Effects of buffering in hypercapnia and hypercapnic hypoxemia

Anesthetized, paralyzed and mechanically ventilated pigs were exposed to extreme hypercapnia (Paco_2-20 kPa) at Fio₂ 0.4 for 480 min, with (n = 6) or without (n = 6) continuous infusion of isotonic buffers (bicarbonate and trometamol). Arterial pH was higher in buffered animals than controls, 7.21 ±0.01 vs 7.01±0.01 (mean ± s.e.mean, P < 0.01). Serum osmolality and Paco₂ did not differ between groups throughout the experiment. The hemodynamic response to hypercapnia was attenuated in the buffered group, who had lower heart rate, 133 ± 6 vs 189±12 min^-1 (P < 0.01), mean arterial pressure (MAP) 109 ± 4 vs 124 ± 4 mmHg (14.5 ± 0.5 vs 16.5 ± 0.5 kPa) (P < 0.05), mean pulmonary arterial pressure 16±1 vs 23 ± 1 mmHg (2.1 ±0.1 vs 3.1 ±0.1 kPa) (P < 0.01), and pulmonary vascular resistance (PVR) 249 ± 21 vs 343 ± 20 dyn s-cm^-5 (2490±210 vs 3430±200 μN-s-cm^-5) (P < 0.01), compared with the control group. Subsequently, both groups were exposed to hypercapnic hypoxemia by stepwise increases in Fio₂ (0.15, 0.10, 0.05) at 30-min intervals, while Fico₂ was kept at 0.2. PVR increased in both groups (P < 0.05) but, except for heart rate, all hemodynamic differences between the groups disappeared during hypoxia. At Fio₂ 0.15, buffered animals had higher arterial oxygen saturation (73 ± 5%) than the controls (55 ± 5%), (P < 0.05). The control animals died after 1–29 min (mean 14 min) at Fio₂ 0.10, while all buffered animals survived Fio₂ 0.10 with stable MAP (122 ± 14 mmHg (16.3 ± 1.9 kPa). The buffered animals died after 4–22 min (mean 15 min) at Fio₂ 0.05. We conclude that buffering to a pH of 7.21 attenuates the observed hemodynamic response in extreme hypercapnia and improves survival in hypercapnic hypoxemia.     

Morphological changes in chest radiographs of patients with acute respiratory distress syndrome (ARDS)

Objective: To determine whether the quality of infiltrations in chest radiographs can accurately predict the histological extent of fibrotic change in patients with acute respiratory distress syndrome (ARDS). Design: Retrospective clinical investigation. Setting: Intensive care unit (ICU) of a university teaching hospital. Patients and methods: Of 47 patients treated with extracorporeal membrane oxygenation (ECMO) for severe ARDS over a 5-year period, 23 patients underwent open lung biopsy at thoracotomy for treatment, mostly of pneumothorax. Chest films obtained by portable chest roentgenography preceding the operation were reviewed retrospectively and compared to the histomorphological results of the lung specimen. Results: Chest radiographs displayed mixed alveolar-reticular opacification in 60.2 %, alveolar patterns in 22.9 % and reticular opacities in 10.5 %. In 0.4 % there were no infiltrates, 6 % could not be evaluated because of insufficient quality. There was no relevant difference between the right and left lungs. Subdividing patients into two groups according to the histological results of either absent or mild (1) or severe (2) lung fibrosis, we found an alveolar haziness in 12.3 % in group 1 compared with 28.2 % in group 2, while reticular characteristics were identified in 13 % and 11 %, respectively. Conclusions: The most common opacity in chest radiographs of patients with severe ARDS treated with ECMO is mixed alveolar-reticular opacification. Severe lung fibrosis is not positively correlated with a reticular radiographic pattern. ECMO does not lead to specific radiological changes in conventional radiograms, contrary to clinical findings that treatment with ECMO might induce pleural or pulmonic haemorrhage, especially in the earlier days when systemic heparinization had to be used instead of the heparin-coated tube-surfacing. Received: 24 November 1997 Accepted: 20 July 1998     

Effects of low-dose propofol administration on central respiratory drive, gas exchanges and respiratory pattern

The effects of sedative-hypnotic doses of propofol on respiratory drive and pattern have not yet been extensively described. Repeated small boluses of propofol (0.6-0.3 mg.kg-1) were administered to ten ASA I patients undergoing carpal tunnel release using regional anaesthesia. Airway pressure, capnography and pneumotachography were continuously recorded. With respect to basal values, no significant variations of respiratory rate, minute volume, tidal volume, inspiratory and expiratory time, total expiratory cycle, Ti/Ttot, TV/Ti, P0.1, EtCO2 and blood gas analysis were observed. Low doses of propofol, to maintain conscious sedation of light sleep, have not been shown to cause respiratory depression.     

Effects of Repeated Deep Inspirations on Recovery from Methacholine-Induced Airway Narrowing in Normal Subjects

Background. A single deep inspiration (DI) is known to be a potent bronchodilator but it is not known if repeated DI can accelerate sustained recovery from bronchoconstriction. Methods. We induced sustained bronchoconstriction using increasing concentrations of nebulized methacholine (Mch) during tidal breathing and assessed airway narrowing by measuring respiratory resistance (Rrs) using forced oscillation in six healthy subjects. On separate days we examined the effects of DI every 3 minutes and of prohibition of DI on recovery of Rrs for 30 minutes after the end of Mch nebulization. Results. Bronchoconstriction (Rrs ∼ 150% above baseline) was induced. DI during recovery had a transient bronchodilator effect but no cumulative effect. At 30 minutes after end of nebulization (and 2 minutes after the last DI) Rrs was 87% above baseline compared to 93% above baseline when DI was prohibited. Conclusion. Recovery from induced bronchoconstriction with methacholine was slow (∼ 2%/min) and not accelerated by frequent DI.     

Comparison of class and subclass antibody response to live and UV-inactivated RSV administered intranasally in mice.

To determine the effect of viral dose and replication on the subclass antibody response to RSV, mice were immunized intranasally with different doses of live RSV (10(4)-10(6) pfu) and compared to mice given an immunizing regimen of UV-inactivated RSV. Mice given the 10(6) pfu dose of live RSV and mice given the 40 micrograms dose of UV-inactivated RSV had comparable class specific antibody responses to whole RSV in serum and respiratory secretions. Serum from these two groups of mice were then compared for IgG subclass response to whole RSV. A predominance of IgG2a subclass antibody was found for both immunizing regimens, and no significant differences in subclass proportions were noted between regimens. These two regimens were then compared for serum total IgG response to RSV surface glycoproteins F and G. The serum IgG response to these glycoproteins was lower after immunization with UV-inactivated RSV than after live-RSV immunization (F: P = 0.03; G: P less than 0.05), even though the serum IgG response of the two groups to whole RSV was comparable. The IgG subclass response to surface glycoproteins was evaluated for live RSV immunization. The proportions of subclass antibody responses to glycoprotein F were comparable to the subclass response proportions to whole RSV and were not characteristic of a T-dependent response pattern. The subclass profile for glycoprotein G was not comparable to that of whole RSV but was suggestive of a T-independent response pattern.     

N-乙酰半胱氨酸的抗菌活性及对细菌生物被膜的抑制作用

N-乙酰半胱氨酸(N-acetylcysteine,NAC)是临床常用化痰药.除此之外,NAC还有一定的抗菌活性,可以抑制细菌的黏附,减少细胞外多糖蛋白复合物的产生,破坏已生成的生物被膜,对被膜下细菌也有一定的杀菌作用,并与某些抗菌药物存在协同作用,引起国内外学者越来越多的关注.研究结果提示临床上可以将NAC与抗生素联合应用治疗某些感染性疾病尤其是慢性呼吸道感染,不过尚需进一步大样本临床研究来证明.     

火箭推进剂呼吸防护装备研究现状及发展趋势

本文对呼吸防护装备的应用、发展进行了综述，分析了火箭推进剂毒性对呼吸防护的要求和国内推进剂呼吸防护研究现状，对推进剂专用呼吸防护装备的发展趋势进行了探讨。     

Nasal lavage leukotrienes in infants with RSV bronchiolitis

Respiratory syncytial virus (RSV) bronchiolitis is a very common infection in infants and, after the acute phase, a number of patients develop a reactive airway disease that lasts for years. Although the pathogenesis of the lung damage after RSV bronchiolitis is still largely unknown, previous studies suggest that leukotrienes may play an active part in it. The aim of this study was to measure leukotriene levels in the nasal lavage fluid (NLF) collected in infants during RSV bronchiolitis and 1 month later. Cysteinyl leukotrienes (Cys-LTs) and leukotriene B(4) (LTB(4)) were measured in the NLF of 22 infants with their first episode of RSV bronchiolitis and 16 healthy infants. A second NLF sample was collected to measure leukotriene levels 1 month after the acute disease. NLF Cys-LT levels were significantly higher in infants with RSV bronchiolitis than in healthy controls [950 pg/ml (285.5-2155.9) vs. 110.5 pg/ml (66.5-451.3), p = 0.01], and they remained so a month after the acute infection (p = 0.02). A subanalysis showed no difference in Cys-LTs concentrations, either between bronchiolitis infants with and without a family history of atopy, or between those with and without passive exposure to cigarette smoke. No significant difference was found between the LTB(4) levels measured in the bronchiolitis cases and the control children. Cys-LTs are significantly increased in the NLF of infants with acute RSV bronchiolitis, and remain so at 1-month follow-up, suggesting a possible role of these eicosanoids in the pathogenesis of the disease.     

Respiratory obstruction following vocal cord injection

Two patients who each had a paralysed left vocal cord are discussed. Both had poor coughing ability preoperatively. The affected cords had been injected with tetrafluoroethylene (Teflon) paste 3 days before operation and this had given immediate improvement in coughing and speech. During induction of anaesthesia, respiratory obstruction occurred that was related to the injected cord. This cause of obstruction has not been reported previously. The potential benefits of cord injection for voice, cough and laryngeal competence are reviewed.