Estimates of ventilation from inductance plethysmography in sleeping asthmatic patients

To assess the accuracy of the respiratory inductance plethysmograph (RIP) for monitoring ventilation during sleep-associated bronchoconstriction, five adult patients with nocturnal worsening of their asthma were monitored overnight in the sleep laboratory. Three of the five patients demonstrated episodic paradoxic respiratory motion of the lower rib cage undetected by the RIP. Such paradoxic motion was consistently associated with overestimation of volumetric data by RIP compared to pneumotachygraphic measurements. With onset of lower rib cage paradox, the mean error of RIP-derived VT measurements increased from 9.1 +/- 1.7 to 27.9 +/- 3.8 percent (p less than .001). Flow measurements derived from RIP were also inaccurate in the presence of lower rib cage paradox, with the mean error of the measurement increasing from 9.0 +/- 2.5 to 33.5 +/- 5.3 percent (p less than .001). We conclude that RIP is an unreliable technique for quantitatively monitoring ventilation in sleeping asthmatic patients.