Distal Airway Function Assessed by Oscillometry at Varying Respiratory Rate: Comparison with Dynamic Compliance

Figures & data

Table 1 Clinical characteristics; n = (53)

Age (yr):	43 ± 10
Male:	63%
Current Smokers:	4%
Past Smokers:	14%
Past disease:
Asthma	11%
Allergic rhinitis	23%
Morbid Obesity (BMI > 30)	24%
Pulmonary Function:
FEV1(%)	97 ± 16
FVC (%)	97 ± 17
FEV1 / FVC^†	84 ± 4
Raw^‡ (cmH20/L/s) n = 42	1.7 ± 0.6
TLC^§ (%) n = 44	95 ± 14

*Pulmonary function and compliance data are Mean ± SD expressed as percent of predicted.

^†FEV₁/FVC, ratio between forced expiratory volume in 1 second to forced vital capacity.

^‡R_aw, airway resistance assessed by plethysmography.

^§TLC, total lung capacity assessed by plethysmography.

Figure 1 Baseline impulse oscillometry parameters: R₂₀ (top panel), X₅ (center panel) and frequency dependent parameters: R_{5 − 20} and AX (bottom panel). The dotted line represents the published upper limit of normal for each parameter. Mean values ± SE are graphed pre (•) and post (◯) bronchodilator. Values were abnormal and returned toward normal following bronchodilator. *p < 0.001.

Figure 2 The relationship between R₂₀ obtained by oscillometry and R_L calculated from esophageal manometry is illustrated. A tight correlation between R₂₀ and R_L was demonstrated. Regression line is plotted (r = 0.74; p < 0.001).

Figure 3 X₅ during baseline breathing is plotted for each subject as a function of C_st,l (left panel) and C_dyn,1 at RR60 (right panel). The relationship between X₅ and lung compliance was assessed using a nonlinear inverse regression since reactance is a function of elastance (1/C). There is a statistically significant relationship between X₅ and C_st,l, but with a large variance. The relationship is highly significant when X₅ is related to C_dyn,1 at RR60.

Figure 4 The top panel illustrates a tight correlation between AX and C_dyn,l/C_st,l at RR60 (power function regression). The bottom panel illustrates that the two frequency dependent oscillometric parameters (AX and R_{5 − 20}) are tightly correlated in a linear fashion.

Figure 5 Effects of increased respiratory rate on oscillometric parameters are shown for 18 normal (top 3 panels) and 53 symptomatic subjects (lower 3 panels). Mean data ± SE are presented pre (•) and post (◯) bronchodilator. The dotted line represents the published upper limit of normal for each parameter. Increased respiratory rate had minimal effect on oscillometric parameters in normal subjects. In contrast, in the 53 symptomatic subjects R₂₀ increased minimally, as in normal subjects, but frequency dependent parameters R_{5 − 20} and AX increased markedly. This enhancement was obliterated following bronchodilator administration despite elevated respiratory rate. Statistically significant increases at RR40 compared with baseline are illustrated as *p < 0.05.

Figure 6 The change in R₂₀ and AX at increased respiratory rate relative to baseline are shown for normal subjects (n = 18), subjects without FDC (n = 7) and with FDC (n = 46). R₂₀ increased minimally and with a similar magnitude in all groups. Conversely, AX increased significantly in subjects with FDC compared with both normal subjects and subjects without FDC. * p < 0.05.