Heart rate and blood pressure responses at the onset of dynamic exercise: effect of Valsalva manoeuvre.

The influence of respiration on the mean blood pressure (Pa) and R-R interval responses at the onset of dynamic exercise was studied in 15 healthy subjects who performed 4 s of unloaded cycling at 1.5-2.0 Hz, 4 s of Valsalva manoeuvre at 5.3 kPa, and a combination of both, each during a 12-s long apnoea at total lung capacity. The R-R intervals were obtained from the electrocardiogram, Pa was measured continuously by finger plethysmography, and intra-oral pressure was used to estimate the changes in intrapleural pressure. There was an immediate and significant shortening of the R-R intervals during exercise [mean (SE): 790 (20) to 642 (20) ms] that was not modified when Valsalva manoeuvre was added [783 (28) to 654 (21) ms]. Although 4 s of exercise alone did not alter Pa [13.8 (0.5) to 13.7 (0.7) kPa], this may indicate a pressor response, since Pa decreased during apnoea alone. When exercise was performed simultaneously with Valsalva manoeuvre, Pa increased significantly [13.6 (0.4) to 15.8 (0.5) kPa] and of similar magnitude during Valsalva alone [13.2 (0.4) to 15.3 (0.7) kPa]. In conclusion, 4 s of unloaded cycling elicited a fast R-R shortening with no change in Pa from rest. A concomitant Valsalva manoeuvre had no effect on the R-R interval response but caused a marked increase in Pa. From these findings, it is suggested that respiratory influences should be controlled in studies concerned with the cardiovascular responses at the onset of dynamic exercise.