title: Evidence for a rapid vasodilatory contribution to immediate hyperemia in rest-to-mild and mild-to-moderate forearm exercise transitions in humans.
abstract: Controversy exists regarding the contribution of a rapid vasodilatory mechanism(s) to immediate exercise hyperemia. Previous in vivo investigations have exclusively examined rest-to-exercise (R-E) transitions where both the muscle pump and early vasodilator mechanisms may be activated. To isolate vasodilatory onset, the present study investigated the onset of exercise hyperemia in an exercise-to-exercise (E-E) transition, where no further increase in muscle pump contribution would occur. Eleven subjects lay supine and performed a step increase from rest to 3 min of mild (10% maximal voluntary contraction), rhythmic, dynamic forearm handgrip exercise, followed by a further step to moderate exercise (20% maximal voluntary contraction) in each of arm above (condition A) or below (condition B) heart level. Beat-by-beat measures of brachial arterial blood flow (Doppler ultrasound) and blood pressure (arterial tonometry) were performed. We observed an immediate increase in forearm vascular conductance in E-E transitions, and the magnitude of this increase matched that of the R-E transitions within each of the arm positions (condition A: E-E, 52.8 +/- 10.7 vs. R-E, 60.3 +/- 11.7 ml.min(-1).100 mmHg(-1), P = 0.66; condition B: E-E, 43.2 +/- 12.8 vs. R-E, 33.9 +/- 8.2 ml.min(-1).100 mmHg(-1), P = 0.52). Furthermore, changes in forearm vascular conductance were identical between R-E and E-E transitions over the first nine contraction-relaxation cycles in condition A. The immediate and identical increase in forearm vascular conductance in R-E and E-E transitions within arm positions provides strong evidence that rapid vasodilation contributes to immediate exercise hyperemia in humans. Specific vasodilatory mechanisms responsible remain to be determined.
authors.affiliation: School of Physical and Health Education, Queen's University, Kingston, Ontario, Canada K7L 3N6.
authors.forename: Natasha R
authors.initials: NR
authors.lastname: Saunders
authors.forename: Michael E
authors.initials: ME
authors.lastname: Tschakovsky
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D001783:Blood Flow Velocity; D015444:Exercise; D005260:Female; D005542:Forearm / Q000098:blood supply / Q000503:physiopathology; D006801:Humans; D006940:Hyperemia / Q000503:physiopathology*; D008297:Male; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000098:blood supply* / Q000503:physiopathology*; D005082:Physical Exertion; D012146:Rest; D014664:Vasodilation