Pneumonectomy Case Reveals Surprising CO2 Tolerance After Lung Removal Surgery

When One Lung Isn’t Enough: What a Pneumonectomy Case Teaches Us About CO2 Tolerance

A 59-year-old woman had her entire left lung removed — her total lung capacity was just 43% of predicted — yet she reached 88% of her expected peak work rate on a cycling test. Researchers at the University of British Columbia’s Centre for Heart Lung Innovation wanted to know why, and what breathing training could still change. Their answer, published in the Journal of Applied Physiology in 2021, offers real insight into how the body manages carbon dioxide under extreme respiratory constraint, and why CO2 tolerance matters for everyone, not just post-surgery patients.

Rapid, Shallow Breathing: The Signature of Ventilatory Constraint

Four years after an extrapleural pneumonectomy (EPP), the study participant completed a symptom-limited incremental cycling test plus a constant work rate test at 75% of her peak. Across every intensity, her breathing was rapid and shallow. With one lung gone, her chest wall could not expand tidal volume in the normal way, so her nervous system compensated by raising breathing frequency instead.

That pattern comes at a cost. Mitchell and colleagues found her ratio of minute ventilation to carbon dioxide output was elevated at any given work rate — a sign of ventilatory inefficiency. In plain terms, she had to move more air to clear the same amount of CO2, because each breath was smaller and dead-space ventilation (air moved without gas exchange) took a larger share. This is the same inefficiency pattern that CO2 tolerance training attempts to reduce: when the brain over-reacts to rising CO2, breathing becomes excessive, wasteful, and breathlessness grows. If you want to understand the opposite failure mode — over-breathing that drives CO2 too low — read our piece on hyperventilation alkalosis.

Inspiratory Muscle Training Worked Years After Lung Removal

The intervention was straightforward: two daily sessions of 30 resisted inhalations, five days a week, for 12 weeks. The result was a 36% improvement in maximal inspiratory pressure (from -74.8 to -101.9 cmH2O in absolute terms described as a -27.1 cmH2O gain) and a 31-second gain in constant work rate endurance time.

Notably, no submaximal or peak cardiorespiratory variables changed. Her peak oxygen uptake, ventilation, and breathing pattern during exercise stayed the same. What changed was the strength of the pump itself. This distinction matters for anyone doing CO2 tolerance work: threshold-based muscle training and CO2 tolerance exercises are separate adaptations. IMT builds the diaphragm and intercostals the way weightlifting builds a biceps; CO2 tolerance work retrains the chemoreflex — the brainstem’s sensitivity to dissolved CO2 that drives the urge to breathe. You can read more about the distinction in our guide to CO2 tolerance training and the BOLT test.

One Honest Caveat: Dyspnea Got Worse Before Perception Improved

The study’s uncomfortable finding deserves attention. At the highest matched exercise time, the participant reported dyspnea intensity 2 Borg units higher and unpleasantness 3 units higher after IMT. The authors suggest that being able to exercise 31 seconds longer meant she reached a later, harder stage of the test when comparing equivalent time points, and possibly that stronger respiratory muscles changed her perceptual calibration.

This is a single-case study — one participant, no control, and findings cannot be generalized to every post-pneumonectomy patient. But it is an honest data point: respiratory gains do not always translate linearly into feeling better, and perceptual outcomes should be tracked alongside strength numbers.

What This Means for Practicing CO2 Tolerance Exercises

A parallel cohort study from University Hospitals of North Midlands (BMJ Open Respiratory Research, 2021) examined pectus excavatum patients and found that categorized VO2 max values could distinguish different patterns of exercise dysfunction — confirming that breathing limitations are measurable, classifiable, and trainable rather than vague complaints. Put together with the pneumonectomy case, three practical lessons emerge:

• Train the pump and the controller separately. IMT devices build muscle strength; breath-holds and extended-exhale CO2 tolerance drills (e.g., holding after a normal exhale and extending the hold comfortably over weeks) desensitize the urge to breathe.
• Rapid, shallow breathing is a warning sign. If your breathing rate climbs disproportionately during steady exercise, ventilatory inefficiency may be limiting you before your legs are.
• Conditioning raises CO2 tolerance. The participant’s near-normal work rate with 43% lung capacity reflected years of physical training. Aerobic fitness itself is one of the most effective CO2 tolerance interventions.

Anyone with significant lung disease or post-surgical anatomy should do respiratory training under clinical supervision. For healthy readers, a structured evidence-based breathing exercise routine remains the sensible starting point.

Frequently Asked Questions

What is a CO2 tolerance breathing exercise?

It’s a controlled drill — typically a breath-hold after a normal exhale, or extended exhalations — that mildly raises arterial CO2, gradually reducing the brain’s sensitivity to it and delaying the urge to breathe.

Does the pneumonectomy study prove CO2 tolerance exercises work?

Not directly. It tested inspiratory muscle training, which improved respiratory strength by 36% but not the breathing pattern itself. CO2 tolerance and muscle strength are related but separate adaptations.

Why does rapid, shallow breathing indicate a problem?

Small, fast breaths waste more of each breath on dead space, meaning more air must be moved to clear the same CO2 — a measurable inefficiency that increases breathlessness.

Can aerobic exercise improve CO2 tolerance without special drills?

Yes. The case participant’s near-normal exercise capacity with one lung was attributed largely to her high physical conditioning, which itself improves ventilatory efficiency and CO2 handling.

Sources:
https://pubmed.ncbi.nlm.nih.gov/34709069/
https://pubmed.ncbi.nlm.nih.gov/34362764/
https://pubmed.ncbi.nlm.nih.gov/34110716/
https://pubmed.ncbi.nlm.nih.gov/33238742/
https://pubmed.ncbi.nlm.nih.gov/32956395/