Asia Pac Allergy.  2012 Jan;2(1):49-58. 10.5415/apallergy.2012.2.1.49.

Relationship between sensitivity to dyspnea and fluctuating peak expiratory flow rate in the absence of asthma symptoms

• Kamiya K
• Sugiyama K
• Toda M
• Soda S
• Ikeda N
• Fukushima
• Hirata H
• Fukushima
• Fukuda T

• KMID: 2397411
• DOI: http://doi.org/10.5415/apallergy.2012.2.1.49

Abstract

BACKGROUND
Exacerbation of asthma has a negative impact on quality of life and increases the risk of fatal asthma. One of the known risk factors for patients with a history of near-fatal asthma is reduced sensitivity to dyspnea.
OBJECTIVE
We aimed to identify patients with such risk before they experienced severe exacerbation of asthma.
METHODS
We analyzed asthma symptoms and peak expiratory flow rate (PEFR) values of 53 patients recorded daily in a diary over a mean period of 274 days. Patients matched their symptoms to one of eight categories ranging in severity from 'absent' to 'severe attack'. We then analyzed the relationship between PEFR and asthma symptoms by dividing the PEFR value by the values of clinical parameters, including asthma symptom level.
RESULTS
Average PEFR was 75.2% (50.5-100%) in the 'absent' symptom category, 64.5% (36.6-92.6%) in 'wheeze', 57.3% (25.0-94.7%) in 'mild attack' and 43.6% (20.4-83.1%) in 'moderate attack', with the personal best reading taken as 100%. Thus, differences in PEFR in patients in the same symptom category varied widely. PEFR in wheeze, mild attack and moderate attack did not correlate significantly with duration of asthma, forced expiratory volume in one second or proportion of personal best to standard predicted PEFR values. These PEFRs showed no significant difference in groups divided by type of regular treatment, but showed a significant negative correlation with the coefficient of variation (CV) of PEFR when asthma symptoms were absent. CV for absent symptoms should be between +4.0 and -4.0% when using regression analysis to measure PEFR if the decreased PEFR is in agreement with guidelines.
CONCLUSION
To determine which patients have reduced sensitivity to dyspnea, CV of PEFR should be considered when asthma symptoms are reported as absent. When patients present with more than 8% fluctuation in PEFR, we should intervene in their treatment, even when they claim to be stable.

Keyword

Asthma; Asthma exacerbation; Peak expiratory flow; Severity

MeSH Terms

Asthma*
Dyspnea*
Forced Expiratory Volume
Humans
Peak Expiratory Flow Rate*
Quality of Life
Risk Factors

Figure

• 

  Fig. 1 Flow chart for enrollment. COPD, chronic obstructive pulmonary disease; PEFR, peak expiratory flow rate.

• 

  Fig. 2 For each patient, the average value of peak expiratory flow rate (PEFR) was calculated for moderate attack, mild attack, and wheeze, in relation to personal best as 100%. Patients were divided into groups according to their regular treatment. The relationship between PEFR and regular treatment showed no significant relationship with reduced sensitivity to dyspnea for any of the symptoms of moderate attack, mild attack or wheeze. Data are expressed as mean ± SD. ICS, inhaled corticosteroid; N.S., not significant.

• 

  Fig. 3 For each patient, the average value of peak expiratory flow rate (PEFR) was calculated for moderate attack, mild attack, and wheeze, in relation to personal best as 100%. Correlations between PEFR and pulmonary function were analyzed for each symptom. A significant correlation was seen only for % flow rate at 25% of FVC (V̇25) in the case of mild attack and wheeze. PEFR for each symptom, which is stipulated by the aforementioned guidelines, is shown as a gray line. FVC, forced vital capacity; FEV1, forced expiratory volume in one second.

• 

  Fig. 4 For each patient, the average value of peak expiratory flow rate (PEFR) was calculated for moderate attack, mild attack, and wheeze, in relation to personal best as 100%. Neither the proportion of personal best to standard PEFR (A) nor the duration of asthma (B) showed a significant correlation with PEFR. However, the coefficient of variation (CV) of PEFR when asthma symptoms were reported to be absent showed a significant negative correlation with PEFR (C). PEFR for each symptom, which is stipulated by the aforementioned guidelines, is shown as a gray line. N.S., not significant.

• 

  Fig. 5 Peak expiratory flow rate (PEFR) monitoring for a 39-year-old female patient as an example case. PEFR was decreased to 30.6% in first moderate attack, and average PEFR and coefficient of variation (CV) in the reported absence of asthma symptoms for 1 month before the attack were 77.3% and 0.11, respectively (A). However, when the patient presented the next moderate attack 3 months after her asthma was fully controlled after episode A, PEFR was much less decreased to 67.3%, which the patient presented as shortness of breath (SOB) in episode A. Average PEFR and CV in the absence of asthma for the preceding 1 month were also better at 84.5% and 0.06, respectively (B). Thus, reduced sensitivity to dyspnea was improved.

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