THE CHEMOREFLEX IN 7???9 YEAR OLD BOYS AND GIRLS

Abstract

Differences in cardiovascular responses to static exercise have been reported between boys and girls (Verhaaren et al, J. Appl. Physiol., 1994). PURPOSE: Investigate possible mechanisms responsible for these differences. METHODS Heart rate (HR) and blood pressure (BP) were measured in 35 boys and 35 girls (7–9 yrs old) during 3 min of static handgrip exercise (SHG) at 30% maximal voluntary contraction, followed by 4 min of blood flow occlusion (OCL) in the previously exercised arm, and then 6 min of recovery (REC). RESULTS Maximal SHG was significantly (p ≤ 0.05) higher in boys than girls (19.7 vs 16.5 kg). Maximal SHG reliability was high for both boys (reported elsewhere) and girls (R=0.95). During the 3-min SHG HR (19.4 vs 16.1%), systolic (18.0 vs 15.1%), and diastolic (34.1 vs 32.8%) BP increased the same for boys and girls, respectively. During OCL systolic (51.4 vs 55.3%) and diastolic (42.5 vs 47.0%) BP dropped similarly during minute one in both boys and girls, respectively, yet remained above baseline the entire period. In both boys and girls DBP remained significantly (p ≤ 0.05) above baseline during OCL. SBP also remained significantly above baseline all four minutes of OCL in boys while in girls SBP significance above baseline was only reached during minute one. During minute one of REC systolic (22.5 vs 20.4%) and diastolic (20.4 vs 15.4%) BP decreased in both boys and girls, respectively. In girls DBP remained significantly above baseline for the first minute of REC while in boys it remained significantly above baseline for four minutes. HR in both boys and girls fell to baseline during OCL and remained there throughout REC. CONCLUSION The drop in HR to baseline during post-exercise ischemia with a concomitant maintenance of BP significantly above baseline indicates differential control of the cardiovsacular system in children as has been reported in adults. There is no difference in chemoreflex between young boys and girls since BP responded similarly during OCL and REC.