Ultrasound diaphragmatic manual and semi-automated motion measurements: Application in simulated and in vivo data of critically ill subjects
Introduction
During resting breathing the diaphragm contributes to approximately 70% of tidal volume. Disfunction of the diaphragm may induce respiratory complications, where patients demonstrate severe dyspnea and often prolonged mechanical ventilation [1], [2], [3] is required [4]. Diagnosis of diaphragmatic dysfunction in an early preliminary stage is important, because diaphragmatic paralysis may be amenable to therapeutic strategies and may require adapted and prolonged ventilatory support. Therefore, the need for the assessment and management of the diaphragm function arises in many clinical situations. The diaphragm is the muscle responsible for respiration. It has a dome shaped musculotendinous structure, which contracts during inspiration, flattens the pleural cavity and expands the lungs. When the diaphragmatic function is impaired, accessory muscles must assume this role but are much less efficient, resulting in shortness of breath with exertion in patients with diaphragm dysfunction. Patients have severe dyspnea and often require artificial ventilation to breathe, particularly when supine. The function of the diaphragm is assessed by manually measuring the diaphragmatic motion and excursion [4,5].
Diaphragmatic function may be monitored using an ultrasound video of the diaphragm, from which an M-mode image and its respective motion diagram (see Fig. 1 and Fig. 5i) may be derived [5]. Given an M-mode image (see Fig. 5f) of the diaphragm, one can evaluate the diaphragms’ displacement and kinetics, which can assist the clinical expert in the evaluation and assessment of the diaphragmatic motion. Diaphragmatic motion assessment focuses on estimating the diaphragm's displacement and timing, and their variation for studying dysfunction during breathing. Figure 1 demonstrates the measurements routinely carried out by the experts and these include: (i) diaphragmatic excursion, (ii) inspiration time (Tinsp), and (iii) cycle duration (Ttot). Additional measurements may be derived from Fig. 1, such as the slope of the diaphragmatic curve and the relaxion rate (RR), which may offer additional information on the diaphragmatic function [6]. Furthermore, the assessment of diaphragmatic weakness based on the aforementioned measurements maybe useful in patients under mechanical ventilation for facilitation of their breathing [6], [7], [8]. A number of other studies reported in the literature have investigated the respiratory changes in diaphragmatic thickness and diaphragmatic pressure output. It should be however noted that, the association between diaphragmatic excursion and diaphragmatic thickening and between diaphragmatic excursion and diaphragmatic pressure output is weak [9], [10], [11], [12]. By employing post hoc analysis, investigators have reported associations between diaphragmatic excursions and failure of noninvasive ventilation [13], duration of (invasive) mechanical ventilation [14], weaning outcome [12,[15], [16], [17], [18]] and length of stay [15], but none of the thresholds put forward has been yet prospectively tested.
The objective of this study was to introduce a semi-automated analysis system for the assessment of the diaphragmatic muscle. The proposed system generated an M-Mode image from an ultrasound diaphragmatic video. The M-mode image was used to monitor ultrasonic diaphragmatic displacement and timing as to extract the relaxing and contracting states of diaphragmatic motion as well as to extract several quantitative diaphragmatic motion parameters. The proposed system targets to assist the clinician in the noninvasive evaluation of the diaphragmatic muscle motion. To the best of our knowledge, there were no other studies reported in the literature, investigating the semi-automated, or automated diaphragmatic motion analysis in ultrasound video of the diaphragmatic muscle.
Section snippets
Selected studies of diaphragmatic ultrasound motion measurements
Several studies investigated in detail the assessment of ultrasonic diaphragmatic motion, which are tabulated in Table 1. In the first upper part of Table 1 the studies that evaluated diaphragmatic excursion on normal subjects are presented.
More specifically, in [24] the ventilatory movement of the right dome of the diaphragm was studied over the range of the inspiratory capacity in 50 healthy adults in the supine position using simultaneous ultrasonography and pneumotachography. The
Methodology
In this section, the steps followed for loading the initial ultrasound diaphragmatic video and generating the M-mode image and the measurements of the diaphragmatic motion are given. Furthermore, the generation of the simulated videos is presented. The section also presents the methodology followed in this study in order to extract measurements for the contracting and relaxing diaphragmatic states of the diaphragmatic videos. Furthermore, to assess quantitative measurements for quantifying the
Results
Table 3 tabulates the diaphragmatic motion manual and semi-automated measurements and their corresponding error measures for the four simulated videos (see also subsection 3.1). Normal values, from the literature, for each measurement are also given in the second column of Table 3 based on [6]. For the four simulated videos generated, the median±IQR of all evaluation metrics were zero for the manual measurements and very small for the semi-automated measurements. No %SEM were detected for the
Discussion
The objective of this study was to further validate the system firstly introduced in [18], on simulated videos of the diaphragmatic muscle, as well as in a larger sample of real cases (13 ultrasound videos of the diaphragm in this study versus one in [18]). The proposed system integrates video frame normalization, despeckling, M-mode generation, and accurate segmentation using snakes. Such a system can reduce the time required for the video analysis, and also the subjectivity that accompanies
Concluding Remarks
The objective of this paper was to introduce a simple system for the quantitative analysis of ultrasonic diaphragmatic motion. The measurements routinely carried out by the experts were computed and these include: diaphragmatic excursion, inspiration time and cycle duration, slope of the diaphragmatic curve and RR. The system was evaluated on simulated and real videos of the diaphragmatic muscle. Manual and semi-automated measurements were very close, however further work in a larger number of
Declaration of Competing Interest
There are no conflicts of interest.
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