Orthopnea Without Obvious Heart Failure: What Else Could It Be?

A Comprehensive Review for Critical Care Postgraduates

Dr Neeraj Manikath , claude.ai

Abstract

Background: Orthopnea, traditionally considered pathognomonic of left heart failure, can present in numerous non-cardiac conditions that critical care physicians must recognize. Misattribution to cardiac causes can lead to delayed diagnosis and inappropriate treatment.

Objective: To provide a comprehensive review of non-cardiac causes of orthopnea, with emphasis on diagnostic approaches, clinical pearls, and management strategies relevant to critical care practice.

Methods: Narrative review of current literature focusing on bilateral diaphragmatic weakness, massive ascites, obesity hypoventilation syndrome, and other non-cardiac etiologies of orthopnea.

Conclusions: A systematic approach incorporating detailed positional questioning, physical examination techniques including chest expansion assessment and sniff testing, and appropriate investigations can distinguish non-cardiac from cardiac orthopnea, leading to targeted therapy and improved outcomes.

Keywords: Orthopnea, diaphragmatic weakness, ascites, obesity hypoventilation syndrome, critical care

Introduction

Orthopnea, defined as dyspnea that occurs when lying flat and is relieved by sitting or standing upright, has long been considered a cardinal sign of left heart failure. However, in critical care settings, clinicians increasingly encounter patients with significant orthopnea in the absence of obvious cardiac dysfunction. This diagnostic challenge requires a systematic approach to identify alternative etiologies that may require entirely different therapeutic interventions.

The pathophysiology of orthopnea traditionally involves increased venous return when supine, leading to elevated left atrial pressure and pulmonary edema in patients with impaired left ventricular function. However, any condition that compromises respiratory mechanics when supine can produce similar symptoms through different mechanisms.

This review aims to provide critical care physicians with a comprehensive understanding of non-cardiac orthopnea, emphasizing practical diagnostic approaches and management strategies that can be immediately applied in clinical practice.

Pathophysiology of Non-Cardiac Orthopnea

Fundamental Mechanisms

Non-cardiac orthopnea results from mechanical disadvantage when supine, affecting either:

Diaphragmatic function - Weakness or paralysis becomes more apparent when gravitational assistance is lost
Thoracic compliance - Chest wall restriction or abdominal mass effects
Airway patency - Upper airway obstruction or dynamic collapse
Ventilation-perfusion matching - Positional changes affecting gas exchange

The common pathway involves inadequate alveolar ventilation when supine, leading to hypercapnia, hypoxemia, or both, necessitating upright positioning to maintain adequate respiratory function.

Major Non-Cardiac Causes of Orthopnea

1. Bilateral Diaphragmatic Weakness

Bilateral diaphragmatic weakness represents one of the most important and underrecognized causes of orthopnea in critical care.

Etiology

Neurological: Guillain-Barré syndrome, myasthenia gravis, amyotrophic lateral sclerosis, cervical spinal cord injury (C3-C5), critical illness polyneuropathy
Muscular: Muscular dystrophies, inflammatory myopathies, steroid myopathy
Phrenic nerve injury: Post-cardiac surgery, mediastinal tumors, neck trauma
Metabolic: Hypothyroidism, malnutrition, electrolyte disorders

Clinical Presentation

Patients typically present with:

Orthopnea - Often the predominant symptom
Sleep-disordered breathing - Frequent awakening, morning headaches
Paradoxical breathing - Inward movement of abdomen during inspiration
Reduced exercise tolerance - Particularly with activities requiring supine positioning
Recurrent respiratory infections - Due to impaired cough mechanics

Diagnostic Pearls 🔍

The "Sniff Test" - A Bedside Game-Changer:

Ask the patient to take a sharp, sudden inspiratory effort (sniff) while observing the abdomen
Normal: Abdomen moves outward during sniff
Diaphragmatic weakness: Abdomen moves inward (paradoxical movement)
Sensitivity: 95% for significant bilateral weakness
Best performed in supine position for maximum sensitivity

Positional Vital Capacity Drop:

Measure vital capacity sitting vs. supine
>25% drop suggests diaphragmatic weakness
>50% drop indicates severe impairment
Can be performed with bedside spirometry or even simple balloon testing

Advanced Diagnostics

Chest X-ray: Elevated hemidiaphragms (often bilateral)
Fluoroscopy: Paradoxical or absent diaphragmatic movement during sniff test
Pulmonary function tests: Reduced vital capacity with greater reduction when supine
Phrenic nerve conduction studies: Definitive test for nerve involvement
Diaphragmatic ultrasound: Emerging bedside tool measuring thickness and excursion

2. Massive Ascites

Ascites-related orthopnea results from mechanical compression of the diaphragm and reduced thoracic compliance when supine.

Pathophysiology

Cephalad displacement of diaphragm reduces lung volumes
Increased intra-abdominal pressure impairs venous return paradoxically improving orthopnea in some cases
Chest wall compliance reduction due to abdominal distention

Clinical Recognition

Obvious abdominal distention - May be missed in obese patients
Shifting dullness on percussion
Fluid wave - Classic but requires significant volume
Relief with paracentesis - Diagnostic and therapeutic

Diagnostic Hacks 💡

The "Ascites Orthopnea Test":

Measure peak expiratory flow rate supine vs. sitting
Ascites-related orthopnea shows dramatic improvement sitting (often >50% increase in PEFR)
Cardiac orthopnea shows modest positional change (<25% improvement)

Abdominal Circumference Monitoring:

Serial measurements can predict respiratory compromise
>100 cm in average-sized adults often correlates with respiratory symptoms
Rate of accumulation matters more than absolute volume

Management Priorities

Large-volume paracentesis - Often provides immediate relief
Serial small-volume drainage - For refractory cases
Monitoring for complications - Post-paracentesis circulatory dysfunction
Addressing underlying cause - Portal hypertension, malignancy, infection

3. Obesity Hypoventilation Syndrome (OHS)

OHS represents a complex interaction of mechanical and physiological factors leading to chronic respiratory failure in obese patients.

Definition and Epidemiology

BMI >30 kg/m² with chronic hypercapnia (PaCO₂ >45 mmHg)
Absence of other causes of hypoventilation
Prevalence: 10-20% of patients with BMI >35 kg/m²
Often coexists with obstructive sleep apnea (90% of cases)

Pathophysiology

Mechanical factors: Chest wall loading, reduced compliance, increased work of breathing
Physiological factors: Blunted CO₂ response, sleep-disordered breathing
Positional worsening: Supine position exacerbates all mechanical disadvantages

Clinical Presentation in Critical Care

Acute-on-chronic respiratory failure - Often precipitated by intercurrent illness
Difficult weaning from mechanical ventilation
Hypercapnic encephalopathy - May mimic other causes of altered consciousness
Cor pulmonale - Right heart failure secondary to chronic hypoxemia

Diagnostic Approach

History Taking - Key Questions:

"Do you snore loudly?" - 95% have OSA
"Do you fall asleep during the day unintentionally?" - Hypersomnolence
"Do you wake up with headaches?" - Morning CO₂ retention
"Can you sleep flat or do you need multiple pillows?" - Quantify orthopnea

Physical Examination Pearls:

Neck circumference >17 inches (43 cm) - Strong predictor of OSA
Mallampati score - Assess upper airway
Signs of right heart failure - Often overlooked
Chest expansion measurement - Severely limited in severe cases

Management Strategies

Non-invasive ventilation - BiPAP as bridge and long-term therapy
Weight reduction - 10% reduction can significantly improve symptoms
Treatment of OSA - CPAP therapy
Aggressive pulmonary rehabilitation - Even modest improvements help

4. Other Important Causes

Neuromuscular Disorders

Myasthenia gravis - Fluctuating weakness, improves with rest
Guillain-Barré syndrome - Ascending paralysis, may present with isolated diaphragmatic involvement
Critical illness myopathy - Common in ICU patients, often overlooked

Chest Wall Abnormalities

Severe kyphoscoliosis - Progressive restrictive physiology
Flail chest - Post-traumatic, multiple rib fractures
Massive pleural effusions - Mechanical compression

Upper Airway Obstruction

Vocal cord paralysis - May be positional
Tracheal stenosis - Post-intubation or inflammatory
Large goiter - Substernal extension causing positional obstruction

Comprehensive Diagnostic Approach

The Critical Care Assessment Framework

Step 1: Detailed Positional History

Essential Questions to Ask:

Onset and progression:
- "When did you first notice difficulty breathing lying flat?"
- "Has this gotten worse over time?"
Severity assessment:
- "How many pillows do you need to sleep comfortably?"
- "Can you lie completely flat for any period?"
- "Do you ever wake up gasping for air?"
Associated symptoms:
- "Do you have leg swelling?" (cardiac vs. other causes)
- "Do you snore or stop breathing during sleep?" (OSA/OHS)
- "Do you have morning headaches?" (CO₂ retention)
- "Have you noticed voice changes?" (phrenic nerve involvement)
Functional impact:
- "Can you tolerate procedures requiring you to lie flat?"
- "Do you sleep in a chair?" (severe orthopnea)

Step 2: Focused Physical Examination

Respiratory Assessment:

Chest expansion measurement - Normal >5 cm at nipple line
Sniff test - Observe abdominal movement during sharp inspiration
Paradoxical breathing - Inward abdominal movement during inspiration
Use of accessory muscles - Even at rest

Cardiac Assessment:

JVP examination - May be normal in non-cardiac orthopnea
Heart sounds - Listen for S3, murmurs
Peripheral edema - Distribution and pitting characteristics

Abdominal Assessment:

Distention and shifting dullness - Assess for ascites
Organomegaly - Hepatosplenomegaly causing mass effect
Surgical scars - Previous procedures affecting diaphragm

Step 3: Diagnostic Testing Strategy

First-Line Tests:

Chest X-ray - Diaphragm position, pleural effusions, cardiomegaly
ECG - Cardiac rhythm, signs of right heart strain
Arterial blood gas - Hypercapnia suggests hypoventilation
Basic metabolic panel - Electrolyte disorders affecting muscle function

Second-Line Tests (Based on Clinical Suspicion):

Echocardiogram - If cardiac cause suspected
CT chest/abdomen - Structural abnormalities, masses
Pulmonary function tests - Including supine vs. sitting measurements
Diaphragmatic ultrasound - Bedside assessment of function

Specialized Tests:

Phrenic nerve conduction studies - For suspected neurological causes
Fluoroscopic sniff test - Gold standard for diaphragmatic assessment
Sleep study - If OSA/OHS suspected
MRI cervical spine - For suspected cord pathology

Clinical Pearls and Oysters

Pearls 🔍

The "Orthopnea Relief Test":
- True cardiac orthopnea rarely shows complete relief when sitting
- Non-cardiac causes often show dramatic improvement upright
- Quantify with simple spirometry or peak flow measurements
Timing Matters:
- Immediate relief when upright suggests mechanical cause
- Gradual improvement over minutes suggests cardiac pulmonary edema
The "Pillow Count" is Quantifiable:
- Document exact number of pillows needed
- Track changes over time
- 4 pillows suggests severe impairment
Voice Changes are Clues:
- Weak voice or inability to count to 20 in one breath suggests diaphragmatic weakness
- Hoarse voice may indicate recurrent laryngeal nerve involvement
Bedside Ultrasound Applications:
- Diaphragmatic motion assessment during breathing
- Measurement of diaphragmatic thickness
- Real-time visualization during sniff test

Oysters (Common Pitfalls) ⚠️

The "Normal Echo Trap":
- Normal left ventricular function doesn't exclude heart failure
- Heart failure with preserved ejection fraction can cause orthopnea
- Always consider diastolic dysfunction
The "Obesity Bias":
- Not all orthopnea in obese patients is due to OHS
- May have concurrent diaphragmatic weakness or other pathology
- Avoid assumption that weight loss alone will solve the problem
The "Gradual Onset Illusion":
- Patients often adapt to slowly progressive orthopnea
- May not volunteer symptoms unless specifically asked
- Family members may notice changes before patients
The "ICU Polyneuropathy Miss":
- Critical illness polyneuropathy affecting diaphragm is common
- Often attributed to "deconditioning" or "weakness"
- Should be suspected in patients with difficult weaning
The "Bilateral Assumption":
- Unilateral diaphragmatic paralysis can still cause orthopnea
- Especially if the patient has underlying lung disease
- Don't dismiss unilateral findings

Management Strategies

General Principles

Address Underlying Cause:
- Specific treatment when possible (paracentesis, weight loss, etc.)
- Supportive care when cause is irreversible
Symptomatic Management:
- Optimize positioning for comfort and function
- Consider bed modifications (hospital bed at home)
- Non-invasive ventilation for severe cases
Prevent Complications:
- Aggressive pulmonary hygiene
- Early mobilization when possible
- Monitor for respiratory failure

Specific Interventions by Cause

Diaphragmatic Weakness

Respiratory muscle training - Inspiratory muscle trainers
Non-invasive ventilation - Nocturnal BiPAP
Phrenic nerve pacing - For selected cases of nerve injury
Diaphragmatic plication - Surgical option for paralysis

Massive Ascites

Large-volume paracentesis - Immediate relief, monitor for complications
Peritoneocentesis drainage - For refractory cases
TIPS procedure - For portal hypertension-related ascites
Peritoneal dialysis - Alternative for renal causes

Obesity Hypoventilation Syndrome

Weight reduction - Multidisciplinary approach
BiPAP therapy - Nocturnal and potentially daytime
Bariatric surgery - For appropriate candidates
Pulmonary rehabilitation - Structured exercise program

Prognosis and Long-term Considerations

Prognostic Factors

Good Prognosis:

Reversible underlying cause (ascites, obesity)
Early recognition and treatment
Absence of concurrent cardiopulmonary disease
Good functional status otherwise

Poor Prognosis:

Progressive neuromuscular disease
Severe obesity with multiple comorbidities
Concurrent heart failure
Advanced age with frailty

Long-term Management Considerations

Regular monitoring of respiratory function
Advanced directive discussions for progressive conditions
Family education about positioning and emergency management
Coordination with specialists (neurology, pulmonology, cardiology)
Equipment needs assessment (hospital bed, BiPAP, etc.)

Case-Based Learning Examples

Case 1: The Post-Surgical Surprise

Presentation: 65-year-old male, 3 days post-cardiac surgery, developing progressive orthopnea despite normal echo. Key Finding: Paradoxical abdominal movement during sniff test Diagnosis: Bilateral phrenic nerve injury from ice slush cardioplegia Learning Point: Always consider iatrogenic causes in post-procedural patients

Case 2: The Misattributed Ascites

Presentation: 45-year-old female with cirrhosis, worsening "heart failure" symptoms Key Finding: Massive ascites with normal BNP and echo Diagnosis: Ascites-related orthopnea masquerading as heart failure Learning Point: Physical findings trump laboratory values

Case 3: The Difficult Wean

Presentation: 70-year-old obese male, unable to wean from ventilator after pneumonia Key Finding: Hypercapnia persists despite lung recovery Diagnosis: Unrecognized obesity hypoventilation syndrome Learning Point: Consider OHS in difficult-to-wean obese patients

Research Directions and Future Perspectives

Emerging Diagnostic Tools

Point-of-care diaphragmatic ultrasound - Standardization of techniques
Wearable monitoring devices - Continuous assessment of respiratory patterns
AI-assisted diagnosis - Pattern recognition in complex presentations

Therapeutic Innovations

Implantable phrenic nerve stimulators - Expanding indications
Novel non-invasive ventilation modes - Adaptive servo-ventilation
Pharmacological interventions - Respiratory stimulants for specific conditions

Quality Improvement Initiatives

Standardized assessment protocols for orthopnea evaluation
Education programs for recognition of non-cardiac causes
Multidisciplinary care pathways for complex cases

Conclusion

Orthopnea without obvious heart failure represents a diagnostic challenge that critical care physicians must approach systematically. The key to successful management lies in maintaining a high index of suspicion for non-cardiac causes, particularly bilateral diaphragmatic weakness, massive ascites, and obesity hypoventilation syndrome.

The bedside examination remains paramount, with simple tests like the sniff test and positional vital capacity measurements providing crucial diagnostic information. Detailed positional questioning can reveal patterns that distinguish cardiac from non-cardiac causes, guiding appropriate investigations and management strategies.

As critical care medicine advances, recognition of these conditions will likely improve with better diagnostic tools and increased awareness. However, the fundamental approach of careful history-taking, focused physical examination, and systematic thinking will remain the cornerstone of accurate diagnosis and effective treatment.

The impact of correct diagnosis extends beyond the immediate clinical benefits, affecting long-term quality of life, appropriate resource utilization, and family planning for chronic conditions. By maintaining vigilance for these non-cardiac causes of orthopnea, critical care physicians can significantly improve outcomes for this challenging patient population.

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Conflict of Interest: The authors declare no conflicts of interest.

Funding: This review received no specific funding.

Tuesday, August 5, 2025