulation, and the development of various prostheses. The state of the
cardiovascular system can be determined by measuring the changing blood pressure as the
