evaluating the maximal diaphragm thickening fraction in healthy participants

Ultrasound in Evaluating Diaphragm Dysfunction and Monitoring Treatment

Ultrasound refers to sound waves beyond the upper audible limits of human hearing. Ultrasound has many applications beyond healthcare, the most famous likely being the development of SONAR (sound navigation and ranging) for military use in World War I1; ultrasound is now routinely used in medical diagnosis and therapy. Medical sonography or diagnostic ultrasound utilizes high frequency sound waves (&#62;20 kHz) to provide images of soft tissue structures within the body. These sound waves are pulsed at frequencies of 1 to 20 million cycles/s (megahertz, MHz), which can be transmitted into the body to examine anatomical structures, such as the liver, heart, and skeletal muscle. Point-of-care ultrasound is increasingly becoming a cornerstone of the evaluation and management of critical illness.
The first application of ultrasound in medicine was in the 1940&#39;s by Dr. Karl Dussik, who attempted to locate brain tumors by measuring the transmission of ultrasound beams through the head2. As technology progressed, new techniques were developed, including amplitude mode (A-mode) and brightness mode (B-mode)3, followed by the development of two-dimensional scanners in 19604,5. The field of diagnostic ultrasound has become invaluable in clinical practice, since it avoids exposure to ionizing radiation and can be obtained at the bedside, avoiding the need for in-hospital transport with associated risks. Ultrasound is safe, well-tolerated, reliable, and repeatable in patients6,7.
The diaphragm is a thin, dome-shaped muscular structure that acts as the main respiratory pump driving spontaneous ventilation in humans. The diaphragm separates the thoracic and abdominal cavities and is composed of three separate segments: the central tendon, the costal diaphragm, and the crural diaphragm (Figure 1). The central tendon of the diaphragm is a noncontractile structure that allows major bloods vessels to pass through from the thoracic to the abdominal cavity. The costal diaphragm has fibers running from the rib cage or xiphoid process to the central tendon. The crural diaphragm inserts into the first three lumbar vertebrate. During inspiration, the costal diaphragm contracts, lowering the dome of the diaphragm while expanding the lower rib cage. The costal diaphragm supports the crural diaphragm in the lowering the dome8,9,10.
Transthoracic ultrasound of the diaphragm has gained increasing attention for its ability to monitor diaphragm thickness at the zone of apposition (Figure 1)11,12,13. The diaphragm was first visualized with ultrasound in 1975 by Haber et al.14. Diaphragm contractility and muscular shortening during inspiration can be quantified using M-mode ultrasound to monitor the diaphragm thickness (Tdi) and thickening fraction (TFdi). This assessment of contractility provides a measure of diaphragm muscular performance under a given level of inspiratory drive and effort. Point-of-care ultrasound provides safe, repeatable, and reliable measures of diaphragm function and architecture. In mechanically ventilated patients, changes in diaphragm thickness over time can be used to evaluate the negative impacts of mechanical ventilation, including the effects of myotrauma due to over-assistance (atrophy; decreasing end-expiratory thickness over time) or under-assistance (load-induced injury resulting in inflammation, edema; possibly represented by increasing end-expiratory thickness over time)15. These changes are correlated with adverse clinical outcomes16. Measuring TFdi during tidal breathing permits an assessment of tidal diaphragmatic activity (i.e., inspiratory effort). Measuring TFdi during a maximal inspiratory effort (TFdi,max) provides an assessment of diaphragm strength (since the diaphragm&#39;s force-generating capacity is related to its ability to contract and shorten).
There is substantial consensus on the optimal protocol for acquiring and analyzing measurements17. Competency in diaphragm ultrasound imaging involves a moderately steep learning curve; thorough training in the technique and its potential pitfalls is essential. Studies have shown that proficiency in diaphragm ultrasound expertise can be acquired in a short period of time through remote, web-based training18. Therefore, this protocol has been optimized to provide a consistent measurement of diaphragm thickness and thickening fraction that can be applied to both healthy and patients with suspected respiratory pathology19

Author Spotlight: Unraveling the Impact of Mechanical Ventilation on Diaphragm Function and Patient Outcomes 

Measuring Diaphragm Thickness and Function Using Point-of-Care Ultrasound

We study the effects of mechanical ventilation on diaphragm structure and function, and the impact of those changes on outcomes for patients with acute respiratory failure. Diaphragm atrophy and dysfunction are common in mechanically ventilated patients, and are related to diaphragm inactivity, or excessive loading during ventilation. This ventilator induced diaphragm dysfunction delays recovery and prevents patients from being able to breathe without assistance from the ventilator.Monitoring diaphragm activity during mechanical ventilation is challenging and often requires invasive methods. However, point-of-care ultrasound offers a non-invasive and repeatable approach to visualize and measure diaphragm thickness and function, including changes in structure like atrophy. This protocol provides best practice guidelines for obtaining measures of diaphragm structure and function in healthy and critically ill populations.In mechanically ventilated critical care patients, changes in diaphragm thickness from baseline are associated with diaphragm weakness and failure to wean from mechanical ventilation. Targeting optimal respiratory effort through therapeutic strategies such as respiratory effort targeted sedation and phrenic nerve stimulation may be able to mitigate ventilator induced diaphragm dysfunction and facilitate lung and diaphragm protective ventilation. The effect of these therapeutic strategies on diaphragm structure and function has yet to be evaluated.

Watch this Scientific Journal Video about Evaluating the Maximal Diaphragm Thickening Fraction in Healthy Participants at JoVE.com

Evaluating the Maximal Diaphragm Thickening Fraction in Healthy Participants

Position the patient in a semi recumbent position on their back. Then using the B-mode ultrasound, identify the diaphragm and optimize the image quality. Next, click the M-mode button to place the ultrasound into M-mode.While in M-mode, guide the participant to perform a maximum volitional inspiratory effort against a non occluded airway. Freeze the recording and save the image. Next, measure the diaphragm thickness fraction at end expiration and peak inspiration during a maximum inspiratory trial.Then using the given equation, calculate the diaphragm thickening fraction max for each breath. The max thickening fraction is taken as the highest value from all three trials. The maximal diaphragm thickening fraction in healthy adults ranges from 30 to 130%In critically ill patients, diaphragm thickening fraction max less than 30%predicts a higher risk of failed weaning from mechanical ventilation.

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321 Views.  Toronto General Hospital Research Institute. Position the patient in a semi recumbent position on their back. Then using the B-mode ultrasound, identify the diaphragm and optimize the image quality. Next, click the M-mode button to place the ultrasound into M-mode.While in M-mode, guide the participant to perform a maximum volitional inspiratory effort against a non occluded airway. Freeze the recording and save the image. Next, measure the diaphragm thickness fraction at end expiration and peak inspiration during a maximum inspi...

Video: Evaluating the Maximal Diaphragm Thickening Fraction in Healthy Participants

The diaphragm is the main component of the respiratory muscle pump. Diaphragm dysfunction can cause dyspnea and exercise intolerance, and predisposes affected individuals to respiratory failure. In mechanically ventilated patients, the diaphragm is susceptible to atrophy and dysfunction through disuse and other mechanisms. This contributes to failure to wean and poor long-term clinical outcomes. Point-of-care ultrasound provides a valid and reproducible method for evaluating diaphragm thickness and contractile activity (thickening fraction during inspiration) that can be readily employed by clinicians and researchers alike. This article presents best practices for measuring diaphragm thickness and quantifying diaphragm thickening during tidal breathing or maximal inspiration. Once mastered, this technique can be used to diagnose and prognosticate diaphragm dysfunction, and guide and monitor response to treatment over time in both healthy individuals and acute or chronically ill patients.

Diaphragm thickness and function can be assessed in healthy individuals and critically ill patients using point-of-care ultrasound. This technique offers an accurate, reproducible, feasible, and well-tolerated method for evaluating diaphragm structure and function.

The diaphragm is the main component of the respiratory muscle pump. Diaphragm dysfunction can cause dyspnea and exercise intolerance, and predisposes ...

Evaluating Diaphragm Thickness and Thickening Fraction During Tidal Breathing in Healthy Participants

To begin, position the patient in a semi recumbent position on their back. Cover the tip of the linear array transducer with ultrasound gel. After ensuring the ultrasound is in B mode for positioning, hold the probe by enclosing the tip of the probe with the thumb and index finger.Palpate the chest wall surface to locate the right eighth, ninth, or 10th intercostal spaces between mid and anterior axillary lines. Then place the probe within the zone of apposition, making sure it's entirely situated between the ribs. If a rib appears in the image, adjust the angle of the probe by tilting it up and down until only the diaphragm is visible.On the ultrasound monitor, identify two bright white parallel lines above the liver indicating the pleural and peritoneal membranes. Adjust the depth of the image by clicking on the increase or decrease depth button to maximize the size of the diaphragm. Ensure the diaphragm is visualized in the middle of the monitor.This ensures maximum resolution of the pleural and peritoneal lines from surrounding structures. Next, to optimize image quality, open the ultrasound unit software. Then click the gain button to adjust the image brightness.Increase the gain by clicking the increase button to brighten the image. Conversely, click the decrease button to darken the image. Upon optimizing image quality, click the M mode button to place the ultrasound in the M mode.Position the single vertical scan line between the sections where the pleural and peritoneal lines are the clearest. Run M mode over a full cycle of inspiration and expiration during tidal breathing. Then click on the freeze to capture the actual state and save to save the image.Next, with a skin safe marker, mark the probe's location on the patient's body. Once the examination is complete, click the End Exam button. Next, for image analysis, start the DICOM viewer software and open the necessary DICOM files.Then click on the distance tool and draw a straight line from the inner edge of the pleural membrane to the inner edge of the peritoneal membrane at end expiration. Record this value as diaphragm thickness. Repeat similar measurements at peak inspiration of the same breath to obtain the diaphragm thickness at peak inspiration.Analyze diaphragm thickness at end expiration and peak inspiration from the same breath to assess the diaphragm thickening fraction. Then using the given equation, calculate the diaphragm thickening fraction for each breath. In healthy adults, resting end expiratory diaphragm thickness ranges from 1.5 to 5.0 millimeters, while tidal diaphragm thickening fraction falls between 15 to 30%