Surg Endosc DOI 10.1007/s00464-015-4124-y
and Other Interventional Techniques
NEW TECHNOLOGY
Stochastic resonance enhanced tactile feedback in laparoscopic surgery Hiroyuki Sawada • Hiroyuki Egi • Minoru Hattori Takahisa Suzuki • Shoichiro Mukai • Yuichi Kurita • Wataru Yasui • Hideki Ohdan
•
Received: 19 December 2014 / Accepted: 9 February 2015 Ó Springer Science+Business Media New York 2015
Abstract Background One of the disadvantages of laparoscopic surgery is its decreased tactile feedback. Surgical experience compensates for the decline in the sense of touch due to an improved ability to process visual information. Stochastic resonance (SR) is known to improve tactile sensation. In this study, we sought to improve the tactile feedback in laparoscopic surgery using SR to safely perform laparoscopic surgery. Methods Ten surgeons (nine males and one female, age: 30–44 years, median age: 34) with the experiences of [50 laparoscopic surgeries volunteered to participate in this study. We tested the hypothesis that low-level noise applied to the hand can enhance the tactile sensation during surgery. We performed this experiment under three hand conditions (bare-handed conditions, gloved conditions and using the laparoscopic instrument with gloved hands). A piezoelectric actuator that generates vibrations was H. Sawada H. Egi (&) T. Suzuki S. Mukai H. Ohdan Department of Gastroenterological and Transplant Surgery, Applied Life Sciences, Institute of Biomedical and Health Sciences, Hiroshima University, Hiroshima 1-2-3 Kasumi, Minami-Ku, Hiroshima 734-8551, Japan e-mail: [email protected] H. Egi M. Hattori Advanced Medical Skills Training Center, Institute of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan S. Mukai W. Yasui Department of Molecular Pathology, Institute of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan Y. Kurita Department of Engineering, Hiroshima University, Hiroshima, Japan
attached on the radial side of the participant’s index finger or to the grip of the laparoscopic instrument. Fine-touch tests were performed using the Semmes–Weinstein test kit. Moreover, we planned laparoscopic suturing and knot-tying tasks in the dry box and using an animal model under controlled vibrations. Results In the touch tests using bare hands, gloved hands and the laparoscopic instrument, the mean correct ratio was significantly lower than that observed in the test with no vibrations. Moreover, the OSATS scores for the laparoscopic suturing and knot-tying tasks showed significantly better scores with vibrations. Conclusions This technique has a potential to be a great help in establishing safer and high-quality laparoscopic procedures. Keywords Laparoscopic surgery Tactile feedback Objective assessment Surgical skills Laparoscopic surgery is now recognized to be an effective type of minimally invasive surgery, and many patients come to the hospital requesting laparoscopic procedures. In association with this trend, patients have a strong interest in their surgeon’s performance, especially with respect to laparoscopic surgery, as the differences in surgical skills in laparoscopic surgery are larger than those observed in open surgery. To establish useful training and educational methods, it is necessary to develop a reliable system for objectively assessing the laparoscopic surgical skills. Moreover, research in this field is quickly advancing. The objective structured assessment of technical skills (OSATS) is a system that consists of six stations at which trainees perform tasks on live or bench models. The performance of the trainee is then assessed using checklists and a
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global rating scale [1]. This system has been shown to be reliable for assessing the skills of surgical residents in various environments [1, 2]. Second-generation motion analysis systems have also been developed to assess dexterity. The Imperial College surgical assessment device (ICSAD) [3–6], advanced Dundee endoscopic psychomotor trainer (ADEPT) [7] and Hiroshima University Endoscopic Surgical Assessment Device (HUESAD) [8–10] have previously been validated to be reliable motion analysis systems for assessing endoscopic surgical skills. Research in this field has been used to establish safer procedures for laparoscopic surgery. One of the disadvantages of laparoscopic surgery is the decreased tactile feedback. Surgical experience compensates for the decline in the sense of touch due to an improved ability to process visual information. However, it is necessary to improve the tactile feedback during surgery in order to safely perform laparoscopic procedures, especially for less experienced surgeons. Stochastic resonance (SR) has been shown to improve tactile sensation. In this study, we sought to assess whether the tactile feedback can be improved by using SR during laparoscopic surgery.
vibrations was attached on the radial side of the participant’s index finger, and the vibrations were transmitted to the tip of the index finger (Fig. 1). The vibration signal was produced using a customized LabVIEW program (2011, National Instruments, Austin, TX, USA) and a commercial digital-toanalog converter (Model ATP-8L, CONTEC, Osaka, Japan). The signal was then passed through an amplifier (Piezo Driver, MESS-TEK, Saitama, Japan) to the PZT actuator. The PZT actuator generates a band-limited white noise vibration that is transmitted to tactile receptors around the contact area. Taking the frequency response characteristics of the tactile mechanoreceptors into account, vibrations with a cutoff frequency of 300 [Hz] were adopted in this study. The white noise signal, X(t), was generated according to a Box-Muller’s method, which is defined by Eq. (1) with a standard deviation of r = 1.5: pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi XðtÞ ¼ r 2 ln aðtÞ sin 2pbðtÞ ð1Þ where a and b are the uniform pseudorandom numbers. The generated signal was band-limited with a second-order Butterworth filter. The signal amplitudes were individually determined based on the vibration perception capability of each subject.
Methods Participants Ten surgeons (nine males and one female, age: 30–44 years, median age: 34) with the experiences of [50 laparoscopic surgeries volunteered to participate in this study. All participants were right-handed and free of neurological diseases or conditions potentially affecting cutaneous sensation. The participants were required to attend three experimental sessions. The experiments were approved by Hiroshima University, and informed consent was obtained from each subject prior to participation. Each volunteer was their own control in these three experiments. First experiment In the first experiment, we tested the hypothesis that lowlevel noise applied to the hand can enhance tactile sensation during surgery. We conducted this experiment under two hand conditions (bare-handed conditions and gloved conditions). The participants performed the sensory tests with either bare hands or while wearing rubber gloves (GAMMEX). The gloved condition reflected specific medical settings, such as open surgery.
Procedure for the first experiment At the outset of each experimental condition, the participants determined their own amplitude threshold according to the method of ascending and descending limits. The amplitude of the vibration stimulus was then adjusted so that the stimulus was just beneath this threshold. Fine-touch sensitivity was evaluated by probing the skin over the ball of the index finger using Semmes–Weinstein monofilaments. Each monofilament imparts a known buckling force determined according to its diameter. The Semmes–Weinstein test kit (Touch-Test Kit, North Coast Medical, Inc., San Jose, CA, USA) used in this study consisted of 20 different monofilament diameters (hence, 20 different forces, ranging from 0.008 to 300 g). The participants were provided no vibrations (0 %) and five different amplitudes, i.e., 50, 75, 100, 125 and 150 (%) of the subthreshold values. These six vibration levels were tested in a randomized order. The information about the vibration amplitude was not provided to the participants. The participants were asked to report if they could feel the filament in contact under the aforementioned six vibration levels. Each participant performed two trials for each hand condition.
The experimental setting of the first experiment
Second experiment
During the tests, the participants sat in a chair with their right arm extended. A piezoelectric (PZT) actuator that generates
In experiment 1, we demonstrated that low-level vibrations enhanced tactile sensation under both bare-handed and
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Surg Endosc Fig. 1 Experimental setup under the conditions of open surgery
gloved conditions. In experiment 2, the participants touched monofilaments via laparoscopic instruments. Our hypothesis was that low-level vibrations transmitted via laparoscopic instruments would also enhance the tactile sensation. The experimental setting and procedure for the second experiment The PZT actuator was attached on forceps for laparoscopic surgery, and the vibrations were transmitted to the participant’s finger via the forceps (Fig. 2). The participants were asked to grasp the forceps and close their eyes. The controlled flow of the vibrations and the process used to determine each participant’s amplitude threshold were the same as described in experiment 1. The experimenter pressed a monofilament against a rubber plate pinched at the tip of the forceps until buckling occurred and then removed the monofilament. The
participants were asked to report when they could feel the filament. The participants were provided either no vibrations or vibrations at five different amplitudes, i.e., 50, 75, 100, 125 and 150 (%) of the subthreshold values. These six vibration levels were tested in a randomized order, as in experiment 1. Information regarding the vibration amplitude was not provided to the participants. Each participant performed two trials for each hand condition. Experiment mimicking the clinical situation In experiment 3, participants performed laparoscopic suturing and knot tying in a dry box. The participants were provided no vibrations or vibrations of five different amplitudes, i.e., 50, 75, 100, 125 and 150 (%) of the subthreshold values. These six vibration levels were tested in a randomized order, as in experiments 1 and 2. Information regarding the vibration amplitude was not provided to the participants. We assessed their performances using the
Fig. 2 Experimental setup under the conditions of laparoscopic surgery
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OSATS checklist score for laparoscopic suturing (Fig. 3) as in the clinical situation. Moreover, the participants also performed suturing and knot tying using a porcine model as a more realistic clinical situation, and the outcomes were checked via the pathological findings. Statistical analysis The statistical analysis of the data was performed using the SPSS version 19.0 for Windows software package (PASW Statistics 19, IBM Corporation, NY, USA). To detect differences in sensory test performance among the six vibration levels under each test condition, the nonparametric Friedman test was used. When the differences were significant, we performed a post hoc Wilcoxon signed-rank test. The level of statistical significance was set at an alpha of 0.05 or less. All results were expressed as the medians (range).
Fig. 3 OSATS checklist score for laparoscopic suturing
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Results No participants reported any fatigue or anxiety during the experimental sessions. All participants exhibited clear-cut SR-type behavior elicited by tactile sensation under the bare-handed and gloved conditions. In the first experiment, the mean correct ratios for the 50 % (p = 0.018), 75 % (p = 0.017), 100 % (p = 0.011) and 125 % (p = 0.017) threshold showed significantly higher sensitivity than that for no vibrations (0 %) under the bare-handed conditions (Fig. 4). Under the gloved conditions, the mean correct ratios for the 75 % (p = 0.031), 100 % (p = 0.031) and 125 % (p = 0.034) threshold values showed significantly higher sensitivity than that for no vibrations (0 %) (Fig. 5). In the second experiment, the mean correct ratios for the 50 % (p = 0.046), 75 % (p = 0.042), 100 % (p = 0.012) and 125 % (p = 0.011) thresholds of the participants
Surg Endosc
Fig. 4 Touch test via bare hands. Asterisk indicates p \ 0.05 for the comparison of no vibration
Fig. 5 Touch test via gloved hands. Asterisk indicates p \ 0.05 for the comparison of no vibration
exhibited significantly higher sensitivity than that for no vibrations (0 %) when using the laparoscopic instrument wearing gloves (Fig. 6). Moreover, both experiments showed that the sensitivity with no vibrations (0 %) while using the laparoscopic instrument with gloves was significantly worse than that observed under the bare-handed and gloved conditions with vibrations (Fig. 7). The use of SR with appropriate vibrations improved the tactile sensation under all three conditions, particularly when the participants used the laparoscopic instrument with gloves (Table 1). In the third experiment, we assessed the participants’ performances using the OSATS checklist score for laparoscopic suturing and compared the groups with or without vibrations. There were no significant differences in the groups in terms of needle driving, pulling the suture, the technique used for knotting, knot slipping or the knot quality. However, the total score and needle position showed significantly better scores in the SR group with appropriate vibrations (Table 2). The pathological findings of the porcine model after suturing and knot tying with or without vibrations showed no significant differences in terms of tissue damage between the groups (Fig. 8).
Fig. 6 The touch test via laparoscopic instrument with gloved hands. Asterisk indicates p \ 0.05 for the comparison of no vibration
Fig. 7 Target forces under the three conditions. The asterisks indicate p \ 0.05 in comparison with open surgery
Discussion Stochastic resonance (SR) has been shown to be a mechanism by which noise enhances the detection and transmission of weak signals. SR has been used to improve the flow of information through systems and can be enhanced by the presence of a nonzero level of noise. Current literature is available on this topic, especially in the field of neurology. Neel T. Dhruv et al. hypothesized that the finetouch sensitivity in older adults could be improved by localized low-level electrical noise stimulation and evaluated nine healthy elderly subjects with no neurological disease (69–82 years of age, mean: 75 years). The results of their study showed that seven of the nine subjects exhibited a higher detection rate with electrical noise than under the null condition. These findings suggest that electrical noisebased techniques and devices, such as electrode-lined socks or gloves, can enable people to overcome age-related sensory loss [11]. The authors described two mechanisms underlying this effect. The first suggests that vibratory noise adds mechanical energy to the vibrotactile stimulus, enhancing the transmission of vibrations through dermal tissues. The second is that vibratory noise directly acts upon receptor endings [11]. Another report examined
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Surg Endosc Table 1 Tactile sensation under the three conditions
Zero noise Bare hands
Table 2 OSATS checklist score for laparoscopic suturing (n = 10)
Optimal noise
Zero noise–optimal noise
p
0.055 (0.02–0.16)
0.02 (0.008–0.04)
0.035
0.011
Gloves
0.04 (0.02–0.6)
0.02 (0.02–0.16)
0.02
0.010
Forceps
0.5 (0.4–1.4)
0.4 (0.04–0.6)
0.1
0.007
No vibration
Vibration
P-value
Needle position
7.0 (5.0–8.0)
7.8 (6.3–8.0)
0.016
Needle driving Pulling the suture
5.7 (5.0–6.0) 2.0 (1.7–2.0)
5.7 (5.7–6.0) 2.0 (13–2.0)
0.176 0.625
Technique of knotting
7.3 (4.7–8.0)
7.3 (6.6–8.0)
0.672
Knot slipping
2.0 (2.0)
2.0 (1.7–2.0)
1.000
Knot quality Total
2.5 (2.0–3.0)
2.5 (2.0–3.0)
0.789
26.0 (23.7–28.7)
27.7 (25.3–28.7)
0.020
Fig. 8 Pathological findings of the porcine model after suturing and knot tying
patients with severe diabetic peripheral neuropathy. A total of 20 participants were included in that study. The vibration perception threshold test (VPT) and the Semmes– Weinstein filament (SWF) threshold at the plantar surface of the left foot and the big toe were determined under two mechanical noise stimulus conditions: the null condition and at 10 % lower than each subject’s mechanical noise threshold of perception. That study showed that low levels
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of mechanical noise significantly improved the vibratory and fine-touch sensitivity of the foot in patients with moderate to severe diabetic neuropathy [12]. A significant disadvantage of laparoscopic surgery is decreased tactile feedback. Although experience may be able to compensate for the decline in the sense of touch based on an improved ability to process visual information, the decline in haptic sensitivity information is problematic,
Surg Endosc
especially for less experienced surgeons. Indeed, our experiments showed that the sensitivity of the no vibrations (0 %) condition using the laparoscopic instrument with gloves was significantly worse than that observed in the bare-handed and gloved conditions with vibration (Fig. 7). To overcome this problem, we developed a new laparoscopic instrument based on SR that has the potential to improve tactile sensation, as reported previously [13, 14]. In the present study, we sought to improve the tactile feedback using SR to perform safer laparoscopic surgery. We employed touch tests with a statistical analysis. In the first touch test using bare hands, the mean correct ratios for the 50, 75, 100 and 125 % threshold vibrations were significantly lower than that for the no vibrations condition (0 %). In the second touch test performed with gloved hands, as in the real situation for conventional surgery, the mean correct ratios for the 75, 100 and 125 % threshold vibrations were significantly lower than that of no vibrations (0 %) condition. Surgeons usually use gloves during surgery; therefore, the second touch test simulates the real condition of open surgery. In these situations, the application of SR significantly facilitated tactile sensitivity. However, the load detected in laparoscopic surgery is much heavier than that observed in open surgery (Fig. 7). These results highlight the problem associated with the decreased tactile feedback during laparoscopic surgery. In the third touch test performed with the laparoscopic instrument, which simulated the real conditions of laparoscopic surgery, the mean correct ratios for the 50, 75, 100 and 125 % threshold vibrations were also significantly lower than that for no vibrations (0 %) condition. This finding is very important, because it suggests that SR can be used to establish an environment in which the laparoscopic surgeon is able to sense more tactile information via the laparoscopic instruments. This result also revealed that SR has the potential to improve the surgical performance due to improvements in tactile sensitivity. This finding is supported by the results of our experiments showing that the SR with appropriate vibrations improved tactile sensation under the three conditions, particularly when the participants used the laparoscopic instrument with gloves (Table 1). These results represent a breakthrough that we have been working to apply clinically. In order to apply these findings in the clinical setting, we planned examination 3 to evaluate whether SR was able to enhance the laparoscopic surgical performance. In experiment 3, participants performed laparoscopic suturing and knot tying in a dry box under the controlled vibrations and were assessed by the OSATS checklist score for laparoscopic suturing. The participants showed better scores in terms of total score and needle position when SR was used. Holding the needle is a very sensory-dependent motion, which requires higher sensitivity. Although the
pathological findings of the porcine model after suturing and knot tying showed no significant differences in terms of tissue damage between the no vibrations and SR conditions, there was a trend toward better suturing performance with the SR, which might reach significance if a larger number of animals had been sutured. This result showed that SR may be able to improve the laparoscopic suturing performance in clinical setting. Limitations of this study are which has only small sample size. In the next step, we want to take larger sample size surgeons who have different carriers of laparoscopic surgery to be higher-quality study. In conclusion, the present results may be epoch-making and revolutionary in the field of laparoscopic surgery. This technique has a potential to be a great help in establishing safer and high-quality laparoscopic surgery. Acknowledgments This study was partially funded by the Japanese Society for the Promotion of Science. Disclosures Drs. Hiroyuki Sawada, Hiroyuki Egi, Minoru Hattori, Takahisa Suzuki, Shoichiro Mukai, Yuichi Kurita, Wataru Yasui and Hideki Ohdan have no conflict of interests or financial ties to disclose.
References 1. Martin JA, Regehr G, Reznick R, Macrae H, Murnaghan J, Hutchison C, Brown M (1997) Objective structured assessment of technical skill (OSATS) for surgical residents. Br J Surg 84:273–278 2. Anastakis DJ, Regehr G, Reznick RK, Cusimano M, Murnaghan J (1999) Assessment of technical skill transfer from the bench training model to the human model. Am J Surg 177:167–170 3. Datta V, Mackay S, Chang A, Darzi A (2002) The relationship between motion analysis and surgical technical assessments. Am J Surg 184:70–73 4. Darzi A, Datta V, Mackay S (2001) The challenge for objective assessment of surgical skill. Am J Surg 181:484–486 5. Datta V, Mirren M, Mackay S, Chang A, Cheshire N, Darzi A (2002) Relationship between skill-based model. Surgery 131:318–323 6. Bann S, Datta V, Khan M, Darzi A (2003) The surgical error examination is a novel method for objective technical knowledge assessment. Am J Surg 185:507–511 7. Francis NK, Hanna GB, Cuschieri A (2002) The performance of master surgeons on the advanced Dundee endoscopic psychomotor tester: contrast validity study. Arch Surg 137:841–844 8. Egi H, Okajima M, Yoshimitsu M, Ikeda S, Miyata Y, Masugami H, Kawahara T, Kurita Y, Kaneko M, Asahara T (2008) Objective assessment of endoscopic surgical skills by analyzing direction-dependent dexterity using the Hiroshima University Endoscopic Surgical Assessment Device (HUESAD). Surg Today 38:705–710 9. Egi H, Okajima M, Kawahara T, Yoshimitsu M, Sumitani D, Tokunaga M, Takeda H, Itamoto T, Ohdan H (2008) Scientific assessment of endoscopic surgical skills. Minim Invasive Ther Allied Technol 19:30–34 10. Tokunaga M, Egi H, Hattori M, Yoshimitsu SumitaniD, Kawahara T, Okajima M, Ohdan H (2012) Approaching time is important for assessment of endoscopic surgical skills. Minim Invasive Ther Allied Technol 21:142–149
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Surg Endosc 11. Dhruv NeelT, Niemi JamesB, Harry JasonD, Lipsitz LewisA, Collins JamesJ (2003) Enhancing tactile sensation in older adults with electrical noise stimulation. NeuroReport 13:597–600 12. Khaodhiar Lalita, Lima Christina, Niemi JamesB, Harry JasonD, Earnest Russell, Veves Aristidis (2003) Enhancing sensation in diabetic neuropathic foot with mechanical noise. Diabetes Care 26:3280–3282
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13. Harada N, Griffin MJ (1991) Factors influencing vibration sense thresholds used to assess occupational exposures to hand transmitted vibration. Br J Ind Med 48:185–192 14. Gescheider GA, Bolanowski SJ, Pope JV, Verillo RT (2002) A four-channel analysis of the tactile sensitivity of the fingertip: frequency selectivity, spatial summation, and temporal summation. Somatosens Mot Res 19:114–124
and Other Interventional Techniques
NEW TECHNOLOGY
Stochastic resonance enhanced tactile feedback in laparoscopic surgery Hiroyuki Sawada • Hiroyuki Egi • Minoru Hattori Takahisa Suzuki • Shoichiro Mukai • Yuichi Kurita • Wataru Yasui • Hideki Ohdan
•
Received: 19 December 2014 / Accepted: 9 February 2015 Ó Springer Science+Business Media New York 2015
Abstract Background One of the disadvantages of laparoscopic surgery is its decreased tactile feedback. Surgical experience compensates for the decline in the sense of touch due to an improved ability to process visual information. Stochastic resonance (SR) is known to improve tactile sensation. In this study, we sought to improve the tactile feedback in laparoscopic surgery using SR to safely perform laparoscopic surgery. Methods Ten surgeons (nine males and one female, age: 30–44 years, median age: 34) with the experiences of [50 laparoscopic surgeries volunteered to participate in this study. We tested the hypothesis that low-level noise applied to the hand can enhance the tactile sensation during surgery. We performed this experiment under three hand conditions (bare-handed conditions, gloved conditions and using the laparoscopic instrument with gloved hands). A piezoelectric actuator that generates vibrations was H. Sawada H. Egi (&) T. Suzuki S. Mukai H. Ohdan Department of Gastroenterological and Transplant Surgery, Applied Life Sciences, Institute of Biomedical and Health Sciences, Hiroshima University, Hiroshima 1-2-3 Kasumi, Minami-Ku, Hiroshima 734-8551, Japan e-mail: [email protected] H. Egi M. Hattori Advanced Medical Skills Training Center, Institute of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan S. Mukai W. Yasui Department of Molecular Pathology, Institute of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan Y. Kurita Department of Engineering, Hiroshima University, Hiroshima, Japan
attached on the radial side of the participant’s index finger or to the grip of the laparoscopic instrument. Fine-touch tests were performed using the Semmes–Weinstein test kit. Moreover, we planned laparoscopic suturing and knot-tying tasks in the dry box and using an animal model under controlled vibrations. Results In the touch tests using bare hands, gloved hands and the laparoscopic instrument, the mean correct ratio was significantly lower than that observed in the test with no vibrations. Moreover, the OSATS scores for the laparoscopic suturing and knot-tying tasks showed significantly better scores with vibrations. Conclusions This technique has a potential to be a great help in establishing safer and high-quality laparoscopic procedures. Keywords Laparoscopic surgery Tactile feedback Objective assessment Surgical skills Laparoscopic surgery is now recognized to be an effective type of minimally invasive surgery, and many patients come to the hospital requesting laparoscopic procedures. In association with this trend, patients have a strong interest in their surgeon’s performance, especially with respect to laparoscopic surgery, as the differences in surgical skills in laparoscopic surgery are larger than those observed in open surgery. To establish useful training and educational methods, it is necessary to develop a reliable system for objectively assessing the laparoscopic surgical skills. Moreover, research in this field is quickly advancing. The objective structured assessment of technical skills (OSATS) is a system that consists of six stations at which trainees perform tasks on live or bench models. The performance of the trainee is then assessed using checklists and a
123
Surg Endosc
global rating scale [1]. This system has been shown to be reliable for assessing the skills of surgical residents in various environments [1, 2]. Second-generation motion analysis systems have also been developed to assess dexterity. The Imperial College surgical assessment device (ICSAD) [3–6], advanced Dundee endoscopic psychomotor trainer (ADEPT) [7] and Hiroshima University Endoscopic Surgical Assessment Device (HUESAD) [8–10] have previously been validated to be reliable motion analysis systems for assessing endoscopic surgical skills. Research in this field has been used to establish safer procedures for laparoscopic surgery. One of the disadvantages of laparoscopic surgery is the decreased tactile feedback. Surgical experience compensates for the decline in the sense of touch due to an improved ability to process visual information. However, it is necessary to improve the tactile feedback during surgery in order to safely perform laparoscopic procedures, especially for less experienced surgeons. Stochastic resonance (SR) has been shown to improve tactile sensation. In this study, we sought to assess whether the tactile feedback can be improved by using SR during laparoscopic surgery.
vibrations was attached on the radial side of the participant’s index finger, and the vibrations were transmitted to the tip of the index finger (Fig. 1). The vibration signal was produced using a customized LabVIEW program (2011, National Instruments, Austin, TX, USA) and a commercial digital-toanalog converter (Model ATP-8L, CONTEC, Osaka, Japan). The signal was then passed through an amplifier (Piezo Driver, MESS-TEK, Saitama, Japan) to the PZT actuator. The PZT actuator generates a band-limited white noise vibration that is transmitted to tactile receptors around the contact area. Taking the frequency response characteristics of the tactile mechanoreceptors into account, vibrations with a cutoff frequency of 300 [Hz] were adopted in this study. The white noise signal, X(t), was generated according to a Box-Muller’s method, which is defined by Eq. (1) with a standard deviation of r = 1.5: pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi XðtÞ ¼ r 2 ln aðtÞ sin 2pbðtÞ ð1Þ where a and b are the uniform pseudorandom numbers. The generated signal was band-limited with a second-order Butterworth filter. The signal amplitudes were individually determined based on the vibration perception capability of each subject.
Methods Participants Ten surgeons (nine males and one female, age: 30–44 years, median age: 34) with the experiences of [50 laparoscopic surgeries volunteered to participate in this study. All participants were right-handed and free of neurological diseases or conditions potentially affecting cutaneous sensation. The participants were required to attend three experimental sessions. The experiments were approved by Hiroshima University, and informed consent was obtained from each subject prior to participation. Each volunteer was their own control in these three experiments. First experiment In the first experiment, we tested the hypothesis that lowlevel noise applied to the hand can enhance tactile sensation during surgery. We conducted this experiment under two hand conditions (bare-handed conditions and gloved conditions). The participants performed the sensory tests with either bare hands or while wearing rubber gloves (GAMMEX). The gloved condition reflected specific medical settings, such as open surgery.
Procedure for the first experiment At the outset of each experimental condition, the participants determined their own amplitude threshold according to the method of ascending and descending limits. The amplitude of the vibration stimulus was then adjusted so that the stimulus was just beneath this threshold. Fine-touch sensitivity was evaluated by probing the skin over the ball of the index finger using Semmes–Weinstein monofilaments. Each monofilament imparts a known buckling force determined according to its diameter. The Semmes–Weinstein test kit (Touch-Test Kit, North Coast Medical, Inc., San Jose, CA, USA) used in this study consisted of 20 different monofilament diameters (hence, 20 different forces, ranging from 0.008 to 300 g). The participants were provided no vibrations (0 %) and five different amplitudes, i.e., 50, 75, 100, 125 and 150 (%) of the subthreshold values. These six vibration levels were tested in a randomized order. The information about the vibration amplitude was not provided to the participants. The participants were asked to report if they could feel the filament in contact under the aforementioned six vibration levels. Each participant performed two trials for each hand condition.
The experimental setting of the first experiment
Second experiment
During the tests, the participants sat in a chair with their right arm extended. A piezoelectric (PZT) actuator that generates
In experiment 1, we demonstrated that low-level vibrations enhanced tactile sensation under both bare-handed and
123
Surg Endosc Fig. 1 Experimental setup under the conditions of open surgery
gloved conditions. In experiment 2, the participants touched monofilaments via laparoscopic instruments. Our hypothesis was that low-level vibrations transmitted via laparoscopic instruments would also enhance the tactile sensation. The experimental setting and procedure for the second experiment The PZT actuator was attached on forceps for laparoscopic surgery, and the vibrations were transmitted to the participant’s finger via the forceps (Fig. 2). The participants were asked to grasp the forceps and close their eyes. The controlled flow of the vibrations and the process used to determine each participant’s amplitude threshold were the same as described in experiment 1. The experimenter pressed a monofilament against a rubber plate pinched at the tip of the forceps until buckling occurred and then removed the monofilament. The
participants were asked to report when they could feel the filament. The participants were provided either no vibrations or vibrations at five different amplitudes, i.e., 50, 75, 100, 125 and 150 (%) of the subthreshold values. These six vibration levels were tested in a randomized order, as in experiment 1. Information regarding the vibration amplitude was not provided to the participants. Each participant performed two trials for each hand condition. Experiment mimicking the clinical situation In experiment 3, participants performed laparoscopic suturing and knot tying in a dry box. The participants were provided no vibrations or vibrations of five different amplitudes, i.e., 50, 75, 100, 125 and 150 (%) of the subthreshold values. These six vibration levels were tested in a randomized order, as in experiments 1 and 2. Information regarding the vibration amplitude was not provided to the participants. We assessed their performances using the
Fig. 2 Experimental setup under the conditions of laparoscopic surgery
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OSATS checklist score for laparoscopic suturing (Fig. 3) as in the clinical situation. Moreover, the participants also performed suturing and knot tying using a porcine model as a more realistic clinical situation, and the outcomes were checked via the pathological findings. Statistical analysis The statistical analysis of the data was performed using the SPSS version 19.0 for Windows software package (PASW Statistics 19, IBM Corporation, NY, USA). To detect differences in sensory test performance among the six vibration levels under each test condition, the nonparametric Friedman test was used. When the differences were significant, we performed a post hoc Wilcoxon signed-rank test. The level of statistical significance was set at an alpha of 0.05 or less. All results were expressed as the medians (range).
Fig. 3 OSATS checklist score for laparoscopic suturing
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Results No participants reported any fatigue or anxiety during the experimental sessions. All participants exhibited clear-cut SR-type behavior elicited by tactile sensation under the bare-handed and gloved conditions. In the first experiment, the mean correct ratios for the 50 % (p = 0.018), 75 % (p = 0.017), 100 % (p = 0.011) and 125 % (p = 0.017) threshold showed significantly higher sensitivity than that for no vibrations (0 %) under the bare-handed conditions (Fig. 4). Under the gloved conditions, the mean correct ratios for the 75 % (p = 0.031), 100 % (p = 0.031) and 125 % (p = 0.034) threshold values showed significantly higher sensitivity than that for no vibrations (0 %) (Fig. 5). In the second experiment, the mean correct ratios for the 50 % (p = 0.046), 75 % (p = 0.042), 100 % (p = 0.012) and 125 % (p = 0.011) thresholds of the participants
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Fig. 4 Touch test via bare hands. Asterisk indicates p \ 0.05 for the comparison of no vibration
Fig. 5 Touch test via gloved hands. Asterisk indicates p \ 0.05 for the comparison of no vibration
exhibited significantly higher sensitivity than that for no vibrations (0 %) when using the laparoscopic instrument wearing gloves (Fig. 6). Moreover, both experiments showed that the sensitivity with no vibrations (0 %) while using the laparoscopic instrument with gloves was significantly worse than that observed under the bare-handed and gloved conditions with vibrations (Fig. 7). The use of SR with appropriate vibrations improved the tactile sensation under all three conditions, particularly when the participants used the laparoscopic instrument with gloves (Table 1). In the third experiment, we assessed the participants’ performances using the OSATS checklist score for laparoscopic suturing and compared the groups with or without vibrations. There were no significant differences in the groups in terms of needle driving, pulling the suture, the technique used for knotting, knot slipping or the knot quality. However, the total score and needle position showed significantly better scores in the SR group with appropriate vibrations (Table 2). The pathological findings of the porcine model after suturing and knot tying with or without vibrations showed no significant differences in terms of tissue damage between the groups (Fig. 8).
Fig. 6 The touch test via laparoscopic instrument with gloved hands. Asterisk indicates p \ 0.05 for the comparison of no vibration
Fig. 7 Target forces under the three conditions. The asterisks indicate p \ 0.05 in comparison with open surgery
Discussion Stochastic resonance (SR) has been shown to be a mechanism by which noise enhances the detection and transmission of weak signals. SR has been used to improve the flow of information through systems and can be enhanced by the presence of a nonzero level of noise. Current literature is available on this topic, especially in the field of neurology. Neel T. Dhruv et al. hypothesized that the finetouch sensitivity in older adults could be improved by localized low-level electrical noise stimulation and evaluated nine healthy elderly subjects with no neurological disease (69–82 years of age, mean: 75 years). The results of their study showed that seven of the nine subjects exhibited a higher detection rate with electrical noise than under the null condition. These findings suggest that electrical noisebased techniques and devices, such as electrode-lined socks or gloves, can enable people to overcome age-related sensory loss [11]. The authors described two mechanisms underlying this effect. The first suggests that vibratory noise adds mechanical energy to the vibrotactile stimulus, enhancing the transmission of vibrations through dermal tissues. The second is that vibratory noise directly acts upon receptor endings [11]. Another report examined
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Surg Endosc Table 1 Tactile sensation under the three conditions
Zero noise Bare hands
Table 2 OSATS checklist score for laparoscopic suturing (n = 10)
Optimal noise
Zero noise–optimal noise
p
0.055 (0.02–0.16)
0.02 (0.008–0.04)
0.035
0.011
Gloves
0.04 (0.02–0.6)
0.02 (0.02–0.16)
0.02
0.010
Forceps
0.5 (0.4–1.4)
0.4 (0.04–0.6)
0.1
0.007
No vibration
Vibration
P-value
Needle position
7.0 (5.0–8.0)
7.8 (6.3–8.0)
0.016
Needle driving Pulling the suture
5.7 (5.0–6.0) 2.0 (1.7–2.0)
5.7 (5.7–6.0) 2.0 (13–2.0)
0.176 0.625
Technique of knotting
7.3 (4.7–8.0)
7.3 (6.6–8.0)
0.672
Knot slipping
2.0 (2.0)
2.0 (1.7–2.0)
1.000
Knot quality Total
2.5 (2.0–3.0)
2.5 (2.0–3.0)
0.789
26.0 (23.7–28.7)
27.7 (25.3–28.7)
0.020
Fig. 8 Pathological findings of the porcine model after suturing and knot tying
patients with severe diabetic peripheral neuropathy. A total of 20 participants were included in that study. The vibration perception threshold test (VPT) and the Semmes– Weinstein filament (SWF) threshold at the plantar surface of the left foot and the big toe were determined under two mechanical noise stimulus conditions: the null condition and at 10 % lower than each subject’s mechanical noise threshold of perception. That study showed that low levels
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of mechanical noise significantly improved the vibratory and fine-touch sensitivity of the foot in patients with moderate to severe diabetic neuropathy [12]. A significant disadvantage of laparoscopic surgery is decreased tactile feedback. Although experience may be able to compensate for the decline in the sense of touch based on an improved ability to process visual information, the decline in haptic sensitivity information is problematic,
Surg Endosc
especially for less experienced surgeons. Indeed, our experiments showed that the sensitivity of the no vibrations (0 %) condition using the laparoscopic instrument with gloves was significantly worse than that observed in the bare-handed and gloved conditions with vibration (Fig. 7). To overcome this problem, we developed a new laparoscopic instrument based on SR that has the potential to improve tactile sensation, as reported previously [13, 14]. In the present study, we sought to improve the tactile feedback using SR to perform safer laparoscopic surgery. We employed touch tests with a statistical analysis. In the first touch test using bare hands, the mean correct ratios for the 50, 75, 100 and 125 % threshold vibrations were significantly lower than that for the no vibrations condition (0 %). In the second touch test performed with gloved hands, as in the real situation for conventional surgery, the mean correct ratios for the 75, 100 and 125 % threshold vibrations were significantly lower than that of no vibrations (0 %) condition. Surgeons usually use gloves during surgery; therefore, the second touch test simulates the real condition of open surgery. In these situations, the application of SR significantly facilitated tactile sensitivity. However, the load detected in laparoscopic surgery is much heavier than that observed in open surgery (Fig. 7). These results highlight the problem associated with the decreased tactile feedback during laparoscopic surgery. In the third touch test performed with the laparoscopic instrument, which simulated the real conditions of laparoscopic surgery, the mean correct ratios for the 50, 75, 100 and 125 % threshold vibrations were also significantly lower than that for no vibrations (0 %) condition. This finding is very important, because it suggests that SR can be used to establish an environment in which the laparoscopic surgeon is able to sense more tactile information via the laparoscopic instruments. This result also revealed that SR has the potential to improve the surgical performance due to improvements in tactile sensitivity. This finding is supported by the results of our experiments showing that the SR with appropriate vibrations improved tactile sensation under the three conditions, particularly when the participants used the laparoscopic instrument with gloves (Table 1). These results represent a breakthrough that we have been working to apply clinically. In order to apply these findings in the clinical setting, we planned examination 3 to evaluate whether SR was able to enhance the laparoscopic surgical performance. In experiment 3, participants performed laparoscopic suturing and knot tying in a dry box under the controlled vibrations and were assessed by the OSATS checklist score for laparoscopic suturing. The participants showed better scores in terms of total score and needle position when SR was used. Holding the needle is a very sensory-dependent motion, which requires higher sensitivity. Although the
pathological findings of the porcine model after suturing and knot tying showed no significant differences in terms of tissue damage between the no vibrations and SR conditions, there was a trend toward better suturing performance with the SR, which might reach significance if a larger number of animals had been sutured. This result showed that SR may be able to improve the laparoscopic suturing performance in clinical setting. Limitations of this study are which has only small sample size. In the next step, we want to take larger sample size surgeons who have different carriers of laparoscopic surgery to be higher-quality study. In conclusion, the present results may be epoch-making and revolutionary in the field of laparoscopic surgery. This technique has a potential to be a great help in establishing safer and high-quality laparoscopic surgery. Acknowledgments This study was partially funded by the Japanese Society for the Promotion of Science. Disclosures Drs. Hiroyuki Sawada, Hiroyuki Egi, Minoru Hattori, Takahisa Suzuki, Shoichiro Mukai, Yuichi Kurita, Wataru Yasui and Hideki Ohdan have no conflict of interests or financial ties to disclose.
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