Differing effects of the anxiolytic agents buspirone and diazepam on control of breathing

We compared ventilatory effects of the nonsedating anxiolytic buspirone with those of the sedating anxiolytic diazepam in nine normal men. Resting ventilatory parameters and ventilatory responses to CO2 rebreathing and inspiratory threshold loading were measured before and after placebo, diazepam, and buspirone. Placebo had no ventilatory effects. Diazepam had no effect on resting ventilation but depressed response to CO2. Buspirone had no effect on resting ventilation or CO2 response. During loading, buspirone did not alter the augmentation of mouth pressure; diazepam produced a trend toward less augmentation. Both anxiolytics altered the load compensation response for the group; in particular, an increase in ventilation during loading (seen in three of nine subjects) was suppressed by drug administration. Diazepam also markedly depressed one subject's loaded ventilation below unloaded ventilation. In summary, buspirone did not cause the depression of respiratory center chemosensitivity that was seen with diazepam and produced less depression of load compensation in normal subjects. This suggests that it may be a safer anxiolytic in patients with lung disease.

The acute administration of vasodilators in primary pulmonary hypertension. Experience from the National Institutes of Health Registry on Primary Pulmonary Hypertension

The hemodynamic responses to acute vasodilator administration were evaluated in 163 patients who were entered into the National Institutes of Health Registry on Primary Pulmonary Hypertension (PPH) between 1981 and 1985. Of a total of 491 drug administrations in these patients, 135 administrations in 104 patients were performed in a manner acceptable to the Registry. A single vasodilator was tried in 79 patients and more than one vasodilator in 25 patients. Two-thirds of the patients were in New York Heart Association Functional Classes III or IV. When the effects of all vasodilators were grouped together, there were significant decreases from baseline in mean pulmonary artery pressure (60 +/- 2 to 57 +/- 2 mm Hg, p less than 0.05) and total pulmonary resistance index (32.5 +/- 1.7 to 25.1 +/- 1.4 mm Hg/L/min/m2, p less than 0.0001), and increases in cardiac index (2.1 +/- 0.1 to 2.7 +/- 0.1 L/min/m2, p less than 0.0001). Mean systemic blood pressure fell (88 +/- 1 to 79 +/- 1 mm Hg, p less than 0.0001), whereas PaO2 was unchanged (70 +/- 3 to 71 +/- 3 mm Hg, p = NS). A fall in total pulmonary resistance greater than 20% was observed in 55% of the adequate drug trials. Adverse effects occurred in 32 of the total 491 patient-drug trials and were generally minor. Hypotension requiring treatment developed in six patients. There were two deaths attributable to vasodilator administration. Patients who died or had hypotension requiring treatment had higher right atrial pressures than did other treated patients (15 +/- 2 versus 9 +/- 1 mm Hg, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Volume adjustment of mechanics and diffusion in interstitial lung disease. Lack of clinical relevance

Relationships of lung mechanics and diffusion to lung volume were examined in 38 patients with interstitial lung disease to determine whether patterns of reduction relate to severity of disease, distinguish histologic characteristics or predict prognosis for reversibility. Normal volume-related values for both mechanics and diffusion were seen throughout the range of severity of disease. The ratio of mechanics to lung volume did not correlate with the ratio of diffusion to lung volume in the same patient. Volume relationships of mechanics and diffusion failed to distinguish pathologic predominance of fibrosis or inflammation/granulomas. These ratios failed to predict reversibility in patients who had repeated tests. These results suggest that in patients with interstitial lung disease the significance of "volume-adjustment" of mechanics and diffusion should be viewed with caution; these parameters do not appear to contribute to the assessment of pathophysiology or correlate with clinical spectrum of interstitial lung diseases.

Background ventilatory stimulus as a determinant of load compensation

Compensation for inspiratory flow-resistive loading was compared during progressive hypercapnia and incremental exercise to determine the effect of changing the background ventilatory stimulus and to assess the influence of the interindividual variability of the unloaded CO2 response on evaluation of load compensation in normal subjects. During progressive hypercapnia, ventilatory response was incompletely defended with loading (mean unloaded delta VE/delta PCO2 = 3.02 +/- 2.29, loaded = 1.60 +/- 0.67 1.min-1.Torr-1 CO2, where VE is minute ventilation and PCO2 is CO2 partial pressure; P less than 0.01). Furthermore the degree of defense of ventilation with loading was inversely correlated with the magnitude of the unloaded CO2 response. During exercise, loading produced no depression in ventilatory response (mean delta VE/delta VCO2 unloaded = 20.5 +/- 1.9, loaded = 19.2 +/- 2.5 l.min-1.l-1.min-1 CO2 where VCO is CO2 production; P = NS), and no relationship was demonstrated between degree of defense of the exercise ventilatory response and the unloaded CO2 response. Differences in load compensation during CO2 rebreathing and exercise suggest the presence of independent ventilatory control mechanisms in these states. The type of background ventilatory stimulus should therefore be considered in load compensation assessment.

Primary pulmonary hypertension. A national prospective study

A national registry was begun in 1981 to collect data from 32 centers on patients diagnosed by uniform criteria as having primary pulmonary hypertension. Entered into the registry were 187 patients with a mean age (+/- SD) of 36 +/- 15 years (range, 1 to 81), and a female-to-male ratio of 1.7:1 overall. The mean interval from onset of symptoms to diagnosis was 2 years. The most frequent presenting symptoms included dyspnea (60%), fatigue (19%), and syncope (or near syncope) (13%). Raynaud phenomenon was present in 10% (95% of whom were female) and a positive antinuclear antibody test, in 29% (69% female). Pulmonary function studies showed mild restriction (forced vital capacity [FVC], 82% of predicted) with a reduced diffusing capacity for carbon monoxide (DLCO), and hypoxemia with hypocapnia. The mean (+/- SD) right atrial pressure was 9.7 +/- 6 mm Hg; mean pulmonary artery pressure, 60 +/- 18 mm Hg; cardiac index, 2.3 +/- 0.9 L/min X m2; and pulmonary vascular resistance index, 26 +/- 14 mm Hg/L/min X m2 for the group. Although no deaths or sustained morbid events occurred during the diagnostic evaluation of the patients, the typically long interval from initial symptoms to diagnosis emphasizes the need to develop strategies to make the diagnosis earlier.

Hypercapnia in the obstructive sleep apnea syndrome. A reevaluation of the "Pickwickian syndrome"

The mechanisms of hypercapnia in eight patients with the "Pickwickian" syndrome and obstructive sleep apnea (OSAS) were evaluated pretherapy and posttherapy (tracheostomy in seven patients and chronic nocturnal use of nasal CPAP in one). Four patients (correctors) became eucapnic within two weeks of therapy. Four others (noncorrectors) remained hypercapnic. Neither residual apneas, changes in pulmonary function, change in anatomic dead space, nor changes in ventilatory chemoresponsiveness differentiated the two groups, nor did the last three factors account for return to eucapnia in the correctors. The results indicated two separate mechanisms exist for chronic hypercapnia in OSAS: a critical balance between the ventilation during the time spent awake and hypoventilation due to apneas, a mechanism removed by treatment for obstructive apnea; and sustained hypoventilation independent of the apnea phenomenon and therefore not correctible. The subset of patients with the second mechanism appears to represent the true "Pickwickian" syndrome and can be identified before therapy by measuring a low level of ventilation in the sustained awake state.

Respiratory failure in patients with acquired immunodeficiency syndrome and Pneumocystis carinii pneumonia

Seven patients with acquired immunodeficiency syndrome (AIDS) and Pneumocystis carinii pneumonia were studied to define the pathophysiology of their respiratory failure. The patients had fever, cough, dyspnea, hypoxemia, and diffuse infiltrates on chest x-ray. Biopsies revealed a spectrum of alveolar filling, interstitial edema and infiltration, and fibrosis. The patients were studied on mechanical ventilation to assess the effect of positive end-expiratory pressure (PEEP) and supplemental oxygen on shunt fraction. Mean anatomic shunt (measured on 100% oxygen) was 34 +/- 8%, which increased significantly (p less than .001) to 43 +/- 9% when the FIO2 was decreased to 40% to 60% (physiologic shunt), indicating ventilation/perfusion (V/Q) imbalance or impaired diffusion. Increasing PEEP by 9 +/- 2 cm H2O reduced the anatomic shunt to 30 +/- 7% (p less than .01) and the physiologic shunt to 37 +/- 7% (p less than .02). There was a similar decrease in anatomic and physiologic shunts in five studies, a greater decrease in physiologic shunt in four, and a greater decrease in anatomic shunt in two. Evidence of alveolar recruitment with PEEP, measured by an increase in static thoracic compliance, was found in only one study. There was no correlation between the effect of PEEP on compliance and its effect on shunt. The data suggest that in patients with AIDS and P. carinii pneumonia, PEEP can decrease shunt by reducing the anatomic shunt, improving V/Q imbalance, and converting areas of anatomic shunt to areas of low V/Q. P. carinii pneumonia in patients with AIDS can produce a clinical and pathophysiologic pattern similar to that described in the adult respiratory distress syndrome.

Relationship of functional residual capacity to static pulmonary mechanics in chronic obstructive pulmonary disease

Static pulmonary mechanics may not be the sole determinant of the functional residual capacity (FRC) in the chronic obstructive pulmonary diseases (COPD). To assess the relationship of FRC to pulmonary mechanics, pulmonary function tests such as spirometry, lung volumes, maximum expiratory flow volume curves, and single-breath diffusing capacity were related to compliance measurements in 65 patients with stable COPD. Compliance studies were examined over the range of tidal volume and at maximum lung inflation. The results showed that there was a poor correlation between the degree of hyperinflation at FRC and static compliance in the tidal range. However, there was a highly significant correlation between FRC and static lung mechanics at maximum lung inflation, as well as between FRC and diffusing capacity. Thus, in patients with stable COPD, FRC is a useful guide to static recoil properties of the lung as assessed at maximum lung inflation. Lung compliance measurement in tidal range may not reflect this relationship. An increase in FRC remains a useful index of pulmonary emphysema, even in the presence of chronic airway disease.

CO2 rebreathing and exercise ventilatory responses in humans

The relationship between the resting response to CO2 rebreathing and the ventilatory response to CO2 production during exercise was examined in 20 healthy untrained male subjects and in six patients with obesity hypoventilation syndrome. Patients were chosen because of a severely reduced response to CO2 rebreathing. There was no correlation between the CO2 rebreathing response and the exercise ventilatory response in the normal subjects, the patients, or in the group considered as a whole. This lack of correlation could not be accounted for by differences in ventilatory and occlusion pressure responses nor by reporting responses as a function of a change in hydrogen ion concentration. The independence of the CO2 rebreathing response and the exercise ventilatory response suggests the CO2 rebreathing response does not measure the relevant parameters of ventilatory control during exercise.

Nasal CPAP in obstructive sleep apnea: mechanisms of action

Sixteen patients with the obstructive sleep apnea syndrome (OSAS) were studied for 1-2 h while receiving continuous positive airway pressure (CPAP) delivered via a nasal mask. Obstructive apneas were obliterated in all. Eight patients had studies of genioglossal muscle activity (GG EMG) and one patient had computed tomograms (CT) of the upper airway while on nasal CPAP. The GG EMG studies showed two patterns: suppression and augmentation of GG EMG while on CPAP. The CT scan showed the airway to be narrowed while the patient was awake off CPAP. It returned to a normal caliber when CPAP was applied, despite sleep. These results are interpreted to suggest three potential mechanisms of action for nasal CPAP in OSAS: 1) reduced upper airway resistance due to prevention of sleep-induced collapse of the airway; 2) reduced upper airway resistance due to dilatation of the airway by nasal CPAP beyond its dimension in the awake state; and 3) possible stimulation of mechanoreceptors leading to an increase in airway tone while CPAP is applied.

Combined ventilator and bicarbonate strategy in the management of status asthmaticus

Management of intubated hypercapnic asthmatic patients requires a delicate balance between the control of pH with adequate ventilation and the risk of barotrauma associated with the high pressures that may be required. The present report documents a strategy of mechanical ventilation combined with infusion of large amounts of bicarbonate in three patients with severe status asthmaticus requiring intubation. This strategy reduced peak inflation pressure by decreasing ventilation and maintained a physiologic pH while allowing pCO2 to remain elevated.

Regulation of ventilation in the obstructive sleep apnea syndrome

The recent recognition of the sleep apnea syndrome has forced a re-evaluation of the mechanism of hypercapnia and disordered respiratory control in obese patients. Thirteen obese patients with sleep apnea were studied in an attempt to relate the pattern of sleep abnormality and awake ventilatory control to the presence of chronic hypercapnia. Patients with hypercapnia and/or hypoxemia had reduced ventilatory responses to hypercapnic and hypoxic stimulation, respectively. The presence of hypercapnia, however, did not separate the patients with respect to type, duration, or frequency of apneas. The degree of awake chemical drives could not be related to the severity of the sleep apnea phenomenon. However, patients with intact ventilatory control demonstrated augmented ventilation after apneas, which may explain their eucapnic state.

Sustained reversal of chronic hypercapnia in patients with alveolar hypoventilation syndromes. Long-term maintenance with noninvasive nocturnal mechanical ventilation

Described in this study are eight patients with alveolar hypoventilation syndromes who presented with carbon dioxide narcosis and coma. After reversal of severe hypercapnia, all patients were discharged and maintained at home for an average period of 10 years utilizing "noninvasive" nocturnal mechanical ventilation. The use of "noninvasive" mechanical ventilation at home attempted to void the hazards of tracheostomy and the difficulties inherent in continuous daytime use of oxygen. This form of treatment has allowed these patients to continue their previously productive lives. This study represents the first published long-term follow-up regarding this mode of treatment in patients with alveolar hypoventilation.

Flow-volume curve contour in COPD: correlation with pulmonary mechanics

A study was designed to evaluate the diagnostic usefulness as well as the mechanical determinants of the flow-volume contour in chronic obstructive pulmonary disease (COPD). Twenty patients with COPD of varying etiology were divided equally into two groups. Group 1 had an airway collapse pattern (described in the text) designated type 1, and group 2 had a more curvilinear obstructive pattern designated type 2. Pressure, volume, and flow relationships were examined. The results of our studies showed that a type 1 flow-volume contour in a patient with obstructive airways disease suggests a critical combination of central and peripheral airway collapse at high lung volumes with loss of elastic recoil. However, not all patients with loss of recoil will exhibit this contour. Persistence of type 1 contour suggests that there is a component of airway instability which may be irreversible.

Canopy ventilation monitor for quantitative measurement of ventilation during sleep

A portable, easily assembled system that allows quantitative monitoring of ventilation in the sleeping human subject is described. It is a modification of the system used by Kinney et al. (Metab. Clin. Exp. 13: 205-211, 1964) and Spencer et al. (J. Appl. Physiol. 33: 523-528, 1972). The system directly measures gas flow without reliance on indirect CO2 or temperature sensors or on chest wall motion. It is comfortable and reflects the tidal volume with an accuracy of 92%. It also allows measurement of oxygen consumption and CO2 production. The gas breathed by the subject can be varied in composition. Two illustrative examples of the use of the system are given: 1) a case of obstructive apnea; and 2) a case in which a drop in arterial oxygen saturation is explained by quantified hypoventilation undetected by a nasal CO2 probe.

Hermansky-Pudlak syndrome. Pulmonary manifestations of a ceroid storage disorder

The Hermansky-Pudlak syndrome is a form of oculocutaneous albinism, characterized by a qualitative platelet defect and deposition of ceroid-like material throughout the reticuloendothelial system. During a 16 month period five patients with Hermansky-Pudlak syndrome presented with symptoms, chest films and pulmonary function studies consistent with restrictive pulmonary disease. In two patients, lung biopsies revealed diffuse interstitial fibrosis. However, light and electron microscopy demonstrated ceroid-like material within alveolar macrophages. In addition, two patients presented with inflammatory bowel disease with deposition of ceroid-like material in the colon. This disorder appears to be more common than is currently recognized and should be considered in the differential diagnosis of diffuse interstitial pulmonary disease and inflammatory bowel disease. A relationship between the deposition of ceroid-like material and pulmonary fibrosis is discussed in light of recent research concerning inflammatory processes. In view of the serious pulmonary, gastrointestinal and hematologic consequences of this syndrome, there is a need for genetic counseling of these patients.

The influence of lung volume on expiratory flow rates in diffuse interstitial lung disease

This study evaluated maximum expiratory flow rates with respect to lung volume and maximum recoil pressure in selected patients with diffuse interstitial lung disease who had normal large airway function by standard technique. Coefficient of retraction was normal or greater than normal in all. Peak flow varied directly with lung volume as in normals. At 50% vital capacity (VC) and 25% VC, the absolute flow rates varied from higher to lower than normal. However, when flow was adjusted to volume, the flow/volume ratio was normal or high in all. Flow/volume ratio at mid-lung volume appeared to increase with increase in coefficient of retraction. Patients with frequency dependence of compliance had lower flow/volume ratios at 25% VC than those without, although still within normal range. Thus, despite recognized wide variations in normals, the flow/volume ratio is pertinent to the evaluation of reduced air flow rates in in interstitial lung disease to distinguish abnormal upstream airway resistance from volume-dependent reduction of flow rate. An effort-independent flow rate that yields a supernormal flow/volume ratio suggests increased recoil properties of the respiratory system.

Techniques for measuring the responsiveness of the ventilatory apparatus in man in disease

More complete understanding of the disturbances in the regulation of ventilation in disease must await techniques which can estimate the neural output of the respiratory centers and also the neural inputs. Some of these techniques, such as diaphragmatic electromyography, offer the prospect of clinical usefulness even now and newer techniques, such as mouth occlusion pressure, are promising but have just begun to be evaluated in disease. Despite the limited ability of current techniques to clearly distinguish abnormal central nervous system function of ventilatory control from peripheral mechanical limitations to ventilation, a useful interpretation of clinical tests of ventilatory responsiveness may be gained by an awareness of the many physiologic and pathogenetic factors which are interposed by disease. These factors may reinforce or diminish both stimuli and response. In chronic disease states, these modifying factors must be identified and evaluated for their role in altered ventilatory responsiveness. Frequently, therapeutic measures can induce substantial effects on these modifying factors, whereas primary disturbances of central nervous system function may be difficult to alter. For the above reasons, tests of ventilatory responsiveness which provide information focussed only on the normality or abnormality of responsiveness to CO2 breathing from measurement of minute ventilation and alveolar PCO2 in an unsteady state, as in the CO2 rebreathing test, may, in a patient, require the addition of tests which allow more complete evaluation of these modifying factors. The state of arterial blood gases, hydrogen ion concentration, bicarbonate concentration, pulmonary function, ventilatory response to exercise, as well as understanding of the state of body temperature, catecholamine secretion, the functional state of the muscles of ventilation, as well as the resistances to ventilation are all a necessary part of the evaluation.