PHYSIOLOGIC CHANGES OF PREGNANCY John G. Gianopoulos, M.D.

Introduction “During pregnancy, multiple physiologic adjustments are made to maintain maternal hemostasis. In a non-pregnant patient, many of these alterations would be considered pathologic rather than physiologic. This lecture will present the adjustments and alterations in maternal physiology.”

Cardiovascular Cardiac Output-is  during pregnancy  1.51/min. Cardiac Output = heart rate x stroke volume. CO = HR x SV Output can be measured using direct Fick method, i.e.: Output of L. ventricle = 0 2 consumption (ml/min) A 02 – V 02

Pulse rate  from 70  85 Heart rate  by catecholamines Chromotropic Inotropic Stroke volume increases  10%. Regulated by 2 mechanisms. Heterometric Homometric  CO, by  SV =  heart size

Mean arterial pressure - average pressure throughout cardiac cycle – decreased. Total peripheral resistance – dependent upon arteriole diameter – ie., small changes in caliber = large changes in TRP. R = 8hL  r 4 During pregnancy TPR is reduced.

Increased blood flow – distribution. Uterus* Kidney Skin Breasts Pulmonary Pressure – same as non-pregnant levels, due to:  resistance to flow – vascular dilation  volume – capacitance Radiographic appearance – increased vascularity, enlarged pulmonary vessels.

Venous Pressure -  in femoral pressure: Weight of uterus of iliac veins, inf. Vena cava. Hydrodynamic obstruction – due to  uterine outflow. Supine Hypotensive syndrome.

ECG Changes-elevation of diaphragm heart moved upwards and rotated forward, + enlarged. Therefore, one would predict change in the electrical axis of the heart. Deviation to the left in the electrical axis (  ).

Volume and Composition of Blood.  Plasma volume 40-50%  RBC – 25-30%  Hematocrit  Fibrinogen  Sedimentation rate  Clotting Factors (VII, VIII, IX, X)  Serum alkaline phosphatase

RESPIRATION Definitions Tital volume (TV) - amount of air moving into lungs with each inspiration. Inspiratory Reserve Volume (IRV) – air inspired with maximal inspiratory effort in excess of tidal volume. Expiratory Reserve Volume (ERV) - volume expelled by active expiratory effort after passive expiration. Residual Volume (RV) – air left in lungs after maximal expiratory effort.

Vital Capacity – greater amount of air that can be expired after maximal inspiratory effort. (timed vital capacity) Respiratory Minute Volume (RMV) – amount of air inspired/minute. Maximal Voluntary Ventilation – maximal amount of air that can be moved into and out of the lungs in one minute by voluntary effort.

During Pregnancy the following occurs:  TV  RMV – 40 % Hyperventilation Respiratory alkalosis – compensated  Alveolar CO 2 40mm Hg  30mm Hg  sensitivity of brain stem respiratory centers to pCO 2 – progesterone.

RENAL PHYSIOLOGIC CHANGES: Renal Plasma Flow (RPF) - equals the amount of a substance excreted/unit of time divided by renal arteriovenous difference. (PAH,DIODRAST) RPF = U [x] V P [x] P [x] Renal blood flow – RPF x 1________ 1-hematocrit 1-hematocrit RPF is raised throughout pregnancy by ml/1-min.

Glomerular Filtration Rate (GRF) - of plasma perfusing the glomeruli-about 20% reaches the tubular system of the kidney as an ultrafiltrate-i.e., GFR. GFR = U [x] V = Clearance P [X] P [X] ↑ creatinine clearance ↑ creatinine clearance ↑ urea clearance ↑ urea clearance ↑ uric acid clearance ↑ uric acid clearance

Tubular Function: Na+Excretion-progesterone inhibits reabsorption, however, increasing aldosterone levels counteract this effect. H 2 0=although plasma osmolality is ↓ and ECF ↑, urine volumes are similar to nonpregnant volumes. Hypothalamic resetting of osmoreceptors. Glycosuria-normal in pregnancy. Aminoaciduria-due to high circulating levels of cortisol?

↑ activity of renin-angiotensin- dissociation between pressor and renal effects. ↑ activity of renin-angiotensin- dissociation between pressor and renal effects. ↑ aldosterone ↑ aldosterone ↑ erythropoietin ↑ erythropoietin

GASTROINTESTINAL Decreased motility, delayed absorption ↓ gastric secretion, ↓ tone of cardiac sphincter (reflex esophagitis)

ENDOCRINE STEROIDS: STEROIDS: Progesterone-corpus luteum, fetal-placental unit. Progesterone-corpus luteum, fetal-placental unit. hyperpolarization of smooth muscle membrane potential- tone. hyperpolarization of smooth muscle membrane potential- tone. ↑ temperature ↑ temperature ↑ respiratory rate ↑ respiratory rate combined actions combined actions breast development breast development

Estrogens-ovarian, fetal-lacental unit combined actions with progesterone connective tissue effects liver-binding globulins ↑, serum enzymes ↑.

PROTEIN HORMONES: HCG-human chorionic gonadotrophin-syncytial trophoblast corpus luteum corpus luteum diagnosis of pregnancy diagnosis of pregnancy fetal adrenal fetal adrenal hPL-human placental lactogen-syncytium GH like activity GH like activitydiabetogenic HCT-chorionic thyrotropin TSH like activity

PITUITARY HORMONES: Anterior Lobe ADH, Oxytocin ADRENAL HORMONES : Cortisol-increases Aldosterone-increases Aldosterone-increases PANCREAS - ↑/s cell function, placental insulinase