Measurement of airway resistance (Raw) requires body plethysmography, which makes difficult to monitor in disabled patients. On the other hand, measurement of airway resistance using the ineterrupter technique (Rint) does not require the big and expencive apparatus, and has been reported in animal models, healthy subjects, pre-school children, and geriatric patients. However, little is known about Rint in patients with high airway resistance. In this study, measurements of Rint was compared those of conventional Raw using body plethysmography in patients with airflow limitation such as COPD.
We studied 7 patients including 5 with COPD (M:F 5:2, age 59 ± 6.4 years). Rint was measured using a commercialized system (HI-801, Chest M.I., Tokyo). The algorism of Rint measurement in this system is based on a report by Chowienczyk et al. (Eur Respir J 4: 623, 1991). Raw were measured using body plethysmography.
The mean FEV1, Rint, and Raw were 1.20 ± 0.64L ranged from 0.57 to 2.13L (51 28%pred, 24-92%), 0.59 ± 0.30 kPa/l/sec (0.28-1.12), and 0.30 ± 0.14 kPa/l/sec (0.05-0.46), respectively. Although Rint was significantly correlated with Raw (r=0.86, p<0.05), the differences tended to be bigger in patients with high Raw. Since airway pressure curve after interruption was not linear, the oral pressure determination at the time point (t15) immediately after the valve interruption, computed by back extrapolating a line drawn through two points (t30 and t70), was difficult to interprete.
These results suggest that Rint may be useful to estimate airway resistance even in patients with severe airflow limitation in this system, although the value of the mesurements were higher than the conventionally measured Raw. The determination of the oral pressure at the interruption established by Chowienczyk is needed to be physiologically reexamined.
This technique would provide the rough value of the airway resistance. It will be useful to study at the bedside where the body plethysmography can not work.
Hajime Kurosawa, Employee One of the auther, K Maruta, is an employee of CHEST MI.