An identical procedure was used in the anterior tibial artery, except that the anterior tibial artery was scanned, and the cuff was inflated to 70 mmHg above systolic pressure (or to a pressure sufficient to completely occlude flow as determined by real-time ultrasound for 7 minutes).
Sublingual nitroglycerin - The instrumentation for this was identical to that used during reactive hyperemia. Baseline measurements of brachial and anterior tibial artery diameters and arterial pressure were obtained. A 0.4 mg tablet of nitroglycerin was given to the subject sublingually. Three minutes later the brachial and anterior tibial artery diameters were continuously recorded (using two separate machines) for 3 additional minutes or until artery diameters returned to normal. The subject remained supine and had ECG and blood pressure monitored during this procedure.
This experiment has been discontinued as a bed rest standard measure and is now being conducted as part of the Gender Differences extramural research protocol. Results from the bed rest study indicate that flow-mediated dilation in the leg was significantly increased at bed rest day 49 (6% from pre-bed rest). Arterial responses to nitroglycerin differed in the arm and leg, but did not change as a result of bed rest. Anterior tibial artery intimal-medial thickness markedly decreased at bed rest days 21 (21%), 35 (22%), and 49 (19%). Several cardiac functional parameters, including isovolumic relaxation time (73 ms to 85 ms at day 7) and myocardial performance index, were significantly increased (0.41 to 0.49 by day 7 of bed rest; indicating a decrease in cardiac function) during bed rest. There was a trend for decreased orthostatic tolerance following 60 days of bed rest (P = 0.1). The data suggest that bed rest altered cardiovascular structure and function in a pattern similar to short-duration spaceflight. Additionally, the vascular alterations were primarily seen in the lower body, while vessels of the upper body were unaffected.