Читать книгу Pathy's Principles and Practice of Geriatric Medicine - Группа авторов - Страница 441

The oesophagus incorporates striated muscle in the upper portion and smooth muscle in the lower, with an upper oesophageal sphincter (UOS) and lower oesophageal sphincter (LOS) at either end. The term primary peristalsis refers to the coordinated sequence of contraction associated with swallowing, propagated from proximal to distal oesophagus. The LOS relaxes early in this sequence to allow the swallowed bolus to enter the stomach. Secondary peristalsis is triggered by reflux of gastric contents into the oesophagus, or experimentally by balloon distension, and serves to clear the oesophagus of acid and bile. Tertiary contractions represent spontaneous, uncoordinated oesophageal motor activity. While both tonic contraction of the LOS and its position within the diaphragmatic hiatus are important barriers against acid reflux, transient sphincter relaxations, particularly after a meal, are the most prevalent mechanism of acid reflux in the majority of GORD patients. Defences against reflux include neutralisation of acid by saliva (which contains bicarbonate) together with acid clearance by primary and secondary peristalsis.

Oesophageal motility may be evaluated by manometry, utilizing a transnasal catheter incorporating multiple closely spaced pressure sensors (either water perfused or solid state) positioned along the length of the oesophagus, including the sphincters. This technique provides information about the amplitude, duration, and propagation of pressure waves and relaxation of the sphincters, traditionally displayed as an array of line plots for each measurement site and now frequently as a pressure topography plot (Figure 17.1). The diagnosis of oesophageal motility disorders has evolved over the past decade with the Chicago Classification.¹⁸ Monitoring of pH in the distal oesophagus over 24 hours in an ambulatory setting via an electrode positioned through the nose provides valuable information about acid reflux, while multi‐channel intraluminal impedance, a technique that records electrical impedance between sequential pairs of electrodes, can be used to evaluate the flow of liquid and air in the oesophagus. Radiographic imaging of swallowed contrast can reveal abnormal oesophageal wall movements (especially cineradiography), dilatation, or delayed oesophageal transit. Transit can also be evaluated by the passage of a radiolabelled bolus, imaged by a gamma camera – a technique known as scintigraphy. While endoscopy is most useful in demonstrating mucosal lesions or strictures, it may also provide evidence of abnormal motor activity in disorders such as oesophageal spasm or achalasia.

Figure 17.1 Normal oesophageal manometry displayed as a pressure topography plot. The distance along the oesophagus is represented by the y‐axis and time by the x‐axis, with pressures colour‐coded according to the legend on the left side. During water swallows, an orderly sequence of contractions proceeds aborally (primary peristalsis). Note the high‐pressure zones of the upper (UOS) and lower oesophageal sphincters (LOS) and the swallow‐induced relaxations of the LOS.

The effects of ageing have been studied more extensively in the oesophagus than any other gastrointestinal region, reflecting both its accessibility and the importance of swallowing disorders in the elderly. Soergel et al. coined the term prebyesophagus in 1964 when reporting radiological and manometric observations in a group of nonagenarians.¹⁹ Only 2 of 15 subjects had ‘normal’ oesophageal motility, and on barium examination, there was a high prevalence of tertiary contractions, delayed clearance, and oesophageal dilatation. Manometry showed non‐peristaltic, multi‐peaked pressure waves. These subjects, however, could scarcely be described as healthy elderly, given the high prevalence of dementia and other chronic illnesses, including diabetes. Not surprisingly, more recent studies indicate that the prevalence and severity of oesophageal motor dysfunction in healthy ageing are less than suggested by early reports. A recent systematic review reported that in subjects over 60 years of age, UOS resting pressure was lower than in the young but also exhibited less swallow‐induced relaxation, indicative of a degree of UOS resistance.²⁰ This would intuitively favour a prolongation of the oropharyngeal phase of swallowing and an increase in intra‐bolus pressure in the hypopharynx.²¹ While not clinically significant in the healthy elderly, these findings must be taken into account when evaluating swallowing studies in older patients with oropharyngeal dysphagia, where reference ranges derived from the young should not be used. Reflex responses of the UOS to oesophageal stimuli (increased pressure with oesophageal balloon distension and decreased pressure with air distension) appear to remain intact with healthy ageing, but reflex UOS contraction in response to laryngeal stimulation is impaired,²² which could predispose to aspiration. The fact that the frequency but not the magnitude of the response is diminished suggests that the sensory side of the reflex arc is impaired. In the distal oesophagus, studies in older patients have reported a reduced amplitude of contractions and a greater frequency of failed peristalsis than in the young,²⁰ while secondary peristalsis is less easily elicited.²³ Reductions in primary and secondary peristalsis, as well as changes in biomechanical properties (increased oesophageal stiffness), have been observed from as early as age 40.²⁴

In the elderly, there is an increased prevalence of hiatus hernia (around 60% of those over 60),²⁵ and both the resting pressure and intra‐abdominal length of the LOS decline with age, while acid exposure increases,²⁶ all of which increase the risk of GORD. Other predisposing factors include reduced flow of saliva and impaired acid clearance. The frequency of transient LOS relaxations, the major mechanism of acid reflux in most individuals, has not been specifically studied in the elderly; nor have mucosal repair mechanisms been compared with those in the young. The number of reflux episodes appears similar in both age groups, but their duration may be more prolonged in the elderly,²⁷ which may relate to impaired clearance mechanisms. The refluxate may also be less acidic due to a higher prevalence of atrophic gastritis in the elderly, but it should be recognised that its bile content may be important in mucosal injury (e.g. Barrett’s mucosa); and this has not been studied specifically in relation to age.²⁸