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PubMed2006

Effect of neuromuscular electrical stimulation on cough capacity and pulmonary function in patients with acute cervical cord injury.

OBJECTIVE: To assess the effectiveness of neuromuscular electrical stimulation (NMES) on cough capacity and prevention of pulmonary complication in patients with acute cervical cord injury. DESIGN: A randomized controlled trial. SUBJECTS: Twenty-six tetraplegic patients with cervical spinal cord injury, 13 in the NMES therapy group and 13 in the control group. METHODS: NMES was applied to the clavicular portion of the pectoralis major and abdominal muscle. Pulmonary function tests were performed before and after therapy, and at 3 months and 6 months follow-up. The pulmonary complications in this 6-month follow-up period were also recorded. RESULTS: After the 4-week therapy, and at 3 months and 6 months follow-up testing, patients in the NMES therapy group displayed significant improvement in their peak expiratory flow, forced expiratory volume in 1 second, forced vital capacity, maximal expiratory pressure and maximal inspiratory pressure, compared with those in the control group (p<0.05). Patients in the NMES therapy group also had fewer pulmonary complications in the follow-up period. CONCLUSION: NMES over the pectoralis and abdominal muscles might improve cough capacity and pulmonary function in cervical spinal cord injury with tetraplegia. This improvement might last for 6 months. With this improvement, pulmonary complications were reduced.

Acute Disease↗
PubMed1995

Pathophysiological response of bovine diaphragm function to gastric distension.

Because of the anatomic association of an exceptionally bulky stomach with a striking compartmentation of the chest wall, leading to the most cranial insertion of the diaphragm among mammals, gastric overdistension in the bovine species offers a unique pathophysiological condition for the diaphragm. The purpose of the present study was to determine whether increased intragastric pressure (Pga) (1, 2, 3, 4, and 5 kPa) leads to perturbations of respiratory and diaphragm function in calves. Changes in diaphragmatic strength and inspiratory action followed a biphasic pattern: 1) transdiaphragmatic pressure (Pdi) in response to constant bilateral maximal phrenic nerve stimulation at 30 Hz increased with moderate gastric distension and then fell abruptly as Pga continued to rise and 2) the magnitude of the ratio of the fall in pleural pressure to total Pdi was maintained up to a Pga amounting to 2 kPa but declined at higher pressures. We conclude that gastric distension in the bovine species provokes physiologically significant alterations of the diaphragm excitation-to-pressure generation coupling as well as of its capacity to convert Pdi into useful inspiratory pleural pressure. We suggest that these perturbations resulted from the combination of 1) altered tension-generating capacity due to compromised perfusion, 2) altered diaphragm geometry capable of altering tension-to-pressure generation coupling, and 3) modified coupling of the diaphragm with the chest wall that reduced its ability to drive inspiration.

Animals↗
PubMed2006

Immediate effects of thixotropy conditioning of inspiratory muscles on chest-wall volume in chronic obstructive pulmonary disease.

INTRODUCTION: Thixotropy is a passive property of the skeletal muscle that depends on the muscle's immediate history of contraction and length change. Inspiratory-muscle thixotropy affects the end-expiratory position of the rib cage in normal subjects. OBJECTIVE: To determine whether a reduction in end-expiratory chest-wall volume occurs after thixotropy conditioning of inspiratory muscles in patients with chronic obstructive pulmonary disease. METHODS: Ten male subjects with chronic obstructive pulmonary disease (mean +/- SD forced expiratory volume in the first second 70+/-20% of predicted) showed an increased ratio of residual volume to total lung capacity (49 +/- 4.7%). The subjects conducted inspiratory muscle thixotropy conditioning maneuvers at 3 different chest-wall volumes (end-expiratory volume of baseline breathing, residual volume plus 40% of expiratory reserve volume, and residual volume) and with 3 levels of inspiratory effort (0%, 30%, and 100% of maximal inspiratory mouth pressure at each volume), with airway-closure, in the sitting position. Using respiratory induction plethysmography, we measured the effect of effort-intensity and volume at the time of the conditioning maneuver on the end-expiratory chest-wall volume of the 5 respiratory cycles immediately following the conditioning maneuver. RESULTS: There was a reduction in end-expiratory chest-wall volume after the conditioning maneuver, except when conditioning was performed at end-expiratory baseline with 0% effort. The reduction increased as effort intensity increased (p = 0.011) and as volume decreased (p < 0.001), and the reduction was attained by rib-cage movement rather than abdominal movement. CONCLUSIONS: Thixotropy conditioning of inspiratory muscles, at a reduced chest-wall volume, decreased end-expiratory chest-wall volume in the 5 subsequent breaths in patients with chronic obstructive pulmonary disease.

Aged↗
PubMed1997

Reproducibility of nasal peak inspiratory flow among healthy adults: assessment of epidemiologic utility.

STUDY OBJECTIVE: To assess the reproducibility of nasal peak inspiratory flow (PIFn). PARTICIPANTS: Twelve healthy nonsmoking volunteers were studied. METHODS: Repeated measurements of PIFn and oral (PIFm) peak inspiratory flow were performed for 5 consecutive days. Two methods of inhalation were compared. In the residual volume (RV) method, the forced maximal inspiratory maneuver was initiated from the end of a maximal expiration, while in the functional residual capacity (FRC) method, the maneuver was from the end of a tidal breath. Reproducibility was assessed by the intraclass correlation coefficient. Time trend for the 5 days was assessed by random effect models adjusting for different baseline for each subject. RESULTS: The intraclass correlation coefficient (ICC) of PIFn was 0.89 (lower limit of one-sided 95% confidence interval is 0.80) by the RV method and 0.78 (95% lower limit is 0.63) by the FRC method, suggesting that both methods have good reproducibility. These were similar to the ICCs of PIFm by each method. The FRC method did not show a significant time trend for PIFn. The RV method had a small, but significant, decreasing time trend of a magnitude considered inconsequential for the purpose of epidemiologic study. CONCLUSION: PIFn, measured from either RV or from FRC, showed good reproducibility and can be employed in epidemiologic studies investigating the upper airways' response to air pollutant exposure. Further studies of the relationships between PIFn and signs and symptoms of rhinitis are needed to evaluate the utility of this test for clinical and epidemiologic use.

Adult↗
PubMed1998

Crural diaphragm activation during dynamic contractions at various inspiratory flow rates.

The purpose of this study was to evaluate the influence of velocity of shortening on the relationship between diaphragm activation and pressure generation in humans. This was achieved by relating the root mean square (RMS) of the diaphragm electromyogram to the transdiaphragmatic pressure (Pdi) generated during dynamic contractions at different inspiratory flow rates. Five healthy subjects inspired from functional residual capacity to total lung capacity at different flow rates while reproducing identical Pdi and chest wall configuration profiles. To change the inspiratory flow rate, subjects performed the inspirations while breathing across two different inspiratory resistances (10 and 100 cmH2O . l-1 . s), at mouth pressure targets of -10, -20, -40, and -60 cmH2O. The diaphragm electromyogram was recorded and analyzed with control of signal contamination and electrode positioning. RMS values obtained for inspirations with identical Pdi and chest wall configuration profiles were compared at the same percentage of inspiratory duration. At inspiratory flows ranging between 0.1 and 1.4 l/s, there was no difference in the RMS for the inspirations from functional residual capacity to total lung capacity when Pdi and chest wall configuration profiles were reproduced (n = 4). At higher inspiratory flow rates, subjects were not able to reproduce their chest wall displacements and adopted different recruitment patterns. In conclusion, there was no evidence for increased demand of diaphragm activation when healthy subjects breathe with similar chest wall configuration and Pdi profiles, at increasing flow rates up to 1.4 l/s.

Adult↗
PubMed1991

Target-flow inspiratory muscle training: breathing patterns and metabolic costs.

In target-flow inspiratory muscle training (TF-IMT), the generated inspiratory mouth pressure and the duration of the inspiration and expiration are standardized to given an adequate training stimulus to the inspiratory muscles. The acute effects of TF-IMT on the efficiency of breathing were studied in a group of 12 COPD patients with a ventilatory limitation of their exercise capacity (mean age 58, mean FEV1 46.2% of predicted) and in 15 normal subjects (mean age 30). Also, the effect of a 10 week period of TF-IMT on the maximal inspiratory mouth pressure (PImax) in the COPD patients was measured. After an unloaded baseline period, the subjects started to inspire through a target-flow device during 15 min, followed by a recovery phase of 5 min. During TF-IMT minute ventilation (VE) decreased only in the COPD group. The ventilatory equivalent for O2 (VE/VO2) and the dead space to tidal volume ratio (VD/VT) decreased in both groups. During recovery, VE, VE/VO2 and VD/VT remained below baseline values in the COPD group, but not in the control group. PCO2 and lactate concentrations did not change during TF-IMT. After the 10 week training period, PImax [means) (SD] increased from 5.7(2.2) to 8.2(2.7) kPa (p less than 0.05). The results indicate that with standardized TF-IMT, the inspiratory muscles can be trained effectively in COPD patients with a ventilatory limitation. The persistence of the decrease in VE, VE/VO2 and VD/VT after a training session may be an additional beneficial effect of TF-IMT.

Adult↗
PubMed1999

Characteristics of nasal airflow and the effect of a nasal dilator in normal human subjects.

Nasal resistance contributes to negative airway pressure during breathing. We sought to define normal patterns of nasal flow and the effects of mechanical dilatation and splinting of the nares on flow during forced inspiration and expiration. Maximal inspiratory and expiratory flow volume loops (FVL) were determined in 17 normal subjects. Oral FVL were obtained with nares clamped and nasal FVL through a mask with and without dilatation of nares using a plastic splint (Nozovent). Oral FVL were normal in all. Two patterns of nasal FVL were observed: one indicating 'variable' extrathoracic obstruction, the other indicating 'fixed' extrathoracic obstruction. Maximal inspiratory flow at 50% of vital capacity (FiF50) was improved by the Nozovent only in those with a 'variable' pattern (FIF50 (L/sec): 1.54 +/- 0.3 to 2.86 +/- 0.5; P < 0.05, versus 1.92 +/- 0.3 to 2.21 +/- 0.3: P = 0.5). In subjects with a fixed pattern, failure of dilatation of the nares to increase flow suggests that the site of inspiratory flow limitation is within the bony nostril.

Adult↗
PubMed1991

Inspiratory time and pulmonary function in mechanically ventilated babies with chronic lung disease.

To learn if increasing inspiratory time would improve pulmonary function in mechanically ventilated babies with chronic lung disease, we measured lung mechanics and alveolar ventilation at three inspiratory times: 0.4, 0.6, and 0.8 s. Nine babies were studied. Their mean birth weight was 875 g (range, 570-1,100 g), gestational age 27 (24-34) weeks, and age 7 (4-12) weeks. Their mean oxygen requirement was 40% (29-53), ventilator rate 33/min (20-40), and mean airway pressure 8 (5-10) cmH2O. Ventilator rate was kept constant; therefore expiratory time decreased and mean airway pressure and I:E ratio increased at longer inspiratory times. At 0.6 s and 0.8 s, when compared to 0.4 s, significant increases occurred in tidal volume (10.4, 10.1, and 8.4 mL/kg, respectively), dynamic lung compliance (0.68, 0.68, and 0.53 mL/cmH2O/kg, respectively), and alveolar ventilation (6.0, 6.3, and 4.7 mL/kg/breath, respectively). Airway resistance, anatomical dead space to tidal volume ratio, and functional residual capacity were similar at the three inspiratory times. Our findings suggest that an inspiratory time greater than or equal to 0.6 s (compared to 0.4 s) increases the effectiveness of mechanical ventilation for babies with chronic lung disease.

Chronic Disease↗
PubMed2002

Physical training for bronchiectasis.

BACKGROUND: The pathophysiology of bronchiectasis may result in the development of dyspnoea and decreased exercise tolerance, both of which can impact on a patient's quality of life and ability to perform activities of daily living. There is little information regarding the benefits of physical training in bronchiectasis: however it is probable that the benefits of physical training in bronchiectasis are at least comparable to benefits demonstrated in other respiratory conditions. There is also no information regarding the effects of non-adherence to prescribed physical training in bronchiectasis. However as in patients with COPD non-adherence may contribute to a deterioration in the patient's condition and conceivably the long term prognosis. OBJECTIVES: The objective of this review is to determine whether a prescribed regime of physical training produces improvements or prevents deterioration in physiological and clinical outcomes in bronchiectasis compared to no physical training. SEARCH STRATEGY: We searched the Cochrane Airways Group specialised register and the Cochrane Controlled Clinical Trials Register. SELECTION CRITERIA: Randomised or quasi randomised controlled trials in which a prescribed regime of physical training are compared to no physical training in patients with bronchiectasis. DATA COLLECTION AND ANALYSIS: Three studies were identified. One was did not meet the inclusion criteria and two appeared in abstract form only. More comprehensive data will be incorporated into this review once data from those two trials are published, and when further data is made available to the authors of this review. MAIN RESULTS: Results from the two studies published in abstract showed that inspiratory muscle training compared to sham or no inspiratory muscle training improved endurance exercise capacity: Weighted Mean Difference (WMD) 264 metres (95% CI 16.4 to 512 metres). PiMax improved: WMD 25 cms H20 (95% CI 11.6 to 38.4 cms H2O )as did quality of life measured with the CRQ: WMD 12.4 units (95% CI 2.4 to 22.5 units). REVIEWER'S CONCLUSIONS: This review only provides evidence of the benefits of inspiratory muscle training and provides no evidence of the effect of other types of physical training (including pulmonary rehabilitation) in bronchiectasis.

Bronchiectasis↗
PubMed2005

Supported arm training in patients recently weaned from mechanical ventilation.

STUDY OBJECTIVES: To evaluate the effects of early exercise training in patients recovering from acute respiratory failure needing mechanical ventilation (MV). DESIGN: Prospective, randomized, and controlled study. SETTING: Three respiratory intermediate ICUs (RIICUs). PATIENTS: Of 228 patients admitted to an RIICU, 66 patients weaned from MV from > 48 to < 96 h were considered eligible and enrolled in the study. INTERVENTION: Sixty-six patients were randomized to either supported arm exercise training plus general physiotherapy (gPT) [group 1, 32 patients] or to gPT alone (group 2, 34 patients). MEASUREMENTS AND RESULTS: Twenty-five patients in each group completed the protocol. Group 1 showed a greater improvement in exercise capacity, as assessed by an arm incremental test (IT) [p = 0.003] and an endurance test (ET) [p = 0.021], compared to group 2. Posttraining maximal inspiratory pressure (MIP) significantly improved in both groups (p < 0.001 and p = 0.003 in groups 1 and 2 respectively; not significant). IT isoworkload dyspnea improved significantly in both groups (p = 0.005 and p = 0.009 in groups 1 and 2, respectively; not significant between groups), whereas IT isoworkload peripheral muscle fatigue (p < 0.001), ET isotime dyspnea (p < 0.01), and ET isotime muscular fatigue (p < 0.005) improved significantly in group 1 but not in group 2. IT improvers (chi2 = 0.004) and ET improvers (chi2 = 0.047) were more frequently observed in group 1 than in group 2. Baseline MIP could discriminate for IT (p = 0.013; odds ratio [OR], 1.116) and ET improvers (p = 0.022; OR, 1.067). CONCLUSION: Early upper-limb exercise training is feasible in RIICU patients recently weaned from MV and can enhance the effects of gPT. Baseline inspiratory muscle function is related to exercise capacity improvement.

Aged↗
PubMed1986

Resistive breathing training in patients with chronic obstructive pulmonary disease.

In order to investigate the effect of resistive breathing training on ventilatory muscular endurance, we examined the maximal sustained ventilatory capacity in ten patients with chronic obstructive pulmonary disease (COPD) before and after a six-week program of resistive breathing training. In addition, we investigated the effect of altered breathing strategy on resistive breathing performance. The patients performed two 15-minute sessions of resistive breathing daily for six weeks using an inspiratory resistive device (Pflex). Before and after the training, we found no significant change in spirometric data, pulmonary volumes, maximal inspiratory pressure, and maximal expiratory pressure. Of the ten patients, seven failed to show an improvement in their performance of resistive breathing. Furthermore, the maximal sustained ventilatory capacity was unchanged after the resistive breathing training. After the completion of the training program, seven of the patients participated in an additional experiment in which they were instructed to take long slow inspirations while breathing through the resistive device. With this change in breathing pattern, five of the seven were able to improve their performance of resistive breathing. Analysis of the breathing strategy showed that a reduction in the peak mouth pressure, breathing frequency, and external resistive work with a longer inspiratory time was beneficial. We conclude that neither resistive breathing performance nor ventilatory muscular endurance, as measured by sustained hyperpnea, is improved by resistive breathing training performed according to the current instructions with the resistive device, and alterations in breathing strategy have a profound effect on the performance of resistive breathing. The lack of details of breathing strategy in previous studies of resistive breathing makes it difficult to determine if previously demonstrated improvements were due to a real enhancement of ventilatory muscular performance or merely secondary to a different strategy.

Aged↗
PubMed1993

Importance of inspiratory load in the assessment of severity of airways obstruction and its correlation with CO2 retention in chronic obstructive pulmonary disease.

Different aspects of mechanical loading were analyzed in a group of 25 patients with chronic obstructive pulmonary disease (COPD) who all had severe expiratory airflow limitation but different arterial CO2 values. It was found that the maximal expiratory flow rates (V75, V50, V25, VFRC), functional residual capacity (FRC), residual volume (RV), total lung capacity (TLC), specific airways conductance (SGaw) measured during inspiration or expiration, and lung recoil pressure (PLel) were not correlated to the PaCO2. Only five parameters were significantly linked to the PaCO2; they were the peak inspiratory flow (PIF) (r = -0.57, p < 0.002), the inspiratory vital capacity (IVC) (r = -0.46, p < 0.01), the maximal voluntary ventilation (MVV) (r = -0.49, p < 0.01), the total SGaw (r = -0.40, p < 0.03), and the forced expiratory flow volume in one second (FEV1) (r = -0.36, p < 0.05). It was concluded that the airflow limitation during the inspiratory phase has an important contribution to the CO2 retention in patients with COPD, and therefore analysis of both phases of the respiratory cycle is necessary to assess the severity of airway obstruction in this disease.

Aged↗
PubMed1995

Volume-controlled inverse ratio ventilation in oleic acid induced lung injury. Effects on gas exchange, hemodynamics, and computed tomographic lung density.

STUDY OBJECTIVE: To compare volume-controlled inverse ratio ventilation (VCIRV) with volume-controlled ventilation with conventional inspiratory to expiratory (I:E) ratio (VCV PEEP) at equal levels of end-expiratory pressure. DESIGN: Animal study using an oleic acid lung injury model with random application of VCV PEEP and VCIRV. SETTING: Experimental investigation at the Department of Clinical Physiology at Uppsala University. ANIMALS: Seven pigs. INTERVENTIONS: VCV PEEP, VCIRV at an end-expiratory pressure level of 10 cm H2O. MEASUREMENTS AND RESULTS: Lung mechanics, hemodynamics, gas exchange, and functional residual capacity. Recruitment of lung tissue, regional lung density, and distribution of inspired gas by computed tomography. Mean and peak airway pressures were 22 +/- 4 and 41 +/- 8 cm H2O with VCIRV and 18 +/- 2 and 45 +/- 7 cm H2O with VCV PEEP. Cardiac output and arterial oxygen tension were equal with VCV PEEP and VCIRV as were static compliance, physiologic dead space, and functional residual capacity. End-expiratory, end-inspiratory, and CT densities during a full ventilatory cycle were not statistically different and the amounts of nonaerated and poorly aerated lung areas were of equal size with VCV PEEP and VCIRV. CONCLUSIONS: VCIRV was comparable to VCV PEEP at similar PEEP levels in alveolar recruitment, aeration of the lung tissues, and in oxygenating the blood. Since cardiac output also remained unchanged, oxygen delivery to peripheral tissues did not differ significantly between the two modes. Neither method has thus proved superior to the other one.

Animals↗
PubMed1981

Static transdiaphragmatic pressures in normal subjects and in patients with chronic hyperinflation.

Transdiaphragmatic pressure (Pdi) during static maximal inspiratory effort was measured in 11 normal subjects and in 4 patients with severe chronic hyperinflation (mean total lung capacity, 138% predicted). The Pdi varied widely among subjects, some production positive abdominal pressure (Pab) at all volumes and some producing Pab close to zero or negative. During modified maximal inspiratory efforts in which the abdomen was protruded, several subjects produced greater Pdi, but in none was pleural pressure (Ppl) more negative, possibly because of inhibition of diaphragmatic activation during spontaneous inspiratory efforts. In the hyperinflated patients, spontaneous maximal inspiratory inspiratory efforts produced smaller values of Pdi, but the diaphragm retained an inspiratory effect and Pdi could still be increased by abdominal protrusion during the effort. Although Pdi during such modified maneuvers probably gives a better index of the strength of the diaphragm, this may not be directly related to its effective capacity as an inspiratory muscle, which may be best assessed by comparing Pdi with Ppl during spontaneous maximal inspiratory efforts.

Abdomen↗
PubMed2001

Static and dynamic pressure-volume curves reflect different aspects of respiratory system mechanics in experimental acute respiratory distress syndrome.

INTRODUCTION: A lower inflection point, an upper inflection (or deflection) point, and respiratory system compliance can be estimated from an inspiratory static pressure-volume (SPV) curve of the respiratory system. Such data are often used to guide selection of positive end-expiratory pressure (PEEP)/tidal volume combinations. Dynamic pressure-volume (DPV) curves obtained during tidal ventilation are effortlessly displayed on modern mechanical ventilator monitors and bear a theoretical but unproven relationship to the more labor-intensive SPV curves. OBJECTIVE: Attempting to relate the SPV and DPV curves, we assessed both curves under a range of conditions in a canine oleic acid lung injury model. METHODS: Five mongrel dogs were anesthetized, paralyzed, and monitored to assure a stable preparation. Acute lung injury was induced by infusing oleic acid. SPV curves were constructed by the super-syringe method. DPV curves were constructed for a range of PEEP and inspiratory constant flow settings while ventilating at a frequency of 15 breaths/min and tidal volume of 350 mL. Functional residual capacity at PEEP = 0 cm H2O was measured by helium dilution. The change in lung volume by PEEP at 8, 16, and 24 cm H2O was measured by respiratory inductance plethysmography. RESULTS: The slope of the second portion of the DPV curve did not parallel the corresponding slope of the SPV curve. The mean lower inflection point of the SPV curve was 13.2 cm H2O, whereas the lower inflection point of the DPV curve was related to the prevailing flow and PEEP settings. The absolute lung volume during the DPV recordings exceeded (p < 0.05) that anticipated from the SPV curves by (values are mean +/- SEM) 267 +/- 86 mL, 425 +/- 129 mL, and 494 +/- 129 mL at end expiration for PEEP = 8, 16, and 24 cm H2O, respectively. CONCLUSIONS: The contours of the SPV curve are not reflected by those of the DPV curve in this model of acute lung injury. Therefore, this study indicates that DPV curve should not be used to guide the selection of PEEP/tidal volume combinations. Furthermore, an increase in end-expiratory lung volume occurs during tidal ventilation that is not reflected by the classical SPV curve, suggesting a stable component of lung volume recruitment attributable to tidal ventilation, independent of PEEP.

Animals↗
PubMed1989

Inspiratory and skeletal muscle strength and endurance and diaphragmatic activation in patients with chronic airflow limitation.

To determine whether patients with chronic airflow limitation have a specific alteration in skeletal muscle performance, the strength and endurance of inspiratory and limb muscles were compared in 11 patients with chronic airflow limitation and 11 control subjects during maximal voluntary contractions. Peak inspiratory pressure at observed functional residual capacity (FRC) was significantly less in the patients than in the control subjects (mean 72 (SD 25) v 93 (21) cm H2O), though only two patients had low maximal pressures across a wide volume range. Maximal voluntary torque of the elbow flexor muscles was also reduced in the patients but the difference was not significant (60 (17) v 72 (18) Nm). During the endurance sequence of 18 maximal voluntary contractions (10 s duration, 5 s rest interval) the decline in peak and average force was less for the inspiratory muscles than for the elbow flexors in both groups. Inspiratory muscle endurance was slightly greater in the patients with chronic airflow limitation than in the control subjects, whereas limb muscle endurance was slightly impaired in the patients. In three patients with chronic airflow limitation, two of whom had low maximal inspiratory pressures at FRC, the ability to drive the diaphragm voluntarily was examined by stimulating the phrenic nerves during maximal inspiratory efforts. Each patient was capable of full activation of the diaphragm during the maximal inspiratory efforts. These results suggest that the relative preservation of inspiratory muscle performance in patients with chronic airflow limitation may be an adaptive response to respiratory "loading."

Airway Obstruction↗
PubMed1976

Influence of bronchomotor tone on ventilation distribution and airway closure in asymptomatic asthma.

Simultaneous washouts of nitrogen (N2) and helium (He) boluses were performed in 9 seated symptom-free asthmatic patients. Recent work has indicated a correlation between the height of Phase IV (deltaIV) of a vital capacity washout and the end-inspiratory vertical concentration gradient of the gas in the lung. The deltaIV for both He and N2 washouts increased by a factor of 2 and 1.25, respectively, after isoproterenol inhalation. In addition, the amplitude of the cardiogenic oscillations increased from a mean of 0.32 per cent to 0.51 per cent for N2 and from 0.030 per cent to 0.051 per cent for He. Closing volume measured by the He bolus method was higher than that by the N2 method in 8 of 9 subjects, by 3.7 +/- 0.7 per cent vital capacity (mean +/- 1 SE, P less than 0.001). Similarly, He closing capacity was greater than N2 closing capacity in the same 8 subjects by 2.6 +/- 1.3 per cent total lung capacity (P less than 0.001). Despite a decrease in closing volume in 8 subjects, and in closing capacity in all 9 subjects after isoproterenol, the differences between the results obtained by the 2 methods remained unchanged. The slope of Phase III in both N2 and He washouts was influenced in an inconstant fashion, probably reflecting differing contributions from topographic and intraregional inhomogeneities of ventilation in these subjects. The results suggest that in patients with asymptomatic asthma the vertical gradient of regional residual volume as well as the pattern of airway closure is more uniformly distributed between apex and base of the lung. Furthermore, the slope of Phase III in either N2 or He bolus washouts may not reflect the degree of bronchoconstriction.

Adult↗
PubMed1977

Diaphragmatic fatigue in man.

The time required (tlim) to produce fatigue of the diaphragm was determined in three normal seated subjects, breathing through a variety of high alinear, inspiratory resistances. During each breath in all experimental runs the subject generated a transdiaphragmatic pressure (Pdi) which was a predetermined fraction of his maximum inspiratory Pdi (Pdimax) at functional residual capacity. The breathing test was performed until the subject was unable to generate this Pdi. The relationship between Pdi/Pdimax and tlim was curvilinear so that when Pdi/Pdimax was small tlim increased markedly for little changes in Pdi/Pdimax. The value of Pdi/Pdimax that could be generated indefinitely (Pdicrit) was around 0.4. Hypoxia appeared to have no influence on Pdicrit, but probably led to a reduction in tlim at Pdi greater than Pdicrit for equal rates of energy consumption. Insofar as the behavior of the diaphragm reflects that of other respiratory muscles it appears that quite high inspiratory loads can be tolerated indefinitely. However, when the energy consumption of the respiratory muscles exceeds a critical level, fatigue should develop. This may be a mechanism of respiratory failure in a variety in a variety of lung diseases.

Diaphragm↗