Time course and pattern of pulmonary flow distribution following unilateral airway occlusion in sheep

1. Unilateral bronchial occlusion causes ipsilateral hypoxic pulmonary vasoconstriction, which shifts blood flow towards the other lung. We studied the time course of flow diversion following acute bronchial occlusion, and the temporal effect of the latter on blood gases and vertical distribution of blood flow within the two lungs. 2. Serial infusion of radioactive or fluorescent microspheres were given to each of seven adult standing sheep before, during occlusion of the left mainstem bronchus for up to 6 min, and after release of occlusion. Pulmonary and systemic arterial pressures were recorded continuously and arterial and mixed venous blood gases were determined intermittently. Post-mortem, the lungs were inflated, dried and cut into slices. Relative blood flow at the time of infusion was expressed as the weight-normalized intensity of each tracer in each slice or lung divided by the weight-normalized intensity in the two lungs. 3. Within 30 s, 1 min and 2 min after onset of occlusion, flow in the occluded lung had decreased to 68-84% (range), 51-78% and 43-79% respectively, of the initial value. In the contralateral lung, flow increased by 10-24%, 14-37% and 23-39% respectively. The distribution of flow along the gravitational axis within each lung varied widely between animals, both before and during occlusion. The during-occlusion profiles in the occluded lung differed from those in the non-occluded lung. In either lung, during-occlusion profiles could not be predicted with certainty from the pre-occlusion profiles. Two minutes post-occlusion, inter- and intra-lung flow distribution were nearly the same as before occlusion. Arterial oxygen tension fell in the first minute of occlusion, but never below 7.5 kPa, and increased slowly thereafter. Arterial carbon dioxide tension increased slightly throughout the occlusion period. No appreciable changes in systemic or pulmonary artery pressure were observed. Post-occlusion, arterial oxygen tension was still sub-normal, while carbon dioxide tension continued to increase. 4. We conclude that acute unilateral bronchial occlusion diverts blood flow within 30 s towards the contralateral lung. This rapidly occurring flow diversion prevents the development of severe arterial hypoxaemia. The variable and largely unpredictable distribution of blood flow in the hyperfused non-occluded lung might explain some of the gas-exchange abnormalities observed in physiologically hyperfused lungs and in patients with one hyperfused lung.

Clinical and serological responses to an inactivated influenza vaccine in adults with HIV infection, diabetes, obstructive airways disease, elderly adults and healthy volunteers

To investigate the clinical and serological responses to an inactivated influenza vaccine (split-virion A/Singapore/6/86-like strains H1N1 (15 ug HA), A/Beijing/353/89-like H3N2 (15 ug HA) and B/Yamagata/16/88-like strain (15 ug HA): MFV-JECT, Merieux, UK) in persons with HIV infection, diabetes, obstructive lung diseases, elderly adults and healthy volunteers. Forty-nine HIV-infected persons received 2 doses of the vaccine at one-month intervals; 34 healthy volunteers, 30 elderly persons, 29 with insulin and non-insulin diabetes and 14 with obstructive airways diseases were vaccinated with one single dose between October 1992 to January 1993. Serological testing of antibody responses was done using haemagglutination assay. Beta2-microglobulin in HIV-infected persons was measured using radioimmunodiffusion between 1st and 2nd dose. Fructosamine levels in diabetic persons were assessed for diabetic control and peak expiratory flow rate (PEFR) was self monitored in persons with lung diseases. All groups apart from the elderly filled in a symptom score chart for the first 5 days following vaccination. A 4-fold rise in titre equal to or more than 1:64 to all the 3 antigens occurred in 20 (58.8%) of healthy volunteers compared with 13 (44.8%) diabetics, 5 (35.7%) with lung diseases, 10 (33.3%) elderly and 13 (26.5%) with HIV infection. A significant correlation of serological response to number of CD4 count in persons with HIV infection was noted (H1N1 P=0.0013, H3N2 P=0.025, BYAM P=0.0018). Mean beta2-microglobulin levels did not change significantly post 1st and 2nd vaccination. Mean fructosamine level did not change significantly. There was no significant change in PEFR. The vaccine was well tolerated. Persons with HIV infection and low CD4 count do not serologically respond well to influenza vaccine even with 2 doses compared to the other 4 groups. The other 4 groups had adequate protective serologic responses. The vaccine was well tolerated in all groups.

Circulating endothelin-1 in obstructive sleep apnea

Endothelin (ET)-1 is a potent vasoconstrictive and mitogenic peptide produced by endothelial cells and degraded predominantly in pulmonary vasculature. We measured ET-1 in 9-normotensive and 14 hypertensive men with obstructive sleep apnea. The ET-1 levels were higher in both normotensive (mean +/- SD, 6.3 +/- 2.8 pg/ml) and hypertensive (7.8 +/- 3.0 pg/ml) groups than in 66 healthy controls (2.9 +/- 1.2 pg/ml). Ten patients were restudied after three months of nCPAP treatment. No decrease in ET-1 was observed.

Pulmonary function measurements during repeated environmental challenge of horses with recurrent airway obstruction (heaves)

OBJECTIVES

To evaluate the degree of reproducibility in clinical variables, blood gas measurements, and lung function variables, and the changes in these variables caused by exposure to moldy hay in naturally sensitized and control horses.

PROCEDURE

The magnitude of variation in arterial blood gas and pulmonary function measurements were evaluated in a model of naturally acquired heaves. Horses with heaves and similarly aged control horses were studied prior to moldy hay challenge and again after the horses with heaves manifested clinical signs of airway obstruction. This cycle of testing was repeated 3 times to determine the variation of the before and after challenge measurements. Variables evaluated for repeatability included: clinical score; arterial O2 and CO2 tensions; pulmonary function variables, such as breathing rate (f), tidal volumes, and flow rates; lung resistance (RL); dynamic compliance; and work of breathing (Wb).

RESULTS

Before challenge, significant differences observed between control horses and horses with heaves included clinical score, expiratory flow rate at near-end expiration, RL, and Wb. After exposure to moldy hay, variables measured in control horses were largely unchanged. However, in the afflicted horses, significant changes were observed for clinical score, arterial O2 and CO2 tensions, breathing rate, peak tidal inspiratory and expiratory flow rates, dynamic compliance, RL, and Wb, compared with prechallenge values and with control horses' postchallenge values. Analysis of the data revealed few statistically significant differences between repeats of challenges.

CONCLUSION

Horses afflicted with heaves manifest airway obstruction that can be measured in repeatable fashion.

Cardiac arrhythmias as a result of intravenous infusions of theophylline in patients with airway obstruction

The effect of intravenous theophylline upon the activity of creatinine kinase (CK) and its cardiac specific isoenzyme (CK-MB) and the frequency of cardiac arrhythmias were evaluated in 12 patients with bronchial asthma and spastic bronchitis. Measurements of the peak expiratory flow (PEF) were obtained prior to theophylline administration, immediately after the infusion and at 1, 3 and 6 hours, while serum theophylline levels were determined at the same time by enzyme immunoassay. Continuous 24-hour Holter monitoring of the electrocardiogram before the study and at the first day of the investigations was performed. CK-MB elevation was observed relating to the theophylline infusion. The CK-MB activity prior to theophylline administration was 10.87 +/- 5.2 units and 24.9 +/- 13.4 units at 5 minutes after termination of the infusion. The elevation lasted until the end of the observation period, being 29.4 +/- 17 units at 1 hour, 27.95 +/- 12.1 units at 3 hours and 34.9 +/- 13.9 at 6 hours. No statistically significant differences in CK activity were found. In most patients the heart rate was accelerated during the theophylline infusion and 4 patients developed clinically silent ventricular arrhythmias obviously related to the infusion. In one patient a 5-hour long bout of atrial fibrillation, which resolved spontaneously, was observed. No changes were found in the ST-T segment.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of nasal occlusion on the initiation of oral breathing in preterm infants

The ability to switch from nasal to oral breathing in response to nasal obstruction is crucial for survival, and has been suggested to be an important mechanism in preventing sudden infant death syndrome (SIDS). To know whether the ability to switch from nasal to oral breathing is uniformly present during the early neonatal period, we examined the effects of slow and fast nasal occlusions on the establishment of oral breathing in preterm infants. Slow occlusions were used to mimic more closely occlusions occurring spontaneously. We studied 17 healthy preterm infants [birth weight, 1830 +/- 27 g (mean +/- SE); study weight, 1800 +/- 109 g; gestational age, 32 +/- 1 weeks; postnatal age, 12 +/- 2 days]. We used a nosepiece with a nasal occluder and a flow-through system to measure ventilation. A CO2 sampling catheter at the mouth was used to detect oral breathing. Of 58 occlusions, 29 were slow [resistance increasing slowly from 0 to infinite (occlusion)], and 29 were fast (infinite elastance applied in < 1 sec). Oral breathing was always established following slow and fast occlusions. In 44% of the slow occlusions, oral breathing started before complete occlusion. Arousal was observed in 12/58 (17%) of all occlusions, occurring primarily after initiation of oral breathing. Oxygen saturation and respiratory rate decreased significantly following occlusions, from 96 +/- 0.6 to 87 +/- 1.2% and 49 +/- 2.8 to 38 +/- 2 breaths/min, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Obstructive sleep apnea and the hyoid: a revised surgical procedure

Obstructive sleep apnea syndrome results from a loss of muscular activity of pharyngeal dilators and airway collapse at the hypopharynx-base of tongue or the oropharynx-soft palate. The hyoid arch and its muscle attachments strongly affect hypopharyngeal airway patency and resistance. On the basis of these concepts and previous experience, a modified hyoid suspension procedure is presented. Fifteen consecutively treated surgical patients underwent an isolated modified hyoid suspension procedure to correct hypopharyngeal obstruction. Oropharyngeal-palatal obstruction had previously been corrected or was thought not to be a component of the obstruction. Treatment outcomes were based on objective polysomnographic data and subjective clinical correction of excessive daytime sleepiness. The polysomnographic data included analysis of the respiratory disturbance index and lowest oxyhemoglobin desaturation. On the basis of these criteria, 12 of 15 patients (75%) had correction of their excessive daytime sleepiness and marked improvement in their sleep disorder breathing. The mean preoperative respiratory disturbance index was 44.7 +/- 22.6, and the lowest oxyhemoglobin desaturation was 82% +/- 6%. The postoperative respiratory disturbance index and lowest oxyhemoglobin desaturation were 12.8 +/- 6.9 and 86% +/- 5%, respectively. The modified hyoid suspension procedure appears to offer significant adjunctive treatment for hypopharyngeal obstruction in obstructive sleep apnea syndrome.

Ability of new lung function tests to assess methacholine-induced airway obstruction in infants

We assessed the ability of innovative lung function tests to detect bronchial obstruction induced by methacholine bronchial challenge. Fifty-five recurrently wheezy infants (mean age 16 +/- 5.2 months) free of respiratory symptoms underwent baseline lung function tests. Forty-two completed the methacholine challenge. Maximal flow at functional residual capacity (VmaxFRC) was obtained using the squeeze technique; compliance and resistance of the respiratory system (Crs, Rrs) was measured with the passive expiatory flow volume technique; tidal volume breathing patterns were analyzed from recordings of respiratory rate (RR), tidal volume (VT), and inspiratory time divided by total cycle of duration (Ti/Ttot). Expiratory tidal flow volume (V/VT) curves were described with multiple indices such as the ratio of expiratory time necessary to reach peak tidal expiratory flow (Fpet) to expiratory time (Tme/Te). Transcutaneous oxygen tension (PtCO2) was measured as an indicator of response to methacholine challenge. Of 42 infants 41 responded to methacholine by a change > or = 2 standard deviations from baseline values. The mean SD unit changes were 9.8 in PtCO2, 3.7 for VmaxFRC, 2.8 for Crs, 2.09 for Rrs, 3.1 for RR, 1.6 for Ti/Ttot, 2.2 for Tme/Te 3.9 for PFVt. We conclude that these noninvasive lung function tests, especially VmaxFRC and Fpet, can be used to detect minor or moderate airway obstruction. Further studies are needed to determine the value of the tests in assessing bronchial disease and effects of its treatment.

Accuracy of nine commercially available pulse oximeters in monitoring patients with chronic respiratory insufficiency

9 pulse oximeters (BIOX-III, Nellcor 250, Jaeger CNS, Micro2), Pulsox-8, Oxycount, PulsOXImeter, PalcoLabs and Pulsox-7) were studied in 90 COPD patients. The transcutaneus oxygen saturation (SaO2%) was compared with arterial oxygen saturation calculated simultaneously with drawn blood samples (AVL-995). The measurement of error distribution and the cumulative distribution function (CDF) of measurement errors allows ranking of the pulse oximeters, which can be divided in 3 groups. We conclude that the accuracy of the tested nine pulse oximeter does not enable precise absolute measurements, specially at lower oxygen saturation ranges.

Airflow obstruction and monocyte TNF release in coal workers

Respiratory health of 102 retired coal miners was assessed by chest radiographs, lung function measurements, and questionnaires, and related to tumor necrosis factor-alpha (TNF-alpha) production by blood monocytes upon priming with different stimuli. The objective was to assess a possible relationship between airflow obstruction and TNF-alpha production in retired coal workers. No significant differences in lung function were observed between cases of coal workers' pneumoconiosis (CWP) (n = 27; > %) and references (n = 75; = > %), nor was the effect of cumulative exposure on flow volume or impedance parameters significant. TNF-alpha release upon stimulation of blood monocytes with coal mine dust was significantly increased in cases with International Labour Organisation (ILO) score 0/1 (doubtful cases) compared to references and cases with a higher ILO score. Airflow limitation defined either as a FEV1 < 80% (N = 10; 5 cases of CWP) or as a resonance frequency > 15 Hz accompanied by a negative frequency dependence of resistance (N = 9; 4 cases of CWP) was significantly related to high levels of TNF-alpha release upon stimulation with endotoxin and silica, with silica showing the strongest relation. These data suggest that in this group airflow limitation is associated with an increased expression of inflammatory mediators indifferent of the presence of pneumoconiosis.

Plasma acetylsalicylic acid and salicylic acid levels during aspirin provocation in aspirin-sensitive subjects

The ability of aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) to inhibit the cyclo-oxygenase which catalyzes formation of prostaglandins appears to be central to the mechanisms involved in aspirin sensitivity. We have investigated whether the plasma levels of acetylsalicylic acid (ASA) and its main metabolite salicylic acid (SA) at the time of intolerance reactions correspond with the concentrations required for enzyme inhibition in vitro. Twelve aspirin-sensitive and 15 aspirin-tolerant subjects were followed during provocation with aspirin. ASA and SA concentrations in plasma were determined by HPLC. After oral provocation (up to 460 mg cumulative dose), the levels of ASA and SA in plasma were equivalent in aspirin-sensitive and aspirin-tolerant subjects. For the aspirin-sensitive subjects, at the time of adverse reaction, the concentration range was 2.9-33.3 microM for ASA and 18.1-245 microM for SA. Oral provocation with sodium salicylate yielding 10-fold higher SA levels did not elicit intolerance reactions. Statistically significantly lower levels of ASA and SA (P < or = 0.01) evoked airway obstruction, as compared with merely extrapulmonary symptoms. Bronchial absorption of aspirin was found after inhalation of lysine-aspirin and was comparable in asthmatic and nonasthmatic subjects. In three aspirin-sensitive subjects who developed airway obstruction, the plasma levels for ASA and SA were 0.9-2.6 microM and 0.0-6.7 microM, respectively. In conclusion, the plasma levels of ASA reached at the time of a positive reaction are of the magnitude known to inhibit cyclo-oxygenases. Neither differences in bioavailability of ASA nor the formation of SA seems to contribute to the aspirin-elicited reactions.

Effects of repetitive airway obstruction on O2 saturation and systemic and pulmonary arterial pressure in anesthetized dogs

We examined the effects of multiple repetitive airway obstruction (RAO) on arterial oxygen saturation (SaO2) and pulmonary and systemic arterial pressure in eight anesthetized spontaneously breathing dogs. SaO2 was monitored at the tongue with a pulse oximeter. RAO created by an electrical valve that was attached to a tracheal cannula was alternated with seven consecutive spontaneous breaths until the nadir SaO2 (nSaO2) became constant or decreased to less than 35%. Tracheal occlusion durations of 15, 30, 45 and 60 s were chosen arbitrarily. In each animal nSaO2 decreased with every trial number in an exponential fashion, and the rate of nSaO2 fall was greater for the longer occlusion duration. In each animal the increases in pulmonary arterial pressure (PAP) and systemic arterial pressure (SAP) were inversely related to the nSaO2 values, and the relationship between nSaO2 and PAP or SAP was identical for all occlusion durations. Moreover, when the animals breathed pure oxygen and SaO2 did not decrease, there were no significant increases in the PAP and SAP at similar levels of pleural pressure (Ppl). In another six dogs, the effects of RAO on PAP and SAP were compared with those of intermittent hypoxic exposure without apnea, which was achieved by the inhalation of hypoxic gas (4 to 6% O2, 5% CO2 in N2) instead of RAO, to examine the effects of interruption of ventilation. The relationships between nSaO2 and both pressures did not differ significantly from those during RAO.(ABSTRACT TRUNCATED AT 250 WORDS)

Hemoglobin desaturation during sleep and daytime in patients with cystic fibrosis and severe airway obstruction

Transcutaneous hemoglobin saturation by pulse oximetry was evaluated during sleep and for 2-3 h during the day in 31 patients with cystic fibrosis (median age 15.2 years; range 7.6-33.6 years) and severe airway obstruction. Pulse oximetry readings were analyzed as a cumulative percentage of time in which oxygen saturation was < 90% during both sleep and daytime. Each patient was also examined using clinical and radiological scores, spirometry and arterial blood-gas analysis. The agreement between arterial and transcutaneous saturation was evaluated in 29 patients. The difference between transcutaneous and arterial saturation was 2.4 +/- 2.0% and it increased as arterial saturation decreased. Clinical and radiological scores and spirometry parameters showed a poor correlation with both overnight and daytime desaturation. An arterial saturation < 94% may indicate a risk of consistent desaturation. This occurred for more than 50% of the time in 11 of 20 patients during sleep and in 5 of 20 patients during daytime hours.

Effect of hyperoxia on the arousal response to airway occlusion during sleep in normal subjects

The effect of hyperoxia on the arousal response to airway occlusion during non-rapid eye movement (NREM) sleep was studied in six normal male subjects with a mean age (+/- SD) of 23.5 +/- 8.7 yr by testing the response to the occlusion of a face mask covering the nose and mouth. Occlusion trials while the subjects breathed room air (room air condition) were alternated with trials in which subjects breathed a mixture of room air and oxygen adjusted to maintain a sleeping baseline arterial oxygen saturation of 98% (hyperoxic condition). The time to arousal (mean +/- SEM) was significantly longer during oxygen administration (4.1 +/- 4.5 versus 28.9 +/- 4.6 s; p < 0.002). The maximal deflections in airway pressure were measured at a supraglottic location during airway occlusion to reflect the degree of inspiratory effort. The maximal airway suction pressure preceding arousal did not differ between the room air (27.4 +/- 5.4 cm H2O) and hyperoxic conditions (26.6 +/- 5.9 cm H2O). Conversely, the rate of increase in inspiratory effort (maximal pressure) during occlusion was decreased by oxygen administration. We conclude that hyperoxia prolongs the time to arousal after airway occlusion by decreasing the rate of increase in the magnitude of inspiratory efforts, but it does not change the arousal threshold.

Translaryngeal jet ventilation and end-tidal PCO2 monitoring during varying degrees of upper airway obstruction

STUDY OBJECTIVES

To explore the ventilatory adequacy of translaryngeal jet ventilation (TLJV) during partial upper airway obstruction and the usefulness of monitoring end-tidal CO2 (PETCO2) during this condition.

DESIGN

Prospective, nonrandomized, sequential crossover design.

SETTING AND PARTICIPANTS

Apneic dog model (five dogs; mean weight, 23 kg).

INTERVENTIONS

Animals were intubated with a 9.0-mm endotracheal tube with the tip positioned above the cricothyroid membrane. Upper airway obstructions of 40%, 69%, and 80% were created. TLJV was performed through the cricothyroid membrane using a 13-gauge catheter with 100% oxygen, 45 psi, 15 breaths per minute, and 30% inspiratory time for 15 minutes at each upper airway obstruction. Data collected at baseline (no upper airway obstruction) and one-minute intervals included arterial blood pressures, continuous PaCO2 measurements, and PETCO2 at the TLJV catheter tip and above the level of obstruction. Arterial blood gases were obtained at 0 and 15 minutes. Data were analyzed using Pearson's correlation, analysis of variance, and Turkey's multiple comparisons (significance, P less than .05).

MEASUREMENTS AND RESULTS

Baseline values for all variables did not significantly differ at the onset of each testing phase. Mean pH increased significantly from baseline during 69% upper airway obstruction (7.36 to 7.54, P less than .05) and 80% upper airway obstruction (7.39 to 7.61, P less than .01). Mean PaCO2 decreased significantly from baseline during all upper airway obstructions: 40% upper airway obstruction (39.9 to 33.6 mm Hg, P less than .01), 69% upper airway obstruction (38.3 to 25.6 mm Hg, P less than .001), and 80% upper airway obstruction (36.2 to 18.2 mm Hg, P less than .001). PaCO2, PETCO2, and pH differed significantly between each level of upper airway obstruction (P less than .01). PETCO2 was significantly correlated with PaCO2 (r = .84, P less than .001) and did not significantly differ from PaCO2. No signs of barotrauma were observed in any animal at any degree of upper airway obstruction.

CONCLUSION

TLJV during partial upper airway obstruction in our model provided safe and adequate-to-supranormal minute ventilation. In fact, marked hypocapnia and alkalemia occurred at levels of 69% and 80% upper airway obstruction, thus dispelling concepts that TLJV may cause hypercapnia during partial upper airway obstruction. PETCO2 correlates well with PaCO2 and may be valuable for monitoring ventilation when using TLJV in the nonobstructed or partially obstructed upper airway.

Sleep related upper airway obstruction in a cohort with Down's syndrome

The prevalence of sleep related upper airway obstruction (UAO) was studied in a cohort of 34 children with Down's syndrome from a geographically defined area. Thirty two (94%) of the children, ranging in age between 0.1 and 4.9 years (median 1.4), underwent full clinical assessment for UAO including parental questionnaires and overnight tape recordings of chest wall movements and arterial oxygen saturation (SaO2). Compared with controls, children with Down's syndrome had (a) an increased incidence of stridor and chest wall recession during sleep, (b) an increased frequency of a pattern on inspiration indicating increased upper airway resistance, (c) a reduced baseline oxygen saturation (having excluded recordings on four children with potential for right to left intracardiac shunting), and (d) an increased number of episodes with SaO2 less than or equal to 90% despite continued chest wall movements. At their initial assessment seven children (22%) had evidence of UAO. The 18 youngest children (less than or equal to 1.7 years) underwent repeated recordings and clinical assessment until they had all reached 2 years of age. A further three were found to have developed UAO. Sleep related UAO is a common problem in children with Down's syndrome, occurring in 10 of 32 (31%) of this population based sample.

[Increase in blood pressure due to continuous obstructive snoring]

Sleep-related breathing disorders can strain the cardiovascular system. Link-ups with arterial hypertension have been confirmed in obstructive or mixed sleep apnoea which is characterised by discontinuous nocturnal snoring. On the other hand, it is known that arterial hypertension is very frequently seen in snorers. The present study deals with short-term, breathing-related blood pressure patterns and blood pressure changes during the snoring phase. 18 obstructive snoring phases were identified in 4 male patients aged 50 years (42-65), Broca index 136 (119-171). Polysomnographic measurements were carried out in the sleep laboratory and the blood pressure was continuously recorded via the a. brachialis. The short-term breathing-dependent blood pressure changes were systolic 10.8 (10-30) mmHg at the beginning and 17.5 (10-30) mmHg at the end of the snoring phase (P less than 0.01). Diastolically there was a difference of 9.4 (5-15) mmHg versus 13.9 (5-25) mmHg (P less than 0.01). During the snoring phases the systolic blood pressure increased from 140.3 (120-190) mmHg to 170.0 (145-235) mmHg and the diastolic pressure from 69.7 (50-110) mmHg to 93.1 (70-120) mmHg. The study proves that blood pressure increases occur not only in apnoeic snoring but also in continuous obstructive snoring. It is suspected that these changes are responsible for the high frequency of arterial hypertension among continuous snorers.

Increased airways reactivity after smoke inhalation

13 fire victims who required treatment after smoke inhalation underwent lung function assessment within 3 days of injury and 3 months later. Initial airways hyperreactivity improved over this period, but FEV1 and airways specific conductance did not change significantly. There was a strong correlation between exposure carboxyhaemoglobin concentration (an indicator of smoke exposure) and initial airways specific conductance (r + 0.79; p = 0.006). Airways obstruction after smoke inhalation in house fires may be more common and more persistent than is generally recognised. Early lung function tests would allow the incidence of pulmonary complications after smoke inhalation and the potential benefits of early use of inhaled antiinflammatory drugs to be assessed.

High pressure percutaneous transtracheal ventilation: the use of large gauge intravenous-type catheters in the totally obstructed airway

Percutaneous transtracheal ventilation using a large gauge intravenous-type catheter can be used successfully in the setting of complete upper airway obstruction in animals. In this study, using a large animal model, satisfactory oxygenation and ventilation was achieved by inversely varying the catheter size and the inspiration to expiration ratio (I:E). Specifically, 30 to 63 kg ruminants with an obstructed upper airway were resuscitated for 30 minutes from a hypoxic, hypercarbic, and acidotic state using 12- and 14-gauge catheters connected to a 50 psi oxygen source via a two-way valve with an I:E of 1:4 and 1:9 seconds, respectively. Shorter expiratory time or increased inspiratory time with these intravenous catheters resulted in significant hemodynamic compromise, barotrauma, inadequate carbon dioxide elimination, acidemia, and frequent death.

Pulmonary gas exchange after multiple airway occlusion by beads in the dog

Patients with asthma frequently show a bimodal distribution of ventilation-perfusion (VA/Q) ratios. One mode is centered on a VA/Q ratio of near normal value, whereas the other has a very low VA/Q ratio. There is usually almost no perfusion of unventilated units. We have suggested that this bimodal pattern is caused by complete obstruction of some airways with ventilation of their distal alveoli through collateral channels. To test this hypothesis we occluded airways of anesthetized dogs with beads of 1.6, 2.4, and 4.8 mm in diameter, and measured VA/Q distributions using the multiple inert gas elimination technique. Beads were inserted via a bronchoscope until the Pao2 fell by 20 mm Hg, or its value was less than 70 mm Hg. Occlusion of small airways (1.6 mm diameter) resulted in a mild increase in dispersion of VA/Q ratios. With 2.4 mm beads, the dispersion increased further. By contrast, all dogs given 4.8 mm beads showed a bimodal distribution of VA/Q ratios. All animals developed some shunt. We interpret these results as showing that when 1.6 mm airways are occluded, collateral ventilation to distal units is so efficient that ventilation is only mildly impaired; however, as occlusion becomes more proximal, collateral ventilation is less effective until with 4.8 mm beads, the ventilation of distal units is so poor that a bimodal pattern develops. The results suggest that the bimodal distributions seen in asthma are compatible with complete obstruction of some airways, and that the levels of obstruction may affect the pattern of VA/Q distribution.

Increases in plasma concentrations of a prostaglandin metabolite in acute airway obstruction

Plasma concentrations of a stable prostaglandin F2 alpha metabolite were measured by radioimmunoassay during and after recovery from acute airway obstruction in 15 infants. Mean (SEM) metabolite concentrations (ng/l) in plasma obtained both before (1033 (418)) and after (1470 (413)) initial treatment for airway obstruction were significantly higher than those obtained from the same subjects after resolution of the obstruction--25.5 (6.6)--and those obtained from two comparison groups. Infants positive for respiratory syncytial virus (mean 1122 (227)) had significantly higher concentrations than those who were negative (207.6 (46)). Additionally, seven subjects with a history of recurrent wheezing after resolution of airway obstruction had a significantly higher mean level (3500 (1400)) during attacks of airway obstruction than those without (600 (100)). These data suggest that prostaglandin F2 alpha mediates respiratory inflammation in airway obstruction and that trials of specific anti-inflammatory agents for the treatment of airway obstruction may be warranted.