Wednesday, September 26, 2007
Spirometry
Watch the following animation on spirometry:
http://www.goldcopd.it/spieng_flash.html
Watch the following animation on spirometry:
http://www.goldcopd.it/spieng_flash.html
Spirometry testing
The spirometry test is performed using a device called a spirometer, which comes in several different varieties. Most spirometers display the following graphs:
a volume-time curve, showing volume (liters) along the Y-axis and time (seconds) along the X-axis
a flow-volume loop, which graphically depicts the rate of airflow on the Y-axis and the total volume inspired or expired on the X-axis
The most commonly used guidelines for spirometric testing and interpretation are set by the American Thoracic Society (ATS) and the European Respiratory Society (ERS).
Procedure:
The basic FVC test varies slightly depending on the equipment used.
Generally, the patient is asked to take the deepest breath they can, and then exhale into the sensor as hard as possible, for as long as possible. It is sometimes directly followed by a rapid inhalation (inspiration), in particular when assessing possible upper airway obstruction. Sometimes, the test will be preceded by a period of quiet breathing in and out from the sensor (tidal volume), or the rapid breath in (forced inspiratory part) will come before the forced exhalation.
During the test, soft nose clips may be used to prevent air escaping through the nose. Filter mouthpieces may be used to prevent the spread of microorganisms, particularly for inspiratory maneuvers.
Limitations of test
The maneuver is highly dependent on patient cooperation and effort, and is normally repeated at least three times to ensure reproducibility. Since results are dependent on patient cooperation, FEV1 and FVC can only be underestimated, never overestimated.
Due to the patient cooperation required, spirometry can only be used on children old enough to comprehend and follow the instructions given (typically about 4-5 years old), and only on patients who are able to understand and follow instructions - thus, this test is not suitable for patients who are unconscious, heavily sedated, or have limitations that would interfere with vigorous respiratory efforts. Other types of lung function tests are available for infants and unconscious persons.
Related tests
Spirometry can also be part of a bronchial challenge test, used to determine bronchial hyperresponsiveness to either rigorous exercise, inhalation of cold/dry air, or with a pharmaceutical agent such as methacholine or histamine.
Sometimes, to assess the reversibility of a particular condition, a bronchodilator is administered before performing another round of tests for comparison. This is commonly referred to as a reversibility test, or a post bronchodilator test (Post BD), and is an important part in diagnosing asthma versus COPD.
The spirometry test is performed using a device called a spirometer, which comes in several different varieties. Most spirometers display the following graphs:
a volume-time curve, showing volume (liters) along the Y-axis and time (seconds) along the X-axis
a flow-volume loop, which graphically depicts the rate of airflow on the Y-axis and the total volume inspired or expired on the X-axis
The most commonly used guidelines for spirometric testing and interpretation are set by the American Thoracic Society (ATS) and the European Respiratory Society (ERS).
Procedure:
The basic FVC test varies slightly depending on the equipment used.
Generally, the patient is asked to take the deepest breath they can, and then exhale into the sensor as hard as possible, for as long as possible. It is sometimes directly followed by a rapid inhalation (inspiration), in particular when assessing possible upper airway obstruction. Sometimes, the test will be preceded by a period of quiet breathing in and out from the sensor (tidal volume), or the rapid breath in (forced inspiratory part) will come before the forced exhalation.
During the test, soft nose clips may be used to prevent air escaping through the nose. Filter mouthpieces may be used to prevent the spread of microorganisms, particularly for inspiratory maneuvers.
Limitations of test
The maneuver is highly dependent on patient cooperation and effort, and is normally repeated at least three times to ensure reproducibility. Since results are dependent on patient cooperation, FEV1 and FVC can only be underestimated, never overestimated.
Due to the patient cooperation required, spirometry can only be used on children old enough to comprehend and follow the instructions given (typically about 4-5 years old), and only on patients who are able to understand and follow instructions - thus, this test is not suitable for patients who are unconscious, heavily sedated, or have limitations that would interfere with vigorous respiratory efforts. Other types of lung function tests are available for infants and unconscious persons.
Related tests
Spirometry can also be part of a bronchial challenge test, used to determine bronchial hyperresponsiveness to either rigorous exercise, inhalation of cold/dry air, or with a pharmaceutical agent such as methacholine or histamine.
Sometimes, to assess the reversibility of a particular condition, a bronchodilator is administered before performing another round of tests for comparison. This is commonly referred to as a reversibility test, or a post bronchodilator test (Post BD), and is an important part in diagnosing asthma versus COPD.
A spirometer is an apparatus for measuring the volume of air inspired and expired by the lungs. It is a precision differential pressure transducer for the measurements of respiration flow rates. The spirometer records the amount of air and the rate of air that is breathed in and out over a specified time. The Spirometer and attached flow head function together as a pneumotachometer, with an output signal proportional to airflow. It was invented by John Hutchinson in 1846.
Labels: Spirometer
Wednesday, September 12, 2007
Strain Gauge Plethysmography
Strain Gauge Plethysmography is a standardized technique to measure flow and vascular resistance by using a special transducer (strain Gauge) placed on the forearm and use of two inflated blood pressure cuffs proximal and distal to the site for the temporary occlusion of either venous or arterial flow. This technique also has been used to assess endothelial dysfunction by measurements of blood flow volume and rate of flow into the forearm.
Strain Gauge Plethysmography is a standardized technique to measure flow and vascular resistance by using a special transducer (strain Gauge) placed on the forearm and use of two inflated blood pressure cuffs proximal and distal to the site for the temporary occlusion of either venous or arterial flow. This technique also has been used to assess endothelial dysfunction by measurements of blood flow volume and rate of flow into the forearm.
Labels: Strain Gauge Plethysmography
Optoelectronic plethysmography
Optoelectronic Plethysmography is a method to evaluate ventilation through an external measurement of the chest wall surface motion.
Photoplethsymograph
A photoplethysmograph(PPG) is an optically obtained plethysmograph, a volumetric measurement of an organ. A PPG is often obtained by using a pulse oximeter which illuminates the skin and measures changes in light absorption (Shelley and Shelley, 2001). A conventional pulse oximeter monitors the perfusion of blood to the dermis and subcutaneous tissue of the skin.
In theory the photoplethysmograph is simple - it measures the variation in amount of light passing through your finger caused by the pulsatile nature of blood flow. You will place a light source on one side of your finger, and a light sensitive resistor, a Cadmium Sulfide (CdS) cell, on the other side. By monitoring variations in resistance of the CdS cell you get an indication of blood flow in your finger.
The light passes through the finger and is attenuated a certain amount depending upon how much blood is in the finger. As the amount of light striking the CdS cell varies, so does its resistance. This changing resistance must be transduced, amplified and filtered. The output of the amplifier is sent to an A/D convertor, and finally to the PIC. The relative amount of fluid in the finger should be displayed on the four LEDs. Much fluid (little light) should have all LED's on. Little fluid (much light) should correspond to all LED's off.
Labels: Photoplethsymograph
Tuesday, September 11, 2007
Impedance Plethysmography
Impedance plethysmography, also called impedance test or blood flow or impedance phlebography, is a non-invasive test that uses electrical monitoring in the form of resistance (impedance) changes to measure blood flow in veins of the leg. Information from this test helps doctors detect deep vein thrombosis (blood clots or thrombophlebitis).
Purpose
Impedance plethysmography may be done in order to:
detect blood clots lodged in the deep veins of the leg
screen patients who are likely to have blood clots in the leg
detect the source of blood clots in the lungs (pulmonary emboli)
Accurate diagnosis of deep vein thrombosis (DVT) is critical because blood clots in the legs can lead to more serious problems. If a clot breaks loose from a leg vein, it may travel to the lungs and lodge in a blood vessel in the lungs. Blood clots are more likely to occur in people who have recently had leg injuries, surgery, cancer, or a long period of bed rest.
Precautions
Because this test is not invasive, it can be done on all patients and is easy to perform. However, the accuracy of the results is affected if the patient does not breathe normally or keep the leg muscles relaxed. Compression of the veins because of pelvic tumors or decreased blood flow, due to shock or any condition that reduces the amount of blood the heart pumps, may also change the test results. Both false-positives (e.g. when thrombi are non-occulsive) and false-negatives have been reported using this technique, which justifies repeated testing over a period of seven to ten days for patients with initial negative results. Success rates for this test have been estimated at anywhere from 65–66% to 92–98%.
Description
Using conductive jelly, the examiner strategically places two to four electrodes on the patient's calf (the four-electrode configuration yields a more uniform and precise current density and consequent measurement result). These electrodes are connected to an instrument called a plethysmograph, which records the changes in electrical resistance that occur during the test and produces a graph of the results.
The patient must lie down and raise one leg at a 30° angle so that the calf is above the level of the heart. The examiner then wraps a pressure cuff around the patient's thigh and inflates it to a pressure of 45–60 cm of water for 45 seconds. The plethysmograph records the electrical impedance changes that correspond to changes in the volume of blood in the vein at the time the pressure is exerted and again three seconds after the cuff is deflated. This procedure is repeated several times in both legs.
This test takes 30-45 minutes, costs an estimated $50-$100 (as of 2001), and results can be available within a few minutes.
Impedance plethysmography works by measuring the resistance to the transmission of electrical energy (impedance). This resistance is dependent upon the volume of blood flowing through the veins. By graphing the impedance, the doctor or technician can tell whether a clot is obstructing blood flow.
Preparation
Patients undergoing this test do not need to alter their diet, change their normal activities, or stop taking any medications. They will wear a surgical gown during the test and should be asked to urinate before the test starts. If keeping the legs elevated causes discomfort, mild pain medication can be given.
Aftercare
The patient may resume normal or postoperative activities after the test.
Limb plethysmography
Definition:
Limb plethysmography is a test that compares blood pressure in the legs and arms. It is usually done to check for blood flow blockages in the legs.
Alternative Names:
Plethysmography - limb
How the test is performed:
This test may be done in the health care provider's office or in a hospital. You will be asked to lie in a partially propped-up position.
Three blood pressure cuffs are wrapped snugly around your arm and leg. The health care provider inflates the cuffs and a machine called a plethysmograph measures the pulses from each cuff. The test records the maximum pressure produced when the heart contracts (systolic blood pressure).
Any differences between the pulses are noted. If there is there is a decrease in the pulse between the arm and leg, it may indicate a blockage.
When the test is complete, the blood pressure cuffs are removed.
How to prepare for the test:
Do not smoke for at least 30 minutes before the test. You will be asked to remove all clothing from the arm and leg being tested.
How the test will feel:
You should not have much discomfort with this test. You should only feel the pressure of the blood pressure cuff.
Why the test is performed:
The test is done to help rule out blocked arteries in the arms or legs.
Normal Values:
There should be less than 20 mmHg difference in the systolic blood pressure of the leg compared with that of the arm.
What abnormal results mean:
Abnormal results may be due to:
Arterial occlusive disease
Blood clots
Blood vessel changes due to diabetes
Injury to an artery
Other blood vessel disease (vascular disease)
Other conditions under which the test may be performed:
Deep venous thrombosis
What the risks are:
There are no risks.
Special considerations:
The test is not as accurate as an arteriography. Plethysmography may be done for very ill patients who cannot travel to the arteriography lab. This test can be used to screen for vascular disease or to follow up earlier abnormal tests.
Definition:
Limb plethysmography is a test that compares blood pressure in the legs and arms. It is usually done to check for blood flow blockages in the legs.
Alternative Names:
Plethysmography - limb
How the test is performed:
This test may be done in the health care provider's office or in a hospital. You will be asked to lie in a partially propped-up position.
Three blood pressure cuffs are wrapped snugly around your arm and leg. The health care provider inflates the cuffs and a machine called a plethysmograph measures the pulses from each cuff. The test records the maximum pressure produced when the heart contracts (systolic blood pressure).
Any differences between the pulses are noted. If there is there is a decrease in the pulse between the arm and leg, it may indicate a blockage.
When the test is complete, the blood pressure cuffs are removed.
How to prepare for the test:
Do not smoke for at least 30 minutes before the test. You will be asked to remove all clothing from the arm and leg being tested.
How the test will feel:
You should not have much discomfort with this test. You should only feel the pressure of the blood pressure cuff.
Why the test is performed:
The test is done to help rule out blocked arteries in the arms or legs.
Normal Values:
There should be less than 20 mmHg difference in the systolic blood pressure of the leg compared with that of the arm.
What abnormal results mean:
Abnormal results may be due to:
Arterial occlusive disease
Blood clots
Blood vessel changes due to diabetes
Injury to an artery
Other blood vessel disease (vascular disease)
Other conditions under which the test may be performed:
Deep venous thrombosis
What the risks are:
There are no risks.
Special considerations:
The test is not as accurate as an arteriography. Plethysmography may be done for very ill patients who cannot travel to the arteriography lab. This test can be used to screen for vascular disease or to follow up earlier abnormal tests.
Plethysmography
Definition:
Plethysmography is a test used to measure changes in blood flow or air volume in different parts of the body. It may be done to check for blood clots in the arms and legs, or to measure how much air you can hold in your lungs.
A plethysmography test is performed by placing blood pressure cuffs on the extremities to measure the systolic pressure. The cuffs are then attached to a pulse volume recorder (plethysmograph) that displays each pulse wave. The test compares the systolic blood pressure of the lower extremity to the upper extremity, to help rule out disease that blocks the arteries in the extremities.
