Why inspiratory and expiratory flow rates different

A peak flow meter can help show the narrowing of the airways well before an asthma attack happens. A peak flow meter can help you determine:. A peak flow meter can help you manage asthma. It can give you and your healthcare provider information about how open the airways are in your lungs. The PFM can detect small changes in the large airways before you start to wheeze.

Using a PFM every day will let you know when your peak flows are starting to drop. This allows you to make early changes in your medicine or routine to help keep asthma symptoms from getting worse. The PFM can also identify the reading at which you need to call your healthcare provider or go to the emergency room. Your healthcare provider may not advise you use a PFM unless your asthma is moderate or severe and you are managing it with medicine.

PFM can also be used to assess other lung problems, such as:. This is a chronic lung condition that affects the smallest air sacks in the lungs alveoli.

Chronic bronchitis. This is long-term inflammation of the bronchi. It creates excess mucous and a chronic cough. Use of a different type or brand of peak flow meter, as measurements may vary among brands and types of meters.

Your healthcare provider will explain the procedure to you. Ask him or her any questions you have. You may be asked to sign a consent form that gives permission to do the procedure. Read the form carefully. Ask questions if anything is not clear. Tell your healthcare provider if you take any medicines. This includes prescriptions, over-the-counter medicines, vitamins, and herbal supplements. Before starting daily peak flow meter measuring, your healthcare provider may have you follow a detailed schedule over 2 to 3 weeks.

This value will be used as a baseline for your daily measurements. In patients with severe airflow limitation, a considerable volume of trapped gas may communicate very poorly or not at all.

While sitting in an airtight box, the patient tries to inhale against a closed mouthpiece from FRC. As the chest wall expands, the pressure in the closed box rises. Knowing the pre-inspiratory box volume and the pressure in the box before and after the inspiratory effort allows for calculation of the change in box volume, which must equal the change in lung volume. Knowing FRC allows the lungs to be divided into subvolumes that are either measured with spirometry or calculated see Figure: Normal lung volumes Normal lung volumes Airflow and lung volume measurements can be used to differentiate obstructive from restrictive pulmonary disorders, to characterize severity, and to measure responses to therapy.

In contrast to the spirogram, which displays airflow in L over time in sec , the flow-volume loop see Figure: Flow-volume loops Flow-volume loops Airflow and lung volume measurements can be used to differentiate obstructive from restrictive pulmonary disorders, to characterize severity, and to measure responses to therapy. The principal advantage of the flow-volume loop is that it can show whether airflow is appropriate for a particular lung volume.

For example, airflow is normally slower at low lung volumes because elastic recoil is lower at lower lung volumes. Patients with pulmonary fibrosis have low lung volumes and their airflow appears to be decreased if measured alone.

However, when airflow is presented as a function of lung volume, it becomes apparent that airflow is actually higher than normal as a result of the increased elastic recoil characteristic of fibrotic lungs. A Normal. Inspiratory limb of loop is symmetric and convex.

Expiratory limb is linear. Airflow at the midpoint of inspiratory capacity and airflow at the midpoint of expiratory capacity are often measured and compared. B Obstructive disorder eg, emphysema, asthma. Peak expiratory flow is sometimes used to estimate degree of airway obstruction but depends on patient effort.

C Restrictive disorder eg, interstitial lung disease, kyphoscoliosis. The loop is narrowed because of diminished lung volumes. Airflow is greater than normal at comparable lung volumes because the increased elastic recoil of lungs holds the airways open. D Fixed obstruction of the upper airway eg, tracheal stenosis, goiter.

The top and bottom of the loops are flattened so that the configuration approaches that of a rectangle. E Variable extrathoracic obstruction eg, unilateral vocal cord paralysis, vocal cord dysfunction. When a single vocal cord is paralyzed, it moves passively with pressure gradients across the glottis.

During forced inspiration, it is drawn inward, resulting in a plateau of decreased inspiratory flow. During forced expiration, it is passively blown aside, and expiratory flow is unimpaired.

The analyzer has a response time of about 0. The detail above shows the delay between respiratory phases and the rate of gas sampling: at the end of maximal expiration, a maximal CO 2 content would be recorded. Notice and explain differences in the gas concentrations in relation to the following breathing patterns: during normal breathing during a shallow and rapid respiration following the VC manoeuvre during and following inspiratory apnea.

Your browser does not support script Respiration Laboratory. Lung volume and capacities. The following values are measured: duration of the respiratory cycle inspiratory time and expiratory time peak inspiratory and expiratory flows tidal volume. The following values are calculated: rate of breathing or frequency minute ventilation.

The red trace on top shows flow on Channel 1. Forced Vital Capacity manoeuvre. Also, the decrease in Pel Blow with equivalent breath-hold time was greater in asthmatic subjects, which is consistent with an increase in viscoelastic elements in the lung.

These findings corroborate previous suggestions that inspiratory speed and the duration of breath holding have significant implications in the performance of spirometry and peak flow measurements, and indicate the importance of standardization of the preceding inspiration when determining FEV1 and PEFR.