Effect of Nitrite on Exercise Physiology and Metabolism
Status:
Terminated
Trial end date:
2013-08-16
Target enrollment:
Participant gender:
Summary
This study will examine how nitrite infusions affect exercise tolerance (how much a person
can exercise before having to stop). Exercise ability is limited by how fast oxygen can be
delivered to the body and how fast the body can produce energy. Both of these processes are
affected by nitric oxide (NO), a gas produced by cells that line blood vessels. NO is
important in regulating blood vessel dilation, and consequently, blood flow. Nitrite may act
as a storehouse for nitric oxide and be able to improve exercise tolerance.
Healthy normal volunteers between 21 and 45 years of age who can use an exercise bicycle may
be eligible for this study. Candidates are screened with a medical history, physical
examination, electrocardiogram, breathing tests, blood tests, and a pregnancy test for women
who are able to bear children. Pregnant women are excluded from the study. The screening
session includes practice exercise on the bicycle.
Participants exercise on a stationery exercise bicycle for about 30 minutes on each of two
study days. During the test, they breathe in and out of a mouthpiece that allows inhaled and
exhaled respiratory gases to be measured. Before subjects begin to exercise, a small tube is
placed in the artery of their forearm inside the elbow. A longer tube called a central line
is placed in a deeper vein in the neck after the area has been numbed. A thinner tube, called
a pulmonary artery catheter, is placed through the central line and advanced into the
chambers of the heart, through the heart valve, and into the lung artery. This catheter
measures various pressures directly in the heart and lungs. Blood samples are drawn through
the catheter also, to avoid the need for multiple needle sticks. Another tube is placed in
the vein of the other arm to deliver medications.
Thirty minutes after all the tubes are placed, a blood sample is drawn for baseline
measurements. Then, either saline (sterile salt water) or nitrite is injected into the tube
in the arm vein. Thirty minutes after the injection, the subject starts exercising on the
bicycle. The work setting on the bicycle is increased every minute, and the subject pedals
until he or she is too tired to continue. During the test, a small blood sample is collected
every 2 minutes. Heart rate, blood pressure, and heart rhythms are continuously monitored.
After the test on the first day, participants are admitted to the hospital to rest for the
remainder of the afternoon and evening. The tubes are kept in place for the following
morning, when the procedure is repeated exactly as before, except that subjects who received
saline the first day are given nitrite the second day, and vice versa.
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