INSPIRATORY FALL IN SYSTOLIC PRESSURE IN NORMAL AND ASTHMATIC SUBJECTS

We used a noninvasive monitor of arterial pressure to determine whethe r respiratory changes in arterial pressure were closely correlated wit h airflow obstruction in asthmatic patients during bronchial challenge with methacholine. To validate the noninvasive measurement of respira tory changes in arterial pressure, a preliminary study in 6 subjects w ith normal cardiovascular and respiratory systems was done during card iac catheterization for suspected coronary artery disease. There were no significant differences between inspiratory falls in systolic press ure measured noninvasively and those measured from intraaortic pressur e. In 11 otherwise healthy asthmatic patients we measured finger arter ial pressure, end-expiratory lung volume (FRC), and forced expired vol ume (FEV(1)) during baseline and bronchial challenge in the supine pos ture. 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 FEV(1) = 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 FEV(1) = 22%), IFSP increased to 16.1 mm Hg (p < 0.001 compared wi th baseline). In asthmatic subjects, there was a significant correlati on between IFSP and FEV(1) (mean r = -0.92 +/- 0.05, p < 0.01), and th e average change in IFSP/change in FEV(1) was -0.38 mm Hg per percenta ge change in FEV(1). During subsequent bronchodilation, IFSP decreased with a similar time course as relaxation of airway smooth muscle, ass essed by the breath-to-breath fall in FRC. We conclude that measuremen t of IFSP from finger arterial pressure is a useful index of clinical state in asthmatic patients during moderate bronchoconstriction. The m ethod is sensitive enough to detect differences between normal and bro nchodilated asthmatic subjects and differences in normal subjects betw een upright and supine.