Stone fragmentation efficiency on the phantom gel

Figure 3A summarizes the results regarding the 100% hit rate of the respiration-adjusted lithotripsy. The hit rate is the number of shockwaves focused on the stone out of the total. Without respiration adjustment, the 1 and 1.5 Hz frequencies showed higher hit rates than those of 2 Hz. The hit rate ranged from 50 to 67% in the respiration-electromotive device setting.

Fig. 3

Analysis of stone fragment efficiency. a The hit rate quantification of stone targeting was measured by adjusted respiration compared to non-adjusted respiration. Shock-wave frequency: 60 times/min (1 Hz), 90 times/min (1.5 Hz), and 120 times/min (2 Hz). Respiration rate: slow (12 RR/min), intermediate (15 RR/min), and fast (20 RR/min). Hit rate: a number of shock-waves focused on the stone out of a total number of shock-waves. b The change in the weight of the stone was measured according to respiration rate and shock-wave frequency. The stone weight change was analyzed by adjusted respiration (b), compared to non-adjusted respiration with frequency of 1 Hz (c), 1.5 Hz (d), and 2 Hz (e). f A percentage of phantom gel cavitation numbers was counted according to respiration adjustment. Phantom gel cavitation was individually marked and counted using a Sprinter-HD high-speed camera of the CamRecord-Sprinter series (Optronics GMBH, Ludwigstr, Kehl, Germany

Figure 3B (upper mid) summarizes the results of the respiration adjustment. The percentage of exchanged stone weight calculated the stones’ fragmentation efficiency. When adjusted for respiration and applying the shockwave frequency to 1 Hz, the stones’ fragmentation efficiency increased according to the increase in respiration cycles. The fractions of fragments W2, W1, and Wp were represented in the order of slow RR (70.4%, 6.6%, 23.0%), intermediate RR (65.9%, 14.6%, 19.5%), and fast RR (45.5%, 12.8%, 41.8%) respiration. The highest particles of Wp were fast respiration.

Without respiration adjustment in shockwave frequency applied in the order of 1 Hz (Fig. 3C, upper right), 1.5 Hz (Fig. 3D, under left), and 2 Hz (Fig. 3E, under mid), the stones’ fragmentation efficiency was found to be highest in slow respiration. The fraction of large fragments W2 measured in the slow (78.3%, 79.3%, and 90.7%), intermediate (90.7%, 93.6%, and 91.9%), and fast (92.7%, 88.9%, and 91.4%) respiration. The remaining small particles W1 for slow, intermediate, and fast RR were less than 5%. The opposite result was observed with the fraction of powder Wp, where the slow respiration showed the largest fraction of 7.9–17.3%, contrasting a range from 2.5 to 7.3% for the other two respiration conditions. Slow respiration showed the best fragmentation to Wp at all frequencies.

Patient and overall trial performance

After receiving 58 patients, six were excluded from the experiments because of device errors. As a result, 52 patients (33 males and 19 females) were analyzed in the respiration data set. The mean age was 55 ± 16 years. The stone laterality was 29 patients on the left and 23 patients on the right side, and the mean kidney size was 10.0 ± 1.0 cm. The mean maximal diameter and number of stones were 9.9 ± 3.9 mm, and 1.2 ± 0.6 stones, respectively. The ESWL treatment was conducted for 32 and 14 patients in the first and second sessions, respectively. The mean number of transmitted shockwaves was 2,900 ± 281, and the mean of the total energy was 744.63 ± 105.54 KeV. The respiratory motion range was from 6 to 30 mm, with an average value of 12.8 ± 4.8 mm. The mean maximum volumes of inhalation and exhalation are 0.96 ± 0.4 L and − 1.23 ± 0.57 L, respectively. The mean ESWL execution time and the mean ESWL number were 28.6 ± 2.7 min, 1.65 ± 1.23 times. The mean respiration flow velocity and respiration rate(bpm) were 0.79 ± 0.3, 17.69 ± 0.4, and the mean respiratory duration was 3.4 ± 0.6.

Lithotripsy efficiency according to respiratory regularity

Among the 52 patients, 33 (63.5%) were identified as having respiratory regularity, whereas 19 (36.5%) had respiratory irregularity. Respiratory regularity from 90 to 95% was shown in eight patients (24.2%), and respiratory regularity from 95 to 100% in 25 patients (75.8%). By contrast, irregularities from 80 to < 90% were shown in seven patients, 50 to < 80% in six patients, and < 59% in four patients. Among patients with respiratory regularity > 90%, two patients with non-specific breathing cycles of very slow respiration > 5 s and very rapid breathing shorter than 2 s were excluded from the regular breathing group.

The regular breathing group showed fragmented stones in 22 patients (66.7%) and stationary in 11 patients (33.3%), while the irregular group showed fragmented stones in seven (36.8%) and stationary in 12 patients (63.2%). The stone fragmentation efficiency was 29.9% higher in the regular group than in the irregular group (OR 3.43, 95% CI 1.05–11.16, P = 0.036*). Table 1 shows that the kidney migration (OR 12.14, 95% CI 1.04-141.71, P = 0.046*), the respiration regularity > 95% (OR 6.10, 95% CI 1.04–35.97 and P = 0.046*), and the intensity (OR 1509.06, 95% CI 1.51-1510472.04 and P = 0.038*) were significant predictors for stone-free status.

Table 1 Univariate and multivariate logistic regression analysis for prediction of stone-free status after shockwave lithotripsyRespiratory irregularity and associated events

During the ESWL procedures, five types of events occurred: (1) cough, (2) sleep, (3) mask off, (4) tension or hyperventilation, and (5) conversation or body movements; some patients exhibited two or more events simultaneously. Table 2 summarizes the events in patients with regular and irregular breathing. In regular respiration, cough, hyperventilation, and conversation showed the highest number in cases of < 10%, while in irregular respiration, sleep and tension showed the highest number.

Table 2 Changes in respiration waveforms according to events and degree of event occurrence. Some patients showed two or more events

The group with > 95% of regular breathing exhibited a consistent waveform, and the group with < 95% showed a slight bounce from time to time. In this group, the duration of an event was very short, and the frequency was low. On the other hand, an irregular waveform appeared when an event occurred, such as a cough with a sharp wave, sleep with shallow breathing, conversation and movement with prolonged breathing, etc.

Safety represented by phantom gel damage, complications and degree of pain

The cavitation damage in the respiration-adjusted group was lowest in slow respiration compared to intermediate and fast respirations (23.5 vs. 30 and 29.5, respectively). Without respiration adjustment, no definite differences existed among different respirations (Fig. 3F).

In the clinical investigation, no patients had a high fever, acute pyelonephritis, significant bleeding, or perirenal hematoma. The pain strengths of none, mild, moderate, and severe appeared in 4, 11, 18, and 0 cases in the regular group and 1, 4, 10, and 4 cases in the irregular group, respectively (P = 0.019*). However, the prescription rate of drugs on the procedure day showed no significant differences in 17 cases out of 33 patients (51.5%) in the regular group and 12 cases out of 19 patients (63.2%) in the irregular group (P = 0.563).