VENTILATORY RESPONSES TO HIGH INTENSITY CONSTANT LOAD EXERCISE IN WOMEN RUNNERS

Abstract

We examined the time course of a wide spectrum of ventilatory variables during constant load exercise to exhaustion in a group of women runners. Seventeen active women (VO2max 50 ± 4 ml/kg/min) completed a treadmill run at a constant speed and grade requiring 90 ± 3% of VO2max at 3 min and reaching 95 ± 3% VO2max at exhaustion (15 ± 4 min). Flow volume (F-V) loops were collected and inspiratory capacity maneuvers performed for the calculation of end expiratory lung volume (EEL V). Expiratory flow-limitation (EFL) was expressed as percent of the tidal F-V loop intersecting the maximal expiratory F-V loop. Maximal estimated ventilation available for a given breathing pattern (VECAP) was calculated based on the maximal available expiratory airflow over the range of the actual tidal breath placed at the measured EELV. Two subjects exhibited significant EFL throughout the run (beginning 31.0 ± 11.3%, middle 61.3 ± 2.5%, end 54.0 ± 1.4%), four exhibited mild EFL at varying times during the run (10.75 ± 7.6%) while ten subjects exhibited no EFL. Group VE increased progressively throughout the run from an initial value of 76 ± 9 L/min to a final value of 102 ± 10 L/min. Alveolar ventilation (VA) exhibited a similar upward drift (61 ± 8 to 76 ± 11 L/min). Breathing frequency (fB) increased from 42 ± 9 to 57 ± 9 BPM while VT remained unchanged (initial 1.86 ± .35 to 1.84 ± .33 L); a combination that contributed to a progressively worsening VD/VT (.14 ± .06 to .19 ± .06). Group PaCO2 declined during the run (36.8 ± 2.86 to 33.1 ± 2.81 mmHg) with no difference in the magnitude of the drop between EFL and non flow-limited subjects. EEL V decreased early during exercise by −4 ± 6.4%, thereafter increasing by 2.2 ± 5.8% in 11 subjects, but did not correlate with the amount of EFL developed. A total of six subjects hyperinflated to an EEL V above rest during the run, but EFL was not a pre-requisite for this lung volume shift. VE reached 88 ± 13% of VECAP in the EFL subjects and 65.8 ± 3.5% of VECAP in non flow-limited subjects. These ventilatory responses are similar to those found in men and corroborate previous findings suggesting that ‘extra’ or ‘other disturbing’ influences may override the usual precise association of VA and metabolic demand in exercise. In addition, EFL did not hamper the ability to match ventilation with CO2 production even though EFL subjects reached a very high percent of VECAP during the run. Supported by NHLBI