Expiratory Airway Resistance Research Articles

Short-term respiratory effects of sulfuric acid in fog: a laboratory study of healthy and asthmatic volunteers.

To explore short-term respiratory health risks from acid-polluted fog, 22 normal and 22 asthmatic adult volunteers were exposed in an environmental control chamber to light fogs (∼0.1 g/m3 liquid water content, 10 μm median droplet diameter, 10°C) containing nominally 0, 500, 1000, and 2000 μg/m3 of sulfuric acid. Fog was produced by atomizing dilute acid solution Into purified air humidified to near 100 percent by steam injection. Exposures were administered in random order at 1-week intervals, lasted 1 h, and Included three 10-min periods of moderately heavy exercise. Responses were measured in terms of forced expiratory function, airway resistance, Irritant symptoms, and bronchial reactivity to methacholine aerosol. Sulfuric acid per se showed no more than a slight effect on pulmonary function, even at the highest concentration. Asthmatics experienced bronchoconstrlction, attributable to exercise, under all exposure conditions. Despite the lack of substantial function changes, modest statistically significant Increases in respiratory symptoms occurred with increasing acid concentrations. This unusual response pattern suggests that acid fog effects occur via a mechanism somewhat different from those which govern responses to Irritant gases like SO2 or O3. To the extent these results are relevant to ambient “acid fog” exposures, they predict that no pulmonary dysfunction, and only slight respiratory symptoms if any, are likely to occur.

1790 Use of a Spreadsheet Program to Calculate Pediatric Pulmonary Function Normal Values

The Spreadsheet program Multiplan was used to configure a worksheet for calculating pulmonary function normals on a Fortune 32:16 computer. The worksheet used linear and multiple regression formulas found in the pediatric literature to calculate pulmonary function normal values based on patient sex, race, weight, and height. The program output inculded: Forced Vital Capacity, Residual Volume, Total Lung Capacity, Forced Expiratory Volume, Maximum Midexpiratory Flow Rate, Wright peak Flow Rate, peak Expiratory Flow Rate Maximum Expiratory Flow Capacities, Airway Resistance, and Airway Conductance. The worksheet consisted of a block for used input of patient parameters, a calculation block that calculated normal values using meters, a calculation block for user input of patient parameters, a calculation block that calculated normal values using the regression equations, and an output block that yielded specific normal values for the patient usine the Boolean logic functions of the spreadsheet program. The user cab enter patient pulmonary function test results into the output block to obtain a percentage comparison with the calculated normal values. Since the multiple regression formulas contained complex mathematical constructs of the normal values consumed 20 minutes of technician time; using this spreadsheet the time is reduced to 1 – 2 minutes. Development of the spreadsheet took approximately 1.5 hours, and development of a program in Applesoft BASIC that performed the same calculations took nearly 6 hours. Spreadsheet programs such as Multiplan can reduce development time for calculation intense clinical applications.

1740 LARYNGEAL MUSCLE ACTIVITY REGULATES EXPIRATORY FLOW A AND LUNG VOLUME

In neonatal and adult animals, abduction of the vocal cords by laryngeal muscles regulates airflow by decreasing inspiratory and expiratory airway resistance. To determine if laryngeal muscles modify airflow in neonates, we recorded electromyograms (EMG) in the posterior laryngeal area(LAR) with electrodes attached to the tip of an esophageal catheter inserted 7-9cm beyond the nares. Simultaneous diaphragm(DIA) EMG was recorded from surface electrodes and airflow via mask pneumotachograph. Studies were performed in 12 healthy preterm infants(birthweight 1.6 ±.4kg, gestational age 32±2 weeks, postnatal age 21±8 days) without respiratory distress. Bursts of LAR EMG preceded onset of both DIA EMG and inspiratory airflow by 66±58msec(p<0.05) and 175±75msec(p<0.001), respectively. Retarded expiratory flow during early expiration(expiratory breaking) was observed in 9 infants. Onset of LAR EMG during late expiration in these subjects coincided with development of high end expiratory airflow and exhalation of 3-13cc of air. Thus, laryngeal breaking maintained an increased lung volume throughout most of expiration. In contrast, high flow throughout expiration(absence of breaking) coincided with increased expiratory LAR EMG. We conclude that laryngeal muscle activity regulates respiratory airflow. Control of laryngeal muscle activity maintains an elevated lung volume until end expiration in healthy preterm infants and may assume even greater importance in neonates with decreased functional residual capacity. NIH HL 31173 and HL25830

1812 PULMONARY MECHANICS DURING CONVENTIONAL MECHANICAL VENTILATION AT RAPID RATES IN RABBITS WITH SALINE-LAVAGED LUNGS

Rapid ventilatory rates are commonly used during conventional mechanical ventilation of infants with respiratory distress syndrome to improve pulmonary gas exchange while supposedly reducing barotrauma to the lungs. To understand the effects of this method of ventilation on pulmonary mechanics, we measured inspiratory (RI) and expiratory (RE) airway resistance; pulmonary compliance (CL); tidal volume (VT); and functional residual capacity (FRC) at ventilatory rates of 30, 60, and 90 breaths/min in anesthetized and paralyzed rabbits lungs had been saline-lavaged with 40 ml/kg of normal saline. The rabbits were ventilated with tracheal pressures of 30/6 cm H2O (mean = 11.2), and had a PaO2 and PaCO2, of 40–60 torr and 35–45 torr respectively (FIO=1). I:E ratio was Kept constant at 1:3. We found that RI was approximately 50% lower than RE (P=0.01). RI decreased at higher ventilatory rates (0.046±0.019 vs. 0.019±0.008 at rates of 30 and 90 breaths/min, P=0.05). CL did not change with ventilatory rate (0.30±0.10 vs. 0.28±0.15 ml/cmH2O/kg at rates of 30 and 90 breaths/min). VT and FRC were also rate-independent (6.3±2.7 and 12.4±4.4 ml/kg at a rate of 30 vs. 5.1±0.5 and 11.9±3.5 ml/kg at a rate of 90, respectively). These results demonstrate a rate-independent behavior of the saline-lavaged lung, except for the decrease in RI. The decrease in RI suggests dynamic dilatation of the conducting airways during inspiration at rapid ventilatory rates. Dynamic dilatation of the airways may represent a potential mechanism of barotrauna, reducing the benefit derived from the lower tracheal pressures needed to achieve adequate gas exchange at rapid ventilatory rates. RI may be a sensitive measurement of this effect.

Prolonged expiratory phase in sleep apnea. A unifying hypothesis.

The mechanisms responsible for the various sleep apnea patterns have not been elucidated. In 5 hypersomnolent patients, we analyzed 613 events that would have been labeled mixed and central apneas had usual recording sensitivity been employed. Recording air flow at high sensitivity revealed that in most of these events expiratory flow was present throughout most of the prolonged period during which there was no inspiratory effort. In 378 events, resumption of inspiratory effort was unaccompanied by air flow (occluded events), whereas in 144 events resumption of inspiratory effort was accompanied by inspiratory air flow (not-occluded events). In another 91 events, expiratory air flow ceased during the interval between inspiratory efforts and then recommenced unaccompanied by expiratory effort suggesting airway closure and reopening. Because expiratory air flow is present during a substantial portion of the prolonged interval between inspiratory efforts seen in our sleeping patients, we conclude that "apneas" should be defined relative to absence of inspiratory air flow. In addition, it appears that the initial portion of "mixed," and at least some "central apneas," are associated with increased expiratory upper airway resistance.

Overestimation of inspiratory upper airway resistance.

Inspiratory resistance was found to be 10-50% larger than the expiratory in a model of the upper airways. This was most likely caused by a high kinetic energy component in the airstream close to the constriction reducing the lateral pressure in excess of what could be explained by the frictional pressure drop. Consequently, the inspiratory resistance was overestimated. During expiratory flow, on the other hand, the kinetic energy component at the same site in the trachea was smaller and similar to that in the mouthpiece resulting in an apparently adequate assessment of expiratory resistance. These results may explain why previous authors have found equal inspiratory and expiratory upper airway resistance although the vocal cords abduct during inspiration and adduct during expiration. Pressures obtained by means of the tracheal puncture appeared to be more reliable compared to those obtained from puncture of the cricothyroid membrane.

Pulmonary Function in Patients with Relapsing Polychondritis

Relapsing polychondritis is a disease characterized by progressive inflammation of cartilagenous structures including those of the glottis, trachea, or central bronchi. We performed detailed physiologic and radiologic studies of the respiratory tract in five patients with respiratory involvement due to relapsing polychondritis. We found that the maximal expiratory and inspiratory flow-volume loop and airway resistance together can provide useful clues as to the presence, site, and fixed or dynamic nature of the upper airway obstruction in these patients. However, in patients with fixed upper airway obstruction or compound lesions, computer tomography of the respiratory tract, cinetracheography, or laryngotracheograms at different lung volumes were required to identify the site of the obstruction and to clarify the dynamic nature of the obstruction.

Drug-induced changes in airways obstruction reflected by forced expiratory flows and airway resistance measured with an oscillometric method using quiet breathing.

14 patients with partially reversible airways obstruction were studied with forced expiratory flows (FEV1, PEFR) and with airway resistance measured by an oscillometric method (Siregnost FD-5) before and after drug-induced changes in airways obstruction. 10 inhaled methacholine to induce bronchoconstriction, and 4 inhaled salbutamol and an additional dose of neosynephrine to induce bronchodilation. Intraindividual changes in resistance (Rosc) measured by the oscillometer with quiet breathing showed a fair significant correlation with changes in FEV1 (r = 0.54, p less than 0.05) and changes in PEFR measured by the Wright peak flow meter (r = 0.59, p less than 0.05). The present type of oscillator can be used for provocations starting from normal airway resistance but not for measures of treatment effects in markedly obstructive patients.

Some aspects of nasal physiology studied by rhinomanometry

The nose contributes significantly to the airway resistance. Inspiratory airway resistance is higher than the expiratory airway resistance. Sex and age do not have any significant effect on the values of the airway resistance.

The immediate effect on lung function of smoking filtered and nonfiltered cigarettes.

We measured and compared the effect of smoking a filtered and a nonfiltered cigarette on instantaneous maximal expiratory flow rates (Vmax50 and Vmax25) and airway resistance (Raw). We found a significant increase in Raw after both cigarettes, and a small decrease in Vmax50 after smoking the nonfiltered cigarette. The change in Vmax50 after smoking the filtered cigarette was not significant. We suggest, on the basis of these data, that filtered cigarette smoke reduces some of the constituents that cause bronchoconstriction in the large and central airways.

Pulmonary function in chronic respiratory failure of infancy

We studied pulmonary function in 7 infants age 3-16 months who were dependent upon mechanical ventilation due to bronchopulmonary dysplasia (BPD). Raised lower expiratory airway resistance (RAe), low dynamic lung compliance (CL) and rapid respiratory frequency (f) characterized the breathing pattern in these infants. End-tidal carbon dioxide tension (PECO2) was elevated in spite of abnormally high minute ventilation (VE). One infant died of respiratory failure, 1 died of sepsis and 1 of an occluded tracheostomy after discharge from the hospital. Another infant still requires mechanical ventilation at age 18 months. Recovery from chronic respiratory failure in 4 infants occurred between age 1.2-2.5 years. The infants recovered concomitant with the ability to sustain a high VE in spite of persistently elevated RA and low CL. All of the surviving infants, although developmentally delayed, have the potential for home care with further growth and development.

External Stent for Repair of Secondary Tracheomalacia

Tracheomalacia was created in anesthetized piglets by submucosal resection of 3 to 5 tracheal cartilages. Measurements of airway pressure and flow showed that expiratory airway resistance is maximal at low lung volumes and is significantly increased by creation of the malacic segment. Cervical flexion increases expiratory airway resistance, whereas hyperextension of the neck reduces resistance toward normal. External stenting of the malacic segment reduces expiratory airway resistance, and the combination of external stenting and hyperextension restores airway resistance to normal except at low lung volume. Two patients with secondary tracheomalacia required tracheostomy and could not be decannulated after the indication for the tracheostomy was corrected. Both were successfully decannulated after external stenting of the malacic segment with rib grafts. Postoperative measurements of expiratory pulmonary resistance show a marked decrease from preoperative measurements. External stenting of symptomatic tracheomalacia reduces expiratory airway resistance by supporting and stretching the malacic segment and is preferable to prolonged internal stenting or tracheal resection.

Normal ranges of the mean in- and expiratory airways resistance and gas-dynamic breathing efficiency (author's transl)

Based on measurements in 233 healthy subjects, normal ranges of the mean in- and expiratory airways resistance and gas-dynamic breathing efficiency are presented. Relationships to other gas-dynamic parameters and to age, height and body weight are investigated.

Decreased lung volume after nasogastric feeding of neonates recovering from respiratory disease

FEEDINGS in small infants are associated with an increased incidence of apnea and bradycardia. Physiologic changes after feeding, such as a decrease in arterial oxygen tension of 15 to 20 mm Hg, also have been demonstrated. 1 Other studies have shown that lung mechanics, including tidal volume, dynamic lung compliance, inspiratory and expiratory airway resistance. and work of breathing are not signific~mtly altered by bolus feeds given by the nasogastric route> 2 Yu and Rolfe :~ found significant changes in tidal volume and respiratory rate after nasogastric feeds in infants with respiratory distress, but observed no change in compliance, resistance, or work of breathing. Lung volume measurements are important in interpreting both changes in arterial oxygen tension and lung mechanics. However. no studies to date have documented serial changes in functional residual capacity after feeding neonates recovering from respiratory disease. The purpose of this study is to examine the effects of nasogastrlc tube feeding on serial measurements of lung volumes. lung mechanics, thoracic and abdominal girths, and gastric pressure in neonates recovering from respiratory disease in an attempt to explain the previously observed postprandial arterial hypoxemia. MATERIALS AND METHODS Eleven newborn infants recovering from pulmonary disease were evaluated following bolus nasogastric feedmg. When Studied the infants' mean age was 9.5 days (range 3 to 23 days), mean weight was 2.05 kg (range 1.12 to 3.70 kg), and the majority of the patients were receiving an inspired oxygen concentration of less than 25%. The infants were fed either Enfamil formula (13 to 20 cal/ ounce) (Mead Johnson Company) or human milk. Informed parental consent was obtained for all patients. The following measurements were made: functional residual capacity, respiratory rate. tidal volume, dynamic

Effects of oral terbutaline in children with bronchial asthma

The cardiopulmonary effects of single oral doses of terbutaline were evaluated in children with chronic bronchial asthma. Fifteen children, 6 to 13 yr of age and weighing 22.3 to 51.8 kg, were treated with 1.25, 2.5, 3.75 and 5.0 mg of terbutaline using a double-blind crossover vs placebo design. Before treatment and at intervals up to 420 min following treatment, measurements were made of lung volumes, vital capacity, FEV 1, maximum expiratory flow volume curves, airway resistance (R aw), and specific airway conductance (G aw/V L). Heart rate, systolic and diastolic blood pressures, and electrocardiograms were also obtained. The most consistent and sensitive indicators of pulmonary function were G aw/V L and FEV 1, both of which showed significant improvement after all doses, The peak improvement of these parameters was proportional to the dose of terbutaline. Cardiovascular effects of terbutaline consisted of small increases in systolic blood pressure or transient EKG changes and were clinically unimportant. Other side effects such as headache, tremor, dizziness, and nausea, although proportional to the dose of terbutaline, were mild and transient. The dose of 2.5 mg terbutaline produced the most improvement in pulmonary function in relation to the number of side effects.

The effects of thoracotomy on coronary blood flow in the dog

A velocity-sensitive catheter-tip flowmeter was used to measure left coronary arterial blood flow prior to, during, and following left lateral thoracotomy in the artificially ventilated dog anesthetized with sodium pentobarbital. Thoracotomy was performed with (six dogs) and without (10 dogs) the addition of an increased expiratory airway resistance. Opening the chest without the increased airway resistance had no effect on coronary blood flow, despite a fall in arterial pressure, because coronary vascular resistance decreased. This was associated with a fall in arterial PO2. Thoracotomy with the airway resistance in place caused a transient slight fall in coronary flow owing to decreased arterial pressure and increased coronary resistance. All changes disappeared by the twelfth minute. Arterial PO2 was unaffected. Under the conditions of this experiment, thoracotomy had surprisingly little effect on coronary blood flow.

Nasal airway resistance computer.

An analogue computing system for the measurement of nasal airway resistance (Rn) has been developed. The instrument operates on the principle of measuring the transnasal pressure required to generate a measured nasal airflow rate. The system computes and displays inspiratory or expiratory nasal airway resistance measured at a preselected flow rate. The values are updated on a breath-by-breath basis and presented to a multi-channel recorder and a digital panel meter for visualization. The continuous Rn (at all inspiratory and expiratory flow rates above zero) can also be recorded. Use of the instrument for the evaluation of nasal decongestants has been demonstrated.

Maximal expiratory flow and airway resistance during induced bronchoconstriction in patients with asthma due to Western red cedar (Thuja plicata).

Eleven patients with asthma due to occupational exposure to western red cedar were studied before and during bronchoconstriction induced by the inhalation of an extract of western red cedar or plic...

Mechanisms limiting airflow in bullous lung disease.

The mechanisms of airflow limitation in bullous lung disease were examined by plotting maximal expiratory airflow and airway resistance against lung elastic recoil pressure. in 5 patients who had evidence of isolated bullae, the abnormalities in airway resistance and in expiratory airflow could be accounted for by loss of lung elastic recoil. in 2 additional patients, the abnormalities could not be accounted for completely by loss of lung elastic recoil, suggesting that intrinsic airway disease was also present; these 2 patients had clinically evident chronic bronchitis. in 2 of the patients, tantalum bronchography confirmed the physiologic studies. Postoperative studies in the one patient who underwent bullectomy demonstrated maintained physiologic improvement in lung elastic recoil and in airway resistance.

Metabolic acidosis and lung mechanics in dogs to simulate a clinical condition.

The changes in lung mechanics, e.g., dynamic compliance, expiratory airway resistance, and the components of the work of breathing, i.e., total work, elastic work, resistive work, and negative work were studied at constant tidal volume during the following conditions: (1) increased frequency of breathing from a control rate of 10 to 40 breaths per minute in increments of 5 per minute while acid-base status was held constant; (2) induced acute metabolic lactic acidosis with a fixed arterial carbon dioxide tension and breathing rate of 10 breaths per minute; (3) during increased frequency of breathing superimposed on profound metabolic acidosis. The effect on lung mechanics of increased frequency of breathing combined with metabolic acidosis was considerably greater than the effect of frequency of breathing or acidosis alone. The deleterious effect of metabolic acidosis on lung mechanics is accentuated by the increased work of breathing that results from the concomitant increase of respiratory frequency.