A cycle is the combination of one rarefaction and one compression equals one cycle.

Bicycle stress echocardiography can be used instead of treadmill. Bicycle exercise is particularly useful for patients with valvular heart disease or for evaluated pulmonary artery pressures. It is also used as a substitute for treadmill exercise testing when the heart performance at each stage of exercise needs to be assessed and the patient is capable of bicycle exercise. Bicycle stress echocardiography has no additional risk compared to routine exercise.

See also M-Mode Echocardiography.

(F) The number of cycles of a periodic process per unit time. Frequency and wavelength are inversely related. The higher the frequency the smaller the wavelength. The frequency of ultrasound is expressed in units of hertz (Hz), where 1 Hz = 1 cycle per second.
The effect of different frequencies on tissue penetration:
The higher the frequency the less the penetration, the lower the frequency the greater the penetration. As frequency increases, resolution improves but the imaging depth or penetration decreases. The lower the axial resolution, the more detail can be seen.
Usual frequencies for pediatric ultrasound: 5.0mHz to 7.5mHz and 10mHz.
Usual frequencies for adult ultrasound: 2.0mHz to 3.0mHz.

See also Doppler Interrogation Frequency, Multi-frequency Probe, and Huygens Principle.

Stress echocardiograms are used for detection of coronary artery disease, or to determine the cardiac performance. Stress echocardiograms are less performed to evaluate pulmonary artery pressures, pulmonary hypertension or the significance of valvular heart disease.
Stress increases the degree to which the heart contracts. After a myocardial infarction there will be a region of the heart muscle that contracts abnormal at rest. This area may worsen with stress. A coronary artery blockage most often do not impairs the function of the heart at rest. With stress, a region of the heart does not receive enough blood to work effectively and wall motion abnormalities occur. The echocardiographer compares rest and exercise and can determine the presence and severity of a coronary artery blockage.

Stress echocardiograms involve:
A bicycle stress echocardiogram involves transthoracic echocardiography performed at the rest baseline and after or during different stages of physical exercise.
A dobutamine stress echocardiography uses the drug dobutamine instead physical exercise.
Transthoracic echocardiograms are routinely performed during stress and rest.
Cardiovascular stress represents a minimal risk to the patient.

See also Transesophageal Echocardiography, Echocardiography, M-Mode, Curved Transducer, Doppler Ultrasound, History of Ultrasound and History of Ultrasound Contrast Agents.

Cardiac ultrasound, also known as echocardiography or echocardiogram, is used to provide several different levels and types of heart testing. Cardiac ultrasound utilizes the same ultrasound principles as used for obstetric and gynecologic evaluations of pregnant women, gallbladder ultrasound and other abdominal structures.
The ultrasound is directed out of a hand held probe which can be moved to image the heart from different positions. Additionally, so that heart events can be timed, ECG leads are placed on the chest. The reflected wave is converted into an actual image of the heart and displayed in a real-time mode or M-mode ultrasound format. M-mode recordings permit measurement of cardiac dimensions and detailed analysis of complex motion patterns depending on transducer angulations. Also the time relationships with other physiological variables such as ECG, heart sounds, and pulse tracings, can be recorded simultaneously. A stress echocardiogram provides information about the cardiac performance.
Two-dimensional tomographic images of selected cardiac sections give more information than M-mode about the shape of the heart and also show the spatial relationships of its structures during the cardiac cycle (diastole to systole).

See also M-Mode Echocardiography, and Myocardial Contrast Echocardiography.