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PubMed2003

The issue of dynamic hyperinflation in acute respiratory distress syndrome patients.

Dynamic hyperinflation is produced by a diffuse expiratory flow limitation impairing exhalation under mechanical ventilation. It constitutes a serious clinical problem in patients exhibiting bronchial asthma or chronic obstructive pulmonary disease, when mechanical ventilation is required. But this phenomenon may also complicate respiratory support in acute respiratory distress syndrome (ARDS) patients. The presence of diffuse airflow limitation in ARDS patients has sometimes been noticed in the past, but its consequences have only recently been emphasised in a dynamic study, using bedside recording of flow/volume loops during respiratory support. More recently, by recording systematically a prolonged expiration, the current authors have observed a localised airflow limitation in a majority of ARDS patients, constituting another potential factor of dynamic hyperinflation under respiratory support. In the same report, the current authors' have emphasised the impact of this limitation on the shape of the pressure/volume loop. At a time when increasing respiratory support is proposed to improve carbon dioxide clearance in acute respiratory distress syndrome submitted to protective ventilation, dynamic hyperinflation may become a major clinical problem in this setting.

Airway Resistance↗
PubMed2005

Use of continuous positive airway pressure during flexible bronchoscopy in young children.

Young children are at increased risk for hypoxaemia and hypercapnia during flexible bronchoscopy due to the small size and increased collapsibility of their airways. Various strategies are used to prevent hypoventilation and to provide oxygen during the procedure. The aim of this study was to assess the impact of continuous positive airway pressure (CPAP) on ventilation during flexible bronchoscopy in infants and young children. Tidal breathing was measured in 16 spontaneously breathing and deeply sedated children, aged 3-25 months, by ultrasound spirometry via an airway endoscopy mask. Measurements were made with the tip of the bronchoscope positioned in the pharynx with no CPAP, and in mid-trachea with 0, 5 and 10 cmH2O of CPAP. Transition of the bronchoscope through the vocal cords was associated with significant decreases of tidal volumes (5.0+/-0.5 versus 3.4+/-0.5 mL.kg(-1)), peak tidal expiratory flows (78+/-12 versus 52+/-10 mL.s(-1)) and peak tidal inspiratory flows (98+/-15 versus 66+/-12 mL.kg(-1)). CPAP (5-10 cmH2O) induced almost complete reversal of these changes. In conclusion, it is shown here that flexible bronchoscopy in spontaneously breathing young children is associated with significant decreases in tidal volume and respiratory flow. These changes are largely reversible with continuous positive airway pressure.

Bronchoscopy↗
PubMed1995

Activity of latissimus dorsi muscle during inspiratory threshold loads.

The ability of the latissimus dorsi muscle (LD) to participate as an accessory inspiratory muscle has been the subject of controversy. Electromyographic (EGM) activity of LD was evaluated in 11 healthy subjects (aged 30 +/- 2 yrs; forced expiratory volume in one second (FEV1) 106 +/- 5% predicted; maximal inspiratory pressure (Pmax), 120 +/- 6 cmH2O) under different breathing conditions. The ipsilateral biceps brachii was chosen as the control muscle. The EMG was recorded from surface electrodes, but needle electrodes were also used for LD evaluation in a subset of three subjects. The EMG signal from both muscles was recorded simultaneously, rectified and integrated, with subtraction of the electrocardiographic signal. Situations evaluated were: 1) maximal voluntary contraction (MVC); 2) apnoea; and 3) breathing under progressive inspiratory threshold loads (20-100% Pmax, at 20% intervals). A close relationship was evident between LD recordings from surface and needle electrodes (r = 0.975). Activity of LD at baseline was 1.8 +/- 0.4% MVC, and showed a phasic increase during inspiration under loads. This change had a linear tendency and was significant for loads corresponding to 40, 60, 80 and 100% of Pmax when compared to the control muscle. At this latter level, LD activity was equivalent to 32 +/- 5% MVC (range 11-61%), whereas mean activity of the control muscle was less than 7.5% MVC.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1996

Differential effects of nasal continuous positive airway pressure on reversible or fixed upper and lower airway obstruction.

Our study was to assess whether there were differential effects of nasal continuous positive airway pressure (nCPAP) on different kinds of obstruction in either upper or lower airways in patients with chronic obstructive pulmonary disease (COPD). nCPAP (6 cmH2O for ten minutes) was applied to 7 patients with reversible extrathoracic upper airway obstruction (RUAO) and 3 patients with fixed extrathoracic upper airway obstruction (FUAO). Eighteen stable asthmatics, receiving methacholine challenge to induce a more than 20% reduction in FEV1, were randomly investigated for the effect of nCPAP or sham pressure on reversible lower airway obstruction. Nine stable COPD patients were enrolled to study the effect on irreversible lower airway obstruction. Maximal expiratory and inspiratory flow volume curves and dyspnoea scores were obtained before and after immediate withdrawal of nCPAP. In the RUAO group, nCPAP significantly improved stridor and dyspnoea scores, decreased the ratio of FEF50/FIF50 from 2.05 +/- 0.25 to 1.42 +/- 0.16, and increased peak inspiratory flow (PIF) as well as forced inspiratory vital capacity by 26 +/- 8% and 9 +/- 4%, respectively. In expiratory phase, there was no significant change in pulmonary functions. In asthmatics, nCPAP significantly reversed methacholine-induced bronchoconstriction increasing forced vital capacity by 10 +/- 3%, FEV1 by 15 +/- 4% and PIF by 32 +/- 11%. nCPAP significantly increased the response to bronchodilators. The improvement in airflow rate persisted for at least 5 min after nCPAP withdrawal and was highly correlated with the response to bronchodilators. There was no significant effect of nCPAP on airflow rate in COPD patients. Subjective dyspnoea score changes paralleled the pulmonary function improvement. We conclude that there are differential effects of nCPAP on airflow rates in patients with different nature of airway obstruction. Patients with airway obstruction caused by structural changes may not benefit from the use of nCPAP in improving airflow rates.

Adolescent↗
PubMed1997

Lung deposition from the Turbuhaler in children with cystic fibrosis.

Drug delivery to patients using dry powder inhalers, such as the Turbuhaler, is believed to be influenced by the inspiratory flow used. Clinical studies have indicated that this delivery system can be used effectively by children. However, it is not known how the total and weight-corrected dose delivered to the airways varies with age. A deposition study using technetium-99m (99mTc)-labelled budesonide was performed in order to determine the effect of age on delivery. Twenty one children with cystic fibrosis, aged 4-16 yrs, were recruited. They were clinically stable with normal lung function. Initially, a gamma camera scan was taken in front of a flood source containing 37 MBq of 99mTc. Subsequently, subjects inhaled through a low resistance inspiratory filter connected to a commercially available Turbuhaler. Immediately afterwards they inhaled from a noncommercial Turbuhaler containing budesonide labelled with 99mTc, and then underwent anterior and posterior gamma camera scans. Both Turbuhaler inhalers were attached to a portable spirometer and the peak inspiratory flow through the Turbuhaler was recorded for each inhalation. The total body dose was calculated from the dose deposited on the inspiratory filter connected to the commercial Turbuhaler. Analysis of the gamma camera images provided information on the proportion of the radiolabel delivered to the lungs compared to that deposited in the upper airway and stomach. As expected, a highly significant positive correlation was noted between the peak inspiratory flow generated by the patient through the Turbuhaler and the dose delivered to the lung. Similarly, there was a highly significant positive correlation between age and "total lung dose". However, when total lung dose was corrected for body weight, there was a nonsignificant negative correlation with age. This study suggests that the "weight-corrected lung dose" achieved when children aged > 6 yrs use the Turbuhaler, is largely independent of age. It would appear that the flow-dependent properties of this device are such that the reduced peak inspiratory flow generated by younger children results in a lower dose to the lungs, but that this is off-set by their lower body weight. This is unlikely to be a property of other devices with different flow/drug delivery characteristics.

Adolescent↗
PubMed1997

Effects of inspiratory flow waveforms on arterial blood gases and respiratory mechanics after open heart surgery.

The clinical usefulness of inspiratory flow pattern manipulation during mechanical ventilation remains unclear. The aim of this study was to investigate the effects of different inspiratory flow waveforms, i.e. constant, sinusoidal and decelerating, on arterial blood gases and respiratory mechanics, in mechanically ventilated patients. Eight patients recovering after open heart surgery for valvular replacement and/or coronary bypass were studied. The ventilator inspiratory flow waveform was changed according to a randomized sequence, keeping constant the other variables of the ventilator settings. We measured arterial blood gases, flow, volume and pressure at the proximal (airway opening pressure (Pao)) and distal (Ptr) ends of the endotracheal tubes before and after 30 min of mechanical ventilation with each inspiratory flow waveform. We computed breathing pattern, respiratory mechanics (pressures and dynamic elastance) and inspiratory work, which was then partitioned into its elastic and resistive components. We found that: 1) arterial oxygen tension (Pa,O2) and arterial carbon dioxide tension (Pa,CO2) were not affected by changes in the inspiratory flow waveform; and 2) peak Pao and Ptr were highest with sinusoidal inspiratory flow, whilst mean Pao and Ptr and total work of breathing were least with constant inspiratory flow, mainly because of a concomitant decrease in resistive work during constant flow inflation. The effects of the inspiratory flow profile on Pao, Ptr and total inspiratory work performed by the ventilator were mainly due to the resistive properties of the endotracheal tubes. We conclude that the ventilator inspiratory flow waveform can influence patients' respiratory mechanics, but has no impact on arterial oxygen and arterial carbon dioxide tension.

Adult↗
PubMed1998

Introduction to a new inspiratory threshold loading device.

Inspiratory threshold loading is an important tool in assessing inspiratory muscle function and has been widely used in studies of respiratory mechanics. A simple system was designed to provide a pure and precise inspiratory threshold load. The inspiratory threshold loading system comprises a flow generator attached via a pressure chamber, to the inspiratory port of a Hans-Rudolph valve. By limiting the circulation of air generated by the flow generator between the room and the pressure chamber, different levels of negative pressure are produced in the pressure chamber and applied to the inspiratory valve. An inspiratory pressure equal to the negative pressure in the chamber has to be generated to open the inspiratory valve for flow. The system was tested in four subjects by measuring mouth pressure (Pm), threshold pressure (Pth) and valve resistance (R). The Pm at the beginning of inspiratory flow was defined as the opening pressure (Pop). The Pth was constant throughout inspiration. Pop was linearly related to Pth (p<0.0001), with slopes within 2% of identity and intercepts within +/-0.2 cmH2O. R was between 0.7-1.1 cmH2O x L(-1) x s(-1) under all conditions and was independent of both Pth (p=0.76) and inspiratory flow (p=0.24). The results demonstrate that this system can provide a constant inspiratory threshold load throughout inspiration with little flow resistance, and is therefore ideal for respiratory studies.

Adult↗
PubMed1998

Validation of respiratory inductive plethysmography using the Qualitative Diagnostic Calibration method in anaesthetized infants.

The aim of this study was to compare tidal volume (VT) derived from the Qualitative Diagnostic Calibration (QDC) method (VT,QDC) with measurements from pneumotachography (VT,PN,T) in anaesthetized infants. Measurements were made during spontaneous (SV) and intermittent positive pressure (IPPV) ventilation, sighs and airway occlusions. The VT,DIF was the difference between VT,QDC and VT,PNT (%VT). The contribution of the ribcage (rc) to VT,QDC (%rc) and the thoracoabdominal phase lag were also derived. Twenty-eight infants, mean (SD) age 14.0 (6.2) months were studied. VT,QDC represented VT,PNT most closely when > or = 20 breaths were analysed. There was close agreement during SV immediately after the calibration period (95% limits of agreement (LA; QDC - PNT) -23, 3.0%). The 95% LA increased to -9.6, 10.2% after 10 min. Accuracy diminished during IPPV (95% LA -38, 31%), and sighs. During airway occlusions, when VT,PNT was zero, the 95% LA were -63, 4.1 mL x kg(-1). Mean phase lag was 36 and 2%, respectively, during SV and IPPV (p<0.05). The %rc appeared to be overestimated, being in excess of 50% in infants under 12 months. The Qualitative Diagnostic Calibration method used to estimate tidal volume in anaesthetized infants was limited by the need to analyse > or = 20 breaths and by a loss of within-subject accuracy if measurement conditions or pattern of breathing changed.

Anesthesia, General↗
PubMed1999

Mechanisms underlying effects of nocturnal ventilation on daytime blood gases in neuromuscular diseases.

The hypothesis that, in neuromuscular and chest wall diseases, improvement in central respiratory drive explains the effects of night-time ventilation on diurnal gas exchanges was tested. The effects at 6 months, 1, 2 and 3 yrs of intermittent positive pressure ventilation (IPPV) on arterial blood gas tension, pulmonary function, muscle strength, sleep parameters, respiratory parameters during sleep and ventilatory response to CO2 were evaluated in 16 consecutive patients with neuromuscular or chest wall disorders. As compared with baseline, after IPPV daytime arterial oxygen tension (Pa,O2) increased (+2.3 kPa at peak effect) and arterial carbon dioxide tension (Pa,CO2) and total bicarbonate decreased (-1.8 kPa and -5 mmol x L(-1), respectively) significantly; vital capacity, total lung capacity, maximal inspiratory and expiratory pressures and alveolar-arterial oxygen gradient did not change; the apnoea-hypo-opnoea index and the time spent with an arterial oxygen saturation (Sa,O2) value <90% decreased (-24 and -101 min, respectively), sleep efficiency and mean Sa,O2 increased (+16% and +5%, respectively); and ventilatory response to CO2 increased (+4.56 L x min(-1) x kPa(-1)) significantly. The reduction in Pa,CO2 observed after IPPV correlated solely with the increase in the slope of ventilatory response to the CO2 curve (r=-0.68, p=0.008). In neuromuscular or chest wall diseases, improvement of daytime hypoventilation with nocturnal intermittent positive pressure ventilation may represent an adaptation of the central chemoreceptors to the reduction of profound hypercapnia during sleep or reflect change in the quality of sleep.

Adult↗
PubMed2004

Inspiratory flow rates and volumes with the Aerolizer dry powder inhaler in asthmatic children and adults.

OBJECTIVE: To assess the peak inspiratory flow rate (PIFR) and forced inspiratory vital capacity (FIVC) through the formoterol (Foradil*) Aerolizer* in patients with mild, moderate and severe asthma. RESEARCH DESIGN AND METHODS: PIFR and FIVC were assessed in 33 adults and 32 children using a spirometer alone (baseline), a spirometer with an adaptor, and a spirometer with an adaptor and the Aerolizer inhaler (placebo loaded). RESULTS: Of adult patients using the Aerolizer inhaler, 73% had PIFR values of >100 l/min and 91% had values of >60 l/min. PIFR in adults was reduced from a mean baseline of 283 l/min to 118 l/min through the loaded Aerolizer inhaler. Similarly, 75% of children using the Aerolizer inhaler had PIFR values >80 l/min and 91% had values of > 60 l/min. The mean PIFR in children was reduced from a baseline of 154 l/min to 100 l/min through the loaded Aerolizer inhaler. Only small mean decreases from baseline were observed in FIVC through the loaded Aerolizer inhaler: 8.4% in adults and 3.8% in children. FIVC values of > 2.0 litre were achieved in 82% of adults, and 81% of children achieved FIVC values of >1.5 litre. CONCLUSIONS: This study, albeit in a relatively small patient population, suggests that most children and adults with asthma can generate PIFRs of > 60 l/min and FIVCs of > 1.5 litre through the Aerolizer inhaler regardless of their disease severity. Such findings compare extremely favourably with other dry powder inhalers.

Adolescent↗
PubMed1977

The effect of gestational age on the effective elastance of the respiratory system in neonates.

We measured the effective elastance of the respiratory system (E'RS) in 38 "healthy" neonates, gestational ages ranging from 28-42 weeks. E'RS was calculated by dividing the inspiratory pressure generated after nasal occlusion by the tidal volume of the breath preceding occlusion (E'RS = P/VT). E'RS decreased from 790 +/- 0.070 cm H2O/liter at 30.4 +/- 0.4 weeks of gestation to 520 +/- 0.030 at 34.5 +/- 0.3 weeks (P less than 0.01); then to 340 +/- 0.020 at 40 +/- 0.2 weeks (P less than 0.01). E'RS corrected for lung volume ("specific" E'RS) were 32 +/- 2,32 +/- 4, and 28 +/- 2 cm H2O at the above gestational ages, respectively (P greater than 0.05). We suggest: (1) the increased E'RS observed in preterm infants is lung volume dependent. Changes in lung volume may alter the geometry of the thorax, and therefore, the force/length characteristics of the respiratory muscles; (2) this increased E'RS is not of much benefit to preterm infants who have little respiratory stability when E'RS is maximum; and (3) if E'RS is an index of mechanical stability, apnea in preterm infants is independent of the mechanical properties of the respiratory system.

Gestational Age↗
PubMed2002

Novel system to investigate the effects of inhaled volume and rates of rise in simulated inspiratory air flow on fine particle output from a dry powder inhaler.

This study evaluated the effect of inhaled volume and simulated inspiratory flow rate ramps on fine particle output from dry powder inhalers (DPIs). A simple, robust system was developed to account for "rate of rise" (ramp) effects while maintaining a constant air flow through a multi-stage liquid impinger (MSLI), used for sizing the emitted particles. Ramps were programmed to reach 30 and 60 L/min over 100 milliseconds; 500 milliseconds; and 1, 2, and 3 seconds. Rotahaler was chosen as the test DPI. Testing was done with simulated inhalation volumes of 2 L and 4 L. Testing was also carried out using the USP apparatus 4. At 30 L/min, for a 2 L volume, the amount of drug exiting the device in fine particle fraction (FPF) increased from 2.33 microg to 6.04 microg from the 3-second ramp to the 100-millisecond ramp, with 11.64 microg in FPF for the USP (no ramp) method. At the same flow rate, for a 4 L volume, FPF increased from 2.23 microg to 8.45 microg, with 10.25 microg for the USP method. At 60 L/min, similar trends were observed. In general, at both flow rates, an increase in FPF was noted going from the shallowest to the steepest ramp. However, there were no significant differences in FPF when a 2 L inhaled volume was compared with a 4 L volume at each flow rate. Overall, these data suggest that the existing USP apparatus may overestimate FPF at flow rates lower than those recommended by the USP.

Administration, Inhalation↗
PubMed1992

Differential sensitivity to halothane anesthesia of the genioglossus, intercostals, and diaphragm in kittens.

Recent studies in humans and animals have indicated that different inspiratory muscles have different sensitivities to respiratory depressants. The sensitivity of inspiratory muscles during early growth and development relative to that in adults of the same species, however, has not been studied. We therefore studied the activity of the diaphragm, the external intercostals, and the genioglossus by means of electromyography and its moving time average with different concentrations of halothane in seven 2-mo-old kittens. The kittens spontaneously breathed 1.0%-2.0% halothane in oxygen while PaCO2 was maintained at about 60 mm Hg by adding CO2 to the inspired gas as needed. Muscle activity was evaluated in terms of the peak height of the moving time average. Activity at 1% halothane was used as the control measurement because measurements at zero inspired concentrations of halothane could not be obtained without sedation, which is known to depress respiratory muscle activity. Halothane anesthesia significantly (P less than 0.01) decreased phasic inspiratory activity of the inspiratory muscles in a dose-dependent fashion. Genioglossal activity was completely abolished at 1.5% and 2.0% halothane. By contrast, in our previous study in adult cats under nearly identical experimental conditions, the phasic genioglossal activity was depressed but present even at 3.0% halothane. The degree of depression at 1.5% and 2.0% halothane was least in the crural diaphragm (71.8% +/- 5.8%, 66.6% +/- 4.5% of control, respectively), intermediate in the intercostals (68.9% +/- 9.6%, 35.4% +/- 8.8%), and greatest in the genioglossus (0.0%, 0.0%).(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed2007

Analysis of relationship between peak inspiratory flow rate and amount of drug delivered to lungs following inhalation of fluticasone propionate with a Diskhaler.

A Diskhaler is a dry powder type of inhaler that utilizes a breath controlled drug delivery system. The inspiratory flow rate of the patient would have a significant influence on the effects of drugs administered by a Diskhaler. Thus, we investigated the relationship between inspiratory flow rate and amount of drug delivered into the lungs when using a fluticasone propionate dry powder inhaler with a Diskhaler (FP-DH). To investigate the amount of drug inhaled, we used an inhalation simulator, which consisted of a flow recorder placed in a plastic air-tight box that covered the FP-DH equipped with a twin impinger and a vacuum pump. Drugs located in a plastic box, as well as the device, throat, and stage 1 and stage 2, were assayed by HPLC-UV, following in vitro inhalation at the various flow rates ranged from 18.7 to 77.3 l/min for 2 s. The relationship between peak inspiratory flow rate and amount of drug released from the device was analyzed. A positive linear correlation between the dose released from the device and amount of drug deposited in stage 2 was observed (r=0.899, p<0.001). The doses deposited in stage 2 were estimated to be 2.9 microg at a flow rate of 20 l/min, 6.6 microg at 30 l/min, 8.4 microg at 40 l/min, 10.1 microg at 60 l/min, and 11.3 microg at 90 l/min. It was suggested that the amount of drug in the lungs decreased along with a decrease in peak inspiratory flow rate when it was lower than 60 l/min. Our results were found to be very useful to estimate lung deposition by using peak inspiratory flow rate for administration planning, especially in patients with a flow rate of less than 60 l/min.

Administration, Inhalation↗
PubMed1989

Ventilatory control during exercise in children with mild or moderate asthma.

The aim of this study was to specify whether during exercise the neural response to increased resistive load in asthmatic children corresponds to a modification of the neuromuscular inspiratory drive, to a modification of the breathing pattern, or to both. Thus, nine children with mild or moderate asthma (aged 10-15 yr) and nine normal children (aged 11-16 yr) were studied during an incremental load exercise with a cyclic ergometer, the load of which was increased by steps of 30 W.3 min-1. During the 3rd min of each workload, we measured the following parameters: O2 consumption (VO2), CO2 production (VCO2), ventilation (VE), tidal volume (VT), respiratory frequency (f), ratio of inspiratory to total time of respiratory cycle (T1/TTOT), mean inspiratory flow (VT/T1) as well as mouth occlusion pressure measured at 100 ms (P0.1), and inspiratory power for breathing (W). At maximum level, the two groups showed identical values for heart rate, ventilation divided by weight (VEBW), T1/TTOT), VT/T1, P0.1, and W. However, asthmatic children had lower maximal power (P less than 0.02), higher tidal volume divided by weight (VTBW) (P less than 0.05), and lower f (P less than 0.01). At a same level of exercise (60, 90, or 120 W), in both groups, we found identical values for P0.1, VEBW, VO2, T1/TTOT, and VTBW/T1. However, asthmatic patients exhibited higher VTBW and lower f(limit of significance). This resulted from higher inspiratory and total time durations. Furthermore, they showed a higher inspiratory power for breathing. It was the same for f and VTBW if the results were expressed in relation to the VO2 in ml.kg-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1990

Maximal inspiratory pressure following maximal exercise in trained and untrained subjects.

Previous investigators have demonstrated that 5-10 min of fatiguing exercise would lead to respiratory muscle fatigue in normal subjects. The purpose of this study was to determine if there was a differential inspiratory pressure response to maximal cycle ergometer exercise in trained and untrained subjects. Six highly trained cross country skiers and five untrained college students were studied prior to and 10, 60, and 120 s postexercise (incremental VO2max to exhaustion). On each occasion, maximal inspiratory pressure (MIP) was measured at the mouth from residual volume. Prior to exercise, the two groups had similar MIP values. After exercise, the sedentary subjects experienced significant decreases in MIP compared to the preexercise values. These decreases averaged 10%, 17%, and 13% at 10, 60, and 120 s postexercise, respectively. The skiers, on the other hand, showed no evidence of a decrease in MIP postexercise, with the postexercise values being slightly, but not significantly, higher than the preexercise values. From these results, we conclude that maximal exercise results in inspiratory muscle dysfunction in normal subjects but not in athletes training at or near elite levels. Thus, it appears that endurance exercise training induces an adaptive change in the inspiratory muscles that protects them from the acute loss of strength seen following exercise in normal subjects.

Adolescent↗
PubMed2003

Specificity and reversibility of inspiratory muscle training.

PURPOSE: The purpose of this study was to evaluate the pressure-flow specificity of adaptations to inspiratory muscle training (IMT), in addition to the temporal effects of detraining and reduced frequency of training upon these adaptations. METHODS: Twenty-four healthy subjects were assigned randomly to one of four groups (A: low-flow-high-pressure IMT; B: high-flow-low-pressure IMT; C: intermediate flow-pressure IMT; and D: no IMT). Subjects performed IMT 6 d.wk(-1) for 9 wk, and inspiratory muscle function was evaluated at baseline and every 3 wk. Groups A, B, and C were then assigned randomly to either a maintenance group (M) (IMT 2 d.wk(-1) ) or a detraining group (DT) (no IMT). Inspiratory muscle function was reassessed at 9 and 18 wk post-IMT. RESULTS: At 9 wk, group A exhibited the largest increase in pressure, B a large increase in flow, C more uniform increases in pressure and flow, and D no changes in pressure or flow. Maximum inspiratory muscle power increased in groups A, B, and C by 48 +/- 3%, 25 +/- 3%, and 64 +/- 3%, respectively (mean +/- SEM, P < or = 0.01). Maximum rate of pressure development increased in groups A, B, and C by 59 +/- 1%, 10 +/- 1%, and 29 +/- 1%, respectively ( P < or = 0.01). A decrease in inspiratory muscle function was observed at 9 wk post-IMT in DT. Inspiratory muscle function plateaued between 9 and 18 wk but remained above pre-IMT values. Group M retained the improvements in inspiratory muscle function. CONCLUSION: These data support the notion of pressure-flow specificity of IMT. Detraining resulted in small but significant reductions in inspiratory muscle function. Reducing training frequency by two thirds allowed for the maintenance of inspiratory muscle function up to 18 wk post-IMT.

Adult↗