A new method for evaluation of intestinal muscle contraction properties: studies in normal subjects and in patients with systemic sclerosis

Systemic sclerosis is a connective tissue disease that involves the gastrointestinal (GI) tract. Seventy-five per cent of systemic sclerosis patients experience symptoms arising from oesophagus. The intestine has less frequently been subject for studies than the oesophagus. When the small intestine becomes involved, nausea, vomiting, bloating, diarrhoea and malabsorption may occur. Previous studies have shown decreased and abnormal intestinal motility, dilatation and a stiffer wall. The aim was to study muscle mechanics in systemic sclerosis patients using novel analysis of intestinal muscle contraction force-velocity and power. A volume-controlled duodenal ramp-distension protocol was used in nine patients and eight healthy controls. The wall stretch ratio, tension, shortening velocity and muscle power were computed from pressure and cross-sectional area data recorded by an impedance planimetry system. The tension-stretch ratio relation obtained in patients was shifted to the left, indicating a stiffer wall. The in vivo tension-shortening velocity relationship was quantified using Hill's equation. The maximum preload tension (tension at zero velocity) was lower in the patients than in the healthy controls (P < 0.001). The muscle power was lowest in the patients. An association was found between the duration of the disease and the maximum stretch ratio (P < 0.05). The study represents the first data with application of in vivo muscle force-velocity relations in patients with gastrointestinal diseases. Systemic sclerosis patients had increased stiffness and impaired muscle dynamics of the duodenum. Decreased muscle function and increased wall stiffness may explain the GI symptoms reported in this patient group.