Language of dyspnea in assessment of patients with acute asthma treated with nebulized albuterol

To investigate whether the language of dyspnea provides relevant clinical information in addition to that provided by ratings of overall dyspnea intensity when assessing subjective response to therapy, we conducted a prospective study in a cohort of 25 patients with acute asthma presenting to the emergency department of a tertiary care hospital. Patients received nebulized albuterol treatments every 20 min with a maximum of three doses. At presentation and after each treatment, patients completed spirometry, rated overall dyspnea intensity on a modified Borg scale, and selected phrases that described qualities of breathlessness from a 15-item questionnaire. Paired Student's t tests revealed significant improvements in FEV1 (from 1.39 +/- 0.66 L to 1.80 +/- 0.76 L, p < 0. 001) and reductions in dyspnea intensity (from 5.12 +/- 2.08 to 2.82 +/- 1.59, p < 0.001) after the first albuterol treatment. Dyspnea intensity continued to decrease significantly in response to the second treatment, modified Borg rating 2.26 +/- 1.52, although there was no positive bronchodilator response. The results from Cochran Q tests revealed that the frequency of the experience of "chest tightness" decreased significantly across the phases of treatment. However, the sensations of "work" or "breathing effort" persisted at the same time that the FEV1 revealed ongoing airways obstruction. We conclude that attention to the language of dyspnea would alert health care providers to residual air flow obstruction despite decreases in overall dyspnea intensity.

Work of breathing in anesthetized patients: laryngeal mask airway versus tracheal tube

STUDY OBJECTIVE

To compare the work of breathing associated with the laryngeal mask airway (LMA) and tracheal tube (TT) in spontaneously breathing anesthetized patients.

DESIGN

Randomized, prospective, controlled trial.

SETTING

University teaching hospital.

SUBJECTS

20 ASA physical status I and II patients scheduled for elective peripheral surgery with general anesthesia.

INTERVENTIONS AND MEASUREMENTS

A standardized anesthetic protocol was utilized, and patients were allowed to breathe spontaneously through a circle absorption system. Patients were randomly assigned to receive either LMA (n = 10) or TT (n = 10) for airway management. Work of breathing was determined after the patients' ventilatory status had been allowed to stabilize for 15 minutes and before the onset of the surgical stimulus. Airflow and esophageal pressures were measured using a pneumotachograph and an esophageal balloon, respectively, and the values were subsequently integrated to determine work of breathing.

MAIN RESULTS

The two groups were similar with respect to demographic characteristics and the end-tidal concentrations of carbon dioxide and isoflurane. Work of breathing per minute through the LMA (1.4+/-0.3 J/min) was significantly lower than that through the TT (1.9+/-0.4 J/min).

CONCLUSION

In healthy, anesthetized, spontaneously breathing patients, work of breathing is significantly lower through the LMA than the TT.

Susceptibility to upper airway obstruction during partial neuromuscular block

BACKGROUND

Airway obstruction after anesthesia may be caused or exaggerated by residual neuromuscular block, with loss of muscle support for collapsible upper airway structures.

METHODS

Six male volunteers were studied before treatment, during stable partial neuromuscular block with vecuronium at a mean train-of-four (TOF) ratio of 50% (95% CI, 36-61%), and after reversal by neostigmine. Catheter-mounted transducers were placed in the pharynx and esophagus to estimate, respectively, the upper airway resistance, and the work of breathing (calculated as the time integral of the inspiratory pressure developed by the respiratory muscles, esophageal pressure time product) during quiet breathing, during breathing 5% carbon dioxide, and while breathing with an inspiratory resistor. Breathing with pressure at the airway opening held at pressures from -5 to 40 cm H2O were also tested to assess airway collapsibility.

RESULTS

Although breathing through a resistor increased upper airway resistance from 1.2 (0.67, 1.72) cm H2O x l(-1) x s to 2.5 (1.32, 3.38) cm H2O x l(-1) x s, and carbon dioxide stimulation reduced resistance to 0.8 (0.46, 1.33) cm H2O x l(-1) x s, no effect of partial neuromuscular block (mean TOF ratio, 52%) on upper airway properties could be shown.

CONCLUSIONS

Neuromuscular block with a TOF ratio of 50% can be present yet clinically difficult to detect in patients recovering from anesthesia. This degree of block has no effect on airway patency in volunteers, even during challenge. Airway obstruction during recovery from anesthesia thus is more likely to be caused by residual effects of general anesthetic agents or centrally acting analgesics, either alone or perhaps in concert with residual neuromuscular block.

Effect of bedtime alcohol on inspiratory resistance and respiratory drive in snoring and nonsnoring men

We measured inspiratory resistance (R1), inspiratory occlusion pressure (P0.1), and the ventilatory responses to hypercapnia and isocapnic hypoxia during waking and during stage 2 non-rapid eye movement sleep in nine young men who were habitual snorers. They were studied on 2 nights during the 3 hours after receiving a bedtime drink containing either a placebo or 100-proof vodka (1.5 ml/kg) in orange juice. We compared the results with those we reported previously in 10 nonsnoring but otherwise similar men. Waking R1 was the same in nonsnorers and snorers, and it was not affected by ethanol. During sleep on the control night, R1 increased by 70% in nonsnorers and by 280% in snorers. On the ethanol night, the increase from waking to sleeping was more than doubled in both nonsnorers and snorers. P0.1 and the responses to hypercapnia and hypoxia showed no differences between nonsnorers and snorers, therefore the results from the two groups were pooled. Minute ventilation and the hypercapnic response decreased from waking to sleeping and P0.1 was more negative during sleep, but there was no significant effect of ethanol. There was a significant correlation between the changes from waking to sleeping in R1 and P0.1 on the ethanol night suggesting that inspiratory effort increased in response to the increased resistance. The response to isocapnic hypoxia showed no effect of either sleep state or drink. Inspiratory time did not change but mean inspiratory flow (VT/T1) was significantly reduced during sleep on both control and ethanol nights. The duty cycle ratio (T1/Ttot) was significantly increased during sleep on the ethanol night. Despite its great effect on inspiratory resistance, especially in snorers, ethanol, in the dose used in our study, does not augment the depression of minute ventilation or of the hypercapnic response that occur normally in stage 2 non-rapid eye movement sleep. After ethanol, our subjects showed the decreased VT/T1 and the increased T1/Ttot that occur normally during sleep in response to an inspiratory resistive load. However, they also showed increased inspiratory effort. The combination of increased inspiratory resistance and greater inspiratory effort would increase the tendency of an unstable upper airway to collapse and could account for the aggravation of obstructive sleep apnea by ethanol.

Inhaled helium-oxygen revisited: effect of inhaled helium-oxygen during the treatment of status asthmaticus in children

OBJECTIVES

To assess the effects of breathing a low-density gas mixture on dyspnea and the pulsus paradoxus in children with status asthmaticus.

DESIGN

In an urban academic tertiary referral center, 18 patients, aged 16 months to 16 years, who were being treated for status asthmaticus with continuously inhaled beta-agonist and intravenously administered methylprednisolone and had a pulsus paradoxus of greater than 15 mm Hg received either an 80%:20% helium-oxygen gas mixture (HELIOX patients) or room air (control patients) at 10 L/min by nonrebreathing face mask in a double-blind, randomized, controlled trial. In all patients, baseline data, including pulsus paradoxus (determined by sphygmomanometer or arterial catheter blood pressure readings), respiratory rate, heart rate, investigator-scored dyspnea index, and oxygen saturation, were compared with values obtained 15 minutes during and after intervention. In a subset of patients, peak flows before and after breathing HELIOX or room air were measured. When clinically indicated, arterial blood gases were obtained.

RESULTS

The pulsus paradoxus (in millimeters of mercury) fell significantly from an initial mean value of 23.3 +/- 6.8 to 10.6 +/- 2.8 with HELIOX breathing (p < 0.001) and increased again to 18.5 +/- 7.3 after cessation of HELIOX. Peak flow increased 69.4% +/- 12.8% during HELIOX breathing (p < 0.05). The dyspnea index decreased from an initial mean value of 5.7 +/- 1.3 to 1.9 +/- 1.7 with HELIOX breathing (p < 0.0002) and increased again to 4.0 +/- 0.5 after cessation of HELIOX breathing. In control patients, there was no significant difference in pulsus paradoxus or dyspnea index at any time during the study period. Mechanical ventilation was averted in three patients in whom dyspnea lessened dramatically during breathing of HELIOX.

CONCLUSION

During acute status asthmaticus, inhaled HELIOX significantly lowered the pulsus paradoxus, increased peak flow, and lessened the dyspnea index. Moreover, HELIOX spared three patients a planned intubation and caused no apparent side effects. Thus HELIOX reduces the work of breathing and may forestall respiratory failure in children with status asthmaticus, thus preventing the need for mechanical ventilation.

Treatment of acute bronchospasm with beta-adrenergic agonist aerosols delivered by a nasal bilevel positive airway pressure circuit

STUDY OBJECTIVE

To determine whether beta-adrenergic agonist aerosols are more effective in treating acute bronchospasm if delivered by nasal bilevel positive airway pressure (BiPAP) than by a small-volume nebulizer (SVN). We hypothesized that BiPAP would reduce the work of breathing in asthmatic patients and thereby hasten improvement of bronchospasm from beta-agonist therapy. Previous trials with aerosols given by intermittent positive-pressure breathing were unrewarding, but BiPAP is unique in that inspiratory (IPAP) and expiratory (EPAP) support pressures may be set separately.

DESIGN

Convenience-randomized prospective clinical study.

SETTING

Emergency department of an urban tertiary care teaching hospital.

PARTICIPANTS

Afebrile, wheezing patients between 18 and 40 years of age.

INTERVENTIONS

Patients were randomly assigned to receive two doses of aerosolized albuterol (2.5 mg in 3 mL normal saline solution), 20 minutes apart, delivered by either SVN (n = 40) or BiPAP (n = 60) by nosemask or facemask (IPAP, 10 cm H2O; EPAP, 5 cm H2O).

RESULTS

Peak expiratory flow rate (PEFR), arterial blood oxygen saturation (by pulse oximetry), and pulse and respiratory rates were measured at baseline and after each treatment. The two treatment groups had similar values for pulse oximetry, pulse rate, respiratory rate, and percent of predicted peak expiratory flow rate (%PPEFR) at entry, and all patients experienced similar changes in the first three of these variables through the course of treatment. BiPAP patients had a significantly greater increase in %PPEFR after each treatment (P = .0011) and from baseline to completion (P = .0013). Increase in absolute PEFR was greater in the BiPAP group (from 211 +/- 89 [mean +/- SD] to 357 +/- 108 L/minute for BiPAP, from 183 +/- 60 to 280 +/- 87 L/minute for SVN; P = .0001).

CONCLUSION

In this population, response to initial ED management of bronchospasm, as measured by PEFR, was better with aerosols delivered by BiPAP than with those delivered by SVN.

Acetazolamide-induced inhibition of carbonic anhydrase influences energy metabolism and respiratory work in healthy subjects

To assess the usefulness of acetazolamide in weaning a patient from a respirator, we monitored the changes in the respiratory quotient ratio (RQ ratio), the ventilation volume (VE; l/min.), carbon dioxide elimination (VCO2; ml/min.), the oxygen consumption (VO2; ml/min.) and the metabolic energy expenditure (EE; Cal/day) for 6 hours before (baseline) and after the intravenous administration of acetazolamide, 6 mg/kg, in 12 healthy adult volunteers. The RQ ratio decreased significantly from 0.88 to 0.82 after the injection of acetazolamide, 6 mg/kg, and remained below baseline throughout the 6 hours of observation. VCO2 decreased significantly and VE increased significantly after acetazolamide administration. There were no significant changes in VO2 or EE. The RQ ratio increased only slightly, from 0.85 to 0.87, in the control group (no acetazolamide). No significant changes in VCO2 or VE were observed in the control group. Findings suggest that acetazolamide may alter the main pathway of energy metabolism from being carbohydrate-dominant to being fat-dominant, with a resulting fall in CO2 production to maintain the adequate work of ventilation. The inhibition of carbonic anhydrase by acetazolamide may be useful in reducing respiratory work in a patient who is weaned from a respirator.

Heliox improves pulsus paradoxus and peak expiratory flow in nonintubated patients with severe asthma

Heliox is a blend of helium and oxygen with a gas density less than that of air that decreases airway resistance (Raw) in patients ventilated for status asthmaticus. We tested whether breathing an 80:20 mixture of helium:oxygen would reduce pulsus paradoxus (PP) and increase peak expiratory flow (PEF) in patients presenting to the emergency room with an exacerbation of asthma. After receiving 30 min of beta-agonist aerosols and intravenously administered methylprednisolone, 27 patients whose PP remained greater than 15 mm Hg and whose PEF remained less than 250 L/min consented to breathe heliox or room air for 15 min. PP decreased and PEF increased with time in control patients, indicating a time-related effect of routine bronchodilator therapy (p < 0.05). PP decreased in 15 of 16 patients during heliox, and the change with heliox was significantly greater than that during air breathing (p < 0.01). PEF measured with a Wright's peak flow meter calibrated for heliox increased in all patients breathing heliox. Again, the increase in PEF during heliox breathing was significantly greater than the corresponding change in control patients breathing air (p < 0.001). To the extent that PP reflects the inspiratory fall in pleural pressure, this reduction in PP indicates a substantial reduction in inspiratory Raw when the less dense gas is inspired through narrowed bronchi having turbulent flow regimes. The 35% increase in PEF while breathing heliox signals a similar reduction in expiratory Raw, which might diminish the hyperinflation often observed during an exacerbation of asthma.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of opioids on inspiratory muscle fatigue during inspiratory resistive loading

The effect of opioids on inspiratory muscle function under high mechanical load is still unknown. Even less clear is the extent to which opioids influence the shift of the electromyographic power spectrum of the inspiratory muscles to lower frequencies during ventilatory stress. We studied seven healthy subjects breathing against high inspiratory threshold loads until exhaustion while keeping the minute ventilation constantly high. We compared runs with and without administration of 0.2 mg kg-1 of morphine sulphate intramuscularly; two subjects were given 30 mg morphine sulphate so that we could study the effect of higher opioid concentration. The endurance time (Tlim), the diaphragmatic electromyogram (EMG), the transdiaphragmatic pressures (Pdi) and the ventilatory effort sensation were analysed. Morphine did not have any effect on Tlim or on the effort sensation elicited by the inspiratory resistance in both concentrations. Analysing the spectral shifts of the diaphragmatic EMG, we did not find any significant difference in the decrease of the centroid frequency between drug and control runs. Furthermore, the activation pattern of the diaphragm and the intercostal muscles, evaluated from the percentage contribution of oesophageal and gastric pressures on the transdiaphragmatic pressure swings, did not change following the administration of morphine. Our study shows that morphine does not change the function of the inspiratory muscles during high-resistive breathing. Morphine does not affect the electromyographic power spectrum of the diaphragm during those resistive breathing runs, either. This points out that during stressful ventilatory situations, the shift of the electromyographic power spectrum is attributed to a peripheral (muscular) event consequent to muscle fatigue and not to the elaboration of endogenous opioids.

Effects of albuterol inhalation on the work of breathing during weaning from mechanical ventilation

The work of breathing is a major determinant of the success of weaning from mechanical ventilation. The aim of this study was to assess whether an inhaled bronchodilator could reduce the mechanical load on the respiratory muscles and diminish the work. For this purpose, 15 intubated patients in the process of weaning from mechanical ventilation inhaled the beta 2-agonist bronchodilator albuterol via a spacer device filled with 1 mg of the drug and connected to the endotracheal tube. During spontaneous breathing, the mean work of breathing diminished significantly after albuterol, from 9.35 +/- 1.05 to 8.33 +/- 1.13 J/min (p less than 0.01), and seven patients exhibited a decrease superior or equal to 15%. This decrease resulted from a marked reduction in lung and airway resistance, from 12.0 +/- 1.7 to 9.8 +/- 1.4 cm H2O.L-1.s (p less than 0.05). No significant changes were observed in the breathing pattern, intrinsic PEEP or arterial blood gas measurements after albuterol, and peripheral cardiovascular effects were not significant. In seven patients, we were able to compare the changes that occurred after albuterol in the work of breathing during weaning from mechanical ventilation with the changes in pulmonary function induced by albuterol after extubation, as assessed by the forced oscillation method. A close correlation was found between the two types of change, further indicating that the reduction in the work of breathing was more likely to occur in patients with the largest bronchodilating effect of albuterol at baseline.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of codeine on the sensations elicited by loaded breathing

The present study examined the effect of codeine, a centrally acting opiate, on the respiratory sensations elicited in normal subjects by breathing to exhaustion against externally applied inspiratory threshold loads. Subjects were tested on two separate days following the double-blind, randomized administration of either placebo or codeine (90 mg). The intensity of the sensations of effort and discomfort experienced during two loaded breathing trials (a "high" load that was 73% of the maximum inspiratory pressure (MIP) and a "low" load that was 63% of the MIP) was evaluated using category (Borg) scores on each day of study. To verify that the dosage of codeine administered was sufficient to produce analgesia, we also determined the effect of this dosage on the time that subjects could tolerate immersion of one hand in ice water. Codeine altered neither the perceived effort nor the sense of discomfort associated with breathing against external loads and had no appreciable effect on the time to exhaustion during loaded breathing trials. This dose of codeine did, however, increase the time that ice water immersion could be tolerated and reduced the rate at which the sense of discomfort increased over time during ice water trials. These results indicate that, provided the pressure-time index of respiratory muscle contraction remains constant, analgesic doses of codeine alter neither the sensations elicited by loaded breathing nor the total time that breathing against a fatiguing inspiratory load can be tolerated.

Meclofenamate increases ventilation in lambs

To investigate the effects of the prostaglandin synthetase inhibitor, meclofenamate, on postnatal ventilation, we studied 11 unanaesthetised, spontaneously-breathing lambs at an average age of 7.9 +/- 1.1 days (SEM; range 5-14 days) and an average weight of 4.9 +/- 0.5 kg (range 3.0-7.0 kg). After a 30-min control period we infused 4.23 mg/kg meclofenamate over 10 min and then gave 0.23 mg/h per kg for the remainder of the 4 h. Ventilation increased progressively from a control value of 515 +/- 72 ml/min per kg to a maximum of 753 +/- 100 ml/min per kg after 3h of infusion (P less than 0.05) due to an increased breathing rate; the effects were similar during both high- and low-voltage electrocortical activity. There were no significant changes in tidal volume, heart rate, blood pressure, arterial pH or PaCO2, the increased ventilation resulted from either an increase in dead space ventilation or an increase in CO2 production. This study indicates that meclofenamate causes an increase in ventilation in lambs but no changes in pH of PaCO2. The mechanism and site of action remain to be defined.

Indoor and outdoor pollutants and the upper respiratory tract

The health effects of both indoor and outdoor air pollutants are of increasing concern. The health effects of outdoor air pollutants traditionally have been assessed through measurements of lower respiratory tract changes. However, it has been shown that one outdoor air pollutant, sulfur dioxide, decreases nasal mucus flow and increases nasal airway resistance. Along with cigarette smoke, indoor air pollutants such as formaldehyde, cadmium, and ammonium or sulfate ions have been shown to alter upper airway mucociliary function. Emissions from wood stoves are known to irritate the upper airways. Measurement of nasal airway resistance using posterior rhinomanometry allows quantification of nasal function. This technique recently has been used to demonstrate that adolescents with allergic asthma have increased work of breathing after inhalation of 0.5 ppm sulfur dioxide. Another study using posterior rhinomanometry showed that clerical workers had increased work of breathing after exposure to carbonless copy paper as compared with bond paper. This brief review of upper respiratory tract changes after pollutant exposure should serve as a reminder that a complete clinical history must include questions designed to ascertain the patient's exposure history to both outdoor and indoor air pollutants. These exposures can have a major impact on the health of the upper respiratory system.

Theophylline as a bronchodilator in COPD and its combination with inhaled beta-adrenergic drugs

The bronchodilating action of theophylline in COPD has been examined, with emphasis on its combined use with inhaled beta 2 agonists. The suggestion is made that failure to recognize the nonlinearity of the dose-response curves for bronchodilators has resulted in underestimating their combined action. Recent studies suggest that systemic theophylline has somewhat different actions on the airways in COPD than inhaled beta agonists, and that more bronchodilation may be possible when the two are used together than large doses of either one. By analogy, with asthma the suggestion is also made that the addition of theophylline is also likely to provide a more constant bronchodilation, reducing peak-trough variations in flow. The most complete clinical comparison to date suggests that, in currently sanctioned doses, a regimen containing both theophylline and an inhaled beta 2 agonist provides significantly greater bronchodilation than either drug alone, with fewer patient withdrawals. Further carefully designed studies are needed to resolve this issue, and particularly, to identify those patients who will derive the greatest benefit from a combined regimen.

Effects of barbiturate anesthesia on functional residual capacity and ribcage/diaphragm contributions to ventilation

The effect of iv methohexital infusion anesthesia on functional residual capacity (FRC) (helium dilution) in 14 surgical patients (age 23 to 59 years) was determined. Eight subjects were studied wearing an inflatable mask, sealed with surgical lubricant. They showed a mean +/- SD 3.5 +/- 6.4% FRC decrease (no significance). Six subjects studied via mouthpiece awake and via endotracheal tube during anesthesia showed a mean 22 +/- 19% reduction in FRC, significantly greater than face mask studies (P less than 0.05). The greatest FRC decrease occurred in subjects with repetitive or protracted coughing after intubation. The serum methohexital level was 6.6 +/- 3.6 micrograms/ml for intubated patients, and 6.0 +/- 1.1 micrograms/ml in those with face mask (no significance). The depth of anesthesia was sufficient to produce a 50% reduction in ventilatory response to CO2 rebreathing, from 15.8 to 8.7 l/min/% CO2. Respitrace plethysmography indicated a 38 +/- 12% ribcage contribution to tidal volume during quiet breathing, which increased to 47 +/- 14% with CO2 breathing (end-tidal FCO2 9-10%). There was no dimunition of ribcage contribution during anesthesia in either group, irrespective of CO2 concentration. The authors interpret their findings to indicate that iv methohexital anesthesia does not produce FRC reduction, in contrast to an inhaled anesthetic such as halothane. It is proposed that this difference may be related to maintenance of coordinated ribcage/diaphragm muscle activity, because ribcage activity is markedly suppressed by halothane. In addition, it is proposed that FRC reduction in intubated subjects was the result of a confounding variable, namely coughing in response to the endotracheal tube.

Physiologic effects of terbutaline on pulmonary function of infants with bronchopulmonary dysplasia

This study defines the physiologic changes in pulmonary mechanics induced by subcutaneous terbutaline administration in ventilator-dependent infants with severe bronchopulmonary dysplasia (BPD). Eight such infants (mean +/- SEM weight = 2.56 +/- 0.32 kg, postnatal age = 13.0 +/- 3.2 weeks) were chosen for the study. Pulmonary mechanics and arterial blood gases were measured in the control state and at 30 and 60 minutes following the subcutaneous injection of 5 micrograms/kg terbutaline. There was a significant (p less than 0.001) improvement in lung compliance from baseline values at 30 minutes and at 60 minutes (38%). A significant (p less than 0.05) decrease of 23% in the average pulmonary resistance at 30 minutes and a 26% decrease at 60 minutes from control values were observed. An increase in the I/E ratio occurred in all patients at 60 minutes (p less than 0.01). In addition, clinical improvement was noted in six of eight infants. Administration of terbutaline demonstrated a significant improvement in the pulmonary mechanics of infants with severe BPD.

Control of larynx during loaded breathing in normal subjects

We examined laryngeal resistance (Rla) in six normal subjects in control and four kinds of loaded breathing: hypercapnia, chest strapping, added external resistance, and inhaled methacholine. Rla was measured with a low-frequency sound methed (Sekizawa et al., J. Appl. Physiol. 55: 591-597, 1983). In control and the four kinds of loaded breathing, changes in Rla were tightly coupled with ventilation and Rla decreased during inspiration and increased during expiration. Hypercapnia and chest strapping significantly decreased Rla in both inspiration and expiration in all subjects. Added external resistance decreased inspiratory Rla in all subjects, but decreased expiratory Rla in three subjects, did not change it in two subjects, and increased it in one subject. Inhaled methacholine increased Rla in both inspiration and expiration in all subjects. The present study suggests that although laryngeal movement is tightly coupled with ventilation, laryngeal aperture may be determined by the complex competition of dilating and constricting mechanisms associated with the activity of the respiratory center and neural reflexes from the airway.

Halothane anesthesia reduces pulmonary function in the newborn lamb

To study the effects of anesthesia on respiratory function of the neonate, the authors investigated the effect of breathing 100% oxygen and of breathing oxygen plus 0.75 MAC halothane on functional residual capacity, lung and airway resistance, expired minute volume, work of breathing, lung compliance, and blood gases and pH in nine 5-8-day-old, 4.6-7.7-kg lambs. Breathing 100% oxygen increased PaO2 but had no effect on PaCO2, minute ventilation, or lung mechanics. Three-fourths MAC halothane depressed minute ventilation 34% +/- 13% (P less than 0.05) and increased PaCO2 50% +/- 5% (P less than 0.05). Lung and airway resistance increased 59% +/- 26% (P less than 0.05); work of breathing decreased (P less than 0.05); and lung compliance was unchanged. Functional residual capacity was reduced 32% +/- 6% (P less than 0.05), which may be due to loss of diaphragm and intercostal muscle function and to an inability to take deep breaths. The authors conclude that 0.75 MAC halothane significantly impairs the pulmonary function of lambs who breathe spontaneously. Similar changes in human infants could account for the hypoxemia and hypercarbia that often are seen during anesthesia.

Influence of brotizolam on the ventilatory and mouth-occlusion pressure response to hypercapnia in patients with chronic obstructive pulmonary disease

Effect of 0.25 mg brotizolam on patients with chronic obstructive lung disease of moderate to severe degree was studied. There was no difference between the slopes of ventilation vs alveolar CO2 for brotizolam and placebo as compared with base line values. Mouth-occlusion pressures did not change under the influence of drug or placebo. Brotizolam (0.25 mg) is without adverse side-effects on respiratory centre output or on mechanics of ventilation.

The effect of pulmonary stretch receptor activity on the respiratory response to ammonia-inhalation

The contribution of pulmonary stretch receptor (SR) activity to the changes in breathing pattern (f, VT, tI, tE, tI: tE) following inhalation of ammonia vapour has been studied in rabbits at three levels of lung distension, i.e., three levels of SR activity, and during reversible SO2-blockade of SR. The result show that the increase in breathing frequency (f) and the decrease in tidal volume (VT) due to ammonia inhalation are almost identical for animals with and without blockade of SR, whereas the duration of inspiration and expiration (tI, tE) as well as their relationship (tI:tE) vary considerably, the variations depending on the level of SR activity. For a given tI the expiration was longer in animals with SR intact than in animals with SR blocked. It is concluded that in rabbits the increased activity of SR after inhalation of ammonia counteracts significantly the predominant effects of irritant (deflation) receptor stimulation, thus rendering possible a longer expiration.