What Personal Devices Still Don’t Understand About the Human Body

Why Misreading Saturation Is Making People Breathe Worse

Over the past ten years, personal health devices—watches, rings, apps, fingertip oximeters—have quietly become the main way people interpret their own physiology. A single number appears on a screen and immediately shapes how a person thinks they are breathing, sleeping, recovering or functioning.

The problem is that these numbers are being interpreted through a model of physiology that is incomplete. Even in medicine, many of these metrics are poorly understood. Pulse oximetry in particular has migrated from the operating theatre into everyday life without the context or education that originally justified its use.

To understand the consequences, we need to be clear about what the devices measure—and what they don’t.

The Original Purpose of Pulse Oximetry

Pulse oximetry was never designed as a wellness metric.
Its purpose was—and remains—safety monitoring during anaesthesia.

When a patient is unconscious, paralysed, and covered in drapes, you cannot see their chest rise. You cannot hear their breath or see their colour. The oximeter is there to alert the anaesthetist to mechanical problems:

• a kinked tube

• a disconnected circuit

• obstruction

• a failed oxygen supply

• a ventilator malfunction

In this context, a falling saturation is a useful alarm: something in the delivery system needs to be checked immediately.

But outside of this narrow setting, oximetry struggles to tell us anything meaningful about everyday breathing.

Why 95% vs 99% Is a Misleading Distinction

In healthy, conscious adults, oxygen saturation remains high across an enormous range of respiratory variation.
A drop from 99% to 95% does not mean oxygen is “running low,” the airway is failing, or that urgent intervention is required.

It often reflects subtle shifts in CO₂, posture, temperature, or autonomic tone—none of which indicate pathology.

Yet people (and many clinicians) interpret 95% as a deficiency and attempt to “correct” it by taking bigger, faster breaths. This is physiologically backwards.

The Critical Point People Need to Understand

Hyperventilating to raise saturation often reduces cellular oxygenation.

Here is the exact mechanism:

1. A person sees 94–96% on the device.
   They assume they need “more oxygen.”

2. They take deeper, faster breaths.
   This does not meaningfully increase oxygen intake, because haemoglobin was already nearly saturated.

3. But it does reduce CO₂.
   Hyperventilation blows off CO₂ rapidly.

4. Lower CO₂ stiffens haemoglobin.
   The Bohr effect:
   Low CO₂ = haemoglobin holds its oxygen instead of releasing it.

5. Oxygen delivery to cells decreases.
   Ironically, even if the saturation number increases to 98–99%,
   the tissues are now receiving less oxygen.

6. The nervous system becomes more sympathetic.
   Low CO₂ triggers heart rate elevation, anxiety, dizziness, and a sense of air hunger—despite “good numbers.”

This is how misunderstanding saturation leads people to sabotage their own physiology.

The device shows a number.
The number is pursued.
And the pursuit disrupts the very system the person is trying to regulate.

CO₂, Not Oxygen, Is the Primary Regulator of Breathing and Cellular Oxygenation

Breathing is controlled by CO₂ levels, not oxygen levels.
The body maintains oxygen saturation easily at rest; what it monitors is CO₂, because CO₂ determines:

• pH

• haemoglobin’s willingness to release oxygen

• cerebral blood flow

• autonomic tone

• smooth muscle behaviour

• metabolic efficiency

A saturation of 95% is rarely an emergency.
A saturation of 99% achieved through hyperventilation may actually indicate impaired oxygen delivery.

This is the central misunderstanding in both public use and much of modern clinical practice.

Why Devices Don’t Capture This Reality

Personal health devices cannot measure:

• CO₂ levels

• the Bohr effect

• autonomic balance

• tissue oxygenation

• nervous-system state

• breath efficiency

• whether the person is over-breathing

They measure superficial signals—pulse waveform, light absorption, motion—and attempt to interpret them without any reference to the central regulators. The result is a distorted picture of human physiology.

People are coached by their devices into behaviours that push them further from stability: habitual deep breathing, constant self-surveillance, and responding to harmless numbers as if they signal danger.

The Broader Context: Medicine Lost Holistic Physiology

Before the mid-20th century, physiology was taught as an integrated whole.
Breathing, circulation, pH, autonomic function, and metabolic state were understood as one system.

After the world wars, medicine fragmented into organ-based specialities. Understanding of breath-driven autonomic regulation faded, replaced by narrow metrics and isolated measurements.

Personal devices inherited this fragmented worldview. They detect numbers but cannot interpret the system that produces them.

The Way Forward

To use technology without being misled by it, we need a return to foundational physiology:

• Breathing regulates the nervous system.

• CO₂ regulates oxygen delivery.

• Saturation is a crude tool, useful in anaesthesia and emergencies, not daily life.

• Numbers do not equal physiology.

• The body’s patterns matter more than the device’s thresholds.

Wearables will only become truly useful when they integrate CO₂ dynamics and autonomic physiology into their frameworks. Until then, their alerts must be interpreted with caution.

The human body is coherent.
The devices are still catching up.