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At least 811 records · Page 45Linked to original sources
PubMed1993

Expiratory flow limitation and regulation of end-expiratory lung volume during exercise.

To investigate the impact of expiratory flow limitation (FL) on breathing pattern and end-expiratory lung volume (EELV), we imposed a small expiratory threshold load for a few breaths during exercise in nine volunteers (29-62 yr): six were healthy and three had mild-to-moderate airflow obstruction (67-71% predicted forced expiratory volume in 1 s). Six subjects showed evidence of FL, i.e., tidal expiratory flow impinging on maximal forced expiratory flow, at one or more exercise levels. Whenever an expiratory threshold load was imposed, mean expiratory flow decreased (P < 0.02) in association with an increased expiratory time (TE; P < 0.05). When the load was imposed during non-FL conditions, TE increased less than expiratory flow decreased and EELV tended to increase. In contrast, during FL, with the load, TE increased more than expiratory flow decreased, subjects did not achieve maximal expiratory flow until a lower volume, and EELV decreased (P < 0.001). Under both FL and no-FL conditions, unloading reversed the changes associated with loading. These data indicate that the increase in EELV during exercise is linked to the occurrence of FL. We suggest that compression of airways downstream from the flow-limiting segment may elicit a reflex mechanism that influences breathing pattern by terminating expiration prematurely, thus increasing EELV.

Adult↗
PubMed2001

The effects of carbon dioxide on exercise-induced asthma: an unlikely explanation for the effects of Buteyko breathing training.

OBJECTIVES: To examine the effect of breathing 3% CO2 on exercise-induced asthma (EIA), as a raised airway CO2 level is suggested to mediate the effects of Buteyko breathing training (BBT). DESIGN: Double-blind crossover study, using a standard laboratory-based exercise challenge, with EIA defined as a fall of 15% or greater in the forced expiratory volume in one second (FEV1) within 30 minutes of completing a standard exercise protocol. SUBJECTS: 10 adults with confirmed EIA. INTERVENTION: Air enriched with 3% CO2 during and for 10 minutes after exercise. OUTCOME MEASURES: Maximum percentage fall in FEV1 after exercise. Area under curve (AUC) of the decrease in FEV1 with time. RESULTS: Mean maximum fall in FEV1 was similar: 19.9% with air, and 26.9% with 3% CO2 (P = 0.12). The mean AUC for the total 30-minute post-exercise period was 355 for air and 520 for 3% CO2 (P = 0.07). After discontinuing the 3% CO2 at 10 minutes after exercise, there was a further and sustained fall in FEV1. Mean AUC for the period 10-30 minutes post-exercise was significantly greater for CO2 than air (275 and 137, respectively [P = 0.02]). Mean minute ventilation was increased when subjects exercised breathing 3% CO2: 77.5 L/min for 3% CO2, compared with 68.7 L/min for air (P = 0.02). CONCLUSION: Breathing 3% CO2 during exercise does not prevent EIA. The shape of the FEV1 response curve after 3% CO2 suggests that a greater degree of EIA (because of increased minute ventilation during exercise) was opposed by a direct relaxant effect of CO2 on the airway. Increased airway CO2 alone is an unlikely mechanism for the reported benefits of BBT; nevertheless, further study of the effects of voluntary hypoventilation in asthma is warranted.

Administration, Inhalation↗
PubMed1990

Significance of airway resistance for the pattern of breathing and lung volumes in exercising humans.

The effects of increased airway resistance on lung volumes and pattern of breathing were studied in eight subjects performing leg exercise on a cycle ergometer. Airway resistance was changed 1) by increasing the density (D) of the respired gas by a factor of 4.2 and changing the inspired gas from O2 at 1.3 bar to air at 6 bar and 2) by increasing airway flow rates by exposing the subjects to incremental work loads of 0-200 W. Increased gas D caused a slower and deeper respiration at rest and during exercise and, at work loads greater than 120 W, depressed the responses of ventilation and mean inspiratory flow. Raised airway resistance induced by increases in D and/or airway flow rates altered respiratory timing by increasing the ratio of inspiratory time (TI) to total breath duration. Furthermore, analyses of the relationships between tidal volume and TI and between end-inspiratory volume and TI revealed elevation of Hering-Breuer inspiratory volume thresholds. We propose that this elevation, and hence exercise-induced increases of tidal volume, can largely be explained by previous observations that the threshold of the inspiratory off-switch mechanisms depends on central inspiratory activity (cf. C. von Euler, J. Appl. Physiol. 55: 1647-1659, 1983), which in turn increases with airway resistance (Acta Physiol. Scand. 120: 557-565, 1984).

Airway Resistance↗
PubMed1981

[Work of breathing during high altitude exercise].

Measurements of oxygen consumption, ventilation and dynamic respiratory work in three males during ergometer bicycle exercise at sea level and at 3500 m altitude are reported. At submaximal work load, dynamic respiratory work proved 140-180% greater at 3500 m than at sea level; at a given ventilation, on the other hand, dynamic respiratory work is 20% less at 3500 m. During maximum oxygen consumption, this respiratory work reaches its peak value at 5800 m a.s.l. (30% more than what it is at sea level). It can be stated that the altitude ventilation cost during exercise is nothing but a small portion of total oxygen expenditure because the energy required for a given work load is not significantly different from sea level controls.

Adult↗
PubMed1980

Blood lactate after strenuous exercise with and without breath-holding.

Lactic acid concentration of venous blood was determined in healthy male subjects after strenuous exercise with and without breath-holding. It was found that in all subjects the peak and total values of lactate during recovery was higher in the breathing run than in the breath-holding run, though the running time was the same.

Adult↗