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Question 1Maternal and Fetal Physiology

During a contraction, uterine blood flow to the intervillous space decreases primarily because of which mechanism?

  1. Dilation of the umbilical vein
  2. Increased maternal cardiac output
  3. Compression of the spiral arteries by myometrial contraction Correct answer.
  4. Reduced maternal oxygen saturation

Explanation

Myometrial contraction raises intramyometrial pressure, which compresses the spiral arteries and reduces perfusion of the intervillous space. This is why fetal oxygenation is most vulnerable during the contraction phase and why prolonged or excessive contractions cause fetal hypoxemia.

Question 2Maternal and Fetal Physiology

Which fetal shunt directs the most highly oxygenated blood from the umbilical vein toward the left atrium and coronary/cerebral circulation?

  1. Foramen ovale Correct answer.
  2. Umbilical arteries
  3. Ductus venosus
  4. Ductus arteriosus

Explanation

The foramen ovale allows oxygen-rich blood from the right atrium to pass into the left atrium, supplying the brain and heart preferentially. This streaming pattern is central to fetal oxygen delivery priorities.

Question 3Maternal and Fetal Physiology

The fetal heart rate baseline is best described as which of the following?

  1. The FHR measured only during uterine relaxation
  2. The highest FHR recorded during any 30-minute window
  3. The average of all accelerations in a 20-minute strip
  4. The mean FHR during the last 10 minutes, excluding accelerations and decelerations Correct answer.

Explanation

Baseline FHR is the mean rate rounded to 5 bpm over a 10-minute window, excluding accelerations, decelerations, and periods of marked variability. At least 2 minutes of interpretable tracing must be present in that window.

Question 4Maternal and Fetal Physiology

Fetal hemoglobin has a higher affinity for oxygen than adult hemoglobin mainly because fetal red cells contain which feature?

  1. More 2,3-diphosphoglycerate
  2. Higher intracellular pH than adult cells
  3. Hemoglobin F that binds 2,3-DPG less avidly Correct answer.
  4. Greater carbonic anhydrase activity

Explanation

Hemoglobin F has a lower affinity for 2,3-DPG, so its oxygen dissociation curve shifts left and it holds oxygen at lower partial pressures. This improves placental oxygen uptake.

Question 5Maternal and Fetal Physiology

Maternal cardiac output increases during pregnancy by approximately what percentage above prepregnancy values?

  1. 10% to 15%
  2. 70% to 90%
  3. 20% to 25%
  4. 30% to 50% Correct answer.

Explanation

Cardiac output rises about 30% to 50% in pregnancy, driven by increased stroke volume and later by heart rate. This supports the added demands of the uteroplacental circulation.

Question 6Maternal and Fetal Physiology

Uterine blood flow at term is approximately what value?

  1. 150 mL/min
  2. 50 mL/min
  3. 500 to 750 mL/min Correct answer.
  4. 1500 mL/min

Explanation

Uterine blood flow rises steeply in pregnancy and reaches roughly 500 to 750 mL/min at term, about 10% to 20% of cardiac output. This large flow supports placental exchange.

Question 7Maternal and Fetal Physiology

Which structure carries deoxygenated fetal blood from the fetus to the placenta?

  1. Foramen ovale
  2. Ductus venosus
  3. Umbilical arteries Correct answer.
  4. Umbilical vein

Explanation

The two umbilical arteries carry deoxygenated blood from the fetal iliac arteries to the placenta for gas exchange. The single umbilical vein returns oxygenated blood to the fetus.

Question 8Maternal and Fetal Physiology

Baseline variability is generated primarily by which physiologic mechanism?

  1. Fetal body movement
  2. Umbilical cord compression
  3. Autonomic modulation of the sinoatrial node Correct answer.
  4. Maternal respiration

Explanation

Beat-to-beat variability reflects continuous interaction between sympathetic and parasympathetic tone at the sinoatrial node. It is a marker of intact autonomic and central nervous system function, not of movement alone.

Question 9Maternal and Fetal Physiology

A tracing shows a baseline of 140 bpm with a deceleration that begins at contraction onset and returns to baseline well after the contraction ends. Which type of deceleration is this?

  1. Early deceleration
  2. Variable deceleration
  3. Prolonged deceleration
  4. Late deceleration Correct answer.

Explanation

Late decelerations have a gradual onset and return that lag the contraction, reflecting uteroplacental insufficiency. The delayed timing relative to the contraction defines the pattern.

Question 10Maternal and Fetal Physiology

Which finding is the best indicator of fetal metabolic acidemia on a fetal heart rate tracing?

  1. A single acceleration of 20 bpm
  2. Baseline tachycardia of 165 bpm with moderate variability
  3. Isolated variable decelerations with moderate variability
  4. Recurrent late decelerations with minimal variability Correct answer.

Explanation

Recurrent late decelerations combined with minimal or absent variability indicate compromised oxygen delivery and possible metabolic acidemia. The combination of patterns, not a single feature, predicts acidemia.

Question 11Maternal and Fetal Physiology

Which mechanism produces variable decelerations?

  1. Umbilical cord compression Correct answer.
  2. Maternal hypotension
  3. Uteroplacental insufficiency
  4. Fetal head compression

Explanation

Variable decelerations are abrupt in onset and reflect umbilical cord compression, which transiently reduces umbilical blood flow. They are defined by their abrupt shape rather than by contraction timing.

Question 12Maternal and Fetal Physiology

During the second stage of labor, the maternal supine position can reduce uteroplacental perfusion mainly by which effect?

  1. Increasing uterine contractility
  2. Compressing the inferior vena cava Correct answer.
  3. Raising maternal oxygen saturation
  4. Increasing venous return

Explanation

Supine positioning compresses the inferior vena cava, reducing venous return and cardiac output, which lowers uteroplacental perfusion. Repositioning to a lateral tilt often improves the tracing.

Question 13Maternal and Fetal Physiology

Which is the normal range for a fetal heart rate baseline?

  1. 90 to 110 bpm
  2. 160 to 180 bpm
  3. 70 to 90 bpm
  4. 110 to 160 bpm Correct answer.

Explanation

A baseline of 110 to 160 bpm is considered normal. Values below 110 indicate bradycardia and above 160 indicate tachycardia.

Question 14Maternal and Fetal Physiology

Fetal breathing movements on ultrasound are used clinically to assess which aspect of fetal status?

  1. Fetal acid-base status and well-being Correct answer.
  2. Fetal position
  3. Amniotic fluid volume alone
  4. Fetal lung maturity only

Explanation

Fetal breathing movements are a component of the biophysical profile and reflect central nervous system and acid-base status. Their presence is reassuring for fetal well-being.

Question 15Maternal and Fetal Physiology

Maternal oxygen consumption increases during pregnancy by approximately what amount?

  1. 100%
  2. 5%
  3. 15% to 20% Correct answer.
  4. 50%

Explanation

Oxygen consumption rises about 15% to 20% in pregnancy to meet fetal and maternal metabolic demands. This contributes to the increased respiratory minute ventilation observed.

Question 16Maternal and Fetal Physiology

A fetus with chronic placental insufficiency typically shows which growth pattern?

  1. Symmetric growth restriction from early chromosomal abnormality
  2. Macrosomia with symmetric growth
  3. Normal growth with accelerated head growth
  4. Asymmetric growth restriction with head sparing Correct answer.

Explanation

Chronic placental insufficiency causes asymmetric growth restriction because the fetus redistributes blood flow to the brain, sparing head growth. This brain-sparing effect is a compensatory response to hypoxemia.

Question 17Maternal and Fetal Physiology

Which condition is the most common cause of fetal bradycardia during labor?

  1. Fetal anemia
  2. Maternal fever
  3. Umbilical cord prolapse
  4. Uterine hyperstimulation Correct answer.

Explanation

Uterine hyperstimulation, often from oxytocin or prostaglandins, reduces placental perfusion and can cause sustained fetal bradycardia. Reducing or stopping the agent is a key initial response.

Question 18Maternal and Fetal Physiology

Which fetal heart rate pattern is most consistent with a sinusoidal rhythm?

  1. Abrupt decelerations with moderate variability
  2. Baseline wandering between 120 and 160 bpm
  3. Accelerations followed by late decelerations
  4. Smooth undulating waves at 3 to 5 cycles per minute with absent variability Correct answer.

Explanation

A sinusoidal pattern is a smooth, undulating wave at 3 to 5 cycles per minute with absent variability, often associated with severe fetal anemia. It is distinct from normal baseline wandering.

Question 19Maternal and Fetal Physiology

Which factor most directly determines umbilical blood flow?

  1. Maternal blood pressure alone
  2. Fetal heart rate alone
  3. Umbilical vessel length
  4. Pressure gradient between umbilical artery and vein Correct answer.

Explanation

Umbilical blood flow depends on the pressure gradient across the umbilical circulation and vascular resistance, analogous to other vascular beds. Vessel length is a minor contributor compared with the gradient.

Question 20Maternal and Fetal Physiology

Which statement best describes the fetal response to acute hypoxemia?

  1. Peripheral vasodilation with increased cerebral blood flow
  2. Immediate cessation of all fetal movement
  3. Peripheral vasoconstriction with preferential cerebral and myocardial perfusion Correct answer.
  4. Increased umbilical artery resistance with decreased cerebral flow

Explanation

Acute hypoxemia triggers a chemoreceptor-mediated redistribution of blood flow, with peripheral vasoconstriction and preferential perfusion of the brain, heart, and adrenals. This brain-sparing response is a key compensatory mechanism.

Question 21Maternal and Fetal Physiology

Which change in maternal physiology explains the increased risk of supine hypotension in late pregnancy?

  1. Increased uterine artery resistance
  2. Increased baroreceptor sensitivity
  3. Compression of the inferior vena cava by the gravid uterus Correct answer.
  4. Decreased maternal blood volume

Explanation

The gravid uterus compresses the inferior vena cava when the mother lies supine, reducing venous return and cardiac output. This produces supine hypotension, which can in turn reduce uteroplacental perfusion.

Question 22Maternal and Fetal Physiology

Which pattern of fetal heart rate change is most consistent with fetal anemia?

  1. Sinusoidal pattern with absent variability Correct answer.
  2. Variable decelerations with normal variability
  3. Early decelerations with moderate variability
  4. Tachycardia with accelerations

Explanation

Severe fetal anemia can produce a sinusoidal pattern with absent variability due to altered autonomic control of the heart rate. It is an ominous finding that warrants urgent evaluation.

Question 23Maternal and Fetal Physiology

Which factor best explains why fetal oxygen saturation is lower than maternal oxygen saturation despite efficient placental exchange?

  1. Placental oxygen diffusion is inherently inefficient
  2. The fetal oxygen dissociation curve is shifted left Correct answer.
  3. Fetal blood flow to the placenta is greater than maternal flow
  4. Fetal hemoglobin binds oxygen less avidly

Explanation

The leftward shift of the fetal oxygen dissociation curve allows the fetus to load oxygen at low partial pressures, but fetal arterial oxygen saturation remains lower than maternal because of the parallel arrangement of the circulations and mixing of blood. The shift improves uptake rather than raising saturation to maternal levels.

Question 24Maternal and Fetal Physiology

Which mechanism best explains the fetal heart rate acceleration seen with fetal movement?

  1. Decreased fetal oxygen consumption
  2. Reduced umbilical blood flow
  3. Increased vagal tone alone
  4. Parasympathetic withdrawal with sympathetic activation Correct answer.

Explanation

Accelerations reflect a transient shift toward sympathetic dominance with parasympathetic withdrawal at the sinoatrial node. Their presence is a reassuring sign of intact autonomic function.

Question 25Maternal and Fetal Physiology

Which statement about the ductus arteriosus in fetal circulation is correct?

  1. It shunts blood from the right atrium to the left atrium
  2. It connects the umbilical vein to the inferior vena cava
  3. It shunts blood from the pulmonary artery to the aorta Correct answer.
  4. It carries oxygenated blood to the liver

Explanation

The ductus arteriosus connects the pulmonary artery to the descending aorta, diverting blood away from the unventilated lungs. Functional closure occurs after birth as pulmonary vascular resistance falls and oxygen levels rise.

Question 26Maternal and Fetal Physiology

During fetal life, which vessel carries the most highly oxygenated blood directly to the fetal brain?

  1. The left umbilical artery
  2. The ductus arteriosus
  3. The umbilical vein Correct answer.
  4. The superior vena cava

Explanation

Oxygenated blood returns from the placenta through the umbilical vein, and a large share is streamed through the foramen ovale into the left atrium and then to the brain. The umbilical vein therefore carries the highest oxygen content in the fetal circulation, not the arteries.

Question 27Maternal and Fetal Physiology

Maternal cardiac output typically changes during pregnancy in which way?

  1. It remains essentially unchanged until labor begins
  2. It rises only during the third trimester
  3. It falls by about 15 percent by term
  4. It rises by roughly 30 to 50 percent above prepregnancy values Correct answer.

Explanation

Cardiac output increases early in pregnancy, driven mainly by a larger stroke volume and later by a higher heart rate, reaching roughly 30 to 50 percent above baseline by term. This supports the added uteroplacental and renal demands of pregnancy.

Question 28Maternal and Fetal Physiology

A laboring patient at 39 weeks has a baseline fetal heart rate of 145 bpm. Which feature of the baseline is generated mainly by parasympathetic and sympathetic interaction at the sinoatrial node?

  1. The depth of variable decelerations
  2. The presence of accelerations
  3. The frequency of contractions
  4. The baseline rate itself Correct answer.

Explanation

The baseline rate reflects the net balance of sympathetic and parasympathetic tone acting on the fetal sinoatrial node. Variability and accelerations involve additional modulation, but the average rate is set by autonomic tone.

Question 29Maternal and Fetal Physiology

A pregnant patient at 32 weeks has a hemoglobin of 10.5 g/dL with normal red cell indices. Which physiologic explanation best accounts for this finding?

  1. Suppression of erythropoietin by placental progesterone
  2. Increased destruction of red cells by the placenta
  3. True iron-deficiency anemia requiring transfusion
  4. Expansion of plasma volume exceeding the rise in red cell mass Correct answer.

Explanation

Plasma volume expands proportionally more than red cell mass during pregnancy, producing a dilutional fall in hemoglobin concentration. This physiologic anemia of pregnancy is expected when indices are normal and does not by itself indicate iron deficiency.

Question 30Maternal and Fetal Physiology

A fetus with a complete heart block is evaluated. Which structure normally delays conduction between the atria and ventricles, and its failure explains the dissociation seen here?

  1. The sinoatrial node
  2. The atrioventricular node Correct answer.
  3. The bundle of His
  4. The Purkinje fibers

Explanation

The atrioventricular node introduces a brief conduction delay between atrial and ventricular activation, allowing coordinated filling and contraction. When this node fails to conduct, atrial and ventricular activity become independent, producing complete heart block.

Question 31Fetal Monitoring Equipment and Techniques

Which ultrasound transducer frequency is typically used for external fetal heart rate monitoring to provide adequate penetration for obese patients?

  1. 5 MHz
  2. 2 MHz Correct answer.
  3. 8 MHz
  4. 10 MHz

Explanation

External Doppler monitors commonly use a 2 MHz transducer because lower frequencies penetrate deeper tissue better, which helps obtain a signal in patients with a thick abdominal wall. Higher frequencies give better resolution but poorer penetration depth.

Question 32Fetal Monitoring Equipment and Techniques

What is the primary purpose of the tocodynamometer (toco) in intrapartum monitoring?

  1. Detecting uterine contraction frequency and relative duration Correct answer.
  2. Measuring maternal blood pressure during contractions
  3. Measuring intrauterine pressure quantitatively
  4. Detecting fetal heart rate variability

Explanation

The external tocodynamometer senses changes in abdominal wall tension and is used to identify contraction frequency and approximate duration, not absolute intensity. It cannot quantify intrauterine pressure in mmHg.

Question 33Fetal Monitoring Equipment and Techniques

Which device provides a direct, quantitative measurement of uterine contraction intensity?

  1. Doppler ultrasound transducer
  2. Intrauterine pressure catheter Correct answer.
  3. External tocodynamometer
  4. Fetal scalp electrode

Explanation

An intrauterine pressure catheter measures actual pressure changes within the amniotic cavity, expressed in mmHg, and quantifies contraction intensity. External devices only show relative tension changes and cannot measure pressure directly.

Question 34Fetal Monitoring Equipment and Techniques

A fetal scalp electrode primarily detects which signal to determine fetal heart rate?

  1. Fetal ECG Correct answer.
  2. Fetal pulse oximetry
  3. Maternal aortic pulse
  4. Umbilical artery flow

Explanation

The fetal scalp electrode is a direct electrode applied to the fetal presenting part that records the fetal electrocardiogram, from which heart rate is derived. This direct method is less affected by maternal movement than ultrasound.

Question 35Fetal Monitoring Equipment and Techniques

What does the fetal heart rate baseline represent on a monitor tracing?

  1. The FHR averaged over the entire labor course
  2. The FHR recorded only during the second stage
  3. The highest FHR recorded during any contraction
  4. The mean FHR rounded to the nearest 5 bpm during a 10-minute window, excluding accelerations and decelerations Correct answer.

Explanation

The baseline is defined as the mean fetal heart rate rounded to 5 bpm over a 10-minute segment, excluding accelerations, decelerations, and periods of marked variability. A minimum of 2 minutes of interpretable tracing is required within that window.

Question 36Fetal Monitoring Equipment and Techniques

Which monitor display parameter reflects beat-to-beat changes in the fetal heart rate?

  1. Variability Correct answer.
  2. Contraction frequency
  3. Deceleration depth
  4. Baseline rate

Explanation

Variability describes the fluctuations in the fetal heart rate around the baseline from beat to beat and is a key indicator of fetal autonomic and oxygenation status. It is distinct from the baseline rate itself.

Question 37Fetal Monitoring Equipment and Techniques

Why is maternal pulse oximetry sometimes used alongside fetal monitoring in labor?

  1. To confirm maternal oxygenation during periods of concern Correct answer.
  2. To calibrate the fetal scalp electrode
  3. To replace the tocodynamometer
  4. To measure fetal oxygen saturation directly

Explanation

Maternal pulse oximetry assesses the mother's oxygen saturation, which is relevant because maternal hypoxemia can impair fetal oxygenation. It does not measure fetal saturation directly.

Question 38Fetal Monitoring Equipment and Techniques

What is the recommended action when the external fetal monitor tracing shows an intermittent loss of signal due to maternal position?

  1. Turn off the uterine channel
  2. Reposition the patient and adjust the transducer Correct answer.
  3. Increase the paper speed
  4. Decrease the ultrasound gain to zero

Explanation

Intermittent signal loss is often caused by transducer displacement or maternal position, so repositioning the patient and adjusting the transducer usually restores the signal. Altering gain or paper speed does not resolve a mechanical signal loss.

Question 39Fetal Monitoring Equipment and Techniques

A nurse notes that the external tocodynamometer tracing shows frequent low-amplitude waves that do not correspond to palpable contractions. What is the most likely cause?

  1. True uterine hyperstimulation
  2. Maternal breathing or movement artifact Correct answer.
  3. Umbilical cord prolapse
  4. Fetal accelerations

Explanation

The external toco is sensitive to abdominal wall movement, so maternal breathing, coughing, or repositioning can produce artifact waves that do not match palpable contractions. Correlating the tracing with palpation helps distinguish artifact from true contractions.

Question 40Fetal Monitoring Equipment and Techniques

When using an intrauterine pressure catheter, how is resting tone typically estimated?

  1. The difference between systolic and diastolic maternal pressure
  2. The peak pressure during a contraction
  3. The pressure reading between contractions Correct answer.
  4. The average pressure during the second stage

Explanation

Resting tone is the baseline intrauterine pressure measured between contractions, usually reported in mmHg. Peak contraction pressure reflects the intensity of a contraction rather than the resting tone.

Question 41Fetal Monitoring Equipment and Techniques

A tracing shows the fetal heart rate baseline of 145 bpm with absent variability and recurrent late decelerations. Which monitoring limitation should be considered when interpreting this pattern?

  1. Maternal oximetry masks late decelerations
  2. External Doppler may misrepresent true variability Correct answer.
  3. The toco always overestimates contraction intensity
  4. Scalp electrodes cannot detect decelerations

Explanation

External Doppler ultrasound can produce artifact that alters the apparent variability, so direct fetal ECG or careful verification may be needed when the pattern is concerning. The toco cannot measure intensity quantitatively, and oximetry does not mask decelerations.

Question 42Fetal Monitoring Equipment and Techniques

Which factor most affects the accuracy of external Doppler fetal heart rate measurement?

  1. Correct placement of the transducer over the fetal heart Correct answer.
  2. The number of staff present
  3. The color of the display screen
  4. The paper speed setting

Explanation

Accurate external Doppler measurement depends on placing the transducer over the fetal heart and adjusting gain appropriately. Display color, paper speed, and staffing do not influence the acquired Doppler signal.

Question 43Fetal Monitoring Equipment and Techniques

What does the ultrasound gel serve in external fetal monitoring?

  1. It conducts electrical current to the scalp electrode
  2. It measures uterine pressure
  3. It sterilizes the transducer between patients
  4. It improves acoustic coupling between the transducer and skin Correct answer.

Explanation

Gel eliminates air between the transducer and skin, allowing ultrasound waves to pass efficiently and improving signal quality. It has no electrical, sterilizing, or pressure-measuring function.

Question 44Fetal Monitoring Equipment and Techniques

A patient with a high body mass index has poor external Doppler signal despite repositioning. What is the most appropriate next step?

  1. Discontinue monitoring entirely
  2. Increase the paper speed to 3 cm/min
  3. Use a lower-frequency transducer and adjust placement Correct answer.
  4. Apply the toco to the fetal scalp

Explanation

Lower-frequency ultrasound penetrates tissue better, so switching to a 2 MHz transducer and optimizing placement can improve the signal in patients with greater abdominal tissue. Paper speed and discontinuing monitoring do not address signal acquisition.

Question 45Fetal Monitoring Equipment and Techniques

What is a key advantage of the fetal scalp electrode over external Doppler monitoring?

  1. It detects fetal oxygen saturation
  2. It provides a clearer signal less affected by maternal movement Correct answer.
  3. It measures uterine contraction intensity
  4. It eliminates the need for any other monitoring

Explanation

The direct fetal ECG signal from a scalp electrode is less susceptible to maternal movement and position artifact than external Doppler. It does not measure uterine pressure, replace all monitoring, or measure oxygen saturation.

Question 46Fetal Monitoring Equipment and Techniques

Which pattern on the uterine channel suggests that the tocodynamometer may be recording artifact rather than true contractions?

  1. Waves that peak at the same time as decelerations
  2. Waves that do not coincide with the patient's reported or palpable contractions Correct answer.
  3. Waves that occur every 2 to 3 minutes
  4. Waves that increase in amplitude with pushing

Explanation

Artifact is suspected when toco waves do not align with palpable contractions or the patient's sensation of contractions. True contractions should correlate with palpation and with the patient's experience.

Question 47Fetal Monitoring Equipment and Techniques

What information does fetal pulse oximetry provide when used during labor?

  1. Maternal cardiac output
  2. Fetal heart rate baseline
  3. Uterine resting tone
  4. Fetal arterial oxygen saturation Correct answer.

Explanation

Fetal pulse oximetry estimates fetal arterial oxygen saturation using a sensor placed against the fetal presenting part. It does not measure uterine tone, baseline heart rate, or maternal cardiac output.

Question 48Fetal Monitoring Equipment and Techniques

A monitor tracing shows the baseline shifting upward from 140 to 160 bpm over 10 minutes. How should this be documented?

  1. A single acceleration
  2. A baseline change requiring reassessment of the tracing Correct answer.
  3. A deceleration
  4. Artifact that should be ignored

Explanation

A sustained shift in the baseline over a 10-minute window represents a baseline change and warrants reassessment of the clinical context. It is not a single acceleration or deceleration, and it should not be dismissed as artifact without evaluation.

Question 49Fetal Monitoring Equipment and Techniques

What is the purpose of the event marker button on an electronic fetal monitor?

  1. To increase the ultrasound gain
  2. To calibrate the tocodynamometer
  3. To document clinical events or interventions on the tracing Correct answer.
  4. To measure intrauterine pressure

Explanation

The event marker annotates the tracing with the timing of clinical events, such as examinations, medications, or repositioning, so they can be correlated with FHR changes. It does not alter gain, measure pressure, or calibrate the toco.

Question 50Fetal Monitoring Equipment and Techniques

Which statement best describes the relationship between the toco and intrauterine pressure catheter regarding contraction intensity?

  1. Both devices measure absolute pressure in mmHg
  2. The toco estimates relative intensity, whereas the catheter measures absolute pressure Correct answer.
  3. The toco measures absolute pressure, whereas the catheter estimates relative intensity
  4. Neither device provides information about contractions

Explanation

The external toco reflects relative changes in abdominal tension and cannot quantify pressure, while the intrauterine catheter measures absolute pressure in mmHg. This distinction matters when evaluating contraction intensity and resting tone.