Effect of atropine on the biomechanical properties of the oesophageal wall in humans

Abstract

The effect of atropine, a smooth muscle relaxant, has often been determined as a change of compliance in the gastrointestinal (GI) tract. There are reports that atropine increases, decreases or has no effect on the compliance of the oesophagus in isovolumic distension studies (Barish et al. 1984;Richter et al. 1986;Paterson, 1991;Paterson et al. 1991a;Mayrand & Diamant, 1993;Mayrand et al. 1994). The compliance, however, is not an accurate measure of the wall stiffness. The elastic modulus, which is determined from the stress-strain relationship, is a more accurate measure of the wall stiffness. It has not been possible, however, to measure stress and strain in vivo in humans because previous methods could not measure wall thickness, luminal radius and pressure simultaneously. We recently developed a novel ultrasound technique that can measure all of the above-mentioned parameters simultaneously, in real time. Therefore, our technique allows accurate measurement of loading and deformation and subsequent computation of stress, strain and elastic modulus of the human oesophagus in vivo.The oesophagus consists of several layers, mucosa, submucosa and muscularis propria. The latter consists of circumferential and longitudinal muscle fibres. The muscle layer has both passive and active properties consistent with the Hill's three elements model and the non-muscle tissue has only passive properties. The active contraction of the muscle can be described by a combination of 'contractile element' in series with an 'elastic element'. The passive component can be described by a 'parallel element'. The goals of our study were to determine: (1) the effect of atropine on the stress-strain properties of the human oesophagus under isovolumic and isobaric test conditions, and (2) the active and passive components of the wall stress properties of the human oesophagus. Effect of atropine on the biomechanical properties of the oesophageal wall in humansTorahiko Takeda*, Ghassan Kassab †, Jianmin Liu*, Toshinaga Nabae* and Ravinder K. Mittal* Recently, we reported a novel ultrasound technique to assess biomechanical properties of the oesophagus in human subjects. In the present study, we use the technique, in combination with atropine, to determine the active and passive biomechanical properties of the oesophagus in normal healthy humans. A manometric catheter equipped with a high-compliance bag and a high-frequency intraluminal ultrasonography probe was used to record pressure and oesophageal geometry. Oesophageal distensions with either isovolumic (5-20 ml water) or with isobaric (10-60 mmHg) technique were performed. Intra-bag pressure and ultrasound images of the oesophagus were recorded simultaneously. Following injection of atropine (15 mg kg _1 , I.V.), the oesophageal distensions were repeated. The oesophageal wall compliance, circumferential wall tension, stress, strain and elastic modulus were calculated. Atropine resulted in an increase in the oesophageal wall compliance during isobaric distension, but no change in complia...

Dimensions and Circumferential Stress-Strain Relation in the Porcine Esophagus in Vitro Determined by Combined Impedance Planimetry and High-Frequency Ultrasound

“…However, it seems difficult to obtain more accurate stress-strain relation data in vivo because the esophageal wall connected to the surrounding organs. For example, at a strain of 1.0, the corresponding stress is about 5 kPa in our study and thus much smaller than that about 13 kPa for isovolumic distension and 12 kPa for isobaric distension as found in the human studies under muscle relaxation [25]. Thus, it is important to obtain accurate passive wall properties of the isolated esophagus in vitro without interfering factors to understand the conditions in vivo.…”

“…It was demonstrated that the stress-strain relationship of esophageal wall revealed a linear shape. The active component (muscle contraction) was different during isovolumic and isobaric distensions, but the passive components (after atropine) were similar [24,25]. However, it seems difficult to obtain more accurate stress-strain relation data in vivo because the esophageal wall connected to the surrounding organs.…”

“…Recently, ultrasound combined with manometry or impedance planimetry was used to study the biomechanical wall properties as well as the motility of human esophagus [20][21][22][23][24][25][26]. It was demonstrated that the stress-strain relationship of esophageal wall revealed a linear shape.…”

“…The novel potential of the system is that it allows direct measurement of wall thickness; most previous studies of cylindrical organs are based on the computation of wall thickness and assume incompressibility [8,18]. Ultrasound combined with manometry or impedance was used to study the biomechanical wall properties as well as the motility of human esophagus [20][21][22][23][24][25][26]. However, in such in vivo studies it is difficult to estimate the "true" biomechanical properties such as stress-strain owing to the contribution of surrounding organs.…”

Deterioration of Muscle Function in the Human Esophagus with Age

“…The interested reader is referred to those and other publications for methodological and analytical considerations and interpretation of the in vivo muscle function curves [10,13,15,[18][19][20][21][22][23][24][25]. Corresponding analysis on length-tension relations in muscle strips in vitro has been described in other papers [26,27].…”