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Influence of p2-Adrenergic Receptor Genotype on Airway Function During Exercise in Healthy Adults: Subject Characteristics

Published in Pulmonary Function

Influence of p2-Adrenergic Receptor Genotype on Airway Function During Exercise in Healthy Adults: Subject CharacteristicsThe demographic data were examined using independent t tests with an a = 0.05. We used analysis of variance to examine differences in the primary outcome measure, FEF50 (SPSS; Chicago, IL). An analysis of covariance was also performed between the groups with epinephrine as the covariate and FEF50 as the dependent variable. Prior to beginning the study, and based on previous data from our laboratory on measures of FEF50 at rest and during exercise (and the changes observed with exercise), we estimated that we could detect a difference between genotype groups (homozygous Arg16 vs Gly16) for the percentage change from baseline of 3.5% with n = 16 and n = 26, respectively, for the groups with 85% power.
Subject characteristics did not differ significantly between genotype groups (Table 1). Baseline pulmonary function did not differ between the groups, although absolute lung volumes and flow rates tended to be slightly higher in the Gly16 subjects relative to the Arg16 subjects. Both groups of subjects demonstrated small but significant increases in FEF50 and the average forced expiratory flow over the middle portion of the vital capacity (FEF25-75) with the inhaled P-agonist (p < 0.05). No significant differences, however, were observed between groups: FEV1, + 4.0 ± 1.1% vs + 4.0 ± 1.0%; FEF50, + 14.0 ± 5.0% vs + 15.0 ± 2.0%; and FEF25-75, + 18.3 ± 4.2 vs + 16.6 ± 3.0% for the Arg16 and Gly16 groups, respectively. http://buy-asthma-inhalers-online.com/

Both groups exercised at similar workloads (38 ± 2% vs 36 ± 6% and 75 ± 4% vs 75 ± 6% of peak work for the Arg16 and Gly16 groups, respectively, and percentages of their peak V02 (Table 2) during low- and high-intensity exercise. The Arg16 subjects tended to have a more tachypneic ventilatory response with a lower tidal volume (Vt) than the Gly16 subjects, particularly at the higher exercise intensity, even when normalized for VC (p < 0.01), while respiratory rate was faster at rest and throughout exercise (p < 0.01). Inspiratory capacity, expressed as a percentage of pre-exercise FVC, was significantly higher, indicating a lower end-expiratory lung volume in the Gly16 subjects at 40% and 75% of maximal work (69% vs 65% of FVC at both work intensities in the Gly16 vs Arg16 groups, respectively; p < 0.05).

Table 1—Subject Characteristics, Baseline Pulmonary Function, and Maximal Exercise Data According to Genotype

Variables Arg/Arg (n = 16) Gly/Gly (n = 26)
Female gender, % 56 58
Age, yr 29 ± 2 30 ± 1
Height, cm 171 ± 2 171 ± 2
Weight, kg 67 ± 3 72 ± 2
Body mass index, kg/m2 23 ± 1 25 ± 1
FVC, L (% predicted) 4.51 ± 0.23 (100 ± 3) 4.74 ± 0.19 (100 ± 2)
FEVb L (% predicted) 3.73 ± 0.18 (99 ± 3) 4.00 ± 0.17 (99 ± 2)
FEF50, L/s (% predicted) 4.54 ± 0.25 (98 ± 5) 4.72 ± 0.29(98 ± 4)
Urine sodium, mEq/L/d 73 ± 8 68 ± 4
Peak workload, W 185 ± 15 197 ± 10
Peak Vo2, mL/kg/min 32 ± 2 33 ± 1

Table 2—Ventilatory Response to Exercise According to fi2AR Genotype

Variables Rest 40% Peak Work 75% Peak Work
Arg/Arg Gly/Gly Arg/Arg Gly/Gly Arg/Arg Gly/Gly
‘Vo2, % of peak 13 ± 1 11 ± 1t 53 ± 2 52 ± 1 86 ± 2 86 ± 2
Minute ventilation, L/min 11 ± 1 9 ± 1t 33 ± 2 34 ± 1 68 ± 4 69 ± 4
Vt, L 0.80 ± 0.08 0.88 ± 0.07 1.68 ± 0.13 1.80 ± 0.12 2.10 ± 0.15 2.43 ± 0.141
Vt/VC, % 19 ± 2 19 ± 1 39 ± 2 41 ± 2 51 ± 2 56 ± 2
Respiratory rate, breaths/min 16 ± 1 14 ± 1 26 ± 1 23 ± 1 38 ± 2 33 ± 2