Sniff nasal inspiratory pressure as a marker of respiratory function in motor neuron disease

Vital capacity (VC) and maximum mouth pressures are often used to monitor r espiratory function in motor neuron disease (MND), but require the use of a mouthpiece. Sniff nasal inspiratory pressure (SNIP) is a simple and reliab le means of measuring inspiratory muscle strength; it does not involve the use of a mouthpiece and might therefore be better than VC or mouth pressure s for assessing patients with bulbar disease. SNIP, maximum inspiratory (MIP) and expiratory mouth pressure (MEP), VC and arterial carbon dioxide tension (Pa,CO2) were measured in 59 consecutive p atients attending a specialist MND clinic. Thirty-one had bulbar involvemen t on clinical grounds. Both SNIP and VC were inversely related to Pa,CO2 in nonbulbar patients only. Neither MIP nor MEP were related to Pa,CO2. The 1 0 patients with an elevated Pa,CO2 (>6 kPa) had significantly lower SNIP an d VC than normocapnic patients. Sniff nasal inspiratory pressure can be used to monitor respiratory functio n in motor neuron disease. It is quick and easy for patients to perform, bu t otherwise appears to offer little advantage over vital capacity measureme nt. Patients with bulbar disease are often poor at performing sniff nasal i nspiratory pressure manoeuvres, possibly because of upper airway collapse o r inability to close the mouth completely during the manoeuvre.