Tuesday, February 19, 2008

Flow-mediated vasodilation

They're not just passive pipes anymore. No longer do scientists view our blood vessels as mere conduits that carry blood from heart to bod and back again. The worthy endothelial cells that line our arteries and veins not only respond to signals from the kidneys and adrenal glands to dilate and constrict, they actively produce substances themselves that affect their functioning.

One way that researchers test the health of blood vessels is through an indirect method called flow-mediated vasodilation (FMV). This test, an indirect measure of the ability of the arterial system to respond to increased demand, is performed by pumping up a blood pressure cuff on the subject's arm to some intolerable level for a few minutes, releasing it, and then calculating the subsequent surge of blood flow through the brachial artery at the elbow with ultrasound technology.

A small study from Italy looked at the effects of a high-fat meal on blood vessel reactivity in ten postmenopausal women. The ladies were invited down to the lab for an 'oral fat load,' doubtless a large piece of tiramisu. At two hourly intervals thereafter, their FMV was measured. At baseline, the ladies sent nearly 8% more blood coursing through their fingertips after the cuff was removed. Two hours after the high-fat treat, this number fell by two-thirds, meaning that their blood vessels' capacity to dilate in response to increased blood flow fell by over 60%.

Theoretically, then, a high fat meal, whether consumed in a fast food joint or as part of an Atkins diet, can wreak havoc in an individual with unsuspected coronary artery disease. A burst of activity after the feast, say a sprint up the block to catch a bus, calls on diseased arteries to provide extra blood flow at a time when they are clamped down from a load of Nacho Belle Grande. When blood supply can't keep up with demand, the oxygen-starved portion of the heart can be damaged.

Air pollution, cigarette smoke, and early morning hours all can muck up your FMV. Vitamin E, oatmeal, dark chocolate, green tea, JuicePlus, and ACE inhibitors (a class of blood pressure meds that includes lisinopril and enalopril) all support your endothelial cells to expand on demand.


rlbates said...

I really like that dark chocolate is on the list along with the greens.

JeanMac said...

Terrific post - read in a magazine (Preven*ion?),that it's good to drink a warm tea or other fluid after a meal to help - not sure if it's based on medical fact but now I end my dinner with a cuppa.

Mauigirl said...

What an interesting post! And I love your way of explaining it (Tiramasu, indeed!).

Very helpful information, will make sure not to run for a bus after a fat-laden meal. I remember one time we got out of a taxi in NYC and ran about 5 blocks to make it to a concert in time. The whole time my 50-something husband and I (also already 50-something) were doing this I was thinking "Please don't let us have a heart attack and die." Luckily we hadn't eaten any fatty meals beforehand so we survived!