Ventilatory mechanics and expiratory flow limitation during exercise in normal subjects

Ólafsson, Snorri; Hyatt, Robert E.

doi:10.1172/jci106015

Cited by 119 publications

(70 citation statements)

References 15 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Percentage changes in mechanical and respiratory variables at maximal exercise during He-Oµ breathing case (Murphy et al 1969). Secondly, mechanical limitation of exercise hyperpnoea, although barely apparent during maximal exercise in air (Olafsson & Hyatt, 1969;Younes & Kivinen, 1984), may prevent a greater increase in ýE than that observed in the present study. Finally, the hyperventilation induced by respiratory unloading is obviously accompanied by a reduction of Pa,COµ.…”

Section: Discussioncontrasting

confidence: 50%

The Effects of Breathing He–O₂ Mixtures on Maximal Oxygen Consumption in Normoxic and Hypoxic Men

Esposito¹,

Ferretti²

1997

The Journal of Physiology

View full text Add to dashboard Cite

The hypothesis that the ventilatory resistance to O2 flow (RV) does limit maximal O2 consumption (V̇O2 max) in hypoxia, but not in normoxia, at least in non‐athletic subjects, was tested. RV was reduced by using He–O2 mixtures. V̇O2, max was measured during graded cyclo‐ergometric exercise in eight men (aged 30 ± 3 years) who breathed N2–O2 and He–O2 mixtures in normoxia (inspired oxygen fraction (FI,O2= 0.21) and hypoxia (FI,O2= 0.11). O2 consumption, expired and alveolar ventilations (V̇E and V̇A, respectively), blood lactate and haemoglobin concentrations, heart rate and arterial oxygen saturation (Sa,O2) were determined at the steady state of each work load. Arterial O2 and CO2 partial pressures (Pa,O2) and Pa,CO2, respectively) were measured at rest and at the end of the highest work load. Maximal V̇E and V̇A were significantly increased by He—O2 breathing in normoxia (+27 and +18%, respectively), without significant changes in Pa, O2, Sa, O2V̇O2, max In hypoxia, V̇E and V̇A increased (+31 and +24%, respectively), together with Pa,O2 (+17%), Sa, O2 (+6%) and V̇O2, max (+14%). The results support the hypothesis that the role of RV in limiting V̇O2,max is negligible in normoxia. In hypoxia, the finding that higher V̇E and V̇A values during He–O2 breathing led to higher V̇O2,max values suggests a greater role of RV as a limiting factor. It is unclear whether the finding that the V̇O2 max values were the same during He–O2 and N2–O2 breathing in normoxia is due to a non‐linear response of the O2 transfer system, as previously proposed.

show abstract

Section: Discussioncontrasting

confidence: 50%

The Effects of Breathing He–O₂ Mixtures on Maximal Oxygen Consumption in Normoxic and Hypoxic Men

Esposito¹,

Ferretti²

1997

The Journal of Physiology

View full text Add to dashboard Cite

show abstract

“…During MIV, expiratory Pga substantially exceeds the pressure required to reach maximal expiratory flow. The excessive Pga in expiration during isocapnic hyperpnoea might reflect an undesirable overriding of the normal control mechanisms that operate during exercise in normal subjects, where expiratory pressure rarely exceeds that necessary to generate maximal flow [23,32,33]. Alternatively, vigorous abdominal muscle contraction during expiration might be of functional importance by displacing the diaphragm cranially.…”

Section: Changes In Pressure-time Product and Ventilationmentioning

confidence: 99%

Diaphragm fatigue following maximal ventilation in man

Hamnegärd

Wragg²,

Kyroussis³

et al. 1996

Eur Respir J

View full text Add to dashboard Cite

When highly motivated normal subjects perform maximal isocapnic ventilation, a substantial fall in ventilation is observed during the first minute associated with slowing of the maximum relaxation rate (MRR) of the inspiratory muscles. This suggests that these muscles are excessively loaded, raising the possibility that overt contractile failure of the diaphragm contributes to the fall in ventilation.We therefore investigated the effect of maximal isocapnic ventilation (MIV) on twitch transdiaphragmatic pressure (Pdi,Tw) elicited by cervical magnetic stimulation. We measured Pdi,Tw before and after 2 min MIV in nine normal subjects.Initial mean (SD) ventilation for the nine subjects was 196 (15) L·min -1 falling by 35% at 1 min. Pdi,Tw fell following MIV, at 10 min was reduced by 24%, and remained substantially reduced 90 min after MIV. No change in Pdi,Tw was observed during control studies in which subjects were studied with the same protocol but omitting MIV.We conclude that diaphragmatic contractility is reduced after 2 min maximal isocapnic ventilation and diaphragmatic fatigue may be a limiting factor in maximal ventilation in man.

show abstract

“…Unlike healthy subjects who do not develop expiratory flow limitation (EFL) even during exhaustive exercise [1], many chronic obstructive pulmonary disease (COPD) patients are flow-limited (FL) at rest [2]. These patients can only increase their expiratory flow rate during exercise by allowing their end-expiratory lung volume (VL) to rise, an energetically inefficient strategy that is accompanied by severe dyspnoea that reduces exercise duration [3,4].…”

mentioning

confidence: 99%

Detection of expiratory flow limitation in COPD using the forced oscillation technique

et al. 2004

View full text Add to dashboard Cite

Expiratory flow limitation (EFL) during tidal breathing is a major determinant of dynamic hyperinflation and exercise limitation in chronic obstructive pulmonary disease (COPD). Current methods of detecting this are either invasive or unsuited to following changes breath-by-breath. It was hypothesised that tidal flow limitation would substantially reduce the total respiratory system reactance (Xrs) during expiration, and that this reduction could be used to reliably detect if EFL was present.To test this, 5-Hz forced oscillations were applied at the mouth in seven healthy subjects and 15 COPD patients (mean¡SD forced expiratory volume in one second was 36.8¡11.5 % predicted) during quiet breathing. COPD breaths were analysed (n=206) and classified as flow-limited if flow decreased as alveolar pressure increased, indeterminate if flow decreased at constant alveolar pressure, or nonflow-limited.Of these, 85 breaths were flow-limited, 80 were not and 41 were indeterminate. Among other indices, mean inspiratory minus mean expiratory Xrs (DXrs) and minimum expiratory Xrs (Xexp,min) identified flow-limited breaths with 100% specificity and sensitivity using a threshold between 2. Unlike healthy subjects who do not develop expiratory flow limitation (EFL) even during exhaustive exercise [1], many chronic obstructive pulmonary disease (COPD) patients are flow-limited (FL) at rest [2]. These patients can only increase their expiratory flow rate during exercise by allowing their end-expiratory lung volume (VL) to rise, an energetically inefficient strategy that is accompanied by severe dyspnoea that reduces exercise duration [3,4]. The severity of dyspnoea in COPD is better predicted by the presence of EFL during tidal breathing than by the forced expiratory volume in one second (FEV1) [5,6]. Thus, a simple method of detecting EFL during tidal breathing would be a potentially useful clinical tool. Several noninvasive methods have been proposed to detect tidal EFL in COPD patients, but each has its limitations and, to the best of the authors9 knowledge, to date none has been tested against any form of "gold standard" in spontaneously breathing patients.In 1993, PESLIN et al. [7] reported that some COPD patients during mechanical ventilation developed large negative swings in the respiratory system input reactance (Xrs, i.e. the imaginary part of total input impedance) measured by a forced oscillation technique (FOT). Similar behaviour was observed in a simplified mechanical model of the respiratory system when a flow-limiting segment was included [8] and in mechanically ventilated rabbits [9] after intravenous methacholine infusion. This phenomenon occurs because the linear velocity of gas passing through flow-limiting segments (choke points) equals the local speed of wave propagation [10]. Normally the reactance reflects the elastic and inertial properties of the respiratory system but when flow limitation is present, the oscillatory signal cannot pass through the choke points and reach the alveoli, producing a ...

show abstract

Ventilatory mechanics and expiratory flow limitation during exercise in normal subjects

Abstract: A B S T R A C T

Cited by 119 publications

References 15 publications

The Effects of Breathing He–O₂ Mixtures on Maximal Oxygen Consumption in Normoxic and Hypoxic Men

The Effects of Breathing He–O₂ Mixtures on Maximal Oxygen Consumption in Normoxic and Hypoxic Men

Diaphragm fatigue following maximal ventilation in man

Detection of expiratory flow limitation in COPD using the forced oscillation technique

Contact Info

Product

Resources

About

Ventilatory mechanics and expiratory flow limitation during exercise in normal subjects

Abstract: A B S T R A C T

Cited by 119 publications

References 15 publications

The Effects of Breathing He–O2 Mixtures on Maximal Oxygen Consumption in Normoxic and Hypoxic Men

The Effects of Breathing He–O2 Mixtures on Maximal Oxygen Consumption in Normoxic and Hypoxic Men

Diaphragm fatigue following maximal ventilation in man

Detection of expiratory flow limitation in COPD using the forced oscillation technique

Contact Info

Product

Resources

About

The Effects of Breathing He–O₂ Mixtures on Maximal Oxygen Consumption in Normoxic and Hypoxic Men

The Effects of Breathing He–O₂ Mixtures on Maximal Oxygen Consumption in Normoxic and Hypoxic Men