The diaphragm is the principal muscle used in respiration. Excursion of the diaphragm is driven by the phrenic nerve. Diaphragmatic contraction causes expansion of the thoracic cavity, which results in lung inflation in a craniocaudal direction.1–3 The range of diaphragmatic movement is directly related to the inspiratory volume.
Unilateral or bilateral diaphragmatic paralysis is caused by insufficiency of the phrenic nerve in adverse neuromuscular conditions (eg, trauma, compression or degeneration of the phrenic nerve, and myopathy) and other conditions (eg, pneumonia and idiopathic conditions).4–8 Unilateral diaphragmatic paralysis is often not associated with clinical signs and only observed incidentally or may manifest as orthopnea or dyspnea during exertion. Bilateral impairment is usually not associated with clinical signs, which results in ventilatory failure, followed by cyanosis with apnea.4,7,9–12
Various imaging modalities have been proposed for use in the evaluation of diaphragmatic excursion. For radiographic evaluation of dogs, the dependent crus in lateral radiographs typically is cranial to the contralateral crus, and asymmetry between the crura may represent normal variation, except that 1 crus is consistently located cranial to the other crus, regardless of positional changes.13,14 In addition to the confusion caused by these imaging variations, detection and characterization of diaphragmatic dysfunction are unreliable when using conventional radiography because of variations in the x-ray beam center, respiration, and gastric pressure and the posture, size, breed, age, and obesity of the patient.5,14 Therefore, a dynamic imaging technique is essential for precise diagnosis of diaphragmatic paralysis.
Fluoroscopy and ultrasonography are currently the diagnostic tools of choice for such a diagnosis.7 Ultrasonography is a good modality for subjective evaluation of diaphragmatic movement, but it does not allow simultaneous visualization of both the right and left sides of the diaphragm. Fluoroscopy allows observation of diaphragmatic excursion during breathing in real time as well as simultaneous examination of the right and left sides of the diaphragm. Inherent characteristics of fluoroscopy allow qualitative assessment of diaphragmatic motility as well as quantitative measurement of excursion.5,15 In fluoroscopic images of the diaphragm of humans, both the right and left parts of the diaphragm move caudally as the anterior chest wall moves upward during respiration.16 Unequal movement between the diaphragmatic crura has been suggested to indicate unilateral paralysis. It may be more difficult to confirm bilateral paralysis with fluoroscopy when compensatory abdominal muscle contractions cause diaphragmatic movement. Nevertheless, minimal or absent diaphragmatic movement or a paradoxical cranial displacement of a flaccid diaphragm may be observed during inspiration in patients with diaphragmatic paralysis.11
Fluoroscopic diagnosis of diaphragmatic paralysis has been reported in only a few dogs, including 1 dog with unilateral paralysis10 and 2 dogs with bilateral paralysis.10,11 Radiographically, the dog with unilateral paralysis had cranial displacement of the left crus relative to the right crus, which was separated by a gap corresponding to the length of 2 vertebrae. Unequal movement was observed fluoroscopically, and the left crus had minimal movement, with an amplitude of less than one-half of an intercostal space. For the 2 dogs with bilateral paralysis, no diaphragmatic movement was detected radiographically, although cranial displacement of both crura was observed radiographically and paradoxical cranial motion of a flaccid diaphragm during inspiration was observed fluoroscopically. For these dogs, fluoroscopic diagnosis of diaphragmatic paralysis was based on subjective determination of diaphragmatic motion during respiration. Quantitative data on diaphragmatic motion, particularly crural excursion, on the basis of the phase of respiration and dog's position may facilitate detection of abnormal diaphragmatic motion. Quantitative data on diaphragmatic movement in humans measured fluoroscopically have been reported.5,15,17–19
The purpose of the study reported here was to quantitatively evaluate diaphragmatic movement in clinically normal Beagles by use of fluoroscopy. The hypotheses were that excursion would differ among parts of the diaphragm during physiologic respiration and that excursion for the various parts of the diaphragm would be affected by the position of each dog during respiration.
Supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Science, Information and Communication Technology, and Future Planning (grant No. 2015R1A2A2A01003313).
Intraclass correlation coefficient
PcCR1417, OREX Computed Radiography Ltd, Yokneam, Israel.
KMC-950, Gemss-Medical, Seoul, Republic of Korea.
CXView, version 3910, Gemss-Medical, Seoul, Republic of Korea.
INFINITT, Infinitt Healthcare, Seoul, Republic of Korea.
SPSS for Windows, release 21.0, SPSS Inc, Chicago, Ill.
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