A method for analyzing the respiratory activity of a patient includes steps for acquiring at least one respiratory activity signal including at least one elementary signal corresponding to a respiratory cycle, the general form of which may be expressed by x(t)=x0+x1 cos(Φ(t)), wherein Φ(t) is the phase of the elementary signal, and for analyzing the respiratory activity signal. The analysis includes steps for extracting, from the respiratory activity signal, the elementary signal, for determining an expression of a phase equation F ⁡ ( Φ ) = ⅆ Φ ⅆ t of the elementary signal and for determining an expression of the phase Φ(t) of the elementary signal as a function of parameters measuring the anharmonicity of the elementary signal and its morphology, from p cosn and p sinn functions defined by: p ⁢ ⁢ cos n ⁡ ( t , r ) = ∑ k = 1 ∞ ⁢ cos ⁡ ( kt ) ⁢ r k k n ⁢ ⁢ and ⁢ ⁢ p ⁢ ⁢ sin n ⁡ ( t , r ) = ∑ k = 1 ∞ ⁢ sin ⁡ ( kt ) ⁢ r ⁢ r k k n .