BACKGROUND

Asthma is diagnosed by a combination of positive family history of allergy or asthma, a history of cough which worsens at night, wheeze, difficulty in breathing, and chest tightness. However, the medical history may not be reliable in diagnosing asthma. Furthermore, the physical examination may be normal as asthma symptoms are characteristically episodic. An objective measure is needed to diagnose asthma accurately and to monitor response to treatment. Objective documentation of variable and reversible airflow obstruction can be obtained through measurement of forced expiratory volume (FEV), Peak expiratory flow (PEF) or hyper-responsiveness to methacholine inhalation challenge. A reversibility of 15% in forced expiratory volume in one second (FEV₁) following inhaled short acting bronchodilator or after a 7 to 14 days course of inhaled glucocorticoid or oral prednisolone is diagnostic of asthma.¹

A diurnal variation in PEF of more than 20% is also considered to be diagnostic of asthma. Mean morning PEF provides information about current clinical control of asthma, and peak flow variability provides independent information about risk of future exacerbations. When PEF variability increases it is associated with an increased risk of asthma exacerbations.² It was suggested by The British and International guidelines that the PEF is an alternative to FEV₁ when expressed as percentage of normal value. PEF is a simple reproducible measure that correlate well with FEV₁.^3,4 The PEF is widely used in different settings such as home monitoring,⁵ emergency departments⁶ and its role is increasing in the diagnosis and management of asthma. In ambulatory lung function    monitoring, PEF is highly responsive to inhaled corticosteroid (ICS) or long-acting B-agonist (LABA) treatment, with morning PEF more responsive than evening PEF compared to FEV₁.^7,8

However, some investigators have demonstrated that there is a considerable disagreement between FEV₁ and PEF in estimating the degree of airway obstruction.^9,10 They added that PEF is inferior to FEV₁ as a clinic-measured parameter of airways obstruction and may underestimate airway obstruction in individuals with airway remodelling. Peak expiratory flow can be measured with a simple peak flow meter without spirometry. On the other hand, FEV₁ measured in spirometry is the gold standard for airway obstruction because it has less intra subject variability,¹¹ but it is not available to most Clinicians managing asthmatic patients in Nigeria. It is thus necessary to understand how PEF measures relate with FEV₁.

The aim of this study is to investigate the spirometric findings and the relationship between PEF measured by Wright peak flow meter and FEV₁ among asthmatic patients and to compare them as absolute and as percentage of predicted values.

MATERIALS AND METHODS

This was a cross-sectional descriptive study carried out in the medical outpatient clinics of Obafemi Awolowo University Teaching Hospitals Complex (OAUTHC), Ile-Ife and the OAUTHC, Wesley Guild Hospital, Ilesa, from February 2011 to July 2011. These hospitals provide primary, secondary and tertiary health care services. Ile-lfe and Ilesa are both semi-urban towns in South-West, Nigeria.

Patients with asthma were selected from among the patients attending the Outpatient Clinic. Asthmatics included in the study were aged between 16-55 years without acute severe asthma in the prior 4 weeks and with spirometric evidence of asthma as defined by a bronchodilator reversibility test with change in FEV₁ > 15% and/or 200ml, 20 minutes after inhalation of 400 microgram of short-acting B- agonist (salbutamol).¹² All asthmatics who had comorbid conditions like hypertensive heart failure and COPD and patients with uncertain diagnosis of asthma were excluded from the study.

The study procedure was explained to the patients and a proforma was used to document information on socio-demographic data, clinical features and spirometric parameters of each study subject. Spirometry was performed according to the ATS guidelines.¹² PEF was measured using a Peak Flow meter after thorough explanation and practical demonstration of the procedure. The best out of three satisfactory readings was recorded. FEV₁ and Forced Vital Capacity (FVC) were measured using a standardized spirometer which utilizes a turbine sensor and is therefore not affected by temperature, pressure or gas density and does not require calibration. Inhalation of bronchodilator was withheld for a minimum of 12 hours before spirometry was performed. The lung function indices were assessed before and 20 minutes after the inhalation of 400ug of salbutamol using Metered Dose Inhaler (MDI) which is attached to a spacer device. 

The highest lung volume values were accepted for calculation. The measured value of FEV₁ and PEF obtained were changed to percent predicted based on the race, sex, age, height and weight of the patient and were compared. Data analysis was done using a statistical computer software, IBM-SPSS version 15.0. Categorical variables were expressed as percentages, and student t-test was used for the continuous variables. P-value of less than 0.05 was recorded as statistically significant.

RESULTS

Shown below on table1 is the spirometric parameters among the subjects. Mean pre-bronchodilator FEV₁ was 1.97 ± 0.87L, while the post-bronchodilator FEV₁ was 2.32 ± 0.951. Mean pre-bronchodilator PEF was 286 ± 107 (L/ Min) while the post-bronchodilator PEF was 348 ± 114(L/Min). The predicted pre-bronchodilator FEV₁ was 75±25.7L. Table 2 shows the distribution of the study subjects based on predicted FEV₁. As shown, 60% of the study population had predicted FEV₁ of less than 80%. There was a significant correlation between PEF and FEV₁ as shown on table 3 below. Table 4 shows the sex differences in the spirometric parameters of the participants. The males had higher values when compared with females in FEV₁ and FVC. The difference was statistically significant.

Table l: Lung function values for the subjects

Table 2: Percentage predicted FEV₁ and PEF values of the study subjects.

Table 3: Lung function values obtained before and after bronchodilator inhalation

Table 4: Gender differences in the lung functions test of the subjects

NS = Not Significant, S= Significant

DISCUSSION

Spirometry is often used in determining the extent of airways impairment. Spirometric parameters used for the estimation of pulmonary functions are FVC, FEV₁ and PEF. Both FEV₁ and PEF are useful in the assessment and monitoring of asthmatic patients on treatment. Spirometry is the gold standard in the evaluation of pulmonary function, but it is observed that most health facilities in Nigeria still do not have Spirometers to carry out spirometry on patients with respiratory diseases, likely due to cost. On the other hand, peak flow meter is portable, less expensive and the simplest of the tools of lung function measurement.

In this study the mean pre-bronchodilator FEV₁ was I .97 ± 0.87L, as against the post bronchodilator FEV₁, value of 2.32 ± 0.951. The mean pre-bronchodilator PEF was 286 ± 107 L/min while the post-bronchodilator PEF was 348 ± 114L/min. The predicted pre-bronchodilator FEV₁ was 75 ±25.7L. Only 40% of the study subjects had normal predicted FEV₁ values as against 35.4% for PEF. Sixty percent of the respondents had predicted FEV₁ value of < 80% in contrast to 64.4% for PEF. One of the significant findings of this study was that the same number of subjects, 23 (34.6%) had FEV₁ and PEF predicted values of <59%.

These results demonstrated the usefulness of PEF monitoring in the assessment of airways obstruction although it is not an equal alternative to FEV₁. PEF and FEV₁ represent function of airway portions different from each other¹³ and PEF may underestimate or overestimate the severity of airway obstruction. A study had shown that in asthma clinical trials, FEV₁ is better than PEF as a clinic-measured physiologic parameter, but PEF is useful in ambulatory monitoring.⁷

Pulmonary function is affected by various factors including sex, age, height, weight, environment and ethnicity.^14,15 Our study revealed that the males had higher values when compared with females in FEV₁ and FVC and the difference was statistically significant. Spirometric indices for the study subjects showed a mean pre-bronchodilator FEV₁ of 2.29± 1.00 and 1.75 ± 0.59L, FVC of 3.13± I.28L and 2.34 ± 0.60L for males and females respectively. Generally, the lung volumes and capacities of males were higher than females. When males and females were matched for height, weight and age, males were found to have higher lungs volumes and capacities than females. This could be explained by the gender-dependent lung size differences.

In this index study, there was a significant correlation between PEF and FEV₁. These findings are similar to the work of Gautrin, et al¹⁶ who found a high correlation between FEV₁ and PEF among their study subjects. A study among acute asthmatics in Korea by Iseon, et al¹⁷ also revealed a high correlation between PEF and FEV₁, but PEF was found to underestimate severity of bronchial obstruction in acute asthma. However, change in FEV₁ was only moderately associated with change in PEF in another study.¹⁸

CONCLUSION

This study showed a statistically significant correlation between PEF and FEV₁ among the study subjects. Since PEF correlates with FEV₁ and peak flow meter is portable, affordable and accessible, the use of peak flow metres should be encouraged as self-monitoring tools of airway obstruction and a tool for monitoring the response to a bronchodilator therapy among patients with bronchial asthma.

STUDY LIMITATIONS

The relatively small sample size of this study could limit the generalization of the findings to the general population of asthmatics.

ACKNOWLEDGEMENT

The authors wish to express our profound gratitude to all staff of the Respiratory Unit, Department of Internal Medicine, OAUTHC Ile-lfe and OAUTHC, Wesley Guild Hospital, Ilesa for their support. We also thank all the study subjects for their cooperation.

AUTHOR CONTRIBUTIONS

Author JJ conceptualized the research, collected data and wrote the draft of the manuscript. Author ATE conducted data analysis. Author IPO prepared the final draft of the manuscript. All authors read and approved the final draft of the manuscript.

FUNDING

None.

COMPETING INTERESTS

The authors declare that there are no competing interests.

ETHICAL CONSIDERATION

Ethical clearance was obtained from the Research and Ethical Clearance Committee, OAUTHC and informed consent was obtained from all the study subjects.