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N. S. (1975). Thorax, 30,[337][338][339][340][341][342][343] Evaluation of breath holding in hypercapnia as a simple clinical test of respiratory chemosensitivity. Breath holding was used as the basis of a simple test of respiratory chemosensitivity. Breath holding was begun at selected degrees of hypercapnia produced by CO2 rebreathing. In 16 healthy control subjects there was a linear regression of the log of breath-holding time on the Pco2 at the start of breath holding. Breath-holding time (BHT) and the slope of a log BHT/Pco2 plot were closely correlated with the ventilatory response to CO2. In five cases of the idiopathic hypoventilation syndrome, CO2 retention and reduced ventilatory response to CO2 were accompanied by prolonged breath-holding time and the regression of log BHT on Pco0 was abnormally flat. However, in 17 patients with chronic airways obstruction, breath-holding time was never prolonged and the log BHT/Pco2 relationship was normal, even though 13 had a diminished ventilatory response to CO2 and four had chronic CO2 retention. It is concluded that the BHT/Pco2 relationship provides a useful index of respiratory chemosensitivity which is not influenced by airways obstruction. This may be helpful in the detection of impaired chemosensitivity as a cause of CO2 retention even when the ventilation CO2 response is reduced non-specifically by coexisting airways obstruction.Chronic CO2 retention is most frequently due to chronic airways obstruction which hinders the translation of respiratory motor activity into ventilation. Another important cause of chronic hypercapnia is impairment of respiratory chemosensitivity as in the idiopathic hypoventilation syndrome. The recognition of impaired chemosensitivity in cases of this syndrome is sometimes made difficult by the coexistence of chronic airways obstruction (McNicol and Pride, 1965;Rhoads and Brody, 1969). Respiratory chemosensitivity is usually measured by the increment in ventilation elicited by a change in the alveolar or arterial CO2 tension produced by breathing a C02-enriched gas mixture. However, the ventilatory response to CO2 is altered if ventilation is obstructed even when respiratory chemosensitivity is normal (Cherniack and Snidal, 1956). This has stimulated a search for other tests of respiratory 'Present address:

A B S T R A C T Semicarbazide, a lathyrogen. was given to growing rats to elucidate the consequences of altering the molecular structure of fibrous proteins within the lung. Static pressure-volume (P-V) measurements during deflation of saline-filled lungs showed normal recoil pressure and compliance values within the physiological range of lung volume. Quasi-static P-V measurements were also normal during slow reinflation, even beyond physiological limits to a recoil pressure of 20 cm H20. However, the lungs of experimental rats ruptured at much lower recoil pressures than controls. Histology was normal in lungs fixed at 20 cm H20. In contrast, lungs showed dilatation of terminal air spaces, rupture of alveolar walls, and an increase in mean linear intercept in experimental compared with control specimens, when fixed at 30 cm H20. Biochemical analyses revealed reduced cross-linking of lung collagen without change in its total content. There were no detectable changes in the quantity or quality of lung elastin. It is concluded that semicarbazide may selectively impair the maturation of lung collagen and that immaturity of lung collagen is associated with a reduction in the tensile strength of lung tissue, without changes in elasticity within physiological volume limits.

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Pleural empyema is a collection of pus between the lungs and the chest wall. Approximately 50% of cases complicate pneumonia. It is a cause of significant morbidity and mortality despite appropriate antibiotic therapy and various options for drainage. The purpose of this report is to present the case of an human immunodeficiency virus (HIV)-positive and injection drug user male who presented with a unilateral apical sterile pleural empyema. A 36-year-old male, HIV-positive and chronic injection drug user, was admitted to our institution due to a left upper lobe lung mass seen by chest x-ray and chest pain. Left chest pain has been of 3 months of evolution, pressure-like, aggravated by deep inspiration and coughing. Patient was hospitalized 3 months before in the same institution due to a left leg cellulitis. Upon physical exam, patient is febrile with painful palpation in lower posterior left lung, decreased breath sounds throughout left lung field (worst in base) otherwise clear to auscultation bilaterally, and dull percussion in upper and middle posterior left lung field. Infectious foci and nosocomial infections were considered and he was treated intravenously with ceftriaxone and vancomycin. A soft tissue density in apical region of the left hemithorax suggestive of pleural or extrapleural origin, with increased opacification of the left upper lung parenchyma was seen during his previous hospitalization. A thorax computerized tomographic (CT) scan without contrast, performed during this hospitalization, showed a left-sided homogenously round structure with thick margins starting at the apicoposterior portion of the left upper lobe of lung. A CT-guided aspiration was performed, with almost complete resolution of the empyema. Pleural fluid was of exudative nature, with leukocytosis, no organism growth, no fungi, and no acid-fast bacilli. Two weeks after aspiration, the empyema was reaccumulating. A bronchoalveolar lavage was negative for malignancy, acid fast stain, and Grocott stain, without evidence of Actinomyces. The fact that the empyema was sterile may be explained by the long-term antibiotic therapy the patient received before samples were obtained. Pulmonary complications of HIV have been well studied, mainly caused by opportunistic infections due to their impaired immune function. Injection drug users are predisposed to a wide range of infectious processes. The pathophysiology, diagnosis, and management of this entity will be presented.