Failure of prostaglandins to modulate the time course of blood flow during dynamic forearm exercise in humans.

The time course and magnitude of increases in brachial artery mean blood velocity (MBV; pulsed Doppler), diameter (D; echo Doppler), mean perfusion pressure (MPP; Finapres), shear rate (gamma = 8.MBV/D), and forearm blood flow (FBF = MBV.pi r2) were assessed to investigate the effect that prostaglandins (PGs) have on the hyperemic response on going from rest to rhythmic exercise in humans. While supine, eight healthy men performed 5 min of dynamic handgrip exercise by alternately raising and lowering a 4.4-kg weight (approximately 10% maximal voluntary contraction) with a work-to-rest cycle of 1:1 (s/s). When the exercise was performed with the arm positioned below the heart, the rate of increase in MBV and gamma was faster compared with the same exercise performed above the heart. Ibuprofen (Ibu; 1,200 mg/day, to reduce PG-induced vasodilation) and placebo were administered orally for 2 days before two separate testing sessions in a double-blind manner. Resting heart rate was reduced in Ibu (52 +/- 3 beats/min) compared with placebo (57 +/- 3 beats/min) (P < 0.05) without change to MPP. With placebo, D increased in both arm positions from approximately 4.3 mm at rest to approximately 4.5 mm at 5 min of exercise (P < 0.05). This response was not altered with Ibu (P > 0.05). Ibu did not alter the time course of MBV or forearm blood flow (P > 0.05) in either arm position. The gamma was significantly greater in Ibu vs. placebo at 30 and 40 s of above the heart exercise and for all time points after 25 s of below the heart exercise (P < 0.05). Because PG inhibition altered the time course of gamma at the brachial artery, but not FBF, it was concluded that PGs are not essential in regulating the blood flow responses to dynamic exercise in humans.

Forearm blood flow by Doppler ultrasound during test and exercise: tests of day-to-day repeatability.

The between-day repeatability of simultaneous measures of brachial artery diameter (D) (echo Doppler) and mean blood velocity (MBV) (pulsed Doppler) was tested during rest and exercise. On 3 separate days, six volunteers performed one trial of 1-min rest followed by a step increase in dynamic handgrip exercise for 4 min which required the lifting and lowering of a 4.4-kg weight (approximately 8-12% MVC) in a 1s/2s (work/rest) cadence. Measures for MBV and D were collected continuously on a beat-by-beat basis during the transition from rest to end exercise. The mean rest values over one min, and single data points at 30, 60, 120, and 240 s of exercise were extracted from the time series data. At all exercise time points, MBV was greater than rest (P < 0.05), but these levels were not different across test days. Arterial D at all exercise time points ranged from 3.8 +/- 0.1 mm to 4.1 +/- 0.1 mm (mean +/- SEM) and did not differ from rest (3.9 +/- 0.1 mm) (P > 0.05), nor did D differ between days. The mean between-day coefficient of variation for D was 4.08 +/- 0.7% at rest and ranged from 2.90 +/- 0.4% to 3.96 +/- 0.5% during exercise. The coefficient of variation for MBV was 13.2 +/- 2.6% at rest and reached 20.2 +/- 3.1% during the final min of exercise; the exercise variability was reduced to 14.9 +/- 2.4% by averaging MBV over 3 s (the duration of a contraction/relaxation duty cycle) (P < 0.05) with no further advantage of averaging over ten 60-s sample periods. The data indicate that, for the six subjects tested, Doppler ultrasound measures of arterial MBV and diameter during both rest and exercise were reproducible across different test days and can be used as a reliable, noninvasive means of testing hypotheses pertaining to blood flow control.