Maximum insufflation capacity - Vital capacity and cough flows in neuromuscular disease

Objective: To investigate the relationships between vital capacity (VC), ma ximum insufflation capacity (MIC), and both unassisted and assisted peak co ugh flows (PCFs). Design: The 108 patients were divided into two groups, those whose MICs wer e greater than their VCs (group 1) and those whose MICs could not exceed th eir VCs (MIC = VC, or group 2). Results: The MIC correlated positively with the VC for group 1 patients, bu t the percent increase in MIC correlated negatively with VC. Both VC and MI C correlated significantly with both unassisted and assisted PCF, respectiv ely. Assisting the cough increased the PCF of 37 patients over a previously defined critical level of 2.7 L/sec. The MIC VC difference and percent inc rease in MIC also correlated significantly with the difference between unas sisted and assisted PCF. Although the group 2 patients did not have true co ugh flows because of inability to close the glottis, their peak expiratory flows were significantly less than the unassisted and assisted PCF of the g roup 1 patients. Conclusions: The greater the MIC VC difference, the greater the PCF, and, t hereby, the ability to expel airway mucus and avert respiratory complicatio ns. The lower the VC, the greater the percent increase in MIC and the great er the percent increase in assisted PCF. Maximal insufflations are extremel y important to increase PCF for patients with neuromuscular conditions who have VCs of <1500 ml.