CALM! visualizes autonomic nervous system activity in just 30 seconds using only your iPhone and heart rate variability (HRV) analysis.

Depending on your state, it offers bilateral stimulation, breathing techniques, and mindfulness practices to help regulate both body and mind.

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The app records overall autonomic activity as well as the balance between sympathetic and parasympathetic nervous system activity, allowing you to track daily changes. You can also log your mood during each session to better understand and manage your condition.

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In addition, CALM! provides tailored visual and auditory stimuli to optimize your mental and physical state.

 

Subscription: $1.99/month

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< Technical Background >

Recent studies have reported that HRV estimated from smartphone-based photoplethysmography (PPG) shows a high correlation with HRV derived from standard electrocardiogram (ECG) measurements.

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Furthermore, the relationship between HRV and autonomic nervous system activity has been well established in international guidelines. According to the Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology (Circulation, 1996):

• RMSSD (Root Mean Square of Successive Differences): Reflects parasympathetic activity. Higher values indicate parasympathetic predominance.

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• HF component (High Frequency, 0.15–0.40 Hz): Represents respiratory-related variability and a direct index of parasympathetic activity.

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• LF/HF ratio: Indicates the balance between sympathetic and parasympathetic activity.

 

By applying these scientific insights, we have successfully developed a method to estimate autonomic nervous system activity using only the iPhone.