Physiology and Pathology of Uterine Contractions

Michael G. Halaška, M.D.Department of Obstetrics and Gynaecology

of 2nd Medical Faculty

Physiology

myometrium – smooth muscleenlargment of the muscle cellsbasal tonusfirst contractions from 20thweek of gravidityBraxton-Hick contractions

Physiology

Montevid Units

Montevid Units – addition of amlitudes of contractions in 10 minutes pacemaker – contraction wave – 2cm/samplitude of an contraction 1st stage – 40-60 mm Hg 2nd stage – 80 mm Hg

closure of blood-vessels veins : 20 mm Hg artery: 60 mm Hg

Physiology

basal tonus 10 mm Hg1. stage of labour 30-40 mm Hg - 120 MU2. stage of labour 50-60 mm Hg - 250 MUresting time >30 s

Physiology

Proper shape of the contractions 1. stage

2. stage

3. stage

Physiology – starting factors 1. mechanical - ↑ pressure, ↓ volume2. endocrine

estrogen - ↑ number of estro receptors, ↓ membrane potential, ↑ ATP in myocytes

oxytocine - ↓ membrane potential, ↑ PG prostaglandins – preparing of cervix, contract.

3. neurogen Fergusson reflex Parasympaticus reflex

Recording the contractions

absolute – intrauterine- intrauterine catheter

relative – external - using piesoelectric effect

Indications and contraindications

Type of sensor

Conditions Indications Contraindications

External anytime non-ivasive

as CTG nonenot recommended- obesity

Internal cervix dilatated at least 2-3 cm, ruptured membranes,

tonus of the uterusmostly scientific use

placenta praevia,face presentation,intraovulatory infection

Pathology

1. hypertonus2. hyperactivity3. hypoactivity4. dystokia 5. failure of the abdominal muscle

Pathology

1. hypertonus2. hyperactivity3. hypoactivity4. dystokia 5. failure of the abdominal muscle

Pathology - hypertonus

etiology: macrosomy, multiple pregnancy,premature separation of placentapathophysiology: ↑ basal tonus - ↑blood in veins – hypoxyclinics: palpable, changes on CTGtreatment: tocolysis

Pathology

1. hypertonus2. hyperactivity3. hypoactivity4. dystokia 5. failure of the abdominal muscle

Pathology - hyperactivity

> 390 MU, >7 contrac/min, resting time <30 setiology: hypersensitivity, overstimulation of the uterusclinics: CTG changestherapy: less oxytocine, tocolysis

Pathology

1. hypertonus2. hyperactivity3. hypoactivity4. dystokia 5. failure of the abdominal muscle

Pathology - hypoactivity< 100 MU, < 30 mm Hg, < 2 contract/mintype: primary – from the beginning

secondary – during the labouretiology: primary: hypoplasia of U., dystokia

secondary: prolonged labour, overstimulation by oxytocine, exhaustion of the mother

clinics: CTG, no postup of the labourtherapy: oxytocine, tocolysis, rest

Pathology

1. hypertonus2. hyperactivity3. hypoactivity4. dystokia 5. failure of the abdominal muscle

Pathology - dystokia

etiology: hypertonus of the cervix, failure of pacemakers, exhaustion of

uterusclinics: CTG, no postup of the labourtherapy: tocolysis, S.C.

Pathology

1. hypertonus2. hyperactivity3. hypoactivity4. dystokia 5. failure of the abdominal muscle

Pathology - failure of abd. muscle

etiology: disease of the muscle or inervation disease which unables higher activity ( heart,

eyes .. ) epidural anesthesia exhaustion of the mother obesity not cooperating mother

therapy: forceps, VEX, S.C.