OSPE Station - Complete Answers

PROCEDURE STATION

ESR (Erythrocyte Sedimentation Rate) - Westergren Method

1. Add 2 mL of whole blood to 0.5 mL of sodium citrate and mix by inversion (4:1 ratio)
2. Fill a Westergren tube/pipette to the 0 mark
3. Place the tube exactly vertical in the rack at room temperature
4. Away from vibration and direct sunlight
5. After exactly 60 minutes, record the distance (in mm) from the 0 mark to the top of the red cell column

Knee Jerk (Patellar Reflex)

• Procedure: Patient seated with legs hanging freely. Strike the patellar tendon just below the patella with a reflex hammer. Normal response: extension of the knee (L3-L4 arc).
• Grading: 0 (absent) to 4+ (clonus)

Pulse

• Procedure: Place 2-3 fingers over the radial artery at the wrist. Count for 60 seconds (or 15 s x 4).
• Record: Rate, rhythm, volume, character
• Normal: 60-100 bpm

Blood Grouping (ABO + Rh)

• Instruments needed: Glass slides or tiles, anti-A serum, anti-B serum, anti-D serum, applicator sticks, lancet
• Procedure: Place drops of anti-A, anti-B, and anti-D on a slide. Add a drop of patient blood to each. Mix gently and observe for agglutination within 2 minutes.

Q1 - Ovulation

Definition:

4 Indications / Signs of Ovulation:

Q2 - Differentiate UMNL vs LMNL

Note: In acute UMNL (e.g. spinal shock), tone and reflexes may initially be reduced - hyperreflexia develops over hours to weeks. (Neuroanatomy through Clinical Cases, 3rd Ed.)

Q3 - HR = 72 b/min; CO = ?

CO = Stroke Volume (SV) x Heart Rate (HR)

• Normal Stroke Volume = 70 mL/beat
• Heart Rate = 72 beats/min

Cell Identification: Neutrophil (Microscopy Station)

• Multi-lobed (2-5 lobes) nucleus connected by thin chromatin strands - "segmented" nucleus
• Pale pink cytoplasm with fine granules
• Largest proportion of WBCs (50-70%)
• Functions in phagocytosis and killing of bacteria (first responders)
• Increased in: bacterial infections, inflammation, stress

OSPE Cross Questions (Viva)

🔬 CROSS Q's on ESR

ESR measures the rate at which red blood cells settle in a tube over 1 hour. RBCs normally repel each other (negative charge). In infection/inflammation, fibrinogen and immunoglobulins coat RBCs, neutralize the charge, and cause rouleaux formation (stacking like coins), which increases the sedimentation rate.

• Infections (TB, bacterial infections)
• Inflammatory conditions (Rheumatoid arthritis, SLE, vasculitis)
• Malignancy (multiple myeloma - most dramatically raised)
• Anemia (fewer RBCs settle slower, paradoxically raises ESR)
• Pregnancy
• Old age

• Polycythemia (too many RBCs, resist rouleaux)
• Sickle cell disease (abnormal shape prevents rouleaux)
• Spherocytosis
• Congestive cardiac failure
• Hypofibrinogenemia

Sodium citrate (3.8%) in a 4:1 ratio (blood:citrate). Heparin cannot be used because it alters the membrane zeta potential of RBCs and artificially increases the ESR, giving false results.

The tube must be perfectly vertical. Even a 3-degree tilt can accelerate the ESR by as much as 30% because plasma rises along the upper wall while RBCs settle along the lower wall, reducing resistance.

• Men: Age / 2
• Women: (Age + 10) / 2 (Wills Eye Manual formula for practical use)

🦵 CROSS Q's on Knee Jerk (Patellar Reflex)

• Receptor: Muscle spindle (in quadriceps muscle)
• Afferent (sensory): Femoral nerve → dorsal root → L3, L4 spinal segments
• Synapse: In anterior horn of spinal cord (monosynaptic reflex)
• Efferent (motor): Anterior horn cell → femoral nerve → quadriceps
• Effector: Quadriceps contraction → knee extension

It is a monosynaptic stretch reflex (only one synapse between sensory and motor neuron). It is also a deep tendon reflex (DTR).

In lower motor neuron lesion affecting L3/L4:

• Peripheral neuropathy (diabetic, GBS)
• Tabes dorsalis
• Poliomyelitis
• Direct femoral nerve damage

In upper motor neuron lesion (lesion above L3/L4):

• Stroke
• Multiple sclerosis
• Cervical myelopathy
• Spinal cord compression above L3

Clonus is a series of rhythmic involuntary contractions (5-7 Hz) in response to a sustained stretch stimulus. It occurs in UMN lesions due to hyperexcitability of alpha and gamma motor neurons from loss of supraspinal inhibition. (Adams & Victor's Neurology)

💉 CROSS Q's on Neutrophil

50-70% of total WBC count. Normal absolute count: 2,500 - 7,500 cells/µL.

• Primary (azurophilic) granules: Contain myeloperoxidase, lysozyme, elastase - kill bacteria
• Secondary (specific) granules: Contain lactoferrin, collagenase - help in inflammation
• Tertiary granules: Gelatinase - help in tissue invasion Function: Phagocytosis + destruction of bacteria via reactive oxygen species (ROS) and anti-microbial peptides; also form NETs (Neutrophil Extracellular Traps). (Firestein & Kelley's Rheumatology)

• Neutrophilia: >7,500/µL - seen in bacterial infections, stress, steroids, burns
• Neutropenia: <2,500/µL - seen in viral infections, SLE, chemotherapy, aplastic anemia

Increased release of immature neutrophils (band cells, metamyelocytes) into the blood, indicating a severe or overwhelming infection where the bone marrow is pushed to its limit.

• Neutrophil: Pale pink cytoplasm, fine granules, multilobed nucleus (2-5 lobes)
• Eosinophil: Bright orange-red large granules, bilobed nucleus (classically 2 lobes)

🩸 CROSS Q's on Ovulation

The LH surge (Luteinizing Hormone). A sudden peak in LH (caused by high estrogen positive feedback on the anterior pituitary) triggers ovulation 24-36 hours later. (Berek & Novak's Gynecology)

After ovulation, the corpus luteum secretes progesterone. A serum progesterone level >3 ng/mL on day 21 (mid-luteal phase) is presumptive evidence ovulation occurred. Progesterone also raises the basal body temperature by ~0.3-0.5°C. (Costanzo Physiology)

Just before and at ovulation, estradiol causes cervical mucus to become:

• More abundant
• Watery and clear
• Highly stretchy (spinnbarkeit)
• Penetrable by sperm After ovulation, progesterone makes it thick, scanty, and hostile to sperm.

The luteal phase is always 14 days, regardless of cycle length. The follicular phase is variable. So in a 35-day cycle, ovulation is on day 21; in a 24-day cycle, it's day 10.

FSH → Follicle growth → ↑ Estradiol → Positive feedback → LH surge → Ovulation (day 14) → Corpus luteum → ↑ Progesterone + Estradiol (luteal phase)

⚡ CROSS Q's on UMNL vs LMNL

Upper motor neurons normally inhibit the spinal reflex arc. When this inhibitory control is lost (due to cortical/spinal cord damage), the lower motor neurons become disinhibited and hyperresponsive, resulting in exaggerated reflexes and increased tone (spasticity).

• In LMNL: the motor neuron itself is damaged → muscle receives no signal → flaccid, hypotonic
• In UMNL: the inhibitory descending control is removed → spinal circuits are over-active → spastic, hypertonic

Elicited by stroking the lateral plantar surface of the foot from heel to ball.

• Normal (negative): Flexion (plantar flexion) of toes
• Babinski positive: Extension (dorsiflexion) of great toe + fanning of other toes
• Significance: Indicates UMNL / corticospinal tract damage at any level
• Normal in infants under 1 year (myelination incomplete) (Adams & Victor's Neurology)

Initially decreased / flaccid (spinal shock). Hyperreflexia and spasticity develop hours to weeks later as spinal circuits reorganize. (Neuroanatomy through Clinical Cases)

• UMNL: Stroke (internal capsule), Multiple sclerosis, cervical myelopathy
• LMNL: Guillain-Barré syndrome, diabetic peripheral neuropathy, poliomyelitis

❤️ CROSS Q's on Cardiac Output (HR = 72, CO = 5 L/min)

CO = Stroke Volume (SV) × Heart Rate (HR) = 70 mL × 72 bpm = 5,040 mL/min ≈ 5 L/min

SV = volume ejected per beat = EDV - ESV (~70 mL normally) Three determinants:

1. Preload - end-diastolic volume (Frank-Starling: more stretch → more force → more SV)
2. Afterload - resistance the ventricle must overcome (↑ afterload → ↓ SV)
3. Contractility - intrinsic ability of the myocardium to contract (independent of preload/afterload)

EF = SV / EDV × 100 = 70/120 × 100 ≈ 55-65% EF < 40% = systolic heart failure

Not always. At very high HRs, diastolic filling time decreases, reducing EDV and SV. So CO may actually decrease at extremely high heart rates (e.g., tachyarrhythmias).

The greater the end-diastolic volume (preload), the greater the stroke volume - up to a physiological limit. This is because more myocardial stretching leads to greater force of contraction (more actin-myosin overlap). (Costanzo Physiology, 7th Ed.)