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To assess the mechanisms of pulsus paradoxus (i.e., inspiratory decline of greater than or equal to 10 Torr in systolic pressure) in airway obstruction, we studied 12 patients with chronic airflow obstruction before and during breathing through an external resistance that provided loads during both inspiration and expiration. Esophageal pressure (Ppl) and brachial artery pressure, relative to either atmospheric (Pa) or esophageal pressure (Patm), were measured simultaneously during normal and loaded breathing. It was assumed that changes in intrathoracic systemic arterial transmural pressure were adequately represented by Patm. During control, no significant difference between systolic fluctuation (delta Pa) and pleural swings (delta Ppl) was found. Concurrently, inspiratory and expiratory Patm were nearly identical. By contrast, under maximally loaded conditions, higher magnitudes of delta Ppl than delta Pa were found and consequently Patm rose with inspiration. In this connection, the plot of delta Pa against delta Ppl showed that the slopes for delta Ppl less than or equal to 15 Torr (1.2 Torr delta Pa/delta Ppl) and delta Ppl greater than 15 Torr (0.4 Torr delta Pa/delta Ppl) were significantly different. Under all experimental conditions we found during inspiration a rise in diastolic Patm that is consistent with an increase in left ventricular afterload.(ABSTRACT TRUNCATED AT 250 WORDS)

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Bronchial hyperreactivity in asthmatics has been demonstrated after inhalation of specific allergen, histamine (6), hyperventilation (26), exposure to cold air (13) or exercise (22). Bronchoconstriction is also sometimes induced by forced breathing during spirometry (24, 11). We report an asthmatic atopic patient who showed this effect after repeated recordings of forced expiratory vital capacity. We have investigated the mechanics of this patient's performance in order to discover the reason for the bronchoconstriction and to study the way in which several drugs prevent it. SUBJECT AND METHODSThe patient, a 16-year-old boy, had a history of wheezing attacks for about 8 years; he showed skin sensitivity to several antigens. When his forced vital capacity (FVC) and forced expiratory volume in i sec (FEVi) were measured, using a waterless spirometer (Vitalograph®), they were normal on the first occasion; but in successive recordings the measurements fell and were associated with wheezing. At the fifth run FEVi was 60 per cent of the initial value. More complete studies were then carried out.-^ .\ct3 .^Itergologica, 30, 6