Modeling of the expiratory flow pattern of spontaneously breathing cats.

A mathematical model was developed describing the entire expiratory flow pattern during spontaneous, tidal breathing in the absence of expiratory muscle activity. It provides estimates for the time constants of the respiratory system (tau RS(model)) and of the decay of continuing inspiratory muscle activity in early expiration (tau mus(model)). In ten anesthetized, tracheostomized cats flow, tracheal pressure and diaphragmatic EMG were measured during normal expirations and expirations with four different added resistances. No significant differences were found between tau RS(model) (0.21-0.49 sec) obtained by fitting the model to the flow data and tau RS obtained from the straight part of the expiratory flow-volume curve. tau mus(model) (0.050-0.052 sec) was comparable to similar time constants obtained from the integrated diaphragmatic EMG or from end-inspiratory, tracheal occlusion pressure. Fitted peak flow and time to peak tidal expiratory flow were not significantly different from those measured. In conclusion, for spontaneously breathing, anesthetized cats our model provides a close fit of the expiratory flow and parameter estimates were comparable with independently measured values.

Effects of fluticasone propionate in COPD patients with bronchial hyperresponsiveness.

BACKGROUND: Treatment of chronic obstructive pulmonary disease (COPD) with inhaled corticosteroids does not appear to be as effective as similar treatment of asthma. It seems that only certain subgroups of patients with COPD benefit from steroid treatment. A study was undertaken to examine whether inhaled fluticasone propionate (FP) had an effect on lung function and on indices of inflammation in a subgroup of COPD patients with bronchial hyperresponsiveness (BHR). METHODS: Twenty three patients with COPD were studied. Patients had to be persistent current smokers between 40 and 70 years of age. Non-specific BHR was defined as a PC(20) for histamine of

Effect of expiratory resistance on gas-exchange and breathing pattern in chronic obstructive pulmonary disease (COPD) patients being weaned from the ventilator.

BACKGROUND: The majority of patients with severe chronic obstructive pulmonary disease (COPD) have flow limitation, which has deleterious side effects. If these patients are mechanically ventilated, this often results in difficult weaning. Spontaneously breathing COPD patients experience a beneficial effect of pursed lip breathing. We investigated whether in intubated COPD patients application of an external resistance could produce the same beneficial effects on breathing pattern and gas-exchange as pursed lip breathing. METHODS: Ten COPD patients with flow limitation were studied during pressure support mechanical ventilation. Two types of expiratory resistances were applied: one fixed level of resistance and one with a resistive pressure decay. Each resistance was applied in 5 patients and the highest level was chosen that did not cause hyperinflation. Blood gas values and breathing pattern with and without resistance were compared. RESULTS: With resistance 1, gas-exchange and breathing pattern did not change significantly; average PCO2 changed from 8.0 to 8.1 kPa, PO2 from 10.2 to 10.3 kPa, tidal volume from 0.380 to 0.420 l, respiratory rate from 25 to 23 bpm and inspiratory:expiratory ratio from 1:1.9 to 1:2.0. With resistance 2, gas-exchange and breathing pattern did not change significantly; average PCO2 changed from 5.8 to 6.0 kPa, PO2 from 11.1 to 12.1 kPa, tidal volume from 0.733 to 0.695 l, respiratory rate from 16 to 18 bpm and inspiratory:expiratory ratio from 1:2.3 to 1:2.9. CONCLUSION: In intubated COPD patients being weaned from the ventilator, application of an external resistance did not have the same beneficial effects as pursed lip breathing.

Detection of flow limitation in mechanically ventilated patients.

OBJECTIVE: In mechanically ventilated patients flow limitation often goes unrecognised. We compared three methods for detection of flow limitation in mechanically ventilated patients: the resistance method, the negative expiratory pressure (NEP) method, and the interrupter method. DESIGN: Prospective study. SETTING: A medical intensive care unit in a university hospital. PATIENTS: Twenty-six patients (20 COPD, six other pathology), mechanically ventilated under sedation. MEASUREMENTS AND RESULTS: Respiratory mechanics were obtained during application of the three methods. For the resistance method, flow limitation was expressed as percentage of expiratory tidal volume, in which flow did not decrease (FLP-R). For the NEP method, flow limitation was expressed as percentage of expiratory tidal volume in which flow did not increase (FLP-NEP). For the interrupter method, flow limitation was expressed as area of spike-overshoot in flow after interruption. In 18 COPD patients, flow limitation was detected by all methods; mean FLP-R 76% (SD 12%), mean FLP-NEP 90% (SD 11%), mean spike area 21 ml (SD 7 ml). In three patients with other pathology, these values were, respectively, 20% (SD 19%), 48% (SD 21%), and 5 ml (SD 4 ml). The three methods were in close agreement. In nine patients the resistance method increased flow and in six patients the NEP method decreased flow compared to the unimpeded breath. CONCLUSIONS: In mechanically ventilated patients, flow limitation can well be detected by the resistance-, NEP-, and interrupter methods. However, the NEP method can overestimate the flow limited portion, while the resistance method can underestimate the flow limited portion. The interrupter method is found to be less practical.

Children with asthma and physical exercise: effects of an exercise programme.

OBJECTIVE: To evaluate the effects of a physical exercise programme for children with asthma on an outpatient basis. DESIGN: Intervention study: a randomized pretest-post-test control group design. SETTING AND SUBJECTS: Forty-seven children with clinically diagnosed asthma participated in the intervention study, including 34 boys and 13 girls, from 8 to 13 years of age (mean age 10.6). INTERVENTIONS: The physical exercise programme consisted of regular group exercises and home exercises for a period of three months. It was based on a theoretical model describing the relationships between physical competence (condition), perceived physical competence, self-esteem and coping behaviour. MAIN OUTCOME MEASURES: Maximum incremental exercise test, endurance test, the Self-Perception Profile for Children (CBSK), the Asthma Coping Test (ACBT), lung function and exercise-induced bronchoconstriction. RESULTS: The results showed significant effects of the intervention programme on physical condition. There was a significant improvement of 15 W on the maximal workload (Wmax) (p < 0.001), of 7% on VO2max (oxygen uptake) (p = 0.002) and a significant decrease on heart rate submaximal of 6% (p = 0.001). There was also a significant improvement of 50% in running time measured with the endurance test (p = 0.021). Furthermore, a significant effect of the intervention was seen on coping with asthma (p = 0.003). CONCLUSION: It was concluded that participation in the physical exercise programme not only enhanced physical fitness, but also improved coping behaviour with asthma.

Effect of series of resistance levels on flow limitation in mechanically ventilated COPD patients.

In severe chronic obstructive pulmonary disease (COPD) lung emptying is disturbed by airways compression and expiratory flow limitation. Application of an external resistance has been suggested to counteract airways compression and improve lung emptying. We studied the effect of various resistance levels on lung emptying in mechanically ventilated COPD patients. In 18 patients an adjustable resistor was applied. The effect on airways compression was assessed by iso-volume pressure--flow curves (IVPF) and by interrupter measurements. Respiratory mechanics during unimpeded expirations were correlated to the results obtained with the resistances. The resistances caused an increase in iso-volume flow at the IVPF-curves in six patients, indicating that airways compression was counteracted. Interrupter measurements showed that overshoots in flow (as measure of flow limitation) were significantly reduced by the resistor. These effects could be predicted on basis of respiratory mechanics during unimpeded expiration. In conclusion, mechanically ventilated COPD patients can be identified in whom application of external resistances counteracts airways compression and reduces flow limitation.

Multivariable assessment of the 6-min walking test in patients with chronic obstructive pulmonary disease.

Functional exercise tolerance in patients with chronic obstructive pulmonary disease (COPD) is often assessed by the 6-min walking test (6MWT). To assess if the use of multiple factors adds to walking distance in describing performance in the 6MWT, an exploratory factor analysis was performed on physiological measurements and dyspnea ratings recorded during testing. Eighty-three patients with mild to severe COPD performed repeated 6MWTs before inpatient pulmonary rehabilitation. Factor analysis on 15 variables yielded a stable four-factor structure explaining 78.4% of the total variance. Recorded heart rate variables contributed to factor 1 (heart rate pattern), walking distance, heart rate increase, and decrease contributed to factor 2 (endurance capacity), oxygen desaturation variables contributed to factor 3 (impairment of oxygen transport), and dyspnea and effort variables contributed to factor 4 (perceived symptoms). Walking distance decreased in half of the 53 patients measured posttreatment, but self-perceived change in exercise tolerance improved in 84% and was explained by change in walking distance, by less desaturation, and by less dyspnea (R(2) = 0.55, p = 0.005). Qualitative analysis showed that 29 of 53 patients improved in three or four factors. Performance in the 6MWT can be described with four statistically independent and clinically interpretable factors. Because clinically relevant changes consist of more than only walking distance, assessment of functional exercise tolerance in patients with COPD improves by reporting multiple variables.

A new approach to mechanical simulation of lung behaviour: pressure-controlled and time-related piston movement.

A mechanical lung simulator is described (an extension of a previous mechanical simulator) which simulates normal breathing and artificial ventilation in patients. The extended integration of hardware and software offers many new possibilities and advantages over the former simulator. The properties of components which simulate elastance and airway resistance of the lung are defined in software rather than by the mechanical properties of the components alone. Therefore, a more flexible simulation of non-linear behaviour and the cross-over effects of lung properties is obtained. Furthermore, the range of lung compliance is extended to simulate patients with emphysema. The dependency of airway resistance on lung recoil pressure and transmural pressure of the airways can also be simulated. The new approach enables one to incorporate time-related mechanics such as the influence of lung viscosity or cardiac oscillation. The different relations defined in the software can be changed from breath to breath. Three simulations are presented: (1) computer-controlled expiration in the artificially ventilated lung; (2) simulation of normal breathing; and (3) simulation of viscoelastance and cardiac influences during artificial ventilation. The mechanical simulator provides a reproducible and flexible environment for testing new software and equipment in the lung function laboratory and in intensive care, and can be used for instruction and training.

Central airways behave more stiffly during forced expiration in patients with asthma.

Chronic inflammation and extracellular remodeling of the airway wall characterize asthma. The purpose of this study was to examine whether these features cause a change in airway mechanical properties. We examined 14 healthy and 10 young adults with long-lasting asthma, the latter treated with inhaled bronchodilators and corticosteroids. To obtain area-versus-transmural pressure (A-Ptm) curves during forced expiration (Pedersen, O. F., et al. J. Appl. Physiol. 1982;52:357-369), we used an esophageal balloon and a Pitot static probe positioned at five locations between the right lower lobe and midtrachea. Cross-sectional area (A), airway compliance (Caw = dA/dPtm), and specific airway compliance (sCaw = Caw/A) were obtained from the A-Ptm curves. Results showed that: (1) A was larger in males than in females; (2) Caw and sCaw decreased with a more downstream position; and (3) Caw and sCaw were significantly lower in the patients with asthma, with the differences between the asthmatic patients and the healthy subjects becoming smaller toward the trachea. The lower Caw and sCaw in the patients with long-lasting asthma support the concept that chronic inflammation and remodeling of the airway wall may result in stiffer dynamic elastic properties of the asthmatic airway.

Influence of lung parenchymal destruction on the different indexes of the methacholine dose-response curve in COPD patients.

STUDY OBJECTIVES: The interpretation of nonspecific bronchial provocation dose-response curves in COPD is still a matter of debate. Bronchial hyperresponsiveness (BHR) in patients with COPD could be influenced by the destruction of the parenchyma and the augmented mechanical behavior of the lung. Therefore, we studied the interrelationships between indexes of BHR, on the one hand, and markers of lung parenchymal destruction, on the other. PATIENTS AND METHODS: COPD patients were selected by clinical symptoms, evidence of chronic, nonreversible airways obstruction, and BHR, which was defined as a provocative dose of a substance (histamine) causing a 20% fall in FEV(1) (PC(20)) of

Long-term results of uvulopalatopharyngoplasty for obstructive sleep apnea syndrome.

OBJECTIVES: Assessment of the long-term effect of uvulopalatopharyngoplasty (UPPP) on snoring, excessive daytime sleepiness, and nocturnal oxygen desaturation index (ODI) in patients with obstructive sleep apnea syndrome. STUDY DESIGN: Evaluation of snoring, excessive daytime sleepiness, and ODI in patients treated by UPPP earlier. MATERIALS AND METHODS: Patients (n = 58) with a follow-up period of 11 to 74 months (median, 34 mo) were included in this study. Snoring and excessive daytime sleepiness were scored on specially designed semiquantitative scales. In all patients ODI was calculated from pulse-oximetry combined with polysomnography at base line and by polygraphy (MESAM 4) during follow-up in 38 patients. Long-term response was compared with 6-month response in the same cohort. RESULTS: There was a long-term improvement of snoring in 63% of patients, no change in 23%, and a deterioration in 14% (P < .00001). Overall snoring increased slightly between 6 months and long-term follow-up. There was an improvement of excessive daytime sleepiness in 38%, no change in 27%, and a deterioration in 35% (P = .80). Excessive daytime sleepiness showed a relapse to preoperative levels between 6 months and long-term follow-up. The median improvement of ODI was -1 (95% interpercentile range, 73-51) and was not significant (P = .35). In 5 of 13 patients in whom ODI at baseline exceeded 20, ODI was reduced to less than 20. In 4 of the 38 patients ODI was reduced to less than 5. The improvement of ODI decreased significantly between 6 months and long-term follow-up (P = .03). No relation was found between body mass index, Mueller maneuver, X-cephalometry, and long-term outcome. An additional finding was that the ODI decreased after UPPP in combination with tonsillectomy, compared with a slight increase after UPPP alone; the difference was significant (P = .008). CONCLUSION: The response to UPPP for obstructive sleep apnea syndrome decreases progressively over the years after surgery. UPPP in combination with tonsillectomy was more effective than UPPP alone.

Expiratory time constants in mechanically ventilated patients with and without COPD.

OBJECTIVE: In mechanically ventilated patients, the expiratory time constant provides information about the respiratory mechanics and the actual time needed for complete expiration. As an easy method to determine the time constant, the ratio of exhaled tidal volume to peak expiratory flow has been proposed. This assumes a single compartment model for the whole expiration. Since the latter has to be questioned in patients with chronic obstructive pulmonary disease (COPD), we compared time constants calculated from various parts of expiration and related these to time constants assessed with the interrupter method. DESIGN: Prospective study. SETTING: A medical intensive care unit in a university hospital. PATIENTS: Thirty-eight patients (18 severe COPD, eight mild COPD, 12 other pathologies) were studied during mechanical ventilation under sedation and paralysis. MEASUREMENTS AND RESULTS: Time constants determined from flow-volume curves at 100%, the last 75, 50, and 25% of expired tidal volume, were compared to time constants obtained from interrupter measurements. Furthermore, the time constants were related to the actual time needed for complete expiration and to the patient's pulmonary condition. The time constant determined from the last 75% of the expiratory flow-volume curve (RCfv75) was in closest agreement with the time constant obtained from the interrupter measurement, gave an accurate estimation of the actual time needed for complete expiration, and was discriminative for the severity of COPD. CONCLUSIONS: In mechanically ventilated patients with and without COPD, a time constant can well be calculated from the expiratory flow-volume curve for the last 75% of tidal volume, gives a good estimation of respiratory mechanics, and is easy to obtain at the bedside.

Compliance, hysteresis, and collapsibility of human small airways.

We tested the hypothesis that airway wall dimensions are important determinants for the mechanical properties of airways. Lung tissue was obtained from 31 smokers with different degrees of chronic obstructive pulmonary disease (COPD) who were operated on for a solitary lung lesion. Segments of small airways (n = 35) were mounted on cannulas in an organ bath and inflated and deflated cyclically between +15 and -15 cm H(2)O. For each airway this was done at baseline, after methacholine, and after isoprenaline. Specific compliance (sCdyn), specific hysteresis (seta), and pressure at which the airways collapsed (Pcol) were calculated from each recording. Airway wall dimensions were measured morphometrically. Lung function parameters of airflow obstruction were correlated to sCdyn, seta, and Pcol. At baseline, after methacholine, and after isoprenaline sCdyn was 0.059, 0.052, and 0. 085 cm H(2)O(-)(1), seta was 13.5, 12.9, and 7.1%, and Pcol was -3.4, -3.5, and -1.9 cm H(2)O, respectively. Differences between sCdyn, seta, and Pcol after methacholine and after isoprenaline were highly significant (p < 0.001). Of all dimensions studied, smooth muscle area, but not total wall area, was the most important determinant for sCdyn and for seta after methacholine. Specific hysteresis at baseline correlated to residual volume as a fraction of total lung capacity (RV/TLC) (r = 0.5, p = 0.05) and, in the presence of methacholine, to FEV(1)/FVC (r = -0.68, p = 0.02) and RV/TLC (r = 0. 5, p = 0.05). We conclude that, in this study, smooth muscle area and smooth muscle tone, but not total wall area, are determinants for compliance, hysteresis, and collapsibility of isolated airways obtained from smokers.

Flow-volume curves as measurement of respiratory mechanics during ventilatory support: the effect of the exhalation valve.

OBJECTIVE: To assess the feasibility of expiratory flow-volume curves as a measurement of respiratory mechanics during ventilatory support: to what extent is the shape of the curve affected by the exhalation valve of the ventilator? DESIGN: Prospective, comparative study. SETTING: Medical intensive care unit of a university hospital. PATIENTS: 28 consecutive patients with various conditions, mechanically ventilated with both the Siemens Servo 900C and 300 ventilators, were studied under sedation and paralysis. INTERVENTIONS: The ventilator circuit was intermittently disconnected from the ventilator at end-inspiration in order to obtain flow-volume curves with and without the exhalation valve in place. MEASUREMENTS AND RESULTS: Peak flow (PEF) and the slope of the flow-volume curve during the last 50 % of expired volume (SF50) were obtained both with and without the exhalation valve in place. The exhalation valve caused a significant reduction in peak flow of 0.3 l/s (from 1.27 to 0.97 l/s) with the Siemens Servo 900 C ventilator and of 0.42 l/s (from 1.36 to 0.94 l/s) with the Siemens Servo 300 ventilator (p < 0.001). The SF50 was not affected. CONCLUSION: In mechanically ventilated patients, the exhalation valve causes a significant reduction in peak flow, but does not affect the SF50. This study further suggests that the second part of the expiratory flow-volume curve can be used to estimate patients' respiratory mechanics during ventilatory support.

Eosinophils in the bronchial mucosa in relation to methacholine dose-response curves in atopic asthma.

Asthma is characterized by both local infiltration of eosinophils in the bronchial mucosa and bronchial hyperreactivity (BHR). A detailed characterization of BHR implies analysis of a histamine or methacholine dose-response curve yielding not only the dose at 20% fall of baseline forced expiratory volume in 1 s (FEV1), but also a plateau (P) representing the maximal narrowing response in terms of percent change in FEV1 and reactivity as the steepest slope at 50% of P (%FEV1/doubling dose). In the baseline condition, the specific airway conductance (sGaw) may be considered closely related to airway lumen diameter. In 20 nonsmoking asthmatic patients, methacholine dose-response curves were obtained, and a sigmoid model fit yielded the BHR indexes. Immunohistochemistry with the monoclonal antibodies (EG1 and EG2) was used to recognize the total number of eosinophils and activated eosinophils, respectively. The number of activated eosinophils was significantly correlated to both P (r = 0.62; P < 0.05) and sGaw (r = -0.52; P < 0.05), whereas weaker and nonsignificant correlations were found for dose at 20% fall of baseline FEV1 and the total number of eosinophils. We conclude that the number of activated eosinophils can be considered a marker of the inflammation-induced decrease of airway lumen diameter as represented by the plateau index and sGaw.

Expiratory flow-volume curves in mechanically ventilated patients with chronic obstructive pulmonary disease.

BACKGROUND: Forced expiratory flow-volume curves are commonly used to assess the degree of airflow obstruction in patients with chronic obstructive pulmonary disease (COPD). In mechanically ventilated subjects, expiratory airways obstruction can only be estimated from relaxed expirations. The aim of this study was to quantify the degree of airways obstruction from relaxed expiratory flow-volume curves in mechanically ventilated patients with COPD. METHODS: As measure of airflow obstruction, the effective time constant during the last 50% of expired volume (tau) was calculated. For bedside monitoring, tau was recalculated as the slope of the flow during the last 50% of expired volume (SF50). In order to study reproducibility, the variables were calculated from consecutive breaths and at different levels of end-expiratory lung volume (EEV). The SF50 and the tau-were correlated with the forced expiratory volume in 1 s (FEV1) measured prior to the start of ventilatory support. RESULTS: Twenty-seven patients were studied with a FEV1 expressed as percentage predicted of 31 +/- 12% (mean +/- SD). The SF50 amounted to 19 +/- 10 degrees. A positive linear correlation was established between SF50 and the FEV1, (%pred), (r = 0.90, P < 0.0001). The tau showed an exponential relationship with FEV1 (%pred), (r2 = 0.78). From 5 consecutive breaths the mean variation coefficient of SF50 was 5 +/- 2%. Changes of delta EEV from 0.05 to 1.00 L did not affect the SF50-values. In 12 patients, mechanically ventilated for respiratory diseases other than COPD, mean tau and SF50 were significantly different from the COPD-patients (P < 0.0001). CONCLUSIONS: This study indicates that relaxed expiratory flow-volume curves can be used to assess airflow obstruction in mechanically ventilated patients with COPD. This information can be used to adapt ventilatory settings.

Computer-controlled flow resistance.

A computer-controlled flow resistance (CCR), to be used in a computer-controlled lung model, is presented. Flow is forced through a slit between a cylinder and a sleeve around the cylinder. The resulting flow resistance depends on the width, circumferences and the variable length of the slit. The variation in the length is computer-controlled by the position of the sleeve with respect to the cylinder. The total flow resistance also depends on inlet and outlet resistance at both sides of the slit and on flow. The dependence on flow is primarily due to the shape of the inlet of the slit. The resistance of the slit itself is almost independent of flow. The resistance is calculated during a calibration phase at different positions of the sleeve, for flow values from 0.05 to 1.0 litre.s-1 (inflow) and from -0.05 to -1.0 litre.s-1 (outflow). To simulate a required resistance pattern, as, for instance, will occur during breathing, at each moment the set position of the sleeve is calculated by means of an interpolation from the relationship between flow resistance and position of the sleeve. The internal diameter of the sleeve is fixed. To tune the resistance range for a specific simulation, the cylinder is changed for one with different diameter, changing the width of the slit.

Time to peak tidal expiratory flow and the neuromuscular control of expiration.

The ratio of the time needed to reach peak tidal expiratory flow (tPTEF) and the duration of expiration (tE) is used to detect airflow obstruction in young children. tPTEF is decreased in patients with asthma, but knowledge about the physiological determinants of this parameter is scarce. This study examined the relationship between tPTEF and postinspiratory activities of inspiratory muscles and evaluated the effects of changing sensory information from the lung. Airflow patterns and electromyographic (EMG) activity of inspiratory muscles were recorded in seven spontaneously breathing, anaesthetized cats. The trachea was cannulated and, as a result, the larynx and upper airways were bypassed. Changes in postinspiratory muscle activity were induced by changing afferent sensory nerve information (by cooling the vagus nerves, by administration of histamine and by additional application of continuous positive airway pressure (CPAP)). Durations of postinspiratory activities of the diaphragm and intercostal muscles (characterized by their time constants tau diaphr and tau interc) correlated strongly with tPTEF (r=0.85 and 0.77, respectively). Tau diaphr, tau interc and tPTEF were significantly increased during cooling of the vagus nerves (4-8 degrees C) compared with values at 22 and 37 degrees C (p<0.05). Conversely, administration of histamine and CPAP caused significant decreases in tau diaphr, tau interc and tPTEF, which were absent during cooling of the vagus nerves. In conclusion, the time needed to reach peak tidal expiratory flow is highly influenced by the activities of inspiratory muscles during the early phase of expiration which, in turn, depend on the activities of vagal receptors in the lung.

Effect of a nasal dilatator on nasal patency during normal and forced nasal breathing.

A nasal dilatator contains two elastic strips, which provide the dilatator with a spring action. The aimed function of the nasal dilatator is to slightly open the nares and hereby facilitate nasal breathing. The aim of this study was to evaluate the effect of a nasal dilatator by measuring nasal airway resistance during normal breathing and nasal forced expiratory and inspiratory flows and volumes with and without use of the nasal dilatator. Nasal resistance was measured with a whole body plethysmograph; maximal expiratory and inspiratory flow-volume curves were obtained with a pneumotachometer. These measurements were performed in ten healthy volunteers. No significant difference was found between nasal resistance with and without the nasal dilatator. However, values for forced inspiratory volume in 1 s (FIV 1) with the nasal dilatator, proved to be significantly higher (p=0.045,paired t-test) than values obtained without the nasal dilatator; mean improvement was 0.26 L (sd = 0.36). No significant improvement in peak inspiratory flow (PIF) was found, as was the case for the other flows and volumes. It is concluded that the nasal dilatator causes no appreciable improvement of nasal patency during normal breathing. In view of the fact that FIV 1 values increased significantly, we believe that the nasal dilatator prevents collapse of the external nares during forced inspiration. A beneficial effect during exercise when ventilation is increased is however doubtful because in that situation most volunteers switch to oronasal breathing already at submaximal exercise.