Abstract: Apparatus for supplying in a controlled and automatic way boli of nitric oxide (NO) to patients ‘(50)’ affected by respiratory diseases. The apparatus comprises a reservoir (20) connected an electro-valve (21) for adjusting the flow. The electro-valve (21) is switched on/off by a microprocessor (40) in order to supply the medical gas contained in the reservoir, (20) in synchronism with the respiratory rhythm of the patient (50). This rhythm can be outlined on the basis of the temperature values of the respiration flow by measuring, means (80) comprising a first thermistor (81) and a second thermistor (82) electrically connected to each other. The temperature values are then computed by the micropocessor (40). The flow controlled is sent to the respiratory airways of the patient (50) through a thin nasal tube (2).