Time Course and Degree of Hyperinflation with Metronome-Paced Tachypnea in COPD Patients

Figures & data

Table 1 Patient characteristics

	All Subjects
Subjects, n	14
Age, yrs	71 ± 8
Height, cm	176 ± 6
Weight, kg	83 ± 20
Body Mass Index, kg/m^2	26.6 ± 6.3
FEV1, L	1.22 ± 0.41
% predicted	43 ± 14
FEV1/FVC, %	40 ± 12
TLC, L	7.19 ± 1.66
% predicted	119 ± 29
FRC, L	4.88 ± 1.66
% of predicted	137 ± 41
RV, L	4.09 ± 1.62
% of predicted	165 ± 66
DLCO, ml/min/mm Hg	13.0 ± 4.8
% of predicted	53 ± 22
IC, L	2.05 ± 0.56
% of predicted	82 ± 26
IC/TLC, %	30 ± 11

Data are presented as mean ± SD. FEV₁: forced expiratory volume in one second; FVC: forced vital capacity; TLC: total lung capacity; FRC: functional residual capacity; RV: residual volume; DL_CO: diffusing capacity of the lung for carbon monoxide; IC: Inspiratory Capacity.

Figure 1 Time course and degree of dynamic hyperinflation produced by metronome paced tachypnea. There is a graded decline in IC corresponding to the graded increase in f_R. For each f_R the decline in IC occurs by 30 seconds and does not decline further by 60 seconds. The IC returns to baseline between episodes of paced tachypnea. The plot's horizontal line represents the median, the box encompasses the 25th to 75th percentile and the error bars encompass the 10th to the 90th percentile. Repeated Measures ANOVA P < 0.001. * p < 0.05 compared to Baseline 1. **P < 0.05 compared to Baseline 1 and f_R 20/min (30s). *** p < 0.05 compared to Baseline 1, f_R 20/min (30s and 60s), and f_R 30/min (30s and 60s).

Table 2 Inspiratory capacity differences over time and between frequencies of respiration

Comparison		Mean IC Difference (L)	95% CI	p value	Bonferroni Adjusted p Value
20/min (30s) vs.	20/min (60s)	−0.025	−0.107 to 0.057	0.5	…
30/min (30s) vs.	30/min (60s)	0.014	−0.067 to 0.096	0.7	…
40/min (30s) vs.	40/min (60s)	0.035	−0.054 to 0.123	0.4	…
Baseline 1 vs.	20/min (30s)	−0.216	−0.349 to −0.084	0.004	0.03
	30/min (30s)	−0.397	−0.582 to −0.212	0.0005	0.004
	40/min (30s)	−0.535	−0.706 to −0.364	< 0.0001	< 0.001
20/min (30s) vs.	30/min (30s)	−0.181	−0.286 to −0.076	0.003	0.02
30/min (30s) vs.	40/min (30s)	−0.138	−0.181 to −0.095	< 0.0001	< 0.001

A negative mean IC difference indicates a decline in IC between first and second measurement being compared. IC: inspiratory capacity; 20/min (30s): IC measurement after 30 seconds of metronome-paced respiration at 20 breaths per minute; 20/min (60s): IC measurement after 60 seconds of metronome-paced respiration at 20 breaths per minute; 30/min (30s): IC measurement after 30 seconds of metronome-paced respiration at 30 breaths per minute; 30/min (60s): IC measurement after 60 seconds of metronome-paced respiration at 30 breaths per minute; 40/min (30s): IC measurement after 30 seconds of metronome-paced respiration at 40 breaths per minute; 40/min (60s): IC measurement after 60 seconds of metronome-paced respiration at 40 breaths per minute; Baseline 1: first baseline IC measurement.

Table 3 Respiratory rate and P_ETCO₂ at baseline and following 60 seconds of metronome-paced tachypnea

Baseline		Metronome Paced
fR (/min)	PETCO2 (mm Hg)	fR (/min)	PETCO2 (mm Hg)
18.6 ± 6.5	31.0 ± 5.8	20	29.5 ± 5.2
18.1 ± 4.8	29.9 ± 5.3	30	28.1 ± 5.6
19.1 ± 5.9	30.2 ± 6.5	40	25.8 ± 5.9

Data are expressed as mean ± SD. f_R (/min): frequency of respiration in breaths per minute; P_ETCO₂; end-tidal carbon dioxide tensions.

Figure 2 (A) Correlation between FEV₁ percent predicted and change in inspiratory capacity (IC) percent of predicted. (B) Correlation between DL_CO percent predicted and change in inspiratory capacity (IC) percent of predicted.

Figure 3 Correlation between FEV₁ percent predicted and EELV expressed as a percent of TLC at baseline (A) and at maximal DH (f_R 40/min x 30 secs) (B).