Regulation of ventilatory capacity during exercise in asthmatics

Abstract

In asthmatic and control subjects, we examined the changes in ventilatory capacity (VECap), end-expiratory lung volume (EELV), and degree of flow limitation during three types of exercise: 1) incremental, 2) constant load (50% of maximal exercise capacity; 36 min), and 3) interval (alternating between 60 and 40% of maximal exercise capacity; 6-min workloads for 36 min). The VECap and degree of flow limitation at rest and during the various stages of exercise were estimated by aligning the tidal breathing flow-volume (F-V) loops within the maximal expiratory F-V (MEFV) envelope using the measured EELV. In contrast to more usual estimates of VECap (i.e., maximal voluntary ventilation and forced expiratory volume in 1 s x 40), the calculated VECap depended on the existing bronchomotor tone, the lung volume at which the subjects breathed (i.e., EELV), and the tidal volume. During interval and constant-load exercise, asthmatic subjects experienced reduced ventilatory reserve, higher degrees of flow limitation, and had higher EELVs compared with nonasthmatic subjects. During interval exercise, the VECap of the asthmatic subjects increased and decreased with variations in minute ventilation, due in part to alterations in their MEFV curve as exercise intensity varied between 60 and 49% of maximal capacity. In conclusion, asthmatic subjects have a more variable VECap and reduced ventilatory reserve during exercise compared with nonasthmatic subjects. The variations in VECap are due in part to a more labile MEFV curve secondary to changes in bronchomotor tone. Asthmatics defend VECap and minimize flow limitation by increasing EELV.

Pulmonary hyperinflation a clinical overview

“…Increasing hyperinflation appears to be a consequence of expiratory flow limitation. In mild asthma, as in healthy subjects, FRC may fall during light exercise, but in heavier exercise it increases again as flow limitation develops [61]. This pattern is similar to that seen in healthy elderly subjects, in whom flow limitation at lower lung volumes can occur during heavy exercise [61].…”

Advanced Mechanical Ventilatory Constraints During Incremental Exercise in Class III Obese Male Subjects

“…28 The expiratory flow limitation was expressed as the percentage of the tidal volume over which expiratory flow met or exceeded the maximum flow-volume envelope flow at the same lung volume. 20 The ventilatory response to exercise was determined below and above ventilatory threshold by least squares regression as described previously.…”

Lungs And Legs: Entrainment Of Breathing To Locomotion In Highly Trained Distance Runners

“…Graphs can be generated for different intensities of exercise, with the tidal flow-volume loops produced during exercise plotted within a larger reference expiratory flow-volume loop obtained from a maximal breathing maneuver during rest. This method has been widely used to assess the degree of expiratory flow limitation and ventilatory constraint (Aaron et al, 1992;Babb et al, 1991;Chapman et al, 1998;Derchak et al, 2000;Grimby, 1969;Johnson et al, 1991aJohnson et al, ,b, 1992Johnson et al, , 1995Marciniuk et al, 1994;McClaran et al, 1999;Martinez et al, 1996;Mota et al, 1999;Regnis et al, 1996;Stubbing, 1980a). Indeed, Bye et al (1983) suggest that pulmonary flow-volume characteristics are perhaps the most important determinant of exercise limitation because of their implications for matching ventilation to metabolic demand.…”

“…Indeed, Bye et al (1983) suggest that pulmonary flow-volume characteristics are perhaps the most important determinant of exercise limitation because of their implications for matching ventilation to metabolic demand. The degree of flow limitation during exercise is commonly expressed as the percent of the tidal volume that meets or exceeds the expiratory boundary of the maximal flow-volume loop (Johnson et al, 1995(Johnson et al, , 1991a1999a,b) ( Figure 2). However, unlike the use of a minimal value of S a O 2 to determine the presence of EIH, there is no accepted minimal value for the percent of tidal volume overlapping the maximal flow-volume loop to determine the presence of flow limitation.…”

“…With intense exercise, expiratory flow limitation in athletes increases to greater than 50% of the tidal volume, representing a severe mechanical ventilatory constraint (Johnson et al, 1999a). Even in the face of additional ventilatory stimuli, these flow-limited athletes are unable to increase V E during maximal exercise (Chapman et al, 1998;Johnson et al, 1992 It has been argued that flow limitation prevents a full expiration, causing an increase in end-expiratory lung volume (EELV) (Johnson et al, 1995;Pellegrino et al, 1993), which has been observed in patients with pulmonary disease (Grimby & Stiksa, 1970;Leaver & Pride, 1971;Potter et al, 1971;Stubbing et al, 1980b), older, highly-fit individuals (Johnson et al, 1991a), and elite endurance athletes (Grimby et al, 1971;Jensen et al, 1980;Mota et al, 1999). In contrast, EELV decreases in healthy, unfit subjects with exercise (Aliverti et al, 1997;Babb et al, 1991;Henke et al, 1988;Younes & Kivinen, 1984), by 0.1 to 0.3 liter during mild exercise and 0.5 to 1.0 liter during intense exercise (Henke et al, 1988).…”