Flow-mediated dilation (FMD) refers to

dilation Dilation (or dilatation) may refer to: Physiology or medicine * Cervical dilation, the widening of the cervix in childbirth, miscarriage etc. * Coronary dilation, or coronary reflex * Dilation and curettage, the opening of the cervix and surgic ...

(widening) of an

artery An artery (plural arteries) () is a blood vessel in humans and most animals that takes blood away from the heart to one or more parts of the body (tissues, lungs, brain etc.). Most arteries carry oxygenated blood; the two exceptions are the pul ...

when blood flow increases in that artery. The primary cause of FMD is release of

nitric oxide Nitric oxide (nitrogen oxide or nitrogen monoxide) is a colorless gas with the formula . It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes denoted by a dot in its che ...

endothelial cell The endothelium is a single layer of squamous endothelial cells that line the interior surface of blood vessels and lymphatic vessels. The endothelium forms an interface between circulating blood or lymph in the lumen and the rest of the vessel ...

s. To determine FMD,

brachial artery The brachial artery is the major blood vessel of the (upper) arm. It is the continuation of the axillary artery beyond the lower margin of teres major muscle. It continues down the ventral surface of the arm until it reaches the cubital fossa ...

dilation following a transient period of forearm ischemia is measured using

ultrasound Ultrasound is sound waves with frequency, frequencies higher than the upper audible limit of human hearing range, hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hea ...

. Because the value of FMD can be compromised when improperly applied, attempts have been made to standardize the methodology for measuring FMD.

Clinical significance

FMD is a noninvasive measure of blood vessel health (

endothelial dysfunction In vascular diseases, endothelial dysfunction is a systemic pathological state of the endothelium. Along with acting as a semi-permeable membrane, the endothelium is responsible for maintaining vascular tone and regulating oxidative stress by ...

) which (when low) is at least as predictive of

cardiovascular disease Cardiovascular disease (CVD) is a class of diseases that involve the heart or blood vessels. CVD includes coronary artery diseases (CAD) such as angina and myocardial infarction (commonly known as a heart attack). Other CVDs include stroke, h ...

as traditional risk factors. Major cardiovascular disease associated with low FMD include cardiac death,

myocardial infarction A myocardial infarction (MI), commonly known as a heart attack, occurs when blood flow decreases or stops to the coronary artery of the heart, causing damage to the heart muscle. The most common symptom is chest pain or discomfort which may ...

, and

stroke A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop functionin ...

. Low FMD is a stronger predictor of future cardiovascular disease events in patients with existing cardiovascular disease than in healthy normal persons. FMD is a sensitive marker for the amount of blood vessel damage caused by cigarette smoke. So-called light cigarettes (having reduced tar and nicotine) were shown to impair FMD as much as regular cigarettes. Improved FMD results in greater perfusion and oxygen supply to peripheral tissue. An Israeli study of 618 healthy subjects found FMD to be an excellent predictor of long-term adverse cardiovascular events. Participants with below-mean FMD were 278% more likely to experience cardiovascular events during the 4.6 year average follow-up period than participant with above-mean FMD (95%

Confidence Interval In frequentist statistics, a confidence interval (CI) is a range of estimates for an unknown parameter. A confidence interval is computed at a designated ''confidence level''; the 95% confidence level is most common, but other levels, such as 9 ...

: 135-571%,

p-value In null-hypothesis significance testing, the ''p''-value is the probability of obtaining test results at least as extreme as the result actually observed, under the assumption that the null hypothesis is correct. A very small ''p''-value means ...

<0.001). The clinical value of FMD is limited by the fact that FMD is difficult to measure, requiring a skilled and well-trained clinician.

Effects of exercise

A study of healthy young men who normally take over 10,000 steps per day, but were restricted to less than 5,000 steps per day for five days showed impaired FMD in the popliteal (leg) artery, but not the brachial (arm) artery. The reduction of leg FMD caused by prolonged sitting can be reduced by

fidgeting Fidgeting is the act of moving about restlessly in a way that is not (socially recognized as) essential to ongoing tasks or events. Fidgeting may involve playing with one's fingers, hair, or personal objects (e.g. glasses, pens or items of cloth ...

(periodic leg movement). An eight-week program of brisk walking resulted in a 50% increase in brachial artery FMD in middle-aged and older men, but failed to produce this benefit in

estrogen Estrogen or oestrogen is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal acti ...

-deficient post-

menopausal Menopause, also known as the climacteric, is the time in women's lives when Menstruation, menstrual periods stop permanently, and they are no longer fertility, able to bear children. Menopause usually occurs between the age of 47 and 54. Medic ...

women. Forty-five minutes of cycling exercise before sitting has been shown to eliminate the impaired leg FMD due to three hours of sitting. Athletes over age 40 show greater FMD than their age-matched peers. A

meta-analysis A meta-analysis is a statistical analysis that combines the results of multiple scientific studies. Meta-analyses can be performed when there are multiple scientific studies addressing the same question, with each individual study reporting me ...

of 182 subjects showed twice the improvement in FMD resulting from

high-intensity interval training High-intensity interval training (HIIT) is a training protocol alternating short periods of intense or explosive anaerobic exercise with brief recovery periods until the point of exhaustion. HIIT involves exercises performed in repeated quick bu ...

compared to

endurance training Endurance training is the act of exercising to increase endurance. The term endurance training generally refers to training the aerobic system as opposed to the anaerobic system. The need for endurance in sports is often predicated as the need o ...

References

{{reflist Medical diagnosis Cardiovascular diseases

Clinical significance

Effects of exercise

See also

References