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Regulation of Stroke Volume

Regulation of Stroke Volume The stroke volume is regulated by three variables: the end-diastolic volume (EDV), which is the volume of blood in the ventricles at the end of diastole; the total peripheral resistance, which is the frictional resistance, or impedance to blood flow, in the arteries; and the contractility, or strength, of ventricular contraction. The end-diastolic volume is the amount of blood in the ven- tricles immediately before they begin to contract. This is a work- load imposed on the ventricles prior to contraction, and thus is sometimes called a preload. The stroke volume is directly proportional to the preload; an increase in EDV results in an increase in stroke volume. (This relationship is known as the Frank-Starling law of the heart, discussed shortly.) The stroke volume is also directly proportional to contractility; when the ventricles contract more forcefully,...
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Sleep ( physiology )

Sleep Although environmental factors affect sleep, there is evidence that sleep is genetically controlled. This is shown by sleep dis- orders that run in families and the heritability of sleep patterns. Histamine and several other neurotransmitters promote wake- fulness, while adenosine and GABA promote sleep. The neural control of sleep and arousal is discussed in conjunction with the reticular activating system in section 8.4. Two categories of sleep are recognized. Dreams—at least those that are vivid enough to recall upon waking—occur dur- ing rapid eye movement (REM) sleep. The name describes the characteristic eye movements that occur during this stage of sleep. The remainder of the time sleeping is spent in non-REM, or resting, sleep. These two stages of sleep can also be distin- guished by their EEG patterns. The EEG pattern during REM sleep consists of theta waves (5 to 8 cycles per second), although the EEG is often desynchronized as in...
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What types of medicines can treat heart failure?

Many different types of medicines help treat heart failure. Some of the more common types are: ACE inhibitors : Widen your blood vessels to lower blood pressure so your heart doesn't have to work as hard, and help your kidneys get rid of extra water Beta-blockers : Slow your heart rate so your heart doesn't have to work as hard, and can help a stiff heart relax so it fills with blood better Diuretics (water pills) : Help your kidneys get rid of the extra water by making you urinate more If you have very bad heart failure that isn’t responding to medicines, doctors may suggest a heart transplant or a mechanical device that helps pump blood.
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