Absence of long-term modulation of ventilation by dead-space loading during moderate exercise in humans |
| |
Authors: | A J Cathcart N Herrold A P Turner J Wilson S A Ward |
| |
Institution: | (1) School of Sport and Exercise Sciences, University of Leeds, Leeds, LS2 9JT, UK;(2) Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow, G12 8QQ, UK;(3) Department of Physical Education, Sport and Leisure Studies, University of Edinburgh, Edinburgh, EH8 8AQ, UK |
| |
Abstract: | The stability of arterial PCO2 (PaCO2) during moderate exercise in humans suggests a CO2-linked control that matches ventilation (E) to pulmonary CO2 clearance (CO2). An alternative view is that E is subject to long-term modulation (LTM) induced by hyperpnoeic history. LTM has been reported with associative conditioning via dead-space (VD) loading in exercising goats (Martin and Mitchell 1993). Whether this prevails in humans is less clear, which may reflect differences in study design (e.g. subject familiarisation; VD load; whether or not E is expressed relative to CO2; choice of PaCO2 estimator). After familiarisation, nine healthy males performed moderate constant-load cycle-ergometry (20 W-80 W-20 W; <lactate threshold, L): day 1, pre-conditioning, n=3; day 2, conditioning (VD=1.59 l, doubling E at 20 W and 80 W), n=8 with 10 min rest between tests; and, after 1 h rest, post-conditioning, n=3. Gas exchange was determined breath-by-breath. Post-conditioning, neither the transient phase 1, phase 2 (1, 2)] nor steady-state E exercise responses, nor their proportionality to CO2, differed from pre-conditioning. For post-conditioning trial 1, steady-state E was 28.1 (4.7) l min–1 versus 29.1 (3.8) l min–1 pre-conditioning, and mean-alveolar PCO2 (a validated PaCO2 estimator) was 5.53 (0.48) kPa 41.5 (3.6) mmHg] versus 5.59 (0.49) kPa 41.9 (3.7) mmHg]; the 1 E increment was 4.2 (2.9) l min–1 versus 5.2 (1.9) l min–1; the 2 E time-constant () was 64.4 (24.1) s versus 64.1 (25.3) s; E/CO2 was 1.12 (0.04) versus 1.10 (0.04); and the E-CO2 slope was 21.7 (3.4) versus 21.2 (3.2). In conclusion, we could find no evidence to support ventilatory control during moderate exercise being influenced by hyperpnoeic history associated with dead-space loading in humans. |
| |
Keywords: | Arterial PCO2 Breathing pattern Kinetics Mean alveolar PCO2 Memory |
本文献已被 PubMed SpringerLink 等数据库收录! |
|