Summary of Human Respiratory System Measurement

• The respiratory system provides a means for acquiring oxygen and eliminating carbon dioxide.
• Internal respiration is the exchange of gases between blood stream and nearby cells.
• External or lung respiration is the exchange of gases between lungs and blood stream.
• It helps to avoid sudden changes in blood pH and body fluids. Respiratory system also protects the surface membranes from harsh environments such as temperature.
• Nose and nasal cavities, pharynx, larynx, tracheae, bronchi, bronchioles etc are the major parts of respiratory system.
• Tidal volume is called the depth of breathing and it is defined as the volume of gas inspired or expired during each respiratory cycle.
• IRV is the maximum amount of gas that can be inspired with effort from end inspiratory position.
• Residual volume is the amount of gas remaining in lungs after maximal expiration.
• Total lung capacity is the amount of gas contained in the lungs at the end of maximal inspiration. It is the sum of Inspiratory Capacity (IC) and Functional Residual Capacity(FRC).
• Spirometer is the most widely used instrument for the measurement of various lung capacities and respiratory volume.
• The standard spirometer consists of a movable bell inverted over a chamber of water. To balance the bell jar we use a weight to maintain the gas inside the atmospheric pressure.
• Respiratory therapy is a biomedical field in which mechanical assistance is provided for patients in respiration. Also some patients require higher than normal concentration oxygen. It is also provided by respiration therapy.
• Oxygen therapy is a means for providing oxygen for the treatment of various conditions resulting from oxygen deficiency.
• Inhalators are devices used to supply oxygen or some other therapeutic gases to the patient. It is mainly used in the treatment of conditions such as asthma.
• Ventilators are used when artificial ventilation is to be provided to the patient for a long time. It is otherwise called a respirator.
• Most ventilators used normally in positive pressure condition where the inspiratory flow is generated by applying a positive pressure greater than the atmospheric pressure.
• In pressure cycled ventilators, the inflation of lungs continues till the delivered gas to the patients reaches a predetermined level of pressure.
• In volume cycled ventilators, the ventilation of lungs continues till a specified volume of gas has been delivered to the patient.
• In a time cycled ventilator, the patient is supplied with oxygen and other gases for a certain period of time.
• In assist-control mode the ventilator is triggered by the patient’s attempt to breath. If the patient fails to breath within a predetermined level, the control mode come into action and the timer automatically triggers the device to inflate the lungs.
• So all respiratory therapy equipments include special devices called humidifiers to humidify the air by bubbling an air stream through a water container.
• Nebulizer is a special device used to administer medication to the people in the form of a mist inhaled into the lungs.
• In an ultrasonic nebulizer, an ultrasonic device is used to produce high intensity ultrasonic waves so that the medication can be easily disintegrated.
• Impedance pneumography is an indirect method used for the measurement of respiratory rate. It is comparatively simpler method because it does not require any placement of mask on the face, fixing of tubes etc. In this method we place only an electrode over the thorax region of patient.
• Aspirator is a device which is used as a part of ventilator or inhalator to remove mucus and other fluids from the airways so that the patient can breath smoothly.
• In an impedance pneumograph, Amplitude variations in output voltage is caused due to change in resistance(AR) which changes the respiration waveform. A LPF is used after the synchronous detector to remove carrier signal.
• DC amplifier after LPF is used to increase the output waveform up to a level as required by the display device.

The Author of this article, Sreejith is writing articles on Human Respiratory System and Electronics and Communications