Inspiratory fall in systolic pressure in normal and asthmatic subjects

We used a noninvasive monitor of arterial pressure to determine whether respiratory changes in arterial pressure were closely correlated with airflow obstruction in asthmatic patients during bronchial challenge with methacholine. To validate the noninvasive measurement of respiratory changes in arterial pressure, a preliminary study in 6 subjects with normal cardiovascular and respiratory systems was done during cardiac catheterization for suspected coronary artery disease. There were no significant differences between inspiratory falls in systolic pressure measured noninvasively and those measured from intraaortic pressure. In 11 otherwise healthy asthmatic patients we measured finger arterial pressure, end-expiratory lung volume (FRC), and forced expired volume (FEV1) during baseline and bronchial challenge in the supine posture. Finger arterial pressure was also measured in 11 normal control subjects seated and supine. Normal subjects had an inspiratory fall in systolic pressure (IFSP) of 3.2 mm Hg supine and 5.1 mm Hg seated (p < 0.01). Asthmatic patients when bronchodilated (seated FEV1 = 83 +/- 7% of predicted) had an IFSP of 5.9 mm Hg supine (p < 0.01 compared with supine normal subjects). During bronchial challenge (average fall in FEV1 = 22%), IFSP increased to 16.1 mm Hg (p < 0.001 compared with baseline). In asthmatic subjects, there was a significant correlation between IFSP and FEV1 (mean r = -0.92 +/- 0.05, p < 0.01), and the average change in IFSP/change in FEV1 was -0.38 mm Hg per percentage change in FEV1. During subsequent bronchodilation, IFSP decreased with a similar time course as relaxation of airway smooth muscle, assessed by the breath-to-breath fall in FRC.