Capnometry & Heart Rate Variability (HRV)

An Integrated Assessment of Breathing and Physiological Regulation

Breathing is closely connected with cardiovascular function, neural regulation, acid–base balance and the way the body responds to physical and emotional demands.

At The Health Equation, capnometry and Heart Rate Variability (HRV) are used together to provide a non-invasive, real-time assessment of breathing physiology and cardiorespiratory regulation.

Capnometry measures breathing rate and the concentration of carbon dioxide at the end of each exhalation. HRV measures variation in the time interval between successive heartbeats. When interpreted together—and alongside the patient’s history, symptoms and clinical examination—these measurements can reveal patterns that may not be apparent during a conventional assessment.

They are used as part of the Diagnostic Consultation and, where appropriate, to guide personalised breathing re-training and biofeedback.

What Does Capnometry Measure?

Capnometry provides a continuous, breath-by-breath measurement of:

• End-tidal carbon dioxide (ETCO₂): the concentration of carbon dioxide at the end of exhalation
• Breathing rate: the number of breaths taken per minute
• Breathing stability: including changes associated with speaking, movement, stress or deliberate breathing
• Breath pauses and recovery: how respiratory physiology responds to short end-in and end-out pauses

The CapnoTrainer also displays the respiratory waveform—a process known as capnography—allowing the pattern and quality of each breath to be observed in real time.

A resting ETCO₂ level of approximately 35 mmHg or above is commonly used at The Health Equation as a practical clinical aim, although measurements must always be interpreted in relation to the individual patient, their medical history and the circumstances of testing. Stability and comfort are as important as reaching a particular numerical value.

Why Carbon Dioxide Matters

Carbon dioxide is not simply a waste gas. It plays an essential role in regulating breathing, maintaining acid–base balance, influencing blood flow and helping oxygen move from haemoglobin into the tissues where it is needed.

When a person breathes more than their current metabolic requirements—a pattern known as overbreathing—too much carbon dioxide may be exhaled. This can produce hypocapnia, or an abnormally low level of carbon dioxide.

Low carbon dioxide may:

• Reduce cerebral blood flow
• Alter blood pH and increase neural excitability
• Affect the release of oxygen from haemoglobin to the tissues
• Contribute to dizziness, tingling, chest tightness or breathlessness
• Reinforce feelings of anxiety, panic or loss of respiratory control

These effects can occur even when oxygen saturation measured by a pulse oximeter remains normal. Simply taking larger or deeper breaths may therefore intensify the problem rather than correct it. The aim is to restore breathing that is quiet, efficient and appropriate to the body’s metabolic needs.

What Do Heart Rate Variability and RSA Measure?

Heart Rate Variability refers to the natural variation in time between successive heartbeats. A healthy heart does not beat with metronomic regularity; its rhythm continually adapts to breathing, posture, activity, emotion and other internal and external demands.

During relaxed breathing, heart rate usually increases slightly during inhalation and decreases during exhalation. This normal cardiorespiratory interaction is called respiratory sinus arrhythmia (RSA). It is sometimes described visually as the Breathing Heart Wave because the heart-rate pattern rises and falls in relation to the breathing cycle.

HRV and RSA provide information about the flexibility of neural and cardiovascular regulation. However, a single result should never be interpreted simply as “high is good” or “low is bad.” Measurements are influenced by:

• Age and general health
• Breathing rate, depth and pattern
• Posture and recent physical activity
• Sleep, stress and emotional state
• Medication, stimulants and alcohol
• Heart rhythm disturbances, including ectopic beats
• Movement or measurement artefact

The HRV scale displayed by the CapnoTrainer is specific to that system and should not be confused with the different HRV measurements produced by ECGs, wearable devices or other clinical equipment. The pattern, context and quality of the recording are therefore more important than any isolated number.

Why Capnometry and HRV Are Assessed Together

Capnometry shows how a person is breathing, while HRV and RSA show how the cardiovascular and neural systems are responding to that breathing pattern.

Interpreting both measurements together can help identify:

• Rapid, irregular or unstable breathing
• Persistent or intermittent overbreathing
• Low or fluctuating end-tidal carbon dioxide
• Poor coordination between breathing and heart-rate rhythm
• Physiological changes during speaking, movement or emotional stress
• The patient’s response to slower, quieter nasal breathing
• Whether a breathing exercise improves regulation or inadvertently causes further overbreathing

A slow breathing rate alone is not necessarily optimal. If breaths become unnecessarily large or forced, carbon dioxide may still fall. Real-time measurement allows breathing strategies to be adjusted according to the patient’s physiological response rather than relying on a standard breathing formula.

The findings are interpreted alongside the patient’s symptoms, medical history, clinical examination and any other relevant investigations. Capnometry and HRV support clinical reasoning; they are not used as isolated diagnostic tests.

What Happens During the Assessment?

For new patients, capnometry and HRV assessment takes place within the New Patient Diagnostic Consultation when clinically appropriate.

A small nasal cannula measures exhaled carbon dioxide and breathing rate, while a sensor records pulse rate and heart-rate variability. The equipment is non-invasive and displays the measurements continuously on screen.

The assessment may include periods of:

• Natural, unobserved breathing
• Deliberately mindful breathing
• Quiet nasal breathing
• Speaking or reading aloud
• Short end-in and end-out breath pauses
• Postural change or gentle movement
• A personalised breathing exercise

Comparing these different conditions helps identify whether the breathing pattern changes with attention, activity or stress and whether conscious attempts to “breathe better” genuinely improve respiratory physiology.

Patients can view the measurements in real time, helping them connect how breathing feels with what is physiologically occurring. The findings are then explained within the context of their wider clinical assessment.

From Assessment to Breathing Re-training

Not every variation in breathing requires treatment. Where the assessment identifies a clinically relevant breathing pattern disorder, Gerry may recommend individualised breathing re-training.

This may include:

• Developing quiet, comfortable nasal breathing
• Reducing unnecessary breathing rate or volume
• Improving the stability of end-tidal carbon dioxide
• Using short end-in or end-out pauses where appropriate
• Coordinating breathing with movement, speech and physical activity
• Supporting respiratory sinus arrhythmia without forced or excessive breathing
• Recognising triggers for intermittent overbreathing
• Using capnography and HRV as real-time biofeedback

Follow-up sessions may combine breathing re-education with Osteopathic Manual Treatment (OMT) where restrictions within the thorax, diaphragm, spine, rib cage or associated soft tissues appear to be contributing to the breathing pattern.

The number and frequency of appointments are determined by the assessment findings, the complexity of the presentation and the patient’s response, rather than applying the same programme to everyone.

Home Practice and Integration with Wider Care

Lasting improvement usually depends on short, regular periods of practice rather than occasional lengthy breathing exercises.

Patients may be encouraged to practise quiet nasal breathing for one to two minutes at intervals throughout the day, sometimes using gentle end-in or end-out pauses. The precise exercise is selected according to the individual’s assessment and should remain comfortable rather than becoming forced or competitive.

Breathing re-training may also be integrated with:

• Mindfulness or meditation
• Sleep and recovery strategies
• Posture, mobility and rehabilitation
• Walking and graded physical activity
• Speech, singing or performance
• Stress-management and psychological support
• Management of asthma or other respiratory conditions alongside appropriate medical care

The aim is not to control every breath. It is to help a more efficient breathing pattern become familiar and increasingly automatic during everyday life.

When May This Assessment Be Helpful?

Capnometry and HRV assessment may be considered when symptoms or clinical findings suggest that breathing physiology or cardiorespiratory regulation could be contributing to the presentation.

This may include patients experiencing:

• Unexplained breathlessness or frequent sighing
• Anxiety, panic or a sense of being unable to take a satisfying breath
• Dizziness, tingling, chest tightness or palpitations
• Poor sleep, fatigue or reduced resilience
• Headache, migraine or persistent pain
• Asthma with symptoms not fully explained by airway obstruction
• Difficulty regulating breathing during speech or exercise
• Stress-related or functional symptoms
• Persistent multisystem symptoms without a single clear explanation

These symptoms can have many possible causes. Assessment of breathing physiology does not replace appropriate medical investigation, and potentially important cardiac, respiratory, neurological or metabolic causes must be considered. Its purpose is to determine whether breathing pattern and physiological regulation form a meaningful and potentially modifiable part of the patient’s overall presentation.

Clinical Interpretation and Limitations

Capnometry and HRV provide useful physiological information, but neither measurement establishes a diagnosis in isolation.

• A low end-tidal carbon dioxide reading may reflect overbreathing, but it can also be influenced by respiratory disease, circulation, posture, speech, movement or sampling quality.
• HRV is affected by many factors and does not, by itself, diagnose an autonomic nervous system disorder.
• Ectopic beats and recording artefact can produce misleadingly high HRV values.
• Normal oxygen saturation does not necessarily confirm that breathing physiology is optimal.
• Capnometry does not replace spirometry, ECG assessment, diagnostic imaging or other medical investigations when these are indicated.

Repeated measurements under standardised conditions can be more informative than a single recording. Results are therefore considered alongside the patient’s history, examination, symptoms and relevant medical investigations, with referral for further assessment where appropriate.

Book a Capnometry and HRV Assessment

New patients should begin with a New Patient Diagnostic Consultation, during which capnometry and HRV can be included when clinically appropriate.

Existing patients wishing to review their breathing physiology or undertake further breathing re-training should book a suitable follow-up consultation.

Assessments are available at The Health Equation London and The Health Equation Marlborough.