Related work

Expiratory capnography in asthma: evaluation of various shape indices

B. You*, R. Peslin**, C. Duvivier**, V. Dang Vu*, J.P. Grilliat*
* Médecine H, Hôpital Central, 54000 Nancy , FRANCE
** INSERM Unité 14, Hôpital de Brabois, 54500 Vandoeuvre-lès-Nancy, FRANCE
Eur Respir J., 1994, 7, 318-323.

Authors' e-mail : capno@infonie.fr

Abstact
The shape of the capnogram is modified by airway obstruction, and the evaluation of this deformation, using measurable indices, could allow an indirect measurement of bronchial patency. A previous study undertaken in asthmatic subjects showed a good correlation between a capnographic index (end-tidal slope) and a spirometric parameter (forced expiratory volume in one second as a percentage of predicted (FEVl %pred)) and suggested the study of other indices.
The correlations between capnographic and spirometric indices were measured in 10 healthy subjects and 30 asthmatic patients. The usefulness of eight descriptive indices, analysing the successive phases of the capnogram, was assessed by measuring their reproducibility and their sensitivity to airway obstruction. The intraindividual and interindividual variabilities (Vi and VI) and the noise/signal ratio (Vi/VI) were measured by comparing the resuIts of two successive capnographic measurements in 14 asthmatic subjects. The results show an increasing noise/signal ratio along the expiration (between 23 and 62 %).
Significant correlations between spirometry and capnography were found with all indices but the strongest were observed with indices analysing tbe intermediate phase of the capnogram, that is the angle between tbe ascending phase (E2) and the alveolar plateau (E3).
The correlations show that the analysis of the capnogram's shape is a quantitative method for evaluating the severity of bronchospasm. This ability, added to specific advantages (noninvasiveness, effort-independency, measurements during tidal breathing) opens new fields of application to capnography, such as measurement of bronchospasm in children and computerized monitoring of asthma.

 [Back to abstract]

	S1	S2	S3	SR	AR	SD
Vi/VI %	35.1	35.2	61.7	28.2	23.3	24.9
FEV1 % Pred	0.73	0.89	0.90	0.89	0.85	0.93

Reproduceability and correlations of capnographic indices with FEV1.

Reproducibility of each index was evaluated by calculating the noise/signal ratio Vi/VI (intra-individual /inter-individual variabilities). Good overall results were found (25-35%) except for later indices (SD3 and S3) which appear to be artefact dependent.

Correlations to FEV1 are very good (r=.73-.93) for all indices (p<.001 in all cases).

 
[Back to abstract]

	Controls		Asthmatics
			Total asthm.	FEV1>80%		FEV1 40-80		FEV1<40%
	n=10		n=30	n=10		n=10		n=10
FEV1 %P	104 ±7.7	***	62 ±26	89 ±7.1	***	67 ±10	***	29 ±6.4
S1	15.0 ±1.8	***	11.4 ±2.3	11.4 ±2.3	*	11.5 ±1.2	**	9.3 ±1.7
S2	0.23 ±0.06	***	0.55 ±0.3	0.31 ±0.1	ns	0.45 ±0.2	***	0.90 ±0.2
S3	0.16 ±0.05	***	0.35 ±0.2	0.18 ±0.04	ns	0.28 ±0.1	**	0.59 ±0.2
SR	1.6 ±0.05	***	5.5 ±3.9	2.4 ±0.9	*	4.0 ±2	**	10.1 ±3
AR	88 ±3	***	78 ±9	86 ±6	*	79 ±6	**	20.0 ±5.6
SD	18.2 ±2	***	11.2 ±4.3	15.3 ±1.35	*	12.2 ±2.5	***	6.5 ±1.9

Mean values of FEV1 and capnographic indices in control subjects and in asthmatic patients
There are significant differences (p<.001) between capnographic indices values in healthy and asthmatic subjects. There are also differences between three subgroups of asthmatic patients classified according to spirometric criteria (FEV1%Pred >80, 40-80, <40).
[Back to abstract]

  [Back to abstract]