RELATIONSHIP BETWEEN EXTERNAL RESISTANCES, LUNG-FUNCTION CHANGES AND MAXIMAL EXERCISE CAPACITY

In upper airway obstruction (UAO) the relationship between the degree of obstruction, exercise limitation and lung function indices is not w ell established,Therefore, we investigated in nine healthy subjects (a ge 36+/-9 yrs) the effects of two added resistances at the mouth (R1= added resistance with 7.8 mm diameter; R2 = 5.7 mm) on forced expirato ry volume in one second (FEV1), peak expiratory flow (PEF), airway res istance (Raw) and maximal breathing capacity (measured during 15 s = m easured maximum breathing capacity (MBCm); calculated as FEV1x37.5 =: calculated maximum breathing capacity (MBCc)) on the one hand, and max imum exercise capacity (W'max), minute ventilation (V'E) and CO2 elimi nation (V'CO2) on the other. We found that R1 had almost no influence on FEV1 but decreased PEF by similar to 35% and increased Raw by almos t 300%; it decreased W'max by merely similar to 10% while maximal exer cise ventilation (V'Emax) was only 65% of control and only reached sim ilar to 40% MBCc and similar to 70% MBCm; yet V'E and V'CO2, were sign ificantly reduced at high exercise levels indicating hypoventilation, With R2, FEV1 was reduced by 25% and PEF by 55%, and Raw was increased by 600%; W'max: was similar to 60% of control, V'Emax was only 35% of control and reached similar to 30% MBCc and similar to 60% MBCm, V'E was already reduced at moderate exercise levels. We conclude that : 1) an upper airway obstruction of 6 mm diameter (but not of 8 mm) had a marked influence on maximum exercise capacity due to hypoventilation; 2) calculated maximum breathing capacity markedly overestimated measur ed maximum breathing capacity because the forced expiratory volume in one second is an insensitive index of upper airway obstruction and bec ause it does not take inspiratory flow limitation into account; and 3) a 10% decrease in maximum exercise capacity was linearly related with a 7% decrease in the forced expiratory volume in one second and a 150 % increase in airway resistance. A 10% decrease in maximal exercise ve ntilation was related to a 8.5% decrease in peak expiratory flow and 9 % decrease in measured maximum breathing capacity.