title: Influence of body position and stool characteristics on defecation in humans.
abstract: BACKGROUND
  Whether defecation is influenced by body position or stool characteristics is unclear.
  
  
  OBJECTIVE
  We investigated effects of body position, presence of stool-like sensation, and stool form on defecation patterns and manometric profiles.
  
  
  METHODS
  Rectal and anal pressures were assessed in 25 healthy volunteers during attempted defecation either in the lying or sitting positions and with balloon-filled or empty rectum. Subjects also expelled a water-filled (50 cc) balloon or silicone-stool (FECOM) either lying or sitting and rated their stooling sensation.
  
  
  RESULTS
  When attempting to defecate in the lying position, a dyssynergic pattern was seen in 36% of subjects with empty rectum and 24% with distended rectum. When sitting, 20% showed dyssynergia with empty rectum and 8% with distended rectum. More subjects (p < 0.05) showed dyssynergia in lying position. When lying, 60% could not expel balloon and 44% FECOM. When sitting, fewer (p < 0.05) failed to expel balloon (16%) or FECOM (4%). FECOM expulsion time was quicker (p < 0.02). Stool-like sensation was more commonly (p < 0.005) evoked by FECOM than balloon.
  
  
  CONCLUSIONS
  In the lying position, one-third showed dyssynergia and one-half could not expel artificial stool. Whereas when sitting with distended rectum, most showed normal defecation pattern and ability to expel stool. Thus, body position, sensation of stooling and stool characteristics may each influence defecation. Defecation is best evaluated in the sitting position with artificial stool.
authors.affiliation: Division of Gastroenterology/Hepatology, Department of Internal Medicine, University of Iowa Carver College of Medicine, Iowa City, Iowa 52242-1009, USA.
authors.forename: Satish S C
authors.initials: SS
authors.lastname: Rao
authors.forename: Renae
authors.initials: R
authors.lastname: Kavlock
authors.forename: Sheila
authors.initials: S
authors.lastname: Rao
mesh_terms: D000328:Adult; D000368:Aged; D001003:Anal Canal / Q000502:physiology; D003672:Defecation / Q000502:physiology*; D005243:Feces; D005260:Female; D006801:Humans; D008297:Male; D008365:Manometry; D008875:Middle Aged; D010812:Physical Stimulation / Q000295:instrumentation; D011187:Posture / Q000502:physiology*; D012007:Rectum / Q000502:physiology; D012016:Reference Values