Ultrasound findings
The M-mode sonographic findings of diaphragm thickness, TF, EXC, IS, ES, and total duration time of the respiratory cycle of the patients enrolled in this study are shown in Table 1. The mRDAI scores and BUS values had a significant positive correlation (p < 0.001, r : 0.760). There was a positive correlation between IS and respiratory rate at admission (p < 0.001, r : 0.637). As the clinical score increased, IS (p < 0.001,r : 0.775), ES (p < 0.001, r: 0.444), and EXC (p < 0.001, r : 0.200) measurements rose and these were positively correlated (Table 2). Additionally, BUS values had a correlation with both IS (p < 0.001, r : 0.562) and ES (p : 0.012, r : 0.244) values. Because there were few patients in the severe group according to mRDAI and BUS values, we divided the patients into two groups for comparison as the mild and moderate-severe groups. According to this classification, there were 71 (68.3%) patients in the mild and 27 (31.7%) patients in the moderate-severe group for mRDAI scores and there were 55 (52.9%) patients in the mild and 49 (47.1%) patients in the moderate-severe group for BUS values. Furthermore, values of IS, ES, EXC, and total duration time of the respiratory cycle were also higher in the moderate-severe group than the mild group for both mRDAI scores (for IS and ES: p < 0.001; for EXC: p : 0.003; for total duration: p : 0.014) and BUS values (for IS: p < 0.001; for ES: p : 0.014; for EXC: p : 0.036). Patients who received HFNC oxygen therapy had higher IS (p : 0.028) and TEE (p : 0.023) measurements and, although not statistically significant, higher EXC values (p : 0.053). We could repeat the measurements of diaphragm parameters for 2 patients in 2 hours after starting HFNC oxygen therapy; although we did not have enough patients to statistically evaluate this, we observed that IS, ES, EXC, TEI, and TEE were all decreased as the respiratory support reduced the work of breathing. Values of IS were correlated with both the length of stay in the emergency department (p : 0.002, r : 0.316) and the total stay in the hospital (p < 0.001, r : 0.492).