Forced oscillation total respiratory resistance and spontaneous breathing lung resistance in COPD patients.
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Forced-oscillation total respiratory resistance (Rrs) has been shown to underestimate spontaneous breathing lung resistance (RL,sb) in patients with airway obstruction, probably owing to upper airway shunting. The present study reinvestigates that relationship in seven severely obstructed chronic obstructive pulmonary disease patients using a technique that minimizes that artefact. Rrs at 8 and 16 Hz was computed for each successive forced oscillation cycle. Inspiratory and expiratory RL,sb were obtained by analysing transpulmonary pressure (Ptp) with a four-coefficient model, and compared to Rrs over the same periods. "Instantaneous" values of RL,sb were also obtained by computing the dynamic component of Ptp, and compared to simultaneous values of Rrs. In both respiratory phases, good agreement between Rrs and RL,sb was observed up to RL,sb values of approximately 15 hPa x s(-1) x L(-1) at 8 Hz and 10 hPa x s(-1) x L(-1) at 16 Hz. Instantaneous Rrs and RL,sb varied systematically during the respiratory cycle, exhibiting various amounts of flow- or volume-dependence in the seven patients; the amplitudes of their variations were significantly correlated, but Rrs was much more flow-dependent than RL,sb in three patients. Also, Rrs exceeded RL,sb at end-expiration in three instances, which could be related to expiratory flow limitation. In conclusion, total respiratory resistance is reliable up to much higher levels of airway obstruction than previously thought, provided upper airway shunting is avoided. (+info)
Dynamic hyperinflation and flow limitation during methacholine-induced bronchoconstriction in asthma.
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Although persistent activation of the inspiratory muscles and narrowing of the glottic aperture during expiration have been indicated as relevant mechanisms leading to dynamic hyperinflation in acute asthma, expiratory flow limitation (EFL) has recently been proposed as a possible triggering factor for increasing endexpiratory lung volume (EELV). To establish whether the attainment of maximal flow rate during tidal expiration could elicit dynamic elevation of EELV, breathing pattern, change in EELV by measuring inspiratory capacity (IC) and occurrence of EFL by the negative expiratory pressure (NEP) method were monitored in 10 stable asthmatic subjects during methacholine-induced, progressive bronchoconstriction in seated position. Change in dyspnoea was scored using the Borg scale. At maximum response forced expiratory volume in one second (FEV1) fell on average by 45+/-2% (p<0.001 versus control), while IC decreased 29+/-2%, (by 0.89+/-0.07 L, (p<0.01 versus control)). Only 2 subjects exhibited EFL at the end of methacholine challenge. In 7 subjects EELV started to increase before the occurrence of EFL. Dyspnoea, which increased from 0.2+/-0.1 to 5.5+/-1.0 (Borg scale) at maximum response (p<0.001), was significantly related to the level of bronchoconstriction as assessed by change in (delta)FEV1 (r=0.72; p<0.001) and to dynamic hyperinflation as measured by deltaIC (r=0.50; p<0.001). However, for both deltaFEV1 and deltaIC the slope of the relationship with increasing dyspnoea was highly variable among the subjects. It is concluded that in acute methacholine-induced bronchoconstriction, dynamic hyperinflation may occur in the absence of expiratory flow limitation and that expiratory flow limitation does not represent the triggering factor to generate dynamic hyperinflation. In these circumstances, dyspnoea appears to be related to the increase in end-expiratory lung volume and not to the onset of expiratory flow limitation. (+info)
Characterization of the inspiratory manoeuvre when asthmatics inhale through a Turbohaler pre- and post-counselling in a community pharmacy.
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Dose emission from a Turbohaler has been shown to be dependent on the rate of inhalation, with an optimal flow of 60 l min(-1) recommended. Some patients may need counselling to achieve this fast inhalation. Inhalation rate profiles of 24 asthmatics were measured when they inhaled through a placebo Turbohaler. The setting was a community pharmacy when the asthmatics came to collect their next supply of medication. Profiles were measured before and after counselling on how to use the Turbohaler. The mean (SD) peak inhalation rate through the Turbohaler pre- and post-counselling was 48.0 (16.8) and 54.7 (17.6) l min(-1), and their inspiratory volume was 1.75 (0.68) and 1.94 (0.62) l, respectively. Their mean (SD) percent predicted FEV1 was 57.0 (18.9)%. After counselling, 12 patients achieved an inhalation rate of > 60 l min(-1) and a further four obtained > 55 l min(-1). Emphasis should be placed on counselling patients prescribed all types of inhaled devices rather than concentrating on metered dose inhalers. (+info)
Maximal inspiratory mouth pressures (PIMAX) in healthy subjects--what is the lower limit of normal?
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BACKGROUND: Maximal inspiratory mouth pressures are suitable for non-invasive evaluation of respiratory muscle function. Different studies on PIMAX give predicted normal values and their relation to anthropometric data. Due to a large inter-subject variation of PIMAX, predicted values, however, maximal inspiratory mouth pressures are not suitable to define the individual expected normal PIMAX. What is the lower limit of the normal range? METHODS: PIMAX has been prospectively measured in a representative sample of 504 healthy volunteers (248 males and 256 females) between 18 and 82 years of age with normal lung function. Age, height, weight, body mass index (BMI) and smoking status were recorded and incorporated stepwise in a multiple regression analysis to determine prediction equations. Lower limits of the normal range were defined as the fifth percentile of the residuals derived from the regression model. RESULTS: Mean values of PIMAX were 9.95 kPa for men and 7.43 kPa for women. Significant correlations were found with height, weight, BMI, FEV1, PEF and FVC (P<0.01). The strongest correlation appeared with sex and age (P<0.001). Smoking status and smoked pack-years were not independent predictors of inspiratory pressures. Lower limits of normal were 59% for women and 60% for men of the predicted PIMAX. CONCLUSIONS: In the interpretation of maximal inspiratory mouth pressures, normal values should represent the lower limit of the normal range derived from the regression model in order to avoid false pathological results. Prediction equations as well as lower limits of normal resulting from a study cohort of healthy 18-82-year-olds are given and are recommended to be used by pulmonary function laboratories in young and old patients. (+info)
Role of inspiratory capacity on exercise tolerance in COPD patients with and without tidal expiratory flow limitation at rest.
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Expiratory flow limitation promotes dynamic hyperinflation during exercise in chronic obstructive pulmonary disease (COPD) patients with a consequent reduction in inspiratory capacity (IC), limiting their exercise tolerance. Therefore, the exercise capacity of patients with tidal expiratory flow limitation (FL) at rest should depend on the magnitude of IC. The presented study was designed to evaluate the role of FL on the relationship between resting IC, other respiratory function variables and exercise performance in COPD patients. Fifty-two patients were included in the study. Negative expiratory pressure (NEP) uptake (VO2,max) were measured during an incremental symptom-limited cycle exercise. Twenty-nine patients were FL at rest. The IC was normal in all non-FL patients, while in most FL subjects it was decreased. Both WRmax and VO2,max were lower in FL patients (p<0.001, each). A close relationship of WRmax and O2,max to IC was found (r=0.73 and 0.75, respectively; p<0.0001, each). In the whole group, stepwise regression analysis selected IC and forced expiratory volume in one second (FEV1)/forced vital capacity (FVC) (% predicted) as the only significant contributors to exercise tolerance. Subgroup analysis showed that IC was the sole predictor in FL patients, and FEV1/FVC in non-FL patients. Detection of flow limitation provides useful information on the factors that influence exercise capacity in chronic obstructive pulmonary disease patients. Accordingly, in patients with flow limitation, inspiratory capacity appears as the best predictor of exercise tolerance, reflecting the presence of dynamic hyperinflation. (+info)
Assessment of maximum inspiratory pressure. Prior submaximal respiratory muscle activity ('warm-up') enhances maximum inspiratory activity and attenuates the learning effect of repeated measurement.
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BACKGROUND: The variability of maximal inspiratory pressure (PImax) in response to repeated measurement affects its reliability; published studies have used between three and twenty PImax measurements on a single occasion. OBJECTIVE: This study investigated the influence of a specific respiratory 'warm-up' upon the repeated measurement of inspiratory muscle strength and attempts to establish a procedure by which PImax can be assessed with maximum reliability using the smallest number of manoeuvres. METHODS: Fourteen healthy subjects, familiar with the Mueller manoeuvre, were studied. The influence of repeated testing on a single occasion was assessed using an 18-measurement protocol. Using a randomised cross-over design, subjects performed the protocol, preceded by a specific respiratory warm-up (RWU) and on another occasion, without any preliminary activity (control). Comparisons were made amongst 'baseline' (best of the first 3 measurements), 'short' series (best of 7th to 9th measurement) and 'long' series (best of the last 3 measurements). RESULTS: Under control conditions, the mean increase ('baseline' vs. 'long' series) was 11.4 (5.8)%; following the RWU, the increase (post RWU 'baseline' vs. 'long' series) was 3.2 (10.0)%. There were statistically significant differences between measurements made at all 3 protocol stages ('baseline', 'short' and 'long' series) under control conditions, but none following the RWU. CONCLUSIONS: The present data suggest that a specific RWU may attenuate the 'learning effect' during repeated PImax measurements, which is one of the main contributors of the test variability. The use of a RWU may provide a means of obtaining reliable values of PImax following just 3 measurements. (+info)
Single-breath washouts in a rotating stretcher.
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Vital capacity single-breath washouts using 90% O2-5% He-5% SF6 as a test gas mixture were performed with subjects sitting on a stool (upright) or recumbent on a stretcher (prone, supine, lateral left, lateral right, with or without rotation at end of inhalation). On the basis of the combinations of supine and prone maneuvers, gravity-dependent contributions to N2 phase III slope and N2 phase IV height in the supine posture were estimated at 18% and 68%, respectively. Whereas both He and SF6 slope decreased from supine to prone, the SF6-He slope difference actually increased (P = 0.015). N2 phase III slopes, phase IV heights, and cardiogenic oscillations were smallest in the prone posture, and we observed similarities between the modifications of He and SF6 slopes from upright to prone and from upright to short-term microgravity. These results suggest that phase III slope is partially due to emptying patterns of small units with different ventilation-to-volume ratios, corresponding to acini or groups of acini. Of all body postures under study, the prone position most reduces the inhomogeneities of ventilation during a vital capacity maneuver at both inter- and intraregional levels. (+info)
Leak compensation in positive pressure ventilators: a lung model study.
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Leak compensating abilities of six different positive pressure ventilators commonly used to deliver noninvasive positive pressure ventilation, including the bilevel positive airway pressure (BiPAP) S/T-D and Quantum (Respironics Inc, Murrysville, PA, USA), 335 and O'NYX (Mallinckrodt Inc, St Louis, MO, USA), PLV 102 (Respironics), and Siemens Servo 900C (Siemens Inc, Danvers, MA, USA). Using a test lung model, compensatory capabilities of the ventilators were tested for smaller and larger leaks using the assist/control or timed modes. Back-up rate was 20 min(-1), inspiratory pressure was 18 cmH2O, and expiratory pressure was 5 cmH2O. It was found that even in the absence of air leaking, delivered tidal volume differed substantially between the ventilators during use of pressure-targeted modes, depending on inspiratory flows, inaccuracies in set versus delivered pressures, and inspiratory duration. Also during pressure-targeted ventilation, increasing the tI/ttot up to, but not beyond, 0.5 improved compensation by lengthening inspiratory duration, whereas use of a sensitive flow trigger setting tended to cause autocycling during leaking, interfering with compensation. Leaking interfered with cycling of the BiPAP S/T, inverting the I:E ratio, shortening expiratory time, and reducing delivered tidal volume. Volume-targeted modes achieved limited compensation for small air leaks, but compensated poorly for large leaks. To conclude, leak-compensating capabilities differ markedly between ventilators but pressure-targeted ventilators are preferred for noninvasive positive pressure ventilation in patients with substantial air leaking. Adequate inspiratory flows and durations should be used, triggering sensitivity should be adjusted to prevent autocycling, and a mechanism should be available to limit inspiratory time and avoid I:E ratio inversion. (+info)