What This Test Measures

• PImax (Maximal Inspiratory Pressure) - the maximum pressure the breathing-in muscles (mainly the diaphragm and external intercostals) can generate. The patient exhales fully to residual volume, then inhales against a blocked airway as hard as possible.
• PEmax (Maximal Expiratory Pressure) - the maximum pressure the breathing-out muscles (abdominal muscles, internal intercostals) can generate. The patient inhales fully to total lung capacity, then exhales as forcefully as possible.

Reading Your Results

• Both values are severely reduced - only about 40-43% of what is expected for this patient's age/sex/height.
• Normal PImax is typically more negative than -75 cmH2O (~7.5 kPa); this patient's value is only ~4.57 kPa.
• Normal PEmax is typically >125 cmH2O (~12.5 kPa); this patient's value is only ~3.94 kPa.

The Graphs

Technical Notes from the Report

• Armspan was used to measure height - this is standard when a patient cannot stand straight (e.g., scoliosis, elderly, wheelchair users).
• Patient effort was just satisfactory; poor acceptability in PImax - the patient could only sustain the inspiratory effort for less than 2 seconds. A valid PImax requires sustaining pressure for at least 1-2 seconds. This means the PImax value may actually underestimate the true weakness (or it could reflect genuine inability to sustain effort due to weakness itself).
• No post-bronchodilator values were recorded (Post column is blank), so this was not a reversibility study.

Conclusion (as printed on the report)

"BOTH PI MAX AND PE MAX ARE REDUCED"

• Neuromuscular diseases (e.g., motor neuron disease/ALS, myasthenia gravis, muscular dystrophy, Guillain-Barre syndrome)
• Severe malnutrition/cachexia
• Bilateral diaphragm paralysis
• Systemic myopathy (steroid myopathy, inflammatory myopathy)
• Critical illness/prolonged ICU stay

Why Do PImax and PEmax Become Reduced?

1. Diseases of the Motor Neuron (Upper & Lower)

• Amyotrophic Lateral Sclerosis (ALS / Motor Neuron Disease) - the most common cause of bilateral diaphragm weakness from motor neuron disease
• Poliomyelitis - viral destruction of anterior horn cells
• Cervical spinal cord injury - cuts off nerve signals to the diaphragm (phrenic nerve originates at C3-C5)
• Cervical spondylosis - compression of the spinal cord in the neck

2. Peripheral Nerve / Phrenic Nerve Damage (Neuropathic)

• Cardiac surgery (cold cardioplegia - ice used to protect the heart can freeze and damage the phrenic nerve)
• Blunt chest/neck trauma
• Radiation injury to the chest or neck
• Lung cancer or metastatic mediastinal tumor compressing the phrenic nerve
• Guillain-Barre syndrome - autoimmune attack on peripheral nerves; tends to cause less severe weakness than motor neuron disease
• Neuralgic amyotrophy (Parsonage-Turner syndrome) - inflammatory neuritis
• Vasculitis / Mononeuritis multiplex
• Paraneoplastic syndrome (cancer releasing substances that attack nerves)
• Diabetes mellitus - causes peripheral neuropathy that can involve the phrenic nerve

3. Neuromuscular Junction Disorders

• Myasthenia gravis - autoimmune destruction of acetylcholine receptors; the muscle cannot respond even when the nerve fires
• Lambert-Eaton myasthenic syndrome (paraneoplastic)
• Organophosphate poisoning - cholinesterase inhibition causing paradoxical weakness after initial overstimulation

4. Muscle Diseases (Myopathic)

• Duchenne & Becker muscular dystrophy
• Limb-girdle muscular dystrophy

• Acid maltase deficiency (Pompe disease) - often first presents as respiratory failure
• Hyperthyroidism or hypothyroidism - both can cause proximal muscle weakness
• Vitamin deficiencies (B6, B12, folate)

• Dermatomyositis / Polymyositis
• Systemic Lupus Erythematosus (SLE)
• Mixed connective tissue disease

• Malnutrition / cachexia - loss of muscle mass affects respiratory muscles just like limb muscles
• Amyloidosis infiltrating the muscle

5. Other Contributing Factors

• Hyperinflation (severe COPD/emphysema) - the diaphragm gets flattened by overinflated lungs and loses its mechanical advantage, reducing PImax even without true muscle disease
• Severe obesity - extra load on chest wall increases the work demand
• ICU-acquired weakness - prolonged bed rest, mechanical ventilation, and critical illness rapidly waste respiratory muscles
• Steroid myopathy - long-term corticosteroid use weakens proximal muscles including the diaphragm

Key Point: Both PImax AND PEmax Reduced Together

1. Neuromuscular disease (ALS, myasthenia gravis, muscular dystrophy)
2. Systemic myopathy (inflammatory, metabolic, rheumatologic)
3. Malnutrition / severe cachexia
4. Critical illness weakness

How Spinal Surgery Causes Reduced PImax & PEmax

The Anatomy - Which Level Controls Which Muscles

Why This Patient Fits

• At low cervical level: PImax ~61% predicted, PEmax ~30% predicted
• At mid-thoracic level: PImax ~69% predicted, PEmax ~32% predicted

1. PImax is reduced because the diaphragm and inspiratory muscles (scalenes, intercostals) lose some nerve supply
2. PEmax is reduced even more because the abdominal muscles and internal intercostals - which drive forceful expiration and coughing - are paralyzed when the thoracic spinal cord is affected

Specific Ways Spinal Surgery Can Cause This

• The phrenic nerve roots (C3-C5) can be injured during cervical spine surgery
• This directly weakens or paralyzes the diaphragm

• Surgical manipulation, retraction, or post-operative swelling/hematoma near the cord can functionally injure it
• Even without complete cord injury, temporary or partial dysfunction reduces muscle signals

• After spinal surgery, pain prevents the patient from taking deep breaths or coughing forcefully
• This contributes to poor effort - consistent with the report's note: "patient effort was just satisfactory"

• If the patient had surgery because of cord compression (e.g. cervical myelopathy, disc prolapse, stenosis), the nerve damage may have been present before surgery
• The test may be reflecting the underlying disease, not the surgery itself

• Thoracic spine surgery (T1-T12) can damage the nerve roots supplying intercostal muscles (inspiration) and abdominal muscles (expiration/cough)
• Loss of abdominal muscle function directly explains the drastically low PEmax

• Post-spinal surgery patients are often immobile for weeks
• The diaphragm is sensitive to inactivity - disuse atrophy sets in rapidly, especially if the patient was also on a ventilator

The Technical Note Explains It Too

• Cannot stand due to spinal pathology
• Have significant spinal deformity (scoliosis, kyphosis)
• Are wheelchair-bound from spinal cord disease

Bottom Line

C4 Surgery - Direct Hit on the Breathing Nerve

What C4 Surgery Damages

1. The Phrenic Nerve - Direct Diaphragm Weakness (PImax reduced)

• Partially or completely interrupt the nerve signal to the diaphragm
• The diaphragm is the primary breathing muscle - responsible for 70-80% of inspiratory effort
• This directly explains why PImax is only 40% of predicted - the diaphragm simply cannot contract with full force

2. Intercostal Muscles Lost (both PImax and PEmax reduced)

• Help expand the ribcage during inspiration (contributes to PImax)
• Help compress the chest during forced expiration (contributes to PEmax)

3. Abdominal Muscles Paralyzed (PEmax severely reduced)

• Forced expiration
• Coughing
• Generating high expiratory pressures

The C4 Clinical Picture - What Happens

Why C4 is the "Danger Zone"

"Patients with C3-C4 injuries may eventually achieve at least partial ventilator independence. Lesions below C4 are usually compatible with unassisted ventilation - unless there are complicating processes."

• Above C4 (C1-C3): Complete respiratory paralysis, permanent ventilator
• At C4: Partial diaphragm function - may breathe independently but with significant weakness (exactly what this patient's test shows)
• Below C4 (C5-C8): Diaphragm largely intact, intercostals lost, PEmax affected more than PImax

What This Means Practically for the Patient

1. Weak cough - cannot clear secretions properly, high risk of chest infections and pneumonia
2. Breathless on exertion - respiratory reserve is used up just by the effort of normal breathing
3. Worse when lying flat - without abdominal muscle tone, the abdominal contents push up into the chest in the supine position, compressing the lungs further
4. Sleep risk - hypoventilation during sleep is common, may need nocturnal ventilation
5. Any chest infection is dangerous - already at 40% capacity, any further reduction (from mucus, pneumonia) can push into respiratory failure

Full Clinical Picture - Explained

What This Patient Had

Why PImax and PEmax Are Reduced - Now Fully Explained

Reason 1 - Surgical Fusion Level C5 to T8

Reason 2 - Thoracic Scoliosis from Neurofibromatosis

• Restricts chest wall expansion physically
• Creates a mechanical disadvantage for the respiratory muscles
• Reduces lung volumes (restrictive pattern)
• Even if muscles were strong, the bent cage limits how much pressure they can generate

Reason 3 - Original C8 Complete Tetraplegia (Pre-improvement)

• Muscle atrophy - the muscle fibers waste away
• Even after partial neurological recovery, the muscles may not have regained full strength
• Recovery of motor function after spinal cord injury is partial and incomplete in most cases

Reason 4 - Sacral Ulcers + Prolonged Immobility

• Disuse atrophy of all muscles including respiratory muscles
• The diaphragm is especially sensitive - it weakens rapidly with inactivity
• General deconditioning reduces exercise tolerance and respiratory reserve

Why the Test Results Make Perfect Sense

PImax = 40% of predicted  →  Diaphragm partially preserved (C3-C4 above fusion)
                               but scalenes (C4-C8) and intercostals (T1-T8) lost

PEmax = 43% of predicted  →  Intercostal expiratory muscles (T1-T8) denervated
                               Abdominal muscles (T7-L1) at least partially denervated
                               Only pectoralis major (C5-T1) partly available for forced expiration

Clinical Implications for This Patient

1. Cough is severely impaired - PEmax at 43% means mucus clearance is very poor → high risk of recurrent chest infections and pneumonia (leading cause of death in SCI patients)
2. No respiratory reserve - at 40% capacity, any additional load (infection, obesity, lying flat) can precipitate respiratory failure
3. Scoliosis compounds everything - the bent spine and ribcage mean even the remaining muscle strength is mechanically inefficient
4. Nighttime hypoventilation likely - may need to be assessed for sleep-disordered breathing or nocturnal non-invasive ventilation (NIV/BiPAP)
5. The "just satisfactory" effort noted in the test is actually typical in SCI patients - they struggle to sustain the maneuver because of genuine weakness, not just poor cooperation
6. Armspan used for height - confirms the patient cannot stand, consistent with paraplegia and spinal fusion

Summary in One Sentence