Effect of β-adrenergic blockade on <img src="/fulltext-image.asp?format=htmlnonpaginated&src=J2608P43633155M8_html\421_2004_Article_BF00713500_TeX2GIFIE1.gif" border="0" alt=" $$\left( {\dot VO_2 } \right)$$ " /> kinetics during pseudorandom binary sequence exercise

The effect of β-adrenergic blockade on the dynamic response characteristics of oxygen uptake <img src="/fulltext-image.asp?format=htmlnonpaginated&src=J2608P43633155M8_html\421_2004_Article_BF00713500_TeX2GIFIE2.gif" border="0" alt=" $$\left( {\dot VO_2 } \right)$$ " /> was examined in seven healthy men. Cycle ergometer exercise consisted of a pseudorandom binary sequence (PRBS) with 15 units per sequence, each unit lasting 15 s, for a total period of 225 s. Work rate was either 25 W or 125 W. Six identical sequences were performed continuously in a single exercise test. Each subject was studied on three occasions after 48 h treatment of placebo (CON); a nonselective β-blocker, propranolol (PROP); and a β₁-selective blocker, metoprolol (MET). <img src="/fulltext-image.asp?format=htmlnonpaginated&src=J2608P43633155M8_html\421_2004_Article_BF00713500_TeX2GIFIE3.gif" border="0" alt=" $$\dot V_{O_2 } $$ " /> was measured breath-by-breath. The data were analyzed in the frequency domain by Fourier analysis to yield amplitude and phase shift coefficients for the relationship between the input work rate and output <img src="/fulltext-image.asp?format=htmlnonpaginated&src=J2608P43633155M8_html\421_2004_Article_BF00713500_TeX2GIFIE4.gif" border="0" alt=" $$\dot V_{O_2 } $$ " />. Time domain analysis was performed on the cross-correlational analysis of <img src="/fulltext-image.asp?format=htmlnonpaginated&src=J2608P43633155M8_html\421_2004_Article_BF00713500_TeX2GIFIE5.gif" border="0" alt=" $$\dot V_{O_2 } $$ " /> (output) · work rate (input) to determine the total lag time. The amplitude of the <img src="/fulltext-image.asp?format=htmlnonpaginated&src=J2608P43633155M8_html\421_2004_Article_BF00713500_TeX2GIFIE6.gif" border="0" alt=" $$\dot V_{O_2 } $$ " /> · W⁻¹ relationship was lower (P<0.0022) and the phase shift was greater (P<0.0039) with β-blockade compared to CON; no differences were found between PROP and MET. The total lag time was longer (P<0.0053) in PROP (34.3±2.2s) and MET (34.4±1.6s) compared to CON (29.8±1.3s). These data indicate that β-adrenergic blockade causes a significant slowing of kinetics of the O₂ transport system as determined by both frequency and time domain analysis. In addition, the PRBS exercise test is a sensitive indicator of change in function of the O₂ transport system.